Simulation Of A Double High Pollution Process Of Ozone And PM_2.5 In The Fenwei Plai

In recent years,the PM_2.5 concentration often exceeds the national air quality standard,and the ozone level is also increasing.Moreover,ozone and PM_2.5 pollutions often occur at the same time in rapidly developing city clusters including Yangtze River Delta,Pearl River Delta and North China Plain.These two pollutants sometimes show a positive correlation in summertime.In this study,the Weather Research and Forecasting model coupled to Chemistry（WRF-Chem model）was employed to simulate the co-occurrence of ozone and PM_2.5 pollution in Fenwei Plain from May 20 to May 29,2015.We first validated the model performance of predicting meteorological parameters and pollutant concentrations and concluded the characteristics of the complex air pollution in Fenwei Plain.Based on the observation and the simulation,we found that WRF-Chem performed well on predicting the trends and the peak values of meteorological parameters（i.e.,temperature and the wind speed）and pollutant concentrations(i.e.,ozone and PM_2.5 concentrations).Furthermore,the model reproduced the severe air pollution process in Fenwei Plain from 27 May to 28 May.According to the simulation,polluted areas in Shanxi province and Shaanxi province were concentrated in Fenwei Plain,which is consistent with the distribution of anthropogenic emission sources.In addition,based on the highly modular process in the model,we analyzed the contributions of each process to pollutant concentrations to reveal the causes of pollution formation in Taiyuan.The results showed that the PM_2.5 pollution is caused by local emission,horizontal transportation and the vertical mixing of aerosol at high altitude,and the major process caused the increase of surface ozone is vertical mixing,which diffused the high-altitude ozone contributed by advection transport and chemical generation.A series sensitivity experiments were also conducted to quantify the impact of surrounding emissions on pollution from 27 May to 28 May in Taiyuan.According to the results,turning off the anthropogenic emissions in Taiyuan,Beijing-Tianjin-Hebei and Eastern Henan basin in turn resulted in a decrease of 49%,52%and 38%to PM_2.5 in Taiyuan,respectively.In addition,turning off the emissions in Taiyuan,Fenhe Plain and Eastern Henan basin resulted in a decrease of 7%,12%and 11%decrease in ozone in Taiyuan,respectively.