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Spatial and temporal variation of surface ozone, NO and NO2 at urban, suburban, rural and industrial sites in the southwest of the Iberian Peninsula
Environmental Monitoring and Assessment
Abstract
Surface ozone is one of the most important photochemical pollutants in the low atmosphere, causing damage to human health, vegetation, materials and climate. The weather (high temperatures and high solar radiation), orography (presence of the Guadalquivir valley) and anthropogenic (the cities of Cádiz, Córdoba, Huelva and Seville and two important industrial complexes) characteristics of the southwestern Iberian Peninsula make this region ideal for the formation and accumulation of ozone. To increase the knowledge of ozone behaviour in this area, the monthly, daily and weekly variations of ozone and its precursors, nitrogen oxides (NOx = NO + NO2), were analysed over a 4-year period (2003 to 2006). Using the k-means cluster technique, 12 representative stations of five different areas with different ozone behaviour were selected from a total of 29 monitoring sites. This is the first time that the analysis of these atmospheric pollutants has been carried out for the whole area, allowing therefore a complete understanding of the dynamics and the relationships of these compounds in this region. The results showed an opposite behaviour among ozone and NO and NO2 concentrations in urban and suburban zones, marked by maximums of ozone (minimums NOx) in spring and summer and minimums (maximums) in autumn and winter. A seasonal behaviour, with lower amplitude, was also observed in rural and industrial areas for ozone concentrations, with the NO and NO2 concentrations remaining at low and similar values during the year in rural zones due to the absence of emission sources in their surroundings. The daily cycles of ozone in urban, suburban and industrial sites registered a maximum value in the early afternoon (14:00-17:00 UTC) while for NOx two peaks were observed, at 7:00-10:00 UTC and 20:00-22:00. In the case of rural stations, no hourly peak of ozone or NOx was registered. The weekend effect was studied by using a statistical contrast tests (Student's t). The results indicated that only areas influenced by important traffic emissions presented a weekend effect for NO and NO2, whereas an ozone weekend effect was not detected in any case.
... During summer, most winds originate from the southwest [54]. Furthermore, synoptic conditions, such as sea-land breezes, high surface pressure in the north and west of the Iberian Peninsula, and anticyclonic conditions, favor the accumulation of pollutants near the surface, preventing their mixture with the air above [58,59]. According to Millán-Martínez [60] and Diéguez et al., [44], aged air masses from the WMB may enter the Guadalquivir Valley through the Gibraltar Strait and increase pollution levels. ...
... The behavior of these pollutants in rural areas depends on natural sources, and they present no hourly peak. The weekend effect on these pollutants is only present in areas with high traffic emissions [58]. ...
... Both lie within the Guadalquivir Valley, the first one between the bays of Algeciras and Cadiz, and the second one north of Sevilla city. The Guadalquivir Valley, dominated by southwestern winds that carry O3 from the lower basin, is a natural channel for the transport and dispersion of polluted air from the Huelva towards the northeastern inner regions of the basin, where they mix with local traffic emissions in Sevilla's metropolitan area [54][55][56][57][58]. Its terrain is relatively homogenous and flat, which favor the penetration of polluted air loads. ...
Background: Many annual deaths in Spain could be avoided if pollution levels were reduced. Every year, several municipalities in the Community of Andalusia, located in southern Spain, exceed the acceptable levels of atmospheric pollution. In this sense, the evolution of primary air pollutants during the March–June 2020 lockdown can be taken as reliable evidence to analyze the effectiveness of potential air quality regulations. Data and Method: Using a multivariate linear regression model, this paper assesses the levels of NO2, O3, and PM10 in Andalusia within the 2017–2020 period, relating these representative indices of air quality with lockdown stages during the pandemic and considering control variables such as climatology, weekends, or the intrusion of Saharan dust. To reveal patterns at a local level between geographic zones, a spatial analysis was performed. Results: The results show that the COVID-19 lockdown had a heterogeneous effect on the analyzed pollutants within Andalusia’s geographical regions. In general terms, NO2 and PM10 concentrations decreased in the main metropolitan areas and the industrial districts of Huelva and the Strait of Gibraltar. At the same time, O3 levels rose in high-temperature regions of Cordoba and Malaga.
... Usually, urban and suburban zones are VOC-limited due to higher levels of NO x emissions, while less-populated zones (rural sites) are NO x -limited [8,9]. Domínguez-López et al. [10] analysed the effect of NO x (NO 2 and NO) concentrations in surface ozone at different locations through a spatial and temporal variation study. An opposite daily variance was observed between O 3 , NO, and NO 2 concentrations in urban and suburban areas. ...
... Being a pollutant resultant of a radiation-induced chemical reaction, O 3 shows higher levels with clear skies, which is also related to the presence of anticyclones. The association of O 3 concentrations with different weather conditions is more detailed in Domínguez-López et al. [10]. ...
... Ferreira et al. [37] presented the same connection between O 3 and NO 2 levels in the Lisbon region, registering a higher ozone concentration in the periphery of the urban centre. In the southwest of the Iberian Peninsula, a study of O 3 , NO, and NO 2 trends was developed at rural, urban, suburban, and industrial sites by Domínguez-López et al. [10]. According to their reports, most rural sites presented a low and constant NO x level. ...
Surface ozone (O3) is a secondary air pollutant, harmful to human health and vegetation. To provide a long-term study of O3 concentrations in Portugal (study period: 2009–2019), a statistical analysis of ozone trends in rural stations (where the highest concentrations can be found) was first performed. Additionally, the effect of nitrogen oxides (NOx) and meteorological variables on O3 concentrations were evaluated in different environments in northern Portugal. A decreasing trend of O3 concentrations was observed in almost all monitoring stations. However, several exceedances to the standard values legislated for human health and vegetation protection were recorded. Daily and seasonal O3 profiles showed high concentrations in the afternoon and summer (for all inland rural stations) or spring (for Portuguese islands). The high number of groups obtained from the cluster analysis showed the difference of ozone behaviour amongst the existent rural stations, highlighting the effectiveness of the current geographical distribution of monitoring stations. Stronger correlations between O3, NO, and NO2 were detected at the urban site, indicating that the O3 concentration was more NOx-sensitive in urban environments. Solar radiation showed a higher correlation with O3 concentration regarding the meteorological influence. The wind and pollutants transport must also be considered in air quality studies. The presented results enable the definition of air quality policies to prevent and/or mitigate unfavourable outcomes from O3 pollution.
... Similar trend can also be observed for the diurnal variations of NO 2 and CO concentrations ( Fig. 4b and c). As ambient O 3 concentrations are negatively correlated with its key precursor nitrogen oxides (NOx) in NO x -saturated regions of urban areas [40], the daily variation of O 3 exhibited the opposite trend to that of NOx at each station (Fig. 4d). The patterns of diurnal variations revealed in this study are also consistent with previous research [41][42][43][44][45]. Regarding the spatial variations, pollutants levels at XHCX station was generally more severe than that at the JAGH station, especially during the daytime. ...
... We explored the relationships between pollutants. Spearman's rank correlation coefficients (r 2 ) were calculated for air pollutants [40], on the basis of their hourly mean concentrations from 2018 to 2019. Table 2 compares the correlation matrices of air pollutants between the XHCX and the JAGH stations. ...
... Further, CO concentrations were also significantly positively correlated with PM 2.5 and PM 10 (p < 0.001, r 2 = 0.63 and 0.60, r 2 = 0.64 and 0.60 respectively) at both stations. As CO is not a precursor of secondary aerosols, the positive association between CO and particulate matter was mainly attributed to the similar emission sources [40]. O 3 concentrations were significantly negatively correlated with NO, and NO/NO 2 , but positively with NO 2 /NOx at both stations. ...
The socio-economic effects of urban elevated roads have been well-documented in previous studies. Nevertheless, the environmental impacts of the elevated road location are rarely considered. In this study, we quantified
such impacts on four traffic pollutants (e.g., NO, NO2, CO, and O3) in Shanghai, using the two-year observation
data from Shanghai roadside air quality monitoring stations—under the elevated road and on the side of the
elevated road. Auto-correlation analysis was employed to identify the periodic patterns of air pollutants. The
results showed that the severer traffic pollution and more notable daily periodic characteristics of air pollutants
were observed under the elevated road. This result may be attributed to the elevated “cap” structure, which has
become a barrier to prevent the pollutant diffusion in street canyon. Further, a novel Long Short-Term Memory
model with the identified periodicity was proposed to predict air quality. The proposed model achieved higher
goodness of fit and lower prediction error in prediction of four pollutants compared to other baseline models, and
that the forecasting accuracy was higher under the elevated road. These findings ascertain the effect of the
elevated road location on the variations of atmospheric pollutants and could provide implications in taking
control measures to mitigate traffic pollution under the elevated road.
... The fact that NO does not present a secondary maximum in the evening, due to elevated O 3 concentration usually found in rural areas, means that the Giordan Lighthouse station is indeed rural in character and acts as a background station for the Maltese Islands. Similar observations for NO have been observed in the case of rural sites such as that reported for Southern Spain [39] and the Marmara Region of Turkey [40]. The percentage diurnal amplitudes, after normalisation, for NO, NO 2 , and NO x concentrations are 148%, 46%, and 44%, respectively, for the thirteen-year period considered. ...
... Sci 2025, 7, x FOR PEER REVIEW 8 of 12 have been observed in the case of rural sites such as that reported for Southern Spain [39] and the Marmara Region of Turkey [40]. The percentage diurnal amplitudes, after normalisation, for NO, NO2, and NOx concentrations are 148%, 46%, and 44%, respectively, for the thirteen-year period considered. ...
Measurements of concentrations of nitrogen oxides (NOx) were collected over a period of thirteen years (2011–2023). The data were collected at Giordan Lighthouse atmospheric monitoring and research station on the Island of Gozo, forming part of the Maltese Archipelago, in the Central Mediterranean. Trend analysis shows that NOx concentrations are decreasing at an annual rate of 0.15 ppbv per year. This is in comparison to what has been recorded across Europe due to stricter regulations and improvements in vehicle technologies. Significant reductions were observed during the COVID-19 pandemic due to the implementation of lockdowns and restrictions on mobility. NOx concentrations also exhibit an amplitude seasonal variability of 35% with a maximum in October and a minimum in December, while the nitric oxide (NO) component of NOx presents a broad maximum in May/June and a minimum in February. NOx concentrations also show a strong diurnal variability with a maximum in the morning and a minimum in the afternoon. The diurnal amplitude of NOx and NO is 44% and 148%, respectively. With respect to wind direction, the NOx concentrations exhibit a maximum when the prevailing wind is from the South-East sector and a minimum when the wind is blowing from the West sector.
... The data were supplied by EPA Barranquilla Verde [56], the entity in charge of monitoring air quality data, and meteorological variables for the study area. It is important to mention that the Policía, Tres Ave Marías, and, Móvil stations have data for pollutants (PM10, PM2.5, O3, CO), since 1 January 2018 and for meteorological data since 1 January 2019, for which an adjustment of the study periods was made, according to the availability of data [40,57]. The 95% confidence interval of measured concentration of each pollutant was estimated as the statistic given by a Student's t-distribution with n−1 degrees of freedom, which considers the sample size, the sample mean, the expected mean value, and the sample standard deviation [58][59][60]. ...
... The data were supplied by EPA Barranquilla Verde [56], the entity in charge of monitoring air quality data, and meteorological variables for the study area. It is important to mention that the Policía, Tres Ave Marías, and, Móvil stations have data for pollutants (PM 10 , PM 2.5 , O 3 , CO), since 1 January 2018 and for meteorological data since 1 January 2019, for which an adjustment of the study periods was made, according to the availability of data [40,57]. The 95% confidence interval of measured concentration of each pollutant was estimated as the statistic given by a Student's t-distribution with n−1 degrees of freedom, which considers the sample size, the sample mean, the expected mean value, and the sample standard deviation [58][59][60]. ...
This work presents an analysis of fire events recorded in Isla Salamanca Natural Park and their impact on the air quality in the district of Barranquilla, with an emphasis on 2020 due to the increase in the number of ha burned by forest fires that year. The analysis was based on the data provided by the environmental authority for 2015–2020. The average number of ha burned in 2020 was 50% (events recorded since 2015), with a total area of fires corresponding to 256.9 ha, which is of concern considering the ecological importance of the park and its proximity to the district of Barranquilla, Colombia. The study evaluated the spatial–temporal distributions of forest fires and their possible direct effects on air quality. For 2020, it was found that the maximum hourly measurements of the Tres Ave Marias station for particulate matter less than 2.5 (135.013 µg/m³) corresponded to the recorded event that occurred in June 2020, whereas those of the Móvil station for PM10 (263.98 µg/m³) and PM2.5 (278.7 µg/m³) corresponded to the events of 28 June 2020, and 9 August 2020. These concentrations were higher than the standard values of the average maximum limits for 24 h established in the current Colombian regulations, and both events coincided with fire events reported by the environmental authorities, where a total of 249 ha of Isla Salamanca Natural Park were burned. These things considered, it was evident that the Policía station had the highest concentrations of pollutants on average.
... In 2010, 1.1 million premature respiratory deaths (people ≥ 30 years of age) globally were attributed to ozone, including 0.86 million ozone-attributable COPD (chronic obstructive pulmonary disease) deaths (Malley et al. 2017). Previous studies focused on the spatial and temporal distribution characteristics and causes of ozone pollution (Dominguez-Lopez et al. 2014;Silva et al. 2016;Wilson et al. 2012). It was found that the main reason for the higher ozone concentration was the increase of anthropogenic emissions of ozone precursors (Jonson et al. 2006), also long-range transport would lead to the spatial agglomeration of ozone pollution (Akimoto et al. 2015;Kleanthous et al. 2014). ...
... Previous studies also showed that the ozone precursors emitted into the atmosphere were transformed and transported between regions, resulting in ozone pollution having significant spatial agglomeration characteristics (Cooper et al. 2014). In addition, the difference of social and economic development level, land surface temperature, and topography of cities increased the spatial heterogeneity of ozone pollution (Dominguez-Lopez et al. 2014). ...
