Sources Of Non-Methane Hydrocarbons And Their Impacts On O₃ And SOA Formation In Urban Areas Of Beijing

Non-methane hydrocarbons（NMHCs）can produce a series of chemical reactions with oxidants in the troposphere,resulting in the formation of secondary pollutants,such as ozone（O₃）and secondary organic aerosol（SOA）.Therefore,as the important precursor for O₃ and SOA formation,it is necessary to carry out comprehensive and systematic field observation of NMHCs.Hence,the field observations of NMHCs was conducted at Beijing urban areas in 2020 and 2021 in this study.The sources of NMHCs,and their impacts on O₃ and SOA formation in the atmosphere were systematically studied.The main contents and conclusions were as follows:1.Sources of ambient NMHCs and their impacts on O₃ formation during autumn,Beijing.The field observation of 54 NMHCs was conducted from September 1 to October 20 in 2020 during autumn in Haidian District,Beijing.The mean concentration of total NMHCs was 29.81±11.39 ppbv during this period,and alkanes were the major components.There were typical festival effects of NMHCs with lower concentration during the National Day.Alkenes and aromatics were the dominant groups in ozone formation potential（OFP）and OH radical loss rate(L_OH).The positive matrix factorization（PMF）running results revealed that vehicular exhaust became the biggest source in urban areas,followed by liquefied petroleum gas（LPG）usage,solvent usage,and fuel evaporation.The box model coupled with master chemical mechanism（MCM）was applied to study the impacts of different NMHCs sources on O₃ formation in an O₃ episode.The simulation results indicated that reducing NMHCs concentration could effectively suppress O₃ formation.Moreover,reducing traffic-related emissions of NMHCs was an effective way to control O₃ pollution at an urban site in Beijing.2.Sources of NMHCs and their impacts on SOA formation during the haze periods at an typical urban site in Beijing.The field observation of 54 NMHCs was conducted from March 1 to March 30 in 2021 during spring in Haidian District,Beijing.The mean concentration of NMHCs was 33.54±16.69 ppbv during the whole observation period.Compared with non-haze days,unfavorable atmospheric conditions and local NMHCs emissions were important reasons for the formation of haze.The PMF model results showed that coal combustion and LPG usage were the main sources of NMHCs during the observation period.Aromatics were the largest contributor to secondary organic aerosol potential（SOAP）.In addition,solvent usage and gasoline vehicular exhaust source was the main contributors to SOAP,accounted for 52.19%.Therefore,aromatics were the dominant species for SOA formaiton in the atmosphere.From the perspective of source governance,controlling NMHCs emission of solvent usage and gasoline vehicular exhaust was effective to suppress SOA formation at urban areas in Beijing.