Study On The Emission Characteristics Of Gaseous Pollutants From Vehicles In Zhengzhou Based On The Tunnel Experiment

With the rapid development of economy and urbanization in China,automobile exhaust has become the primary anthropogenic sources of air pollution in some large and medium-sized cities,and the control of vehicle pollution has become an important part of air pollution control in China.Characteristics of localized vehicle emission could provide guidance for formulating local vehicle pollution control strategies,but in Zhengzhou,where ethanol gasoline is the only fuel for gasoline vehicles,there are few relevant studies.Therefore,Zhengzhou North Third Ring Tunnel was selected for tunnel experiments in this study,and the gaseous pollutants of carbon monoxide(CO),carbon dioxide(CO2),nitric oxide(NO),nitrogen dioxide(NO2),sulfur dioxide(SO2)and ozone(O3)in the tunnel were determined.In addition,more attention was paid to the volatile organic compounds(VOCs)and carbonyl compounds in the tunnel.Concentration measurement and component analysis were carried out to obtain the localized emission characteristics of gaseous pollutants from vehicles fuelled by ethanol gasoline in Zhengzhou.Finally,the maximum incremental reactivity method and the fractional aerosol coefficient method were used to study ozone formation potential and secondary organic aerosol formation potential of VOCs,respectively.The main findings are as follows:(1)During the test period,41974±2115 vehicles passed through the North Three Ring Tunnel per day,and small vehicle was the most abundant vehicle type,accounting for more than 85%,and the diurnal variation of the proportion of each vehicle type was relatively stable.In the tunnel,the measured average vehicle speed was 42.3±0.8 km/h,the average wind speed was 3.5±0.9 m/s,and the wind speed was positively correlated with the vehicle speed.The ambient weather conditions such as temperature,relative humidity and air pressure in the tunnel were relatively stable.(2)In the tunnel,the mass concentrations of all detected pollutants(except O3)at sampling point 2 were higher than that at sampling point 1.It could be seen that pollutants emitted from vehicles could accumulate significantly in the tunnel.In addition,the mass concentration of CO would be as high as 4-6 mg/m~3 when the traffic flow was heavy during the morning and evening peak hours.Therefore,it was suggested that the jet fan along the ceiling throughout the tunnel should be turned on to speed up the diffusion of pollutants,during the morning and evening peak hours.The average emission factors of CO,CO2,NO,NOx,and SO2 were 1408.7 mg/km/veh,180.2 g/km/veh,50.9 mg/km/veh,85.8 mg/km/veh and 0.8 mg/km/veh,respectively.(3)A total of 105 VOCs species were detected in this study.Compared the composition of VOCs at two sampling points showed that alkanes,oxygenated volatile organic compounds(OVOCs),alkenes and aromatics were the main groups in the vehicular VOCs emissions,accounting for approximately 90%.The most abundant species among all VOCs were ethane,acrolein,ethanol,ethylene and toluene;the VOCs species with the high contribution to ozone formation potential were ethylene,acrolein,propylene,toluene and n-butane;and they were toluene,m,p-xylene,1,2,4-trimethylbenzene,1-ethyl-3-methylbenzene and m,p-diethylbenzene in secondary organic aerosol formation potential.(4)The high proportion of OVOCs in the vehicular VOCs emissions was related to the use of ethanol gasoline throughout Henan Province.Among the detected 16carbonyl compounds,the small-molecule carbonyl compounds,such as C1-C3carbonyls,were the most abundant species,accounting for more than 80%by mass.In terms of specific species,the most abundant species were acetone,formaldehyde,acetaldehyde and butanone.The emission factor of the total detected carbonyl compounds was 6.52±2.98 mg/km/veh.(5)The toluene/benzene value was 1.0 and showed that the VOCs in the tunnel were greatly affected by vehicle emissions.According to the isobutane/n-butane value and the recorded videos,natural gas-fuelled vehicles accounted for a certain proportion among the vehicle fleet passing through the tunnel.Finally,the positive matrix factorization(PMF)model was used to analyze the sources profile of VOCs.The results showed that vehicle emissions were the main source of VOCs,and the contribution of vehicle evaporative emissions exceeded vehicle exhaust emissions.