Concentration Distribution And Source Apportionment Of Volatile Organic Compounds In Typical Areas Of A City

Volatile organic compounds（VOCs）are of great importance in the formation of secondary pollution in air.It is vital to study the concentration and components of VOCs in atmosphere,identify the key species to urban air quality and explore their major sources.These researches can provide a scientific basis for making effective control measurements and improving air quality.In this study,a field sampling campaign of VOCs was conducted in an eastern city called A.The concentration levels and spatiotemporal distribution of VOCs were showed,and the contribution to secondary pollution and major emission sources were explored.The main contents of this study are listed as follows:（1）A field sampling campaign of VOCs was conducted on 17 May,26 June,20July,24 August,26 September 2018 and 3 Jan,18 Jan 2019 at three functional sites of botanic gardens（HP）,industrial areas（XS）,and traffic residential mixed areas（ZH）in the city.A total of 107 species of VOCs for each sample were quantified using PAMS and TO-15 standard gases with a pre-concentrator coupled by GC/MS.The concentration levels and spatiotemporal distribution of VOCs were analyzed.It was found that because of the diversity of emission sources,different characteristics of VOCs species composition were showed at three sampling sites.Isoprene in HP,isopropyl alcohol in XS,and n-butane in ZH were the characteristic species,respectively.In regarding to three sites,the most abundant species were acetone,propane,ethane and ethylene in A city during the sampling period.（2）The VOCs reactivity was calculated,and the key species to secondary pollution was found based on propylene-equivalent concentrations（Prop-E）and ozone formation potential（OFP）.Alkenes,alkynes and aromatics were the active VOCs,and they altogether contributed reactivity by over 65%,only with 18.78%～21.35%of volume mixing ratio.At three sites,the species that contributed the most to O₃ formation were ethylene,isoprene,toluene,propylene and m-xylene.And the species that contributed the most to SOA formation were toluene,m-xylene,ethylbenzene,o-xylene and p-xylene.（3）Based on the pollutants concentrations and diffusion conditions,the causes of O₃ and PM_2.5 exceedance during sampling period were investigated.The extent of reaction E（t）indicated that O₃ formation was generally VOCs-limited in the morning and evening,and a NOx-limited and transition regime at noon.The high concentrations of O₃ and PM_2.5 was influenced by both local photochemical reaction and regional transport.（4）In order to identify the tracers of different emission,source apportionment was performed by the Positive Matrix Factorization（PMF）model during summer and winter.Five local VOCs emission profiles,including on-road mobile sources,gasoline vehicle exhaust,solvent painting,biomass burning,and cooking fumes,were constructed to examine the accuracy of PMF results.Factors were identified with PMF in summer,consisting of LPG/NG usage,solvent utilization,biomass burning,vehicle exhaust,aged background,secondary source,and biogenic emission.And the major contributors to VOCs concentrations were LPG/NG usage and secondary source.Factors were identified in winter,similar with summer,except for biogenic emission.And the major contributors to VOCs were vehicle exhaust and solvent utilization in winter.