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Monocyclic Aromatic Hydrocarbons in Kathmandu During the Winter Season
Abstract
Mixing ratios of seven monocyclic aromatic hydrocarbons, as well as NO2, SO2 and O3, were measured by long path differential optical absorption spectroscopy (DOAS) at a suburban site in Kathmandu, Nepal, during Jan.–Feb. 2003. The results showed average benzene (3.9 ± 1.8 ppbv), toluene (13.3 ± 7.1 ppbv), and sum of xylene isomers (42.2 ± 15.7 ppbv) mixing ratios in Kathmandu. The xylenes concentrations were higher than in the large cities that have been studied. The observed ratio of toluene to benzene (2.9 ± 1.8) reflected the small fraction of vehicles with catalytic converters in the Kathamndu. Analysis of the late afternoon time series of aromatics, NOx
, and wind data indicated that road traffic was one of the main sources of aromatics in the urban air. In addition, the correlations between aromatics, SO2, NOx
, and PM10 during the night strongly suggested that fossil and biomass fuel burning made an important contribution to air pollution in the Kathmandu valley. Aromatic pollution was further strengthened by daily recurring stable meteorological conditions and the surrounding topography. The chemical reaction of aromatics with free radicals during the daytime could also be deduced. High ratios of phenol/benzene and para-cresol/toluene could not be explained by chemical processes, and suggested direct emission of phenol and para-cresol in the Kathmandu atmosphere.
... Due to the different source strengths, aerosol burdens, and the composition of aerosol and ground surfaces, the HONO chemistry in South Asia is expected to have different features than what is found in Europe or the North America. For example, the average aerosol bur-5 den in the atmosphere of Kathmandu is much higher than in European and US cities (Sharma et al., 2002;Sharma, 1997;Yu et al., 2008a;Giri et al., 2006) in the winter. Moreover, strong nocturnal inversion layer (Kondo et al., 2002;Regmi et al., 2003;Panday, 2006) and low mixing layer height keeps pollutants close to the ground providing a large reactive ground surface for HONO formation. ...
... DOAS measurements were carried from 10 January to 11 February 2003. The mea- (Yu et al., 2004(Yu et al., , 2008a. ...
... The water uptake processes can lead to the fog formation. The fog that usually 25 formed in the early morning in Kathmandu in winter has been reported by many researchers (Kondo et al., 2002;Regmi et al., 2003;Panday, 2006;Yu et al., 2008a). The water uptake processes can take place on the ground surface in addition to the aerosol surface in Kathmandu atmosphere. ...
Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmosphere during January–February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO2 (17.9±10.2 ppbv), and PM10 (0.18±0.11 mg m−3) in urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO2] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion of NO2 to HONO in Kathmandu. The ratios of [HONO]/[NO2] at nights are much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influence of aerosol plumes, relative humidity, aerosol surface and ground reactive surface, temperature on NO2-HONO chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and serious aerosol pollution burden may explain the particularly efficient conversion of NO2 to HONO.
... With regard to quantification of volatile organic compounds (VOCs) in downtown Kathmandu and a rural site in Nagarkot, data pertaining to light C2-C6 compounds were obtained in a study in November 1998 using 38 whole air samples analysed offline with a GC-FID (Sharma et al., 2000). Subsequently Yu et al. (2008) measured mixing ratios of seven monocyclic aromatic hydrocarbons, using long-path differential optical absorption spectroscopy (DOAS) at a suburban site in Kathmandu during January-February 2003. All these initial studies highlighted that traffic sources were major contributors to air pollution in the Kathmandu Valley (Yu et al., 2008). ...
... Subsequently Yu et al. (2008) measured mixing ratios of seven monocyclic aromatic hydrocarbons, using long-path differential optical absorption spectroscopy (DOAS) at a suburban site in Kathmandu during January-February 2003. All these initial studies highlighted that traffic sources were major contributors to air pollution in the Kathmandu Valley (Yu et al., 2008). In the time since these studies, due to rapid urbanisation and population growth over the last decade, the wintertime air quality has deteriorated severely. ...
... Whereas benzene is emitted in almost equal proportion from fossil fuel and biomass combustion sources (Henze et al., 2008), fossil fuel combustion and industrial processes contribute a much larger fraction to the global budgets of toluene and sum of C8 and C9-aromatics. The observed trend in concentrations of some of the aromatic compounds measured using PTR-TOF-MS in this study differs from the trend reported in a previous study by Yu et al. (2008) ployed the long-path DOAS technique to make measurements of monoaromatic VOCs in Kathmandu during winter 2003. In that study, xylene (a C8-aromatic compound) concentrations were reported to be the highest followed by toluene and benzene respectively. ...
The Kathmandu Valley in Nepal suffers from severe wintertime air pollution.
Volatile organic compounds (VOCs) are key constituents of air pollution,
though their specific role in the valley is poorly understood due to
insufficient data. During the SusKat-ABC (Sustainable Atmosphere for the
Kathmandu Valley–Atmospheric Brown Clouds) field campaign conducted in Nepal
in the winter of 2012–2013, a comprehensive study was carried out to
characterise the chemical composition of ambient Kathmandu air, including the
determination of speciated VOCs, by deploying a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) – the first such deployment in South
Asia. In the study, 71 ion peaks (for which measured ambient concentrations exceeded the
2σ detection limit) were detected in the PTR-TOF-MS mass scan
data, highlighting the chemical complexity of ambient air in the valley. Of
the 71 species, 37 were found to have campaign average concentrations greater
than 200 ppt and were identified based on their spectral
characteristics, ambient diel profiles and correlation with specific emission
tracers as a result of the high mass resolution (m ∕ Δm > 4200) and temporal resolution (1 min) of the PTR-TOF-MS. The
concentration ranking in the average VOC mixing ratios during our wintertime
deployment was acetaldehyde (8.8 ppb) > methanol (7.4 ppb)
> acetone + propanal (4.2 ppb) > benzene (2.7 ppb) >
toluene (1.5 ppb) > isoprene (1.1 ppb) > acetonitrile
(1.1 ppb) > C8-aromatics ( ∼ 1 ppb) > furan
( ∼ 0.5 ppb) > C9-aromatics (0.4 ppb). Distinct diel
profiles were observed for the nominal isobaric compounds isoprene
(m ∕ z = 69.070) and furan (m ∕ z = 69.033).
Comparison with wintertime measurements from several locations elsewhere in
the world showed mixing ratios of acetaldehyde ( ∼ 9 ppb),
acetonitrile ( ∼ 1 ppb) and isoprene ( ∼ 1 ppb) to
be among the highest reported to date. Two "new" ambient compounds,
namely formamide (m ∕ z = 46.029) and acetamide
(m ∕ z = 60.051), which can photochemically produce isocyanic
acid in the atmosphere, are reported in this study along with nitromethane (a
tracer for diesel exhaust), which has only recently been detected in ambient
studies. Two distinct periods were selected during the campaign for detailed
analysis: the first was associated with high wintertime emissions of biogenic
isoprene and the second with elevated levels of ambient acetonitrile,
benzene and isocyanic acid from biomass burning activities. Emissions from
biomass burning and biomass co-fired brick kilns were found to be the
dominant sources for compounds such as propyne, propene, benzene and
propanenitrile, which correlated strongly with acetonitrile (r2 > 0.7), a
chemical tracer for biomass burning. The calculated total VOC OH reactivity
was dominated by acetaldehyde (24.0 %), isoprene (20.2 %)
and propene (18.7 %), while oxygenated VOCs and isoprene
collectively contributed to more than 68 % of the total ozone
production potential. Based on known secondary organic aerosol (SOA) yields and measured ambient concentrations in the Kathmandu Valley, the relative SOA production potential of VOCs were benzene > naphthalene > toluene > xylenes > monoterpenes > trimethylbenzenes > styrene > isoprene.
The first ambient measurements from any site in South Asia of compounds with
significant health effects such as isocyanic acid, formamide, acetamide,
naphthalene and nitromethane have been reported in this study. Our results
suggest that mitigation of intense wintertime biomass burning activities, in
particular point sources such biomass co-fired brick kilns, would be
important to reduce the emission and formation of toxic VOCs (such as benzene
and isocyanic acid) in the Kathmandu Valley.
... With regard to quantification of volatile organic compounds in downtown Kathmandu and a rural site in Nagarkot, data pertaining to light C2-C6 com- 15 pounds was obtained in a study in November 1998 using thirty-eight whole air samples analyzed offline with a GC-FID (Sharma et al., 2000). Subsequently Yu et al. (2008) measured mixing ratios of seven monocyclic aromatic hydrocarbons, using long path differential optical absorption spectroscopy (DOAS) at a suburban site in Kathmandu during January-February 2003. All these initial studies highlighted that traffic sources 20 were major contributors to air pollution in the Kathmandu Valley (Yu et al., 2008). ...
... Subsequently Yu et al. (2008) measured mixing ratios of seven monocyclic aromatic hydrocarbons, using long path differential optical absorption spectroscopy (DOAS) at a suburban site in Kathmandu during January-February 2003. All these initial studies highlighted that traffic sources 20 were major contributors to air pollution in the Kathmandu Valley (Yu et al., 2008). In the time since these studies, due to rapid urbanization and population growth over the last decade, the wintertime air quality has deteriorated severely. ...
... Whereas benzene is emitted in almost equal proportion from fossil fuel and biomass combustion sources (Henze et al., 2008), fossil fuel combustion and industrial processes contribute a much larger fraction to the global budgets of toluene and sum of C8 and C9-aromatics. The observed trend in concentrations of some of the aromatic compounds measured using PTR-TOF-MS in this study differs from the trend reported in a previous study by Yu et al. (2008) who employed the long path differential optical absorption spectroscopy (DOAS) technique to make measurements of monoaromatic VOCs in Kathmandu during winter 2003. In that study, xylene (a C8-aromatic compound) concentrations were reported to be the highest followed by toluene and benzene respectively. ...
