The Impact of City Anti-Contagion Policies (CAPs) on Air Quality Evidence from a Natural Experiment in China

In order to control the spread of the Coronavirus Disease 2019 (COVID-19), many countries around the world adopted aggressive anti-contagion policies (APs), the most common of which was to restrict people's transportation and economic activities, which not only curbed the spread of the epidemic but also improved urban air quality during the APs' implementation. However, the impact that these policies had in the post-AP period is unclear. Using daily air quality data for prefecture-level cities in China in early 2020 and the Difference-in-Differences (DiD) models, we measured the short-term (AP implementation period) and medium-term (post-AP period) impacts of the city APs (CAPs) on different kinds of air pollutants and considered the meteorological conditions. We found that the policies significantly reduced air pollution (i.e., particulate matter [PM2.5, PM10] and nitrogen dioxide [NO2]) in the short term; although the medium-term impacts are in line with the short-term impacts, they are not significant. The effects were reduced in cities with higher incomes, larger populations, more industrial activities, and greater traffic volumes, and without a central heating system. Although the CAPs did not improve air quality in the long run, they improved air quality and health benefits in the short term. In addition, the policies' experiments verified the complexity of environmental governance.