With the rapid urbanization and industrialization in China, ozone pollution has become increasingly serious and poses a greater threat to human health. In this study, the spatiotemporal distribution of ozone pollution in China’s cities and urban agglomerations from 2015 to 2019 was analyzed. The health effects and health economic costs of ozone pollution in China were estimated by applying the environmental Benefits Mapping and Analysis Program-Community Edition (BenMAP-CE) model. The results are as follows: (1) ozone pollution was more serious in Chinese urban agglomerations from 2015 to 2019; (2) the hot spots of ozone concentration mainly distributed in the North China Plain, expanding from north to south; the cold spots decreased year by year and were located in the northeast, northwest, and southwest of China, shifting from northwest to southwest; (3) the seasonal average of ozone concentration in China was the highest in summer, followed by spring and autumn, and the lowest in winter; (4) the number of all-cause premature deaths of ozone pollution in China increased slowly from 2015 to 2019, and the average of urban agglomerations was significantly higher than cities, with similar spatial distribution characteristics as ozone concentration; (5) the health economic costs of ozone pollution from 2015 to 2019 slowly expanded to surrounding cities with Beijing, Shanghai, Xi’an, and Chongqing as the centers of high values, while the low value areas decreased year by year and were mainly concentrated in southwest and northeast China. The health economic costs of ozone pollution at urban agglomerations scale were higher in the eastern coastal regions and lower in the northwest inland regions. Thus, this study presents policy recommendations to provide decision-making reference for realizing the inter-regional prevention and control of ozone pollution.
... In the urban atmosphere, NO and NO2 are emitted from anthropogenic activities, including combustion processes (e.g., traffic and industrial activities). Their daily patterns (Figures 2 and 3) are, therefore, controlled by these emissions [21][22][23]. Since NO is a primary pollutant and acts to form NO2 upon a series of reactions [24], the NO2 morning peak appears one hour later than the NO peak. ...
... In the urban atmosphere, NO and NO 2 are emitted from anthropogenic activities, including combustion processes (e.g., traffic and industrial activities). Their daily patterns (Figures 2 and 3) are, therefore, controlled by these emissions [21][22][23]. Since NO is a primary pollutant and acts to form NO 2 upon a series of reactions [24], the NO 2 morning peak appears one hour later than the NO peak. ...
Ground level ozone (O3) plays an important role in controlling the oxidation budget in the boundary layer and thus affects the environment and causes severe health disorders. Ozone gas, being one of the well-known greenhouse gases, although present in small quantities, contributes to global warming. In this study, we present a predictive model for the steady-state ozone concentrations during daytime (13:00–17:00) and nighttime (01:00–05:00) at an urban coastal site. The model is based on a modified approach of the null cycle of O3 and NOx and was evaluated against a one-year data-base of O3 and nitrogen oxides (NO and NO2) measured at an urban coastal site in Jeddah, on the west coast of Saudi Arabia. The model for daytime concentrations was found to be linearly dependent on the concentration ratio of NO2 to NO whereas that for the nighttime period was suggested to be inversely proportional to NO2 concentrations. Knowing that reactions involved in tropospheric O3 formation are very complex, this proposed model provides reasonable predictions for the daytime and nighttime concentrations. Since the current description of the model is solely based on the null cycle of O3 and NOx, other precursors could be considered in future development of this model. This study will serve as basis for future studies that might introduce informing strategies to control ground level O3 concentrations, as well as its precursors’ emissions.
... In order to determine the weekend effect, the difference between weekend and weekday of O 3 levels was investigated. Increase in the levels of O 3 (coincide with drop in the values of O 3 precursors) during weekend as compared to observed levels of weekdays is known as "weekend effect" [39]. Despite of no definitive theoretical explanation for the weekend effect, few hypothesis have been proposed to understand the weekend phenomenon such as (Monday to Friday) and weekends (Saturday to Sunday) were calculated for monitoring period to examine the difference between weekend and weekday. ...
... The weekend effect of O 3 is also characterized by the difference in the decay rate of precursor gases and prevailing ratio between VOCs and NOx. The observed results are in agreement with the studies performed by others [12,23,39]. In addition, Blanchard and Fairly established a classification of O 3 weekend effect having three types of scenarios according to peak difference of O 3 as: (a) > 30 mg m À3 , intense; (b) 10e30 mg m À3 , moderate; (c) 10 mg m À3 , no weekend effect [43]. ...
The present study summarizes the continuous measurements of ozone (O3) and oxides of nitrogen (NOx = NO + NO2) along with meteorological conditions in the ambient atmosphere of semi-arid urban site of western India during the year 2012-13. Seasonal and diurnal variations of gaseous pollutants were investigated and compared using the results of time series analysis. The marked seasonal difference was observed for O3 as highest/(lowest) during pre-monsoon/(monsoon), respectively. In contrast, NO and NO2 exhibit the highest and lowest levels during post-monsoon and monsoon, respectively. The diurnal cycle of O3 and NOx exhibited inverse relationship where surface O3 showed mid-day peak and lower night-time concentrations. The dataset was used to examine the association of O3 with the ambient levels of NO, NO2 and NOx during day-time and night-time, separately. The variation of an oxidant OX (O3 + NO2) with the levels of NOx was examined to infer the atmospheric sources of OX as sum of NOx-independent regional and NOx-dependent local contributions. Significantly strong positive correlations were observed of O3 with temperature and solar radiation with strong negative correlation with relative humidity during the studied seasons. Inconsiderable difference (<10 μg m⁻³) was observed between weekends and weekdays for the levels of O3 during entire observation period.
... This is known as the "weekend effect". This effect was intensively studied using groundbased (Butenhoff et al., 2015;Domínguez-López et al., 2014;Khoder, 2009;Nishanth et al., 2012) and satellite data (Beirle et al., 2003;Goldberg et al., 2021a;Jeong and Hong, 2021;Kaynak et al., 2009;Stavrakou et al., 2020). The estimated amplitude of the workday-weekend difference is about 20 %-40 % (Goldberg et al., 2021a;Murphy et al., 2007), although it is different from city to city (Lange et al., 2022). ...
The tropospheric NO2 vertical column density (VCD) values measured by the Tropospheric Monitoring Instrument (TROPOMI) were used to study the NO2 variability and estimate urban NOx emissions for 261 major cities worldwide. The used algorithm isolated three components in tropospheric NO2 data – background NO2, NO2 from urban sources, and NO2 from industrial point sources – and then each of these components was analyzed separately. The method is based on fitting satellite data by a statistical model with empirical plume dispersion functions driven by a meteorological reanalysis. Unlike other similar studies that studied plumes from emission point sources, this study included the background component as a function of the elevation in the analysis and separated urban emissions from emissions from industrial point sources. Population density and surface elevation data as well as coordinates of industrial sources were used in the analysis. The largest per capita emissions were found in the Middle East, and the smallest were in India and southern Africa. The largest background component was observed over China and parts of Europe, while the smallest was over South America, Australia, and New Zealand. Differences between workday and weekend emissions were also studied. Urban emissions on Sundays (or Fridays for some countries) are typically 20 %–50 % less than workday emissions for all regions except China. The background component typically does not show any significant differences between workdays and weekends, suggesting that background NO2 has a substantially longer lifetime compared to that in the urban and industrial plumes.
... It is worth noting that the consumption of this pollutant in urban areas, emitted mainly by mobile sources related to automobiles, chemically reacts with O 3 to form NO 2 (D. M. Agudelo Castañeda et al. 2016;Domínguez-López et al. 2014). ...
This research examines particulate matter with a diameter of 2.5 micrometers (PM2.5) and ozone (O3) variation across the climatic mesoregions of Alagoas. Mean PM2.5 and O3 concentrations across three mesoregions were as follows: East (5.91; 44.22 μg.m−3), Hinterland (6.90; 44.18 μg.m−3), and Arid (7.03; 44.23 μg.m−3). Spatial and temporal variations were observed, with PM2.5 concentrations highest in the northwest (NW) and O3 concentrations in the east (E), influenced by local sources, weather, and transportation. Differences between rainy and dry years were noted, attributed to biomass burning and dust particle transport. This study establishes a baseline for understanding air quality, lacking monitoring stations, aiding policymaking. It provides insights into PM2.5 and O3 dynamics, with PM2.5 concentrations highest in the NW and lower O3 concentrations in the E. Temporal variations emphasize the need for dynamic monitoring. Positive correlations between PM2.5 and O3 highlight complex relationships. Practical implications include proactive policymaking and the necessity for monitoring stations. Rigorous statistical methodologies inform model selection, enhancing environmental data understanding. Despite changes in land use, studies on extreme probability distributions are limited, emphasizing the need for robust methodologies for environmental data analysis to address air pollution challenges effectively in Alagoas.
... /fpubh. . of NO 2 (36)(37)(38)(39)(40)(41)(42). This spatial pattern between rural areas and O 3 concentration is rather general, as O 3 in troposphere is a secondary pollutant that is produced after NO 2 reacting with UV light (40,43). ...
Respiratory system cancer, encompassing lung, trachea and bronchus cancer, constitute a substantial and evolving public health challenge. Since pollution plays a prominent cause in the development of this disease, identifying which substances are most harmful is fundamental for implementing policies aimed at reducing exposure to these substances. We propose an approach based on explainable artificial intelligence (XAI) based on remote sensing data to identify the factors that most influence the prediction of the standard mortality ratio (SMR) for respiratory system cancer in the Italian provinces using environment and socio-economic data. First of all, we identified 10 clusters of provinces through the study of the SMR variogram. Then, a Random Forest regressor is used for learning a compact representation of data. Finally, we used XAI to identify which features were most important in predicting SMR values. Our machine learning analysis shows that NO, income and O3 are the first three relevant features for the mortality of this type of cancer, and provides a guideline on intervention priorities in reducing risk factors.
... In contrast to the other five pollutants, the concentration of O 3 Level 2 increased by 26%, 23% and 24%, respectively, over the previous years. The consumption of O 3 near the ground was mainly completed by titration reaction [22,23]. The blockade period restricted people's travel, and the reduction of automobile exhaust emissions led to the decline of NO, which weakens the titration reaction. ...
This paper explored the changes of six significant pollutants (PM2.5, PM10, SO2, NO2, O3, and CO) in Jilin City during the coronavirus disease 2019 (COVID-19) epidemic in 2022, and compared them with the same period of previous years to analyze the impact of anthropogenic emissions on the concentration of pollutants; The Weather Research and Forecasting Community Multiscale Air Quality (WRF–CMAQ) model was used to evaluate the effect of meteorological factors on pollutant concentration. The results showed that except for O3, the concentrations of the other five pollutants decreased significantly, with a range of 21–47%, during the lockdown period caused by the government’s shutdown and travel restrictions. Compared with the same period in 2021, the decrease of PM2.5 was only 25% of PM10. That was because there was still a large amount of PM2.5 produced by coal-fired heating during the blockade period, which made the decrease of PM2.5 more minor. A heavy pollution event caused by adverse meteorological conditions was found during the lockdown period, indicating that only controlling artificial emissions cannot eliminate the occurrence of severe pollution events. The WRF–CMAQ results showed that the lower pollutant concentration in 2022 was not only caused by the reduction of anthropogenic emissions but also related to the influence of favorable meteorological factors (higher planetary boundary layer thickness, higher wind speed, and higher temperature).
... In contrast, the suburban and rural environments practically kept polluting levels. This fact may be explained by the emission sources being more numerous in urban environments than at suburban and rural sites, which translated into the highest NO 2 urban levels (Domínguez-López et al. 2014;Núñez-Alonso et al. 2019;Oleniacz and Gorzelnik 2021). The leading polluting sources in urban locations drive road traffic, public and private transport networks, industrial activities, and domestic heating systems. ...
This work presents a new methodological approach to evaluating the long-term performance of an existing air quality monitoring network (AQMN). The AQMN is essential in controlling human beings' exposure to air pollutants, and the performance should be assessed over time. Still, there is not a harmonised method at the legislative level. In this work, 2008-2016 NO 2 data recorded by the Community of Madrid's AQMN were used for developing the suggested methodology, and 2007, 2017, and 2020 NO 2 data were involved in testing the aptitude of the proposed methodology to check the performance along the time. Chemometric techniques were employed to suggest the most representative non-redundant fixed stations within the target AQMN, reducing up to ~ 80% of the original number of fixed monitoring stations (from 23 to 5 fixed stations). The influence of the temporal frame used in developing the exposed methodology showed a variability lower than 5%. The spatial NO 2 distribution pictured by the current versus recommended fixed stations showed a higher than 95% similarity. This recommended approach can also be applied to short-time data. The exhibited methodology is a valuable tool for supporting AQMN managers in decision-making concerning AQMN management and complementing European Legislation guidelines concerning air pollutants monitoring using AQMN.
... Cluster analysis can specify groups (clusters) of elements (in this case, AQMSs) with similar characteristics based on a specific aggregation variable. Elements in each group must exhibit statistically similar behavior, whereas elements from different groups have different behaviors (Anderberg 2014;Domínguez-López et al. 2014). The nonhierarchical (k-means) algorithm, where its validity in the analysis of surface O 3 and NO x has previously been demonstrated, was used in Tehran for AQMSs clustering (Adame et al. 2012;Tarasova et al. 2007). ...
Particulate matter is usually regarded as the dominant pollutant in Tehran megacity in Iran. However, the number of ozone exceedance days significantly increased in recent years. This study analyzes simultaneous measurements of O3 and NOx (NO+NO2) concentrations to improve our understanding of ozone evolution during the summers of 2017 to 2019. The k-means clustering technique was used to select five representative air quality monitoring sites in Tehran to capture O3 and NOx concentrations’ variability. The findings show that all of the investigated sites failed to meet the ozone non-attainment criterion. The ozone weekend effect is seen in the study of weekday/weekend differences in 2017 and 2018, but not in 2019, which can be due to the shift in the ozone production regime. The summer mean variation analysis can also be used to deduce this regime change. In 2017, the O3 and NO2 summer mean variations suggest a holdback in the NO2 upward trend and a reversal in the O3 downward trend that had been in place since 2012. Air mass back trajectory clustering reveals that east and north-east air mass clusters have the most significant impact on Tehran’s O3 pollution and the highest regional contribution to OX. The study of OX against NOx shows that the regional contribution to OX increased from 2017 to 2018 and then decreased in 2019; however, the local contribution is the opposite. The diurnal analysis of the regional and local contributions to OX indicated that OX in Tehran might be primarily affected by pollutants from a short distance. The findings reveal critical changes in the behavior of O3 in recent years, indicating that decision-makers in Tehran should reconsider air pollution control measures.