The Kathmandu Valley in Nepal suffers from severe wintertime air pollution. Volatile organic compounds (VOCs) are key constituents of air pollution, though their specific role in the Valley is poorly understood due to insufficient data. During the SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley-Atmospheric Brown Clouds) field campaign conducted in Nepal in the winter of 2012–2013, a comprehensive study was carried out to characterize the chemical composition of ambient Kathmandu air, including the determination of speciated VOCs by deploying a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS)–the first such deployment in South Asia. 71 ion peaks (for which measured ambient concentrations exceeded the 2 σ detection limit) were detected in the PTR-TOF-MS mass scan data, highlighting the chemical complexity of ambient air in the Valley. Of the 71 species, 37 were found to have campaign average concentrations greater than 200 ppt and were identified based on their spectral characteristics, ambient diel profiles and correlation with specific emission tracers as a result of the high mass resolution (m/Δm > 4200) and temporal resolution (1 min) of the PTR-TOF-MS. The highest average VOC mixing ratios during the measurement period were (in rank order): acetaldehyde (8.8 ppb), methanol (7.4 ppb), acetone (4.2 ppb), benzene (2.7 ppb), toluene (1.5 ppb), isoprene (1.1 ppb), acetonitrile (1.1 ppb), C8-aromatics (~ 1 ppb), furan (~ 0.5 ppb), and C9-aromatics (0.4 ppb). Distinct diel profiles were observed for the nominal isobaric compounds isoprene (m/z = 69.070) and furan (m/z = 69.033). Comparison with wintertime measurements from several locations elsewhere in the world showed mixing ratios of acetaldehyde (~ 9 ppb), acetonitrile (~ 1 ppb) and isoprene (~ 1 ppb) to be among the highest reported till date. Two "new" ambient compounds namely, formamide (m/z = 46.029) and acetamide (m/z = 60.051), which can photochemically produce isocyanic acid in the atmosphere, are reported in this study along with nitromethane (a tracer for diesel exhaust) which has only recently been detected in ambient studies. Two distinct periods were selected during the campaign for detailed analysis: the first was associated with high wintertime emissions of biogenic isoprene, and the second with elevated levels of ambient acetonitrile, benzene and isocyanic acid from biomass burning activities. Emissions from biomass burning and biomass co-fired brick kilns were found to be the dominant sources for compounds such as propyne, propene, benzene and propanenitrile which correlated strongly with acetonitrile (r2 > 0.7), a chemical tracer for biomass burning. The calculated total VOC OH reactivity was dominated by acetaldehyde (24.0 %), isoprene (20.2 %) and propene (18.7 %), while oxygenated VOCs and isoprene collectively contributed to more than 68 % of the total ozone production potential. Based on known SOA yields and measured ambient concentrations in the Kathmandu Valley, the relative SOA production potential of VOCs were: benzene > naphthalene > toluene > xylenes > monoterpenes > trimethyl-benzenes > styrene > isoprene. The first ambient measurements from any site in South Asia of compounds with significant health effects such as isocyanic acid, formamide, acetamide, naphthalene and nitromethane have been reported in this study. Our results suggest that mitigation of intense wintertime biomass burning activities, in particular point sources such biomass co-fired brick kilns, would be important to reduce the emission and formation of toxic VOCs (such as benzene and isocyanic acid) in the Kathmandu Valley and improve its air quality.
... In the troposphere, O 3 is produced mainly by the photochemical reaction of CO, HC, and NOx (Fishman and Crutzen, 1978). Like in other cities, higher surface O 3 concentration in urban areas in the Indian region including Kathmandu valley have been reported (Kondo et al., 2005;Ahammed et al., 2006;Pudasainee et al., 2006;Mittal et al., 2007;Yu et al., 2007). ...
... Like in other urbanized valleys, a higher air pollutant concentration was reported at the Kathmandu valley too (e.g. Yu et al., 2007;Kondo et al., 2005;Sharma et al., 2000). The earlier paper by the authors was mainly focused on explaining the diurnal and seasonal variations of surface ozone, the role of NOx and meteorological parameters. ...
... This study incorporated NOx and O 3 but lacks VOCs and to our knowledge, status and behavior of VOCs has not been systematically studied in the valley atmosphere. Some sporadic studies in the past have reported higher VOC emission in the valley atmosphere such as Sharma et al. (2000) and Yu et al. (2007). In the absence of VOC data, the general explanation is proposed as follows. ...
In this paper, variations of nitric oxide (NO), nitrogen dioxide (NO2), oxides of nitrogen (NOx), ozone (O3) and total oxidant (OX) concentration in ambient air of Kathmandu valley are presented. O3 behavior during weekdays, weekends and bandhas (general strike) is analyzed and the mechanism related to it is discussed. The increased NO2/OX ratio with increasing NOx concentration and the inverse relation between NOx and O3 imply that the residual O3 remaining after the NO–NO2–O3 reaction chain controlled O3 concentration in the valley atmosphere and the radical channel was likely to have a minor contribution. The higher positive correlation coefficient for O3 variation during weekdays and bandhas, weekdays and weekends suggests common sources for the weekends and bandhas O3 variation. The higher O3 concentration during weekends and bandhas compared to weekdays was due to less destruction of O3. Enhanced reduction in traffic emission levels, enforcement of stringent emission standards within the valley and the surroundings may help to address the O3 problem in the valley atmosphere.
... Another measurement study examined PAH concentrations in PM 10 in an urban area in the Kathmandu Valley (Kishida et al., 2009). Biomass and fossil fuel combustion especially by vehicles were identified as the main source of polycyclic aromatic hydrocarbons (Yu et al., 2008). Other study showed higher PM concentrations and lead levels in PM samples near roads (Aryal et al., 2008). ...
Concentration of PAHs, hopanes, and elements in PM10 aerosol samples was measured in two Nepalese urban centers, Tulsipur (725 m above sea level; 150,000 inhabitants) and Charikot (1,550 m above sea level; 23,000 inhabitants) in the monsoon period (August 2018) and pre-monsoon period (April–May 2019). The 24-h PM10 limit value of 50 µg m⁻³ for human health was significantly exceeded at all locations, and the Nepal concentration limit of 150 µg m⁻³ was exceeded at Tulsipur-bus station, Tulsipur-village, and Charikot-hospital in the pre-monsoon season. The average daily PM10 and PAHs concentrations showed seasonal variations, with lower concentrations in the monsoon season and the higher values in pre-monsoon season. The average daily PM10 and PAHs concentrations in the both sites were 133 μg m⁻³ and 23.8 ng m⁻³ in the pre-monsoon period and 49.6 μg m⁻³ and 2.30 ng m⁻³ in the monsoon period, respectively. The average daily hopane concentration during the pre-monsoon period was 1.40 ng m⁻³ in Tulsipur and 0.70 ng m⁻³ in Charikot. The IndP / (IndP + BghiP) ratio was higher than 0.5 during monsoon period, indicating combustion of biomass and charcoal burning. IndP / (IndP + BghiP) between 0.2 and 0.5 during pre-monsoon season indicates petroleum combustion. Fla / (Fla + Pyr) ratio between 0.3 and 0.5 during pre-monsoon and monsoon periods indicates high proportion of petroleum product combustion. The biomass burning associated with dense traffic in the center of the two cities was the main source of PAHs. The average daily element concentration was 6.80 ng m⁻³ in both locations during the monsoon period.
... Due to the different source strengths, aerosol burdens, and the composition of aerosol and ground surfaces, HONO chemistry in South Asia is expected to have different features from what has been found in Europe or North America. For example, the average atmospheric aerosol burden in Kathmandu in winter is much higher than in European and US cities (Sharma et al., 2002;Sharma, 1997;Yu et al., 2008a;Giri et al., 2006). Moreover, strong nocturnal inversion layer (Kondo et al., 2002;Regmi et al., 2003;Panday, 2006;Panday and Prinn, 2009) and the In this study, we present measurements of HONO and NO 2 using long path DOAS in Kathmandu, Nepal, over several weeks in 2003. ...
Nitrous acid (HONO) plays a significant role in
the atmosphere, especially in the polluted troposphere. Its
photolysis after sunrise is an important source of hydroxyl
free radicals (OH). Measurements of nitrous acid and other
pollutants were carried out in the Kathmandu urban atmosphere
during January–February 2003, contributing to the
sparse knowledge of nitrous acid in South Asia. The results
showed average nocturnal levels of HONO (1.7±0.8 ppbv),
NO2 [NO subscript 2] (17.9±10.2 ppbv), and PM10(0.18±0.11 mgm−3 [mg m superscript -3]) in urban
air in Kathmandu. Surprisingly high ratios of chemically
formed secondary [HONO] to [NO2] [NO subscript 2] (up to 30%) were
found, which indicates unexpectedly efficient chemical conversion
of NO2 [NO subscript 2] to HONO in Kathmandu. The ratios of
[HONO]/[NO2] [NO subscript 2] at night were found to be much higher than
previously reported values from measurements in urban air in
Europe, North America and Asia. The influences of aerosol
surface, ground reactive surface, and relative humidity on
NO2-HONO [NO subscript 2 - HONO] chemical conversion were discussed. The high
humidity, strong and low inversion layer at night, and high
aerosol pollution burden in Kathmandu may explain the particularly
efficient conversion of NO2 [NO subscript 2] to HONO.
... The overall approach is unique, to our knowledge, although the method is based on the DOAS (Differential Optical Absorption Spectroscopy) technique (Platt et al., 1979) which has been used in various applications over the last 30 yr. This includes long path measurements of pollutants (Yu et al., 2008), ground based multi-axis DOAS measurements of skylight to retrieve volcanic gas fluxes of SO 2 (Galle et al., 2003) and mobile zenith sky measurements of gas fluxes from industrial conglomerates (Rivera et al., 2009). The DOAS technique is also operated from numerous satellite sounders measuring reflected solar light from the earth surface. ...
A unique methodology to measure gas fluxes of SO 2 and NO 2 from ships using optical remote sensing is described and demonstrated in a feasibility study. The measurement system is based on Differential Optical Absorption Spectroscopy using reflected skylight from the water surface as light source. A grating spectrometer records spectra around 311 nm and 440 nm, respectively, with the telescope pointed downward at a 30°angle from the horizon. The mass column values of SO 2 and NO 2 are retrieved from each spectrum and integrated across the plume. A simple geometric approximation is used to calculate the optical path. To obtain the total emission in kg h -1 the resulting total mass across the plume is multiplied with the apparent wind, i.e. a dilution factor corresponding to the vector between the wind and the ship speed. The system was tested in two feasibility studies in the Baltic Sea and Kattegat, from a CASA-212 airplane in 2008 and in the North Sea outside Rotterdam from a Dauphin helicopter in an EU campaign in 2009. In the Baltic Sea the average SO 2 emission out of 22 ships was (54 ± 13) kg h -1, and the average NO 2 emission was (33 ± 8) kg h -1, out of 13 ships. In the North Sea the average SO 2 emission out of 21 ships was (42 ± 11) kg h -1, NO 2 was not measured here. The detection limit of the system made it possible to detect SO 2 in the ship plumes in 60% of the measurements when the described method was used. A comparison exercise was carried out by conducting airborne optical measurements on a passenger ferry in parallel with onboard measurements. The comparison shows agreement of (-30 ± 14)% and (-41 ± 11)%, respectively, for two days, with equal measurement precision of about 20%. This gives an idea of the measurement uncertainty caused by errors in the simple geometric approximation for the optical light path neglecting scattering of the light in ocean waves and direct and multiple scattering in the exhaust plume under various conditions. A tentative error budget indicates uncertainties within 30-45% but for a reliable error analysis the optical light path needs to be modelled.
A ship emission model, FMI-STEAM, has been compared to the optical measurements showing an 18% overestimation and a correlation coefficient (R 2) of 0.6. It is shown that a combination of the optical method with modelled power consumption can estimate the sulphur fuel content within 40%, which would be sufficient to detect the difference between ships running at 1% and at 0.1%, limits applicable within the IMO regulated areas.
