Urban vegetation and particle air pollution: Experimental campaigns in a traffic hotspot

Uneven PM2.5 dispersion pattern across an open-road vegetation barrier: Effects of planting combination and wind condition

The increased traffic-induced emissions contribute to the exacerbation of airborne particulate matter (PM) pollution. The vegetation barrier (VB) provides a means of reducing the traffic-induced pollutants. However, the effects of VB configuration and local environment on PM dispersion and reduction remain unclear, and thereby needs further advancement on VB design and characteristics. This study constructed a 3D numerical model based on field survey in an open-road VB of Shanghai urban area, and then simulated PM2.5 dispersion under various VB configurations and wind conditions. The results consolidated that the presence of the VB reduced PM2.5 concentration by over 15 % across the VB. A greater bush coverage (2/3 and more) reduces over 14 % more PM2.5 pollution across the VB than that for a greater arbor coverage, and reduces 6 % more PM2.5 pollution in the sidewalk canyon. Given a certain bush planting coverage, planting bushes in the windward area is beneficial to the overall PM2.5 reduction by approximately 4-14 %. The wind directions determine the overall pattern of PM2.5 dispersion across the VB plot, decreasing trends for perpendicular winds but fluctuating curves for parallel winds Wind velocities largely contribute to the changing rates of PM2.5 concentration, the increased wind speed from 1 m/s to 7 m/s accumulated 5-11 % more PM2.5 pollution across the VB plot. This study provides practical insights for effective VB designs in order to mitigate the PM pollution and the human's exposure to PM2.5 in urban open-road environments.

Quantifying the contribution of environmental variables to cyclists' exposure to PM2.5 using machine learning techniques

Cyclists are particularly vulnerable to travel-related exposure to air pollution. Understanding the factors that increase exposure is crucial for promoting healthier urban environments. Machine learning models have successfully predicted air pollutant concentrations, but they tend to be less interpretable than classical statistical ones, such as linear models. This study aimed to develop a predictive model to assess cyclists' exposure to fine particulate matter (PM2.5) in urban environments. The model was generated using geo-temporally referenced data and machine learning techniques. We explored several models and found that the gradient boosting machine learning model best fitted the PM2.5 predictions, with a minimum root mean square error value of 5.62 μg m-3. The variables with greatest influence on cyclist exposure were the temporal ones (month, day of the week, and time of the day), followed by meteorological variables, such as temperature, relative humidity, wind speed, wind direction, and atmospheric pressure. Additionally, we considered relevant attributes, which are partially linked to spatial characteristics. These attributes encompass street typology, vegetation density, and the flow of vehicles on a particular street, which quantifies the number of vehicles passing a given point per minute. Mean PM2.5 concentration was lower in bicycle paths away from vehicular traffic than in bike lanes along streets. These outcomes underscore the need to thoughtfully design public transportation routes, including bus routes, concerning the network of bicycle pathways. Such strategic planning attempts to improve the air quality in urban landscapes.

Towards sustainable and net-zero cities: A review of environmental modelling and monitoring tools for optimizing emissions reduction strategies for improved air quality in urban areas

Climate change is a defining challenge for today's society and its consequences pose a great threat to humanity. Cities are major contributors to climate change, accounting for over 70% of global greenhouse gas emissions. With urbanization occurring at a rapid rate worldwide, cities will play a key role in mitigating emissions and addressing climate change. Greenhouse gas emissions are strongly interlinked with air quality as they share emission sources. Consequently, there is a great opportunity to develop policies which maximize the co-benefits of emissions reductions on air quality and health. As such, a narrative meta-review is conducted to highlight state-of-the-art monitoring and modelling tools which can inform and monitor progress towards greenhouse gas emission and air pollution reduction targets. Urban greenspace will play an important role in the transition to net-zero as it promotes sustainable and active transport modes. Therefore, we explore advancements in urban greenspace quantification methods which can aid strategic developments. There is great potential to harness technological advancements to better understand the impact of greenhouse gas reduction strategies on air quality and subsequently inform the optimal design of these strategies going forward. An integrated approach to greenhouse gas emission and air pollution reduction will create sustainable, net-zero and healthy future cities.

