Inappropriate planting patterns can increase pollutant concentrations and threaten human health. This study examined three greening patterns (trees, trees + hedges, and hedges) using the ENVI-met model to evaluate the different effects of various planting patterns on PM2.5 dispersion within an idealized 3D street canyon under three typical wind directions. Results showed that street greenbelts alter the PM2.5 concentration field within canyons, and the horizontal and vertical distribution characteristics of PM2.5 under different wind directions were significantly different. The arbor-hedge vegetation structure showed the highest total vegetation deposition amount due to larger canopy volumes while hedges have better deposition amounts per unit volume due to their proximity to emission sources. Additionally, this research selected the averaged relative difference in PM2.5 concentration (ARDC) indicator to assess the influence of different green scenarios on the dispersion of PM2.5 concentrations. Wind direction and planting patterns jointly affect the dispersion of PM2.5 in canyons, and the ARDC varied from -4.39 % to 105.36 %. Unilateral-trees on the windward side or two rows of hedges may be the optimal vegetation layout by trade-off with other services. ARDC was significantly correlated (p < 0.01) with most of the 3D green indicators. These results could provide effective suggestions for optimizing the layout of greenbelts in street canyons to improve air quality.

Syringa oblata is an important garden plant whose leaf colour turns from green to red in autumn when air temperature and daylength decrease. This study explored the reasons for leaf reddening by detecting phenotypic characteristics and pigment types and contents. With leaf reddening, luminance L * increased and chrominance a * decreased significantly. Chlorophyll and carotenoid contents significantly decreased in accordance with the distribution change of green pigment in leaf cells. Conversely, the red pigment distribution increased and the total polyphenol, total flavonoid and total anthocyanin contents evidently increased. Anthocyanin accumulation was the important reason for leaf reddening. Of the anthocyanins detected in leaves, cyanidin and delphinidin-3- O-rutinoside contents gradually increased with leaf reddening and were negatively correlated with L * . They were considered key anthocyanins influencing leaf colour. Apigenin and syringic acid were correlated with delphinidin-3- O-rutinoside and cyanidin, and they could be the anthocyanin copigments. Cyanidin-3- O-arabinoside and taxifolin were more abundant polyphenols in leaves. In summary, anthocyanin accumulation and chlorophyll degradation occurred along with leaf reddening. Temperature, light, and other co-pigments influenced the anthocyanin and chlorophyll contents. This study provides evidence for applications of S. oblata as a coloured-leaf plant in gardens and as a source of active ingredients in the commercial market.

Syringa oblata (So) and its variety S. oblata var. alba (Soa) are famous flowering shrubs with high ornamental value due to their beautiful inflorescence. The flower colors of So (purple) and Soa (white) differ significantly. In this study, pigment contents were detected and flavonoid and anthocyanin metabolites were determined by UPLC-ESI-MS/MS methods. Combined with transcriptome analysis, the key genes related to anthocyanin accumulation were obtained to explore the reasons for the difference in flower colors. The results showed that the total anthocyanin content was obviously higher in So than in Soa. The differential metabolites annotated in anthocyanin biosynthesis were significantly up-regulated, and conversely, the differential metabolites in biosynthesis of secondary metabolites and flavone and flavonol biosynthesis were down-regulated in So compared by Soa, with similar results revealed by the analysis of the top 20 fold change metabolites. It is explained that the anthocyanins and chlorophylls were the key pigment for the difference in flower color between So and Soa. Furthermore, the quantitative analysis of anthocyanins showed that delphinidin-3-O-rutino- O-rutino- side and cyanidin-3-O-rutinoside O-rutinoside were the major anthocyanins in So, and their contents were significantly higher than other anthocyanins. However, the levels of major anthocyanins in Soa were very low, resulting in its white flower. In addition, high levels of kaempferol-3-O-rutinoside, O-rutinoside, rutin, quercetin-3-O-glucoside O-glucoside and naringenin were detected in flowers. These metabolites could play the roles of co-pigments in So and major pigments in Soa, respectively. Cyanidin-3-O-rutinoside O-rutinoside were markedly elevated from initial flower bud (IFB) to flower bud (FB), which contributed to the anthocyanin accumulation and the flower color change in So, while the reduction of chlorophyll content was the main reason for the change in flower color from green to white in Soa. The integrated analysis showed that the genes ( F3GT, FLS and F3H) ) might play the key roles in flower color formation. The study revealed the reason for the flower color variation between So and Soa and the flower color change during the development. It will provide the metabolites fundamental for research on flower color breeding in Syringa. .