... Ambient ozone levels are strongly dependent on the previous day concentrations (Otero et al., 2016), as the ozone accumulated during daytime is not often fully destroyed during the night, nor are its precursors (Mazzeo et al., 2005;Geddes et al., 2009). In many densely populated areas, where the footprint of a multitude of urbanization activities is prevalent, ozone follows a weekly pattern characterized by higher ozone concentration from Saturday to Sunday (weekends, when local traffic is lower) than Monday to Friday (weekdays, when emissions from vehicular traffic scavenge ozone; especially during morning rush hour with low solar radiation) (Cleveland et al., 1974;Shan et al., 2008;Domínguez-López et al., 2014;Huryn and Gough, 2014;Abeleira and Farmer, 2017;de Foy et al., 2020). This counterintuitive phenomenon -regarded as the "ozone weekend effect"-has been observed in Ontario's major cities (Beaney and Gough, 2002;Huryn and Gough, 2014;Leung, 2015), as well as in other cities around the world (Lebron, 1975;Elkus and Wilson, 1977;Silva Júnior et al., 2009;Im et al., 2013;Wang et al., 2014;Szep et al., 2016). ...
Ozone is a serious health concern and the only major pollutant in Ontario that is increasing, despite major efforts to control atmospheric pollutants in North America. Ambient ozone levels are affected by local atmospheric conditions (temperature, humidity, radiation, precipitation) and the concentration of its main precursors, nitrogen oxides (NOx) and volatile organic compounds (VOCs). In the present study, our aim is to elucidate the day-to-day and seasonal variability of the influence of synoptic atmospheric descriptors on daily average ozone concentrations, as well as to establish a predictive framework of the likelihood of exceedance of harmful levels in Southern Ontario. Using 31 stations in Southern Ontario with daily ozone concentration data from 2007 to 2015, we developed parsimonious models using as predictors a suite of atmospheric variables, available from the National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset, and terms that recreate the seasonality and weekend/weekday effects of the previous day ozone concentrations. In all sites, seasonal (among-month) variability was distinctly lower than within-month variability. Our analysis showed that the population size reduced the average ambient ozone concentrations, increased their variability, and decreased the predictive power of our models. Ambient ozone levels in higher latitude sites displayed stronger dependence on the antecedent conditions, whereas the human activities weakened the serial correlation in the ozone time series in urban areas. Seasonal changes in the magnitude and sign of the slopes of the atmospheric predictors were consistent within the spatial domain of our study: shortwave radiation consistently increased ambient ozone levels, temperature displayed a positive relationship during the summer but a negative one during the winter; humidity was characterized by a negative relationship with ozone; precipitation increased ozone during late summer and winter, with no consistent effect during the rest of the year; wind speed and direction also showed contrasting effects between summer and winter months. Seasonality strongly affected the probability of exceedance in low population sites but had a minor role in more densely populated areas, while the difference in ozone concentrations between weekend and weekdays increased in urban sites. Overall, our results suggest that population and seasonality of the prevailing ambient conditions affect the local daily average ozone concentrations by modulating the importance of different processes and can thus be used to understand why high ozone concentrations may occur locally even during winter months.
... The hourly [O 3 ] is used to study the diurnal variation (Fig. 5a). During daytime, the absolute Δ[O 3 ] peaks at 0800 LST (local standard time) in most sub-regions, especially for BTH (−8.7 ppbv) and SCB (−5.5 ppbv), likely due to high NO x emissions from traffic in the rush hour (Dominguez-Lopez et al., 2014). Traffic emissions are also an important driver for Δ[PM 2.5 ], the peak of which (21.0 μg m −3 ) is found at 0800 LST in BTH (Fig. 5e, Table S2). ...
Surface ozone (O3) and fine particulate matter (PM2.5) are dominant air pollutants in China. Concentrations of these pollutants can show significant differences between urban and nonurban areas. However, such contrast has never been explored on the country level. This study investigates the spatiotemporal characteristics of urban-to-suburban and urban-to-background difference for O3 (Δ[O3]) and PM2.5 (Δ[PM2.5]) concentrations in China using monitoring data from 1171 urban, 110 suburban, and 15 background sites built by the China National Environmental Monitoring Center (CNEMC). On the annual mean basis, the urban-to-suburban Δ[O3] is −3.7 ppbv in Beijing-Tianjin-Hebei, 1.0 ppbv in the Yangtze River Delta, −3.5 ppbv in the Pearl River Delta, and −3.8 ppbv in the Sichuan Basin. On the contrary, the urban-to-suburban Δ[PM2.5] is 15.8, −0.3, 3.5 and 2.4 µg m−3 in those areas, respectively. The urban-to-suburban contrast is more significant in winter for both Δ[O3] and Δ[PM2.5]. In eastern China, urban-to-background differences are also moderate during summer, with −5.1 to 6.8 ppbv for Δ[O3] and −0.1 to 22.5 µg m−3 for Δ[PM2.5]. However, such contrasts are much larger in winter, with −22.2 to 5.5 ppbv for Δ[O3] and 3.1 to 82.3 µg m−3 for Δ[PM2.5]. Since the urban region accounts for only 2% of the whole country’s area, the urban-dominant air quality data from the CNEMC network may overestimate winter [PM2.5] but underestimate winter [O3] over the vast domain of China. The study suggests that the CNEMC monitoring data should be used with caution for evaluating chemical models and assessing ecosystem health, which require more data outside urban areas.
... This process is repeated until each cluster is stable. This algorithm is widely used in pollution studies, especially in cases that a priori information on the possible clusters is available (Adame et al., 2012;Austin et al., 2013;Domínguez-López et al., 2014;Jin et al., 2011;Vargas et al., 2015;Zhang et al., 2016). In this study, cluster analysis was used to investigate different diurnal patterns of ozone during the daytime and early night (7:00-22:00) since that this time period features most peak values of concentration and most obvious ozone variations, while the change in ozone concentration around 00:00-06:00 is relatively small. ...
Ozone (O3) pollution has aroused increasing attention in China in past years, especially in the Yangtze River Delta (YRD), eastern China. Ozone and its precursors generally feature different diurnal patterns, which is closely related to atmospheric physical and chemical processes. This work aims to shed more light on the causes of ozone pollution from the perspective of the diurnal patterns. Hundreds of ozone pollution days (with maximum hourly O3 concentration over 100 ppb) during 2013–2017 were identified and then clustered into 4 typical types according to the diurnal variation patterns. We found that ozone pollution in Shanghai was particularly severe when anthropogenic pollutant mixed with biogenic volatile organic compounds (BVOCs) under the prevailing southwesterly wind in summer. The reason could be attributed to the spatial disparities of ozone sensitivity regime in YRD: VOC-limited regime around in the urban area and NOx-limited regime in the rural forest regions in the southern and southwest. The transition of sensitivity regimes along south/southwest wind tended to promote the photochemical production of ozone, making daily O3 pollution time exceeding 6 h of the day. In addition, ozone peak concentration in Shanghai was highly dependent on the evolution of sea-land breezes (SLBs). Earlier sea breeze associated with approaching typhoon in the West Pacific caused less cloud (−25%) and more solar radiation (11%) in YRD, which subsequently led to a rapid increase of O3 concentration in the morning and a deteriorated ozone pollution during noon and the afternoon. This study highlights the importance of observation-based processes understanding in air quality studies.
... During weekends the increase in O 3 levels compared to the levels observed during weekdays is known as the weekend effect (Dominguez-Lopez et al., 2014). The weekend effect phenomena may occur during weekends despite lower levels of O 3 precursors; NO X and VOCs (Alghamdi et al., 2014). ...
Abstract Two years of continuous monitoring data over two time‐spans (2004–2005 and 2014–2015) were used to investigate the relationship between ozone (O3) and nitrogen oxides (NOX ≈ NO + NO2) in Fahaheel urban area (Kuwait). Their relationship was used to understand their chemical reactions and the NO2 and O3 concentration ratio to gain an insight into the sources of total atmospheric oxides (OX = O3 + NO2) levels. A Chemical Mass Balance (CMB) model was developed to detect likely point sources around the monitoring station and quantify their contribution to the overall air pollution load. Hourly diurnal variations in O3 ground level concentrations during weekends showed a slight increase in O3 levels. In addition, it was observed that overall hourly average O3 concentration reached higher levels during weekdays and weekends in 2004–2005 compared to 2014–2015. The concentration of photochemical oxidants (e.g., O3 and NO2) can be decreased by controlling the emissions of their precursors; NOX and VOCs. The net effect of NOX emissions on O3 concentrations was negative with a weak exponential decline correlation between NOX and O3, indicating Fahaheel urban area's VOC‐sensitive characteristics. For all years considered, the slopes of the linear OX–NOX relationships were higher during daytime compared to night‐time, showing that NO2 oxidations were dominant during daytime and that O3 net production was high. The study also showed the high NOX oxidation level and the possible presence of O3 net production. The slopes during night‐time indicated that NO2 consumption exceeded its formation rate. During day and night‐time, the NO2/NOX ratio was found to decline significantly as newly emitted NOX increased, supporting the area's VOC‐sensitive nature. By setting up a CMB model around the Fahaheel receptor point, it was revealed that downstream petroleum facilities have been the major contributor to pollutants environmental load over the years.
... The climatic conditions are typical of a Mediterranean area, where there are several Mediterranean climate subtypes, with Atlantic influence at its westernmost end and continental influence at its northern boundary (Marín et al. 2012). The weather of this region is characterised by mild and dry winters, springs and autumns with very variable synoptic conditions and, hot and dry summers (Cuadrat and Martín Vide 2007). The mean annual and absolute maximum temperatures are 20 and 43.7°C, respectively, while mean annual precipitation is 600 nm (Instituto Geográfico Nacional 2019). ...
In Extremadura, Southwest Spain, environmental conditions combined with a complex mixture of natural and anthropogenic precursors favour the appearance of episodes of high concentrations of tropospheric ozone, whose levels sometimes exceed legal thresholds. In this mainly rural region, no study has been carried out to identify and interpret regional ozone episodes, so this work aims to fill this gap. Ozone and precursor (nitrogen oxides and organic compounds) levels from six representative air quality monitoring stations located in suburban and rural areas have been used to investigate selected ozone episodes during 2014 and 2015. Air mass back-trajectories were used to assess the contribution of long-range transport, resulting in Europe, Mediterranean and Peninsular routes. The analysis of synoptic patterns revealed that high pressures with stationary character, which occur in different synoptic conditions, have an important role in the increment of the ozone values. Finally, the evaluation of the results showed that the daily ozone cycle is mainly regulated by the emissions of precursors in the surrounding environment, the high temperatures that occur during the day and the influence of atmospheric conditions on the low troposphere under anticyclonic conditions that promote ozone accumulation.
... The region where it is placed is the western part of Andalusia (Spain). Since as exposed previously (Domínguez-López et al., 2014), this area meets the weather conditions (high temperatures and solar radiation), orographic (the valley of the Guadalquivir river) and anthropic ones to be potentially vulnerable to pollution by ground-level ozone and nitrogen oxide. The climate of the zone of study, according to the Köppen-Geiger classification, is defined as Csa, with warm average temperatures and hot and dry summer. ...
The usage of multilayer complex networks for the analysis of correlations among environmental variables (such as O3and NO2concentrations from the photochemical smog) is investigated in this work. The mentioned technique is called Multiplex Visibility Graphs (MVG). By performing the joint analysis of those layers, the parameters named Average Edge Overlap and Interlayer Mutual Information are extracted, which accounts for the microscopical time coherence and the correlation between the time series behavior, respectively.
These parameters point to the possibility of using them independently to describe the correlation between atmospheric pollutants (which could be extended to environmental time series). More precisely the first one of them is considered to be a potential new approach to determine the time required for the correlation of NO2and O3to be observed, since it is obtained from the correlation of the pollutants at the smallest time scale. As for the second one, it has been checked that the proposed technique can be used to describe the variation of the correlation between the two gases along the seasons. In short, MVGs parameters are introduced and results show that they could be potentially used in a future for correlation studies, supplementing already existing techniques.
... This clustering technique have been used successfully in atmospheric studies in the past Domínguez-López et al., 2014;Vargas et al., 2015). A general description of clustering techniques can be found in Everitt et al. (2011) while a more applied and specific explanation appears in Beaver and Palazoğlu (2006). ...
Radon measurements were performed in Huelva, a city located near a phosphogypsum repository in the SW of the Iberian Peninsula, between March 2015 and March 2016. The mean values of this gas oscillate between 5.6 and 10.9 Bq m⁻³ and maximum ranges between 36.4 and 53.4 Bq m⁻³. Radon shows the expected monthly variation with higher levels in November and December. Typical daily evolutions were also observed, with maximum between 06:00 and 08:00 UTC (Coordinated Universal Time) and minimum around noon. To extract daily radon patterns, the cluster technique of K-means was applied. Based on this classification, four different case study periods were analyzed in detail, describing two events with high radon levels and two with low radon. Local meteorology, back-trajectories computed with the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model and meteorological fields from the WRF (Weather Research and Forecasting) model, were used to analyze the four case study periods selected. Low radon periods are characterized by the occurrence of non-pure breezes and maritime air masses from the Atlantic Ocean, whereas high radon periods occur under pure sea-land breezes affected by Mediterranean air masses. Factors such as meteorology or local emission sources alone may not be enough to explain the high radon events in the area. Other factors could be playing a major role in the radon levels. The obtained results indicate the contribution of radon transported from medium-long range, suggesting that, under specific weather conditions, the Gulf of Cadiz could act as a radon trap and the continental areas around the Western Mediterranean Basin could act as a radon source.
... En cuanto a los resultados obtenidos con los datos observados se demuestra la correlación negativa entre el O 3 y el NO 2 en las tres ciudades españolas, con correlaciones más significativas en Madrid y menos en Sevilla y Barcelona, por la escasez de datos ya comentada. Nuestros resultados son consistentes con los obtenidos por otros autores en otras ciudades españolas, y a los cuales ya se ha hecho referencia en la sección estado de la cuestión (Domínguez-López et al., 2014;Felipe-Sotelo et al., 2006). Song et al. (2011) detectaron correlaciones negativas entre O 3 y NO x durante la primavera en estaciones próximas a las autovías de la costa este de Estados Unidos, con una r 2 de 0,576 por el día y de 0, 605 por la noche, ajustando los datos con un modelo exponencial. ...
