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Abstract

The metaphor “lungs of cities”, initially a slogan for the preservation of urban parks, has been retained almost as common sense to the present. It implies that parks provide urban dwellers spaces for breathing in polluted cities. Observations on air pollutants in urban parks detect imprints left by emissions from local vehicles and industries, although they also reveal cleaner park interiors. There has been divergence about the way enhanced air quality in urban parks has been interpreted, some seeing this as the result of pollutant dispersion, while others believe it arises through pollutant uptake by vegetation. A bibliometric analysis suggests that studies considering only deposition found pollutant reduction, while those which account dispersion are less consistent, but street trees often fail to improve air quality. The balance between pollutant dispersion and deposition processes varies with spatial scale and is an important determinant of the roles played by vegetation in improving air quality. In small parks, common in dense cities, pollutant removal by vegetation is unlikely to make the major contribution to improved air quality in their interiors. Moreover, dense tree canopies supress dispersion so can increase localised pollutant concentrations. The contemporary understanding of air-vegetation interactions has yet to be widely adopted in park design and urban planning. Although the metaphor “lungs of cities” may inspire enthusiasm for urban parks, it should not frustrate the use of emerging research in design.

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... La investigación actual sobre el rol del verde urbano en la salud de la urbe y sus habitantes aplica tratativas multidisciplinarias combinando variables como fisonomía, función, estructura biológica, estructura física y salud de la vegetación (esta última con frecuencia subroga a la estética) asociándolas a conceptos como servicios ecosistémicos, infraestructura verde y soluciones basadas en la naturaleza (Escobedo et al., 2018). La investigación sobre el rol del arbolado y parques urbanos en la calidad del aire, la captura de polucionantes, la remoción de excedentes de CO2, el manejo de la escorrentía urbana y la mitigación del ruido ha sido muy prolífica en los últimos 15 años, y a la fecha ya se han hecho revisiones prolijas de resultados (Escobedo et al., 2018;Xing y Brimblecombe, 2020;Ordoñez et al., 2020). Estas revisiones concuerdan en que el potencial del arbolado urbano para proveer los servicios ambientales antes mencionados es limitado, sujeto además a densidad y mantenimiento (Xing y Brimblecombe, 2020) comparado con el potencial de los remanentes naturales periurbanos (bosques protectores, cobertura vegetal de microcuencas), y urbanos como parques, ríos, quebradas, taludes, etc. (Millenium Ecosystem Assessment, 2005;Escobedo et al., 2018). ...
... .3. Árboles y bienestar humanoLa influencia de parques y jardines en el bienestar de citadinos es conocida desde la antigua Roma, pero no es sino hasta mediados del siglo XVIII que se reconoce su importancia en la calidad del aire de las urbes(Xing y Brimblecombe, 2020). En las ciudades industrializadas del Reino Unido, entre ellas Londres, los parques cumplían una función purificadora del aire, y en tal razón se les llamó pulmones de la ciudad, metáfora que trascendió a otras ciudades industrializadas del mundo que integraron el arbolado a las plazas públicas como una medida de salud, ya que el rol purificador se atribuía al dosel de los árboles(Xing y Brimblecombe, 2020). ...
... Árboles y bienestar humanoLa influencia de parques y jardines en el bienestar de citadinos es conocida desde la antigua Roma, pero no es sino hasta mediados del siglo XVIII que se reconoce su importancia en la calidad del aire de las urbes(Xing y Brimblecombe, 2020). En las ciudades industrializadas del Reino Unido, entre ellas Londres, los parques cumplían una función purificadora del aire, y en tal razón se les llamó pulmones de la ciudad, metáfora que trascendió a otras ciudades industrializadas del mundo que integraron el arbolado a las plazas públicas como una medida de salud, ya que el rol purificador se atribuía al dosel de los árboles(Xing y Brimblecombe, 2020). ...
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La Red de Desarrollo Urbano Sostenible de Cotopaxi (Red DUS Cotopaxi), con el apoyo de instituciones aliadas en el marco del Laboratorio Urbano, lideró una iniciativa de recolección de datos ciudadanos para el registro de áreas verdes y árboles. Esta iniciativa se implementó bajo la modalidad de un Datatón Ciudadano: una metodología pensada para activar a la ciudadanía a que forme parte de procesos de levantamiento de datos sobre temáticas y problemas relevantes a nivel urbano. El Datatón que se aplicó en Latacunga en el año 2020 consistió en una maratón de tres semanas para recoger a través del uso de la tecnología y una encuesta en línea, la mayor cantidad de datos sobre la situación del arbolado urbano y las áreas verdes de la ciudad.
... 21 It is clear that LAI, hairiness, and wax content affect deposition, but also meteorological variables (precipitation, solar radiation, humidity, wind speed, temperature, and turbulence) have an impact on the magnitude of deposition velocity and thus the capacity of plants to ameliorate air quality. 22,23 Urban planning and management (plant species or planting configuration) has also an impact on dry deposition at the stand/regional level. 23 Because most particles are deposited on leaves, higher deposition can be expected on evergreen species rather than on deciduous species. ...
... It must be taken into account that by applying the AIRTREE model, we indirectly assumed a homogeneous canopy distribution in the parks and a horizontally homogeneous distribution of pollutants with downward flux. As discussed by Xing and Brimblecombe (2020), 22 spatial scale is of high relevance for estimating pollutant deposition. Although we strongly believe that the mesoscale approach we adopt is more appropriate to describe pollutant deposition than laboratory measurements on a single leaf upscaled to a forest, 65 the weak point in such a mesoscale approach is that this may not be the best approximation for street trees or very small parks where vehicles and street canyon dynamics induce strong turbulence affecting both concentrations and deposition velocities close to the leaves. ...
... Although this was not the object of this work, another relevant effect exerted by urban trees is on air flow and thus pollutant dispersion. A recent bibliometric analysis by Xing and Brimblecombe (2020) 22 suggests that urban parks can ameliorate air quality through two main pathways: on the one hand, they accelerate PM dispersion, and on the other hand, they reduce pollutant concentration by deposition. The authors argue that the balance between dispersion and deposition processes varies with spatial scales. ...
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Cities are responsible for more than 80% of global greenhouse gas emissions. Sequestration of air pollutants is one of the main ecosystem services that urban forests provide to the citizens. The atmospheric concentration of several pollutants such as carbon dioxide (CO 2), tropospheric ozone (O 3), and particulate matter (PM) can be reduced by urban trees through processes of adsorption and deposition. We predict the quantity of CO 2 , O 3 , and PM removed by urban tree species with the multilayer canopy model AIRTREE in two representative urban parks in Italy: Park of Castel di Guido, a 3673 ha reforested area located northwest of Rome, and Park of Valentino, a 42 ha urban park in downtown Turin. We estimated a total annual removal of 1005 and 500 kg of carbon per hectare, 8.1 and 1.42 kg of ozone per hectare, and 8.4 and 8 kg of PM 10 per hectare. We highlighted differences in pollutant sequestration between urban areas and between species, shedding light on the importance to perform extensive in situ measurements and modeling analysis of tree characteristics to provide realistic estimates of urban parks to deliver ecosystem services.
... In the literature, vegetation-based benefits are often linked to larger UGI installations, like parks, and their attribution to smaller installations like SCMs is assumed but not verified. Many of the vegetation-based benefits, such as improved air quality and urban heat island mitigation, are derived from literature on the impacts of urban trees and turf grass (Berland et al. 2017;Nowak et al. 2006;Xing and Brimblecombe 2020;Yu et al. 2020), but their transferability to SCMs along the gray-green continuum has not been proven. More effort has been dedicated to identifying potential vegetation-based benefits and creating metrics for their incorporation (GIVaN 2010; Guo and Correa 2013;McGarity et al. 2015). ...
... Tree canopies can also trap pollutants at ground level and emit volatile organic compounds (VOCs) depending on the tree species (Berland et al. 2017;Nowak et al. 2006). In parks, lower pollution rates measured may be due to the distance between the measurement and the sources of pollution, not due to the air pollution mitigation of vegetation (Xing and Brimblecombe 2020). Smaller parks (which may be equivalent in size to some SCMs) that are closer to streets often see no improvement in air quality (Xing and Brimblecombe 2020). ...
... In parks, lower pollution rates measured may be due to the distance between the measurement and the sources of pollution, not due to the air pollution mitigation of vegetation (Xing and Brimblecombe 2020). Smaller parks (which may be equivalent in size to some SCMs) that are closer to streets often see no improvement in air quality (Xing and Brimblecombe 2020). Ultimately, more locationspecific empirical research needs to be performed at variable scales to characterize the air quality mitigation potential of SCMs while accounting for ecosystem disservices like VOCs and pollen (Pataki et al. 2011). ...
Article
As we move into an era of increased urbanization, stormwater practitioners are charged with creating multibenefit solutions through the installation of stormwater control measures (SCMs). Two drivers facilitate the accrual of benefits in SCMs: hydrologic or water quality process and vegetation. This study investigated the feasibility of incorporating benefits beyond water quality and quantity control into the SCM planning process. A critical review was used to determine which benefits would be assessed with hydrologic and water quality modeling or a complementary conceptual framework. Drawing on common themes in the literature, the conceptual framework of the 4 Cs (community, context, connectivity, and canopy) was created to assess vegetation-based benefits. To demonstrate the coupled benefit assessment, a case study was performed in a neighborhood of Denver, Colorado. Results from hydrologic and water quality modeling show that vegetated swales provide the most preferred solution. From the vegetation-based benefit perspective, we find that the modeled area of the vegetated swales is only 0.2% by area, which is likely too small to have a measurable benefit effect at the neighborhood scale. We show how the 4 Cs can be used to leverage existing greenness to maximize the potential vegetation-based benefit of swales and consider how existing sociodemographic and vegetation trends can be leveraged to make benefit-driven decisions.
... A las investigaciones que resaltaban la función purificadora de los árboles a través de la captura de carbono y liberación de oxígeno, les siguieron otras que argumentaban sobre la capacidad del dosel del árbol para detener infecciones y emanaciones nocivas formando una barrera rompe flujo capaz de "absorber partículas toxicas y generar oxígeno" (Rauch, 1869). Para mediados del siglo 19 algunas ciudades industrializadas de Europa incluían parques densamente arbolados considerados "los pulmones de la ciudad" (Xing & Brimblecombe, 2019). Esta metáfora luego trascendió a otras ciudades industrializadas del mundo en las que se integraron árboles a las plazas públicas como una medida de salud, ya que el rol purificador del aire se atribuía al dosel de estos (Xing & Brimblecombe, 2019). ...
... Para mediados del siglo 19 algunas ciudades industrializadas de Europa incluían parques densamente arbolados considerados "los pulmones de la ciudad" (Xing & Brimblecombe, 2019). Esta metáfora luego trascendió a otras ciudades industrializadas del mundo en las que se integraron árboles a las plazas públicas como una medida de salud, ya que el rol purificador del aire se atribuía al dosel de estos (Xing & Brimblecombe, 2019). ...
Research
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El objetivo de esta investigación fue evaluar la diversidad y la funcionalidad del arbolado de Quito en base a la información recabada previamente y hacer recomendaciones que permitan mejorar el rendimiento ambiental y ecológico de los árboles de la urbe. Para este efecto se llevó a cabo un análisis espacial de variables asociadas a la diversidad biológica (i.e. procedencia de la especie, caracterización fisonómica y fisiológica básica y estrategia de reproducción) y al estado de mantenimiento del arbolado urbano al momento de la adquisición de los registros fotográficos (edad, densidad de follaje, continuidad de dosel y poda).
... A las investigaciones que resaltaban la función purificadora de los árboles a través de la captura de carbono y liberación de oxígeno, les siguieron otras que argumentaban sobre la capacidad del dosel del árbol para detener infecciones y emanaciones nocivas formando una barrera rompe flujo capaz de "absorber partículas toxicas y generar oxígeno" (Rauch, 1869). Para mediados del siglo 19 algunas ciudades industrializadas de Europa incluían parques densamente arbolados considerados "los pulmones de la ciudad" (Xing & Brimblecombe, 2019). Esta metáfora luego trascendió a otras ciudades industrializadas del mundo en las que se integraron árboles a las plazas públicas como una medida de salud, ya que el rol purificador del aire se atribuía al dosel de estos (Xing & Brimblecombe, 2019). ...
... Para mediados del siglo 19 algunas ciudades industrializadas de Europa incluían parques densamente arbolados considerados "los pulmones de la ciudad" (Xing & Brimblecombe, 2019). Esta metáfora luego trascendió a otras ciudades industrializadas del mundo en las que se integraron árboles a las plazas públicas como una medida de salud, ya que el rol purificador del aire se atribuía al dosel de estos (Xing & Brimblecombe, 2019). ...