Increasing heat stress in urban environments due to climate change has a significant adverse impact on human work and daily life. Street canyons as the main component of the underlying surface of the city and the main place of residents’ activities, a comprehensive understanding of street morphology and tree planting practices can help to improve thermal comfort. Based on survey data and field experiments, this study designed 30 scenarios and employed ENVI-met model (version 5.0.3) to quantify the effect of street aspect ratio (H/W: H is building height and W is street width) and tree spacing (TS) on pedestrian thermal comfort in two differently oriented streets (north–south and east–west) in Taiyuan, China. Results showed that H/W ratio and TS significantly influenced the street thermal comfort mainly owing to shading. H/W ratio played a pivotal role in reducing mean radiant temperature (Tmrt) and physiological equivalent temperature (PET), and was negatively correlated with Tmrt and PET. Compared to no-tree scenarios, street trees significantly improved thermal comfort (mean reductions of Tmrt and PET were 12.74℃ and 5.66℃, respectively), and PET and Tmrt were significantly negatively correlated with TS. The improvement effect of street trees on Tmrt and PET in east–west oriented street was better than north–south oriented street. H/W = 1.0 and TS = 6 m appeared as the proposed combination to mitigate the summer thermal comfort in the temperate monsoon climate zone. These quantitative results provide new insights into renewal and design strategies for future urban planning.

When developing strategies aimed at mitigating air pollution in densely populated urban areas, it is vital to accurately investigate the vertical distribution of airborne particulate matter (PM) and its primary influencing factors. For this study, field experiments were conducted to quantify the vertical distribution and dispersion processes of PM at five vertical heights related to trees—including at street level near vehicular emission sources (0.3 m), pedestrian breathing height (1.5 m), beneath the canopy (6 m), mid-canopy (9 m), and the top of the canopy (12 m)—within a street-facing building in Wuhan, China. Comparing the vertical dispersion patterns of PM with six particle sizes (PM1, PM2.5, PM4, PM7, PM10, and total suspended particulates—TSPs), larger particles exhibited more pronounced variations with height, notably TSPs (correlation coefficient of −0.95) and PM10 (−0.84). The findings consistently revealed a downward trend in PM concentrations across various particle sizes with increasing height, indicating a negative linear correlation between particle concentrations and altitude within the street canyon. For every 1% increase in vertical height, the PM2.5 concentration decreased by approximately 5.44%, the PM10 concentration decreased by 132.1%, and the TSP concentration decreased by 180.6%. These findings show potential for guiding building designers in developing effective strategies, such as optimal vent placement, in order to mitigate the intrusion of outdoor air pollution—particularly PM2.5—into indoor environments. Furthermore, this research provides novel insights for residents living in street-facing buildings and individuals with respiratory diseases, aiding them in the selection of residential floors to minimize health risks associated with exposure to respirable PM.

Time-varying characteristics of particulate matter (PM) pollution play a crucial role in shaping atmospheric dynamics, which impact the health and welfare of urban commuters. Previously published studies on the diurnal patterns of PMs are not consistent, especially in the context of field experiments in central China, and most field studies have only focused on particles with a single particle size. This study conducted regional-scale studies across 72 street canyon sets in Wuhan, China, investigated diurnal and seasonal PM concentration variations while also evaluating various PM size and the key driving factors. During summer (July, August, and September), evergreen tree-lined street canyons maintained a stable linear trend for smaller dp particulates (i.e., PM1, PM2.5, and PM4), while deciduous street canyons exhibited a bimodal distribution. In winter (January and February), fine particulates (i.e., PM1 and PM2.5) remained a linear trend in evergreen street canyons, while deciduous street canyons show a slightly wavy fluctuating pattern. Meanwhile, it exhibited quadrimodal-peak and triple-trough patterns in both PM7, PM10, and TSP concentrations. The lowest PM concentrations were observed between 14:00 and 16:00 for all particle sizes, with decreased summer pollution (7.81% lower in PM2.5, 53.47% lower in PM10, and 50.3% lower in TSP) noted in our seasonal analysis. Among the various meteorological factors, relative humidity (RH) was identified as the dominant influencing PM factor in both summer and winter. Results from this study will help us better understand field-based air pollutant dispersion processes within pedestrian spaces while laying the groundwork for future research into street PM experiments.

It is of great practical significance to identify service blind area, scientifically select park construction areas, and clarify the priority of parks' construction based on the co-ordination of supply-demand evaluation. With the urban parks within the Taiyuan Ring Expressway as the research subjects, we estimated the accessibility range and the service pressure of each park by using the application programming interface of Gaode map route planning and point of interest data to characterize their supply and demand levels. We identified the service blind areas of parks by overlay analysis, and used the location-allocation (LA) model to purposefully supply park green space. Results showed that the accessibility coverage rates of the parks by walking and bicycling within 15 minutes were 35.6% and 71.7%, respectively, indicating insufficient supply capacity of parks. The areas with large potential demand for park green space in Taiyuan were mainly concentrated in the business district of Qinxian-Changfeng Street and the Shuangta business district within Dongzhong ring road, which existed the obviously invisible blind areas. Finally, we proposed new park green space site selection proposal based on LA model. Optimization results indicated that the coverage rates of walking and bicycling within 15 minutes increased to 46.7% and 81.0%, respectively, and that the service pressure of parks was relieved. We combined the leisure demands of urban residents and the distribution of urban parks by utilizing network big data, which could promote the scientific nature and accuracy of the optimizing site selection and provide scientific method and theory basis for urban park construction.

