Study On Pollution Characteristics And Chemical Reactivity Of Volatile Organic Compounds By PMF In Atmospheric Environment,Taiyuan

Recently,there is growing concern about ozone?O₃?and fine particle pollution.Taiyuan is one of the top heavily polluted cities in China,and the level of fine particulate matter is high,and concentration of ozone increases year by year.However,volatile organic compounds?VOCs?,the important precursor of O₃ and secondary organic aerosols?SOA?,have not been reported in details in Taiyuan.In this study,SUMMA canisters were used for sampling and gas chromatograph-mass spectrometer was used to analyze VOCs from March 30,2016 to January 20,2017 in Taiyuan.The pollution levels and variation characteristics of VOCs in Taiyuan city were reported.In addition,positive matrix factorization model?PMF?and potential source contribution function?PSCF?were applied to analyze pollution sources and potential pollution source areas.Finally,the potential contribution of VOCs and each source of VOCs to O₃ and SOA were estimated by OH radical consumption rate,Maximum Incremental Reactivity?MIR?and Fractional Aerosol Coefficient?FAC?.The main conclusions were as follows:1.The total concentration of 48 VOCs was 5.95?109.37 ppbv,with an average of 24.22 ppbv,which was higher than that in Wuhan and Jinan.Low-carbon Alkanes?44.43%?were the largest contributors to the total VOCs,followed by aromatics?18.95%?.2.The highest concentration was observed in winter?35.36 ppbv?,followed by spring?19.39 ppbv?,autumn?16.82 ppbv?,and summer?11.37 ppbv?.TVOC has negative correlations with temperature,boundary layer height,and wind speed.However,due to the influence of wind direction,there is seasonal variation in the correlation between TVOC and wind speed.Due to the input of the coking source under the southwest wind with high wind speed,the correlation between wind speed and TVOC was poor in the spring,summer and autumn.In the condition of enhanced pollution emissions in winter,there was a significant negative correlation between wind speed and TVOC.3.OH radical consumption rate indicated that alkene contributes the most to VOCs chemical reaction activity in Taiyuan.The total OH reaction rate constant of 48 VOCs showed high level,with a value of12.9×10^-12·cm³·molecule^-1·s^-1.Aromatic hydrocarbons accounted for most of Ozone Formation Potential?OFP??48.55%?,followed by alkenes?36.46%?.As for VOCs species,Ethylene,propylene,xylene,trimethylbenzene and toluene were the greatest contributor to OFP in Taiyuan.The contribution of aromatic compounds to SOA reached up to 95.01%.4.Source apportionment by ratio analysis and PMF model found that combustion source and coal coking contributed the most?28.15%and 27.13%?to the total VOCs,followed by motor vehicle related emissions?18.15%?.Local combustion source and the coking source located in the west and southwest direction of Shanxi province was the main potential source of VOCs in Taiyuan.The potential sources of solvent use and Liquefied petroleum gas/natural gas/coal bed methane.?LPG/NG/CBM?were located in the southwest of hebei province and west of Inner Mongolia.Local emission was the main source of motor vehicle pollution.In addition to spring,the source of combustion was the maximum emission source in other seasons.Affected by high wind speed from southwest,coking source contributed most in spring.In summer,plant sources increased significantly compared to other seasons.In autumn and winter,combustion source increased significantly,especially in winter because of coal-fired heating.5.The source of solvent source and motor vehicle related sources,were the largest contributor to the formation of O₃ and SOA.And the contribution of coking source also cannot be ignored,with a proportion of nearly 20%.