Effects Of Urban Green Space Landscape Pattern On Air Pollutant Concentration And Its Spatio-temporal Evolution

With the continuous improvement of urbanization level,the continuous improvement of living conditions also brings serious ecological environment destruction and air pollution,which causes people to pay unprecedented attention to the scientific city construction environment and healthy urban green space construction.Under the new era of development,the construction of healthy urban greenbelt landscape pattern will play an important role in promoting the construction of ecological civilization.Relevant studies have shown that urban green space plays an important role in alleviating air pollution and improving residents’ public health.Therefore,it is of great significance to explore the influence of urban green space landscape pattern on air pollutant concentration and its spatio-temporal evolution characteristics for the optimization of urban green space landscape pattern,protection of ecological environment and improvement of urban air quality.Based on the MODISAOD data from 2015 to 2018 and the annual mean data of PM2.5,PM10,SO2 and NO2 air pollutants,this paper analyzed the spatio-temporal distribution characteristics and landscape pattern changes of the four air pollutants in seven major regions(241 prefection-level cities)as the study area.Through fixed effect panel regression model,linear fitting analysis and other methods,the correlation between urban landscape pattern index and air pollutant concentration and the threshold effect of core landscape pattern index in seven regions were quantitatively studied,and the following research results were obtained:(1)Spatial and temporal distribution characteristics of the four air pollutantsThe concentration of PM2.5,PM10,SO2 and NO2 in seven major regions showed obvious temporal characteristics from 2015 to 2018.In addition to the slight decrease of NO2 concentration in the annual mean fluctuation,the pollution of particulate matter(PM2.5,PM10)and SO2 has been significantly improved.The spatial distribution characteristics of air pollutants are obvious,showing the phenomenon of regional concentration.PM2.5 and PM10 pollution values showed the characteristics of "high in the middle and low in the surrounding areas",SO2 pollution values showed a trend of low in the north and south and high in the middle,and NO2 pollution values showed a trend of increasing gradually from northeast and southwest to inland.The hot spot analysis diagram shows that the high value area of particulate matter pollution decreases over time,the high value area of SO2 decreases in the fluctuation,and the high value area of NO2 increases continuously.(2)Changing characteristics of landscape pattern of Chinese greenbelt and seven regionsFrom 2015 to 2018,the overall proportion of woodland landscape increased,while the proportion of grassland and farmland area decreased to different degrees.The land use developed in the direction of uniformity and diversity,and the control of dominant landscape on landscape pattern weakened.With the change of time,the proportion of woodland landscape increased in central China,North China,Northwest China and Northeast China,while the proportion of grassland and farmland landscape decreased in different degrees.The other three regions,East China,South China and Southwest China,showed different changes in the area proportion of green landscape types.(3)Regression analysis results of urban green space landscape pattern in seven regions on air pollutantsThere was a significant negative correlation between forest PD and PM2.5,PM10 and NO2,and a significant positive correlation between grassland PD and SO2 in East China.There was a significant negative correlation between PD and PM2.5 and PM10 in northwest China.There was a significant positive correlation between PD and SO2 in grassland,and a significant negative correlation between PD and SO2 in farmland in Northeast China.In the other four regions of South China,Central China,North China and Southwest China,the landscape pattern index of three green patch types(forest land,grassland and farmland)was significantly correlated with the four air pollutants.(4)Threshold value of core landscape pattern index and green space planning suggestionsThe concentrations of PM2.5,PM10,NO2 and SO2 air pollutants in the seven regions are not only significantly affected by the urban green space landscape pattern index(LSI,PD,PLAND),but also have an obvious threshold effect for some landscape pattern indexes with significant influence on air pollutants.For example,the PD threshold of forest land with significant influence on PM2.5 and PM10 in East China is0.03 and 0.003 respectively,and the threshold of grassland patch shape index with significant influence on PM2.5 concentration in South China is 29.635.Through quantitative regulation and control,the urban green space landscape pattern index is properly close to or far from the threshold value to effectively reduce the concentration of air pollutants.Based on the correlation regression research results of urban green space landscape pattern in seven regions and four air pollutant concentrations,this paper proposes to combine the correlation regression analysis results and the threshold effect of each pollutant to scientifically regulate the area of various urban green space types,canopy density and vegetation coverage,urban green space boundary and urban green space patch dispersion.To optimize the landscape pattern of urban greenbelts in different areas,so as to improve the ability of greenbelts to alleviate air pollution.