Impacts of applying ethanol blended gasoline and evaporation emission control to motor vehicles in a megacity in southwest China

Abstract

The use of ethanol blended gasoline and evaporation emissions control are effective means to reduce air pollutant emissions from motor vehicles. However, there is currently a lack of comprehensive assessment of the impact of these measures on air quality, in particular to control volatile organic compounds (VOCs), an important precursor to PM2.5 and O3 formation. Therefore, this study sets up different motor vehicle pollution control scenarios based on ethanol gasoline substitution and evaporative emission control, respectively. The emission changes of atmospheric pollutants, O3 formation potential (OFP) and VOCs species from motor vehicles under each control scenario were analyzed, and the chemical transport model WRF/CMAQ was used to evaluate the changes of pollutant concentration in the ambient air under different scenarios. The results show that the VOCs emissions from motor vehicles in Chengdu increased by 25% from 2014 to 2019, which is attributed to the rapid growth of motor vehicle population and the aggravation of road congestion. Under different control scenarios, the emission of NOx, VOCs and PM2.5 decreased to different degrees, mainly from evaporation emissions control measures. The use of ethanol blended gasoline can reduce the VOCs emissions while increased OFP by 26%, due to the presence of highly reactive species in the VOCs source profiles, which ultimately determined the OFP of motor vehicles. Thus, it is necessary to the control of alkenes, aromatics, oxygenated VOCs (OVOCs) and other highly reactive characteristic emission species of gasoline vehicles. The simulation results of model show that under different control scenarios the PM2.5 concentrations decreased to different degrees, the urban area with the maximum decrease rate of 9.0–9.2%. The combination of the use of ethanol blended gasoline and evaporation emissions control had a good effect on PM2.5 concentration control, while the evaporation emissions control of motor vehicles alone can lead to a decrease in O3 concentration, i.e. a decrease by 1.9–2.5%.