Research On The Temporal And Spatial Distribution Characteristics Of High-resolution PM_2.5 In The Sichuan Basin Based On MODIS AOD Inversion Based On Ground-based Observations And Corrections

In recent years,more and more air pollution problems have appeared in the process of economic development in China,and the influence of fine particulate matter(PM_2.5)on air quality is particularly significant,which has attracted extensive attention from scholars and the general public at home and abroad.However,the number of surface PM_2.5.5 monitoring sites is limited and mainly concentrated in urban areas,and there are few monitoring sites for air pollution in suburban and vast rural areas. Therefore,the use of satellite aerosol remote sensing products to estimate the mass concentration of PM_2.5.5 near the ground becomes an effective way to solve the low resolution of surface monitoring sites.On the one hand it can make up for the lack of space coverage of monitoring stations in the suburbs and vast rural areas.On the other hand,it can correct the monitoring results obtained from the limited monitoring stations and improve our awareness of the air quality in the whole region.Taking Sichuan basin as the main research object,This article is based on the accepted relationship between AOD and PM_2.5,comprehensively use of MODIS AOD data from TERRA satellites and ground-based data of The Campaign on atmospheric Aerosol Research network of China（CARE-CHINA）and the Chinese Sun Hazemeter Network（CSHNET）,The causes of the conclusions are as follows:（1）During the observation period,the average annual AOD of ground aerosol in three research sites of Chongqing,Yanting and Gongga mountain were respectively（1.06±0.54）、（0.75±0.36）and（0.35±0.29）,indicating that Gongga mountain at the edge of the basin was the lowest,while the average annual AOD in Yanting and Chongqing within the basin was higher,indicating that AOD was negatively correlated with altitude in space.In terms of seasons,the three stations show the highest annual average optical thickness in spring,followed by winter and the lowest in summer.（2）The linear correlation coefficients of MODIS AOD and CE318 AOD from ground observation at Chongqing,Yanting and Gongga mountains were 0.64,0.86 and0.87,respectively.The fitting equations were y=0.94x-0.1,y=1.17x-0.83,and y=0.68x+0.12,meeting the accuracy requirements of NASA.The relative error of subgrade AOD and MODIS AOD in most areas of the basin is small,and the error is concentrated between-5%and-5%.（3）The AOD space in Sichuan basin after the correction shows the distribution characteristics of high in the middle and low around the basin,among which "Mianyang-Deyang-Chengdu-Meishan-Leshan",the urban agglomeration in southern Sichuan and the western part of Chongqing are high value areas.From 2008to 2017,AOD presented a"decrease--increase--decrease"change,and reached the lowest value in 2017.The seasons are high in spring and winter and low in summer and autumn.（4）AOD and PM_2.5.5 appear high linear correlation,thus build the Sichuan basin after the correction of AOD and PM_2.5.5 fitting equation,to the inversion of the Sichuan basin from 2008 to 2017 resolution to county-level cities of PM_2.5.5 mass concentration spatial distribution,peaked around 2013,roughly 60μg/m³,has significantly decreased after 2014,to 2017 basin in the internal quality of PM_2.5.5 probably dropped to about 42μg/m³.From the perspective of spatial distribution,there are mainly three high-value areas:Chengdu-Deyang plain urban agglomeration,Zigong-Neijiang urban agglomeration in southern Sichuan and Chongqing.The mass concentration around the basin is low,showing a spatial distribution pattern of high in the middle part of the basin and low in the surrounding area.In terms of seasons,the mass concentration of PM2.5 in sichuan basin is about 55μg/m³in spring,summer,autumn and winter,34μg/m³,47μg/m³and 86μg/m³,respectively,reaching the highest in winter,followed by spring and the lowest in summer.Only using the actual PM2.5 monitoring data of municipal sites to reflect the regional pollution situation of sichuan basin will be overestimated by about 21%,affecting people’s judgment on the regional pollution situation.Therefore,with the increase of economic development and environmental governance,counties should continue to deeply arrange monitoring sites.