... Since WRF predefined buildings height is 10 m in HR, and on the other hand, building roof fraction is more significant in this area than that of LR area (75 % vs. 50 % urban fractions), these results seem rational. Indeed, in the first scenario, trees change roughness length and increase obstacles against wind flow (Xing and Brimblecombe, 2020) which reduce near-surface momentum and its transfer from the upper levels. On the other hand, green roofs increase surface friction which follows by wind speed reduction at the roof level (10 m in HR area). ...
... The balance between pollutant deposition and dispersion changes with spatial scale of green covers. This is an important factor of the roles played by vegetation in improving air quality (Xing and Brimblecombe, 2020). ...
Article
Two applicable green space development scenarios (surface with vegetation and green roof) are investigated, using Weather Research and Forecasting model (WRF) coupled with the Single Layer Urban Canopy Model (SLUCM) over Tehran Metropolis in an early summertime period, with special attention to variables related to the atmospheric dispersion and circulation. Results are reported for two High and Low Residential areas of Tehran (HR and LR). Reductions in the daytime Turbulence Kinetic Energy (TKE) budget (down to -0.5 m²/s² ∼25%), potential temperature (down to -0.2 K) and wind speed are observed. Surfaces with vegetation show more significant reductions of TKE buoyancy forcing in both areas. In the case with mainly shear generation of turbulence, the surface with vegetation shows increased (decreased) values during the day in HR (LR). Green roof (surface with vegetation) approach shows more reduction in wind speed in HR (LR). Slightly increased observed values for heat and momentum eddy diffusivities up to +11.99 m²/s (∼20%) and +8.63 m²/s (∼10%), respectively, limit the air circulation and upward transfer of near-surface polluted air especially in HR area, and these values are more pronounced in the first scenario and especially during the convective daytime conditions. The planetary boundary layer growth decreased (by about 50 m in HR, ∼7%) due to the reduction in the daytime near-surface air temperature and hence convective turbulence. Findings indicate that green scenarios (particularly surface with vegetation) could have negative side effects on atmospheric dispersion, natural air ventilation and air circulation, and consequently have undesirable impacts on Tehran air quality which have to be considered in any green space development programs.
... Trees and other vegetation types in conjunction with landforms reduce road noise by 6-15 decibels, while trees in combination with solid barriers reduce noise by 5-8 decibels; in comparison, a masonry wall, a typical sound barrier, reduces noise levels by 15 decibels [27], but imposes high costs [28]. ...
... The soundscape in an urban park with little noise pollution is perceived as more pleasant, more relaxing, less irritating, and less stressful than that next to a busy street [29]. Xing and Brimblecombe (2020) state that the central areas of the parks normally present lower noise levels derived from traffic, and it is necessary to implement barriers at the edges of the parks so that the noise does not impair their visitation. ...
Article
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The objective of this study was to evaluate both the landscape's visual and sound quality influence on propagating noise pollution in the Botanical Garden and the São Lourenço Park in Curitiba, Brazil. Data were collected in three transects (A, B, and C), representing different vegetation densities. Landscape visual quality was characterized through a direct method for valuing landscape elements. The visual quality was classified as Good, Average, or Bad. We used two INSTRUTHERM DEC-470 decibel meters with 1.5-decibel precision for the sound analysis. The landscapes evaluated at site C showed variation in the landscape visual quality from 1 to 21.57, with the best visual and noise attenuation qualities. Correlation analysis between the landscape visual quality and the amount of blocked noise showed a strong correlation coefficient (0.65; p = 0.0001). Landscapes with better visual quality resulted in a greater amount of attenuated noise, mainly due to the presence of vegetation.
... Plants affect the quality of the atmosphere mainly through three basic processes: deposition of dust pollutants, dispersion thereof and vegetation air emissions (VOCs) [30,31]. The adopted method envisages the procedure in individual stages, generating a holistic algorithm. ...
... Despite numerous studies showing the ambivalent effects of vegetation on the quality of urban air [19,23,34,[41][42], green infrastructure is commonly perceived as a tool for its improvement, even to the point of being called the "lungs of cities" [8,31,43]. Although the appropriate composition of the plant community and estimation of its efficiency seems extremely important in this perspective, it remains a non-normalized process and allows a large dose of design improvisation. ...
Article
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Vegetative barriers, arranged as isolating and filtering structures, are introduced into the urban tissue to improve the quality of urban air. As passive methods of space organisation, they are tools for mitigating, alleviating the effects of pollution and improving the comfort of space utilisation. The shaping of such objects is a process which requires taking into consideration numerous factors including the recognition of mechanisms and processes that occur between the barriers and the stream of pollutants, as well as meteorological and geometric conditions of the location. The method of organising vegetative barriers proposed in the present article has allowed for the inclusion of many aspects of the design process. This approach has provided a design procedure regime in a clear layout of individual stages. Based on the conducted implementation, a scenario of interactions of the vegetative barriers with the stream of pollutants was modelled, supplementing the canon of parameterisation of structures and employed qualities, relevant for the effectiveness of the composed plant assemblies in the process of cleaning the urban atmosphere of dust pollution.
... Consequently, PM 2.5 has a substantial negative impact on human health and air quality [4,5]. Due to the retention effect of vegetation on PM, green space construction has become an important measure to prevent and control PM pollution [6,7]. ...
... Many studies have explored, from different perspectives, the ability of vegetation to retain dust. Leaf characteristics, green space structure, and meteorological conditions all affect the deposition of PM on the surface of vegetation [7][8][9]. Existing studies have generally concluded that rough and sticky blades are more conducive to dust retention; the blade size and inclination angle also affect the process for the dry deposition of PM [10,11]. The green space structure has a significant impact on the PM retention effect of the green space [9,12]. ...
Article
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Green space can effectively retain particles and improve air quality. However, most studies have focused on leaf-scale measurements or regional-scale model simulations, and few focus on individual trees. In this study, 176 urban park green spaces were selected within the 5th Ring Road in Beijing, and the i-Tree Eco model was used to estimate the PM2.5 retention levels of individual trees and sample plots. The results show that the retention capacity varied according to tree species. The PM2.5 retention of each sample plot was significantly affected by the tree coverage, species richness, mean tree height, mean crown width, and number of trees. The PM2.5 retention of urban park green spaces in the study area was estimated to be about 6380 t·year−1, and the air quality improvement rate was 1.62%. After structural optimizing, PM2.5 retention of the mixed coniferous and broad-leaved green space was as high as 80,000 g·year−1. This study studied the effects of trees on PM2.5 retention at multiple scales to fill the gaps in existing research at the scales of individual trees and communities, and it can serve as a reliable reference for the design and construction of green spaces aimed at improving air quality.
... The efficiency in capturing and retaining particles was proved to be, first and foremost, site-specific; then, within the same site, a great variability was found between the species. In a 10 ha park located in Brighton, in the immediate vicinity of a major road, a 21-m-tall English elm (Ulmus procera) adsorbed, in a single vegetative season, 1071 g of suspended particulate, corresponding According to Xing and Brimblecombe [78], we can state that a poor design can degrade air quality in parks with inappropriate plantings and encourage the use of highly polluted zones, while a good design can help eliminate negative health impacts. Therefore, creating new green areas is of paramount importance, and research on air quality in parks needs better links to planning and design [78]. ...
... In a 10 ha park located in Brighton, in the immediate vicinity of a major road, a 21-m-tall English elm (Ulmus procera) adsorbed, in a single vegetative season, 1071 g of suspended particulate, corresponding According to Xing and Brimblecombe [78], we can state that a poor design can degrade air quality in parks with inappropriate plantings and encourage the use of highly polluted zones, while a good design can help eliminate negative health impacts. Therefore, creating new green areas is of paramount importance, and research on air quality in parks needs better links to planning and design [78]. In open spaces, several studies have suggested that roadside vegetation barriers may provide a cost-effective strategy to mitigate near-road air pollution [79][80][81][82]. ...
Article
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It is known that the urban environment amplifies the effects of climate change, sometimes with disastrous consequences that put people at risk. These aspects can be affected by urban vegetation and planting design but, while there are thousands of papers related to the effects of climate change, a relatively limited number of them are directly aimed at investigating the role of vegetation as a mitigating factor in the urban context. This paper focuses on reviewing the research on the role of urban vegetation in alleviating the adverse conditions of the urban environment in order to provide some practical guidelines to be applied by city planners. Through an analysis of the documents found in Scopus, Web of Science, and Google Scholar using urban vegetation and climate change-related keywords we selected five major issues related to the urban environment: (1) particulate matter, (2) gaseous pollution, (3) noise pollution, (4) water runoff, (5) urban heat island effect. The analysis of existing knowledge reported here indicates that the roles of urban vegetation on the adverse effect of climate change could not be simply deemed positive or negative, because the role of urban green is also strongly linked to the structure, composition, and distribution of vegetation, as well as to the criteria used for management. Therefore, it could help to better understand the roles of urban green as a complex system and provide the foundation for future studies.
... Green spaces provide a wide range of ecosystem services to cities (Niemelä et al., 2010) by improving air quality (Xing and Brimblecombe, 2019), mitigating urban thermal environments (Bowler et al., 2010), and reducing rates of urban flooding . Moreover, they also provide city dwellers with opportunities to interact with nature, encouraging outdoor activities and promoting physiological and psychological health (Hartig et al., 2014;Zhang et al., 2020). ...
Article
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Due to the shortage of green space in urban built environments, access to peri-urban parks in the suburbs has been a focus of planning practices to meet increasing resident demands for recreational visits to natural settings. However, accurate approaches to evaluating peri-urban park accessibility and monitoring underserved areas are lacking. In this study, we propose an integrated accessibility index for peri-urban parks that is calculated using an improved Huff-2SFCA (two-step floating catchment area) model that considers the tradeoffs between quality, park size, and travel time. We first propose a peri-urban park quality index and then integrate it into an accessibility assessment. Furthermore, we employ a variable catchment to ensure that the larger and high-quality parks correspond to higher travel time thresholds. To demonstrate the practicality of the integrated index, Nanjing, a rapidly urbanizing Chinese city, was selected as a case study. The results demonstrate that (1) the quality of peri-urban parks is unevenly distributed, with high-quality parks primarily being distributed in western urban suburbs and occupying a total area of approximately 5665 ha; (2) approximately 92% of communities can enjoy peri-urban park services, while high-quality parks are more accessible to residents living in urban centres; and (3) 220 residential communities are identified as underserved areas, and 142 communities are identified as potentially underserved areas due to long travel times and the poor quality or small sizes of accessible parks. The integrated accessibility index can be employed to accurately monitor (potentially) underserved areas and assist decision-makers in formulating effective policies and strategies for improving residential access to peri-urban landscapes.
... Janhäll, 2015). Xing and Brimblecombe (2020a) conclude upon their bibliometric analysis that studies including dispersion in their air pollution mitigation analysis of green spaces are less consistently reporting pollutant reductions than those focusing on deposition. We found several papers underlining possible pollution concentration effects by dispersion, particularly if exposure is critical between pollution source and green space, below green space structures (e.g. ...
Article
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Air pollution causes the largest death toll among environmental risks globally, but interventions to purify ambient air remain inadequate. Vegetation and green spaces have shown reductive effects on air-borne pollutants concentrations, especially of particulate matter (PM). Guidance on green space utilisation for air quality control remains scarce, however, as does its application in practise. To strengthen the foundation for research and interventions, we undertook a critical review of the state of science from a public health perspective. We used inter-disciplinary search strategies for published reviews on green spaces and air pollution in key scientific databases. Using the PRISMA checklist, we systematically identified reviews with quantitative analyses. For each of the presented PM mitigation mechanisms, we conducted additional searches focused on the most recent articles published between 2016 and early 2021. The included reviews differentiate three mitigation mechanisms of green spaces for PM: deposition, dispersion and modification. The most studied mechanism is deposition, particularly measures of mass and settling velocity of PM on plant leaves. We consolidate how green space setups differ by scale and context in their potentials to reduce peak exposures, stationary (point) or mobile (line) pollution sources, and the potentially most harmful PM components. The assessed findings suggest diverse optimisation options for green space interventions, particularly concerning plant selection, spatial setup, ventilation and maintenance – all alongside the consideration of supplementary vegetation effects like on temperature or water. Green spaces' reductive effects on air-borne PM concentrations are considerable, multi-mechanistic and varied by scale, context and vegetation characteristics. Such effect-modifying factors must be considered when rethinking public space design, as accelerated by the COVID-19 pandemic. Weak linkages amid involved disciplines motivate the development of a research framework to strengthen health-oriented guidance. We conclude on an urgent need for an integrated and risk-based approach to PM mitigation through green space interventions.
