Aerosol Optical Properties And Evolution In Arid And Semi-arid Regions Of China

Aerosols are one of the most important and uncertain factors affecting the climate and atmospheric environment,and have significant implications on human health.Drought is one of the primary natural causes leading to the gradual deterioration of human living environment.Hexi Corridor is located in arid and semi-arid areas of northwest China,with fragile ecological environment and more affected by dust weather.It is a sensitive area of climate change.Long-term and large-scale aerosol observation in the region can provide data support for the study of long-term aerosol changes in the region and their impact on climate and environment.It can also provide data reference for ecological protection,sustainable development,air pollution prevention,improvement of human living environment and environmental governance in the region.This thesis selects four representative observation stations located in the Hexi Corridor,namely SACOL Station(also known as Lanzhou Station),Minqin Station,Zhangye Station and Dunhuang Station,which are distributed in the Hexi Corridor from east to west.Based on the aerosol observation data of CE-318 solar radiometer at these stations,the aerosol optical depth(AOD),(?)ngstr(?)m exponent,and complex refractive index in Hexi Corridor were analyzed,and some important characteristics and trends were found.The main conclusions are as follows :(1)Variation characteristics of AOD : from the perspective of space,there is a clear trend of high western and low eastern AOD in the region,but the AOD in Lanzhou is significantly higher than that in Minqin,which is also an eastern region.This is mainly due to the high population density in Lanzhou and the excessive aerosols produced by human activities.From the perspective of time,this area has the characteristics of the highest AOD in spring and the lowest in autumn.This is mainly due to the higher wind speed in spring,coupled with the increase in natural aerosols caused by the exposed ground.However,the AOD in Lanzhou region is also high in winter,which is mainly due to the increase of black carbon particles produced by heating combustion in winter.In terms of annual mean changes,the comprehensive data from the four stations found that AOD fluctuated but did not change much before2020,while AOD showed a significant increase in 2020,suggesting that the changes in climate and environment in the region in the last two years deserve attention and in-depth study.(2)Variation characteristics of (?)ngstr(?)m exponent : from the perspective of space,the (?)ngstr(?)m exponent for the region is clearly characterized by a low west and high east.This is mainly because the western region is more affected by the desert and produces more large particles,resulting in smaller (?)ngstr(?)m exponent.Lanzhou has the highest (?)ngstr(?)m exponent,because there are more aerosols generated by human activities in Lanzhou,and these particles are mainly small particles,resulting in an increase in the (?)ngstr(?)m exponent.From the perspective of time,the (?)ngstr(?)m exponent is the smallest in spring and the highest in autumn,which is due to the fact that the aerosols in this region are mainly large particles such as dust in spring.In terms of annual mean changes,Lanzhou showed only slight fluctuations,but Minqin and Zhangye showed a dynamic downward trend,indicating that the impact of human activities on aerosols in Lanzhou remained basically unchanged,but the impact of human activities on aerosols in Minqin and Zhangye decreased year by year.(3)Variation characteristics of the complex refraction index: complex refraction index has no obvious spatial distribution difference in this region.From the perspective of time,the real part of the complex refractive index in spring and winter is larger than that in summer and autumn,and the real part is the smallest in summer;the imaginary part is larger in winter than in summer.However,the imaginary part of refraction index in Lanzhou showed a significant downward trend from 2006 to 2013,indicating that the absorption of aerosol was decreasing,which was conducive to the increase of rainfall.The aerosol characteristics and evolution rules in this region are given in the thesis with detailed data and charts,which provide scientific and reliable data support for the study of climate and environmental changes in this region.