Pollution Characteristics And Aqueous-Phase Process Of Oxygenated Organic Compounds In Wintertime North China Plain: Insight From FIGAERO-I-CIMS

Fine particulate matter is the main component of air pollution,which has an important impact on public health and global climate change.Organic compounds from secondary sources（Secondary organic aerosols,SOA）are the main components of fine particulate.The main components of fine particulate matter are secondary organic compounds（secondary organic aerosols,SOA）.Traditionally,SOA is thought to be formed via gas-phase oxidation of volatile,intermediate-and semi-volatile organic compounds（VOCs and I/SVOCs）followed by partitioning into the preexisting organic aerosol（OA）.However,chemical reactions in the aqueous phase are poorly explored but potentially important pathways in SOA formation.Therefore,it is necessary to carry out research on the sources and pollution characteristics of SOA in aqueous-phase environment,which is helpful to understand the chemical process and importance of SOA in atmosphere.In this research,the emission characteristics of PM_2.5 at a higher concentration level in winter in the North China Plain were observed,and the effect of aqueous phase process on OA evolution was studied at the molecular level by taking advantage of the soft ionization advantages of FIGAERO-I-CIMS.According to FIGAERO-I-CIMS online measurement,we can comprehensively understand the characteristics of pollution emissions from regional sites in the North China Plain in winter,and identify important species such as levoglucosan,dicarboxylic acid and nitrophenol compounds during the campaign,which is highly correlated with local anthropogenic emissions.In addition,we also found these typical high-concentration species have different performance between high and low humid environments,which provides guidance for us to understand the influence of aqueous-phase process on SOA.Therefore,based on the results from a non-targeted analysis of FIGAERO-I-CIMS mass spectra of organic aerosol,we show that enhancement ratios of four different dicarboxylic acids to SOA and their growth rate during the daytime are significantly larger during the periods with higher aerosol liquid water content（ALWC）than the other periods by a factor of 5-10,suggesting that secondary formation of these dicarboxylic acids is promoted by daytime aqueous-phase reactions in the particles.In contrast to dicarboxylic acids,levoglucosan demonstrated larger depletion during the periods with more aqueous-phase reactions,implying aqueous reactions during the daytime are a main chemical removal pathway of levoglucosan in the atmosphere.This work provides the observation evidence of aqueous reactions in organic aerosol at a molecular level in the real ambient air.Secondary formation of dicarboxylic acids and/or depletion of levoglucosan investigated in this study may act as potential indicators of the aqueous-phase reaction in the atmosphere.