... Among the ecosystem services, the impact on urban air quality was documented in several studies, but it is not yet completely established. Recent reviews [3,5,[9][10][11][12] showed the potential of vegetation, especially trees, in mitigating air pollution, while leaving open questions regarding the impact that trees have on air quality in urban areas, since they may lead to increased or decreased concentrations. In general, air pollutant concentration is affected by vegetation due to two effects: (1) aerodynamic effects (or blocking effects) and (2) removal of air pollutants by deposition/absorption. ...
Article
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This paper is devoted to the assessment of urban greening effects on two important ecosystem services, i.e., air quality and CO 2 storage, including the corresponding economic impacts in a real urban area, i.e., a district located in the Mediterranean city of Lecce (southern Italy). Two tools were employed, i-Tree Canopy and the computational fluid dynamics (CFD) microclimate model ENVI-met. i-Tree Canopy allowed fully determining the land-cover percentage on the basis of different ground cover classes and obtaining an estimate of annual values of CO 2 storage, air pollutant removal, and economic benefits in the presence of urban greening. The estimate in i-Tree Canopy considered only the amount of greening; therefore, air pollutant removal estimates were only potential. As the vegetation was located in street canyons, its interaction with local meteorology and urban geometry strictly affected the dispersion of nitrogen oxides (NOx) (taken here as an example) as obtained from ENVI-met simulations. In ENVI-met, both deposition/absorption and aerodynamic effects were considered, and local increases in concentration were found in the district. The analysis of results obtained from different tools (one complex (CFD model) and the other simple (i-Tree model)) showed the error associated with the simple model in the computation of impacts if the interaction among the vegetation characteristics, the meteorological conditions, and the urban geometry was neglected; however, it also uncovers a novel approach for comprehensively characterizing a given area in terms of its vegetation cover, CO 2 storage, and economic benefits, as well as local effects on air quality. This study is set in a broader context aimed at assessing the air quality in urban canopies of Mediterranean areas characterized by the presence of narrow street canyons where pollutants can accumulate due to ineffective air exchange with the above atmosphere.
... In addition, trees may exacerbate rates of asthma due to the release of allergens and this is seldom accounted for in assessments of the impacts on trees on public health (Lovasi et al., 2013). In recent comprehensive reviews, Eisenman et al. (2019) and Xing and Brimblecombe (2020) both concluded that as a result of the many influences of trees on atmospheric composition besides dry deposition rates, current empirical evidence does not support the assumption that trees significantly and consistently reduce pollution concentrations. ...
Article
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Many of the world’s major cities have implemented tree planting programs based on assumed environmental and social benefits of urban forests. Recent studies have increasingly tested these assumptions and provide empirical evidence for the contributions of tree planting programs, as well as their feasibility and limits, for solving or mitigating urban environmental and social issues. We propose that current evidence supports local cooling, stormwater absorption, and health benefits of urban trees for local residents. However, the potential for urban trees to appreciably mitigate greenhouse gas emissions and air pollution over a wide array of sites and environmental conditions is limited. Consequently, urban trees appear to be more promising for climate and pollution adaptation strategies than mitigation strategies. In large part, this is due to space constraints limiting the extent of urban tree canopies relative to the current magnitude of emissions. The most promising environmental and health impacts of urban trees are those that can be realized with well-stewarded tree planting and localized design interventions at site to municipal scales. Tree planting at these scales has documented benefits on local climate and health, which can be maximized through targeted site design followed by monitoring, adaptive management, and studies of long-term eco-evolutionary dynamics.
... Roadside tree planning in urban systems is playing a vital role since roadside trees act as local biodiversity reservoirs and reduce the pollution of the atmosphere by having a carbon stock [7]. The roadside ecosystem has significant importance because of its involvement in the diversity patterns of the biological life. ...
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Roads have a great impact on the structure and functioning of the diversity pattern in an ecological environment and play the role of altering biotic and abiotic factors. Clusters of plants grow along the roadside due to the interplay between the arrival of propagule and seedling establishment, which depends on the road’s specifications, land pattern, and road administration and protection practices. It is very important to study the diversity pattern in a metropolitan city to improve the ecological environment. Karachi is one of the world’s largest and fastest-growing metropolitan cities; however, little is known about the urban forest of the area. In Karachi, which is in the province of Sindh, Pakistan, roadside trees along various road types (e.g., wide, medium and narrow roads) have been studied. Based on a field study, various measures of diversity were utilized to investigate the diversity of tree species on different types of paths. A total of 180 plots, divided into three primary road groups, were surveyed. The highest quantity of tree biomass per unit area was found on wide roads, followed by medium roads. On narrow roads, the least biomass was detected. A single species or a limited number of species dominated the diversity of species. Conocarpus erectus was the most dominant non-native species along all types of roads, followed by the species Guaiacum officinale. A total of 76 species (32 non-native and 44 native) that were selectively spread along the roadsides of the city were studied. There was a significant difference in phylogenetic diversity (PD), phylogenetic mean pairwise distance (MPD) and phylogenetic mean nearest taxon distance (MNTD) between wide, medium, and narrow roads. Management practices have a significant positive correlation with diversity indices. Our study identified patterns of diversity in roadside trees in Karachi. It provided the basis for future plant conservation planning, such as the conservation of plant species, the maintenance of plant habitats, and the coordination of plant management in Karachi.
... Therefore, a series of strict pollution reduction policies have been implemented (Li et al., 2019;Liu et al., 2019b). While urban green space construction is considered an important measure for PM pollution control (Yang et al., 2005;Cetin and Sevik, 2016;Zhang et al., 2016;Muñoz-Pizza et al., 2020;Xing and Brimblecombe, 2020), the interaction and mechanism between green space and PM remains unclear (Han et al., 2020). ...
Article
While the spatial distribution of airborne particulate matter (PM) inside and outside urban green spaces is affected by many environmental factors, the mechanism of the inside-outside difference (IOD) remains unclear. Particle size is an important attribute of PM, but the relationship between IOD and particle size is unknown. By measuring the IOD and external environmental conditions of 188 green spaces in Beijing city (China), we found that the distribution of PM inside and outside green spaces is size-dependent. According to the particle size dependence of PM, they can be divided into three classes (i.e., PM1, PM1-5, and PM5-25). The motion characteristics of particles, influence of environmental factors, and their coupling effect might be responsible for this size dependence. This study highlights the importance of size dependence in understanding the mechanism of PM distribution in urban green space through field experiments and puts forward a new concept of particle size classification that might be more suitable for actual environmental conditions and can support the improvement of related models.
... Hence, reducing air pollution is usually regarded as an important pathway by which green spaces relieve asthma, as well as asthma-related symptoms [18,19]. Notably, the characteristics of green spaces, especially type, structure, and quantity, create significant differences in their mitigation effects [15,20]. For example, air pollution is negatively correlated with the percentage of tree cover areas and positively with mixing layer heights [15]. ...
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Asthma is a chronic inflammatory disease that can be caused by various factors, such as asthma-related genes, lifestyle, and air pollution, and it can result in adverse impacts on asthmatics’ mental health and quality of life. Hence, asthma issues have been widely studied, mainly from demographic, socioeconomic, and genetic perspectives. Although it is becoming increasingly clear that asthma is likely influenced by green spaces, the underlying mechanisms are still unclear and inconsistent. Moreover, green space influences the prevalence of asthma concurrently in multiple ways, but most existing studies have explored only one pathway or a partial pathway, rather than the multi-pathways. Compared to greenness (measured by Normalized Difference Vegetation Index, tree density, etc.), green space structure—which has the potential to impact the concentration of air pollution and microbial diversity—is still less investigated in studies on the influence of green space on asthma. Given this research gap, this research took Toronto, Canada, as a case study to explore the two pathways between green space structure and the prevalence of asthma based on controlling the related covariates. Using regression analysis, it was found that green space structure can protect those aged 0–19 years from a high risk of developing asthma, and this direct protective effect can be enhanced by high tree diversity. For adults, green space structure does not influence the prevalence of asthma unless moderated by tree diversity (a measurement of the richness and diversity of trees). However, this impact was not found in adult females. Moreover, the hypothesis that green space structure influences the prevalence of asthma by reducing air pollution was not confirmed in this study, which can be attributed to a variety of causes.
... Xing et al. [1][2][3] noticed improved air quality in small urban parks within a distance from surrounding streets due to the dispersion of air pollutants within park areas. Importantly in this context, trees can reduce wind speed and potentially trap pollutants. ...
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Parks embody an important element of urban infrastructure and a basic type of public space that shapes the overall character of a city. They form a counterweight to built-up areas and public spaces with paved surfaces. In this context, parks compensate for the lack of natural, open landscapes in cities and thus have a fundamental impact on the quality of life of their inhabitants. For this reason, it is important to consider the quality of the environment in urban parks, air quality in particular. Concentrations of gaseous pollutants, namely, nitric oxide (NO), nitrogen dioxide (NO2), and ozone (O3), were measured in parks of Brno, the second-largest city in the Czech Republic. Relevant concentration values of PM10 solids were determined continuously via the nephelometric method, followed by gravimetric method-based validation. The results obtained through the measurement of wind direction, wind speed, temperature, and relative humidity were used to identify potential sources of air pollution in parks. The "openair" and "openairmaps" packages from the OpenSource software R v. 3.6.2 were employed to analyze the effect of meteorological conditions on air pollution. Local polar concentration maps found use in localizing the most serious sources of air pollution within urban parks. The outcomes of the analyses show that the prevailing amount of the pollution determined at the measuring point most likely originates from the crossroads near the sampled localities. At the monitored spots, the maximum concentrations of pollutants are reached especially during the morning rush hour. The detailed time and spatial course of air pollution in the urban parks were indicated in the respective concentration maps capturing individual pollutants. Significantly increased concentrations of nitrogen oxides were established in a locality situated near a busy road (with the traffic intensity of 33,000 vehicles/d); this scenario generally applied to colder weather. The highest PM10 concentrations were measured at the same location and at an average temperature that proved to be the lowest within the entire set of measurements. In the main city park, unlike other localities, higher concentrations of PM10 were measured in warmer weather; such an effect was probably caused by the park being used to host barbecue parties.
... In FHWA TNM2.5, the scenario using broadleaf trees was not available as the tree type is fixed as noted in the model description. The leaf area densities (m −1 ) and heights (m) of vegetation applied in the simulations (Table 1) were derived from field measurements in urban parks by Xing and Brimblecombe (2020a). The morphological characteristics are typical for park trees, including conifer trees (e.g., Juniperus chinensis 'Kaizuca') and broadleaf trees (e.g., Cinnamomum camphora, Ficus benjamina, Ficus microcarpa). ...
Article
Parks provide a range of ecosystem services and make major contributions to urban life. Improved environmental quality was observed in urban parks as pollutants and noise disperse. Numerical models were used to assess the role of various design elements in air pollution and noise attenuation in parks. The walls reduced pollutants and sound noticeably in its shadow. Dense conifers can trap pollutants in park borders and lower concentrations in interiors, but less efficient in noise reduction. A study of a design for a small urban park suggests principles for achieving lower user exposure to pollution and healthier park environment.
... Various bibliographic elements in publications (countries, journals, title words, author keywords, etc.) were visualized in environmental sciences (e.g., cities' ecological infrastructure; Sun et al., 2020). Terms dealing with trees and parks in the city were mapped into clusters by Xing and Brimblecombe (2020). Sometimes, the principal publications were assessed, for example, on the topic of creative cities (Rodrigues & Franco, 2020). ...
... Some reduction in exposure is possible through careful building design, perhaps with the use of air conditioning [16,17], or the careful layout and placement of school buildings and the diversion of nearby traffic [18]. Much less is written about school playgrounds and roads that border schools [19,20], although there has long been a focus on air pollution in playgrounds and parks [21,22]. ...
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Children are sensitive to air pollution and spend long hours in and around their schools, so the school day has an important impact on their overall exposure. This study of Kuala Lumpur, Selangor and its surroundings assesses exposure to PM2.5 and NO2, from travel, play and study over a typical school day. Most Malaysian children in urban areas are driven to school, so they probably experience peak NO2 concentrations in the drop-off and pick-up zones. Cyclists are likely to receive the greatest school travel exposure during their commute, but typically, the largest cumulative exposure occurs in classrooms through the long school day. Indoor concentrations tend to be high, as classrooms are well ventilated with ambient air. Exposure to PM2.5 is relatively evenly spread across Selangor, but NO2 exposure tends to be higher in areas with a high population density and heavy traffic. Despite this, ambient PM2.5 may be more critical and exceed guidelines as it is a particular problem during periods of widespread biomass burning. A thoughtful adjustment to school approach roads, design of playgrounds and building layout and maintenance may help minimise exposure.
