Source profiles and impact of volatile organic compounds in vehicle exhaust in Luohe City
Background,aim,and scope O3 has replaced PM2.5,which will cause secondary atmospheric pollution like haze and photochemical smog.VOCs,as important precursors,can cause health problems and even carcinogenic risks with long-term exposure.Vehicle exhaust is a major source of VOCs in cities.With the development of vehicle technology and emission standards,source profile of VOCs emitted by vehicle need to be updated.Thus,studying the emission composition,secondary pollution contribution and health risk of VOCs in exhaust is crucial for the management of VOCs and health protection.Materials and methods 26 Gasoline and diesel vehicles under different emission standards were selected for bench tests at the inspection plant to detect VOCs in vehicle exhaust emissions,using the Simple Operating Condition Method(SOCM).The VOCs were sampled using PTFE bags with volume of 3 L,and an online pre-concentration-gas chromatography/mass spectrometry(GC-MS/FID)analyzer(Thermo Scientific 5800GM)was used to analyze 114 VOCs(including 29 alkanes,11 alkenes,1 alkyne,17 aromatics,35 halogenated hydrocarbons,and 21 OVOCs)using the standard gas CNEMC MIX-117(Linde,USA).In terms of the contribution of exhaust emissions to secondary air pollution,the maximum incremental reactivity(MIR)method was used to estimate the ozone production potential(OFP)and the toluene weighted mass contribution method was used to estimate the secondary organic aerosol potential(SOAP)values of VOCs species emitted from the exhausts of various types of vehicles in Luohe City.Both non-carcinogenic and carcinogenic health risks were assessed for inspection plant workers.Results The VOCs emitted from the exhaust of light-duty gasoline vehicles are mainly OVOC and alkanes,followed by aromatic hydrocarbons,accounting for 43.6％,35.0％and 11.6％,respectively.VOCs emitted from the exhaust of national Ⅳ light-duty petrol vehicles were mainly alkanes(52.0％),followed by OVOC(28.4％);VOCs emitted from the exhaust of national Ⅴ light-duty petrol vehicles were mainly OVOC(57.1％),followed by alkanes(23.8％).Characteristic species of petrol vehicles mainly included acetone(18.9％),isopentane(10.3％),acetaldehyde(5.7％),2,3-dimethylbutane(3.0％)and ethylene(2.9％).The characteristics of VOC emission from diesel vehicles of different emission standards were similar,which were mainly consisted of OVOC(51.1％—64.4％),followed by alkenes(19.0％—22.4％).Diesel vehicles mainly emitted acetone(23.4％),ethylene(13.6％)and acetaldehyde(10.4％).Alkane emissions from petrol vehicles increased by 47.3％and aromatic emissions decreased by 122.4％as the cumulative mileage increased.Among the exhaust emissions of gasoline and diesel vehicles,OVOC and alkenes had the greatest impact on OFP,while aromatic hydrocarbons contributed over 70％on SOAP among all types of vehicle exhaust emissions.The O3 source reactivity(SR(O3))of national Ⅳ,national Ⅵ light-duty diesel vehicles and national Ⅳ heavy-duty diesel vehicles was higher than 4.0 g·g-1,while the SR(SOA)of national Ⅳ light-duty diesel vehicles was the highest,more than 0.01 g·g-1.The hazard index(HI)values for the workshop,the petrol vehicle testing process and the diesel vehicle testing process were 4.4,3.7 and 4.8,respectively,which were higher than the acceptable level(=1).The corresponding carcinogenic risks for the three scenarios were 0.006,0.004 and 0.007,respectively,which were all above acceptable levels(=1 × 10-6).The risk values for acetaldehyde reached the defined risk level,and the exposure risks for 1,3-butadiene,propionaldehyde,1,1,2-trichloroethane,naphthalene,acetaldehyde,and 1,2-dichloroethylene propane should also cause the public attention.Discussion In this study,the characteristics of VOCs emitted from the exhaust of China Ⅲ light-duty diesel vehicles are similar to those emitted from the exhaust of China Ⅴ light-duty diesel vehicles,indicating that the VOCs emitted from vehicles are not only related to the emission standards,but also related to the age of the vehicle and the cumulative mileage travelled.OVOCs emitted in the exhaust of motor vehicles are mainly due to incomplete combustion in the chamber and the weak oxidation of alcohols by the three-way catalyst.National Ⅲ and national Ⅴ petrol vehicles mainly emit acetone,isopentane and acetaldehyde,which is due to incomplete combustion of some of the oil and gas under low and stable working conditions.Iso-pentane,acetone and 2,3-dimethylbutane are the main VOCs species emitted by national Ⅳ petrol vehicles.The difference in VOCs emissions between national Ⅳ and national Ⅴ petrol vehicles is mainly caused by the upgrading of exhaust gas recovery systems.The TVOC mass concentration of diesel vehicles is lower than that of light-duty diesel vehicles.The VOCs emissions from national Ⅳ,national Ⅴ and national Ⅵ light-duty diesel vehicles decrease sequentially.The characteristics of diesel vehicles emission are similar,and OVOCs are generated due to oxygen-rich combustion.As the cumulative mileage increases this leads to more C5-C7 alkanes from incomplete combustion.Considering the contribution of vehicle exhaust to OFP and SOAP,OVOC,alkenes,and aromatic hydrocarbons are the key VOCs species for VOC control.Priority should be given to the control of national Ⅳ and national Ⅵ light diesel vehicles and national Ⅳ heavy diesel vehicles with high SR(O3)and SR(SOA).The exposure to VOCs during vehicle inspection carries non-carcinogenic and carcinogenic risks,so the health protection of vehicle inspectors should be concerned.Conclusions(1)The VOC in the exhaust of light-duty petrol vehicles are mainly OVOC and alkanes.The characteristic species of petrol vehicles primarily include acetone,isopentane and acetaldehyde.The main VOC components in diesel vehicle exhaust are OVOC and alkenes.Alkane emissions from petrol vehicles increase with cumulative mileage.(2)Under the guidance of synergistic control of PM2.5 and O3,OVOC,alkenes and aromatic hydrocarbons of national Ⅳ,national Ⅵ light-duty diesel vehicles and national Ⅳ heavy-duty diesel vehicles should be the key control targets in Luohe City.(3)VOCs exposure of vehicle inspection workers could induce non-carcinogenic and carcinogenic risks,and 1,3-butadiene,acetaldehyde,naphthalene,1,2-dichloroethane and benzene have higher risk values,which are recommended to further strengthen the health protection of vehicle inspection workers.Recommendations and perspectives Vehicle exhaust is one of the major sources of urban VOCs,which will induce both environmental and health effects.Therefore,VOCs source profiles for different vehicle types with various emission standards need to be supplemented and updated.In addition,the contribution of VOCs source emissions to secondary air pollution also deserves attention to provide a scientific basis for the synergistic control of O3 and SOA.
NETL
NSTL
万方数据