街道峡谷(街谷)绿化是我国城市绿地系统的重要组成部分,在大气污染物控制方面具有非常重要的作用.植物类型、配置模式和结构特征会显著影响街谷中颗粒物的吸附、沉降和扩散等过程,直接而显著地影响着行人健康.街谷绿化优化设计已成为多学科领域的研究热点.本文总结了街谷绿化特征参数,探讨了街谷绿化调控颗粒物扩散的研究方法和机制,分析了街谷绿化对颗粒物扩散的影响效果及相关影响因素(街谷形态、街谷走向、屋顶形式、天空可视率、气象因素和排放强度),并从街谷绿化参数化、多因素耦合、多尺度研究、权衡多种生态服务功能等方面提出了未来需进一步开展的研究工作,以期为改善街谷空气质量和城市街谷绿化建设提供理论依据.

More evidence has shown that exposure to particulate matter (PMs) within urban streets increases adverse health risks, and vegetation barriers have the potential to improve near-road air quality. To gain insight into the influences of vegetation barrier characteristics on the dispersion of PMs (TSP, PM10, PM2.5), field measurements were performed in Wuhan, China. Twenty-four sample belts were selected within oblique wind canyons, on road and roadside TSP, PM10 and PM2.5 concentration were simultaneously monitored in steady periods. Layer shelterbelt porosity was used to represent the vertical configurations of the vegetation barriers. The result indicated that vegetation combination of trees, shrubs, and herbs is effective for reducing the concentration of PMs. Vegetation barriers can reduce TSP and PM10 concentrations to a certain level (5 similar to 23 %) in the areas behind vegetation barriers compared to the control within oblique wind canyons. In contrast, the reduction effect of the vegetation barrier on PM2.5 could be positive or negative was inconsistent. Pearson correlation analysis results indicated that TSP and PM10 reduction efficiencies were negatively correlated with shelterbelt porosity in the 0 similar to 2 m height section, but the vegetation barrier indicators had no obvious effects on the reduction efficiency of PM2.5. To improve roadside air quality, the use of shrubs or hedges with heights lower than 2 m should be encouraged, and large, dense trees should be avoided around roads with heavy traffic. These results provide insight on how to improve roadside air quality by mitigating PM pollution in urban street canyons.

Changes in vegetation traits influence the particulate pollution mitigating effects of trees in street canyons; however, it remains unclear whether tree canopy density (i.e. the proportion of the street floor covered by the vertical projection of the tree canopy) promotes or reduces this effect. A 12-day field experiment was conducted in four representative street canyons to examine the mitigating effects of street trees on particulate matter (PM) for PM1, PM2.5, PM4, PM7, PM10, and total suspended particles (TSP) among four canopy density treatments, including (1) open spaces and areas with (2) sparse (<= 35%), (3) medium (35-70%) and (4) dense (>= 70%) canopy densities. The results showed that canopy density is the dominant vegetation trait that affects PM dispersion, with peak decreases occurring at a canopy density of similar to 30%. The particulate matter attenuation coefficient (PMAC) indicates the PM reduction capability of trees. The PMAC of each particle size class correlated negatively with canopy density and TSP (<100 mu m) showed the greatest attenuation. In relation to open space treatment, a canopy density range 30-36% showed the largest reductions in the PM10 and TSP concentrations of 26.75% and 27.49%, respectively. And for the PM2.5 concentration, a canopy density range 24-36% exhibited the largest reduction (7.44%). It was also concluded that sparse canopy density is optimal for trees in areas with high PM concentration. Medium canopy density also promotes pollutant dispersion (especially PM2.5), while dense canopy density causes air quality deterioration. This study will provide new insights into the response of atmospheric PM spatial dispersion to the characteristics of tree cover in street canyons, as well as the regulation mechanism of this response. By investigating this issue under different scenarios, this study aims to contribute to the quantitative tree planting design in urban planning.

交通污染已成为城市空气颗粒物污染的主要来源之一,对居民的生活、工作、出行产生了严重影响,而绿化隔离带可作为优化非机动车道和人行道空气质量的一种有效且经济地措施.基于实验测定评价道路绿化隔离带对非机动车道空气颗粒物浓度的影响,并提出分层疏透度来表征样带垂直结构特征,分析绿化隔离带配置方式对街道空气颗粒物浓度的影响.研究结果显示,绿化隔离带可较好地改善街道空气质量,对TSP和PM10的消减效果较PM2.5好;颗粒物的消减效果与样带的植物配置结构有紧密联系,分析结果显示颗粒物消减效率均与0～2m高度区间内的疏透度呈显著负相关.在交通流量较大的城市干道上,应该减少或者避免使用冠大荫浓的高大乔木,多配置结构紧密和叶密度较大的灌木植物.本研究结果可为城市道路绿化参数化设计和优化提供理论支撑,为改善人居生活环境作出贡献.

