COVID-19, City Lockdown, and Air Pollution: Evidence from China

Guojun He; Yuhang Pan; Takanao Tanaka

In Panel B of Figure 2 , we look at the second margin: to what extent the control cities were also affected by the counter-virus measures. We see the AQI levels were almost equivalent before the Spring Festival in 2019 and 2020, implying the parallel trend assumption is likely to hold. In 2020, shortly after the festival, we observe that the air pollution levels became slightly lower, relative to the 2019 post-festival season. This result suggests that air quality in the control cities marginally improved, although they were not formally locked down. Table 1 summarizes the regression results. Here, we estimate the relative change in air pollution levels in the treatment group (locked-down cities) relative to the control group (non-locked-down cities) by fitting the DiD model described in the equation (A1). We find that a lockdown indeed improved the air quality: compared to cities without formal lockdown policies, the weekly Air Quality Index (AQI) and PM2.5 declined respectively by 19.4 points (18%) and 13.9 µg/m 3 (17%) when including weather controls and a set of fixed effects (in columns (2) and (4)). 4 These estimates are remarkably robust to the inclusion of weather variables, indicating that the changes in air pollution caused by city lockdown are not correlated with weather conditions. We also provide the results for other air pollutants (Appendix Table A3) In Columns (5) to (8), we estimate the changes in air pollution levels in the control (nolockdown) cities before and after the Spring Festival relative to the previous year by fitting the second DiD model described in the equation (A3). We find that air quality in 2020 improved relative to the previous year's air quality after the Festival. The results show that 4 The Air Quality Index (AQI) is a comprehensive measure of air pollution in China and also widely used around the world. The index is constructed by PM2.5, PM10, SO2, CO, O3, and NO2 concentrations. A lower AQI means better air quality. All rights reserved. No reuse allowed without permission. the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.