... Emissions from burning of waste vehicle tires during general strikes, when all vehicles and industries cease operation, were estimated in a laboratory study (e.g., sulfur dioxide (SO 2 ) 102-820 μg/g) (e.g., Shakya et al., 2008). Findings identify key sources as biomass burning and fossil fuels, especially from vehicles (e.g., Shrestha and Malla, 1996;Yu et al., 2008). Several studies observed high pollutant levels (e.g., nitrogen dioxide (NO 2 ), SO 2 ) and emissions (e.g., Kitada and Regmi, 2003). ...
... One study quantified 28 nonmethane hydrocarbons in 38 flask samples collected around Kathmandu [Sharma et al., 2000] and found significant weekday to weekend differences in species emitted by automobiles. High-frequency measurements of atmospheric turbidity over 21 days [Sapkota and Dhaubadel, 2002] and of condensation nuclei count over 9 days [Hindman and Upadhyay, 2002] [Yu et al., 2008]. ...
[1] During the dry season of 2004–2005 we carried out field measurements of air pollution and meteorology in the Kathmandu Valley, Nepal, a bowl-shaped urban basin in the Himalayan foothills of Nepal. We measured the trace gases carbon monoxide (CO) and ozone (O3) and particulates (PM10), as well as meteorological variables. In our field observations we noted a very regular pattern of morning and evening peaks in CO and PM10 occurring daily in the valley bottom, interspersed with low values in the afternoons and at night. This pattern occurred even on days with unusual timing of emissions and was influenced by the timing of ventilation from the valley. Meteorological variables showed great day-to-day similarity, with a strong westerly wind blowing through the valley from late morning until dusk. We found that the air mass on nearby mountaintops was disconnected from pollution within the valley during the night, but received significant pollution during the morning, when up-slope flows began. At a pass on the western edge of the valley we found a diurnal switch in wind direction, with an inflow from late morning until late evening, and an outflow during the rest of the time. We found that part of the morning peak in pollution was caused by recirculation of pollutants emitted the night before, which spend the night in elevated layers over the valley.
... The overall approach is unique, to our knowledge, although the method is based on the DOAS (Differential Optical Absorption Spectroscopy) technique (Platt et al., 1979) which has been used in various applications over the last 30 yr. This includes long path measurements of pollutants (Yu et al., 2008), ground based multi-axis DOAS measurements of skylight to retrieve volcanic gas fluxes of SO 2 (Galle et al., 2003) and mobile zenith sky measurements of gas fluxes from industrial conglomerates (Rivera et al., 2009). The DOAS technique is also operated from numerous satellite sounders measuring reflected solar light from the earth surface. ...
A unique methodology to measure gas fluxes of SO2 and NO2 from ships has been developed in a Swedish national project using optical remote sensing. The measurement system is based on Differential Optical Absorption Spectroscopy using reflected skylight from the water surface as light source. A grating spectrometer records spectra around 311 nm and 440 nm, respectively, with the telescope pointed downward at a 30° angle from the horizon. The mass column values of SO2 and NO2 are retrieved from each spectrum and integrated across the plume. To obtain the total emission in kg h-1 the resulting total mass across the plume is multiplied with the apparent wind, i.e. a dilution factor corresponding to the vector between the wind and the ship speed. The system was tested in two feasibility studies in the Baltic Sea and Kattegat, from a CASA-212 airplane in 2008 and in the North Sea outside Rotterdam from a Dauphin helicopter in an EU campaign in 2009. In the Baltic Sea the average SO2 emission out of 22 ships was (54 ± 13) kg h-1, and the average NO2 emission was (33 ± 8) kg h-1, out of 13 ships. In the North Sea the average SO2 emission out of 21 ships was (42 ± 11) kg h-1, NO2 was not measured here. The system was able to detect plumes of SO2 in 60% of the measurements when the described method was used. The optical measurement carried out on a passenger ferry on two consecutive days was compared to onboard emission data obtained from analysed fuel content and power consumption. The comparison shows agreement of (-30 ± 14) % and (-41 ± 11) %, respectively, for two days, with equal measurement precision of about 20%, this indicates the presence of systematic error sources that are yet unaccounted for when deriving the flux. Two such error sources are the difficulty in estimating the optical path of the ocean scattered light due to waves, and direct and multiple scattering in the exhaust plume. Rough estimates of these sources have been accounted for in the total uncertainty, 30-45 %. A ship emission model, FMI-STEAM, has been compared to the optical measurements showing a 18% overestimation and a correlation coefficient (R2) of 0.6. It is shown that a combination of the optical method with modelled power consumption can estimate the sulphur fuel content within 40%, which would be sufficient to detect the difference between ships running at 1% and at 0.1%, limits applicable within the IMO regulated areas.
... Emissions from burning of waste vehicle tires during general strikes, when all vehicles and industries cease operation, were estimated in a laboratory study (e.g., sulfur dioxide (SO 2 ) 102-820 μg/g) (e.g., Shakya et al., 2008). Findings identify key sources as biomass burning and fossil fuels, especially from vehicles (e.g., Shrestha and Malla, 1996;Yu et al., 2008). Several studies observed high pollutant levels (e.g., nitrogen dioxide (NO 2 ), SO 2 ) and emissions (e.g., Kitada and Regmi, 2003). ...
... Kumar and Viden (2007) reviewed the concentration levels of VOCs and the methodologies used for their analysis in major cities of the world. The weekly average concentrations of these compounds in different cities of the world can be found in Gee and Sollars (1998), Hsieh and Tsai (2003), Filella and Penuelas (2006) and Yu et al. (2008). ...
Diffusive samplers were used to measure the vertical concentrations of benzene, toluene, n-hexane, cyclohexane, ethylbenzene and o-, m- and p-xylenes on both sides of two NS-oriented street canyons in Murcia (Spain) during a 5-day period. Non-dimensional relationships of concentration and height were calculated in order to study the behaviour of their concentration vertical profiles. The results show that the vertical profiles of benzene, toluene, n-hexane and cyclohexane concentrations were similar in both streets and on both sides of each street. Some differences were found in vertical profiles between streets and sides for ethylbenzene and xylenes, probably due to their higher affinity for adsorption into building materials. The similarities found for the first set of VOCs suggest that the dynamics of the dispersion was the same for both streets and was mainly influenced by microscale thermal effects. Finally, the concentration measurements of benzene, toluene, n-hexane, cyclohexane, and ethylbenzene were adjusted to expressions in the form c = c
0(h/h
0)A
, and a regression coefficient R
2 = 0.962 (p = 0.0000) was obtained. The decreasing concentration of these compounds with height should be taken into account when assessing population exposure to these pollutants.
... Emissions from burning of waste vehicle tires during general strikes, when all vehicles and industries cease operation, were estimated in a laboratory study (e.g., sulfur dioxide (SO 2 ) 102-820 μg/g) (e.g., Shakya et al., 2008). Findings identify key sources as biomass burning and fossil fuels, especially from vehicles (e.g., Shrestha and Malla, 1996;Yu et al., 2008). Several studies observed high pollutant levels (e.g., nitrogen dioxide (NO 2 ), SO 2 ) and emissions (e.g., Kitada and Regmi, 2003). ...
Kathmandu Valley, Nepal, has severe air pollution, although few studies examine air pollution and health in this region. To the best of our knowledge, no previous studies in Nepal used time-activity diaries or conducted personal monitoring of individuals' exposures. We investigated personal exposure of particulate matter (PM) with aerodynamic diameter ≤2.5 μm (PM(2.5)) by location, occupation, and proximity to roadways. PM(2.5) monitoring, time-activity diary, respiratory health questionnaire, and spirometer testing were performed from 28 June 2009 to 7 August 2009 for 36 subjects, including traffic police (TP), indoor officer workers next to main road (IOWs_NMR) and away from main road (IOWs_AMR), in urban area (UA), urban residential area, and semi-UA (SUA). TP had the highest exposure of all the occupations (average 51.2 μg/m(3), hourly maximum >500 μg/m(3)). TP levels were higher at the UA than other locations. IOW_NMR levels (averaged 46.9 μg/m(3)) were higher than those of IOW_AMR (26.2 μg/m(3)). Exposure was generally higher during morning rush hours (0800-1100 hours) than evening rush hours (1500-1800 hours) for all occupations and areas (78% of days for TP and 84% for urban IOW). PM(2.5) personal exposures for each occupation at each location exceeded the World Health Organization ambient PM(2.5) guideline (25 μg/m(3)). Findings suggest potential substantial health impacts of air pollution on this region, especially for TP.
... Due to the different source strengths, aerosol burdens, and the composition of aerosol and ground surfaces, HONO chemistry in South Asia is expected to have different features from what has been found in Europe or North America. For example, the average atmospheric aerosol burden in Kathmandu in winter is much higher than in European and US cities (Sharma et al., 2002;Sharma, 1997;Yu et al., 2008a;Giri et al., 2006). Moreover, strong nocturnal inversion layer (Kondo et al., 2002;Regmi et al., 2003;Panday, 2006;Panday and Prinn, 2009) and the In this study, we present measurements of HONO and NO 2 using long path DOAS in Kathmandu, Nepal, over several weeks in 2003. ...
Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmosphere during January–February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO<sub>2</sub> (17.9±10.2 ppbv), and PM<sub>10</sub> (0.18±</sub>0.11 mg m<sup>−3</sup>) in urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO<sub>2</sub>] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion of NO<sub>2</sub> to HONO in Kathmandu. The ratios of [HONO]/[NO<sub>2</sub>] at nights are much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influence of aerosol plumes, relative humidity, aerosol surface and ground reactive surface, temperature on NO<sub>2</sub>-HONO chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and serious aerosol pollution burden may explain the particularly efficient conversion of NO<sub>2</sub> to HONO.
The global atmospheric budget and distribution of monocyclic aromatic compounds is
estimated, using an atmospheric chemistry general circulation model.
Simulation results are evaluated with an ensemble of surface and aircraft observations
with the goal of understanding emission, production and removal of these compounds.Anthropogenic emissions provided by the RCP database represent the largest
source of aromatics in the model (≃ 23 TgC year−1) and biomass burning
from the GFAS inventory the second largest (≃ 5 TgC year−1).
The simulated chemical production of aromatics accounts for ≃ 5 TgC year−1.
The atmospheric burden of aromatics sums up to 0.3 TgC.
The main removal process of aromatics is photochemical decomposition (≃ 27 TgC year−1), while wet and dry deposition are responsible for a removal of
≃ 4 TgC year−1.Simulated mixing ratios at the surface and elsewhere in the troposphere show good spatial and
temporal agreement with the observations for benzene, although the model generally underestimates
mixing ratios. Toluene is generally well reproduced by the model at the
surface, but mixing ratios in the free troposphere are underestimated.
Finally, larger discrepancies are found for xylenes: surface
mixing ratios are not only overestimated
but also a low temporal correlation is found with respect to in situ observations.
A wide number of studies show that the Iberian Peninsula (IP) exceeds
some of the thresholds of air quality established in the legislation.