Particulate matter resuspension from simulated urban green floors using a wind tunnel-mounted closed chamber

Background

Green areas are thought to reduce particulate matter (PM) concentrations in urban environments. Plants are the key to PM reduction via various mechanisms, although most mechanisms do not lead to the complete removal of PM. Ultimately, PM falls into the soil via wind and rainfall. However, the fallen PM can re-entrain the atmosphere, which can affect plants capacity to reduce PM. In this study, we simulated an urban green floor and measured the resuspension of PM from the surface using a new experimental system, a wind tunnel-mounted closed chamber.

Methods

The developed system is capable of quantifying the resuspension rate at the millimeter scale, which is measured by using the 1 mm node chain. This is adequate for simulating in situ green floors, including fallen branches and leaves. This addressed limitations from previous studies which focused on micrometer-scale surfaces. In this study, the surfaces consisted of three types: bare sand soil, broadleaves, and coniferous leaves. The resuspended PM was measured using a light-scattering dust detector.

Results

The resuspension rate was highest of 14.45×10^-4 s^-1 on broad-leaved surfaces and lowest on coniferous surfaces of 5.35×10^-4 s^-1 (p < 0.05) and was not proportional to the millimeter-scale surface roughness measured by the roller chain method. This might be due to the lower roughness density of the broad-leaved surface, which can cause more turbulence for PM resuspension. Moreover, the size distribution of the resuspended PM indicated that the particles tended to agglomerate at 2.5 µm after resuspension.

Conclusion

Our findings suggest that the management of fallen leaves on the urban green floor is important in controlling PM concentrations and that the coniferous floor is more effective than the broadleaved floor in reducing PM resuspension. Future studies using the new system can be expanded to derive PM management strategies by diversifying the PM types, surfaces, and atmospheric conditions.

Effect of air quality improvement by urban parks on mitigating PM2.5 and its associated heavy metals: A mobile-monitoring field study

Field mobile monitoring of PM_2.5, equipped with a highly accurate device, was performed for two types of urban parks in Taiwan. Measurements were taken in the morning and evening rush hours, on certain weekdays and weekends, every month over a year. We designed six calculation schemes of the rate of PM_2.5 mitigation by urban parks to comprehensively compare the average and maximum mitigation effects in relation to the vegetation barriers. The mitigation rate, from the lowest (2.51%) to the highest (35.57%) depended on the calculation schemes. The Taipei Botanical Garden (TBG) with a dense, multilevel forest has a stable PM_2.5 mitigation effect and strong ability to improve air quality inside the park under severe PM_2.5 pollution. In contrast, Zhonghe No.4 Park (ZHP), an open park with mostly a single-storied stand, has variable PM_2.5 mitigation effect, leading to either quick dissipation or accumulation of PM_2.5 inside the park. Furthermore, the dry deposition of PM and the associated heavy metals were investigated using camphor trees as bioaccumulators. Dry deposition flux of the leaf-deposited PM_2.5 exhibited similar results in ZHP; whereas, noticeable higher results were observed inside TBG. In addition, most of the PM_2.5 deposition flux from field estimations were similar to those in i-Tree Eco when considering the loss of mass due to the dissolution through water filtration, indicating that i-Tree Eco may be reliable to model the removal of PM_2.5 in the parks in Taiwan. Moreover, we examined nine heavy metals' content in the deposited PM, and most of the detectable elements were significantly higher outside both parks, demonstrating the mitigation effects of urban parks in reducing not only the PM_2.5 concentration but also the toxicity of the pollutant. This study provides direct evidence of the important ecosystem services, namely air quality improvement and biomonitoring effect, derived from urban parks.

Association of decreases in PM2.5 levels due to the implementation of environmental protection policies with the incidence of obesity in adolescents: A prospective cohort study

AIMS

To explore the association between decreased levels of particulate matter (≤2.5 µm; PM_2.5) due to the implementation of environmental protection policies and the incidence of obesity in adolescents in Chongqing, China through a prospective cohort study.

METHODS

A total of 2105 children (52.02% male; aged 7.33 ± 0.60 years at baseline) were enrolled from the Chongqing Children's Health Cohort. A mixed linear regression model was used to analyse the relationships of PM_2.5 levels with obesity indicators after adjusting for covariates. Additionally, a Poisson regression model was used to determine the relationship between PM_2.5 exposure and the incidence of overweight/obesity.