... Indeed, urban green spaces play an important role in reducing PAH concentrations in the air. A plant canopy can impede airflow and thus reduce the diffusion of pollutants (Xing et al. 2020). The morphological characteristics of plant leaves can greatly influence PAHs at the micromolar scale, and leaf wax has a strong ability to retain PAHs with intermediate molecular weight and multiple rings (Tian et al. 2019). ...
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PM2.5 samples were collected from residential, commercial, plaza and public green spaces in Lin’an, Hangzhou, in spring (March and April) and winter (February and December) in 2017. PAHs were detected by gas chromatography-mass spectrometry (GC-MS), and their sources were identified using the diagnostic ratio (DR) and principal component analysis-multiple linear regression (PCA-MLR). The average PAH concentration in winter was 1.3 times that in spring (p < 0.01). The PAH concentrations in the green spaces decreased as commercial > residential > plaza > public green space (p < 0.05). The sources of PAHs were vehicle emissions and coal combustion pollution transported by northern Chinese air masses. Slightly higher excessive cancer risks were determined in the commercial and residential green spaces than in the plaza and public green spaces. Green coverage, pedestrian volume, traffic flow and building density greatly influenced the decrease in the PAH concentration in the green spaces. Among the 4 types of green spaces, public green space had the most ecological benefits and should be fully utilized in urban green space planning to improve public health in urban spaces.
... Vegetation, predominantly leafy surfaces, can accumulate ambient particles through dry deposition (Han et al., 2020), and expanses of green open area can aid in dispersing airborne pollutants (Xing & Brimblecombe, 2020a), thus reducing ambient concentrations. In a review by Diener and Mudu (2021), greater reductions have been observed via dispersion (up to 50% of PM 2.5 [Xing & Brimblecombe, 2020b]) compared to deposition (up to 15% of PM 1 [Viippola et al., 2020]). ...
... Trees are porous and exible, and can therefore absorb momentum and reduce the turbulent intensity and the velocity of the wind ow, even during the winter when there are no leaves, and therefore trees can deteriorate the air quality locally. [28][29][30][31][32] Furthermore, certain tree species can release signicant amounts of biogenic volatile organic compound (BVOC), 33 contributing to ozone formation in the atmosphere. However, there are still considerable uncertainties in the net impact of trees on air quality in different urban areas, for example in urban parks and street canyons. ...
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The effects of the urban morphological characteristics on the spatial variation of near-surface PM2.5 air quality were examined. Unlike previous studies, we performed the analyses in real urban environments using continuous observations covering the whole scale of urban densities typically found in cities. We included data from 31 measurement stations divided into 8 different wind sectors with individually defined morphological characteristics leading to highly varying urban characteristics. The urban morphological characteristics explained up to 73% of the variance in normalized PM2.5 concentrations in street canyons, indicating that the spatial variation of the near-surface PM2.5 air quality was mostly defined by the characteristics studied. The fraction of urban trees nearby the stations was found to be the most important urban morphological characteristic in explaining the PM2.5 air quality, followed by the height-normalized roughness length as the second important parameter. An increase in the fraction of trees within 50 m of the stations from 25 percentile to 75 percentile (i.e. by the interquartile range, IQR) increased the normalized PM2.5 concentration by up to 24% in the street canyons. In open areas, an increase in the trees by the IQR actually decreased the normalized PM2.5 by 6% during the pre-COVID period. An increase in the height-normalized roughness length by the IQR increased the normalized PM2.5 by 9% in the street canyons. The results obtained in this study can help urban planners to identify the key urban characteristics affecting the near-surface PM2.5 air quality and also help researchers to evaluate how representative the existing measurement stations are compared to other parts of the cities.
... Roadside trees in urban systems play a vital role since roadside trees act as local biodiversity reservoirs and reduce atmospheric pollution by having a carbon stock (Xing and Brimblecombe 2020). The roadside ecosystem has significant importance because of its involvement in the diversity patterns of biological life. ...
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Roadside trees alter biotic and abiotic factors of plants diversity in an ecosystem. Rows of plants grow along the roadside due to the interplay between the arrival of propagule and seedling establishment, which depends on the road’s specifications, land pattern, and road administration and protection practices. A field study was conducted to measure the roadside tree diversity in the city of Karachi (Pakistan). A total of 180 plots, divided into three primary road groups, were surveyed. The highest quantity of tree biomass per unit area was found on wide roads, followed by medium roads. On narrow roads, the least biomass was detected. A single species or a limited number of species dominated the tree community. Conocarpus erectus was the most dominant non-native species on all types of sidewalks or roadsides, followed by Guaiacum officinale. A total of 76 species (32 non-natives and 44 natives) that were selectively spread along the roadsides of the city were studied. There was a significant difference in phylogenetic diversity (PD), phylogenetic mean pairwise distance (MPD), and phylogenetic mean nearest taxon distance (MNTD) among wide, medium, and narrow roads. Management practices have a significant positive correlation with diversity indices. Our study identified patterns of diversity in roadside trees in Karachi. It provides the basis for future planning for plant protection, such as the protection of plant species, the maintenance of plant habitats, and the coordination of plant management in Karachi.
... Vegetation, predominantly leafy surfaces, can accumulate ambient particles through dry deposition (Han et al., 2020), and expanses of green open area can aid in dispersing airborne pollutants (Xing & Brimblecombe, 2020a), thus reducing ambient concentrations. In a review by Diener and Mudu (2021), greater reductions have been observed via dispersion (up to 50% of PM 2.5 [Xing & Brimblecombe, 2020b]) compared to deposition (up to 15% of PM 1 [Viippola et al., 2020]). ...
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The presence of urban greenspace may lead to reduced personal exposure to air pollution via several mechanisms, for example, increased dispersion of airborne particulates; however, there is a lack of real-time evidence across different urban contexts. Study participants were 79 adolescents with asthma who lived in Delhi, India and were recruited to the Delhi Air Pollution and Health Effects (DAPHNE) study. Participants were monitored continuously for exposure to PM2.5 (particulate matter with an aerodynamic diameter of less than 2.5 μm) for 48 hours. We isolated normal day-to-day walking journeys (n = 199) from the personal monitoring dataset and assessed the relationship between greenspace and personal PM2.5 using different spatial scales of the mean Normalised Difference Vegetation Index (NDVI), mean tree cover (TC), and proportion of surrounding green land use (GLU) and parks or forests (PF). The journeys had a mean duration of 12.7 (range 5, 53) min and mean PM2.5 personal exposure of 133.9 (standard deviation = 114.8) μg/m³. The within-trip analysis showed weak inverse associations between greenspace markers and PM2.5 concentrations only in the spring/summer/monsoon season, with statistically significant associations for TC at the 25 and 50 m buffers in adjusted models. Between-trip analysis also indicated inverse associations for NDVI and TC, but suggested positive associations for GLU and PF in the spring/summer/monsoon season; no overall patterns of association were evident in the autumn/winter season. Associations between greenspace and personal PM2.5 during walking trips in Delhi varied across metrics, spatial scales, and season, but were most consistent for TC. These mixed findings may partly relate to journeys being dominated by walking along roads and small effects on PM2.5 of small pockets of greenspace. Larger areas of greenspace may, however, give rise to observable spatial effects on PM2.5, which vary by season.
Article
The objective of this study was to evaluate both the landscape’s visual and sound quality influence on propagating noise pollution in the Botanical Garden and the São Lourenço Park in Curitiba, Brazil. Data were collected in three transects (A, B, and C), representing different vegetation densities. Landscape visual quality was characterized through a direct method for valuing landscape elements. The visual quality was classified as Good, Average, or Bad. We used two INSTRUTHERM DEC-470 decibel meters with 1.5-decibel precision for the sound analysis. The landscapes evaluated at site C showed variation in the landscape visual quality from 1 to 21.57, with the best visual and noise attenuation qualities. Correlation analysis between the landscape visual quality and the amount of blocked noise showed a strong correlation coefficient (0.65; p = 0.0001). Landscapes with better visual quality resulted in a greater amount of attenuated noise, mainly due to the presence of vegetation.
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COVID-19 has had economic, social and environmental impacts worldwide. Governments have adopted containment measures to limit the spread of the virus. Urban green spaces (UGSs) were included among the non-essential activities and were consequently closed during the lockdown periods in some countries. This study analysed tweets posted by users to understand the citizens' perception and sentiment in relation to the closure of UGS in Italy. Results revealed that people felt a strong deprivation feeling in relation to the restrictions imposed on UGS access, which limited the number of spaces for supporting mental and physical wellbeing of citizens. Users from urban areas were more affected by the lockdowns and more willing to share thoughts on social media, demonstrating a strong emotionality. Furthermore, findings show that users seemed concerned about their children's health, expressing awareness about the benefits of being in contact with nature. UGS is able to provide services to citizens, and close-to-home parks are fundamental for the community, in particular during a health emergency. The implementation of urban design, which includes green areas to support health and environment challenges, should be addressed by policy-makers to create opportunities for a green and resilient recovery of cities, and prepare for future emergencies.
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Urban trees provide vital ecosystem services such as mitigating heat island, improving air quality by removing various air pollutants, capturing rainwater, and acting as topsoil carbon storage. The aesthetic value of urban trees is also another feature that has to be considered in the context of urban greening. Classical criteria for the selection of urban trees have to respond to new challenges imposed to the cities in a near future. Global climate change factors increase the harshness of our cities, and thereby the plant resilience to abiotic stresses has also to be seriously considered for planning the urban greening. Red-leafed species, characterized by the permanent presence of foliar anthocyanins, show a greater tolerance to different environmental cues than green-leafed species commonly used in our cities. In addition, red tree species own a great aesthetic value which has been underestimated in the context of urban areas, especially in the harsh Mediterranean cities. In this study, we emphasize the “privilege of being red” from different point of view, in order to drive the attention to the possibility to increase the use of red-leafed species for urban “greening”. Some possible negative aspects related to their use are rebutted and the direction of future researches are proposed.
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Krupnova TG, Rakova OV, Plaksina AL, Gavrilkina SV, Baranov EO, Abramyan AD. 2020. Effect of urban greening and land use on air pollution in Chelyabinsk, Russia. Biodiversitas 21: 2716-2720. Chelyabinsk is a major industrial Russian city that faces diverse environmental issues, the most important of which is air emissions. The primary sources of air pollution in Chelyabinsk are industry (concrete product plants, ferrous and nonferrous metallurgy such as zinc production plants, and pulp production), thermal power stations, and transport. People have known that trees can help to reduce air pollutants for a long time. We studied 8 zones within a radius of one kilometer from state air pollution monitoring stations. Eight land-use types such as industrial category, residential category, natural and semi-natural broadleaved vegetation, natural and semi-natural coniferous vegetation, broadleaved forest, coniferous forest, artificial broadleaved vegetation, and artificial coniferous vegetation, were obtained. The response of air pollution to land-use and urban greening was analyzed. Analysis results showed that there was no correlation between industrial and residential categories of land-using and concentrations of the most dangerous air pollutants in Chelyabinsk (formaldehyde, hydrogen fluoride, and nitrogen dioxide). The dominant factor affecting urban air quality was urban greening.
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This article analyses the ways that young people create new futures in Taranto, Southern Italy, a city hosting one of the largest and most polluting steel factories in Europe. It draws on ethnographic fieldwork in Taranto and uses storytelling to understand how young people – a minority of residents aged between 24 and 35 years – shape futures in industrially polluted environments. The study weaves together geographic and anthropological scholarship about futures in (post‐)industrial cities, conceptualisations of breathing as well as lived experiences in highly polluted areas. Through mobilising the notion of breathing we highlight the embodied, entangled and emotional dimensions of the young people’s everyday practices and develop our concept of “breathing new futures”. We argue that both pollution and the envisioning of a new future become visible in everything the study’s participants do; the ways they promote environmental awareness, take care of animals or seek to foster children’s education. By focusing on generational differences, the study expands on recent scholarship analysing environmental pollution in relation to intersectional identities such as race, ethnicity and gender, and sheds light on the activities of young people to imagine and live new futures in polluted environments.
