Aerosol Physical-Optical Properties Under Different Stages Of Continuous Wet Weather Over The Guangdong-Hong Kong-Macao Greater Bay Area,China

With the accelerating development of urbanization in China,the atmospheric environment problem has become more and more serious,making it now one of the environmental topics to which people attach great importance,especially in South China,where a large number of aerosols with different properties are distributed,and the spatial and temporal distribution and physical-optical properties of aerosols are of great scientific significance for the study of climate change and atmospheric environment.Persistent humid weather is a special weather phenomenon that occurs frequently in late winter and early spring in South China.This weather is characterized by high temperature,high humidity and cloudiness.What are the characteristics of aerosols under persistent high humidity conditions? In this thesis,we analyze the aerosol optical properties of a total of 68 persistent humid weather processes in the Guangdong,Hong Kong and Macao(HK)Greater Bay Area from 2012-2021 using CALIPSO satellite data and ERA5 and MERRA-2 reanalysis data.The changes of meteorological conditions and physical-optical properties of aerosols under different humidity conditions in the before-stage,wet-stage and after-stage of continue wet weather are explored.The main research work of this thesis is as follows:(1)A classification method of humidity levels was defined based on the range of the daily average of absolute humidity during the study time.And three humidity levels were proposed,including slight humidity,moderate humidity and heavy humidity.At the same time,the continuous wet weather process is defined in three stages,before-stage,wet-stage and afterstage,to study the influence of different conditions on aerosols.(2)The spatial distribution of meteorological conditions before and after the continue wet weather was analyzed using ERA5 reanalysis data.It is found that the distribution of meteorological parameters is basically the same under different humidity levels,and the main difference lies in the temperature and humidity and wind field in different phases.The maintenance height of this wind direction also increases as the humidity level increases.(3)The optical properties of aerosols are closely related to the changes of meteorological conditions,and we analyzed the optical properties of aerosols before and after persistent wet weather using MERRA-2 reanalysis data and CALIPSO satellite data.In the before-stage driven by northeasterly winds,aerosols in the Guangdong-Hong Kong-Macao Bay area are mainly from regional transport making the AOD values relatively high.During the wet-stage,the AOD is maintained at a low level under the influence of clean ocean airflow.When the cold high pressure is controlled again,the wet-stage ends with coldness.The after-stage has basically the same atmospheric circulation as the former phase,but a significant feature is the existence of an inversion layer in the after-stage,which hinders the diffusion of aerosols,and at the same time,the regional transport also increases the aerosols themselves and their precursors,producing a large amount of secondary aerosols,leading to a significant increase in AOD.The analysis of the contribution of different aerosol species revealed that the rapid increase and decrease of sulfate aerosol AOD dominated the total AOD throughout the process AOD.(4)Taking Zhuhai area as an example,we analyzed in detail the causes and changes of meteorological parameters and aerosol optical properties generated by a typical continuous humid weather process with the help of ground-based and satellite data.In the before-stage,influenced by the weak cold high pressure centered in Shanghai,the temperature and humidity were low,northeasterly winds prevailed,and aerosols mainly came from northeastern coastal cities.In the wet-stage,the cold high pressure moves eastward out of the sea,the warm low pressure develops in the northwest of Guangdong-Hong Kong-Macau Greater Bay Area.And the temperature and humidity rise rapidly,the air masses mainly come from the southeast of the sea area,and the small particle size aerosols dominate the low AOD.The after-stage is influenced by strong cold high pressure from the north,the wind speed increases than the previous stage,and there is inverse temperature at 775 hpa height.The aerosol mainly comes from the northern neighboring cities of regional transport and local generation,the sulfate AOD rises rapidly so that the total AOD is maintained at a high level.This study reveals the physical-optical properties of aerosols in three stages of continue wet weather in Guangdong-Hong Kong-Macau Greater Bay Area,and the mechanism of meteorological factors on aerosols,which can provide a scientific basis for future research on persistent wet weather.