Chemistry transport models (CTMs) play a key role in forecasting the
threshold exceedances for human health and ecosystems, and to understand
the causes of these extreme air pollution events. Despite improvements
due to European legislations, particulate matter and ground-level ozone
remain important pollutants affecting human health. However, the
short-term forecasts available today (generally less than 48 hours) may
hamper the decision-making and the design of abatement strategies to
comply with air quality standards in the Iberian Peninsula. In this
sense, a characterization of the types extreme air pollution events
could help to characterize and understand future exceedances. Moreover,
the variation of several circulation types projected under future
climate scenarios may increase of the frequency of extreme events
related to air pollution over southwestern Europe and the Iberian
Peninsula. In this context, a definition of extreme air pollution
events based on a regionalization process has been carried out, applied
to a model climatology of air pollution over the Iberian Peninsula. Data
from the regional modeling system MM5-CHIMERE-EMEP (driven by ERA40
reanalysis) for the period 1970-2000 is used in this study. The studied
pollutants are PM10 and ozone. The domain of study covers the Iberian
Peninsula with a horizontal resolution of 25 km and a vertical
resolution of 23 layers in the troposphere. The thresholds set for
defining the extreme events are characterized from the objective and
limit values defined in the Directive 2008/50/EC for ozone (120 µg
m-3, 8-hour) and PM10 (50 µg m-3, daily mean). In order to
identify locations with similar patterns in terms of the studied
pollutants, a principal component analysis was carried out. This
analysis helped us to group areas which usually present the same level
of each pollutant concentration over the extreme events. The results of
this study could lead to a more efficient design of the measurement
locations, reducing their number and/or finding their optimal
location.To complete the study, a cluster analysis helped to identify
those extreme events which produced similar pollution patterns over the
IP. This classification is useful to group similar extreme events and
find relationships with e.g., climatology. The results indicate that
all the PM10 winter mean fields follow the same spatial pattern for most
of the clustered events. The highest mean values are located in the
southwestern Iberian Peninsula. The extreme events are generally
associated to anticyclonic situations during wintertime. The histograms
are characterized by an important skewness indicating that extreme
events of PM10 concentration level are most of time in the very high
percentiles. The number of days with exceedances follow the same
spatial pattern for most of the groups. Only differences in the
frequency appear. In the case of ozone, the spatial pattern of the
ozone concentration in summer is different from the PM10, indicating
that the episodes originating exceedances of the ozone threshold are not
related to those provoking PM10 episodes. The highest number of days
with exceedances is located in the northeastern and eastern Iberian
Peninsula, except in the Ebro valley, where the ozone concentration is
very low. The Cantabrian and Portuguese coast are always affected by
exceedances, although there is a higher frequency when the Iberian
thermal low appears at the central part of the IP. This leads to
exceedances appearing in southeastern Spain. Another cluster clearly
depicts a canalization and run-off along the Rhone Valley into the
central-east of the Mediterranean Cost, leading to a transport and
canalization along the Jucar Valley (Valencia).
In order to study the levels of BTX (benzene, toluene, xylene, etc) nearby the main roads of Guangzhou from November 2010 to December 2010 during the Asian Games, BTX and conventional pollutants such as NO2, O3 in the air were monitored by the DOAS system nearby Huangsha Road, which is in the Liwan District of Guangzhou City. The results showed that, during the entire period, BTX showed a high concentration in the evening and the average concentrations of benzene, toluene, p-xylene, m-xylene and phenol were 15.9 microg x m(-3), 61.3 microg x m(-3), 6.5 microg x m(-3), 16.9 microg x m(-3), 0.88 microg x m(-3), respectively. The average concentrations of benzene and toluene were close to those in other cities, and the ratio of toluene to benzene was in range of 1.2-6.16. Throughout the monitoring period, the correlation coefficient of benzene and toluene was 0.86 and it rose to 0.985 during the high concentration period, indicating that they had the same source in this region. The correlation coefficient between toluene and CO was 0.78, indicating that traffic emissions was the major source of benzene and toluene. Based on the combination of wind speed, wind direction and other meteorological data, it was found that the weather condition was an important factor which affected the BTX concentration, and some possible point sources were suggested nearby the site.
The air pollution concentration in the winter season of Katmandu valley is very high compared with summer season, because the air pollution concentration was strongly influenced by the inversion layer that is formed at Katmandu valley. This mechanism was simulated by a water tank experiment and by numerical calculation. Thermal stratification was made at the start of the experiment, and the temperature on the bottom of water tank was changed with the period of 12 minute. The updraft wind on the slope and Bénard convection occurred while the bottom temperature was maintained in high temperature. The downdraft wind on the slope occurred and the inversion layer was formed while the bottom temperature was maintained in low temperature. The calculated pollution concentration was qualitatively agreed with the field observation in Katmandu valley.
Measurements from the Transport and Chemical Evolution over the Pacific (TRACE-P) and Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) field experiments obtained during the period of March–April 2001 are used to evaluate the impact of megacity emissions on regional air quality in east Asia. A classification method built upon back trajectory analysis and sensitivity runs using the Sulfur Transport and Emissions Model 2001 (STEM-2K1) regional chemical transport model are used to identify the aircraft observations that were influenced by megacity emissions. More than 30% of measurement points are classified as urban points, with a significant number of plumes found to have originated from Shanghai, Qingdao, Beijing, Taiyuan, Tianjin and Guiyang, Seoul, and Pusan. These data are then analyzed, and chemical characteristics of these megacities are compared. Emission estimates for the megacities are also presented and discussed in the context of expected similarities and differences in the chemical signals in the ambient air impacted by these cities. Comparisons of the observation-based ratios with emission-based estimates are presented and provide a means to test for the consistency of the emission estimates. The observation-based ratios are shown to be generally consistent with the emissions ratios. The megacity emissions are used in the STEM-2K1 model to study the effects of these emissions on criteria and photochemical species in the region. Over large portions of the Japan Sea, Yellow Sea, western Pacific Ocean, and the Bay of Bengal, megacity emissions contribute in excess of 10% of the near-surface ambient levels of O3, CO, SO2, H2SO4, HCHO, and NOz. The megacity emissions are also used to study ozone levels in Asia under a scenario where all cities evolve their emissions in a manner such that they end up with the same VOC/NOx emission ratio as that for Tokyo. Monthly mean ozone levels are found to increase by at least 5%.
Air pollution transport in the Kathmandu valley/basin has been investigated by numerical simulation of local flows and the observation of NO2 and SO2. The observation was performed at 22 sites with passive samplers from February to April 2001, and the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) was utilized for the flow simulation. The calculation reproduced reasonably well the surface wind and temperature at the Tribhuvan International Airport (TIA) as well as the vertical wind profile taken at the center of the valley by sodar observation. The calculation showed that two characteristic local flows tend to intrude into the valley/basin in the afternoon through the mountain gaps surrounding Kathmandu, that is, the southwesterly from the Indian Plain and the northwesterly from the valley west to Kathmandu. These cool wind layers meet at the center of the Kathmandu basin and form a double-layering structure there. The lower layer is shallow with a depth of about 250 m, being composed of the cooler southwesterly air mass from the Indian Plain. It was concluded that this local flow structure suppresses vertical mixing and leads to high air pollution by decreasing the daytime ventilation of air mass over the valley. The observations performed during the period confirmed it.
Air pollution characteristics over the Kathmandu Valley in wintertime were numerically investigated by using a comprehensive transport chemistry deposition model of air pollutants together with the fifth-generation Pennsylvania State University NCAR Mesoscale Model (MM5). In Kathmandu, Nepal, it is known that double-layered local flows, that is, the southwesterly and northwesterly winds, formed as combined valley wind and plain-to-plateau wind, develop every day in the afternoon. In this study, the effect of local flows on air pollution in Kathmandu has been clarified. Detailed analysis of diurnal variation of air pollution transport elucidated the basic nature of the air pollution: 1) the vertical spreading of the pollutants, accumulated during the nighttime, by mixing-layer activity in the late morning, before the intrusion of the two local flows; 2) the late afternoon redevelopment of a shallow polluted layer and the pollutant transport toward the eastern neighboring valley, caused by the double-layered local flows; and 3) the nighttime partial comeback of the pollutants from the eastern mountain pass to the Kathmandu Valley and the gradual spreading of the pollutants over the valley caused by intermittent but organized horizontal flow caused by mountain winds, which also suppresses excess accumulation of fresh pollutants in the source area. Mass balance of sulfur compounds in the Kathmandu Valley is also discussed.
During two field campaigns in 1993 and 1994, measurements of aromatic compounds [benzene, toluene, ethylbenzene, m-/p-/o-xylenes (BTEX)] were carried out at urban and rural sites in the greater Munich area. These field campaigns represent a unique study using quasi-continuous gas chromatography/flame ionization detection methods concurrently at various sites. The impact of Munich's urban plume on photochemical processes downwind from the urbanized area was observed. Most BTEX compounds showed good correlation with other primary species such as nitrogen oxides and carbon monoxide at the rural site. High mixing ratios of primary compounds at the rural site were always correlated to transport of polluted air masses from the urban area. In addition, every time the rural site encountered the urban plume, selected BTEX ratios changed significantly and the formation of ozone and peroxyacetyl nitrate occurred. This fact demonstrates that BTEX compounds play an important role in regional photochemical smog formation. BTEX ratios may be a useful tool to assess the anthropogenically driven nonmethane hydrocarbon photochemistry in future air quality studies.
In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NOx
) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C2–C10 aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO2 converter were used for measuring NO and NO2. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5 ppbv para-cresol and 4.4 ppbv benzaldehyde, in comparison with the measured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para-Cresol was for the first time selectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NOx
ratios from 0.6 up to 3.0 ppbC/ppb in the traffic tunnel air and 3.4 ± 0.5 in the city air of Wuppertal were obtained. From the observed para-cresol/toluene and ortho-cresol/toluene ratios in the city air, evidence was found that also during daytime NO3 radical reactions play an important role in urban air.
Mixing ratios of carbon monoxide (CO), methane (CH4), non-methane hydrocarbons, halocarbons and alkyl nitrates (a total of 72 species) were determined for 78 whole air samples collected during the winter of 1998–1999 in Karachi, Pakistan. This is the first time that volatile organic compound (VOC) levels in Karachi have been extensively characterized. The overall air quality of the urban environment was determined using air samples collected at six locations throughout Karachi. Methane (6.3 ppmv) and ethane (93 ppbv) levels in Karachi were found to be much higher than in other cities that have been studied. The very high CH4 levels highlight the importance of natural gas leakage in Karachi. The leakage of liquefied petroleum gas contributes to elevated propane and butane levels in Karachi, although the propane and butane burdens were lower than in other cities (e.g., Mexico City, Santiago). High levels of benzene (0.3–19 ppbv) also appear to be of concern in the Karachi urban area. Vehicular emissions were characterized using air samples collected along the busiest thoroughfare of the city (M.A. Jinnah Road). Emissions from vehicular exhaust were found to be the main source of many of the hydrocarbons reported here. Significant levels of isoprene (1.2 ppbv) were detected at the roadside, and vehicular exhaust is estimated to account for about 20% of the isoprene observed in Karachi. 1,2-Dichloroethane, a lead scavenger added to leaded fuel, was also emitted by cars. The photochemical production of ozone (O3) was calculated for CO and the various VOCs using the Maximum Incremental Reactivity (MIR) scale. Based on the MIR scale, the leading contributors to O3 production in Karachi are ethene, CO, propene, m-xylene and toluene.