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Determining the vulnerability of land to degradation is a crucial factor enabling policy makers to take targeted actions. The main aim of this work was to determine vulnerability to land degradation using the Environmentally Sensitive Area Index (ESAI) in the territory of 206 municipalities with extended power (MEPs), regions (NUTS 3) and in the Czech Republic (CR). The other two aims were found out i) whether land degradation is affected by land use characterized by landscape types according to Löw et al . (2006) and ii) whether land degradation occurred in larger territorial units (regions) or scattered across the CR (in individual isolated MEPs). The Environmentally Sensitive Area (ESA) method assesses the vulnerability of an area to land degradation using a composite index containing indicators divided into four thematic groups: human activity pressure and management intensity, vegetation cover and vegetation quality, climate, and soil in the assessed area. The ESAI index is expressed on a semi-quantitative scale ranging from the lowest levels of degradation (land not affected and land potentially affected by degradation) to the highest level of degradation (land at high risk). Most MEPs with a share of more than 70 % of their area were in the category "moderately critical areas" at risk of land degradation were located in the Central Bohemia region (15 MEPs) and in the South Moravia region (14 MEPs). For the whole territory of the Czech Republic, 51 % of the territory was found to be critically vulnerable to land degradation, and 38 % of the republic area was vulnerable to land degradation. Vulnerability to land degradation was strongly influenced by the landscape type. Almost all MEPs with a predominantly agricultural landscapes were critically vulnerable to land degradation, as were about half of the MEPs in the forest-agricultural and urban landscapes and only a few MEPs in the forest landscapes. Given the selected indicators, the MEP seems to be the appropriate smallest administrative unit to assess vulnerability to land degradation in the Czech Republic. The map of individual ESAI values can be viewed free of charge online at http://www.imalbes.cz/vysledek.php . We are currently preparing a proposal for appropriate measures to prevent and reduce land degradation throughout the territory of the Czech Republic, and our proposals are coordinated with representatives of the MEPs and regions.
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This study presents a critical review analysis of greenery systems research through a bibliometric approach. The purpose of this study is to provide a holistic overview by (i) the development of the field; (ii) the research trends and the main issues; and (iii) the main gaps still observed in the literature. Therefore, this paper provides the past, the present and the potential future of this scientific topic and serves as an orientation and guide for researchers who aim for a better understanding of the main progress and gaps. A detailed analysis of 1918 documents found in the Scopus database for the 1974–2019 period was conducted. Content analysis of titles, keywords and abstracts revealed that most of the research has focused on the study of green roofs. Previously this topic was dominated by water runoff analysis, while recent contributions acknowledge greenery as an effective microclimate mitigation strategy, especially in urban areas. The United States was the most productive country, representing almost 20 % of the total documents. Over 86 % of the relevant documents were published since 2009. Overall, research on this topic is increasing, with new methods and directions but some gaps remain particularly on the areas of environmental impact, costs, health, outdoor thermal comfort, and vertical greenery systems.
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To map the advancement of exposure evaluation research for particles less than 100 nm in the breathing zone, we developed a bibliometric analysis using VosViewer 1.6.15 by selecting relevant publications from Scopus on August 10th, 2020. Of 769 relevant documents, 90.64 % (n = 697) were considered, which came from the journal and used English as the language that started to be published in 1985. The results showed that research themes have grown on the three clusters related to inhaled nanoparticles exposure measurement, responses and effects, and their primary existence in consumer products. Moreover, depth analyses by visualizing maps of the top active countries, authors, and top-cited documents on the citation, co-citation, or co-occurrence have revealed several essential pieces of information on this research area. Our findings suggest that a greater depth on appropriate devices for exposure measurements, particularly in nano-sized that matches with the metrics were needed. Through these efforts, the capabilities of analyses can improve for future inhaled nanoparticles exposure assessments.
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Global warming and rapid urbanization have exacerbated the urban heat island effect. Urban parks contribute to alleviating such an effect and achieving the “carbon emission peak before 2030” and “carbon neutrality before 2060” goals of China. Their popularity is considerably influenced by human thermal comfort. However, limited thermal comfort studies have been conducted in the hot-summer and cold-winter region of China. This study examines human thermal comfort in different landscapes of an urban park in Chengdu and determines the thermal benchmarks. A machine learning (random forest) analysis shows that human thermal sensation is affected by different meteorological factors in different seasons. In addition, the influences of landscape space on human thermal comfort in different seasons have considerable differences. Residents prefer strong solar radiation in winter but fast wind speed in summer. UTCI (universal thermal climate index) is better than PET (physiological equivalent temperature) for outdoor thermal comfort assessment in the study area. This study serves as a valuable baseline and technical reference, contributing to sustainable urban park design.
Chapter
Buying housing is often the biggest transaction in the families’ lives. Therefore, this is an important reason to know and to study the determining factors of that purchase. This chapter aims to analyze which factors contribute to the choice of apartments in Portugal the most. To carry out this study, a quantitative methodology based on a questionnaire survey which analyzes both the determining factors in the choice of apartments and the sociodemographic profile was used. The sample is composed of 646 individuals who were looking for an apartment in different regions of mainland Portugal. The results show that the determining factors scale in the choice of apartments presents largely adequate levels of validity and reliability, being composed of four factors: negative externalities, positive externalities, businesses located on the ground floor, and rational interest in proximity to public services. The results also identify that the positive externalities contribute significantly to the apartment’s choice. In Portugal, there is no study with this depth about this subject. The validation of an assessment scale of determining factors in the choice of apartments in the Portuguese real estate market is ground-breaking. This study is expected to contribute to the expansion of scientific knowledge in this theme and to help real estate developers meet their customers’ preferences.
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Rapid economic growth has caused air pollution, particularly in city areas. Removing air pollutants generated by various emission sources is crucial to control PM2.5, improve air quality, and maintain human health in high-density urban areas. In response to air pollution, urban vegetation plays an essential role in providing air quality regulation service. To estimate the air quality regulation service provided by urban vegetation, this study integrated spatial analysis, a dry deposition model, and an atmospheric diffusion model to spatially quantify the air quality regulation service of PM2.5 in Taipei City on a high-resolution scale (30 m × 30 m per spatial unit). The results show that in 2016, total PM2.5 emissions in Taipei City were 1,400.88 tonnes and that urban vegetation removed 18.31 tonnes of PM2.5, with an average PM2.5 removal rate of 0.16 g/m², and the corresponding PM2.5 concentration improvement value of 0.0136 μg/m³. This finding revealed a significant gap between the amounts of emissions and purifications of PM2.5, the air quality regulation service provided by the urban vegetation in Taipei City remains insufficient. The results of this study not only point out the spatial differences of regulation services and propose a new research framework for quantifying the natural benefits, but also as a guideline for governments to form the auxiliary policies of the urban ecosystem service and facilitate the urban green infrastructure planning.
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Air quality in small urban parks improves rapidly with distance from surrounding streets. This arises because air pollutants disperse within parks where there are few sources. This was traditionally thought to arise from pollutant uptake by trees, but they can also reduce wind speed and potentially trap pollutants. It is increasingly evident that relatively little pollution is absorbed by trees over short distances typical of small urban parks. Nevertheless, trees and park infrastructure, also constrain the distribution of park users and thus lower their exposure. In this paper, we explore the exposure to traffic-derived air pollutants in the Hong Kong parks (Sha Tin and Sham Shui Po) and examine the way in which PM 2.5 concentration and user distribution is affected by the spatial layout of park features. The modelled pollutant distribution was validated against measurements made in Sha Tin Park. Population-weighted exposure to traffic-derived pollution was quantified by overlapping pollutant and park user distribution. The results reveal how different design features (i.e. vegetation, earth berms and recreation areas) affect exposure during individual time period; most positively in Sha Tin Park where the design leads to a > 50% reduction in exposure, early morning. In Sham Shui Po Park, exposure increases as park users are often attracted to facilities near a busy trunk road. This study reveals the heterogeneity of park user exposure to traffic-derived air pollution, which leads to uncertainty in health benefits provided by urban parks and suggests fine-scale exposure considered in thoughtful park design.
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Human exposure to airborne ultrafine (<<1 µm) particulate pollution may pose substantial hazard to human health, particularly in urban roadside environments where very large numbers of people are frequently exposed to vehicle-derived ultrafine particles (UFPs). For mitigation purposes, it is timely and important to quantify the deposition of traffic-derived UFPs onto leaves of selected plant species, with particularly efficient particle capture (high deposition velocity), and which can be installed kerbside, proximal to the emitting vehicular sources. Here, we quantify the size-resolved capture efficiency of UFPs from a diesel vehicle exhaust by nine temperate-zone plant species, in wind tunnel experiments. The results show that silver birch (79% UFP removal), yew (71%) and elder (70.5%) have very high capability for capture of airborne UFPs. Metal concentrations and metal enrichment ratios in leaf leachates were also highest for the post-exposure silver birch leaves; scanning electron microscopy shows UFPs concentrated along the hairs of these leaves. For all but two species, magnetic measurements demonstrate substantial increases in the concentration of magnetic particles deposited on the leaves after exposure to the exhaust particulates. Together, these new data show that leaf-deposition of UFPs is chiefly responsible for the substantial reductions in particle numbers measured downwind of the vegetation. It is critical to recognise that the deposition velocity of airborne particulate matter (PM) to leaves is species-specific; and often substantially higher (~10 to 50 times higher) than the ‘standard’ Vd values (e.g. 0.1 – 0.64 cm s-1 for PM2.5) used in most modelling studies. The use of such low Vd values in models results in major under-estimation of PM removal by roadside vegetation, and thus misrepresents the efficacy of selected vegetation species for substantial (>> 20%) removal of PM. Given the potential hazard to health posed by UFPs, and the removal efficiencies shown here (and by previous roadside measurements), roadside planting at PM ‘hotspots’ of selected species (maintained at or below head height) can contribute substantially and quickly to improvement in urban air quality, and reductions in human exposure. These findings can contribute to development and implementation of mitigation policies of traffic-derived PM on an international scale.
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This study is among the first to investigate ozone levels in urban forests in China. It establishes that urban forest air quality in Yuanshan Forest Park (Shenzhen) is suitable for recreational activities and identifies spatial, seasonal, and diurnal O3 patterns and relationships with micrometeorological parameters, suggesting the possibility of manipulating relevant forest characteristics to reduce Surface ozone (O3) levels. An understanding of O3 levels of urban forest environments is needed to assess potential effects on human health and recreational activities. Such studies in China are scarce. This study investigated urban forest O3 levels to improve understanding and support residents engaging in forest recreational activities. We monitored O3 levels in 2015–2016 for three urban forests representing common habitats (foothill, valley, and ridge) in Yuanshan Forest Park and for an adjacent square. The overall mean daily and daily maximum 8 h mean (MDA8) O3 concentrations were highest for the ridge forest and lowest for the valley forest. Each forest’s O3 concentrations were highest in summer. Diurnally, forest O3 concentrations peaked between 13:00 and 17:00 and reached a minimum between 03:00 and 09:00. The correlation between forest O3 concentrations and air temperature (AT) was strongly positive in summer and autumn but negative in spring. In each season, O3 concentration was negatively correlated with relative humidity (RH). No MDA8 or hourly O3 concentrations in the forests exceeded National Ambient Air Quality Standard Grade I thresholds (100 and 160 μg m−3, respectively). O3 accumulation is present in ridge urban forest in all seasons. Foothill and valley urban forests have better air quality than ridge forestation. Urban forest air quality is better in spring and autumn than in summer and is better from night-time to early morning than from noon to afternoon.
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Roadside vegetation has been shown to impact downwind, near-road air quality, with some studies identifying reductions in air pollution concentrations and others indicating increases in pollutant levels when vegetation is present. These widely contradictory results have resulted in confusion regarding the capability of vegetative barriers to mitigate near-road air pollution, which numerous studies have associated with significant adverse human health effects. Roadside vegetation studies have investigated the impact of many different types and conditions of vegetation barriers and urban forests, including preserved, existing vegetation stands usually consisting of mixtures of trees and shrubs or plantings of individual trees. A study was conducted along a highway with differing vegetation characteristics to identify if and how the changing characteristics affected downwind air quality. The results indicated that roadside vegetation needed to be of sufficient height, thickness, and coverage to achieve downwind air pollutant reductions. A vegetation stand which was highly porous and contained large gaps within the stand structure had increased downwind pollutant concentrations. These field study results were consistent with other studies that the roadside vegetation could lead to reductions in average, downwind pollutant concentrations by as much as 50% when this vegetation was thick with no gaps or openings. However, the presence of highly porous vegetation with gaps resulted in similar or sometimes higher concentrations than measured in a clearing with no vegetation. The combination of air quality and meteorological measurements indicated that the vegetation affects downwind pollutant concentrations through attenuation of meteorological and vehicle-induced turbulence as air passes through the vegetation, enhanced mixing as portions of the traffic pollution plume are blocked and forced over the vegetation, and through particulate deposition onto leaf and branch surfaces. Computational fluid dynamic modeling highlighted that density of the vegetation barrier affects pollutant levels, with a leaf area density of 3.0 m² m⁻³ or higher needed to ensure downwind pollutant reductions for airborne particulate matter. These results show that roadside bushes and trees can be preserved or planted along highways and other localized pollution sources to mitigate air quality and human health impacts near the source if the planting adheres to important characteristics of height, thickness, and density with full coverage from the ground to the top of the canopy. The results also highlight the importance of planting denser vegetation and maintaining the integrity and structure of these vegetation barriers to achieve pollution reductions and not contribute to unintended increases in downwind air pollutant concentrations.
