Research On Aerosol Characteristics And Driving Forces Of Haze Weather In Sichuan Province Based On Multi-source Remote Sensing

In recent years,The haze weather in Sichuan Province of China has been frequent and the air quality has dropped,air pollution problem has become the focus of attention of the public.The distribution of atmospheric aerosol optical thickness can reflect the degree of regional air pollution.Therefore,the study of the spatial and temporal distribution of aerosol optical thickness is very meaningful for the analysis of regional pollution.This paper uses CALIPSO and MODIS data products to analyze the temporal and spatial distribution characteristics of aerosol optical thickness in Sichuan during the period 2005-2015,taking both natural and man-made aspects into account,and conducting quantitative studies on the driving forces of aerosol optical thickness in Sichuan Province from a spatial scale.difference and key influence,and the vertical distribution characteristics of aerosols were systematically studied.A case of severe haze pollution incidents in Chengdu in early 2014 was analyzed;the causes of haze pollution were analyzed through the weather conditions of the haze pollution process and the evolution of ground particulate concentrations.Through the above analysis,th e main conclusions are as follows:(1)From the trend of aerosol optical thickness changes in Sichuan Province from 2005 to 2015,it can be seen that the annual average value of AOD in the western Sichuan region has not changed much with the growth of the year and has remained stable below 0.1;The annual average value of AOD in Sichuan Province is similar to the overall change in Sichuan,and it has continued to fluctuate steadily before 2011,and has begun to decline year after year since 2011;The average annual fluctuation of AOD in eastern Sichuan is more obvious,reaching a maximum of 0.5 in 2011 and then decreasing significantly.Seasonal changes show that the highest AOD value is in winter in the eastern part of Sichuan,and the highest AOD value is in the spring in Sichuan and western Sichuan.During monthly changes,the AOD values were most intense in January,February,and December.(2)The spatial-temporal distribution of aerosol optical thickness retrieved by MODIS shows that the distribution of aerosol optical thickness in Sichuan area is affected by the terrain.The optical thickness of aerosols differs significantly between eastern Sichuan and western Sichuan.The high aerosol optical thickness area is located in eastern Sichuan and the low-level area is located in western Sichuan.On the time scale,the seasonal variation pattern is prominently presented: highest in winter,followed by spring and autumn,and lowest in summer.(3)There are many regular aerosols in the eastern Sichuan,of which 85% of aerosol particles have a depolarization ratio below 50%.Irregular coarse particles in the near ground occur frequently.The 2-4km height layer is mostly spherical fine particles,and the upper layer is a more regular medium-sized particle.90% of aerosols in Chuanzhong area have a depolarization ratio of less than 60%.The distribution frequency of regular aerosols is higher than that in the Chuandong Basin.Aerosol coarse particles are mostly distributed in the near-ground layer,and fine particles in the height above 6 km account for more.The depolarization ratio of more than 95% of aerosol particles in western Sichuan is less than 40%,and the total color ratio of particles is in the range of 0.1-1.0,indicating that the aerosols in western Sichuan are mostly spherical or near-spherical fine particles,and near-surface aerosols.The number of large particles is higher than that of high altitude,while the high-level aerosols are almost all small particles.(4)During the 2014-2017 years,the haze weather days in the eastern Sichuan Basin were far more than those in the Western Sichuan Plateau and the Middle Sichuan hilly area.The four cities in Chengdu,Zigong,Deyang and Luzhou were most prominent.Monthly analysis showed that haze season was the two season in winter and spring,followed by autumn.Haze appeared the lowest in summer.In the beginning of 1,February and the end of December,it was haze days.The middle and 6-9 months were haze days.The change of day and day of haze in different degrees is the same as that of the total haze day and day.(5)During the haze development process,the concentrations of AQI,PM2.5,and PM10 are quite high,the relative humidity in the area is high,and the wind speed is small.The vertical characteristics of aerosols observed by the CALIPSO satellites during the haze pollution process are as follows: There is a strong backscattering intensity in the near-surface range below 5 km,and the backscattering coefficient in some areas is close to 2-3 km-1 sr-1,with the increase in altitude.The scattering intensity decreases;the volume depolarization ratio is centered between 0.2-0.8,and the aerosol size is relatively regular;the color ratio is concentrated between 0.2-0.6,mostly small and regular aerosol particles,and the bulk gas Sol particles are concentrated near the ground.(6)The time-space evolution of aerosol optical depth is the result of the action of human and the nature: on the regional scale,human social and economic activities play a leading role on the evolution of aerosol optical depth,show the effect of precipitation and vegetation weak obviously gross national product;on pixel scale,the spatial differentiation characteristics of driving force factors is the result of the spatial differentiation of aerosol optical depth,show aerosol optical depth of Sichuan Basin has been mainly affected by human factors,aerosol optical depth of eastern parallelism valley western Sichuan plateau and Mountainous Area of Southwest Sichuan has been mainly affected by the earth's surface and meteorology factors.