Air quality is determined by a large number of components whose presence and interactions in
environments such as large cities is of singular importance for human life. This article describes a
study of two known pollutants, nitrogen dioxide and tropospheric ozone, with the aim of exploring
and uncovering the form and intensity of the hypothetical relation between the two when is spatially
analysed. With this objective, given the limited information available, a double approach has been
chosen: to analyse, on the one hand, data registered on the surface stations, and on the other hand,
estimates made via spatial interpolation, one of the most commonly used techniques for detecting
this pollution in the urban atmosphere. This allows mutual results to be compared and monitored.
Data from three Spanish cities, namely Madrid, Barcelona and Seville, have been experimentally
examined using a number of statistical, graphic and cartographic techniques, supported by
geographical information systems. The results show that NO2 and O3 exhibit counterposed spatial
patterns and that a spatial dependence exists between the two, both regarding the observed and the
estimated data. Nevertheless, in some cases the form and significance of the spatial relations has not
been clearly determined, to a large extent owing to the scarcity of data observed. The coherence of
results in both approximations thus allows a measure of optimism in drawing up characterisations
and diagnoses of urban air quality with this type of spatial models.
... This phenomenon has been confirmed by some other studies, such as those performed in Spain and Turkey, with higher O 3 concentrations being reported in rural measuring stations in the southwest of the Iberian Peninsula. As in our study, the highest O 3 concentrations were observed during the summer months (Domínguez-López et al. 2014;Tecer and Tagil 2014;Gómez-Carracedo et al. 2015). Another study examining the variety of O 3 concentrations in industrial and suburban sites of Southern Italy concluded that O 3 concentrations at suburban sites are higher in comparison with those in urban areas and, once again, the pollutant concentrations were higher in the summer months (Schipa et al. 2009). ...
Selecting the locations and numbers of air quality monitoring stations is challenging as these are expensive to operate. Representative concentrations of pollutants in certain areas are usually determined by measuring. If there are significant correlations with concentrations of other pollutants or with other monitoring sites, however, concentrations could also be computed, partly reducing the costs. The aim of this study is to provide an overview of such possible relationships using data on concentrations of ambient air pollutants obtained in different areas of a larger city. Presented are associations between industrial (IP) and suburban parts (SP) as well as correlations between concentrations of various pollutants at the same site. Results of air pollutant monitoring come from Ostrava, an industrial city in Central Europe with a population of over 300,000. The study showed that certain pollutants were strongly correlated, especially particulate matter (r = 0.940) and ozone (r = 0.923) between the IP and SP. Statistically significant correlations were also found between different pollutants at the same site. The highest correlations were between PM10 and NO2 (rIP = 0.728; rSP = 0.734), NO2 and benzo(a)pyrene (rIP = 0.787; rSP = 0.697), and NO2 and ozone (rIP = −0.706; rSP = −0.686). This could contribute to more cost-effective solutions for air pollution monitoring in cities and their surroundings by using computational models based on the correlations, optimization of the network of monitoring stations, and the best selection of measuring devices.
... Although a number of criteria air pollutants defined in various countries, ozone in the troposphere is considered as one of the major environmental concerns due to adverse impacts on human health and ecosystems (Hassan et al. 2013;WHO 2000;Han et al. 2011). GLO plays a significant role in the physicochemical processes of the troposphere, contributing to climate change (Domínguez-López et al. 2014). The ozone concentration in the urban environment does not typically result from sudden variations in emissions, but rather from meteorological conditions that influence the atmospheric stability or result in increased ozone formation (Cheng et al. 2007). ...
The present study aims to analyse the influences of five meteorological parameters (temperature, wind speed, barometric pressure, rainfall, and solar radiations) on ground-level ozone (GLO) concentrations over the region of Ranchi Municipal Corporation (Jharkhand, India). The diurnal variation of GLO concentration and the meteorological parameters were analysed in each month to understand the associations. The results indicated that the correlation coefficients of GLO concentration with SR, AT, and DPT are found to be positive in each month and also statistically significant. But, the association between WS and GLO concentration was not uniform between the study days. Furthermore, the study also demonstrates an approach for identifying the hot spots that are having the higher level of GLO concentration. The hot spot maps were produced for each month to understand the shifting of the locations of hot spot locations. The results reveal that the hot spot locations are changes frequently in each case. Since the hot spot analysis was conducted with limited data, the presented hot spots are indicative and dependent on the meteorological conditions of the specific period and cannot be considered as a robust epidemiological study.
... Recent remotely sensed observations provide a complete way to improve the measurement of NO 2 emissions as well as the variation of its spatial and temporal patterns. (e.g., Beirle et al. 2003;Richter et al. 2005;Kim et al. 2006;Van derA et al. 2006;Zhang et al. 2007;Stavrakou et al. 2008;Boersma et al. 2008;Lee et al. 2009;Zyrichidou et al. 2009;Russell et al. 2010;Lu and Streets 2012;Wang et al. 2012;Hilboll et al. 2013;Bechle et al. 2013;Duncan et al. 2013;Domínguez-López et al. 2014;Lamsal et al. 2014;Ting et al. 2015). The present study aims to reveal the longterm temporal and spatial variability of NO 2 concentrations over the Middle East region based on satellite-based measurements of the Ozone Monitoring Instrument (OMI). ...
The present study, aims to assess the spatial and temporal variation of NO2 measurement over the Middle East region within 2005–2014. For this purpose, satellite-based data of the Ozone Monitoring Instrument (OMI) were implemented to measure the NO2 concentrations. The results reveal an average increase of NO2 emission in the Middle East during recent decade. Therefore, the results suggest several hotspots consisted of Tehran–Karaj (Iran), Dubai–Ajman (UAE), Kuwait (Kuwait), Riyadh (KSA), Dammam (KSA), Istanbul–Izmit (Turkey), Doha–Rayyan (Qatar), Manama (Bahrain), Cairo (Egypt), Isfahan (Iran), Lahore (Pakistan), Tashkent (Uzbekistan), Baghdad (Iraq) and Beirut (Lebanon) urban regions, which are the main source of NO2 emissions in decadal scale. This study shows that the remotely sensed data are able to measure and record the spatial and temporal variation of NO2 concentrations as emission inventory documents in the Middle East.
... Site 8 is the Edinburgh St. Leonard's national air quality monitoring station. lower in summer (Lozano et al., 2011;Caballero et al., 2012;Matte et al., 2013;Dominguez-Lopez et al., 2014), but most of the summer measurements in this work coincided with the annual Edinburgh arts festivals, the biggest collection of festival events in the world, which bring in large number of visitors and corresponding elevations in traffic. The general trend for a small decline in NO 2 in winter periods W3 (16e23 Dec) and W4 (23e30 Dec) and rebound in weeks W5 (30 Dece6 Jan) and W6 (6e13 Jan) is presumed [ Leonard's national air quality monitoring station. ...
Ambient NO2, O3 and Ox (the sum of NO2 and O3) are associated with adverse health outcomes. Quantitative assessment of the health burden from these pollutants requires knowledge of small-scale variations in their concentrations in urban environments. In particular, we were interested in the temporal stability of intra-urban spatial contrasts in these pollutants. This was investigated by concurrent measurements of NO2 and O3 by passive samplers at 30 sites in Edinburgh, UK, repeated 12 × 1-weekly for NO2 and 6 × 2-weekly for O3 in summer and winter. Temporally persistent and large spatial variations in both NO2 and O3 concentrations were observed. Concentrations of NO2 across the sites ranged on average by a factor of 14 between suburban parks and heavily-trafficked roadsides, corresponding to a difference in NO2 on average of ∼80 μg m−3. Intra-urban O3 concentrations also varied substantially, on average by a factor of 4 (average range 45 μg m−3) and with strong anticorrelation to NO2 concentrations across the 30 sites. Consequently intra-urban variability was considerably lower for Ox than for NO2 and O3. The temporal stability in relative NO2 and O3 concentrations indicate potential for deriving intra-urban spatial fields of NO2 and O3 at different times by scaling models of long-term spatial patterns of NO2 and O3 by the measurements at a single site. If Ox is a key determinant of adverse health then the large intra-urban spatial contrasts in NO2 and O3 may be less relevant, with Ox concentrations across an urban area determined at a suitable background site.
... Within the last group, it has been widely applied to analyze environmental and climatological data [e.g. Fan et al., 2014;Domínguez-López et al., 2014;Xu et al., 2014]. ...
This work is aimed to propose a methodology for the identification of areas for which extreme climatological conditions may intensify aridity processes and rainfall deficiency. The proposed procedure, which is based on the analysis of climate projections derived from high-resolution regional simulations, is composed of three main elements. First, extreme temperature, extreme precipitation, and extreme dry periods (in terms of consecutive dry days) are modeled using extreme value theory. Second, an aridity index is used as a proxy of long-term processes leading to aridity. Third, clustering techniques are used to group zones with similar climatic parameters. In this way, areas with the more extreme climate conditions are identified. Possible effects due to climate-change scenarios are considered by analyzing possible non-stationary conditions in extreme events and by performing calculations in both a historical period and a projection period (where different scenarios are considered). An application of the proposed procedure is implemented in an area around Ouagadougou, Burkina Faso. From the analyses, it emerged that the eastern part of the case study area will experience both large rainfall deficit and the highest extreme temperatures. Those two aspects, combined with a potential water demand increase (due to the increasing of number of inhabitants), may favor the intensification of the aridity processes.
... The annual mean concentration of O 3 increased from CB to LC, following an opposite order of urban influence to the one found for NO 2 concentration. A similar behaviour has been described in other studies around cities in the Mediterranean area (Domínguez-López et al. 2014;Escudero et al. 2014). CB showed an annual mean similar to values found in 2012 in Spanish suburban areas, while the other sites showed values clearly typical of rural areas (means of 59.0 and 67.8 μg m −3 , respectively; EEA 2014). ...
Oxidative stress and neuroinflammatory changes appear to be the early events involved in AD’s development and progression. The present study was designed to assess the effect of soybean isoflavone extract (SIFE) against colchicine-induced cognitive dysfunction and oxidative stress in male rats.
Fifty adult male Wistar albino rats were divided into five groups: control, ACSF-treated group, soybean isoflavones (SIF)-treated group, colchicine (COL)-treated group, and SIF + COL-treated group. We found that an intracerebroventricular (icv) injection of a single dose of colchicine (7.5 μg/rat bilaterally) resulted in learning deficits in rats subjected to the Morris water maze task associated with marked oxidative damage and decreased acetyl cholinesterase (AChE) activity. In addition, COL caused significant increase in amyloid beta peptide 1-42 (β, amyloid 1-42) interleukin-1β (IL-1β), tumor necrosis factor-α (TNFα), cyclooxygenase-2 (COX-2) and TNF-α genes expression in the brain, and glial fibrillary acidic protein (GFAP) in cortical astrocytes in the brain cortex.
Treatment with SIFE (80 mg/kg b.wt) daily for 14 days followed by a single dose of COL significantly reduced the elevated oxidative stress parameters and restored the reduced antioxidant activities. Besides, the administration of SIFE reversed the overproduction of β, amyloid 1-42, pro-inflammatory cytokines, and GFAP in the brain. The obtained results were confirmed by histological observations that clearly indicate a neuroprotective effect of SIF against AD.
... Due to their aforementioned significance, a number of studies have been done on atmospheric oxidants extensively in many rural and urban areas across the world (Duenas et al. 2004;Pudasainee et al. 2006;Tu et al. 2007;Schipa et al. 2009;Han et al. 2011;Im et al. 2013;Wang et al. 2013;Dominguez-Lopez et al. 2014). In India, several researchers have characterized the levels of O 3 and NO x in different cities (Debaje et al. 2003;Londhe et al. 2008;Reddy et al. 2012;Singla et al. 2011;Swamy et al. 2012). ...
The present study deals with the concentrations of individual and total volatile organic compounds (TVOCs) present in the ambient atmosphere of Delhi. Sampling was done in four different zones, viz. residential, commercial, industrial and heavy traffic density area (HTDA) during rush and non-rush hours. The National Institute for Occupational Safety and Health (NIOSH)-1501 standard method was used for benzene, toluene, ethylbenzene and xylene (BTEX) measurements while real-time monitoring was done for TVOC using a data-logging photoionization detector. Results showed that the mean concentrations of TVOC and ∑BTEX were found to be highest in HTDA as compared to those in other zones. Toluene contributed the most among BTEX as 28.5, 108.6, 129.6 and 104.5 μg/m3 at residential, commercial, industrial and HTDA, respectively. However, the concentrations of TVOC were found to be 518.9 μg/m3 in HTDA followed by industrial (511.3 μg/m3), commercial (429.6 μg/m3) and residential areas (199.5 μg/m3). It is noted that the concentrations of the pollutants were observed to be higher during rush hours in contrast to non-rush hours due to more number of vehicles plying the road. After examining the seasonal variability, the winter samples showed the highest concentrations of the pollutants which could be due to stable environment. In order to identify the sources, characteristic ratios and correlation analysis were also done. Cancer and non-cancer risks were estimated for BTEX using US Environmental Protection Agency (USEPA) guidelines. The estimated lifetime cancer risk (LCR) in this study exceeded the value of 1.0 × 10−6 recommended by the USEPA for adults and children in all zones. The population groups are in the category of “possible risk” after comparing with the Sexton’s classifications of cancer risk.
Atmospheric α-pinene is one of the most important precursors of secondary organic aerosols (SOA). The formation of α-pinene derived SOA is strongly affected by NOx. However, we still do not comprehensively understand the effects of NOx on α-pinene derived SOA formation. Therefore, we conducted α-pinene photooxidation experiments in an atmospheric chamber at different NOx concentrations. The yields of α-pinene SOA increased with NOx concentration under low-NOx conditions, but were suppressed under high-NOx conditions. The maximum SOA yields were 8.0 % and 26.2 % in the low- and high-volatility organic compound (VOC) experiments, respectively. We found the increased SOA yields under low-NOx conditions were related to increased consumption of α-pinene. The products of α-pinene photooxidation were mainly semi-volatile, and the change in the aerosol/gas-phase distribution ratio as the formation of α-pinene photooxidation products increased was identified as the main reason for the enhanced SOA yields with increasing NOx. The sensitivity of the SOA yield to changes in NOx and VOCs under different experimental conditions was also analyzed. This study also quantified the nitrogen-containing organic compound (NOC) concentrations. The mass fraction of NOCs in SOA increased monotonically with NOx in the α-pinene photooxidation process, and the maximum NOC mass fraction made up as much as two-fifths of the α-pinene SOA.
