COVID-2019 lockdown in Beijing: A rare opportunity to analyze the contribution rate of road traffic to air pollutants.

• In Beijing, the lockdown has led to a sharp drop in road traffic. • Road traffic reduced by 46.9 %, while PM2.5 and NO 2 reduced by 5.6 % and 29.2 % respectively. • The Maximum Possible Contribution Rate of road traffic to PM2.5 and NO 2 are 11.9 % and 62.3 %, respectively. In Beijing, the lockdown imposed to curb the spread of COVID-2019 has led to a sharp drop in road traffic. This provides an opportunity to quantify the contribution rate of road traffic to PM2.5 and NO 2 concentrations. This paper creatively puts forward the concept of the Maximum Possible Contribution Rate (MPCR) and estimates the MPCR of road traffic to PM2.5 and NO 2 by analyzing the daily air pollution data and road traffic data in Beijing from January 24 to March 31, 2020 and the same period in 2019. The findings of this paper include: The decrease in SO 2 concentration during the lockdown indicates a reduction in pollutant emissions from industry and households. During the lockdown, road traffic in Beijing reduced by 46.9 %, while the concentrations of PM2.5 and NO 2 in the atmosphere reduced by 5.6 % and 29.2 % respectively. The MPCR of road traffic to PM2.5 and NO 2 concentrations are 11.9 % and 62.3 %, respectively. The concentration of O 3 did not increase significantly with the decrease of PM2.5 and NO 2 concentrations. The findings of this paper provide a reference for city managers to evaluate the contribution rate of Beijing's road traffic to air pollutants and to formulate reasonable emission reduction policies. [ABSTRACT FROM AUTHOR]