RESULTS

The average PM_2.5 exposure levels from participant conception to 2014, from 2015 to 2017, and from 2018 to 2019 were 66.64 ± 5.33 μg/m³, 55.49 ± 3.78 μg/m³, and 42.50 ± 1.87 μg/m³, respectively; these levels significantly decreased over time (P < 0.001). Throughout the entire follow-up period, the incidence of overweight/obesity after a ≥ 25 μg/m³ decrease in the PM_2.5 level was 4.57% among females; this incidence was the lowest among females who experienced remarkable decreases in PM_2.5 exposure. A 1-µg/m³ decrease in the PM_2.5 level significantly decreased the body mass index (BMI), BMI z score (BMI_z), and weight of adolescents (all P < 0.001). Compared with a < 20-μg/m³ decrease in the PM_2.5 level, a ≥ 25-μg/m³ decrease protected against increased BMI (net difference= -0.93; 95% confidence interval [CI]: (-1.23,-0.63) kg/m²), BMI_z (-0.28 (-0.39, -0.17)), weight (-1.59 (-2.44, -0.74) kg), and incidence of overweight/obesity (0.48 (0.37, 0.62), P < 0.001). Moreover, compared with a < 20-μg/m³ decrease in the PM_2.5 level, a ≥ 25-μg/m³ decrease resulted in significant absolute differences in BMI (-1.26 (-1.56, -0.96) kg/m²), BMI_z (-0.53 (-0.65, -0.40)) and weight (-3.01 (-3.8, -2.19) kg) (all P < 0.001).

CONCLUSIONS

This study showed the etiological relevance of declining PM_2.5 concentrations for the incidence of obesity in children and adolescents, suggesting that controlling ambient air pollutants may prevent the development of obesity in this age group. Continuous implementation of environmental protection policies in China has led to substantial health benefits.

Macro-Morphological Traits of Leaves for Urban Tree Selection for Air Pollution Biomonitoring: A Review

Urban trees provide different ecosystem benefits, such as improving air quality due to the retention of atmospheric particulate matter (PM) on their leaves. The main objective of this paper was to study, through a systematic literature review, the leaf macro-morphological traits (LMTs) most used for the selection of urban trees as air pollution biomonitors. A citation frequency index was used in scientific databases, where the importance associated with each variable was organized by quartiles (Q). The results suggest that the most biomonitored air pollutants by the LMTs of urban trees were PM between 1-100 µm (Q1 = 0.760), followed by O₃ (Q2 = 0.586), PM_2.5 (Q2 = 0.504), and PM₁₀ (Q3 = 0.423). PM was probably the most effective air pollutant for studying and evaluating urban air quality in the context of tree LMTs. PM_2.5 was the fraction most used in these studies. The LMTs most used for PM monitoring were leaf area (Q1) and specific leaf area (Q4). These LMTs were frequently used for their easy measurement and quantification. In urban areas, it was suggested that leaf area was directly related to the amount of PM retained on tree leaves. The PM retained on tree leaves was also used to study other f associated urban air pollutants associated (e.g., heavy metals and hydrocarbons).

The relationship between greenspace and personal exposure to PM2.5 during walking trips in Delhi, India

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 PM_2.5 (particulate matter with an aerodynamic diameter of less than 2.5 μm) for 48 h. We isolated normal day-to-day walking journeys (n = 199) from the personal monitoring dataset and assessed the relationship between greenspace and personal PM_2.5 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 PM_2.5 personal exposure of 133.9 (standard deviation = 114.8) μg/m³. The within-trip analysis showed weak inverse associations between greenspace markers and PM_2.5 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 PM_2.5 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 PM_2.5 of small pockets of greenspace. Larger areas of greenspace may, however, give rise to observable spatial effects on PM_2.5, which vary by season.

Assessment of Air Quality and Meteorological Changes Induced by Future Vegetation in Madrid