Though recent studies suggest that aerosols may influence the Asian monsoons, limited knowledge exists regarding aerosol impacts on regional climate and air quality. To improve understanding of aerosols in the Himalaya, mass concentrations (PM10 and PM2.5), chemical composition, and wavelength dependent aerosol optical depth (δλ) were measured from December 1998 through October 2000 at sites on the edge of the Kathmandu valley (Nagarkot) and in the remote Himalaya (Langtang). Though highly variable, aerosol concentrations peaked in February to May with average PM2.5=59±61 μg/m3 and aerosol optical depth at Nagarkot. With arrival of southerly flow and monsoon rains, PM2.5 dropped to 8±7 μg/m3 in June through September. With the cessation of summer rains, aerosol concentrations began steadily increasing with average PM2.5=25±14 μg/m3 during October to January. During all seasons, a large PM2.5/PM10 ratio (0.77±0.21), the predominance of particulate organic material (48±28% of PM2.5), and an ionic composition dominated by SO42−, NH4+, and NO3− (16±14% of PM2.5) all implicated combustion sources. Nonetheless, a large fraction of the aerosol was insoluble and non-carbonaceous (33±27%), particularly during the peak season when it reached 45%. Elemental analysis of a filter subset showed large concentrations of Ca, Si, Al, and Fe, indicating that dust was responsible for much of the remaining material. Though an influence of the Kathmandu valley was likely, evidence supported long-range transport of desert dust to the Himalaya from arid regions ranging from India and the Middle East to perhaps as far as the Sahara.
This well-received and comprehensive textbook on atmospheric processes and numerical methods has been thoroughly revised. This edition includes a wide range of new numerical techniques for solving problems in areas such as cloud microphysics, ocean-atmosphere exchange processes and atmospheric radiative properties. It also contains improved descriptions of atmospheric physics, dynamics, radiation, and aerosol and cloud processes. It is essential reading for researchers, scientists and advanced students to successfully study air pollution and meteorology.
Throughout South Asia biomass is commonly used as a fuel source for cooking and heating homes. The smoke from domestic use of these fuels is expected to be a major source of atmospheric particulate matter in the region and needs to be characterized for input in regional source apportionment models and global climate models. Biomass fuel samples including coconut leaves, rice straw, jackfruit branches, dried cowdung patties, and biomass briquettes manufactured from compressed biomass material were obtained from Bangladesh. The fuel samples were burned in a wood stove to collect and characterize the particulate matter emissions. The bulk chemical composition including total organic and elemental carbon, sulfate, nitrate, ammonium and chloride ions, and bulk elements such as potassium and sodium did not show conclusive differences among the biomass samples tested. Unique features, however, exist in the detailed organic characterization of the combustion smoke from the different sources. The organic compound fingerprints of the particulate matter are shown to be distinct from one another and distinct from North American wood fuels. Fecal stanols including 5b-stigmastanol, coprostanol, and cholestanol are found to be good molecular markers for the combustion of cowdung. Additionally, the patterns of methoxyphenols and plant sterols provide a unique signature for each biomass sample and are conducive as source apportionment tracers. This material is based upon work supported under a National Science Foundation graduate research fellowship.
Because of their continual production increase, wastes and the associated composting have become a problem of great interest. The aim of this work was to identify and quantify some of the main volatile organic compounds (VOCs) emitted by a composting factory during a summer period. Nonane ethyl acetate, tetrachloroethene and aromatic compound concentrations are quite similar as in the urban atmosphere. It can be noticed that heptane, decane and trichloroethene levels are 2 to 4 times higher than the city concentrations. Moreover, limonene concentrations are very high (average of 25 ng/l). Potential sources of these VOCs are the degradation of paints, adhesives, solvents, markers, food, detergents, fresheners, mothballs, etc. Moreover, limonene can result from chemical formula, which are used to mask the odours.
[1] An objective of the 1997 Southern California Ozone Study (SCOS97) was to provide an up-to-date assessment of the importance of biogenic emissions for tropospheric ozone production in the South Coast Air Basin. To this end, ambient air samples were collected during September 1997 at the Azusa air-monitoring station for subsequent measurement of their radiocarbon (C-14) content of the atmospheric nonmethane volatile organic compound (VOC) fraction. The C-14/C-12 ratio is proportional to the fraction of a sample's carbon that is biogenic. The proportionality constant was determined from local samples of vegetation, gasoline, and ambient CO2 collected during the same period. The median fraction of biogenic VOC observed from 0600 to 0900 hours (LT) was 7% (n = 5) with a range of -8% to 24%, from 1300 to 1600 hours it was 27% (n = 4) with a range of 11% to 39%, and from 1700 to 2000 hours it was 34 +/- 7% for a single sample. On the basis of calculated 24-hour back trajectories the dominant source region for the air masses associated with periods of high biogenic VOC-C levels was a sector extending from the north to the east. Over all time and space that the samples represent, the median fraction of biogenic VOC was 18% (n = 10). Expressed as an atmospheric mixing ratio, the overall (median and 95% confidence interval) biogenic VOC-carbon contribution was 80 +/- 50 nmol mol(-1) which may be representative of the natural VOC-C background for the Los Angeles air basin.
Instruments based on the differential optical absorption spectroscopy (DOAS) technique are used for monitoring air pollutants in urban areas all over the world. In Göteborg (Sweden) the DOAS technique has been used for several years for continuous monitoring of aromatic hydrocarbons and other traffic-related air pollutants. In the present study, measurements of benzene, toluene and p-xylene performed by DOAS have been evaluated. In an intercomparison study, adsorbent sampling and gas chromatography were used for measurements at the same sites as the DOAS instruments. The evaluation illustrated that the quality of the DOAS measurements was unsatisfactory even at concentrations exceeding the recommended lower limits. The proportions of benzene, toluene and p-xylene are usually uniform in vehicle polluted urban air. A significant deviation from the expected proportions may be used as an indication that the performance of a DOAS instrument should be checked.
The phenol yield from the OH-radical initiated oxidation of benzene was studied in two simulation chambers: (1) the large-volume outdoor chamber EUPHORE at CEAM, Valencia, Spain and (2) an indoor chamber at NIES, Tsukuba, Japan. In the first study two spectroscopic techniques, i.e. differential optical absorption spectroscopy (DOAS) and Fourier transform infra-red spectroscopy (FTIR) were used to simultaneously measure phenol and benzene. The second study used only FTIR spectroscopy to monitor both compounds. Six different types of OH-radical sources were employed and initial concentrations for benzene and NOx were varied by about a factor of 400 and four orders of magnitude, respectively. The high sensitivity of DOAS towards phenol allowed experiments with initial benzene concentrations similar to those found in the polluted atmosphere. With respect to the NOx concentrations and light conditions employed, the experiments are representative of the atmospheric boundary layer. The phenol yield was determined to be Φphenol=(53.1±6.6)%, which is about twice the value reported in the literature to date. The high phenol yield was found to remain essentially constant for NOx levels of up to several 10 ppb, which are rarely exceeded in the atmosphere. It was also found to be independent of the oxygen concentration under these conditions. With increasing concentrations of NOx (> 100 ppb) the phenol yield was found to decrease. The data could be adequately described if in addition to the kinetics of the aromatic-OH adduct reactions with O2 two reactions involving NOx (i.e. benzene–OH+NO2 and benzene–OH–O2+NO) were considered. The temperature dependence of Φphenol was studied over a limited temperature range of ΔT=20 K. The results indicate that the major part, if not all of the phenol is formed directly from the reaction of the benzene–OH adduct with oxygen. No evidence was found for phenol formation via the photolysis of benzene oxide/oxepin. The atmospheric relevance of the results is discussed.
The measurement of monocyclic aromatic hydrocarbons by Differential Optical Absorption Spectroscopy (DOAS) and Differential Absorption LIDAR (DIAL) in the atmosphere suffers from interfer-ence by the three forbidden Herzberg band systems of O and a fourth band system due to the dimers O —O and O —N at wavelengths below 287 nm. Due to the lack of reference spectra in digital form, until now the oxygen absorptions were difficult to eliminate from atmospheric absorption spectra. In this work, reference spectra of the Herzberg bands of oxygen are presented, that allow to eliminate this oxygen interference for practical purposes. Two sets of oxygen reference spectra were recorded between 240 and 290 nm with spectral resolutions of 0.15 nm (FWHM) and 0.05 nm. Spectra were taken at 240 and 720 m absorption path lengths in several mixtures of oxygen and nitrogen from 10% O /90% N to 100% pure O at atmospheric pressure (O column densities from 6;10 to 1.8;10 molecules cm\). At the resolution of the measurements, the rotational structure of the Herzberg I band Q-branches is not resolved. Therefore, saturation effects of individual transitions of the Herzberg I bands can cause the observed band shape to vary with the column density of oxygen. This apparent deviation from Lambert Beer's law can lead to problems with the oxygen correction of atmospheric DOAS measurements. In the practical application of the oxygen reference spectra, additional problems arise, because the ratio of molecular absorption in the Herzberg bands and dimer absorption changes when the partial pressure of oxygen is varied. Even though this effect is reduced due to the presence of N it needs to be accounted for, if the spectra are applied to atmospheric measurements. Solutions to these problems are discussed and demonstrated together with methods to optimize DOAS measurements of aromatic hydrocarbons. As sample application the oxygen reference spectra were used to correct DOAS measurements of monocyclic aromatic hydrocarbons carried out in the urban air of Heidelberg. Simultaneous time series of mixing ratios are presented for benzene, toluene, p-xylene, m-xylene and phenol. Mean concentrations were found to be 1.8, 2.5, 0.8, 1.2 ppb and 77 ppt, respectively. The spectra are available in digital form from the authors upon e-mail request.
Instruments based on the differential optical absorption spectroscopy (DOAS) technique are used for monitoring air pollutants in urban areas all over the world. In Göteborg (Sweden) the DOAS technique has been used for several years for continuous monitoring of aromatic hydrocarbons and other traffic-related air pollutants. In the present study, measurements of benzene, toluene and p-xylene performed by DOAS have been evaluated. In an intercomparison study, adsorbent sampling and gas chromatography were used for measurements at the same sites as the DOAS instruments. The evaluation illustrated that the quality of the DOAS measurements was unsatisfactory even at concentrations exceeding the recommended lower limits. The proportions of benzene, toluene and p-xylene are usually uniform in vehicle polluted urban air. A significant deviation from the expected proportions may be used as an indication that the performance of a DOAS instrument should be checked.
