Characteristics And Reactivity Of Atmospheric Volatile Organic Compounds In Datong

In recent years,with the rapid economic development and urbanization process,ozone and haze pollution caused by volatile organic compounds（VOCs）in the atmosphere have become serious environmental problems.This study takes Pingcheng District of Datong as the research area,through continuous collection of atmospheric samples,the concentration level,component characteristics and temporal and spatial variation characteristics of VOCs in the atmospheric environment of Datong during 2021.3.1～2022.2.28 are analyzed.And studies the correlation between PM_2.5,O₃,NO₂ and meteorological conditions and TVOCs.The chemical reaction activity of VOCs in Datong was analyzed by estimating the OH radical generation rate(L^OH),ozone generation potential（OFP）and secondary organic vapor generation potential（SOAFP）.The source of VOCs is analyzed according to the PMF model and correlation/cluster analysis model,and the spatial transmission process and potential source areas of VOCs in Datong are analyzed by combining the HYSPLIT backward trajectory model and PSCF function.Finally,health risk assessment was conducted for some VOCs species.However,due to the rapid oxidation of VOCs in the atmospheric transport process,there is inevitably a certain deviation when using the measured VOCs data to calculate the chemical activity and analyze the source of VOCs.Therefore,in order to correct the effect of photochemical loss,the initial VOCs concentration（the sum of measured VOCs concentration and photochemical loss VOCs concentration）is used to calculate L^OH and OFP,and the photochemical loss of VOCs is also considered in VOCs source analysis.The main findings are as follows:（1）The variation range of TVOCs mass concentration during observation was 4.98～50.15μg·m^-3,the average mass concentration was 22.62±8.31μg·m^-3.The composition of TVOCs was characterized by alkanes accounting for 38.2%,OVOCs accounting for 26.5%,alkenes accounting for 11.6%,alkyne accounting for 9.4%,halogenated hydrocarbons accounting for7.4%,aromatics accounting for 6.6%,and sulfide accounting for 0.3%.The seasonal variation of TVOCs concentration was characterized by winter(24.06±9.29μg·m^-3)>autumn(23.39±9.60μg·m^-3)>summer(22.56±6.04μg·m^-3)>spring(21.92±7.82μg·m^-3).Among them,alkanes had the highest contribution to the concentration of TVOCs in Datong in spring,autumn,and winter,and OVOCs had the highest contribution to the concentration of TVOCs in summer.The seasonal distribution characteristics of VOCs during the whole monitoring period were as follows:the mass concentration of alkanes was the highest in winter and the lowest in summer;The mass concentration of VOCs was the highest in summer and the lowest in winter;The mass concentration of halogenated hydrocarbon was the highest in spring and the lowest in autumn;The mass concentration of sulfide was the highest in autumn and the lowest in summer;The seasonal variation of the mass concentrations of alkenes,alkynes and aromatics was the same as that of TVOCs,with the highest in winter and the lowest in spring.In general,compared with most cities in China,the VOCs mass concentration in Datong was relatively low.（2）The correlation analysis results of TVOCs and major atmospheric pollutants(PM_2.5,O₃ and NO₂)show that TVOCs were positively correlated with NO₂ and PM_2.5,and negatively correlated with O₃.In addition,there was a certain correlation between atmospheric pollutants and meteorological factors in each season,indicating that meteorological factors have a certain impact on the concentration of pollutants in the atmospheric of Datong.（3）There was no non-carcinogenic risk for the key pollutants in the atmospheric of Datong,but the carcinogenic risk value of acetaldehyde was 1.01×10^-6,higher than the safety threshold,there was a risk of cancer.In addition,the carcinogenic risk value of benzene was 9.67×10^-6,very close to the safety threshold.Therefore,the future should focus on strengthening the management of acetaldehyde and benzene emissions in Datong.（4）In the summer with the highest ozone concentration in Datong,the formation of O₃was mainly dominated by NO_x,and atmospheric photochemical reaction had a significant impact on VOCs concentration.The L^OH and OFP results calculated based on the initial VOCs concentration show that the total L^OH of the four seasons in Datong was 2.93 s^-1,2.84 s^-1,2.74s^-1,and 2.61 s^-1,while the OFP was 64.38μg·m^-3,64.79μg·m^-3,63.98μg·m^-3,and 63.77μg·m^-3.Among them,ethylene,propylene,acetaldehyde,and propionaldehyde were the key active components of L^OH and OFP in all seasons of Datong,almost unaffected by seasonal changes.The formation potential of VOCs for SOA during four sampling seasons in Datong was 0.086μg·m^-3,0.059μg·m^-3,0.10μg·m^-3,and 0.13μg·m^-3,respectively,the key active species of SOAFP were toluene and m/p-xylene.（5）Based on the initial VOCs concentration,the PMF model was used to determine six VOCs sources in four monitoring seasons:coking process,NG/LPG use,combustion,industrial sources,solvent use and vehicle exhaust emissions.Among them,the coking process was the main source of VOCs pollution in Datong in summer and winter,and the use of NG/LPG was the main source of VOCs pollution in Datong in spring and autumn.The OFP values of various VOCs emission sources show that coking process and combustion are the most influential pollution sources for O₃ generation in Datong.In addition,HYSPLIT backward trajectory model shows that long-distance transportation also has an impact on VOCs pollution in Datong.