[Objectives] T his study aimed to illuminate the influence of different pollution levels and leaf locations on the accumulation ability of particulate matter (PM ) of C .camp hora trees ,and to provide scientific support for air-purif-ying plants selection .[M ethods]C .camp hora was selected as research materials ,and samples were collected from three different geographic sites w here plants suffered from different pollution levels and three different places of each leaf sample.T he number of particulate matter at different sizes were calculated and the micro-structure of plant leaves were observed with the Scanning Electron M icroscope (SEM ) and Image J software .[Results ] A significant difference in term of the PM numbers on the different leaf locations and different pollution areas was observed .PM number on the base vein of adaxial surface was significantly higher than those on both the apex of adaxial surface and w hole abaxial surface .T he particles of PM 2.5 was the major size of the adsorbed PM w hich were mainly gathered around cells and veins of C .camp horaleaves .T he amount of PM w hich were mainly concentrated around the stomaon the abaxial leave surface was increased with the increase of pollution levels .[Conclusion] Pollution level and leaf location can significant-ly influence the PM adsorption ability and PM were mainly adsorbed at the upper surface .

While vegetation in street canyons may improve air quality by removing pollutants, it may also worsen air quality by inhibiting street ventilation. In this study, the isolated effects of roadside greenbelts on footpath air quality were investigated by measuring the coarse particles (PM10) removal efficiency of roadside greenbelts with three different vegetation structures in different grade roads. Results indicated that the three kinds of greenbelts can improve footpath air quality to a certain degree (7-15%). Interestingly, the vegetation structure of shrubs and small trees (about 2-4.5 m in height) with small crown diameter shows the highest PM10 removal efficiency along major or heavy traffic roads. The stratified vegetation structure with trees, shrubs and grass is optimal for sub-arterial road or medium traffic roads as these plants can produce multiple ecological effects and create esthetic pleasant landscapes. For branch roads, a parallel tree stand can bring a cost-effective effect. Results of linear regression analysis and gray relational analysis (GRA) show that the removal percentage has significant negative correlation with the shelterbelt porosity (R-2 = 0.83), and relative humidity has a more significant effect (gamma = 0.68) on the PK removal percentage than temperature (gamma = 0.51) or wind speed (gamma = 0.63). (C) 2015 Elsevier GmbH. All rights reserved.

Plants not only improve air quality by adsorbing particulate matter (PM) on leaf surfaces but can also be affected by their accumulation. In this study, a field investigation was performed in Wuhan, China, into the relationship between seven leaf traits and the accumulation of three different sizes of PM (PM11, PM2.5 and PM0.2) on leaves. The retention abilities of plant leaves with respect to the three sizes of PM differed significantly at different sites and species. The average PM retention capabilities of plant leaves and specific leaf area (SLA) were significantly greater in a seriously polluted area, whereas the average values of chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll, carotenoid, pH and relative water content (RWC) were greater at the control site. SLA significantly positively correlated with the size of PM, but Chl a, Chl b, total chlorophyll, RWC significantly negatively correlated with the size of PM, whereas the pH did not correlate significantly with the the PM fractions. Additionally, SLA was found to be affected by large particles (PM11, p<0.01); PM2.5 had a more obvious effect on plant leaf traits than the other PM (p<0.05). Overall, the findings from this study provide useful information regarding the selection of plants to reduce atmospheric pollution.

园林植物具有显著消减空气颗粒物（PM）污染的作用,能有效地改善城市环境质量。但迄今为止,国内外的大量研究都集中在园林植物对总悬浮颗粒物（TSP）或者粗颗粒物（PM10）的阻滞效应上,植物吸附空气细颗粒物（PM2.5）的研究尚处于探索阶段。本文概述了植物叶片吸附空气PM的方式,叶片PM2.5化学物质的转移过程以及植物吸附PM2.5的周期性,探讨了植物叶片对空气不同粒径颗粒物的吸附特征,园林植物吸附空气PM2.5的能力与机制,并从植物吸附PM2.5的测定方法、园林植物吸附PM2.5能力的测定和评价、高吸附PM2.5能力的园林植物筛选、园林植物吸附PM2.5的机制与影响因素等方面提出了园林植物吸附PM2.5的研究重点与趋势,以期为深化植物吸附PM2.5的机制研究及高吸附PM2.5能力的园林植物筛选提供依据。