Studies On Adsorbing Mechanisms And Reduction Effect Of Urban Green Space On Atmospheric Particulate Matter In Shenyang City

The advancement of urbanization and the continuous growth in car ownership increase the atmospheric particulate matter content in the atmosphere and bring great harm to human health.Aiming at the air quality problem in Shenyang,this study takes roadside green belts,university campus green spaces,and park green spaces as the research objects.By investigating the atmospheric particulate matter data at the automatic monitoring points of city ambient air in Shenyang,selecting representative sample plots to actually set the monitoring points,and involving a total of 23 species of trees and 52 plant communities,setting up 126 monitoring points,on-site monitoring about 17,000 sets of data,it analyzes the pattern of changes of atmospheric particulate matter in Shenyang city and the influence of traffic flow on it;by observing the leaf ultrastructure characteristics,it explores the absorption mechanism of leaf ultrastructure on atmospheric particulate matter,in order to select tree species effective for absorbing atmospheric particulate matter;by analyzing the reduction effects of different types of green space,plant communities,and roadside green belts on the horizontal and vertical scales on atmospheric particulate matter,it determines the appropriate green belt width and effective height;by monitoring the concentration of atmospheric particulate matter at different distances inside and outside the park green space,it determines the range of impact of the park green space on the reduction of atmospheric particulate matter around the city.This study provides scientific basis and guidance for choosing tree species scientifically,planning urban green space types and green space scales reasonably,realizing the systematic and scientific layout of urban green spaces,and pursuing eco-saving and sustainable design philosophy and technology.The main research results are as follows:1.The annual and daily changes of PM₁₀ and PM_2.5 concentrations in Shenyang show a double-peak curve and a single-valley curve,respectively.The highest values of the year appear in March,being 90.65μg/m³ and 60.94μg/m³ respectively,and the lowest values of the year appear in August,being 37.94μg/m³and 18.00μg/m³ respectively;with the advent of autumn and winter,the concentration of atmospheric particulate matter continues to rise,and a second peak appears in November.The concentration of atmospheric particulate matter is stable from night to 9:00,the valley appears at 12:00-18:00 in the day,and the lowest value of the day is around 16:00.ΔPM₁₀ andΔPM_2.5 in Shenyang are significantly related to the traffic flow.The difference between the effects of the traffic flow between 186-300 vehicles/5 min and301-450 vehicles/5 min on theΔPM₁₀ concentration is not significant.When the traffic flow reaches451-819/5 min,the concentration ofΔPM₁₀ andΔPM_2.5 increases significantly,and the increase in traffic flow contributes more toΔPM_2.5 than toΔPM₁₀.In addition,as the distance to the green space is different,the effects of traffic flow on air quality differ.2.Different tree leaves have different absorbing effects of particulate matter due to the ultrastructure of leaf hairs,papillae,stomata and folds.Observation and analysis of the leaf surface ultrastructure of 23kinds of trees in Shenyang show that the length and density of leaf hairs,the perimeter and density of the papillary structure,the area and density of stomata,the width and the concavities and convexities ratio of grooves by first and second folds are the main factors that determine the particulate matter absorbing effect.The order of leaf surface ultrastructure that affects the retention ability of tree species is first-level folds,second-level folds,stomata and leaf hairs.Leaf hairs and first-level folds absorb atmospheric particulate matter with a maximum of 148.71μm;Papillary structure,stomata,and second-level folds absorb atmospheric inhalable particulate matter（≤10μm）with a minimum of 1μm.The recommended coniferous trees in favorable order according to the absorbing effect of atmospheric particulate matter are:Pinus tabuliformis Carr.;Broadleaf trees:Rhus typhina Nutt,Robinia pseudoacacia L.,Gleditsia sinensis Lam.,Acer mono Maxim,Populus alba’Berolinensis’L.,Fraxinus mandshurica Rupr,Salix babylonica L.,etc.;Broadleaf shrubs:Amygdalus triloba（Lindl.）Ricker,Lonicera