This study aimed to examine the validity of a mobile air quality sensor fleet in improving pollution exposure assessments in urban areas. The scope of this study involved experimental setup (sensor validation and calibration), evaluation of spatiotemporal data coverage, and analysis of the representativity of the collected mobile data. The results showed that indicative sensor data quality can be achieved after NO 2 co-location calibration, although particulate matter exhibited unsatisfactory performance. An extensive mobile air quality dataset was collected in Antwerp city between February and September 2021, covering 945 km of road by a total of ∼7.9 million data points, yielding an average segment coverage of 1,050 measurements per street segment (median = 62). The collected mobile data were made available in an open data repository. From the introduced area (%) and street segment (n) coverage, we can conclude that opportunistic data collection using service fleet vehicles (e.g., postal vans) is an efficient approach for covering a wide spatial area and collecting many repeated runs (∼200 measurements/segment/month). Monthly maps showed recurring pollution gradients with hotspot locations both at the suspected (e.g., busy traffic arteries) and unexpected locations, with observed increments greatly exceeding the observed inter-sensor uncertainty. The existing air quality monitoring network (five air quality monitoring stations) properly reflected the observed NO 2 exposure range (temporal variability), which was documented by the sensor fleet in Antwerp. The spatial exposure variability was improved significantly by the sensor fleet with 59% of the total street length covered after 1 month of mobile deployment (February-March). We required ∼45 repeated passages (31 after post-processing) to derive representative long-term NO 2 exposure data from this opportunistic dataset. Our findings suggested that opportunistic data collection using sensors on service fleet vehicles is a valid approach for pollution exposure assessments, through proper validation and calibration strategy. Temporary deployment of mobile sensors was a valuable approach for cities with a less extensive (or lack) air quality monitoring network or those who want a more fine-grained air quality mapping.
Ambient air pollution is the primary environmental health risk concern worldwide that causes seven million preventable deaths per year and the loss of healthy years of life; it threatens the sustaining of the environment through acidification and eutrophication. Almost all of the global population breathes air that exceeds the latest health-based guideline levels set by the World Health Organization, with low- and middle-income countries experiencing the highest exposure. Key sources of air pollution are road transport vehicles, domestic heating and industrial installations, and transboundary emissions. These sources produce the main ambient air pollutants of concern to which the population is exposed: particulate matter, ground-level ozone, nitrogen dioxide, carbon monoxide, and sulphur dioxide.
Air quality models constitute a complementary approach to monitoring and characterising air pollution. Spatial and temporal variability of air pollution is mainly investigated across urban areas or those hosting industrial activities, especially in developed countries, where the highest concentration of air pollutants is expected. Understanding these spatial and temporal variabilities is essential for both the implementation of air quality policies and the definition of effective measures to mitigate air pollution and its effects.
This Special Issue aims to showcase selected and original research articles concerning air quality characterisation and modelling. It includes 16 manuscripts covering a wide range of modelling topics, geographical scopes, and the characterisation of different fractions of air pollution.
Among modelling approaches are emission inventories, simulation scenarios, dispersion models, source contribution techniques, and, more particularly, cluster analysis and linear and non-linear regressions, to cite a few. In some manuscripts, air quality indexes or coefficients are used to characterise air quality; others, such as the thermal sensation index or a particular decomposition of the Gini coefficient, are not as frequently used. The geographical scope was diverse, both in urban agglomerations and rural areas, with air quality studies in several countries. Among the studied facets of air pollution were outdoor and indoor pollution, thermal comfort, or the quantification of suspendable road dust. Other included studies examined the role of administrations in air quality, evaluating the effectiveness of local emission reduction plans or carbon trading policies.
We hope the air quality characterisation and modelling community will find this special issue to be an informative and useful collection of articles and serve as an impetus to spur much more research on the topic.
The main purpose of this paper is to analyze the sensitivity of tropospheric ozone and particulate matter concentrations to changes in local scale meteorology with the aid of meteorological variables (wind speed, wind direction, relative humidity, solar radiation and temperature) and intensity of traffic using hourly concentration of NOX, which are measured in three different locations in Tunis, (i.e. Gazela, Mannouba and Bab Aliwa). In order to quantify the impact of meteorological conditions and precursor concentrations on air pollution, a general model was developed where the logarithm of the hourly concentrations of O3 and PM10 were modeled as a sum of non-linear functions using the framework of Generalized Additive Models (GAMs). Partial effects of each predictor are presented. We obtain a good fit with R² = 85% for the response variable O3 at Bab Aliwa station. Results show the aggregate impact of meteorological variables in the models explained 29% of the variance in PM10 and 41% in O3. This indicates that local meteorological condition is an active driver of air quality in Tunis. The time variables (hour of the day, day of the week and month) also have an effect. This is especially true for the time variable “month” that contributes significantly to the description of the study area.
Air pollution has become a critical issue in urban areas, so a broad understanding of its spatiotemporal characteristics is important to develop public policies. This study analyzes the spatiotemporal variation of atmospheric particulate matter (PM10 and PM2.5) and ozone (O3) in Barranquilla, Colombia from March 2018 to June 2019 in three monitoring stations. The average concentrations observed for the Móvil, Policía, and Tres Avemarías stations, respectively, for PM10: 46.4, 51.4, and 39.7 μg/m³; for PM2.5: 16.1, 18.1, and 15.1 μg/m³ and for O3: 35.0, 26.6, and 33.6 μg/m³. The results indicated spatial and temporal variations between the stations and the pollutants evaluated. The highest PM concentrations were observed in the south of the city, while for ozone, higher concentrations were observed in the north. These variations are mainly associated with the influence of local sources in the environment of each site evaluated as well as the meteorological conditions and transport patterns of the study area. This research also verified the existence of differences in the concentrations of the studied pollutants between the dry and rainy seasons and the contribution of local sources as biomass burnings from the Isla Salamanca Natural Park and long-range transport of dust particles from the Sahara Desert. This study provides a scientific baseline for understanding air quality in the city, which enables government to make efficient policies that jointly prevent and control pollution.
Recently, a set of graph-based tools have been introduced for the identification of singular events of O3, NO2 and temperature time series, as well as description of their dynamics. These are based on the use of the Visibility Graphs (VG). In this work, an improvement of the original approach is proposed, being called Upside-Down Visibility Graph (UDVG). It adds the possibility of investigating the singular lowest episodes, instead of the highest. Results confirm the applicability of the new method for describing the multifractal nature of the underlying O3, NO2, and temperature. Asymmetries in the NO2 degree distribution are observed, possibly due to the interaction with different chemicals. Furthermore, a comparison of VG and UDVG has been performed and the outcomes show that they describe opposite subsets of the time series (low and high values) as expected. The combination of the results from the two networks is proposed and evaluated, with the aim of obtaining all the information at once. It turns out to be a more complete tool for singularity detection in photochemical time series, which could be a valuable asset for future research.
A set of indicators derived from the analysis of complex networks have been introduced to identify singularities on a time series. To that end, the Visibility Graphs (VG) from three different signals related to photochemical smog (O3, NO2 concentration and temperature) have been computed. From the resulting complex network, the centrality parameters have been obtained and compared among them. Besides, they have been contrasted to two others that arise from a multifractal point of view, that have been widely used for singularity detection in many fields: the Hölder and singularity exponents (specially the first one of them).
The outcomes show that the complex network indicators give equivalent results to those already tested, even exhibiting some advantages such as the unambiguity and the more selective results. This suggest a favorable position as supplementary sources of information when detecting singularities in several environmental variables, such as pollutant concentration or temperature.
Coastal tourist towns are subject to considerable population fluctuations between the winter and the summer season, as well as between working days and holidays/weekends.
Through the analysis of the data obtained by noise monitoring for both winter and summer seasons at two different points of the town, it was demonstrated that the environmental noise is directly related to the population behaviour. The analysis and comparison of the sound evolution along both working and weekend days showed very typical patterns, which can be used as keys for the forensic acoustics. By analysing these patterns, this method can be applied to determine whether a certain noise corresponds to a working day or to a holiday or weekend.
Introduction:
This study presents a framework for identifying "high-risk" days for asthma attacks associated with elevated concentrations of criteria pollutants using local information to warn citizens on days when the concentrations differ from Environmental Protection Agency Air Quality Index (AQI) warnings. Studies that consider the unique mixture of pollutants and the health data specific to a city provide additional information for asthma self-management. This framework is applied to air pollution and asthma data to identify supplemental warning days in Houston, Texas.
Methods:
A four-step framework was established to identify days with pollutant levels that pose meaningful increased risk for asthma attacks compared with baseline. Historical associations between 18,542 ambulance-treated asthma attacks and air pollutant concentrations in Houston, Texas (2004-2016; analyzed in 2018), were analyzed using a case-crossover study design with conditional logistic regression. Days with historically high associations between pollution and asthma attacks were identified as supplemental warning days.
Results:
Days with 8-hour maximum ozone >66.6 parts per billion for the 3 previous days and same-day 24-hour nitrogen dioxide >19.3 parts per billion pose an RR of 15% above baseline; concentrations above these levels pose an increased risk of 15% (RR=1.15, 95% CI=1.14, 1.16) and 30% (RR=1.30, 95% CI=1.29, 1.32), respectively. These warnings add an additional 12% days per year over the AQI warnings.
Conclusions:
Houston uses this framework to identify supplemental air quality warnings to improve asthma self-management. Supplemental days reflect risk lower than the National Ambient Air Quality Standards and consecutive poor air quality days, differing from the AQI.
Tropospheric ozone (O3) time series have been converted into complex networks through the recent so-called Visibility Graph (VG), using the data from air quality stations located in the western part of Andalusia (Spain). The aim is to apply this novel method to differentiate the behavior between rural and urban regions when it comes to the ozone dynamics. To do so, some centrality parameters of the resulting complex networks have been investigated: the degree, betweenness and shortest path. Some of them are expected to corroborate previous works in order to support the use of this technique; while others to supply new information.
Results coincide when describing the difference that tropospheric ozone exhibits seasonally and geographically. It is seen that ozone behavior is fractal, in accordance to previous works. Also, it has been demonstrated that this methodology is able to characterize the divergence encountered between measurements in urban environments and countryside.
In addition to that, the promising outcomes of this technique support the use of complex networks for the study of air pollutants dynamics. Particularly, new nuances are offered such as the identification and description of singularities in the signal.
A recent method based on the concurrence of complex networks and multifractal analyses is applied for the first time to explore ground-level ozone behavior. Ozone time series are converted into complex networks for their posterior analysis. The searched purpose is to check the suitability of this transformation and to see whether some features of these complex networks could constitute a preliminary analysis before the more thorough multifractal formalism.
Results show effectively that the exposed transformation stores the original information about the ozone dynamics and gives meaningful knowledge about the time series. Based on these results, the multifractal analysis of the complex networks is performed. Looking at the physical meaning of the multifractal properties (such as fractal dimensions and singularity spectrum), a relationship between those and the degree distribution of the complex networks is found.
In addition to all the promising results, this novel connection between time series and complex networks can deal with both stationary and non-stationary time series, overcoming one of the main limitations of multifractal analysis. Therefore, this technique can be regarded as an alternative to give supplementary information within the study of complex signals.
Nowadays, air pollution is one of the most concerning environmental problems in major cities all over the world. Surface ozone (O3) as one of the most important pollutants in troposphere is one of the major components of smog and is formed through a series of photochemical reactions in the presence of volatile organic compounds (VOCs) and nitrogen oxides (NOx). High oxidizing potential of ozone can lead to respiratory problems. Breathing ground-level ozone can trigger variety of health problems such as chest pain, throat and eye irritation, asthma attacks, bronchitis, emphysema and headaches. Also, high ozone concentrations deeply affect plants and cells, and impact worldwide crop and forest. In the last decade, a number of studies have been done in the case of O3 concentration in urban areas. These studies indicate that O3 concentration has increasing trend in major cities
Ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), and nitrogen oxides (NOx) were measured continuously at three sites viz. urban background (JN), urban/traffic (CP), and rural (DP) in Delhi-NCR during the years 2013–2014. Meteorological parameters (temperature and relative humidity) were also measured in order to evaluate the relationship with targeted pollutants. The study shows that highest concentration of O3 was in summer while the lowest ones were recorded in winter and autumn for all the three sites. However, the level of NOx was observed maximum in CP (22.6 ppb) during winter and minimum in DP (5.3 ppb) during autumn. The diurnal variation of O3 was characterized by day-time maxima/(night-time minima) having concentrations 50.2/(17.2), 46.1/(15.7), and 56.7/(23.6) ppb at JN, CP, and DP, respectively. Distinct differences in concentrations were observed for O3 and its precursors during weekends and weekdays for all the three sites. The analysis revealed that higher/(lower) levels of O3 were observed during weekend/(weekdays). The moderate weekend effect was noticed for all the three sites but highest at rural site; DP.O3 was negatively correlated to RH and NOx, while it was positively correlated to temperature. The observed mean concentrations of O3 and NO2 were found to be below the recommended guideline values established by WHO and the European Union.
Tropospheric ozone is considered one of the most significant air pollutants due to its negative effects on human health, agricultural crops, ecosystems and climate. The features of the southwest of the Iberian Peninsula (high temperatures and high solar radiation, the presence of the Guadalquivir basin and sources of precursors) favour the occurrence of episodes of high concentrations that cause exceedances of legal thresholds with relative frequency. Despite this, no study examining regional ozone episodes has been carried out in this region until now. In the present work a surface hourly ozone dataset (2003–2006) measured at 11 representative stations located in the southwest of the Iberian Peninsula (western Andalusia) was analysed in order to identify and characterise, for the first time, the regional ozone episodes that occur in this area. Using a statistical criterion, eight regional episodes were identified and analysed. The analysis of synoptic weather patterns revealed that these episodes occur in conjunction with two different synoptic conditions (high surface pressure either close to the British Isles or over the Atlantic Ocean). Both conditions generate weak isobaric surface pressure over the Iberian Peninsula, favouring the establishment of easterly winds at 500 m and the development of winds with two main prevailing directions (southwest-northwest, following the Guadalquivir basin) in the study area. During episodic days ozone follows a similar daily cycle to that observed on non-episode summer days, although the levels reached during the former are higher. In both cases, a direct relationship between the daily ozone cycle and the local wind regimen was not observed. This therefore seems to indicate that the daily cycle followed by ozone is mainly regulated by the precursor emissions produced in the environment, by the temperature changes taking place during the day and by the influence of the lower troposphere during anticyclonic weather conditions.
