Numerical Simulation Of Heavy Haze Pollution In North China In Recent Winter

In this paper,two mainstream air quality models,WRF/Chem and CMAQ,are used to analyze the typical heavy pollution events in North China in recent years.(1)Adopted for North China from November 17 to November 23,2014,November 25 to December 2,2015,December 13,2016 to December 23,2016 and December 26,2017 From January to January 1,2018,the analysis of the causes of typical heavy pollution events shows that the proportion of nitrate and sulfate aerosols increased significantly in 2014,mainly due to the accumulation of pollution by the aerosol process.The increase in nitrate content in 2015 was mainly due to the increased content and horizontal transportation of emission sources which aggravated pollution.The proportion of nitrate and organic carbon increased significantly in 2016,and the aerosol process played a leading role during the pollution period.The largest increase in nitrate in 2017 was the accumulation of pollution by aerosol processes.(2)Through comparative analysis of four cases,the simulation of meteorological factors by CMAQ is more accurate than the simulation of WRF / Chem mode in some cases.The WRF / Chem mode is better than the CMAQ mode in the online coupling of meteorology and chemistry.Analysis of chemical composition showed that nitrate increased the most and accounted for the largest proportion in the pollution stage,followed by organic carbon and sulfate.The proportions of the two were not much different,and the black carbon aerosol decreased during the pollution stage.Comparative analysis of pollution cases in different years when IPR> 0 at different stages.During the pollution accumulation stage in 2014,2016 and 2017,the aerosol process is an important cause of pollution accumulation.The increase in emission sources and meteorological conditions jointly cause Important causes of pollution accumulation in 2015.During the pollution period,meteorological factors have more influence on 2014 and 2015.(3)It can be seen from the observation data that Beijing and Tianjin were the most polluted in 2014.Since then,the degree of pollution has decreased year by year.According to the analysis of the IPR process,vertical transportation in other regions of North China in 2014 was an important cause of pollution in this region in 2014.The reason is that the weakening of vertical transportation and the immediate meteorological conditions that are conducive to the diffusion of pollutants made Beijing and Tianjin pollution levels not one of the reasons for severe pollution in 2017.(4)The article simulates a large-scale PM2.5 heavy pollution process from November 25 to December 2,2015.The meteorological dynamic factors mainly affect the pollution event through the weakening of surface wind and vertical wind shear.The boundary layer Thermal factors such as temperature inversion promote the enhancement of atmospheric stability,which is not conducive to the diffusion of pollutants.The chemical conversion of NOx to nitrate plays a leading role in the generation of secondary aerosols.The increase in vehicle emissions may exacerbate the pollution.Further quantitative analysis results using relative contribution rate show that the thermal factor plays the main role,the kinetic factor takes the second place,and finally the chemical conversion factor(relative contribution rate is 52%,34%,and 14%).According to the IPR analysis,the pollution is exacerbated by the combined effects of changes in emission sources,horizontal transportation,and unfavorable pollutant diffusion.