Study On The Potential Contribution Of Volatile Organic Compounds To Ozone And Secondary Organic Aerosols In Summer

A comprehensive analysis of ambient air quality of Shuozhou City in 2014 and 2015,showed that ozone?O₃?pollution was prominent during summer?June August?in 2015,and sustained O₃ pollution will be a serious threat to the local people's health and ecological environment.It is difficult to study O₃ directly because it's a secondary pollutant.Volatile organic compounds?VOCs?,as the important precursor of ozone?O₃?and secondary organic aerosols?SOA?,were selected as the main research objects.In this study,the samples were collected and detected to study the characteristics and sources of VOCs in Shuozhou during summer.In addition,the potential contribution of VOCs sources to ozone and secondary organic aerosols were estimated by positive matrix factorization model?PMF?.The conclusions were as follows:1.The average concentration of total VOCs?TVOCs?was?102.93 ± 35.90??g·m-3 in Shuozhou.The average concentrations of aromatic hydrocarbons,alkanes,alkenes and acetylene were?53.52 ± 17.67??g·m-3,?41.74 ± 15.62??g·m-3,?6.53 ± 5.16??g·m-3and?1.14 ± 0.91??g·m-3,respectively.Aromatic hydrocarbons and alkanes were the major components.The top ten species which had highest contribution to TVOCs were n-undecane,n-dodecane,n-decane,p-diethylbenzene,1,2,4-trimethylbenzene,m,p-xylene,m-diethylbenzene,1,2,3-trimethylbenzene,o-ethyltoluene,toluene,and the total contribution to TVOCs was 46.52%.The aromatic hydrocarbons was the main compounds of VOCs in atmospheric,and n-undecane,n-dodecane,n-decane were the main species in alkane compisition.2.The diurnal variation curve of the TVOCs concentration had a bimodal characteristic.The peak appeared at 8:00-10:00 and 18:00-20: 00 and the values were 135.14 ?g·m-3 and 95.92 ?g·m-3,respectively,while the valley appeared at 16:00-18:00 and the value was 81.92 ?g·m-3.The diurnal variation of aromatics,alkanes,acetylene were consistent with TVOCs.However,the time of the early peak and valley value of alkenes were all advanced comparing with total VOCs,which was mainly related to the strong chemical reactivity and the short life time of alkenes.3.The ozone formation potential?OFP?of TVOCs was 443.85 ?g·m-3.The contribution of aromatics,alkenes and alkanes were 76.66%,15.09% and 8.26%,respetivity.Aromatic hydrocarbons were the key active components of VOCs to generate O₃.The major species of VOCs to convert O₃ were 1,2,3-trimethylbenzene,1,2,4-trimethylbenzene,m-p-xylene,1,3,5-Trimethylbenzene,m-diethylbenzene,propylene and isoprene in Shuozhou during summer.It can be reduce the concentration of O₃ in photochemical reaction,at the same time,prevent the generation of photochemical smog by controlling the major species concetration from source emmisions.4.The SOA concentration value obtained by the VOCs was 2.99?g·m-3,with the aromatic hydrocarbons had the highest contribution to total VOCs.The contribution of aromatics,alkanes and alkenes were 85.82%?13.54%?0.65%,respetivity.5.There were six emission sources of ambient VOCs from positive matrix factorization model?PMF?in Shuozhou,including vehicle exhaust emissions source?26.09%?,combustion source?22.03%?,oil evaporation sourece?17.26%?,solvent usage source?15.39%?,plant emission source?9.70%?and LPG/NG leakage source?9.52%?.6.The potential contribution of VOCs emission sources to O₃ were vehicle exhaust emissions source?25.78%?,combustion source?23.55%?,oil evaporationsource?17.00%?,solvent usage source?15.74%?,plant emission source?10.80%?and LPG/NG leakage source?7.14%?.Potential contribution of VOCs emission sources to SOA were vehicle exhaust emissions source?28.41%?,combustion source?20.69%?,oil evaporation source?18.29%?,solvent usage source?17.01%?,plant emission source?8.80%?and LPG/NG leakage source?6.80%?.7.Aromatic hydrocarbon components had the highest contribution to the TVOCs.It was also the key active component in the process to form O₃ and SOA.The vehicle exhaust emission source and combustion source which contained rich aromatic hydrocarbon components not only the two major sources of VOCs,but also the main two potential contribution to O₃ and SOA.The emissions from oil evaporation source,solvent usage source and LPG/NG leakage source can not be ignored because of the high temperature conditions.In order to reduce the concentration of VOCs,O₃ and SOA,it is important to reduce the emission of combustion source,control simultaneously the emissions of vehicle exhaust and oil evaporation,and reduce the emission of solvent usage.The air qualty of Shuozhou can be improved by this way.