Assessing the COVID-19 Lockdown Impact on Global Air Quality: A Transportation Perspective

To address the COVID-19 pandemic, governments worldwide implemented mandatory restrictions. As an unintended consequence of these responses, significant air pollution reductions have been recorded across the world. We provide cross-national evidence on the causal impact of pandemic-induced lockdowns on air quality. Using daily air pollution data between 1 January and 31 December 2020, covering 596 major cities in 77 countries, we analyzed the data with a generalized difference-in-differences approach. The results show that lockdown restrictions reduced global concentrations of NO2 by 21 similar to 35%, PM10 by 14 similar to 26%, PM2.5 by 9 similar to 18%, CO by 6 similar to 16%, and SO2 by 5 similar to 16%, while the O-3 concentrations increased by 15 similar to 29% under eight specific lockdown measures. Furthermore, a simultaneous equations model suggests that reductions in public and private mobility, measured by changes in public transportation and car ridership, partly explain the observed decreases in air pollution. These findings have significant implications for ongoing global efforts to mitigate air pollution and underscore the pivotal role of public transit in achieving this goal.