Reactive Activity,Source Analysis And Health Risk Assessment Of VOCs In Ambient Air Of Shahekou District,Dalian

Volatile organic compounds are a kind of organic pollutants with complex composition and widespread in the atmospheric environment.They are the key precursors for the formation of ozone and secondary organic aerosols,and have an important impact on urban photochemical smog and haze pollution.In recent years,with the rapid development of regional economy,the emission load of VOCs in China’s urban atmosphere has increased,which has a significant impact on environmental quality and human health.Therefore,studying the concentration level,reactivity and source analysis of VOCs in the atmospheric environment based on observational data is of great significance for improving air quality and protecting public health.In this study,syntech GC955 series online gas chromatography analysis system was used to collect VOCs in the atmosphere of Shahekou District,Dalian from June 2020 to May 2021.50 VOCs species were analyzed.Combined with meteorological parameters and environmental air quality data of observation points of the national urban atmospheric environment monitoring network,the component characteristics,variation law and reaction activity of VOCs in Shahekou District of Dalian were studied.On this basis,positive matrix factorization（PMF）and US EPA health risk assessment model are introduced to study the local sources of VOCs and the impact of toxic and harmful species on human health.Based on the above research results,the following main conclusions are drawn:The average value of VOCs volume fraction during the study period was（16.38±8.57）×10^-9,the proportions of alkanes,alkenes,alkynes and aromatic hydrocarbons are69.65%,12.14%,8.42%and 9.79%respectively.The volume fraction of VOCs has obvious seasonal variation,showing a trend of winter>autumn>spring>summer.The volume fraction of VOCs in Shahekou District of Dalian is at a relatively low level in China.The difference in the proportion of each component may be related to the energy structure,industrial structure and sampling time.The volume fraction of VOCs reaches the peak at 08:00 and the lowest at 16:00.The photochemical reaction is weak at night and the height of boundary layer is low,which makes VOCs gradually accumulate and maintain at a high concentration.O₃presents a single peak distribution,and the maximum value appears at 15:00.The photochemical reaction is strengthened in the daytime,and the production of O₃ increases.NO_x peaked at 08:00 and 21:00,which is related to the morning and evening peak of traffic,and is obviously affected by motor vehicle emission sources.The contribution of alkanes,alkenes,alkynes and aromatics to L_OH was 30.03%,48.83%,2.00%and 19.16%respectively;The contribution to OFP is 28.44%,34.94%,1.84%and 34.78%respectively.The monthly variation trends of L_OH and OFP are generally the same;Considering the species activity,ethylene,1-hexene,propane,m-p-xylene,toluene,n-butane,propylene and isopentane are the key species affecting the atmospheric activity in Dalian.Giving priority to controlling the emission of olefins and aromatic hydrocarbons is the key to improving O₃ pollution in summer in Dalian.SOA_FPin the ambient air is 0.39±0.22μg/m³,the proportion of each component is aromatic hydrocarbon（95.16%）>alkane（4.30%）>olefin（0.54%）.Aromatic hydrocarbons are the key active species affecting the formation of SOA by VOCs in Shahekou District,Dalian.The source of VOCs is qualitatively analyzed by characteristic ratio method（T/B）.The contribution of traffic source in summer and autumn is significant,and the impact of vehicle emission,coal combustion and biomass combustion in winter and spring is prominent.The volume fraction ratio of o-xylene to ethylbenzene is selected to calculate the initial concentration of VOCs.The PMF is used to obtain the main pollution sources in Shahekou District of Dalian from June 2020 to May 2021,which are combustion source（32.67%）,traffic source（25.17%）,gasoline volatilization+LPG/NG（15.62%）,solvent use source（11.40%）,industrial emission source（9.80%）and natural source（5.26%）.Among them,combustion source,traffic source and gasoline volatilization+LPG/NG are the main sources of VOCs Pollution,accounting for 73.46%.The health risk assessment model of US EPA was used to evaluate the non-carcinogenic and carcinogenic risk of VOCs to exposed people in Shahekou District of Dalian.There is no non-carcinogenic risk of toxic VOCs in this area,but there are seasonal differences,which are winter>autumn>summer>spring.Benzene has a potential carcinogenic risk to the human body in autumn and winter;the total carcinogenic risk value in summer,autumn and winter is higher than the US EPA safety threshold,which should be taken seriously.