The Characteristics And Pollution Source Of PM_2.5and PM₁₀ In Heavy Pollution Weather In Hefei,China

China's air quality has improved dramatically in recent years as the pace of air pollution control has accelerated.However,there are still some cities where the average annual concentration of PM2.5 is increasing.Due to the complex and changeable local topography,landform,climatic conditions,social development level and economic structure,as well as the special geographical location,its north,west and east sides are connected to the Beijing-Tianjin-Hebei,Fen-wei plain and the Yangtze River Delta,respectively,causing the atmospheric environment quality of Anhui province is not optimistic.For this reason,it is of great significance to study the formation mechanism of heavy pollution in Anhui province for the fine management of atmospheric environment,as well as the prediction and prevention of heavy pollution.Taking Hefei as the research object,samples of PM2.5 and PM10 were collected in heavy polluted weather from December 2017 to February 2018,and the characteristics of water-soluble ions,carbonaceous components,polycyclic aromatic hydrocarbons(PAHs),inorganic elements,carbon and sulfur isotopes and microstructure in atmospheric particles were tested and analyzed.The main research results are as follows:The air pollution of Hefei city is serious in winter,with the average concentration of PM2.5 and PM10 both exceeding WHO and China's air quality standards,and the pollution level is in the middle position in China.S,Si,SO42-,NO3-,NH4+,OC and EC are the most important components.Except for S and Si,the values of other components(PM2.5/PM10)are above 0.8,indicating that more toxic components are more likely to be enriched in PM2.5.SO42-content,SO42-proportion and aggregate and foamy attached link structure(microstructure)in PM2.5 and PM10 increase significantly with the pollution degree deepening,at the same time,the sulfur oxidation rate(SOR)in severe pollution,but also reached 0.51 and 0.60 respectively,significantly higher than that of non pollution weather,showed more secondary aerosol particles,mainly sulfate,were formed in the severe diurnal pollution.Both EC and OC increased significantly on days of heavy pollution,but EC increased faster than OC,indicating that primary carbon aerosols are the main components of carbon aerosols in heavily polluted weather.The significantly increased concentration of S and Cl and the sulfur isotope analysis results indicate that the emission from coal burning was the main source of aerosol of heavy pollution event in Hefei.The high concentration of 5-ring and 6-ring PAHs and carbon isotope results show that the contribution of vehicle exhaust to air pollution should not be ignored.By comparing and analyzing the meteorological factors under different weather conditions,it is found that the weather pattern is the main factor to control the regional air pollution process,and the conditions of higher humidity,smaller wind,lower temperature and higher pressure lead to the accumulation of PM2.5 and PM10 and the gas-particle transformation process.