| As one of the most developed and fastest-growing regions in China,the rapid economic development of Shanghai in the last decades results in a serious decline in air quality,and haze episodes occur more frequently than before.Recent studies revealed that high level fine particles was the key factor of haze episodes,and submicron aerosol(PM1)has become the main driving force in haze formation.Compared to PM2.5,PM1 has more significant impacts on the environment and health.China has invested a lot of resources to carry out researches on PM2.5 in heavily polluted areas such as BeijingTianjin-Hebei,Yangtze River Delta and Pearl River Delta regions.However,studies on smaller particles,such as PM1 is rarely involved.Studies in compositions,characteristics,formation and evolution of PM1 particles in urban Shanghai are still in its infancy.In this study,a high-resolution time-of-flight aerosol mass spectrometer(HR-To FAMS)was employed to characterize the submicron particles(PM1)in urban Shanghai from 2018 to 2019.The purpose is to investigate the physicochemical characteristics of PM1 in Shanghai,especially the organic aerosols(OA).Positive matrix factorization(PMF)was then applied to explore the sources of the organic aerosols.In addition,the effects of photochemical oxidation and aqueous-phase reactions on the formation and evolution of secondary aerosols were also explored.The main conclusions are as follows:(1)The mean concentrations of PM1 in urban Shanghai in different seasons were: winter(31.4±19.9 ?g·m-3)> autumn(24.2±16.5 ?g·m-3)> spring(21.7±9.5 ?g·m-3)> summer(18.6±13.5 ?g·m-3).Organic matter was dominant in PM1,comprising around 59%,53%,48% and 40% of the total PM1 mass in spring,summer,autumn and winter respectively.SO42-accounted for a larger proportion of PM1 in spring and summer(24% and 25%),while the contributions of NO3-to PM1 exceeded SO42-in autumn and winter(20% and 29%).The particles were generally acidic,and the acidity was the highest in summer and the lowest in winter.(2)The contribution of NO3-to PM1 enhanced significantly with the increasing PM1 concentrations.And the aerosol liquid water content(LWC)was significantly correlated with the NO3-concentration,indicating that the aqueous-phase reactions have a great effect on the formation of NO3-,and this phenomenon was more pronounced in autumn,winter and summer.(3)Elemental analysis shows that annual average of OM/OC in Shanghai was 1.79,significantly higher than the empirical coefficient of 1.4.Indicating that the concentrations of organic matter is likely to be underestimated by the OC/EC method if the normal empirical OM/OC ratio was used.(4)Four types of organic aerosol were identified by PMF: HOA,COA,SV-OOA and LV-OOA,the average contribution to OA was 13.7%,20.0%,35.1%,and 31.2%,respectively.Primary organic aerosols(POA)mainly came from the motor vehicle and cooking emissions,and their contributions to PM1 were roughly stable across different seasons.(5)Aqueous-phase processing has a significant effect on the formation of NO3-and SO42-,especially for NO3-.While photochemical oxidation processing plays an important role in the formation of SO42-,especially in spring and summer.The mass concentration of SV-OOA and its contribution to OA were positively correlated with RH,indicating that the less oxidized SOA is mainly driven by aqueous-phase reaction.The mass concentration of LV-OOA and the contribution of SOA to OA were positively correlated with Ox,photochemical oxidation significantly promotes the formation of SOA,but its impacts on the composition and oxidation states of SOA are different in different seasons.Generally,photochemical oxidation shows more significant impact on the formation of aged SOA than other factors.(6)Overall,the contributions from secondary organic and inorganic aerosols to PM1 were 30% and 50%,respectively.This study highlighted the influences of photochemical and aqueous chemistry in promoting the formation of secondary aerosols in Shanghai. |
PDF Full Text Request