Effect Of Ecological Pressure On PM₁₀,PM_2.5 Reduction From Ambient Air By Urban Green Area

The urbanization process has changed the urban ecological environment,resource utilization and urban land use patterns.It causes a series of environmental problems and the urban environment is under continuous pressure.Urban green space plays an important role in reducing air PM₁₀,PM_2.5 and also subject to certain restrictions.In order to explore the effect of urban green space on reducing air PM₁₀,PM_2.5 under the comprehensive influence of multiple environmental pressure factors,this study takes the main urban area within the Third Ring Road of Wuhan as the research object,and uses remote sensing images and small-scale quantitative measurements to reveal the correlation between air PM₁₀,PM_2.5 and environmental factors.Based on pressure factors（land surface temperature,population density,impervious underlying surface area,water area,road density,building density,average building height）,the potential Environmental factors（normalized vegetation index,green area,and water area）and meteorological conditions（temperature,relative humidity,wind speed）to build an urban ecological environment pressure model under10 different the scales（60 m,90 m,150 m,300 m,450 m,600 m,900 m,1200 m,1500 m,3000 m）.This study defines the impact the key environmental factors and key scales of air PM₁₀,PM_2.5in different condition（green space underlying surface,street trees underlying surface,green space-street trees,green spaces-square（control）,street trees-square（control））.Based on quantitative analysis,provides a scientific theoretical basis for the multi-scale urban planning and design of urban public open space.The main findings are as follows:（1）Air PM₁₀,PM_2.5 concentrations of green space and the effect of green space reduction air PM₁₀,PM_2.5 are significantly correlated with urban environmental pressure.In winter when the background of air PM₁₀,PM_2.5 in high level,the urban environmental pressure has a significant impact on air PM₁₀,PM_2.5.In spring and summer,in the low-pressure area,the difference in air PM₁₀,PM_2.5 between the green space and the square（control point）is larger,indicating that the potential environmental factors（NDVI,GA,WA）in the low-pressure area play a role in reducing air PM₁₀,PM_2.5.（2）There is a spatial scale correlation between urban built environment factors and air PM₁₀,PM_2.5 in the study area within the range of 60-3000 m.The effect of green space on reducing air PM₁₀,PM_2.5 is also related to urban built environment factors.In spring,summer and winter,LST and RD are the key factors affecting the air PM₁₀.And LST,ISA,BH,NDVI,GA,WA are the key factors affecting the air PM_2.5.The key scale of environmental pressure factors（ISA,RD,BH,BD）affecting air PM_2.5 concentration is1500～3000m,and potential environmental factors（NDVI,GA,WA）affect air PM_2.5 is450～600m.In spring,the key scale of environmental pressure factors（LST,PD,ISA,BH）affecting the air PM_2.5 concentration is 450-600 m.（3）Single-variable and multi-variable urban environmental pressure models can explain the systematic effects of urban built environment factors on air PM₁₀,PM_2.5.The model variables that significantly affect the changes in air PM₁₀,PM_2.5 is different in each season.At the same time,there is an interaction between the model variables.The variables enter into the urban environmental pressure model can be considered as key factors.Regulate and control those factors at a specific scale can maximize the effect of green space on reducing air PM₁₀,PM_2.5.In summer,autumn and winter,environmental pressure factors and potential environmental factors affect the air PM₁₀,PM_2.5 of green space and street trees jointly.In spring and summer,environmental pressure factors and potential environmental factors affect the ability of green space in reducing air PM_2.5 jointly.The ability of green space in reducing air PM₁₀,PM_2.5 is mainly affected by environmental pressure factors in winter.（4）Based on the spatial scale correlation and the urban environmental pressure model,potential environmental factors have a greater effect on PM₁₀,PM_2.5 in the heavily polluted season.Improving the quality of green space in high-pressure areas is conducive to alleviating the internal local pollution problems in heavily polluted season.Besides,divide multi-scale control unit is conducive to alleviating the air PM₁₀,PM_2.5 pollution.In block scale（450～600m）,focus on regulating potential environmental factors（NDVI,GA,WA）.In main urban scale（1500～3000m）,focus on regulating environmental pressure factors（LST,PD,ISA,RD,BD,BH）.