An objective of the 1997 Southern California Ozone Study (SCOS97) was to provide an up-to-date assessment of the importance of biogenic emissions for tropospheric ozone production in the South Coast Air Basin. To this end, ambient air samples were collected during September 1997 at the Azusa air-monitoring station for subsequent measurement of their radiocarbon (14C) content of the atmospheric nonmethane volatile organic compound (VOC) fraction. The 14C/12C ratio is proportional to the fraction of a sample's carbon that is biogenic. The proportionality constant was determined from local samples of vegetation, gasoline, and ambient CO2 collected during the same period. The median fraction of biogenic VOC observed from 0600 to 0900 hours (LT) was 7% (n = 5) with a range of −8% to 24%, from 1300 to 1600 hours it was 27% (n = 4) with a range of 11% to 39%, and from 1700 to 2000 hours it was 34 ± 7% for a single sample. On the basis of calculated 24-hour back trajectories the dominant source region for the air masses associated with periods of high biogenic VOC-C levels was a sector extending from the north to the east. Over all time and space that the samples represent, the median fraction of biogenic VOC was 18% (n = 10). Expressed as an atmospheric mixing ratio, the overall (median and 95% confidence interval) biogenic VOC-carbon contribution was 80 ± 50 nmol mol−1 which may be representative of the natural VOC-C background for the Los Angeles air basin.
Roadside particulate levels (PM<sub align="right"> 10 </sub>) at 30 locations throughout the Kathmandu Valley, Nepal are reported. There were seven sampling cycles from January to December 1999. PM<sub align="right"> 10 </sub> levels ranged between 1000 and 6000 µ/m³ for 1-h sampling. There was no consistent trend in PM10 levels with respect to monitoring cycle, average precipitation or wind speed. There is no WHO guideline for PM<sub align="right"> 10 </sub> (no safe exposure threshold), but the EPA 24-h standard is 150 µ/m³. The major sources of roadside PM<sub align="right"> 10 </sub> include dust re-suspension from vehicular movement and human activity, and particulate emissions from old vehicles. Other sources of PM<sub align="right"> 10 </sub> in the valley include cement and brick factories. Studies are currently being conducted to determine the lead content of PM<sub align="right"> 10 </sub> from roadside samples. Additional studies are warranted to assess the potential adverse human health effects of acute or chronic exposure to high particulate levels reported in this study.
Carbon disulfide, CS2, is an important sulfur-containing species in the global environment. Its oxidation to SO2 and COS are basic atmospheric chemical processes in the sulfur cycle. The typical measurement methods for CS2 are gas chromatography with flame photometric detection (GC-FPD) and gas chromatography - mass spectrometry (GC-MS). This paper presents CS2 and SO2 long-term measurements made by the long path Differential Optical Absorption Spectroscopy (DOAS) technique in the winter of 2001 to 2002 in the urban area of Shanghai, China. We found a good correlation between SO2 and CS2 with average [SO2]/[CS2] ~ 2.1. Combined with an analysis of pollution sources near the measurement site, our measurements indicate that CS2 came mainly from a coal burning furnace close to the measurement site.
The leakage of unburned liquefied petroleum gas (LPG) is a major source of urban nonmethane hydrocarbons (NMHCs) in the air of Santiago, Chile. Roughly 5% of the LPG that is sold in Santiago leaks in its unburned form to the atmosphere. Because of the leakage, propane is the most abundant NMHC in Santiago's air, even under heavy traffic conditions. NMHCs are an important precursor to the formation of ground-level ozone, and the LPG leakage may contribute as much as 15% to the excess ozone levels in Santiago. Improvement to the local air quality may be obtained by lowering the rates of LPG leakage, and by minimizing the use of alkene-rich LPG formulations.
Absorption cross sections of 24 volatile and non-volatile derivatives of benzene in the ultraviolet (UV) and the infrared (IR) regions of the electromagnetic spectrum have been determined using a 1080l quartz cell. For the UV a 0.5m Czerny-Turner spectrometer coupled with a photodiode array detector (spectral resolution 0.15nm) was used. IR spectra were recorded with an FT-IR spectrometer (Bruker IFS-88, spectral resolution 1cm-1). Absolute absorption cross sections and the instrument function are given for the UV, while for the IR, absorption cross sections and integrated band intensities are reported.The study focused primarily on the atmospherically relevant methylated benzenes (benzene, toluene, o-xylene, m-xylene, p-xylene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, ethylbenzene, styrene) and their ring retaining oxidation products (benzaldehyde, o-tolualdehyde, m-tolualdehyde, p-tolualdehyde, phenol, o-cresol, m-cresol, p-cresol, 2,3-dimethylphenol, 2,4-dimethylphenol, 2,5-dimethylphenol, 2,6-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, 2,4,6-trimethylphenol and (E,Z)- and (E,E)-2,4-hexadienedial).The UV absorption cross sections reported here can be used for the evaluation of DOAS spectra (Differential Optical Absorption Spectroscopy) for measurements of the above compounds in the atmosphere and in reaction chambers, while the IR absorption cross sections will primarily be useful in laboratory studies on atmospheric chemistry, where FT-IR spectrometry is an important tool.
In the Kathmandu Valley, Nepal faces environmental problems of most industrialized countries whereas it has problems similar to the least developed countries, in the hills. Types and quantity of energy use have a close link with the environmental degradation in Nepal Himalaya. Over dependence on the forest to meet the energy demand in the hills has aggravated the environmental problems. Lack of forest cover on the hills, the intense monsoon rain, the fragile geology and steep terrain are contributing to the acceleration of landslides, soil erosion and temperature rise. The rise of average minimum temperature is causing glaciers to retreat and thereby the development of large bodies of glacial lake. Glacial lake outbursts of 1981 in Kodari and of 1985 in Namche bazar area caused extensive damage on infrastructures down stream.Heavy use of commercial fuel (hydrocarbons) in the bowl shaped Kathmandu valley is causing air and water pollution and an increase in the average minimum temperature.Extensive development of hydropower, biogas plants and massive reforestation on naked hills and efficient use of imported hydrocarbons are the solution to existing energy and environmental problems.
Long-path DOAS (differential optical absorption spectroscopy) in the ultraviolet spectral region has been shown to be applicable for lowconcentration measurements of light aromatic hydrocarbons. However, because of spectral interferences among different aromatics as well as with oxygen, ozone, and sulfur dioxide, the application of the DOAS technique for this group of components is not without problems. This project includes a study of the differential absorption characteristics, between 250 and 280 nm, of twelve light aromatic hydrocarbons representing major constituents in technical solvents used in the automobile industry. Spectral overlapping between the different species, including oxygen, ozone, and sulfur dioxide, has been investigated and related to the chemical structure of the different aromatics. Interference effects in the DOAS application due to spectral overlapping have been investigated both in quantitative and in qualitative terms, with data from a field campaign at a major automobile manufacturing plant.
Measurements of trace gas concentrations and other quantities are a crucial tool for the investigation of the processes in the atmosphere. At the same time the determination of atmospheric trace gas concentrations constitutes a technological challenge, since extreme sensitivity (some species have to be detected at mixing ratios as low as 10-13) is desired simultaneously with high specificity, i.e. the molecule of interest usually must be detected in the presence of a large excess of other species. To date no single measurement technique can, even nearly, fulfil the above and other requirements for trace gas measurements in the atmosphere. Therefore a comprehensive arsenal of techniques has been developed. Besides a large number of special techniques (like the chemiluminescence-detection of NO) universal methods gain interest, due to their relative simplicity—a single instrument can register a large number of trace species. The different types of requirements and the various techniques are discussed, special emphasis is given to spectroscopic methods, which are a successful and promising variety, that plays a large and growing role in atmospheric chemistry research. For instance only spectroscopic methods allow remote sensing of trace gas concentrations, e.g. from satellite platforms. Today many varieties of spectroscopic methods are in use (e.g. tunable diode laser spectroscopy or Fourier transform spectroscopy), the basic properties and recent applications of this technique are presented by the example of differential optical absorption spectroscopy (DOAS). Future requirements and expected developments are discussed.
We have examined sectoral energy-use patterns and estimated the associated emission of key air pollutants in Kathmandu Valley for 1993, as well as the levels of pollutant emissions from fuel use in 2013 under a business-as-usual (BAU) scenario; total emissions of selected pollutants are estimated to be over 63,000 tons in 1993 and to increase five-fold by 2013. The transport sector contributes the largest share of pollutants, followed by the household and industrial sectors. Gasoline, fuelwood and coal were the dominant fuel contributors to total emissions and CO was the dominant pollutant.
A sensitive flame ionization detector was developed for capillary column gas chromatography. The detector used no make-up gas and lower flow-rates of hydrogen and air to suppress detector noise and to achieve maximum response. The detector was responsive down to the 10−13 g level for C2–C11 hydrocarbons. Atmospheric hydrocarbons could be determined at parts per billion or parts per trillion levels by using gas chromatography with the detector via cryogenic concentration of a small volume of air sample.
UV-differential optical absorption spectrometer (DOAS) technique is considered as a promising technique to detect gaseous pollutants and was applied to conduct one-week continuous measurements in the Chinese Petroleum (CPC) refinery plant located in Lin Yuan industrial park of Kaohsiung, Southern Taiwan. With the combination of local meteorological information, including solar radiation, wind direction and speed, the results showed that the concentrations of aromatic compounds and formaldehyde (HCHO) were higher at night while the values of ozone, NO2 and SO2 were high during the day. The major source of aromatics was the aromatic extraction unit in the refinery while NO2 and SO2 were mainly emitted from chimneys with not very high average concentrations. Formaldehyde concentration was above 50ppbv during night. There exists an apparent correlation between the variation of ground-level ozone concentration and photochemical reactions. The results indicate that in addition to benzene and toluene, ozone is a deleterious pollutant. The commercial DOAS system provides reliable information on distribution patterns of major air pollutants depending on their concentration levels in ambient air.
This paper addresses the impact of California phase 2 reformulated gasoline (RFG) on the composition and reactivity of motor vehicle exhaust and evaporative emissions. Significant changes to gasoline properties that occurred in the first half of 1996 included an increase in oxygen content; decreases in alkene, aromatic, benzene, and sulfur contents; and modified distillation properties. Vehicle emissions were measured in a San Francisco Bay Area roadway tunnel in summers 1994−1997; gasoline samples were collected from local service stations in summers 1995 and 1996. Equilibrium gasoline headspace vapor composition was calculated from measured liquid gasoline composition. Addition of methyl tert-butyl ether (MTBE) and reduction of alkenes and aromatics in gasoline between summers 1995 and 1996 led to corresponding changes in the composition of gasoline headspace vapors. Normalized reactivity of liquid gasoline and headspace vapors decreased by 23 and 19%, respectively. Ozone formation should be reduced because of both lower gasoline vapor pressure, which leads to lower mass emissions, and reduced reactivity of gasoline vapors. The reactivity of on-road emissions measured in the tunnel decreased by 8% or less. The reduction in reactivity of on-road emissions was less than that of evaporative emissions because of increased weight fractions of highly-reactive isobutene and formaldehyde in vehicle exhaust, which resulted from the increased use of MTBE in gasoline. On-road vehicle emissions of volatile organic compounds in the tunnel appear to be dominated by vehicles that have reduced catalytic converter activity.
