Spatial And Temporal Variation Of Aerosol Optical Depth In The North China Plain Based On Multi-source Remote Sensing Data

Due to the increasing development of science and technology,the rapid progress of global urbanization and industrialization,the intensity of human social activities has increased,which in turn has led to an increase in air pollutant emissions.It not only affects the visibility of the atmosphere,but also causes various environmental problems and even endangers the health of human beings themselves.Among various atmospheric aerosol parameters,the Aerosol Optical Depth（AOD）is used to describe the attenuation of light by aerosols and also effectively reflects the degree of atmospheric turbidity.In this way,it is essential to identify the spatial distribution characteristics and temporal variation of AOD,to reveal the factors affecting the spatial and temporal variation of AOD,to understand the current situation of atmospheric pollution,to test the implementation of environmental protection policies,and to improve the atmospheric environment.In recent years,the in-depth study of the spatial and temporal distribution characteristics of AOD and the influencing factors has gradually become a hot topic in atmospheric remote sensing.However,most of the current related studies focus on the spatial and temporal distribution of AOD in a specific region,and there is a lack of comparative studies of AOD in various cities within the region.In addition,existing studies are less likely to compare the relative importance of each influencing factor in the same region for different spatial and temporal distribution patterns of urban AOD,and there is also a situation that the number of selected AOD influencing factors is insufficient.In this study,the temporal variation and spatial distribution characteristics of aerosol optical depth in the North China Plain were analyzed using VIIRS IP AOD data from January24,2013 to December 31,2019.Secondly,17 influencing factors such as gross domestic product（GDP）,MODIS NDVI and OMI SO₂,NO₂ multi-source remote sensing data were selected.Based on the e Xtreme Gradient Boosting（XGBoost）model,the connection between AOD and its influencing factors at the surface scale of the whole North China Plain and at the point scale of five representative cities in the region are modeled respectively.The main influencing factors behind the spatial and temporal distribution pattern of AOD were revealed,and the contribution of each influencing factor was quantitatively estimated.The relative importance of 17 influencing factors for AOD was ranked and compared.The main findings are as follows.（1）The AOD of the North China Plain was bounded by the Taihang Mountains,with higher AOD values in the southeast than in the northwest.The high value areas were mainly concentrated in the built-up areas of Beijing and Tianjin,the northern part of Henan Province and the southern part of Hebei Province and Shandong Province except for the central hilly areas.The low value areas were mainly located in the northwestern mountainous areas with less human activities and poor economic development（2）The annual average value of AOD increased significantly in most areas of North China until 2013～2015 and decreased significantly in most areas from 2016 to 2019.Seasonal differences in AOD were evident,with seasonal means of AOD higher in summer than in spring and autumn and lowest in winter.The annual average values of AOD in all five representative cities from 2013 to 2019 showed a decreasing trend.The highest monthly average value of AOD for the five representative cities occurred in July and the lowest value occurred in December.The daily-scale trend fitting of AOD in each city also showed a downward trend in the past 7 years.（3）The R~2 of the XGBoost estimation model in five cities ranged from 0.60 to 0.67.The model R~2of XGBoost estimation model for the factors influencing AOD in the whole region of North China Plain was 0.79.NO₂,SO₂,T and RH contributed the most to the AOD of five representative cities,while SP,BLH,SSRD and TCC contributed the least.NO₂,TP,SO₂ and RH had the greatest impact on the temporal and spatial variation characteristics of AOD in the North China Plain,while TCC,SSRD,BLH and SP had the least impact.The contribution of TP to the region-wide AOD of the North China Plain was significantly higher than its contribution to the AOD of the five representative cities.