The Study Of Pollution Characteristics And Source Apportionment Of Volatile Organic Compounds In The Urban Center Of Changsha

Volatile organic compounds（VOCs）are one of the important precursors for the formation of photochemical smog and PM_2.5,and play an extremely important role in atmospheric chemistry.With the rapid development of the regional economy,Changsha City is facing severe ozone.Therefore,it is of great practical significance to study the pollution characteristics and source analysis of VOCs in the atmospheric environment.This article uses the Nutech 6000-5D VOC atmospheric volatile organic compounds online monitoring system to conduct continuous online monitoring of VOCs in the atmospheric environment of Changsha City from July 2018 to June 2019.And the law of time change,using the characteristic species ratio method and the receptor model method to analyze the source of VOCs in the atmospheric environment of Changsha City.The main performance are as follows:（1）The average annual mass concentration of VOCs in the atmospheric environment of Changsha is 75.71μg/m³,of which alkanes（42.67μg/m³）account for the largest proportion,accounting for 56.35%,followed by aromatic hydrocarbons（27.15%）,molecular weight（22.45%）and acetylene（3.84%）.C₂-C₇ alkane,benzene series,C₂-C₄ alkyl and acetylene are the main types of VOCs in the atmospheric environment of Changsha.（2）According to the correlation of twelve target compounds,it is known that the components are not simple linear relationships.Ethylene and acetylene originate from the same fossil combustion source;propane has a wider source of pollution and is homologous to more species;isobutane/n-butane and n-pentane/isopentane isomers indicate monitoring data It is more reliable;the correlation between isopentane and2-methylheptane is higher,both of which are derived from light gasoline motor vehicle exhaust;the correlation between aromatic hydrocarbon species indicates that the contribution of motor vehicle exhaust emissions to benzene is less than that of solvent use;N-dodecane may be derived from diesel vehicle exhaust emissions.（3）The daily change of VOCs in the atmospheric environment of Changsha has a bimodal distribution,respectively at 10:00 am and 0:00 pm.The daily changes of alkane,aromatic hydrocarbon,carbonyl and acetylene are consistent with the VOCs change curve.Concentration of VOCs The monthly average concentration of VOCs in the atmospheric environment of Changsha has a"V"distribution,with the average mass concentration in December being the highest and the lowest in June.The seasons corresponding to the months also show the same change law,that is,winter>autumn>spring>summer.The seasonal variation characteristics of alkanes,aromatic hydrocarbons,acetic acid and acetylene are consistent with the overall trend of VOCs.（4）According to the analysis of B/T ratio method,it can be seen that Changsha is mainly affected by disturbance emissions in spring and summer,and coal combustion in autumn and winter.According to the isopentane/n-pentane ratio method,it can be known that Changsha is affected by both peak and coal combustion in spring and winter,mainly affected by coal combustion in autumn,and mainly affected by disturbance in summer.（5）The results of the analysis of different receptor models show that solvent use sources and mobile sources are the main sources of VOCs in the atmospheric environment of Changsha City,accounting for 34.0%and 37.2%of the total emission sources respectively,followed by combustion sources,storage and transportation Source and industrial source.