Characteristics And Sources Apportionment Of Ambient Volatile Organic Compounds In Changzhi

Volatile organic compounds(VOCs)are ubiquitous compounds in the atmosphere.These not only have a direct impact on human health and ecological environment,but also participate in atmospheric photochemistry reaction to produce ozone(O3)and secondary organic aerosols(SOA).In this study,VOCs in the ambient air as the main research objects were collected in summer and winter,2017-2018 in five different observation point positions in Changzhi,and analyzed by Gas Chromatography/Mass Spectrometer Detector(GC/MSD/FID).The concentration characteristics and chemical reactivity of VOCs species were studied.Ratio analysis,the backward trajectory model and positive matrix factorization model were used to investigate the sources of VOCs.Ozone formation potential and secondary organic aerosols formation potential were calculated,in order to analyze the environmental implication of the detected VOCs.The main findings are as follows:1.The average concentrations of total volatile organic compounds(TVOC)in summer and winter in Changzhi were 39.78?g·m-3and 48.30?g·m-3 respectively.The dominant species of VOCs in summer are acetylene,ethane and n-butane,while propane,ethane and propylene in winter..The major VOCs groups were alkanes and alkenes in both seasons.There is a similar diurnal trend of VOCs concentration in summer and winter.The peak and valley values appear in periods of 6:00-8:00 and 12:00-14:00 respectively in summer,moreover 10:00-12:00 and 14:00-16:00 in winter.2.The OH consumption rates of VOCs were 4.67 s-1 and 4.50 s-1,in summer and winter,respectively.The chemical reaction activity of VOCs species in two seasons is roughly equal.The most reactive species was isoprene,followed by cis-2-pentene and propene in summer,while propene,followed by ethene,cis-2-pentene in winter.The most reactive VOCs were alkane compounds both in summer and winter,with the proportion of the OH consumption rates being 80.72%and 76.60%respectively.During the two observation periods in summer and winter,the ozone formation potential of alkenes,which had the highest formation potential,were 81.36?g·m-3 and 101.56?g·m-3,respectively,accounting for 62.08%and 64.56%of the total formation potential.3.In summer and winter,the secondary organic aerosols formation potential of TVOC were 0.35?g·m-3 and 0.38?g·m-3,respectively,among them,aromatic hydrocarbons,which had the highest formation potential,were 0.30?g·m-3 and 0.34?g·m-3,respectively,accounting for 86.47%and 92.27%of the total formation potential.Toluene,benzene,m-xylene and other VOCs contributed significantly to the secondary organic aerosol formation potential in summer and winter.4.Ratios of B/T were L48 and 2.65,of i-pentane/n-pentane were 2.29 and 1.45 in summer and winter,respectively,indicating that VOCs were derived from the mixture of road and coal combustion source.Clustered analysis of air masses backward trajectory showed that most of air masses in summer came from the northwest,moreover some came from south and east,and most of air masses in winter came from the northwest,in addition some came from north and east.And a large number of pollutants produced from different regions might have great influence on VOCs of Changzhi through air mass move.The result of source apportionment by positive matrix factorization model shows that,the sources of fuel combustion,vehicle emission,plant emission industrial,solvent usage and industrial emission,contributed 31.27%,28.30%,10.51%,17.93%,11.98%to VOCs in summer,while 46.30%,20.47%,2.29%,11.58%,19.35%in winter,respectively.The largest ratios of ozone formation potential both were combustion sources(15.62?g·m-3,26.97%)and(21.57?g·m-3,43.60%),respectively.Controlling the emission of vehicle exhaust,industrial sources,combustion sources and reducing the using of solvents can effectively reduce the concentration of ozone in ambient air of Changzhi City.The most important of source of secondary organic aerosols formation were solvent usage sources and fuel combustion sources,respectively.Winter is mainly due to coal-fired heating,industrial and civil boiler combustion and motor vehicle use.Controlling the above sources can effectively prevent and control the occurrence of complex pollution weather phenomena such as fog and haze in Changzhi.