Impact of the COVID-19 Lockdown on Vehicular Emission and Air Pollution in Chengdu, China

The spread of coronavirus disease 2019 (COVID-19) has significantly reduced human activities worldwide and thus primary emissions in which vehicular emission was one of the essential sources. We investigated the impacts of traffic activities on vehicular emissions and air quality during the COVID-19 pre-lockdown and lockdown periods in Chengdu, which is located in southwest China. The dynamic traffic emission inventories with high spatial and temporal resolutions were developed. We found that the traffic flow dropped by 50%, while most traffic hotspots were in the central district during the rush hours during the pre-lockdown and lockdown periods. Reduction of CO, HC, NOx, and PM emissions from vehicles has been seen, and the response of NOx to the lockdown was the most sensitive. As the dominant contributors to vehicular emission, light-duty passenger cars and heavy-duty trucks should be focused on being restricted during the rush hours in areas with high population density. Moreover, a significant decline in CO, NO2, PM10, and PM2.5 concentrations was observed after the lockdown, while O3 concentration increased by 39% due to the NO titration, indicating that reducing VOCs emission can realize the O3 control more effectively in Chengdu. The decline of Ox concentration and PNO3 denote the lower atmospheric oxidation capacity after the lockdown in Chengdu. Identifying significant contributors to vehicular emissions and exploring the impact of traffic volume on primary and secondary pollutants have important implications for developing vehicle emission control measures and effective O3 control strategies in Chengdu.