Preliminary Study On The Aqueous Secondary Organic Aerosol In Jinan Of Winter

Volatile organic compounds are oxidized to semi-volatile organic compounds by photochemical reactions and oxidant oxidation in the gas phase,then through gas-particle partition,including nucleation,condensation,heterogeneous chemical reaction and eventually formed to suspended particles in the atmosphere,which is known as secondary organic aerosol(SOA).SOA accounts for about 20%to 90%of organic aerosol in the atmosphere.The formation mechanism of SOA in the atmosphere is complex,including the ways of the reactions in the gas phase and aqueous phase.Currently,many laboratory and model studies have indicated that aqueous phase reaction was one of the potential important sources of SOA.In recent years,Shandong province has suffered from serve particulate pollution,especially coal combustion for warming in winter,which deteriorated the air quality resulting haze occurring frequently.The concentration of particulate matter is higher in heavy pollution with the weakened sunlight and high relative humidity,which provides a favorable condition for the formation of SOA through aqueous phase.In this study,the sampling was conducted in winter of 2016 and 2017 in urban area of Jinan.The primary and secondary WSOC were distinguished by using potassium ion(K+bb)from biomass combustion,which made a preliminary study on the formation of aqSOA in winter of Jinan.Further,the contributions of secondary organic carbon(SOC)under the different haze pollution were evaluated and the relationship of SOC and RH was investigated,meanwhile,the preliminary study on the contribution of the secondary WSOC(WSOCsec)to WSOC was made under different haze pollution.These were used to reveal the formation of aqSOA in different haze pollution.The results showed that in Jinan,62%organic carbon was from the secondary formation in winter of 2017.The concentrations of SOC and WSOC,and the contribution of SOC to OC increased along with the addition of RH,suggesting that aqueous formation pathway plays an important role in SOA production in winter.Under different levels of pollution,the contribution of primary emission to OC decreased and the contribution of secondary formation was on the rise with the increase of haze pollution and RH,indication aqSOA played an important role on the haze.The contribution of WSOCsec to WSOC increased slightly with more and more pollution,while the contribution in the middle haze was the largest(52.5%),that is,SOC in the haze formed more in the aqueous phase.The four factor identified by the positive matrix factorization(PMF)analysis were SO42-from secondary formation related(9.4%),oxalate and NO3-from secondary formation related(30.3%),biomass burning(52.9%)and traffic emissions(7.4%).However,with the pollution worsened,the contribution of the primary emission source decreased gradually,and the contribution of the secondary formation increased gradually.In this study,above results can help understand the formation of aqSOA in the field and provide a strong scientific and technological support in controling and alleviating haze occurrence.