Nature-based solutions and green urban infrastructures are becoming common measures in local air quality and climate strategies. However, there is a lack of analytical frameworks to anticipate the effect of such interventions on urban meteorology and air quality at a city scale. We present a modelling methodology that relies on the weather research and forecasting model (WRF) with the building effect parameterization (BEP) and the community multiscale air quality (CMAQ) model and apply it to assess envisaged plans involving vegetation in the Madrid (Spain) region. The study, developed within the VEGGAP Life project, includes the development of two detailed vegetation scenarios making use of Madrid’s municipality tree inventory (current situation) and future vegetation-related interventions. An annual simulation was performed for both scenarios (considering constant anthropogenic emissions) to identify (i) variations in surface temperature and the reasons for such changes, and (ii) implications on air-quality standards according to EU legislation for the main pollutants (PM10, PM2.5, NO2 and O3). Our results suggest that vegetation may have significant effects on urban meteorology due to changes induced in relevant surface properties such as albedo, roughness length or emissivity. We found a net-heating effect of around +0.18 °C when trees are introduced in dry, scarcely vegetated surfaces in the city outskirts. In turn, this enhances the planetary boundary layer height (PBLH), which brings about reductions in ambient concentrations of relevant pollutants such as NO2 (in the range of 0.5–0.8 µg m−3 for the annual mean, and 2–4 µg m−3 for the 19th highest 1 h value). Conversely, planting new trees in consolidated urban areas causes a cooling effect (up to −0.15 °C as an annual mean) that may slightly increase concentration levels due to less-effective vertical mixing and wind-speed reduction caused by increased roughness. This highlights the need to combine nature-based solutions with emission-reduction measures in Madrid.

Particulate Pollution Capture by Seventeen Woody Species Growing in Parks or along Roads in Two European Cities

This research aims to extend the existing knowledge on air quality improvement by the arboreal–shrub heritage. The PM accumulation (PM10–100, PM2.5–10, and PM0.2–2.5 (µg·cm−2)) was measured with consolidated gravimetric techniques during spring, summer, and fall for 2160 leaf samples belonging to the basal, median, and apical part of the crown of 17 species located in the streets and parks of 2 European cities (Rimini and Krakow). On the same samples, the deposition (PM10 and PM2.5 (µg·cm−2·day−1)) was evaluated according to a model based on the wash-off rain effect. Quercus ilex accumulated more PMx than the other species in Rimini, while in Krakow, the highest accumulators were Pinus nigra for PM10–100, Tilia cordata for PM2.5–10, and Populus nigra for PM0.2–2.5. Only in Krakow was the capture capacity of some species affected by the street or park growing condition. The basal leaves showed greater PM10–100 accumulation than the median and apical ones. In Rimini, the total PM accumulation tended to increase throughout the year, while in Krakow, the opposite occurred. However, as the accumulation increased, the deposition decreased. The PM accumulation was reduced by rainfall and enhanced by the air PM concentration, while the wind speed effect was opposite, depending on the city. These findings are useful for directing decision makers in the design of greener, healthier, and sustainable cities.

Magnetism and Grain-Size Distribution of Particles Deposited on the Surface of Urban Trees in Lanzhou City, Northwestern China

Studies on the variation in the particulate matter (PM) content, Saturation Isothermal Remanent Magnetization (SIRM), and particle grain-size distribution at a high spatial resolution are helpful in evaluating the important role of urban forests in PM removal. In this study, the trees located in dense urban forests (T0) retained more PM than trees located in open spaces (T1–T4); the SIRM and PM weight of T0 were 1.54–2.53 and 1.04–1.47 times more than those of T1–T4, respectively. In addition, the SIRM and PM weight decreased with increasing distance to the road, suggesting that distance from pollution sources plays a key role in reducing the air concentration of PM. The different grain-size components were determined from frequency curve plots using a laser particle-size analyzer. A unimodal spectrum with a major peak of approximately 20 μm and a minor peak between 0.1 and 1 μm was observed, indicating that a large proportion of fine air PM was retained by the needles of the study trees. Additionally, more <2.5 μm size fraction particles were observed at the sampling site near the traffic source but, compared to a tree in a row of trees, the percentage of the >10 μm size fraction for the tree in the dense urban forest was higher, indicating that the particles deposited on the needle surface originating from traffic sources were finer than those from natural atmospheric dust. The exploration of the variation in the PM weight, SIRM, and grain size of the particles deposited on the needle surface facilitates monitoring the removal of PM by urban forests under different environmental conditions (e.g., in closed dense urban forests and in open roadside spaces), different distances to roads, and different sampling heights above the ground.

Street view greenness is associated with lower risk of obesity in adults: Findings from the 33 Chinese community health study

BACKGROUND

Urban greenness may protect against obesity, but very few studies have assessed 'street view' (SV) greenness metrics, which may better capture people's actual exposure to greenness compared to commonly-used satellite-derived metrics. We aimed to investigate these associations further in a Chinese adult study.