Secondary organic aerosol (SOA) yield curves have been obtained for 17 individual aromatic species from an extensive series of sunlight-irradiated smog chamber experiments. These yield curves, interpreted within the framework of a gas/aerosol absorption model, are used to quantitatively account for the SOA that is formed in a series of smog chamber experiments performed with the whole vapor of 12 different reformulated gasolines. The total amount of secondary organic aerosol produced from the atmospheric oxidation of whole gasoline vapor can be represented as the sum of the contributions of the individual aromatic molecular constituents of the fuel.
Experiments on the photooxidation of toluene/NO x /air mixtures were performed in the European Photoreactor (EUPHORE), a large-scale outdoor reaction chamber located in Valencia/Spain. The objective of the study was the in situ determination of the yields of ring-retaining products by differential optical absorption spectroscopy (DOAS) and the elucidation of their formation pathways. The experiments were performed with toluene concentrations between 0.68 and 3.85 ppm and initial NO x concentrations ranging from 3 to 300 ppb, i.e., down to the range actually observed in the lower atmosphere. The ring-retaining product yields were found to be 5.8 (0.8%, 12.0 (1.4%, 2.7 (0.7%, and 3.2 (0.6% for benzaldehyde, o-cresol, m-cresol, and p-cresol, respectively. Under the experimental conditions, no dependency of the yields on the NO x concentration or the toluene/NO x ratio could be found. The formation kinetics of the cresols are in line with a "prompt" formation mechanism, i.e., abstraction of a hydrogen atom from the toluene-OH adduct (toluene-OH + O 2 f cresols + HO 2). In addition, substantial evidence was found that reaction with NO 3 radicals represents an important sink for cresols in smog chamber studies conducted under conditions of NO x concentrations above the range observed in the troposphere, possibly also under tropospheric conditions.
A Differential Optical Absorption Spectroscopy (DOAS) system has been operating by the Laboratory of Atmospheric Physics for almost one year. The DOAS instrument used was constructed by OPSIS AB and monitored O3, SO2, NO2, toluene and benzene, simultaneously. This paper critically discusses continuous UV/VIS-DOAS measurements of O3, NO2, SO2, benzene and toluene performed in parallel with conventional measurements of O3, SO2, NO2 and total non methane hydrocarbons (NMHC).
The emission rates for 221 vapor-phase, semivolatile, and particle-phase organic compounds from motor vehicles plus fine particulate matter mass and some inorganic particle-phase species are calculated based on measurements made inside and outside a Los Angeles roadway tunnel in 1993. These emission rates are calculated based on tunnel dilution rates or air circulation. The results show carbon monoxide emissions rates of 130 g Lâ»Â¹ of gasoline-equivalent fuel burned and volatile organic compound (VOC) emissions of 9.1 g Lâ»Â¹. These values are higher than predicted by the baseline version of California`s EMFAC 7G emissions inventory program but are within the coemission rate range of 108 {+-} 25 g Lâ»Â¹ reported by roadside remote sensing studies in Los angeles. When the VOC emissions composition in the tunnel is compared to that of tailpipe emissions source test data and to the composition of additional unburned whole gasoline, the tunnel atmosphere is found to be consistent with a linear combination of these major contributors over a fairly broad range of about 74--97% vehicle exhaust depending on the tailpipe profiles used.
A novel approach is described for the fractionation of water-soluble organic carbon (WSOC) in atmospheric aerosols and cloud drops. The method is based on the preliminary adsorption of the sample, acidified at pH 2, on a polymeric styrene-divinylbenzene resin (XAD-2) and subsequent elution with a series of solvents, which leads to the fractionation of the sample into three classes of compounds. The method was set up using synthetic mixtures of organic compounds and then applied to selected samples of atmospheric aerosols and cloud drops. All samples and collected fractions were analysed using size exclusion chromatography (SEC). This method proved particularly useful both in providing information on the organic content of the samples and for the characterisation of the macromolecular compounds (MMCs) in the samples. Synthetic samples were prepared using humic, fulvic and tannic acid to simulate naturally occurring MMCs. In the first fraction, eluted with HCl, only the most soluble organic compounds (oxalic acid, formic acid and acetic acid) were collected. In the second fraction, eluted with methanol, the major part of the organic material was collected together with the more hydrophilic constituents of the humic substances. In the third fraction, it was possible to separately recover the more hydrophobic component of the humic substances. A large number of atmospheric samples (fog, aerosol, cloud) were then analysed using SEC. Most of these samples evidenced a noteworthy chromatogram at 254 nm. Moreover, the chromatographic area evidenced a clear linear correlation with the total organic carbon (TOC) values. The fractionation method on XAD-2 was finally applied to selected atmospheric samples, yielding three classes of organic compounds. In each sample, a non-negligible amount of compounds with dimensional and chemical properties similar to humic substances were collected in the third fraction. The carbon content in this latter fraction was estimated both by TOC and by means of the correlation between TOC and SEC area.
Speciation of o-xylene, m-xylene, p-xylene and ethylbenzene was performed by gas chromatography from ambient air and liquid fuel samples collected at various locations in 19 cities in Europe, Asia and South America. The xylene's mixing ratios were compared to each other from the various locations, which included urban air, traffic air and liquid fuel. For all samples, the xylenes exhibited robust correlations, and the slopes remained constant. The m-xylene/p-xylene ratio was found to be 2.33±0.30, and the m-xylene/o-xylene ratio was found to be 1.84±0.25. These ratios remain persistent even in biomass combustion experiments (in South America and South Africa). Comparing the xylenes to toluene and benzene indicate that combustion, but not fuel evaporation, is the major common source of the xylenes in areas dominated by automotive emissions. Although a wide range of combustion types and combustion efficiencies were encountered throughout all the locations investigated, xylenes and ethylbenzene ratios remained persistent. We discuss the implications of the constancies in the xylenes and ethylbenzene ratios on atmospheric chemistry.
The total of 28 different C2–C6 non-methane hydrocarbons including isoprene emitted from natural and anthropogenic sources in urban and rural sites of Kathmandu, capital of Nepal, were characterized for the first time in Nepal, in November 1998. Thirty-eight whole air samples were analyzed by using GC/FID. Ethene, acetylene and C4–C5 alkanes were identified as the source signature in Kathmandu urban ambient air. Hydrocarbon emissions from vehicular exhaust and gasoline evaporation sources were confirmed to outweigh natural gas and biogenic sources. Comparison of NMHCs profile normalized by acetylene between Kathmandu and Tokyo, Japan showed prominent difference in C2–C5 alkanes relative to acetylene. Significant amount of ethene at the rural site was assigned as emitted from biogenic sources because of its significant correlation with isoprene (R2=0.52). Predominant amount of isoprene (average 278 pptv) observed at the urban site were assigned to be emitted from vehicular exhaust as it exhibited high correlation with other anthropogenically emitted hydrocarbons (R2=0.72 with acetylene). Photochemical aging analysis showed that the mixing ratio variation of urban air transporting towards the rural site took place through its OH radical initiated oxidation and the observed alkanes in the rural site were mostly from the transported urban air.
Benzene, toluene and p-xylene were measured above the buildings level in Thessaloniki, Greece for around eight months during the period December 1993–August 1994 by means of a commercial differential optical absorption spectrometer (OPSIS DOAS). Daily mean mixing ratios for benzene and toluene varied between 1–6 and 1–32 ppb, respectively. The data indicate that the annual mean benzene concentrations most probably lie in the range 2–3 ppb, which is below the guide values but above the target values of European countries that have set limits for benzene. Mean diurnal variations of benzene and toluene during summer and winter months reflect the effects of emission, photochemical degradation and mixing. Benzene and toluene hourly values correlated well with each other and with NO2. Toluene and benzene hourly values were negatively correlated with ozone during summertime. During wintertime, considerable enhancements of benzene and toluene mixing ratios might be associated with the passage of synoptic weather systems of fair weather. Although the measurement of p-xylene is, in principle, efficiently performed with the DOAS technique, the OPSIS instrument p-xylene measurements contradict current understanding of its sources and sinks and are thus attributed to errors of the instrument in the evaluation of this substance.
Urban roadside levels of benzene, toluene, ethylbenzene and xylenes (BTEX) were investigated in three typical cities (Guangzhou, Macau and Nanhai) in the Pearl River Delta Region of south China. Air samples were collected at typical ground level microenvironments by multi-bed adsorbent tubes. The BTEX concentrations were determined by thermal desorption–gas chromatography–mass selective detector (TD–GC–MSD) technique. The mean concentrations of benzene, toluene, ethylbenzene and xylenes were, respectively, 51.5, 77.3, 17.8 and 81.6 μg/m3 in Guangzhou, 34.9, 85.9, 24.1, 95.6 μg/m3 in Macau, and 20.0, 39.1, 3.0 and 14.2 μg/m3 in Nanhai. The relative concentration distribution pattern and mutual correlation analysis indicated that in Macau BTEX were predominantly traffic-related while in Guangzhou benzene had sources other than vehicle emission. In Nanhai, both benzene and toluene had different sources other than vehicle emission. The samples collected from Guangzhou showed that BTEX had significant higher concentrations in November than those in July.
Benzene, toluene, sulphur dioxide, ozone and nitrogen dioxide were measured at a mean level of 13.5 m above ground in a narrow, four-lane street canyon (height 30 m, width 20 m) in Thessaloniki, Greece during the period January–July 1997 by means of a commercial differential optical absorption spectrometer (OPSIS DOAS). Primary pollutant levels were found to be 2.5–4.4 times higher during the cold part of the year than during the warm part of the year, the winter/summer ratio increasing with the reaction rate constant with OH for each of the measured species. Ozone, on the other hand, exhibited a winter/summer ratio of 0.36. NO2 originates from both primary and secondary sources; its winter/summer concentration ratio of 1.4 lies, therefore, between those of primary pollutants and ozone. Pollution levels were influenced considerably by wind speed, while for the street canyon under study wind direction did not influence pollutant levels considerably. While primary pollution was found to decrease with increasing wind speed, ozone increased. Benzene mean levels during the study period were around 6 ppb and hence much higher than the EU annual limit value of 5 μg m−3 (1.44 ppb at STP). Toluene mean levels were around 14 ppb and hence also several times above the WHO recommendation of 2 ppb for 24 h. The apportionment of traffic emissions in four time zones used in most inventories in urban airshed models was tested using benzene and toluene measurements at low (<1 m s−1) wind speeds. The agreement between model emissions and calculated emissions apportionment into the four time zones was good, except for Zone D (23:00–1:59), where model inventory emissions were somewhat too low.
