The Distribution And Transport Of Air Aerosol In Northern China And Its Response To The Summer Monsoon

Global climate change has always been a major scientific issue and hot topic.Aerosols play the most uncertain role in the influencing factors of climate change,which has been widely concerned(IPCC,2013).The study of the vertical characteristics,transmission path,occurrence frequency and temporal and spatial distribution of optical thickness of aerosols are the key to the analysis of aerosol climate effect,and also the basis for the study of the interaction between aerosols and global warming,monsoon activity,etc.China is located in the East Asia,and the influence of summer monsoon on rain belt and air pollution is significant.According to the influence degree of summer monsoon,China can be divided into summer monsoon zone,summer monsoon transition zone and non-summer monsoon zone.In this paper,the observation and reanalysis data was used to analysis combined with numerical model.We firstly analyzed the dust particles' vertical distribution in a dust event and contrasted different moving paths distinguishes.In addition,we analyzed the four seasons and annual frequency of different types of aerosols in different optical depth in Northwest China.We analyzed the impacts of the East Asian summer monsoon on aerosol spatial distribution and the response of dust and polluted aerosols in the "summer monsoon transition zone" to abundant and deficient monsoon years.The response of different types of aerosol distribution and the impact on regional temperature was analyzed to the advance and retreat of summer monsoon in China.The main conclusions were as follows:(1)Based on the weather analysis of a dust event in Northwest China,it was found that the instability of atmospheric stratification,strong wind and sand source together caused the dust storm process.The dust particles are mainly distributed within 2-3 km.According to the HYSPLIT backward trajectory model and the dust transport path simulated by NAAPS,the dust weather process was the northwest path and mainly moved eastward,with the maximum lifting to 8 km;in addition,the continuous action in Gansu Province that resulted the blowing sand and floating dust weather.(2)In the events of dust weather in the northwest and west path,the verticaldistribution height of dust aerosol was higher than that in the north route;in the west path,the number of dust particles was more than that in the northwest path.The two weather processes were located in Jiuquan area,but different dust source areas and moving paths leaded to different types of aerosol particles in the atmosphere.The results showed that the mean value of Zhangjiakou depolarization ratio was the lowest in the three dust transmission paths,and the dust particles has been mixed with other aerosol particles at low altitude,which leaded to the decrease of the non sphericity of the particles.The mean value of depolarization ratio was similar in Northwest and West routes,which showed that the components of the dust were basically the same.(3)With the increasing of aerosol optical depth in Northwest China,the frequency of dust aerosol had a downward trend.The polluted dust aerosol was the highest frequency in the six types of aerosols.From the view of observation from space,when the dust storm broke out,there was the migration of pollutants with the sandstorm.In recent years,the aerosol types were basically polluted dust in the dust event;In the case of different aerosol optical depth,the frequency of smoke aerosol was higher than that of the polluted continental aerosol.With the increase of aerosol optical depth,the frequency tended to increasing.In autumn and winter,when the aerosol optical thickness is greater than 0.1,the frequency of the polluted continental aerosol is significantly higher than that of the dust aerosol.(4)In the summer monsoon transition zone of China,dust aerosols were distributed at a height of 2–6 km in the western part of the transition zone,while polluted aerosols were distributed of a height of 0–4 km in the eastern part.In abundant monsoon years,the frequency of occurrence of dust aerosols was significantly lower than in deficient monsoon years,with dust particles accounting for about 19.6% of the total aerosol,while the frequency of occurrence of polluted aerosols displayed the opposite trend,accounting for about 71.8% of the total aerosol and being more frequent in abundant rather than deficient monsoon years.Combined with the wind field analysis,the summer monsoon transported the pollution particles from Southeast China to the transition zone,where they gathered,resulted in more pollution particles in abundant than deficient monsoon years.The total amount of aerosol particles was basically the same in the East Asian the summer monsoon transition zone during different extreme monsoon years,and the proportion of coarse and fine particles was different.(5)In the monsoon region,the aerosol type was mainly sulfate,accounting for71%;in the transition region,the aerosol type was mainly sulfate and dust,accounting for 57% and 27% respectively;in the non-monsoon region,the aerosol type was mainly dust,accounting for 83%.In the monsoon region,the sulfate aerosol has the largest contribution to the total optical thickness of aerosol in the three stages of the development of the monsoon,before the onset of the monsoon.In the transitional region,the contribution rate of dust to the total optical depth of aerosols was 16%,and the contribution rate of sulfate was 18%.After the monsoon onset,the contribution rate of dust was reduced by half to 8%,while the contribution rate of sulfate was slightly increased to 20%.In the non-monsoon region,the contribution rate of dust was always dominant.