Study Of Characteristics And Sources Of Ambient Volatile Organic Compounds In Qingpu District Of Shanghai

Qingpu District is located in the west of Shanghai,with large water area and high greening degree.The state controlling air sampling site set at Dianshan Lake in Qingpu District has been used as the background of Shanghai.Since Shanghai government released the monitoring data of ambient atmosphere at June 27,2012,people found it surprisingly that the concentration of PM2.5 and O3 in Qingpu District were always the highest in Shanghai.In order to find out the reasons,we did research and analysis of VOCs,the most important precursors of PM_2.5 and O₃ in Qingpu District.The ambient concentrations of 58 VOCs species were monitored continuously in November to December 2012 and May to October 2014 by automatic online GC-FID in the Qingpu District of Shanghai,and the chemical properties and variation tendency were analyzed.The overall concentration of the ambient VOCs was at a lower level in Qingpu District,where the average concentration was?28.76±3.59?ppbv,and the chemical components including alkanes,alkenes,aromatics and acetylene,which accounted for 44.73%,16.45%,30.25%and 8.56%,respectively.VOCs were abundant in winter,followed by spring and summer,autumn got the lowest content.Main species of VOCs in spring,summer and autumn were consistent,primarily paraffins of C2^C4,ethylene,toluene,m/p-xylene,ethyl benzene and acetylene;while ethane,propane,ethylene and acetylene were relatively high in winter.Greatly affected by mobile source,diurnal variation of total VOCs as well as the components showed obviously two peaks.With a wide green area,higher VOCs emission from vegetables became a marked feature of local atmospheric VOCs.Its average volume concentration was1.21ppbv,accounting for 4.19%of total VOCs.The main species were isoprene,?-pinene and?-pinene,of which isoprene got the highest content,and had a significant seasonal variation.Since the combine effects of biological factors and environmental factors,isoprene,?-pinene and?-pinene showed different daily trends in different seasons,respectively,and there was no correlation between these species.Atmospheric VOCs exhibited strong chemical reactivity of Qingpu District,whose OH radial loss rate constant was 10.08×10^-12cm³·molecule^-1·s^-1,and the maximum incremental reactivity was 2.90mol/mol.Olefins and aromatics as the key active ingredients,contributing 56.66%and 29.51%to L^OH,46.55%and 39.89%to OFP,respectively,of which the key active species were ethylene,isoprene,toluene,m/p-xylene and propylene.Local atmosphere showed a higher chemical activity in the spring and summer than in autumn and winter,but they shared similar main contributors.Vehicle exhaust was a major contributor to atmospheric VOCs of Qingpu District,biomass burning,paints and solvents usage,industrial emission,LPG leakage and vegetable emission as well,which accounted for 43%,15%,16%,7%,5%and 3%,calculated by CMB model.Vehicle exhaust showed significantly contribution to atmospheric VOCs in different seasons;paint and solvent usage,together with LPG leakage got higher share ratio in summer,as well as vegetable emission;contribution rate of biomass burning was obviously higher in autumn than other seasons;VOCs in winter was influenced mainly by paints and solvents usage.