Pollution Characteristics And Source Analysis Of Secondary Organic Aerosol In Typical Areas Of Southwest Chin

Chongqing is a big city in southwest region.In recent years,with the acceleration of economic development,the air compound pollution problem has become more and more prominent.The acquisition of PM_2.5chemical components such as water-soluble ions,Organic Carbon（OC）,Elemental Carbon（EC）and metallic elements is an important prerequisite for tracing the source of PM_2.5,especially the chemical component data with high time resolution.At present,there is still a large research gap on the spatio-temporal variation characteristics of PM_2.5chemical components with high time resolution in the Sichuan Basin,leading to the failure to deeply understand the causes of serious pollution events.In order to understand the influence of Aerosol formation and evolution on aerosol formation in Sichuan Basin,Time-of Flight Aerosol Chemical Speciation Monitor with high Time resolution is used in this paper.To F-ACSM was conducted in Rongchang District of Chongqing in winter（January 24-February 15,2021）and summer（August 30,2020-October 8,2020）,respectively.This paper mainly explores the concentration characteristics of each component,uses the Positive Matrix Factorization（PMF）PMF model to analyze the source of particulate matter,and analyzes the driving factors of haze period.Finally,the backward trajectory model and potential source contribution analysis model are used to explore the trajectory and potential source of air mass in haze period.The main conclusions are as follows:（1）The analysis of winter observation data in Rongchang showed that the group with the largest proportion in winter was organic matter（48%）,followed by nitrate（22%）,sulfate（14%）,ammonium salt（13%）and chlorine salt（3%）.The Positive Matrix Factorization（PMF）source analysis model was used to analyze five main pollution sources:Traffic source（HOA）,biomass burning source（BBOA）,coal burning source（CCOA）,low oxidation organic aerosol（LO-OOA）and high oxidation organic aerosol（MO-OOA）.（2）Organic compounds（48%）accounted for the largest proportion in summer,followed by sulfate（25%）,ammonium salt（15%）,nitrate（11%）and chlorine salt（1%）.The PMF source analysis model was used to analyze the four main pollution sources:traffic source（HOA）,biomass combustion source（BBOA）,low oxidation organic aerosol（LO-OOA）and high oxidation organic aerosol（MO-OOA）.（3）The study of pollution events in winter and summer shows that the pollution period in winter alternates with the relatively clean period.The duration of pollution days is longer,while the duration of the relatively clean period is usually shorter.The e summer cleaning period is longer,the pollution period is shorter,the air quality is better overall.The development process of haze pollution was studied,and it was found that the haze pollution in winter was mainly driven by BBOA(from 3.36μg m^-3to 10.72μg m^-3).During summer pollution,nitrate concentration increased rapidly(from 4.98μg m^-3to 6.73μg m^-3),while secondary organic aerosol concentration changed little.（4）According to backward trajectory and potential source contribution analysis,regional transport pollution in winter and summer mainly comes from the eastern part of Sichuan Province and the central and western part of Chongqing.The potential sources of winter pollution are mainly in the eastern part of Sichuan Province and the western part of Chongqing,which is consistent with the backward trajectory analysis results.The potential pollution sources in summer are mainly concentrated in southern Henan Province and central and southern Hubei Province.Through the analysis of the above two models,it is found that regional transmission and local generation are the main sources of local haze generation.Regional joint prevention and control is of great significance for controlling PM_2.5pollution in Chongqing.