METHODS

Our analysis included 24,845 adults in the 33 Chinese Community Health Study in 2009. SV images from Tencent Map, segmented by machine learning algorithms, were used to determine the average proportion of green vegetation in SV images at community level in 800m road network buffer. Sensitivity analyses were performed with an alternative buffer size. Overall greenness was assessed as normalized difference vegetation index (NDVI) in 800 m buffer. We used predicted PM_2.5 and monitored NO₂ as proxies of air pollution. Body mass index (BMI), waist circumference (WC) and hip circumference (HC) were regressed on SV greenness by generalized linear mixed models, with adjustment for covariates. Mediation analyses were performed to assess the mediation effects of air pollution.

RESULTS

Each interquartile range (IQR = 3.6%) increase in street view greenness was associated with a 0.15 kg/m² (95% CI: -0.22, -0.09) decrease in BMI and 0.23 cm (95% CI: -0.35, -0.11) reduction in HC, and was associated with 7% lower odds of overweight (OR = 0.93, 95% CI:0.90, 0.96) and 18% lower odds of obesity (OR = 0.82, 95% CI:0.76, 0.89). Similar effect estimation was observed compared with commonly-used NDVI measures. PM_2.5 and NO₂ mediated 15.5% and 6.1% of the effects of SV greenness with BMI, respectively.

CONCLUSIONS

Our findings suggest beneficial associations between community-level SV greenness and lower body weight in Chinese adults. The effects were observed in women but not in men. Air pollution may partially mediate the association. These findings may have implications to support efforts to promote greening in urban areas.

How far climatic parameters associated with air quality induced risk state (AQiRS) during COVID-19 persuaded lockdown in India

Global temperature rises in response to accumulating greenhouse gases is a well-debated issue in the present time. Historical records show that greenhouse gases positively influence temperature. Lockdown incident has brought an opportunity to justify the relation between greenhouse gas centric air pollutants and climatic variables considering a concise period. The present work has intended to explore the trend of air quality parameters, and air quality induced risk state since pre to during the lockdown period in reference to India and justifies the influence of pollutant parameters on climatic variables. Results showed that after implementation of lockdown, about 70% area experienced air quality improvement during the lockdown. The hazardous area was reduced from 7.52% to 5.17%. The spatial association between air quality components and climatic variables were not found very strong in all the cases. Still, statistically, a significant relation was observed in the case of surface pressure and moisture. From this, it can be stated that pollutant components can control the climatic components. This study recommends that pollution source management could be a partially good step for bringing climatic resilience of a region.

Air quality around schools: Part I - A comprehensive literature review across high-income countries

Children are particularly vulnerable to the detrimental health impacts of poor air quality. In the UK, recent initiatives at local council level have focussed on mitigating children's air pollution exposure at school. However, an overview of the available evidence on concentration and exposure in school environments - and a summary of key knowledge gaps - has so far been lacking. To address this, we conducted a review bringing together recent academic and grey literature, relating to air quality in outdoor school environments - including playgrounds, drop-off zones, and the school commute - across high-income countries. We aimed to critically assess, synthesise, and categorise the available literature, to produce recommendations on future research and mitigating actions. Our searches initially identified 883 articles of interest, which were filtered down in screening and appraisal to a final total of 100 for inclusion. Many of the included studies focussed on nitrogen dioxide (NO₂), and particulate matter (PM) in both the coarse and fine fractions, around schools across a range of countries. Some studies also observed ozone (O₃) and volatile organic compounds (VOCs) outside schools. Our review identified evidence that children can encounter pollution peaks on the school journey, at school gates, and in school playgrounds; that nearby traffic is a key determinant of concentrations outside schools; and that factors relating to planning and urban design - such as the type of playground paving, and amount of surrounding green space - can influence school site concentrations. The review also outlines evidence gaps that can be targeted in future research. These include the need for more personal monitoring studies that distinguish between the exposure that takes place indoors and outdoors at school, and a need for a greater number of studies that conduct before-after evaluation of local interventions designed to mitigate children's exposure, such as green barriers and road closures. Finally, our review also proposes some tangible recommendations for policymakers and local leaders. The creation of clean air zones around schools; greening of school grounds; careful selection of new school sites; promotion of active travel to and from school; avoidance of major roads on the school commute; and scheduling of outdoor learning and play away from peak traffic hours, are all advocated by the evidence collated in this review.