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It is generally conceived that trees can clean polluted air in urban areas sufficiently enough to be considered providers of a vital ecosystem service, although there have not been many field studies showing this in practice in the neighborhood scale. Using passive sampling methods, we investigated the effect of urban park trees on the concentrations of gaseous polycyclic aromatic hydrocarbons (PAHs), nitrogen dioxide (NO2), ground-level ozone (O3) and sulfur dioxide (SO2) in early summer in the temperate zone city of Yanji, northeast China. Concentrations of total gaseous PAHs and certain PAH constituents were higher and concentrations of O3 lower in tree-covered areas compared to nearby open areas, while tree cover did not affect the concentrations of NO2 and SO2. The higher PAH concentrations under tree canopies may associate with air-soil gas exchange and the trapping of polluted air under canopies. Lower O3 concentrations in tree-covered areas may result from a combination of absorption of O3 by tree canopies, and lower temperatures and solar radiation under tree canopies compared to open areas.
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Although aggressive emission control strategies have been implemented recently in the Beijing–Tianjin–Hebei area (BTH), China, pervasive and persistent haze still frequently engulfs the region during wintertime. Afforestation in BTH, primarily concentrated in the Taihang and Yan Mountains, has constituted one of the controversial factors exacerbating the haze pollution due to its slowdown of the surface wind speed. We report here an increasing trend of forest cover in BTH during 2001–2013 based on long-term satellite measurements and the impact of the afforestation on the fine-particle (PM2.5) level. Simulations using the Weather Research and Forecast model with chemistry reveal that afforestation in BTH since 2001 has generally been deteriorating the haze pollution in BTH to some degree, enhancing PM2.5 concentrations by up to 6 % on average. Complete afforestation or deforestation in the Taihang and Yan Mountains would increase or decrease the PM2.5 level within 15 % in BTH. Our model results also suggest that implementing a large ventilation corridor system would not be effective or beneficial to mitigate the haze pollution in Beijing.
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Quantifying ecosystem services in urban areas is complex. However, existing ecosystem service typologies and ecosystem modeling can provide a means towards understanding some key biophysical links between urban forests and ecosystem services. This project addresses broader concepts of sustainability by assessing the urban park system in Phoenix, Arizona’s hot urban climate. This project aims to quantify and demonstrate the multiple ecosystem services provided by Phoenix’s green infrastructure (i.e., urban park system), including its air pollution removal values, carbon sequestration and storage, avoided runoff, structural value, and the energy savings it provides for city residents. Modeling of ecosystem services of the urban park system revealed around 517,000 trees within the system, representing a 7.20% tree cover. These trees remove about 3630 tons (t) of carbon (at an associated value of $285,000) and about 272 t of air pollutants (at an associated value of $1.16 million) every year. Trees within Phoenix’s urban park system are estimated to reduce annual residential energy costs by $106,000 and their structural value is estimated at $692 million. The findings of this research will increase our knowledge of the value of green infrastructure services provided by different types of urban vegetation and assist in the future design, planning and management of green infrastructure in cities. Thus, this study has implications for both policy and practice, contributing to a better understanding of the multiple benefits of green infrastructure and improving the design of green spaces in hot arid urban climates around the globe.
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This study attempts to characterize and compare the vertical distributions of the PM2.5 and PM10 concentrations in downtown and surrounding national forest park. A contrastive measurement was performed using the portable particle sampler in Nanjing (China), from Apr. 22, 2016 to Jan. 24, 2017. The particle concentrations were found to be negatively associated with height in the forest park. The same but slighter phenomena were also found in the downtown in most time, however, peak values were observed at the height of roadside tall tree (25 m) instead of at the ground level at most of the sampling time. At 100 m, particle concentrations decreased by about 30% in the forest park, and only a 20% attenuation was found in the downtown. An unmanned aerial vehicle (UAV) measurement was conducted under the hypothesis that the roadside trees can limit the vertical diffusion of particles. It was found that the interception of trees could reduce 24% and 26% of the PM2.5 and PM10 concentrations above the road, respectively. The correlation analysis between the particle concentrations and five meteorological parameters (temperature, relative humidity, air pressure, solar energy and precipitation) showed higher correlations in the downtown than in the forest park. Both the temperature and the relative humidity contributed to the variation of the particle concentrations at different heights. This work serves to better understanding of particles dynamic characteristics in urban areas and has a significant implication for assessment of indoor air quality in high-rise buildings.
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Ecosystem modeling can help decision making regarding planting of urban trees for climate change mitigation and air pollution reduction. Algorithms and models that link the properties of plant functional types, species groups, or single species to their impact on specific ecosystem services have been developed. However, these models require a considerable effort for initialization that is inherently related to uncertainties originating from the high diversity of plant species in urban areas. We therefore suggest a new automated method to be used with the i-Tree Eco model to derive light competition for individual trees and investigate the importance of this property. Since competition depends also on the species, which is difficult to determine from increasingly used remote sensing methodologies, we also investigate the impact of uncertain tree species classification on the ecosystem services by comparing a species-specific inventory determined by field observation with a genus-specific categorization and a model initialization for the dominant deciduous and evergreen species only. Our results show how the simulation of competition affects the determination of carbon sequestration, leaf area, and related ecosystem services and that the proposed method provides a tool for improving estimations. Misclassifications of tree species can lead to large deviations in estimates of ecosystem impacts, particularly concerning biogenic volatile compound emissions. In our test case, monoterpene emissions almost doubled and isoprene emissions decreased to less than 10% when species were estimated to belong only to either two groups instead of being determined by species or genus. It is discussed that this uncertainty of emission estimates propagates further uncertainty in the estimation of potential ozone formation. Overall, we show the importance of using an individual light competition approach and explicitly parameterizing all ecosystem functions at the species-specific level.
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Urban trees perform a number of ecosystem services including air pollution removal, carbon sequestration, cooling air temperatures and providing aesthetic beauty to the urban landscape. Trees remove air pollution by intercepting particulate matter on plant surfaces and absorbing gaseous pollutants through the leaf stomata. Computer simulations with local environmental data reveal that trees in 86 Canadian cities removed 16,500 tonnes (t) of air pollution in 2010 (range: 7500–21,100 t), with human health effects valued at 227.2 million Canadian dollars (range: $52.5–402.6 million). Annual pollution removal varied among cities and ranged up to 1740 t in Vancouver, British Columbia. Overall health impacts included the avoidance of 30 incidences of human mortality (range: 7–54) and 22,000 incidences of acute respiratory symptoms (range: 7900–31,100) across these cities.
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Urban and peri-urban forests are green infrastructures (GI) that play a substantial role in delivering ecosystem services such as the amelioration of air quality by the removal of air pollutants, among which is ozone (O3), which is the most harmful pollutant in Mediterranean metropolitan areas. Models may provide a reliable estimate of gas exchanges between vegetation and atmosphere and are thus a powerful tool to quantify and compare O3 removal in different contexts. The present study modeled the O3 stomatal uptake at canopy level of an urban and a peri-urban forest in the Metropolitan City of Rome in two different years. Results show different rates of O3 fluxes between the two forests, due to different exposure to the pollutant, management practice effects on forest structure and functionality, and environmental conditions, namely, different stressors affecting the gas exchange rates of the two GIs. The periodic components of the time series calculated by means of the spectral analysis show that seasonal variation of modeled canopy transpiration is driven by precipitation in peri-urban forests, whereas in the urban forest seasonal variations are driven by vapor pressure deficit of ambient air. Moreover, in the urban forest high water availability during summer months, owing to irrigation practice, leads to an increase in O3 uptake, thus suggesting that irrigation may enhance air phytoremediation in urban areas.
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The current study evaluates the influence of roadside solid and vegetation barriers on the near-road air quality. Reynolds Averaged Navier-Stokes (RANS) technique coupled with the k−ε realizable turbulence model is utilized to investigate the flow pattern and pollutant concentration. A scalar transport equation is solved for a tracer gas to represent the roadway pollutant emissions. In addition, a broad range of turbulent Schmidt numbers are tested to calibrate the scalar transport equation. Three main scenarios including flat terrain, solid barrier, and vegetative barrier are studied. To validate numerical methodology, predicted pollutant concentration is compared with published wind tunnel data. Results show that the solid barrier induces an updraft motion and lofts the vehicle emission plume. Therefore, the ground-level pollutant concentration decreases compared to the flat terrain. For the vegetation barrier, different sub-scenarios with different vegetation densities ranging from approximately flat terrain to nearly solid barrier are examined. Dense canopies act in a similar manner as a solid barrier and mitigate the pollutant concentration through vertical mixing. On the other hand, the high porosity vegetation barriers reduce the wind speed and lead to a higher pollutant concentration. As the vegetation density increases, i.e. the barrier porosity decreases, the recirculation zone behind the canopy becomes larger and moves toward the canopy. The dense plant canopy with LAD=3.33m−2m3 can improve the near-road air quality by 10% and high porosity canopy with LAD=1m−2m3 deteriorates near-road air quality by 15%. The results of this study can be implemented as green infrastructure design strategies by urban planners and forestry organizations.
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Background: At a time of increasing disconnectedness from nature, scientific interest in the potential health benefits of nature contact has grown. Research in recent decades has yielded substantial evidence, but large gaps remain in our understanding. Objectives: We propose a research agenda on nature contact and health, identifying principal domains of research and key questions that, if answered, would provide the basis for evidence-based public health interventions. Discussion: We identify research questions in seven domains: a) mechanistic biomedical studies; b) exposure science; c) epidemiology of health benefits; d) diversity and equity considerations; e) technological nature; f) economic and policy studies; and g) implementation science. Conclusions: Nature contact may offer a range of human health benefits. Although much evidence is already available, much remains unknown. A robust research effort, guided by a focus on key unanswered questions, has the potential to yield high-impact, consequential public health insights. https://doi.org/10.1289/EHP1663.
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Trees and other vegetation absorb and capture air pollutants, leading to the common perception that they, and trees in particular, can improve air quality in cities and provide an important ecosystem service for urban inhabitants. Yet, there has been a lack of empirical evidence showing this at the local scale with different plant configurations and climatic regions. We studied the impact of urban park and forest vegetation on the levels of nitrogen dioxide (NO2) and ground-level ozone (O3) while controlling for temperature during early summer (May) using passive samplers in Baltimore, USA. Concentrations of O3 were significantly lower in tree-covered habitats than in adjacent open habitats, but concentrations of NO2 did not differ significantly between tree-covered and open habitats. Higher temperatures resulted in higher pollutant concentrations and NO2 and O3 concentration were negatively correlated with each other. Our results suggest that the role of trees in reducing NO2 concentrations in urban parks and forests in the Mid-Atlantic USA is minor, but that the presence of tree-cover can result in lower O3 levels compared to similar open areas. Our results further suggest that actions aiming at local air pollution mitigation should consider local variability in vegetation, climate, micro-climate, and traffic conditions.
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Trees are believed to improve air quality, thus providing an important ecosystem service for urban inhabitants. However, empirical evidence on the beneficial effects of urban vegetation on air quality at the local level and in boreal climatic regions is scarce. We studied the influence of greenbelt-type forest patches on NO2 levels (i) in front of, (ii) inside and (iii) behind greenbelts next to major roads in the Helsinki Metropolitan Area, Finland, during summer and winter using passive collectors. Concentrations of NO2 were significantly higher in front of greenbelts compared to road sides without greenbelts. The more trees there were inside greenbelts the higher the NO2 level in front of greenbelts, likely due to the formation of a recirculation zone of air flow in front of greenbelts. Similarly, NO2 levels were higher inside greenbelts than in open areas without them, likely due to reduced air flow inside greenbelts. NO2 levels behind greenbelts were similar to those detected at the same distance from the road but without greenbelts. Our results suggest that, regardless of season, roadside greenbelts of mostly broadleaf trees do not reduce NO2 levels in near-road environments, but can result in higher NO2 levels in front of and inside greenbelts.