A new approach to modeling regional air chemistry is presented for application to industrialized regions such as the continental US. Rural chemistry and transport are simulated using a coarse grid, while chemistry and transport in urban and power plant plumes are represented by detailed subgrid models. Emissions from urban and power plant sources are processed in generalized plumes where chemistry and dilution proceed for 8-12 hours before mixing with air in a large resolution element. A realistic fraction of pollutants reacts under high-NOâ conditions, and NOâ is removed significantly before dispersal. Results from this model are compared with results from grid odels that do not distinguish plumes and with observational data defining regional ozone distributions. Grid models with coarse resolution are found to artificially disperse NOâ over rural areas, therefore overestimating rural levels of both NOâ and Oâ. Regional net ozone production is too high in coarse grid models, because production of Oâ is more efficient per molecule of NOâ in the low-concentration regime of rural areas than in heavily polluted plumes from major emission sources. Ozone levels simulated by this model are shown to agree with observations in urban plumes and in rural regions. The model reproduces accurately average regional and peak ozone concentrations observed during a 4-day ozone episode. Computational costs for the model are reduced 25-to 100-fold as compared to fine-mesh models.
The authors examine the sensitivity of ozone concentrations in rural areas of the US to emissions of NOâ and hydrocarbons using a regional photochemical model. Ozone production in rural areas appears to be limited by the availability of NOâ. Rural ozone is strongly dependent on emission rates for NOâ but is almost independent of hydrocarbons. This relationship is quite different from that in urban air, where ozone levels depend on both NOâ and hydrocarbons. The predicted relationship between ozone and nitrogen oxides appears to be consistent with observations in rural air. For the low NOâ regime (< 2 ppb) in rural areas, increases in NOâ lead to increases in OH and to corresponding increases in the oxidation rate of hydrocarbons and in levels of ozone. Ozone concentrations in urban plumes appear to be related to regional scale production in addition to production within the plume.
Ozone (O(3)) mixing ratios were measured at three different sites (urban/traffic, semi-rural and rural/island) in Istanbul from September 2007 to December 2009 in order to determine the diurnal, monthly and seasonal variations of O(3) and nitrogen oxides (NO(x)) and to study the local and regional impacts. This is the first study that evaluates the O(3) levels in semi-rural and rural sites in Istanbul in addition to the urban sites. The diurnal O(3) variations are generally characterized by afternoon maxima (64ppb at the urban, 80ppb at the semi-rural and 100ppb at the rural site) and the nighttime minimum being more pronounced at the polluted urban site. The monthly mean O(3) mixing ratios start to increase in March, reaching their maximum values in August for the urban (~25ppb) and semi-rural sites (30ppb). However, at the rural site, the monthly mean O(3) levels reach their maximum value in June (35ppb). The O(3) mixing ratios for weekends were higher than those on weekdays at each site by up to 28%, possibly due to changes in VOC sensitivity and reduction in NO(x) levels. In order to better understand and characterize the relationship between air masses and O(3) levels, cluster analysis was applied to the back-trajectories calculated by the HYSPLIT model for the semi-rural site. The analyses clearly showed that major transport is characterized by northern and western clusters, particularly from the Eastern Europe and the Mediterranean region, as well as recirculation over Istanbul due to high pressure systems leading to accumulated levels of O(3). The results clearly suggest that extended measurement networks from urban to rural sites should be considered for a more comprehensive evaluation of O(3) levels.
A unique, record-breaking, killer heat wave occurred across several European countries during the first two weeks of August
2003. As weather conditions which characterize heat waves are highly conductive to tropospheric ozone formation and persistence,
this is a contributing factor which should be regarded as a major stressor for biota. Hourly ozone means were captured between
1 and 15 August 2003 with automatic analysers in nine stations in Tuscany, distributed into six Districts. Compared to historical
ozone reference climatology, daily maxima of 2003 were systematically higher by a factor of about 1.5, with differences which
approached three times standard deviation. At the end of the period, cumulated ozone exposure over the threshold of 40ppb
(AOT40) was 4,750ppb h in 2003, vs 2,200ppb h of the historical series; such a difference was four times the standard deviation
of the long-term series. Biological data are also enclosed in the present study, in the form of analysis of the ratio between
above ground biomass produced by NC-S and NC-R clones of white clover when exposed to ambient air. Standardised samplings
were performed on a monthly basis, and a significant difference between the two data sets was observed between summer 2003
and the historical series. The close correlation of high-ozone episode with increased temperature (as a consequence of increased
solar radiation) suggests that, if climate change were to result in warmer summers in Europe, more frequent exceedances of
dangerous ozone thresholds would be expected at the current emission levels.
Hourly ozone, NOx
and VOC concentrations, measured during 2001–2003 summer periods, are analyzed in order to examine the interaction patterns between the major photochemical pollutants in İstanbul. 34 high ozone days throughout the summer periods of the three years are determined and examined in the study together with the meteorological parameters like temperature, wind and vertical structure of the atmosphere. The results show that high levels of ozone are observed mostly under anticyclonic conditions with relatively low wind speeds. High ozone days generally experienced maximum concentrations at afternoon hours and minimum concentrations are reached at rush hours due to NOx
– titration by traffic emissions. High negative correlations with NOx
up to -0.84 are observed at the Saraçhane station while higher correlations for VOC species, up to −0.75, are calculated for Kadiköy station. Some individual episodes experiencing high ozone concentrations up to 310 μg m−3 in the early morning hours are also studied. It is found that decreasing inversion heights in the early hours of the day led to suppression of pollutants close to surface and thus, an increase in ozone concentrations was observed. Low wind speeds played a major role in the increase of pollution levels in the region. HYSPLIT model is applied to some particular episodes and the results show that the northeasterly transport to the region was dominant, especially in the early-morning maximums.
Important aspects of the seasonal variations of surface ozone are discussed. The underlying analysis is based on the long-term (1990–2004) ozone records of the Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP) and the World Data Centre of Greenhouse Gases, which provide data mostly for the Northern Hemisphere. Seasonal variations are pronounced at most of the 114 locations at all times of the day. A seasonal-diurnal variations classification using hierarchical agglomeration clustering reveals 6 distinct clusters: clean background, rural, semi-polluted non-elevated, semi-polluted semi-elevated, elevated and polar/remote marine. For the "clean background" cluster the seasonal maximum is observed in March-April, both for night and day. For those sites with a double maximum or a wide spring-summer maximum, the spring maximum appears both for day and night, while the summer maximum is more pronounced for daytime and hence can be attributed to photochemical processes. The spring maximum is more likely caused by dynamical/transport processes than by photochemistry as it is observed in spring for all times of the day. We compare the identified clusters with corresponding data from the 3-D atmospheric chemistry general circulation model ECHAM5/MESSy1 covering the period of 1998–2005. For the model output as for the measurements 6 clusters are considered. The simulation shows at most of the sites a spring seasonal maximum or a broad spring-summer maximum (with higher summer mixing ratios). For southern hemispheric and polar remote locations the seasonal maximum in the simulation is shifted to spring, while the absolute mixing ratios are in good agreement with the measurements. The seasonality in the model cluster covering background locations is characterized by a pronounced spring (April–May) maximum. For the model clusters which cover rural and semi-polluted sites the role of the photochemical production/destruction seems to be overestimated. Taking into consideration the differences in the data sampling procedure, the comparison demonstrates the ability of the model to reproduce the main regimes of surface ozone variations quite well.
Photochemical ozone pollution of the lower troposphere (LT) is a very complex process involving meteorological, topographic emissions and chemical parameters. Ozone is considered the most important air pollutant in rural, suburban and industrial areas of many sites in the world since it strongly affects human health, vegetation and forest ecosystems, and its increase during the last decades has been significant. In addition, ozone is a greenhouse gas that contributes to climate change. For these reasons, it is necessary to carry out investigations that determine the behaviour of ozone at different locations. The aim of this work is to understand the levels and temporal variations of surface ozone in an industrial-urban region of the Southwest Iberian Peninsula.
The study is based on ozone hourly data recorded during a 6-year period, 2000 to 2005 at four stations and meteorological data from a coastal station. The stations used were El Arenosillo and Cartaya--both coastal stations, Huelva--an urban site and Valverde--an inland station 50 km away from the coastline. The general characteristics of the ozone series, seasonal and daily ozone cycles as well as number of exceedances of the threshold established in the European Ozone Directive have been calculated and analysed.
Analysis of the meteorological data shows that winter-autumn seasons are governed by the movement of synoptic weather systems; however, in the spring-summer seasons, both synoptic and mesoescale conditions exist. Average hourly ozone concentrations range from 78.5 +/- 0.1 microg m(-3) at Valverde to 57.8 +/- 0.2 microg m(-3) at Huelva. Ozone concentrations present a seasonal variability with higher values in summer months, while in wintertime, lower values are recorded. A seasonal daily evolution has also been found with minimum levels around 08:00 UTC, which occurs approximately 1-1.5 h after sunrise, whereas the maximum is reached at about 16:00 UTC. Furthermore, during summer, the maximum value at El Arenosillo and Valverde stations remains very uniformed until 20:00 UTC. These levels could be due to the photochemical production in situ and also to the horizontal and vertical ozone transport at El Arenosillo from the reservoir layers in the sea and in the case of Valverde, the horizontal transport, thanks to the marine breeze. Finally, the data have been evaluated relative to the thresholds defined in the European Ozone Directive. The threshold to protect human health has been exceeded during the spring and summer months mainly at El Arenosillo and Valverde. The vegetation threshold has also been frequently exceeded, ranging from 131 days at Cartaya up to 266 days at Valverde.
The results in the seasonal and daily variations demonstrate that El Arenosillo and Valverde stations show higher ozone concentrations than Cartaya and Huelva during the spring and summer months. Under meteorological conditions characterized by land-sea breeze circulation, the daytime sea breeze transports the emissions from urban and industrial sources in the SW further inland. Under this condition, the area located downwind to the NE is affected very easily by high ozone concentrations, which is the case for the Valverde station. Nevertheless, according to this circulation model, the El Arenosillo station located at the coast SE from these sources is not directly affected by their emissions. The ozone concentrations observed at El Arenosillo can be explained by the ozone residual layer over the sea, similar to other coastal sites in the Mediterranean basin.
The temporal variations of the ozone concentrations have been studied at four measurement sites in the southwest of the Iberian Peninsula. The results obtained point out that industrial and urban emissions combined with specific meteorological conditions in spring and summer cause high ozone levels which exceed the recommended threshold limits and could affect the vegetation and human health in this area.
This work is the first investigation related to surface ozone in this region; therefore, the results obtained may be a useful tool to air quality managers and policy-makers to apply possible air control strategies towards a reduction of ozone exceedances and the impact on human health and vegetation. Due to the levels, variability and underlying boundary layer dynamics, it is necessary to extend this research in this geographical area with the purpose of improving the understanding of photochemical air pollution in the Western Mediterranean Basin and in the south of the Iberian Peninsula.
Air quality data from a network of 11 monitoring stations in the Apulia region of southern Italy during the summer of 2005 reveal a high frequency of ozone law limit violations. Since ozone is a secondary pollutant, air quality control strategies aimed at reducing ozone concentration are not immediate. Herein, we analyse weekly changes in concentration levels of ozone (O(3)), nitrogen oxides (NO(x)), carbon monoxide (CO), and volatile organic compounds (VOCs), and evaluate how the differences in primary emissions cause changes in the production of ozone. The comparison between weekend and weekday levels of O(3) and its precursors are direct evidence for the existence of the "ozone weekend effect." This effect was observed at all stations with a considerable variation in the overall ozone magnitude, including both traffic stations and non-traffic stations. Data from VOC measurements at traffic stations primarily indicated elevated levels of benzene, toluene, and xylenes (BTX); all of these substances showed an overall decrease over the weekend. A single station indicated levels of non-methane hydrocarbon (NMHC) and PM10, both of which did not demonstrate any weekly cycle. Analysis of weekly and diurnal cycles of O(3), NO(x), CO, NMHC, and PM10 indicates that higher weekend ozone levels result from a reduction in the emission of nitrogen oxides on weekends in VOC-sensitive regimes. This indicates that a reduction in VOC and NO(x) levels would be more effective than NO(x) reduction alone. Our results underscore the need for improved and more efficient VOC measurements.
A national analysis of weekday/weekend ozone (O3) differences demonstrates significant variation across the country. Weekend 1-hr or 8-hr maximum O3 varies from 15% lower than weekday levels to 30% higher. The weekend O3 increases are primarily found in and around large coastal cities in California and large cities in the Midwest and Northeast Corridor. Both the average and the 95th percentile of the daily 1-hr and 8-hr maxima exhibit the same general pattern. Many sites that have elevated O3 also have higher O3 on weekends even though traffic and O3 precursor levels are substantially reduced on weekends. Detailed studies of this phenomenon indicate that the primary cause of the higher O3 on weekends is the reduction in oxides of nitrogen (NOx) emissions on weekends in a volatile organic compound (VOC)-limited chemical regime. In contrast, the lower O3 on weekends in other locations is probably a result of NOx reductions in a NOx-limited regime. The NOx reduction explanation is supported by a wide range of ambient analyses and several photochemical modeling studies. Changes in the timing and location of emissions and meteorological factors play smaller roles in weekend O3 behavior. Weekday/weekend temperature differences do not explain the weekend effect but may modify it.
Simulations with a regional chemical transport model show that anthropogenic emissions of volatile organic compounds and nitrogen oxides (NO(x) = NO + NO(2)) lead to a dramatic diurnal variation of surface ozone (O(3)) in Houston, Texas. During the daytime, photochemical oxidation of volatile organic compounds catalyzed by NO(x) results in episodes of elevated ambient O(3) levels significantly exceeding the National Ambient Air Quality Standard. The O(3) production rate in Houston is significantly higher than those found in other cities over the United States. At night, a surface NO(x) maximum occurs because of continuous NO emission from industrial sources, and, consequently, an extensive urban-scale "hole" of surface ozone (<10 parts per billion by volume in the entire Houston area) is formed as a result of O(3) removal by NO. The results suggest that consideration of regulatory control of O(3) precursor emissions from the industrial sources is essential to formulate ozone abatement strategies in this region.