maackii（Rupr.）Maxim.,Syringa microphylla Diels,Syringa oblata Lindl.,Ligustrum obtusifolium Sieb.,Forsythia mandschurica Uyeki.The recommended coniferous trees in favorable order according to the absorbing effect of atmospheric inhalable particulate matter are:Sabina chinensis（L.）Ant.,Pinus tabuliformis Carr.;Broadleaf trees:Acer negundo‘Aurea’,Fraxinus chinensis subsp.Rhynchophylla（Hance）E.Murray,Fraxinus mandshurica Rupr.,Acer mono Maxim,Rhus typhina Nutt,Euonymus maackii Rupr.,Prunus cerasifera Ehrh.,Robinia pseudoacacia Linn.,etc;Broadleaf shrubs:Ligustrum obtusifolium Sieb.,Syringa microphylla Diels,Syringa oblata Lindl.,Forsythia mandschurica Uyeki,Amygdalus triloba（Lindl.）Ricker,etc.3.The three different types of green spaces:roadside green belt,university campus green space,and park green space have different reduction effects.Different tree species in roadside green belt have different effects on reducing particulate matter,the reduction effect in roadside green belt of Pinus tabuliformis Carr.on the atmospheric particulate matter is better than that of the mixed forest.In university campus green space and park green space,there is no significant difference in the reduction of atmospheric particulate matter regardless of plant species,community type and location.The reduction effect of plant communities on atmospheric particulate matter is closely related to environmental factors.Relative humidity affects the reduction effect of the community on atmospheric particulate matter,the roadside green belt adjacent to the river does not have significant reduction effect.There is a significant positive correlation between atmospheric particulate matter concentration and relative humidity in the three types of green spaces,and there is a significant negative correlation between atmospheric particulate matter concentration and wind speed in the three types of green spaces.There is no significant relationship between the concentration of atmospheric particulate matter and temperature in the roadside green belt,and there is a significant negative correlation between atmospheric particulate matter and temperature in university campuses and park green spaces.4.Different tree species on the roadside green belt have different widths of effective reduction on the atmospheric particulate matter.That of Populus alba’Berolinensis’L.is 20 m,that of Sabina chinensis（L.）Ant.and Pinus tabuliformis Carr.is 10 m,and when it exceeds these ranges,the concentration and reduction efficiency of atmospheric particulate matter are roughly stable.The optimal height of Pinus tabuliformis Carr.to reduce atmospheric particulate matter is 3 m.The best effect of reducing atmospheric particulate matter in the three forest belts is Sabina chinensis（L.）Ant.Thus,Sabina chinensis（L.）Ant.can be used as the preferred tree species for the roadside green belt.The width of the roadside green belt is10 m for coniferous trees and 20 m for broad-leaved trees,which can reach the effect of significantly reducing atmospheric particulate matter.The traffic flow at the location of the forest belt is the main factor affecting the reduction efficiency of the atmospheric particulate matter,followed by the leaf area index.The reduction effect of forest belts on large-sized particles is better than that of small-sized particles.When there is no difference in traffic flow,coniferous forest（Sabina chinensis（L.）Ant.）has a better reduction effect than broad-leaved forest（Populus alba’Berolinensis’L.）.5.Park green spaces have a reducing effect on the concentration of atmospheric particulate matter in the surrounding urban areas.The effective impact range of Beiling Park and Wanquan Park on the reduction of atmospheric particulate matter around the urban area is 0-200 m from the park.After more than 200 m,the concentration and increase efficiency of atmospheric particulate matter remain flat.Therefore,it is recommended to establish a park or street green space every 400m to achieve the effect of using urban green spaces to reduce atmospheric particulate matter in the surrounding urban areas,and to improve the air quality of the entire city.The reduction effect of park green space on the concentration of atmospheric particulate matter around the urban area has a significant positive correlation with the park area and the ratio of terrestrial green space;it has a significant negative correlation with the park’s blue-green ratio and the traffic flow.