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The potential of emissions from urban vegetation combined with anthropogenic emissions to produce ozone and particulate matter has long been recognized. This potential increases with rising temperatures and may lead to severe problems with air quality in densely populated areas during heat waves. Here, we investigate how heat waves affect emissions of volatile organic compounds from urban/suburban vegetation and corresponding ground-level ozone and particulate matter. We use the Weather Research and Forecasting Model with atmospheric chemistry (WRF-Chem) with emissions of volatile organic compounds (VOCs) from vegetation simulated with MEGAN to quantify some of these feedbacks in Berlin, Germany, during the heat wave in 2006. The highest ozone concentration observed during that period was ∼200 μg/m(3) (∼101 ppbV). The model simulations indicate that the contribution of biogenic VOC emissions to ozone formation is lower in June (9-11%) and August (6-9%) than in July (17-20%). On particular days within the analyzed heat wave period, this contribution increases up to 60%. The actual contribution is expected to be even higher as the model underestimates isoprene concentrations over urban forests and parks by 0.6-1.4 ppbv. Our study demonstrates that biogenic VOCs can considerably enhance air pollution during heat waves. We emphasize the dual role of vegetation for air quality and human health in cities during warm seasons, which is removal and lessening versus enhancement of air pollution. The results of our study suggest that reduction of anthropogenic sources of NOx, VOCs, and PM, for example, reduction of the motorized vehicle fleet, would have to accompany urban tree planting campaigns to make them really beneficial for urban dwellers.
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Intensifying the proportion of urban green infrastructure has been considered as one of the remedies for air pollution levels in cities, yet the impact of numerous vegetation types deployed in different built environments has to be fully synthesised and quantified. This review examined published literature on neighbourhood air quality modifications by green interventions. Studies were evaluated that discussed personal exposure to local sources of air pollution under the presence of vegetation in open road and built-up street canyon environments. Further, we critically evaluated the available literature to provide a better understanding of the interactions between vegetation and surrounding built-up environments and ascertain means of reducing local air pollution exposure using green infrastructure. The net effects of vegetation in each built-up environment are also summarised and possible recommendations for the future design of green infrastructure are proposed. In a street canyon environment, high-level vegetation canopies (trees) led to a deterioration in air quality, while low-level green infrastructure (hedges) improved air quality conditions. For open road conditions, wide, low porosity and tall vegetation leads to downwind pollutant reductions while gaps and high porosity vegetation could lead to no improvement or even deteriorated air quality. The review considers that generic recommendations can be provided for vegetation barriers in open road conditions. Green walls and roofs on building envelopes can also be used as effective air pollution abatement measures. The critical evaluation of the fundamental concepts and the amalgamation of key technical features of past studies by this review could assist urban planners to design and implement green infrastructures in the built environment.
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Ozone concentration in Tokyo Metropolitan area is one of the most serious issues of the local air quality. Tropospheric ozone is formed by radical reaction including volatile organic compound (VOC) and nitrogen oxides (NOx). Reduction of the emission of reactive VOC is a key to reducing ozone concentrations. VOC is emitted from anthropogenic sources and also from vegetation (biogenic VOC or BVOC). BVOC also forms ozone through NOx and radical reactions. Especially, in urban area, the BVOC is emitted into the atmosphere with high NOx concentration. Therefore, trees bordering streets and green spaces in urban area may contribute to tropospheric ozone. On the other hand, not all trees emit BVOC which will produce ozone locally. In this study, BVOC emissions have been investigated (terpenoids: isoprene, monoterpenes, sesquiterpenes) for 29 tree species. Eleven in the 29 species were tree species that did not emit BVOCs. Three in 12 cultivars for future planting (25 %) were found to emit no terpenoid BVOCs. Eight in 17 commonly planted trees (47%) were found to emit no terpenoid BVOC. Lower-emitting species have many advantages for urban planting. Therefore, further investigation is required to find the species which do not emit terpenoid BVOC. Emission of reactive BVOC should be added into guideline for the urban planting to prevent the creation of sources of ozone. It is desirable that species with no reactive BVOC emission are planted along urban streets and green areas in urban areas, such as Tokyo.
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Transportation is one significant factor which contributes to urban air pollution. One of the pollutants emitted from transportation which affect human's health is NO2. Plants, especially trees, have high potential in reducing air pollutants from transportation through diffusion, absorbtion, adsorption and deposition. Purpose of this study was to analyze the effectiveness of several tree canopy types on roadside green belt in influencing distribution of NO2 gas emitted from transportation. The study conducted in three plots of tree canopy in Jagorawi Highway: Bungur (Lagerstroemia speciosa), Gmelina (Gmelina arborea) and Tanjung (Mimusops elengi). The tree canopy ability in absorbing pollutant is derived by comparing air quality on vegetated area with ambience air quality at control area (open field). Air sampling was conducted to measure NO2 concentration at elevation 1.5m, 5m and 10m at distance 0m, 10m and 30m, using Air Sampler Impinger. Concentration of NO2 was analyzed with Griess-Saltzman method. From this research, the result of ANOVA showed that tree plot (vegetated area) affected significantly to NO2 concentration. However the effect of distance from road and elevation was not significant. Among the plots, the highest NO2 concentration was found on Control plot (area without tree canopy), while the lowest NO2 concentration was found in Tanjung plot. Tanjung plot with round shape and high density canopy performed better in reducing NO2 than Bungur plot with round shape and medium density canopy, regardless the sampling elevation and distance. Gmelina plot performed the best in reducing horizontal distribution of NO2 concentration at elevation 1.5 and 5m, but the result at elevation 10m was not significant.
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Parks provide a range of ecosystem services and make major contributions to urban life. Improved environmental quality was observed in urban parks as pollutants and noise disperse. Numerical models were used to assess the role of various design elements in air pollution and noise attenuation in parks. The walls reduced pollutants and sound noticeably in its shadow. Dense conifers can trap pollutants in park borders and lower concentrations in interiors, but less efficient in noise reduction. A study of a design for a small urban park suggests principles for achieving lower user exposure to pollution and healthier park environment.
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Trees offer a range of ecosystem services and remain important in providing human benefits. However, emerging literature questions the long-accepted view of trees being able to improve air quality in urban parks. The aerodynamic effect of trees was identified as a major reason for the change of pollutant distribution in near-road parks, where trees can act as porous barriers and cause localised concentration increase. Although not yet fully developed, planting strategies aiming to mitigate the negative effect of vegetation on air quality should be encouraged in future park design. In this study, we explored the effect of tree planting design on pollutant diffusion by integrating field surveys in urban parks in Hong Kong with computational fluid dynamic (CFD) modelling. A series of indicators associated with tree morphology and landscape were derived from the surveys and their influence on air pollutant distribution in parks was examined using ENVI-MET. Dense trees with low crown base were found effective in improving air quality within parks when planted as barriers with a width of ~15 m at borders. However, more extensive planting led to a decrease in wind velocity and an increase in pollutant concentrations, which should be avoided. Tall trees tended to have little influence on airflow at the pedestrian level, which means they seem appropriate for small urban parks where wide barriers are not applicable and rapid ventilation should be encouraged. The tree distribution also altered the airflow and pollutant dispersion in parks. Our study provides clues for thoughtful planting strategies which can optimise air quality in urban parks.
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A “call to action” has been issued for scholars in landscape and urban planning, natural science, and public health to conduct interdisciplinary research on the human health effects of spending time in or near greenspaces. This is timely in light of contemporary interest in municipal tree planting and urban greening, defined as organized or semi-organized efforts to introduce, conserve, or maintain outdoor vegetation in urban areas. In response to injunctions from scholars and urban greening trends, this article provides an interdisciplinary review on urban trees, air quality, and asthma. We assess the scientific literature by reviewing refereed review papers and empirical studies on the biophysical processes through which urban trees affect air quality, as well as associated models that extend estimates to asthma outcomes. We then review empirical evidence of observed links between urban trees and asthma, followed by a discussion on implications for urban landscape planning and design. This review finds no scientific consensus that urban trees reduce asthma by improving air quality. In some circumstances, urban trees can degrade air quality and increase asthma. Causal pathways between urban trees, air quality, and asthma are very complex, and there are substantial differences in how natural science and epidemiology approach this issue. This may lead to ambiguity in scholarship, municipal decision-making, and landscape planning. Future research on this topic, as well as on urban ecosystem services and urban greening, should embrace epistemological and etiological pluralism and be conducted through interdisciplinary teamwork.
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Air pollution is an important environmental and health concern all over the world and PM 2.5 is one of the most important constituents of air pollution. In urban area with high population density, vehicles contribute a big portion of PM 2.5 . The effect of vegetations along road, i.e., road greenbelts, on PM 2.5 concentration is still a hot research topic. This study used three-dimensional green volume (3DGV, the three-dimensional volume of the crown and stems of all vegetations including trees, shrubs and grass) to evaluate the vegetation quantity of road greenbelts along four main roads in Nanjing, China. High spatial resolution images were collected with unmanned aerial vehicle (UAV) for othomosaic and feature extraction analysis. A Geographic Information System (GIS) database was developed to cover the location, crown diameter, crown height, and 3DGV information of vegetations in the road greenbelts. The environmental benefits of the road greenbelts were evaluated based on 3DGV information. The relationship between 3DGV of road greenbelts and PM 2.5 concentration was analyzed and it was found that large 3DGV does not mean lower PM 2.5 concentration. A road greenbelt with even vertical distribution of biomass and diversified vegetation species works better to reduce PM 2.5 concentration. The implication of this research is that road greenbelt development should systematically consider surface water control, noise reduction, recreation, aesthetic, and air pollution control, thus to maximize its ecoservices to human being.
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Global urbanisation has resulted in population densification, which is associated with increased air pollution, mainly from anthropogenic sources. One of the systems proposed to mitigate urban air pollution is urban forestry. This study quantified the spatial associations between concentrations of CO, NO₂ SO₂ and PM₁₀ and urban forestry, whilst correcting for anthropogenic sources and sinks, thus explicitly testing the hypothesis that urban forestry is spatially associated with reduced air pollution on a city scale. A Land Use Regression (LUR) model was constructed by combining air pollutant concentrations with environmental variables, such as land cover type and use, to develop predictive models for air pollutant concentrations. Traffic density and industrial air pollutant emissions were added to the model as covariables to permit testing of the main effects after correcting for these air pollutant sources. It was found that the concentrations of all air pollutants were negatively correlated with tree canopy cover and positively correlated with dwelling density, population density and traffic count. The LUR models enabled the establishment of a statistically significant spatial relationship between urban forestry and air pollution mitigation. These findings further demonstrate the spatial relationships between urban forestry and reduced air pollution on a city-wide scale, and could be of value in developing planning policies focused on urban greening.
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Ground-level ozone (O3) is an atmospheric pollutant of concern owing to its impacts on both human and environmental health. In southern Ontario, Canada, air pollutants (including O3) are continuously monitored through a network of active monitoring stations; however, these stations are largely located in urban areas. Passive samplers for O3 and NO2 were deployed at 24 sites throughout the Sandbanks Provincial Park, on the shore of Lake Ontario during the summer of 2016 to assess the influence of lake-breeze circulation on air quality. Average O3 measured at the park (39.4 ppb) was higher than inland sites at Belleville (32.6 ppb) and Peterborough (30.0 ppb). A negative-linear relationship (R2 = 0.71) was observed between O3 concentration and distance from shore (<500 m from Lake Ontario). While a positive-linear relationship was observed between exposure wind speed and O3 (R2 = 0.84) when the predominant wind direction was W–SW. The results suggest that the Sandbanks was influenced by lake-breeze circulation, resulting in elevated summertime O3. Similarly, average NO2 concentrations (4.3 ppb) were higher than the inland site at Peterborough (2.9 ppb), suggesting that lake-breeze circulation transported NO2 onshore from Lake Ontario. Elevated levels of O3 at the Sandbanks may be a potential concern for human health; moreover, estimated three-month AOT40 suggest that O3 may also damage vegetation.
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Urban parks have long been considered places of refuge from the bustle, noise and pollutants of the surrounding city. Parks were labelled the lungs of the city, a metaphor which gained support as studies revealed the deposition of pollutants to leaf surfaces. More recently air purification by urban vegetation came to be seen as an ecosystem service, that add to the other important services it provides. However, the significance of deposition to foliage in reducing air pollutant concentrations in cities and the service this provides is often questioned. Although pollutants deposit on vegetation, the change in turbulence and wind speed brought about by increased friction can often limit dispersion and means that pollutant concentrations can be higher than expected. This paper re-analyses pollutant transects away from roads and into parks to compare the relevance of deposition and dispersion to lowered concentrations in park interiors and shows that pollutant concentrations typically decline more rapidly along transects with vegetation than those without. This may support the notion that deposition to vegetation rapidly reduces pollutant concentrations, but simulations using ENVI-MET reveal that even dense foliage offers little improvement to air quality via removal of pollutants in small urban parks with length scale less than 100 m. New field observations show the dominance of aerodynamic factors in changing air quality in urban parks and the way vegetation affects pollutant concentrations through altering air flows. Deposition is generally not important for parks although it plays a role in the rapid removal of large particles with rapid settling velocities (>10 cm s-1) at the park borders (<5 m). Across cities as a whole rarely more than a percent or so of individual pollutants are removed by urban vegetation. Deposition on foliage is not an important contribution to improved air quality. Vegetation can alter the dispersion of pollutants from roads into parks and effectively increase pollutant concentrations. Nevertheless stands of trees or flower beds can affect the distribution of park users, so may change exposure to air pollutants by altering the spatial distribution of occupants.