Asia is undergoing rapid urbanization resulting in increasing air pollution threats in its cities. The contribution of megacities to sulfur emissions and pollution in Asia is studied over a 25-year period (1975–2000) using a multi-layer Lagrangian puff transport model. Asian megacities cover <2% of the land area but emit ∼16% of the total anthropogenic sulfur emissions of Asia. It is shown that urban sulfur emissions contribute over 30% to the regional pollution levels in large parts of Asia. The average contribution of megacities over the western Pacific increased from <5% in 1975 to >10% in 2000. Two future emission scenarios are evaluated for 2020—“business as usual (BAU)” and “maximum feasible controls (MAXF)” to establish the range of reductions possible for these cities. The MAXF scenario would result in 2020 S-emissions that are ∼80% lower than those in 2000, at an estimated control cost of US $87 billion per year (1995 US$) for all of Asia. An urban scale analysis of sulfur pollution for four megacities—Shanghai, and Chongqing in China; Seoul in South Korea; and Mumbai (formerly Bombay) in India is presented. If pollution levels were allowed to increase under BAU, over 30 million people in these cities alone would be exposed to levels in excess of the WHO guidelines.
To investigate if air pollution generated in the Himalayan foothills reached higher elevations, a sequence of surface meteorological and condensation nucleus (CN) measurements were made between October 1995 and May 1996. Measurements were made in the Kathmandu valley of the foothills, in the Dudh Kosi valley of the eastern Himalayas and at the base of Mt. Everest in Nepal and Tibet. The Kathmandu valley measurements revealed a semi-diurnal variation of CN and moisture in the mountain-valley wind system and a reduction of both in strong afternoon convection we call the “Kathmandu chimney”. The air was polluted at all times in the valley. The Dudh Kosi measurements revealed a diurnal variation in CN and moisture; both were drawn into the valley in the strong afternoon valley wind and cleaner and drier air flowed into the valley in the nighttime mountain wind. The air was unpolluted in the mornings and frequently polluted in the afternoon and evenings; some of the evening pollution was from local sources. The CN concentrations in Tibet were smaller than in Nepal at the same elevation due dilution in the deep afternoon convective boundary layer in Tibet; there also may be a “Tibetan chimney”. Evidence is presented for trans-Himalayan pollution transport: a 7-h pollution episode originating in Nepal was advected into Tibet and a 18-h episode originating in Tibet was advected into Nepal.
The oval shaped tectonic basin of Kathmandu valley, occupying about 656 sq.km is situated in the middle sector of Himalayan range. There are three districts in the valley, i.e. Kathmandu, Lalitpur and Bhaktapur. Out of the three, the most populated is Kathmandu city (the capital of Kingdom of Nepal) which has a population of 668,00 in an area of approximately 50 km2. The energy consumption of the city population is about of the total import to Nepal of gasoline, diesel, kerosene, furnace oil and cooking gas. This has resulted heavy pollution of air in the city leading to bronchitis, and throat and chest diseases. Vehicles have increased several fold in recent months and there are 100,000 in number on the road and they have 900 km of road, out of which only 25% is metalled. Most of the two and three wheelers are polluting the air by emission of gases as well as dust particulate. SO2 has been found to go as high as 202 μg cm−3 and NO2 to 126 μg cm−3 particularly in winter months when a thick layer of fog covers the valley up to 10 am in the morning. All the gases are mixed within the limited air below the fog and the ground. This creates the problem. Furthermore, municipal waste of 500 m3 a day and also liquid waste dumped directly into the Bagmati river at the rate of 500,000 ℓ d−1 makes the city ugly and filthy. Unless pollution of air, water and lard are controlled in time, Nepal will lose much of its foreign exchange earnings from the tourist industry. It is found that tourist arrivals have considerably reduced in recent years and most of hotels occupancy is 50–60% in peak time. Nepal is trying to introduce a legal framework for pollution control but it will take time to become effective.
Time-resolved chemical ionization mass spectrometry (CI-MS) has been used to investigate the velocity-dependent emission factors for benzene, toluene, the C2-benzenes (xylenes and ethyl benzene) and nitrogen monoxide of a gasoline-driven passenger car (1.4 l, model year 1995) driven with or without catalytic exhaust gas treatment. A set of seven different driving cycles – including the European Driving Cycle (EDC), the US Urban (FTP 75) and the Highway driving cycles – with a total driving time of 12,000 s have been studied. From the obtained emission data, two sets of 15,300 and 17,200 data points which represent transient driving in the velocity range of 0–150 km h−1 and in an acceleration window of −2–3 m s−2 were explored to gain velocity-dependent emission factors. The passenger car, equipped with a regulated rhodium–platinum based three-way catalyst, showed optimal conversion efficiency (>95%) for benzene in the velocity range of 60–120 km h−1. The conversion of benzene was reduced (<80%) when driving below 50 km h−1 and the BTXE emissions significantly increased when driven at higher speed and engine load (>130 km h−1). Whereas the conversion efficiency for the class of C2-benzenes was reduced to 10%, no net conversion could be found for toluene and benzene when driven above 130 km h−1. In contrast, the benzene and toluene emissions exceeded those of the untreated exhaust gas in the velocity range of 130–150 km h−1 by 50–92% and by 10–34%, respectively. Thus, benzene and toluene were formed across the examined three-way catalyst if the engine is operated for an extended time in a fuel-rich mode (lambda<1).
This paper summarizes the results of a yearlong continuous measurements of gaseous pollutants, NO, NO2, NOx and O3 in the ambient air at Kathmandu valley. Measured concentration of the pollutants in study area is a function of time. NO, NO2 and O3 peak occurred in succession in presence of sunlight. At the time of maximum O3 concentration most of the NOx are utilized. The diurnal cycle of ground level ozone concentrations, revealed mid-day peak with lower nocturnal concentrations and inverse relationship exists between O3 and NOx, which are evidences of photochemical O3 formation. The observed ground level ozone during monsoon is slight lower than the pre-monsoon value. Further, lack of rainfall and higher temperature, solar radiation in the pre-monsoon have given rise to the gradual build up of ozone and it is lowest during winter. Ground level ozone concentrations measured during bandha (general strike) and weekend are 19% and 13% higher than those measured during weekdays. The most effective ozone abatement strategy for Kathmandu Valley may be control of NOx emissions.
Since 1950 the world population has more than doubled, and the global number of cars has increased by a factor of 10. In the same period the fraction of people living in urban areas has increased by a factor of 4. In year 2000 this will amount to nearly half of the world population. About 20 urban regions will each have populations above 10 million people.Seen over longer periods, pollution in major cities tends to increase during the built up phase, they pass through a maximum and are then again reduced, as abatement strategies are developed. In the industrialised western world urban air pollution is in some respects in the last stage with effectively reduced levels of sulphur dioxide and soot. In recent decades however, the increasing traffic has switched the attention to nitrogen oxides, organic compounds and small particles. In some cities photochemical air pollution is an important urban problem, but in the northern part of Europe it is a large-scale phenomenon, with ozone levels in urban streets being normally lower than in rural areas. Cities in Eastern Europe have been (and in many cases still are) heavily polluted. After the recent political upheaval, followed by a temporary recession and a subsequent introduction of new technologies, the situation appears to improve. However, the rising number of private cars is an emerging problem. In most developing countries the rapid urbanisation has so far resulted in uncontrolled growth and deteriorating environment. Air pollution levels are here still rising on many fronts.Apart from being sources of local air pollution, urban activities are significant contributors to transboundary pollution and to the rising global concentrations of greenhouse gasses. Attempts to solve urban problems by introducing cleaner, more energy-efficient technologies will generally have a beneficial impact on these large-scale problems. Attempts based on city planning with a spreading of the activities, on the other hand, may generate more traffic and may thus have the opposite effect.
An in situ field experiment was conducted in a highway road tunnel in the Taipei City to determine the motor vehicle emission factors (EF) of different kinds of air pollution species. These are carbon monoxide (CO), oxides of nitrogen (NOx), non-methane hydrocarbons (NMHC) and VOCs species. About 56 species of VOCs were sampled by canister sampler and followed by the GC-MS analyzing. Furthermore, the tunnel-drafting rate was determined by SF6 tracer method.The EF for the highway vehicles determined from this experiment are 3.64, 0.90, 0.44 and 0.24 gm km−1 veh−1 for CO, NOx, NMHC and the totally measured VOCs, respectively. A comparison of the EFs from the road tunnel experiment to the estimates by the USEPA MOBILE5b (M5b) and the modified Taiwan EPA MOBILE-TAIWAN2.0 (MT2.0) provides a first-hand evaluation of the model characteristics. M5b and MT2.0 both tend to underpredict CO by 10% and 20%, respectively. While M5b overpredicts NOx and NMHC by 40% and 20%, respectively; MT2.0 has fairly good predictions for these two species. From the GC-MS analysis of the canister samples, it was found that the most abundant species from the traffic-emitted VOCs in Taipei road tunnel are toluene, ethene and 1,2,4-trimethyl-benzene (1,2,4-TMB) by the weight basis. However, ethene, acetylene and toluene are the most abundant in VOCs based on volume. The VOCs’ weight composition in terms of the carbon bond classification is 28% by the paraffins, 33% by the olefins and 39% by the aromatics, respectively. In order to evaluate the ozone formation potential from the typical road emission in Taipei area, the maximum increment reactivity is calculated. It was found that about 1015 mg of O3 is induced by per vehicle per kilometer traveled emission. Among them, ethene, 1,2,4-TMB and propene from the road vehicle's emission contribute most to the ozone-formation reactivity.
A photochemical trajectory model is used to describe the ozone production from the oxidation of methane and 95 other hydrocarbons in the presence of sunlight and NOx in air parcels advected across north west Europe towards the British Isles. By adding a small additional mass emission of each hydrocarbon in turn, additional ozone production was stimulated. A photochemical ozone creation potential (POCP) index was generated from the model results showing the relative importance of each hydrocarbon in ozone formation, on a mass emitted basis. Aromatic and olefinic hydrocarbons showed the highest POCP values with halocarbons the lowest. Using the POCP index, motor vehicle exhaust is seen to exhibit the highest ozone-forming potential of all the hydrocarbon emission source categories evaluated. Toluene, n-butane, ethylene and the xylenes, alone, account for over one third of the ozone forming potential of European emissions. Certain hydrocarbons, including acetone and methyl acetate, show significantly lower POCPs and have considerable potential as candidates for substitution in industrial or chemical processes and as solvents.
We have recently found many light hydrocarbons, both alkanes and
alkenes, in trace amounts (ng compound per g sediment) in Recent marine
sediments1-4. These hydrocarbons are believed to originate
from both biological and low-temperature reactions in the sediments.
Understanding their mechanism of formation may allow use of these
compounds to decipher the past biological and thermal history of the
sediments4. To investigate biological origins, we have
cultivated mixed populations of bacteria on natural terpenoids and
found, as degradation products, both alkanes and alkenes in the
C1-C7 range; this is the first report of
C4-C7 hydrocarbons being formed from microbial
activities. Aerobic followed by anaerobic degradation yielded mainly
small amounts of straight-chain alkenes. No such products resulted from
blanks or controls. The results are consistent with products observed in
natural environments.