Chemical characteristics and sources of water-soluble organic aerosol in southwest suburb of Beijing

摘要

PM2.5 filter sampling and components measurement were conducted in autumn and winter from 2014 to 2015 at a suburban site(referred herein as "LLH site") located in the southwest of Beijing.The offline aerosol mass spectrometry(offline-AMS) analysis and positive matrix factorization(PMF) were applied for measurement and source apportionment of watersoluble organic aerosol(WSOA).Organic aerosol(OA) always dominated PM2.5 during the sampling period,especially in winter.WSOA pollution was serious during the polluted period both in autumn(31.1 μg/m3) and winter(31.9 μg/m3),while WSOA accounted for 54.4%of OA during the polluted period in autumn,much more than that(21.3%) in winter.The oxidation degree of WSOA at LLH site was at a high level(oxygen-to-carbon ratio,O/C=0.91)and secondary organic aerosol(SOA) contributed more mass ratio of WSOA than primary organic aerosol(POA) during the whole observation period.In winter,coal combustion OA(CCOA) was a stable source of OA and on average accounted for 25.1% of WSOA.In autumn,biomass burning OA(BBOA) from household combustion contributed 38.3% of WSOA during polluted period.In addition to oxygenated OA(OOA),aqueous-oxygenated OA(aq-OOA) was identified as an important factor of SOA.During heavy pollution period,the mass proportion of aq-OOA to WSOA increased significantly,implying the significant SOA formation through aqueous-phase process.The result of this study highlights the concentration on controlling the residential coal and biomass burning,as well as the research needs on aqueous chemistry in OA formation.