Characteristics Of Aerosols And Cloud Condensation Nuclei (CCN) Over China Investigated By The Two-way Coupled WRF-CMAQ Air Quality Model

The development of the economy will bring a series of atmospheric environmental problems,especially atmospheric aerosol pollution,which has received wide attention all over the world.The effects of aerosols on cloud and climate are one of the most uncertain factors in assessing the impact of human activities on the environment,the climate system and global warming.This paper uses the two-way coupled WRF-CMAQ air quality model to simulate several episodes around the world,and then evaluates the model simulation results of aerosol and cloud condensation nuclei(CCN)by ground observations and satellite data.In addition,this paper analyzes characteristics of spatial and temporal distributions of aerosols and CCN over China on the basis of simulations in January,April,July,and October,2013.The results of this study show that:(1)The two-way coupled WRF-CMAQ model has good performance for simulations of aerosol and CCN concentrations,and can be used to simulate the distributions of the atmospheric aerosol and CCN concentrations reasonably well.This provides the reliable basis for further analysis of temporal and spatial distributions of the CCN concentrations over the China;(2)Under constant other conditions,the higher the supersaturation value,the higher the CCN concentration.When the supersaturation values are relatively high,the increase rates of the CCN concentrations associated with the further increase of supersaturation will significantly decrease.On the other hand,relative to the ground level,the increase rates of the CCN concentrations associated with the increase of supersaturation at the high altitude begin to decrease obviously even when the supersaturation is still relatively low;(3)The CCN concentrations are mainly located below 5000 meters and gradually decrease with the increase of the height;(4)There is no obvious difference for the regional distributions of the CCN concentrations between the ground and high altitudes in China.The CCN peak concentrations for both ground and high altitudes over China are mainly located in the Sichuan basin,north China and central China,while the CCN concentrations over the Northwest and Inner Mongolia areas were relatively low,showing the obviously good correlations with the regional aerosol pollution;(5)The seasonal variation of CCN concentrations in China has the following characteristics:the CCN concentrations in the ground is:winter>autumn>spring>summer,while the CCN concentrations at the high altitude are the lowest in summer with similar values in spring,autumn and winter.The seasonal variation trends of the CCN concentrations in different regions are similar;(6)There is obvious daily variation trends of the CCN concentrations in all regions of China with the stronger daily variation in the low latitudes and heavily polluted areas because of effects mainly caused by solar radiation and the emissions from human activities.The peak CCN concentrations on the ground occurred at 8:00 a.m.in morning and 22:00 at night with the low value occurring at around 15:00 p.m.,while the CCN concentrations at high altitude have upward trends from 9:00 a.m.to 16:00 p.m.every day,and downward trends from 17:00 p.m.to 8:00 a.m.of the next day.