Evaluation of factors influencing road dust loadings in a Latin American urban center

Vehicle non-exhaust emissions are a major component of particle matter, including the direct wear of tires, brakes, road, and the resuspension of deposited particles. It is suggested that resuspended PM (RPM) emissions can be at the same magnitude or even larger than combustion emissions in urban centers. Factors affecting RPM can be included in four categories: road characteristics, traffic condition, land use, and meteorology. In order to study and evaluate these influencing factors, road dust less than 10 micrometers (RD10) was collected in 41 sites across Bogotá. The sampling points had diverse characteristics. RD10 levels varied between 1.0 and 45.8 mg/m² with an average of 8.9 ± 8.4 mg/m². Lower RD10 values were observed when vegetation density was high, pavement condition good, driving speeds fast and construction activities absent. On the contrary, RD10 increased under heavy-duty traffic influence and dry conditions. Among dust mitigation measures, management of land-use variables could be as important as traffic control and road maintenance. Implications: This study documented for the first time in Latin America dust loadings less than 10 micrometers, information that can be used to estimate resuspended particle matter emissions in the region. The influence of meteorology, traffic characteristics, road condition, and land-use variables was analyzed and quantified. The management of land-use variables could be as important as traffic control and road maintenance for road dust mitigation. Further research interests are discussed.

Assessment of the ability of roadside vegetation to remove particulate matter from the urban air

The development of urbanised areas together with the growing transport infrastructure and traffic volume are the main cause of air quality deterioration due to the increasing concentrations of particulate matter. Dust pollution is a threat to human health. It can cause the development of lung, larynx or circulatory system cancer. Due to the ability to accumulate dust particles on the leaf surface, the contribution of trees in the process of phytoremediation of air pollution has started to be appreciated. An analysis of the elemental composition of particulate matter (PM) stored on the leaves surface was also carried out, which showed high average concentration of: C > O > Si > Fe (above 8wt.%). It was also observed single particles with a high concentration of heavy metals: Ti, Mn, Ba, Zn, Cr, Pb, Sn, Ni and REE (rare earth elements). The major origin of PM are vehicular emissions, soil and re-suspended road dust. This paper presents also a comparison of selected tree, shrub and vine species differing in their ability to accumulate particulate matter. It was experimentally determined the average leaf surface of individual plant species and established the amount of particulate matter with aerodynamic diameter between 10 and 100 μm, 2.5 and 10 μm, and 0.2 and 2.5 μm deposited on the leaf surface and in waxes. Some species of vines (Parthenocissus quinquefolia), shrubs (Forsythia x intermediata) and coniferous trees, such as Betula pendula 'Youngii', Quercus rubra, Cratageus monogyna, Acer pseduoplatanus, Tilia cordata Mill. or Platanus orientalis turned out to be the most efficient in the process of phylloremediation.

Particulate matter concentrations and fluxes within an urban park in Naples

Airborne particulate matter can represent a serious issue for human health, especially in densely populated urban areas. Moreover, the inhalation of particulate can be more harmful with decreasing particles diameter. Vegetation can provide many ecosystem services to the citizens, including the removal of many different pollutants in the air, but while the effect on many gaseous compounds has already been widely proved, the capability of particulate matter (PM) sequestration driven by vegetation and its resulting benefit on air quality has not been deeply investigated yet at larger spatial scale, especially in Mediterranean environment. This study was conducted in the Real Bosco di Capodimonte, a green area of about 125 ha located inside the urban area of Naples (Italy) containing different species typical of the Mediterranean forest ecosystem. To better understand the interaction between PM and the park area, we measured fluxes of PM₁₀, PM_2.5 and PM₁ with a fast acquisition analyser, according to the Eddy Covariance technique. We found that the particle deposition was higher during the central hours of the day and it was more evident for smaller size particles. Furthermore, the daily PM fluxes found accorded with evapotranspiration and carbon sequestration operated by plants, suggesting a possible active role of vegetation on the particulate deposition.