Ground level ozone (O3) concentration was monitored during the period of December 2004 to November 2005 in an urban area in Greater Cairo (Haram, Giza). During the winter and summer seasons, nitrogen dioxide (NO2) and nitric oxide(NO) concentrations and meteorological parameters were also measured. The mean values of O3 were 43.89, 65.30, 91.30 and 58.10 ppb in daytime and 29.69, 47.80, 64.00 and 42.70 ppb in whole day (daily) during the winter, spring, summer and autumn seasons, respectively. The diurnal cycles of O3 concentrations during the four seasons revealed a uni-modal peak in the mid-day time, with highest O3 levels in summer due to the local photochemical production. The diurnal variations in NO and NO2 concentrations during the winter and summer showed two daily peaks linked to traffic density. The highest levels of NOx were found in winter. Nearly, 75%, 100%, 34.78% and 52.63% of the mean daytime concentrations of O3 during spring,summer, autumn and the whole year, respectively, exceeded the Egyptian and European Union air quality standards (60 ppb) for daytime (8-h) O3 concentration. About, 41.14% and 10.39% of the daytime hours concentrations and 14.93% and 3.77% of the daily hour concentrations in summer and the whole year, respectively, exceeded the Egyptian standard (100 ppb) for maximum hourly O3 concentration, and photochemical smog is formed in the study area (Haram) during a periods represented by the same percentages. This was based on the fact that photochemical smog usually occurs when O3 concentration exceeds 100 ppb. The concentrations of O3 precursors (NO and NO2) in weekends were lower than those found in weekdays, whereas the O3 levels during the weekends were high compared with weekdays. This finding phenomenon is known as the "weekend effect". Significant positive correlation coefficients were found between O3 and temperature in both seasons and between O3 and relative humidity in summer season, indicating that high temperature and high relative humidity besides the intense solar radiation (in summer) are responsible for the formation of high O3 concentrations.
This paper compares the results from a single-stage clustering technique (average linkage) with those of a two-stage technique (average linkage then k-means) as part of an objective meteorological classification scheme designed to better elucidate ozone’s dependence on meteorology in the Houston, Texas, area. When applied to twelve years of meteorological data (1981–1992), each clustering technique identified seven statistically distinct meteorological regimes. The majority of these regimes exhibited significantly different daily 1 h maximum ozone (O3) concentrations, with the two-stage approach resulting in a better segregation of the mean concentrations when compared to the single-stage approach. Both approaches indicated that the largest daily 1 h maximum concentrations are associated with migrating anticyclones that occur most often during spring and summer, and not with the quasi-permanent Bermuda High that often dominates the southeastern United States during the summer. As a result, maximum ozone concentrations are just as likely during the months of April, May, September and October as they are during the summer months. Generalized additive models were then developed within each meteorological regime in order to identify those meteorological covariates most closely associated with O3 concentrations. Three surface wind covariates: speed, and the u and v components were selected nearly unanimously in those meteorological regimes dominated by anticyclones, indicating the importance of transport within these O3 conducive meteorological regimes.
Studies conducted over the past decades have provided substantial evidence that both the long- and the short-term exposures to ozone and particulate matter are responsible for mortality and cardiopulmonary morbidity. This paper examines the relationship between exposure to ambient concentrations of ozone (O3) and particulate matter with aerodynamic diameter of less than 10 μm (PM10) and public health and provides the quantification of the burden of disease from PM10 and O3-related mortality and morbidity through a Life Cycle Impact Assessment focused on the greater area of Athens, Greece. Thus, characterizations factors (CFs) for human health damage are calculated in 17 sites in Athens, in terms of the annual marginal change in the disability-adjusted life years (DALYs) due to a marginal increase in the ambient concentrations. It is found that the PM10 intake factors range between 1.25 × 10−6 and 2.78 × 10−6, suggesting that 1.25–2.78 μg of PM10 are inhaled by the Athenian population per kg of PM10 in the urban atmosphere. Mortality due to chronic exposure to PM10 has a dominant contribution to years of life lost with values ranging between 6.2 × 10−5 and 1.1 × 10−4. On the other hand, the mortality caused by short-term exposure to O3 is weaker with the CFs ranging between 1.58 × 10−7 years of life lost in the urban/traffic areas and 4.71 × 10−7 years in the suburbs. Finally, it is found that 9,000 DALYs are lost on average in Athens, corresponding to 0.0018 DALYs per person. This is equal to 0.135 DALYs per person over a lifetime of approximately 75 years, assuming constant emission rates for the whole period.
There is good evidence for an increase in the global surface level of ozone in the past century. In this work we present an analysis of 18 surface ozone series over the Iberian Peninsula, considering the target values of ozone for the protection of human health and for the protection of vegetation, as well as the information and alert thresholds established by the current European Directive on ambient air quality and cleaner air for Europe (Directive 2008/50/EC). The results show that the stations located on the Cantabrian coast exceeded neither the target value for the protection of human health nor the target value for the protection of vegetation. The information threshold was exceeded in most of the stations, while the alert threshold was only exceeded in one. The seasonal and daily evolution of ozone concentrations were as expected. A trend analysis of three surface ozone concentration indices (monthly median and 98th percentile, and monthly maximum of the daily maximum 8-h mean) was performed both for the whole period of each station and for the common period from 2001 to 2007 for all the months of the year. It was noted that generally the south of the Iberian Peninsula presented increasing trends for the three indices, especially in the last six months of the year, and the north decreasing trends. Finally, a correlation analysis was performed between the daily maximum 8-h mean and both daily mean temperature and daily mean solar radiation for the whole and the common periods. For all stations, there was a significant positive association at a 5% significance level between the daily maximum 8-h mean and the two meteorological variables of up to approximately 0.5. The spatial distribution of these association values from 2001 to 2007 showed a positive northwest to southeast gradient over the Iberian Peninsula.
The weekend effect on ozone, a phenomenon with high ozone concentration at weekend, was analyzed using the data measured at 7 photochemical assessment monitoring stations (PAMS), (1) volatile organic compounds (VOCs) monitoring station and (2) routine ambient air quality monitoring stations in southern California during ozone season from 1995 to 2001. Weekend/weekday differences of ozone, ozone precursors and PM10 concentrations and the light scatter, composition and reactivity of VOCs in morning traffic rush time and afternoon peak ozone time were compared. The possible causes for the weekend effect were discussed. The significant weekend effect was observed in southern California except in areas close to beach and far downwind direction from L.A. Downtown. On average, the peak O3 and max 8 h average O3 concentrations at weekend were 20% and 22%, respectively, higher than those on weekday while the concentrations of O3 precursors and PM10 and the light scatter were lower at weekday in southern California. In morning traffic rush time, the average concentrations of NOx, CO, NMOC and PM10 and the light scatter at weekend were about 37%, 18%, 15%, 14% and 9%, respectively, lower than those on weekday. In afternoon peak ozone time, the average concentrations of NOx, CO, NMOC and PM10 and the light scatter at weekend were about 29%, 13%, 24%, 17% and 17%, respectively, lower than those on weekday. The reactivities of VOCs in morning traffic rush time and afternoon peak ozone time at weekend were 17% and 26%, respectively, lower than those on weekday. VOCs sensitivity for ozone formation and a decrease NOx emissions at weekend can well explain the weekend effect in southern California. Less scatter of sunlight due to lower fine particle concentration at weekend results in enhanced ozone formation might be another possible cause for the weekend effect.
Continuous ground-based measurements of O3 and its precursors were conducted in Dhaka, Bangladesh during April 2002–December 2005 in order to investigate ozone precursor characteristics and their distribution. Seasonal and diurnal variations of the O3, CO, NOx and SO2 concentrations — are studied and their possible causes are identified. It is shown that most of the trace gases have peak concentrations in winter and base in monsoon period. Two major emission sources, vehicles and brick kilns, are attributed to the high levels of trace gases in winter. O3 formation was mainly due to local activity and relied on photochemical processes with precursors. The occurrence patterns and the shape of a distribution of trace gases are obtained from histogram distribution. In most cases, the frequency distributions of observed trace gases show a peak to the lower concentration ranges (e.g. 0–10 ppb for O3, 0–500 ppb for CO, 0–20 ppb for NO, NO2 and 0–10 ppb for SO2) with a long tail to the right and unimodal in most of the cases.CO, NOx and SO2 are significantly correlated throughout the entire data set, reflecting the overall influence of anthropogenic emissions.
Concentrations of O3, NO, NO2, NOx and oxidant (OX = O3 + NO2) were investigated for the first time, in the southwest of the Iberian Peninsula, in the Seville metropolitan area, during 2004. This area experiences frequent photochemical pollution events, mainly in the warm season. Two different environments were analyzed and compared, an urban traffic station (Torneo) and a suburban station (Aljarafe). The concentration of OX (defined as O3 + NO2) can be described in terms of the sum of a NOx-independent ‘regional’ contribution (i.e. the O3 background), and a linearly NOx-dependent ‘local’ contribution. Monthly dependence of regional and local OX concentration variation at Torneo and Aljarafe stations were studied along with the annual variation of the daily mean NOx and OX. Maximum levels of OX > 190 μg m− 3 where NOx < 70 μg m− 3 at Aljarafe, and OX < 170 μg m− 3 with NOx around 80–90 μg m− 3 can be expected in summer months and during daylight hours. Also during summer, but at night, more elevated NOx levels are needed in order to achieve maximum OX values (OX = 130–150 μg m− 3 with NOx ≥ 100 μg m− 3 at Aljarafe, OX = 110–130 μg m− 3 with NOx ≥ 100 μg m− 3 at Torneo). This can be used as an approximation to estimate the OX concentrations in Seville for each month, as a function of the NOx measured, as well as to improve in the atmospheric photochemical dynamic in the Spanish Western Mediterranean area where there are undeniable air quality problems.
The daily variations of surface ozone, NO2 and SO2 have been investigated in a heavily industrialised area in the centre of the Iberian Peninsula (Puertollano) using hourly values recorded during two years (2008–2009) with an active LP-DOAS system. The meteorological conditions and air masses have been studied using the HYSPLIT model. The maximum hourly levels of these air pollutants exceeded 100 ppb for ozone, 150 ppb for SO2 and 210 ppb for NO2. However, mean values for ozone, NO2 and SO2 were of 49, 10 and 3 ppb respectively. Daily–monthly evolutions (defined as daily evolutions for different months) have been analysed in order to know the general daily behaviour of these species. Air pollution problems have been identified using the thresholds defined in the European Directive 2008. The limits to protect human health (human health protection limitations) have been exceeded during the study period. In order to find a set of representative daily cycles for each pollutant at different air quality regimes, a K-mean cluster technique has been applied. Five and four optimal cluster numbers have been obtained for the daily patterns of ozone and SO2 respectively. In addition, we studied the daily variation of the temperature, relative and specific humidity and wind speed associated with each air pollutant daily pattern. Ozone daily patterns showed typical daily variations with one exception of a cluster which presents a peak in the early morning. For SO2, the first two clusters present a low mixing ratio, however cluster 3 and 4 are less frequent but with higher levels. The more frequent air pollutant daily patterns do not exceed the threshold defined in the Directive. Nevertheless, clusters with lower frequency (representing between 5 and 7% of days) exceed the thresholds and could be considered as air pollution events.
To the authors knowledge, there exists no recent review paper on the computation and use of trajectories. To fill this gap, this study summarizes the current knowledge on the calculation and application of trajectories. The different techniques that can be used to compute trajectories are presented and their error sources are described. The assumptions often made to account for the vertical wind velocity are explained. Most studies agree now that fully three-dimensional trajectories are the most accurate trajectory type. Methods to assess trajectory errors are outlined and a summary of the errors presented in the literature is given. Errors of 20% of the distance travelled seem to be typical for trajectories computed from analyzed wind fields. Finally, some important applications of trajectories, namely Lagrangian particle dispersion models, Lagrangian chemical box models and trajectory statistics, are discussed.
Weekly and seasonal variations of surface ozone and their precursors – nitrogen oxides, carbon monoxide-associated with meteorological parameters (wind direction, temperature, solar radiation) – are reported. Measurements were performed continuously during 2006 at two sampling stations located in the metropolitan area of Porto Alegre, Brazil. Results have shown that O3 concentrations remained almost constant between weekdays. Levels of NOx precursors decreased especially on Sundays, due to lighter traffic. The seasonal variation has shown a maximum O3 concentration during summer and spring while NOx and NO2 have maxima at the colder months. The daily cycle of highest ozone concentrations reveals a lower nightly level and an inverse relation between O3 and NOx, evidencing the photochemical formation of O3. There are seasonal variation and source heterogeneity.
The author presents an analysis of trends in ozone since about 1970 and discusses the quality of the ozonesonde data and inconsistencies among data records. In the troposphere there are significant spatial variations in the trends, with largest increases found over Europe (â¼2% yrâ»Â¹ throughout the troposphere) and no long-term trend over Canada; there is a small (53°N) stations of North America. These seasonal losses are consistent with the patterns reported using TOMS data. Losses are found year round over Syowa, Antarctica, although they are largest in spring. 99 refs., 27 figs., 12 tabs.
Located in the southwest of the Iberian Peninsula, the Guadalquivir valley is a site of frequent problems related to air pollution. The atmospheric dynamics of this region is poorly characterised but is fundamental to understanding the chemical and photochemical processes that contribute to the pollution problems. In this work, the atmospheric mesoscale Weather Research and Forecasting (WRF-ARW) model was used to study the horizontal and vertical development of the two sea–land breeze patterns (pure and non-pure) that are identified in the coastal area as being responsible for many of the air pollution events. In addition, data from five meteorological stations within the valley were used to validate and compare the model results.
Cluster analysis is a collective term covering a wide variety of techniques for delineating natural groups or clusters in data sets. This book integrates the necessary elements of data analysis, cluster analysis, and computer implementation to cover the complete sequence of steps from raw data to the finished analysis. The author develops a conceptual and philosophical basis for using cluster analysis as a tool of discovery and applies it systematically throughout the book. He provides a comprehensive discussion of variables, scales, and measures of association that establishes a sound basis for constructing an operational definition of similarity tailored to the needs of any particular operational definition of similarity tailored to the needs of any particular problem, and devotes special attention to the problems of analyzing data sets containing mixtures of nominal, ordinal, and interval variables. (Author)
In this paper, 10-years of ozone (O3) hourly concentrations collected over the period 2000–2009 in the Iberian Peninsula (IP) are analyzed using records from 11 background sites. All the selected monitoring stations present an acquisition efficiency above 85%. The changes in surface ozone over the Iberian Peninsula are examined by means of quantile regression, which allows to analyse the trends not only in the mean but in the overall data distribution. In addition, the ozone hourly concentrations records are clustered on the basis of their resulting distributions.
