Temporal And Spatial Characteristics Of Air Quality And Its Influencing Factors In The Middle And Lower Reaches Of The Yangtze River

At present,the air pollution in China is still serious and shows the characteristics of continuous explosions.The air quality problem directly affects the regional ecological environment and people's quality of life,and then restricts the social and economic development.As one of the six economic zones mainly divided by economic geographical characteristics,the middle and lower reaches of the Yangtze river are not only the"Land of fish and rice",but also an important industrial base with a high concentration of industries and population.The study of the spatial and temporal characteristics and influencing factors of air quality in the middle and lower reaches of the Yangtze river is helpful to formulate specific measures for the prevention and control of the atmospheric environment in this important region,to avoid the"One-size-fits-all"mode,so as to accurately improve air quality and promote the sustainable development and ecological civilization construction of the region.Based on data from air quality monitoring stations,this paper used statistical analysis and spatial analysis to explore the time-varying characteristics and spatial distribution characteristics of AQI at 374 monitoring stations in the middle and lower reaches of the Yangtze River from 2015 to 2018.Then,taking 2015 as an example,this paper combined socio-economic statistics from statistical yearbooks,meteorological reanalysis grid data with 0.5°x 0.625°accuracy,vegetation index?NDVI?with 1kmx1km accuracy,population density and GDP grid data.This paper used the spatial measurement model and the GWR model to analyze the spatial effect and spatial heterogeneity of the annual,quarterly,and monthly influencing factors of air quality in the middle and lower reaches of the Yangtze River,and discussed the influence,direction,and degree of influence of different factors Changes in seasons and months.The main findings of this paper were as follows:?1?From 2015 to 2018,the air quality in the middle and lower reaches of the Yangtze River improved year by year.The quarterly average value of AQI showed the characteristics of"Excellent summer and poor winter,and the middle of spring and autumn",while the monthly average value of AQI showed a"U"type distribution.?2?From 2015 to 2018,AQI generally showed the spatial distribution characteristics of“High in the west and low in the east,and high in the north and low in the south”.The regions with relatively severe air pollution were mainly central Hubei Province and the junction of northeast Anhui province and northwest Jiangsu Province.?3?During the study period,the numerical imbalance and spatial agglomeration of air quality in the middle and lower reaches of the Yangtze River decreased and expanded with the changes of interannual,seasonal,and monthly.The overall air quality showed a strong spatial positive correlation,and there was a clear HH and LL agglomeration,and the monitoring stations of HH agglomeration are relatively stable in the area north of the Yangtze River.The monitoring stations of the LL agglomeration were mainly distributed in Jiangxi Province and Zhejiang Province south of the Yangtze River.?4?The annual,quarterly,and monthly air quality had a strong spatial endogenous interaction effect,and the interaction effect generally showed the seasonal law of"The strongest in winter,followed by spring,slightly weaker in summer and autumn".The endogenous interaction effect in space was the strongest,and it was the weakest in June and July.?5?The influence degree of AQI influencing factors in different time scales was different and changed with the change of season and month.In terms of the factors affecting the annual AQI,the ranking of the contribution of each factor to the direct effect of the regional annual air quality was:GDP^#>PS^#>TM>IND>MW^#>DUST>NDVI^#>ZW^#?"#"Stands for negative effect,the same below?.The spatial spillover effect of each influencing factor was ranked according to the contribution:GDP^#>PS^#>TM>TP^#>MW^#>SO₂>DUST^#>POP.In terms of influencing factors of quarterly AQI,the leading factors with direct effected varied from season to season.Vegetation coverage had a significant positive effect on the improvement of air quality in the four seasons.Precipitation,meridional wind speed,and air pressure were significant in some seasons.The zonal wind speed in spring,the vegetation coverage and relative humidity in autumn,and the precipitation in winter all had significant spatial spillover effects on air quality in adjacent areas.In terms of monthly AQI influencing factors,air pressure had a significant direct effect in most months,and factors with a significant spatial spillover effected varied from month to month.?6?There were obvious spatial heterogeneities in the influencing factors of AQI at different time scales.In terms of annual AQI influencing factors,the three factors of average GDP,the proportion of secondary industry and industrial smoke dust emissions in the study area had high-value areas and low-value areas with obvious laws,and there were only a few areas where the positive and negative signs of the regression coefficients of the first two factors were opposite to most other areas.In terms of seasonal AQI influencing factors,the overall vegetation coverage had a greater positive effect on the improvement of air quality in some tourism-developed areas.The regression coefficient of air pressure decreased from east to west.Regression coefficient of precipitation and meridional wind speed were mainly distributed in high-value areas and low-value areas with large differences and no regularity.In terms of factors affecting monthly AQI,air pressure,air temperature,precipitation,relative humidity,meridional wind speed and zonal wind speed had different influences in the months where their direct effects were significant,and they varied with time.