Automobile exhaust particles retention capacity assessment of two common garden plants in different seasons in the Yangtze River Delta using open-top chambers

Particulate matter (PM) pollution is a serious environmental problem in most of the cities in the Yangtze River Delta region. Plants can effectively filter ambient air by adsorbing PM. However, only a few studies have paid attention to the dynamic changes and seasonal differences in particle retention capacities of plants under long-term pollution. In this study, we investigated the dynamic changes in particle retention capabilities of the evergreen, broad-leaved, greening plants-Euonymus japonicus var. aurea-marginatus and Pittosporum tobira-in spring and summer. We employed an open-top chamber to simulate the severity of the tail gas pollution. The results showed that, both the plants reached a saturated state in 18-21 days, under continuous exposure to pollution (daily concentration of PM_2.5: 214.64 ± 321.33 μg·cm^-3). This was 6-8 days longer than that in the field experiments. In spring, the maximum retention of total particulate matter per unit leaf area of E. japonicus var. aurea-marginatus and P. tobira was 188.47 ± 3.72 μg cm^-2 (18 days) and 67.63 ± 2.86 μg cm^-2 (21 days), respectively. In summer, E. japonicus var. aurea-marginatus and P. tobira reached the maximum retention of the particle on the 21st day, with a net increase of 94.10 ± 3.77 μg cm^-2 and 27.81 ± 3.57 μg cm^-2, respectively. Irrespective of season, the particle retention capacity of E. japonicus var. aurea-marginatus was higher than that of P. tobira, and it showed a better effect on reducing the concentration of fine particles in the atmosphere. The particle retention of the two plants was higher in spring than that in summer. E. japonicus var. aurea-marginatus displayed a significant difference in particle retention between the seasons, while P. tobira did not show much difference. These results will provide a foundation for future studies on the dynamic changes and mechanism of particle retention in plants and management practices by employing plants for particle retention in severely polluted areas.

Evaluation and sensitivity analysis of the ecosystem service functions of haze absorption by green space based on its quality in China

Evaluation of the ecosystem service functions of haze absorption by green space is important for controlling haze. In this study, the ecosystem service functions of haze absorption by green space in China in 2001, 2004, 2007, 2010, 2013, 2016 and 2018 are analyzed based on green space quality and sensitivity using a geographic information system (GIS) and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. The results showed that the benchmark ecosystem service functions of haze absorption by green space when considering only the area of green space showed a trend that increases first and then decreases in 2001–2018, with 9000458.55 million Kg, 9145110.75 million Kg and 7734526.75 million Kg in 2001, 2013 and 2018, respectively. However, the corrected functions based on green space quality were 7724215.34 million Kg, 8320301.79 million Kg and 6510132.55 million Kg in the corresponding years. This indicated large differences between ecosystem service functions of haze absorption based on the quality and area of green space; only considering the area of green space to evaluate ecosystem service functions will result in overestimation. In terms of the spatial distribution of the ecosystem service functions of haze absorption by green space, there were greater differences in the benchmark and corrected functions, and the spatial distributions of the maximum, intermediate and minimum ecosystem service functions were notably different. However, the benchmark and corrected functions all showed a consistent trend in the rank of their contribution rates and ecosystem service functions as well as consistent distribution trends: the spatial distribution of ecosystem service functions of haze absorption by green space was very different in the same year, but there was little difference among different years. The change coefficients for the ecosystem service functions of haze absorption by arable land and grass land remained stable, whereas the coefficient of sensitivity for forest cover was elastic. Patch density (PD) and the ecosystem service functions of SO2 absorption, NOx absorption, dust retention and total ecosystem services showed a significant negative correlation, with correlation coefficients of -0.407, -0.511, -.330 and -0.332, respectively. In contrast, the area-weighted mean shape index (SAPE_AM) and ecosystem service functions exhibited significant positive relationships with correlation coefficients of 0.650, 0.634, 0.568 and 0.570, respectively. The results provide an improved method for evaluating the ecosystem service functions of haze absorption by green space as well as a reference for the prevention and control of haze and the coordinated development of regional societies, the economy and the environment.

Spatiotemporal variations and influencing factors of PM2.5 concentrations in Beijing, China

Fine particulate matter (PM_2.5) pollution has become a worldwide environmental concern because of its adverse impacts on human health. This study aimed to explore the spatiotemporal variations and influencing factors of PM_2.5 concentrations in Beijing during the 2013-2018 period, and further analyzed the impacts of environmental protection policies implemented in recent years. Notably, this study employed various statistical methods, i.e., ordinary Kriging interpolation, spatial autocorrelation analysis, time-series analysis and the Bonferroni test, to evaluate the regional and seasonal differences of PM_2.5 concentrations based on long-term monitoring data. The results illustrated that PM_2.5 concentrations decreased on a yearly basis, demonstrating that air pollution control policies have achieved initial success. Furthermore, PM_2.5 concentrations were higher in the winter and in the southern regions. Diurnal variation presented a bimodal distribution, which varied slightly with the season. Relative humidity and wind speed were the principal meteorological factors affecting the distribution of PM_2.5 concentrations, while precipitation had essentially no effect. A high positive correlation between PM_2.5 and gaseous pollutants (SO₂, NO₂, and CO) indirectly reflected the contribution of automobile exhaust and coal-fired emissions. Generally, PM_2.5 concentrations demonstrated strong spatiotemporal variations, and meteorological factors and pollutant emissions played an important role in this.

