Research On Emission Deterioration Characteristics Of Urban Light-duty Gasoline Vehicles

The number of motor vehicles in China has grown rapidly in recent years.In 2018,the number of civil automible has reached 230 million.The emission of pollutant exhaust caused by motorization has become an important problem in environmental management.Some researches show that high-polluting vehicles account for 20% of total number of automobile,can exhaust 60% of total pollutant emissions.The technical condition and exhaust aftertreatment system will deteriorate with continuous use,resulting in higher emission level of vehicle.It has great environmental protection value and economic benefits to understand the characteristics of exhaust emission,conduct in-depth and systematic research on influencing factors,as well as furtherly analyze the emission deterioration.This paper collected 751,632 environmental protection annual inspection data of Nanjing’s light-duty gasoline vehicles in 2018.The technology distribution of light-duty gasoline vehicles and overall distribution of pollutant emission concentration in Nanjing were analyzed.Based average value of pollutant emission concentration for vehicles with different cumulative mileage,the relationship between pollutant emission concentration and cumulative mileage was anlysed by classified statistic and curve-fitting.The results show that:(1)With the increase of cumulative mileage,the exhaust emission of motor vehicles continually deteriorates.There are exponential,logarithmic and linear relationship between emission concentration and cumulative mileage.(2)With an increase of use intensity,pollutant emission concentration will decrease.(3)Emission standard update can lower pollutant emission level.The decreasing amplitude is in accordance with the change of limiting value in emission standards for light gasoline vehicles.(4)Pollutant emission concentration has negative correlation with engine displacement.In order to improve the local accuracy of mileage deterioration rule,the quantitative relationships between cumulative mileage,annual mileage,emission standard,engine displacement and pollutant emission are analyzed.This paper used XGBoost algorithm to establish a complex regression model,to furtherly study the characteristics of pollutant emission deterioration.SHAP algorithm was employed to explain the regression model.The influence of single factor and two factors’ interaction value on the emission prediction were analyzed.The value and plus or minus characteristic of each factor influence on every sample were illustrated.Besides,the criterions for heavy-polluting vehicles were proposed.The rank of feature importance on CO and HC emission was: emission standard,cumulative mileage,engine displacemen,annual mileage.The rank of feature importance on NO emission deterioration was: cumulative mileage,engine displacement,emission standard,annual mileage.The criterions for heavy-polluting vehicles are:(1)Emission standard is National stage I,II or III.(2)Cumulative mileage is more than 100,000 km.(3)Engine displacement is smaller than1.6 L.