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Benzene, toluene, ethylbenzene, and xylenes (BTEX) are hazardous air pollutants commonly found in outdoor air. Several studies have explored the potential of vegetation to mitigate BTEX in outdoor air, but they are limited to a northern temperate climate and their results lack consensus. To investigate this subject in a subtropical climate, we deployed passive air samplers for two weeks in parks and nearby residences at four locations: three in an urban area and one in a rural area in Alabama, USA. All BTEX concentrations were below health-based guidelines and were comparable to those found in several other studies in populated settings. Concentrations of TEX, but not benzene, were 3-39% lower in parks than at nearby residences, and the differences were significant. Site type (park vs. residential) was a significant predictor of TEX concentrations, while distance to the nearest major road was a significant predictor of BTX concentrations. In and around two of the parks, toluene:benzene ratios fell outside the range expected for vehicular emissions (p<0.01), suggesting that there were additional, industrial sources of benzene near these two locations. The ratio of m-,p-xylene:ethylbenzene was high at all locations except one residential area, indicating that BTEX were freshly emitted. Concentrations of individual BTEX compounds were highly correlated with each other in most cases, except for locations that may have been impacted by nearby industrial sources of benzene. Results of this study suggest that parks can help reduce exposure to TEX by a modest amount in some situations.
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The use of shade trees is among favorable urban planning strategies to improve outdoor thermal comfort and promote energy efficiency. Meanwhile, the presence of trees alters flow patterns and turbulent transport and influences the dispersion of air pollutants. In this study, we investigated the effects of urban trees on air pollutant dispersion in urban canopy layers using a coupled large-eddy simulation–Lagrangian stochastic modeling framework. The dispersions of two-way traffic emissions were simulated using a set of twenty four scenarios with varying canyon and tree geometries. Results show that tall trees lead to the strongest modification of the canyon flow and pollutant concentration, except in narrow canyons. Trees can exacerbate canyon pollution level in certain built environment owing to the presence of isolated canyon vortices. Trees with high leaf area density are beneficial to reducing concentration in broad street canyons, while trapping of pollutants is manifest in narrow canyons. The participatory role of trees, in conjunction with the effect of urban morphology, is crucial and needs to be meticulously evaluated in urban planning for promoting environmental quality.
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It is clear that the climate is changing and ecosystems are becoming severely degraded. Humans must mitigate the causes of, and adapt to, climate change and the loss of biodiversity, as the impacts of these changes become more apparent and demand urgent responses. These pressures, combined with rapid global urbanisation and population growth mean that new ways of designing, retrofitting and living in cities are critically needed. Incorporating an understanding of how the living world works and what ecosystems do into architectural and urban design is a step towards the creation and evolution of cities that are radically more sustainable and potentially regenerative. Can cities produce their own food, energy, and water? Can they be designed to regulate climate, provide habitat, cycle nutrients, and purify water, air and soil? This book examines and defines the field of biomimicry for sustainable built environment design and goes on to translate ecological knowledge into practical methodologies for architectural and urban design that can proactively respond to climate change and biodiversity loss. These methods are tested and exemplified through a series of case studies of existing cities in a variety of climates. Regenerative Urban Design and Ecosystem Biomimicry will be of great interest to students, professionals and researchers of architecture, urban design, ecology, and environmental studies, as well as those interested in the interdisciplinary study of sustainability, ecology and urbanism. Routledge is trialling a system of letting their authors share their books in their entirety for free (60 days). So... here is a link to the book 'regenerative urban design and ecosystem biomimicry' https://rdcu.be/4ftj Valid till late October 2018. Enjoy!!!
Article
Poor air quality in urban areas has a direct impact on the public health on a global scale. The examples of air pollution are: particulate matter with particles less than 10 μm (PM10) and less than 2.5 μm (PM2.5), as well as carbon dioxide (CO2). Urban greenery can be a way to clean the air in built-up areas. Many urban parks were, however, created long time ago, and it was not examined whether they are useful for the air purification nowadays. In year 2017, in the area of the largest city park in Europe – the Silesia Park (S Poland) – a network of 40 constant points was created, where from June to October the air quality was measured once a month. Research showed that the air quality was lower near the roads, the microclimate affected the concentration of pollutants, and trees of different genera and sizes differed in the efficiency of air cleaning. The greater porosity of tree crowns was associated with a higher concentration of all three measured indicators, suggesting their stagnation between vegetation. Older patches of the park with European hornbeams and beeches deserve protection as the most efficient air filterers. It is recommended to close internal park roads for cars and/or plant a new green barrier around the park. Current density of trees should be constant or increased to maintain the optimal microclimate that decreases air temperature determining effective air cleaning.
Article
This paper is to assess the impact of the vegetation accumulation on the air pollution dispersion. In order to analyze the idea of the paper for examining the influence of vegetation, two parks in different scales were selected by purpose which are at the same distance from the pollution source. Envi-met (version 3) was selected as research tool based on methodology of the research. Two parks with various scales (local and urban scale) and equal vegetation accumulation were simulated in three cases (status quo or 12%, 37% and 62% vegetation density) and analyzed in quantitative results and graphic images. The results revealed that the extent of area and congestion of vegetation is directly related to decreasing air pollution (CO concentration). Vegetation congestion impact on CO concentration is more impressive for urban scale compared with local scale. The results indicate that decrease of CO concentration in urban scale is going under a regular process. Otherwise, the relationship between vegetation congestion and CO concentration will convert in 62% vegetation congestion. The conclusion of this paper emphasizes that the intensity of vegetation is not always helpful and vegetation might be the cause of intensifying air pollution under certain circumstances.
Article
This paper reviews current parameterizations developed and implemented within Computational Fluid Dynamics models for the study of the effects linking vegetation, mainly trees, to urban air quality and thermal conditions. In the literature, passive mitigation via deposition is parametrized as a volumetric sink term in the transport equation of pollutants, while a volumetric source term is used for particle resuspension. The aerodynamics effects are modelled via source and sink terms of momentum, turbulent kinetic energy and turbulent dissipation rate. A volumetric cooling power is finally considered to account for the thermal (transpirational cooling) effects of vegetation. The most recent applications are also summarized with a focus on the relative importance of both aerodynamic and deposition effects, together with recent studies evaluating thermal effects. Those studies have shown that the aerodynamic effects of trees are stronger than the positive effects of deposition, however locally the pollutant concentration increases or decreases depending on the complex inter-relation between local factors such as vegetation type and density, meteorological conditions, street geometry, pollutant characteristics and emission rates. Unlike aerodynamic and deposition effects on pollutant dispersion which were also found in street far from trees, the thermal effects were in general locally restricted to the close vicinity of the vegetation and to the street canyon itself. Future requirements in CFD modelling include more in depth investigation of resuspension and thermal effects, as well as of the VOCs emissions and chemical reactions. The overall objective of this review is to provide the scientific community with a comprehensive summary on the current parameterizations of urban vegetation in CFD modelling and constitutes the starting point for the development of new parametrizations in CFD as well as in mesoscale models.
Article
Scarce land resources in dense cities means that small urban parks are important as a leisure and amenity resource for the urban population. However, streets with heavily traffic often surround these fragmented parks and increase the potential user exposure to air pollutants from vehicles. The dispersion profiles of PM2.5 and black carbon from roadside into urban parks at pedestrian level, in Hong Kong, were measured using mobile high time resolution instruments. In the downwind direction, pollutant concentrations decreased rapidly from roadside and by some tens of metres reached relatively constant values. An even sharper gradient is found in the upwind direction, with a rapid increase detected within 2m of the road edge. The distinct decay profiles were explained with an analytical dispersion model formulated based on the gradient transport theory using an Eulerian approach. The simulations using the dispersion model suggest 17m as a typical halving distance under normal urban conditions, which is introduced to simplify the description of dispersion profiles. Using Hong Kong as an example, ~90% of urban parks, to different extent, overlap with the 17m halving distance from roads, which means few urban parks in Hong Kong avoid the impact from nearby traffic emissions. Thus, from the perspective of human exposure to air pollutants in urban parks, this study provides observations of relevance for future park design in dense cities.
Article
Understanding the benefits provided by urban trees is important to justify investment and improve stewardship. Many studies have attempted to quantify the benefits of trees in monetary terms, though fewer have quantified the associated costs of planting and maintaining them. This systematic review examines the methods used to jointly analyse the costs and benefits of trees in the urban landscape, assesses the relative balance of benefits and costs, and attempts to understand the wide variation in economic values assigned in different studies. The benefits most frequently studied are those related to environmental regulation and property values, and the available data show that these usually outweigh the costs. Aesthetic, amenity, and shading benefits have also been shown to provide significant economic benefits, while benefits in terms of water regulation, carbon reduction and air quality are usually more modest. Variation in benefits and costs among studies is attributed largely to differences in the species composition and age structure of urban tree populations, though methodological differences also play a role. Comparison between studies is made difficult owing to differences in spatiotemporal scope, and in the way urban forest composition and demographic structure were reported. The overwhelming majority of studies concern deciduous trees in Northern America, and much less is known about urban forests in other regions, especially in the tropics. Future work should thus seek to fill these knowledge gaps, and standardise research protocols across cities. In light of ambitious goals in many cities to increase tree cover, ongoing advances in valuation methods need to provide a more comprehensive accounting of benefits and costs, and to better integrate economic assessment into the decision-making process.
Article
Green spaces and urban green infrastructure are new concepts in urban planning, and lately, the influence of green spaces in cities and how this presence affects local climate change have been taken into account. Moreover, some of the ornamental trees most used in cities provoke allergic symptoms in sensitized people. Due to the importance the plane trees in our parks and cities have as ornamental trees, this article assesses the urban Platanus airborne pollen concentration in the air of five cities of the SW Iberian Peninsula and tries to determine the differential factors that its distribution has by means of combining continuous monitoring of the air using volumetric spore traps and the geolocation of plane trees. They were counted separately according to the direction (Q1 NE, Q2 SE, Q3 SW, Q4 NW) around the spore trap location in circles of 100, 200, 300, 400, 500, 1000, 1500, 2000 and 2500 m in diameter. Pollen sums were distributed according to the predominant wind direction for each day. The highest concentrations for Platanus pollen were recorded in Don Benito. Differences amongst pollen stations were found and were mainly related to their degree of maturity and their proximity to spore traps, and finally, with the number of plane trees. Furthermore, other factors, as the pruning, which is different in each city and even in a more local way, affects pollination and is frequently unknown to aerobiological studies. The geolocation of ornamental trees can be a useful tool for providing summarized information about their behavioral differences amongst cities, which can be used to create healthy itineraries, minimizing the natural hazards in human health (allergic diseases) and could be implemented into a model to help policy-makers to create measures to improve green urban development.
Article
Urban forests (UF) provide a range of important ecosystem services (ES) for human well-being. Relevant ES delivered by UF include urban temperature regulation, runoff mitigation, noise reduction, recreation, and air purification. In this study the potential of air pollution removal by UF in the city of Florence (Italy) was investigated. Two main air pollutants were considered – particulate matter (PM10) and tropospheric ozone (O3) – with the aim of providing a methodological framework for mapping air pollutant removal by UF and assessing the percent removal of air pollutant. The distribution of UF was mapped by high spatial resolution remote sensing data and classified into seven forest categories. The Leaf Area Index (LAI) was estimated spatially using a regression model between in-field LAI survey and Airborne Laser Scanning data and it was found to be in good linear agreement with estimates from ground-based measurements (R2 = 0.88 and RMSE% = 11%). We applied pollution deposition equations by using pollution concentrations measured at urban monitoring stations and then estimated the pollutant removal potential of the UF: annual O3 and PM10 removal accounted for 77.9 t and 171.3 t, respectively. O3 and PM10 removal rates by evergreen broadleaves (16.1 and 27.3 g/m2), conifers (10.9 and 28.5 g/m2), and mixed evergreen species (15.8 and 31.7 g/m2) were higher than by deciduous broadleaf stands (4.1 and 10 g/m2). However, deciduous forests exhibited the largest total removal due to the high percentage of tree cover within the city. The present study confirms that UF play an important role in air purification in Mediterranean cities as they can remove monthly up to 5% of O3 and 13% of PM10.