Urban Vegetation in Air Quality Management: A Review and Policy Framework

Recent episodes of high air pollution concentration levels in many Polish cities indicate the urgent need for policy change and for the integration of various aspects of urban development into a common platform for local air quality management. In this article, the focus was placed on the prospects of improving urban air quality through proper design and protection of vegetation systems within local spatial planning strategies. Recent studies regarding the mitigation of air pollution by urban greenery due to deposition and aerodynamic effects were reviewed, with special attention given to the design guidelines resulting from these studies and their applicability in the process of urban planning. The conclusions drawn from the review were used to conduct three case studies: in Gdańsk, Warsaw, and Poznań, Poland. The existing local urban planning regulations for the management of urban greenery were critically evaluated in relation to the findings of the review. The results indicate that the current knowledge regarding the improvement of urban air quality by vegetation is not applied in the process of urban planning to a sufficient degree. Some recommendations for alternative provisions were discussed.

Vertical and Horizontal Profiles of Particulate Matter and Black Carbon Near Elevated Highways Based on Unmanned Aerial Vehicle Monitoring

Highways passing through cities cause additional pollution inside the city. However, most of the current studies are using ground-based monitoring technologies, which make it difficult to capture the dispersion patterns of pollutants near elevated highways or transportation interchanges. The purpose of this study is to discover short-term three-dimensional variations in traffic-related pollutants based on unmanned aerial vehicles. The monitoring locations are at suburban elevated highway and transportation interchanges. The monitoring parameters include the particle number concentration (PN), particle mass concentration (PM), and black carbon (BC). The vertical profiles showed that most air pollutants increased significantly with the height of the elevated highways. Compared with the ground level, PNs increased by 54%–248% and BC increased by 201%. The decline rate of particle concentrations decreased with the increase of height and remained stable after 120 m. Furthermore, the R2 heatmap for regressions between each altitude showed that the linear relationship between 0–120 m was higher than that of other altitudes. In horizontal profiles, PNs spread to 100 m and then began to decline, BC began to decay rapidly after 50 m, but PMs varied less. After crossing another highway, PNs increased by 69–289%, PMs by 7–28%, and BC by 101%. Furthermore, the formation of new particles was observed at both locations as PN3 increased with distance within 100 m from the highway. This paper fills in the void of three-dimensional in situ monitoring near elevated highways, and can help develop and refine a three-dimensional traffic-related air pollution dispersion model and assess the impacts of transportation facilities on the urban environment.

Greenness around schools associated with lower risk of hypertension among children: Findings from the Seven Northeastern Cities Study in China

Evidence suggests that residential greenness may be protective of high blood pressure, but there is scarcity of evidence on the associations between greenness around schools and blood pressure among children. We aimed to investigate this association in China. Our study included 9354 children from 62 schools in the Seven Northeastern Cities Study. Greenness around each child's school was measured by NDVI (Normalized Difference Vegetation Index) and SAVI (Soil-Adjusted Vegetation Index). Particulate matter ≤ 1 μm (PM₁) concentrations were estimated by spatiotemporal models and nitrogen dioxide (NO₂) concentrations were collected from air monitoring stations. Associations between greenness and blood pressure were determined by generalized linear and logistic mixed-effect models. Mediation by air pollution was assessed using mediation analysis. Higher greenness was consistently associated with lower blood pressure. An increase of 0.1 in NDVI corresponded to a reduction in SBP of 1.39 mmHg (95% CI: 1.86, -0.93) and lower odds of hypertension (OR = 0.76, 95% CI: 0.69, 0.82). Stronger associations were observed in children with higher BMI. Ambient PM₁ and NO₂ mediated 33.0% and 10.9% of the association between greenness and SBP, respectively. In summary, greater greenness near schools had a beneficial effect on blood pressure, particularly in overweight or obese children in China. The associations might be partially mediated by air pollution. These results might have implications for policy makers to incorporate more green space for both aesthetic and health benefits.