Analysis Of Temporal And Spatial Characteristics Of AOD And PM_2.5 In Coastal Areas

Aerosol is an important factor affecting the atmospheric environment,aerosol optical thickness（AOD）is one of its important optical parameters,and PM_2.5 concentration is an important index for monitoring air quality.The paper studies the spatial and temporal characteristics of AOD and PM_2.5,which can provide a theoretical basis for understanding the regional distribution and change pattern of atmospheric pollution.Using AERONET ground-based data and MODIS remote sensing data,the spatial and temporal characteristics of AOD and PM_2.5 in the coastal region were analyzed.The main research work and results of this paper are as follows.（1）The 11 AERONET ground-based stations were divided into four types of regions using the hierarchical clustering method and then divided into six aerosol types based on graphical classification:clean,desert dust,continental,subcontinental,urban industrial,and biomass-burning aerosols,and aerosol type analysis and seasonal analysis were conducted for each of the four regions.The main aerosol types in the Beijing region are urban industrial type and continental type;the coastal region is mainly continental type;Tibet region is clean type;Taihu region is mainly urban industrial type aerosol.（2）Using two secondary products of MOD04＿L2 and MOD04＿3K data analysis,the four algorithms are verified and processed,and the AOD values of the combined algorithms for the coastal region can be obtained according to the normalized vegetation index range of each month.（3）Seasonal and interannual spatial and temporal distribution analysis of the decadal AOD in the coastal region,in which the highest season among the four seasons is spring and the lowest in autumn.In the interannual variation,the AOD showed a decreasing trend from2011 to 2020,among which the summer was the most obvious,and the monthly average AOD in the first half of the year was higher than that in the second half of the year as a whole.Using EOF to analyze the spatial and temporal distribution characteristics of AOD in all four seasons,AOD showed a decreasing trend in all four seasons in ten years,spring was mainly bounded by 30°N,summer divided the north-south region with the Yangtze River basin as the dividing line showing obvious inverse phase changes,autumn 2015 AOD increased in some regions north of the Yellow River,the rest of the years showed the opposite trend,winter 2013,2014 and 2016 30°N to 40°N part of the region AOD increased,and the rest of the years showed the opposite trend.（4）The AOD values after the combined algorithm were highly revised and humidity revised,and then PM_2.5 was inverted using AOD,and finally,the spatial and temporal characteristics of PM_2.5 from 2011 to 2020 were analyzed.The results show that the monthly average PM_2.5 in the second half of the ten-year data is higher than that in the first half of the year as a whole and decreases in all seasons,among which the most obvious ten-year difference is-19.6μg/m³ in winter and the PM_2.5 decreases more in the second half of the year than in the first half of the year.When analyzing the ten-year PM_2.5 changes in all seasons using EOF,the first mode shows a trend of PM_2.5 decreasing in all seasons,the first two modes can explain the distribution changes,and the second mode clearly distinguishes the land and sea parts.