Motor Vehicle Pollution Emissions And Their Potential Impact On Air Quality In Xi'an

The number of motor vehicles in Xi'an has increased rapidly with the economic and social development of Xi'an.The emissions of CO,NOx,HC and other motor vehicle pollutants have increased year by year,and become one of the main sources of air pollution in Xi'an,human health and environmental quality are seriously endangered.Vehicle exhaust contributes 80.08%of the NOx in the atmosphere of Xi'an,and NOx is one of the main precursors of ozone generation.A large amount of NOx emissions have caused the ozone concentration in Xi'an to become higher and higher.The pollution caused by ozone has reached 106 days,replacing PM2.5 as the most important pollutant affecting the atmospheric environment of Xi'an.Controlling motor vehicle pollution emissions is of great significance for reducing ozone and NOx pollution and improving ambient air quality.This paper uses the emission inventory preparation method and revised emission factors recommended by the Ministry of Ecology and Environment's "Technical Guide for the Preparation of Air Vehicle Pollutant Emission Inventory for Road Vehicles(Trial)".The emission factors of NOx,HC,PM2.5,and PM10 were calculated,a vehicle pollutant emission inventory was established,the characteristics of vehicle pollutant emissions in Xi'an from 2014 to 2018 were analyzed,and the emission of vehicle pollutants to the atmospheric environment was clarified.This paper proposes measures for the control of motor vehicle pollutant emissions in Xi'an.The specific results are as follows:(1)In 2018,the total emissions of five major pollutants from motor vehicle exhaust were 228,908 tons,of which CO was 14,6643 tons,NOx was 60279 tons,HC was 19301 tons,PM2.5 was 1,394 tons,and PM10 was 1,292 tons.The amount of pollutants emitted by motor vehicles in Xi'an has been increasing year by year,but the emissions of pollutants by per vehicle have been decreasing year by year.Micro and small passenger cars are the main contributors to motor vehicle CO and HC emissions.Although medium and heavy trucks only account for 3%of the vehicle population,they contribute about 50%of NOx,PM2.5 and PM10.Gasoline vehicles,which account for 92%of the vehicle population,contribute 81%of CO and 75%of HC.Diesel vehicles,which account for 8%of the vehicle population,contribute 78%of NOx,73%of PM2.5,and 68%of PM10.(2)Discovered through the vehicle emission inventory calculated based on two different methods based on the Ministry of Environmental Protection's revised emission factor and the COPERT model,There is a strong similarity between the COPERT model and the Ministry of Environmental Protection's revised emission factor calculation results.Through COPERT model simulation experiments,it is found that the emission factors of motor vehicles are closely related to factors such as environmental conditions and driving speed.As the temperature increases,the emission factors of CO and HC gradually decrease,and the emission factors of NOx increase first and then decrease.As the speed of motor vehicles increases,the emission factors of five major pollutants emitted by motor vehicles have gradually decreased.At the same time,with the increase of the service life of vehicles,the exhaust gas exceeding standards will become more and more serious.For motor vehicles that have been used for more than 15 years,the exhaust gas exceeding standards will reach 45%.The analysis also found that the emissions of pollutants from some brands of motor vehicles are higher than those of other brands,and they are more likely to exceed standards.(3)Analyze and calculate the relationship between ambient air quality,climate,human activity levels,and vehicle pollution emissions by Pearson correlation coefficient method,it is found that the concentration of NO2 and O3 in the air of Xi'an city has a significant positive correlation with the emission of NOx and HC from vehicle exhaust.The increase in the total amount of NOx and HC emitted by motor vehicles in Xi'an is the main reason for the increase in the concentration of NO2 and O3 in the atmospheric environment of Xi'an.(4)By analyzing the characteristics of vehicle emission in Xi'an and the key factors affecting vehicle emission,this paper puts forward a series of targeted measures,such as improving vehicle emission standards,accelerating vehicle renewal speed,developing and improving urban public transport system,and improving road traffic conditions.