The chemical processing of pollutants emitted into the atmosphere leads to a variety of oxidised products, which are commonly referred to as secondary pollutants. Such pollutants are often formed on local or regional scales in the planetary boundary layer, and may have direct health impacts and/or play wider roles in global atmospheric chemistry. In the present review, a comparatively detailed description of our current understanding of the chemical mechanisms leading to the generation of secondary pollutants in the troposphere is provided, with particular emphasis on chemical processes occurring in the planetary boundary layer. Much of the review is devoted to a discussion of the gas-phase photochemical transformations of nitrogen oxides (NOx) and volatile organic compounds (VOCs), and their role in the formation of ozone (O3). The chemistry producing a variety of other oxidants and secondary pollutants (e.g., organic oxygenates; oxidised organic and inorganic nitrogen compounds), which are often formed in conjunction with O3, is also described. Some discussion of nighttime chemistry and the formation of secondary organic aerosols (SOA) in tropospheric chemistry is also given, since these are closely linked to the gas-phase photochemical processes. In many cases, the discussion of the relative importance of the various processes is illustrated by observational data, with emphasis generally placed on conditions appropriate to the UK and northwest continental Europe.
Some of the approaches that have been developed in the Aeronomy Laboratory and used to determine the rate and amount of ozone that is photochemically produced in the atmosphere from human-made and natural ozone precursors are reviewed below. The results were obtained from analysis of our field measurements that were made in the United States of the concentrations of O3, O3-precursors, the photochemical intermediates, and other photochemical products, as well as other atmospheric parameters. The utility of these approaches to identify the individual processes that lead to the formation and loss of ozone and O3-precursors are described and some of the crucial uncertainties that still remain are identified. The information obtained using these observational approaches include: (1) the apportionment of volatile organic compounds (VOCs), carbon monoxide (CO) and the oxides of nitrogen (NOx=NO+NO2) among the various anthropogenic sources; (2) the importance of natural VOCs/CO and NOx relative to anthropogenic VOCs/CO and NOx in photochemical ozone production; (3) identification of the mechanism for the photochemical chemical production and photochemical processing; (4) the determination of the instantaneous rate of photochemical production of O3; (5) the efficiency of tropospheric ozone production relative to the NOx concentrations; (6) the importance of NOx relative to VOCs and CO in determining observed O3 levels.
A systematic analysis of surface ozone observations in rural areas surrounding Athens is presented. The analysis is based on ozone data for the rural station Aliartos about 80 km NW of Athens center and for two stations on the northern periphery of the Athens basin: Demokritos, located 10 km NE of Athens center and Liossia, 12 km to the north. The data for these two stations are screened for cases of strong air flow from rural areas. Average hourly summer afternoon ozone mixing ratios are similar for all three stations about 60 ppb and thus exceed for the hours 12:00–20:00 LST the 55 ppb WHO guideline for human health for 8 h ozone exposure. The corresponding winter afternoon mixing ratios are at 35 ppb. However, due to the large diurnal variation, mean monthly ozone mixing ratios at Aliartos, for the months April–September vary from 32 to 40 ppb, which is comparable to the higher average ozone levels at rural stations in south-central Europe. In cases of southerly air flow in the summer in the Athens basin, afternoon ozone levels at Demokritos and Liossia are generally the highest of any in the monitoring network. Hourly average concentrations, however, are only 40% greater than rural values. A background ozone level of such magnitude will have a significant impact on estimates for the effectiveness of pollution control measures for Athens.
A study of ozone concentration measurements at 20 rural sites throughout the UK has enabled the identification of the major variables controlling surface ozone concentrations (wind velocity, topography and local NO sources). Empirical methods to quantify the spatial pattern in surface concentrations at 1 km resolution, incorporating these influences, are developed. The procedure maps ozone concentrations from the period of the day when measurements are representative of large areas of countryside. In these conditions, rural monitoring sites (∼100 km apart) are highly correlated (r2⩾0.8) and least affected by local site characteristics. The effects of boundary layer stability are quantified using the observed relationship between the diurnal variability of surface ozone concentration and altitude. This allows the detailed structure in rural concentrations to be quantified. An urban correction, to account for the gas phase titration of surface ozone by local NO sources, is added to the mapping procedure based on the relationship between urban ozone concentration measurements and those in rural areas.The spatial distribution of the annual average ozone concentration and the accumulated ozone concentration over a threshold of 40 ppb (AOT40) are calculated from UK measurements. Simple assessments of the effects of ozone on materials and vegetation are made. Although 87% of the UK exceeds the critical level for materials (20 ppb annual average), this is less than 0.1% of urban areas and so the risk of damage is probably small. For crops and semi-natural vegetation, the critical level (AOT40 3000 ppb h May–July daylight hours) is exceeded over 71% of the UK; for forests, the critical level (10,000 ppb h April–September daylight hours) is exceeded over 8% of the country. This indicates the potential for effects on large areas of crops and semi-natural vegetation but only small areas of forest.
Ambient aerometric data were used to predict whether ozone formation at specific times and locations in central California was limited by the availability of volatile organic compounds (VOC) or oxides of nitrogen (NOx). The predictions were compared with differences between mean weekday and weekend peak ozone values. The comparison with weekend and weekday ozone levels provided a means for empirically investigating the effects of VOC and NOx reductions on ozone formation, because the relative proportions and levels of ozone precursor species were significantly different on weekends than on weekdays. Weekend NOx levels averaged 27 percent lower than weekday levels at the time of the peak ozone hour. Daytime weekend levels of VOC species were also consistently lower than weekday values throughout the region, though the differences between weekends and weekdays were not always statistically significant (p<0.05). Site-to-site differences between weekend and weekday mean peak hourly ozone were related to whether ozone formation was VOC- or NOx-limited.
To the authors knowledge, there exists no recent review paper on the computation and use of trajectories. To fill this gap, this study summarizes the current knowledge on the calculation and application of trajectories. The different techniques that can be used to compute trajectories are presented and their error sources are described. The assumptions often made to account for the vertical wind velocity are explained. Most studies agree now that fully three-dimensional trajectories are the most accurate trajectory type. Methods to assess trajectory errors are outlined and a summary of the errors presented in the literature is given. Errors of 20% of the distance travelled seem to be typical for trajectories computed from analyzed wind fields. Finally, some important applications of trajectories, namely Lagrangian particle dispersion models, Lagrangian chemical box models and trajectory statistics, are discussed.
An attempt has been made to examine the seasonal variation of the surface ozone mixing ratio in Athens, Greece during the periods 1901–1940 and 1987–1998. The first finding is that in July and August while the daytime surface ozone mixing ratio from the beginning until the end of the 20th century has increased by approximately 1.8 times, the nighttime surface ozone mixing ratio remained approximately at the same level. The second finding is that the increase in the mean daytime mixing ratio during the transition period from winter to summer is equal to the increase in the maximum daytime mixing ratios, whilst the enhancement of the nighttime surface ozone maxima is stronger than that of the nighttime mean surface ozone mixing ratio. Plausible explanation for this finding is given through mechanisms like long-range transport and photochemical processes occurring in the boundary layer, free troposphere and lower stratosphere.
In the frame of a European research project on air quality in urban agglomerations, data on ozone concentrations from 23 automated urban and suburban monitoring stations in 11 cities from seven countries were analysed and evaluated. Daily and summer mean and maximum concentrations were computed based on hourly mean values, and cumulative ozone exposure indices (Accumulated exposure Over a Threshold of 40 ppb (AOT40), AOT20) were calculated. The diurnal profiles showed a characteristic pattern in most city centres, with minimum values in the early morning hours, a strong rise during the morning, peak concentrations in the afternoon, and a decline during the night. The widest amplitudes between minimum and maximum values were found in central and southern European cities such as Düsseldorf, Verona, Klagenfurt, Lyon or Barcelona. In the northern European cities of Edinburgh and Copenhagen, by contrast, maximum values were lower and diurnal variation was much smaller. Based on ozone concentrations as well as on cumulative exposure indices, a clear north–south gradient in ozone pollution, with increasing levels from northern and northwestern sites to central and southern European sites, was observed. Only the Spanish cities did not fit this pattern; there, ozone levels were again lower than in central European cities, probably due to the direct influence of strong car traffic emissions. In general, ozone concentrations and cumulative exposure were significantly higher at suburban sites than at urban and traffic-exposed sites. When applying the newly established European Union (EU) Directive on ozone pollution in ambient air, it was demonstrated that the target value for the protection of human health was regularly surpassed at urban as well as suburban sites, particularly in cities in Austria, France, northern Italy and southern Germany. European target values and long-term objectives for the protection of vegetation expressed as AOT40 were also exceeded at many monitoring sites.
Air monitoring networks are necessary to assess air quality in order to reduce pollution to levels which minimize harmful effects on human health and the environment. This paper describes a method to design or optimize air quality monitoring networks for nitrogen dioxide and ozone and its application in Malaga, a medium large city located in Andalusia, southern Spain, with traffic being the main source of air pollution. The completion of this method revealed that the old assessment network in Malaga was badly designed and made it possible to determine that one traffic-orientated and one background control station were necessary for NO2 assessment in Malaga, as well as two control stations for O3. First the number of stations necessary is obtained from historical data. Sampling campaigns with passive diffusion samplers at 74 sites were then carried out to obtain information on the pollution distribution in Malaga. The average concentrations found for NO2 and O3 were 22.8 μg/m3 and 64.3 μg/m3 respectively. Maximum values of up to 42.2 μg/m3 NO2 were found in Malaga city centre and O3 reached 91.5 μg/m3 downwind from the emission source. After spatial interpolation of the obtained values with Geographical Information Systems, a selection of the best locations for the monitoring stations was made, in line with the macro- and microscale siting requirements of the European Directive 2008/50/EC on ambient air quality and cleaner air for Europe.
This article presents a statistical approach called hypothesis testing. This is based upon information collected from a random sample following which results are generalised for the entire population. Some general concepts and terminology of the methodology are briefly described including statistical hypotheses, types of errors, one- or two-tailed tests and an example of an application is given.
Hypothesis testing is a fundamental process in making a decision about populations of interest in research.
Examination of the distribution of tropospheric ozone indicates that surface destruction in the Northern Hemisphere (NH) should be about three times larger than in the Southern Hemisphere (SH). If, according to the traditional understanding of ozone, this species were a passive tracer in the troposphere, a threefold larger flux out of the stratosphere should exist in the NH than in the SH. However, meteorological analyses fail to support such pronounced hemispheric differences in stratosphere-troposphere exchange. Alternatively, therefore, it is hypothesized that photochemical synthesis of ozone in the troposphere may be particularly important in the NH because of asymmetries in the sources and distribution of carbon monoxide, hydrocarbons and nitric oxide.
A systematic analysis of surface ozone observations at a rural area of the upper Spanish plateau is presented. A near four-year study of ozone concentrations was carried out between February 2000 and October 2003. Diurnal and monthly variations of ozone are studied. The peak concentration levels are obtained between 13:00 and 15:00 GMT and the lowest levels at 4:00 and 5:00 GMT. The highest values together with a slight increase in data variability are found from April to August, when spring and summer maxima are appreciated. The relationship between synoptic-scale atmospheric transport patterns and the maximum ozone concentrations was also examined. Analysis of the 500-hPa synoptic weather patterns revealed that the highest values occur during continental and Atlantic ridges in summer and, to a lesser extent, during troughs in the east-northeast of the Iberian Peninsula in spring. Our approach entailed calculating 3-day isobaric backward air mass trajectories at the observational site sorted on the following main origins: European continent, African continent, Atlantic Ocean and local. The assessment of the results showed the influence of local conditions on the daily maximum ozone concentrations. Moreover, continental air masses provide certain evidence of long-range transport added to the local or regional contribution of the main cities affecting the sampling site. Conversely, Atlantic trajectories show the least contribution to ozone levels.
Ozone impact on Mediterranean forests remains largely under-investigated, despite strong photochemical activity and harmful effects on crops. As representative of O3 impacts on Mediterranean vegetation, this paper reviews the current knowledge about O3 and forests in Italy. The intermediate position between Africa and European mid-latitudes creates a complex patchwork of climate and vegetation. Available data from air quality monitoring stations and passive samplers suggest O3 levels regularly exceed the critical level (CL) for forests. In contrast, relationships between O3 exposure and effects (crown transparency, radial growth and foliar visible symptoms) often fail. Despite limitations in the study design or underestimation of the CL can also affect this discrepancy, the effects of site factors and plant ecology suggest Mediterranean forest vegetation is adapted to face oxidative stress, including O3. Implications for risk assessment (flux-based CL, level III, non-stomatal deposition) are discussed.
In order to improve our knowledge of the surface ozone in the south of the Iberian Peninsula, annual, monthly, weekly and daily ozone concentrations have been closely monitored in the Seville metropolitan area highlighting those episodes that exceed the European Ozone Directive. A three-year period (2003-2005) and eight ozone stations were used; five of them located in the city's busiest areas and the rest in adjacent zones ( approximately 25km). In addition, the wind regime was also studied in order to understand the main characteristics of the surface atmospheric dynamics. The lowest ozone concentrations 17-33microgm(-3) took place in January while the highest 57-95microgm(-3) occurred in June. The ozone concentration week-weekend differences from May to September indicate that this phenomenon does not affect the ozone stations analysed. Daily cycles show minimum values between 7:00 and 8:00 UTC and maximum at noon, exceeding 90microgm(-3) during summer months. From March to October the ozone concentrations were above the target value for the protection of human health, especially during the summer months, with values up to 30% over the limit. The information threshold has been exceeded at all ozone stations studied but with greater frequency in the stations far from the city centre. In addition, at these latter stations the alert threshold was also exceeded on six occasions. This study in the city of Seville indicates that the high ozone levels are due to local atmospheric effects, mainly since the ozone air masses may undergo recirculation processes. The ozone is transported to the city from the S-SW, having a major impact in the NE areas.
Caracterización y comportamiento del ozono y los óxidos de nitrógeno en Andalucía occidental
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del ozono y los óxidos de nitrógeno en Andalucía occidental.
Ph.D. thesis, University of Huelva, Huelva, Spain, 284 pp.,
ISBN: 978-34-92944-59-0.
Caracterización meteorológica y modelización de Andalucía occidental
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Hernández-Ceballos, M.A. (2012) Caracterización meteorológica
y modelización de Andalucía occidental. Ph.D. thesis,
University of Huelva, Huelva, Spain, 284 pp., ISBN: 978-84-15147-73-2.
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