Research On Main Pollutant Emissions And Nitrate Nitrogen Isotope Characteristics Of Motor Vehicle Exhaust Based On Bench Test

With the continuous growth of the inventory,road vehicle exhaust emissions have increasingly become an important source of pollutants in the atmosphere.However,China lacks a comprehensive study of current vehicle exhaust pollutant emissions.At the same time,stable nitrogen isotope technology is a traceability tool for NO_x（nitrogen oxide）emissions that has emerged in recent years.Motor vehicles,as the most important NO_x emission source in the atmosphere,occupies an especially important proportion in the traceability.However,in the current source spectrum,motor vehicles have a wide range and overlaps with other sources and needs further research and subdivision.Therefore,this study selected 15 motor vehicles in use,including most types of road vehicles,using chassis dynamometers combined with WLTC（World Light Vehicle Test Procedure）,C-WTVC（China Heavy Commercial Vehicle Transient Cycle）and NEDC（New European Driving Cycle）tested the emission factors of main greenhouse gases,PM,carbonaceous components and major pollutants emitted by motor vehicle exhaust,and measured the phasedδ¹⁵N-NO_x value.The main results are as follows:1)Due to the extremely high CH₄ emissions of natural gas taxis,the greenhouse gas emissions of natural gas taxis are the same as that of similar light-duty gasoline vehicles,and even 16.7%higher on urban roads.Compared with heavy-duty diesel trucks with similar displacement,natural gas buses with National Sixth Standard can effectively reduce greenhouse gas emissions by 31.5%,so they are worthy of vigorous promotion.2)The results of this study found that the CO,HC,PM and NO_x emission factors of long-mileage natural gas taxis under the cold start procedure under WLTC driving cycle are higher than those recommended by the corresponding EI guidelines.The emission factors were 21.2 times,35.7 times,44.2 times and 100.6 times higher.This shows that long-mileage natural gas taxis are a neglected source of high pollutant emissions.3)As NEDC operating conditions lack phases corresponding to the high-speed and ultra-high-speed phases of WLTC operating conditions,the CO emissions of light gasoline vehicles and the PM emissions of natural gas taxis will be underestimated by 88.4%and 83.8%,respectively.4)Theδ¹⁵N-NO_x value of motor vehicle exhaust measured in this study is-22.8‰～+15.8‰,and the average value is-5.2±6.6‰.The increase in the mileage of motor vehicles will cause theδ¹⁵N-NO_x value of exhaust gas to be positive in the middle-and high-speed phases.Without considering the influence of mileage,the NO_x concentration in motor vehicle exhaust has a good negative correlation with the δ¹⁵N-NO_x value.