  Air pollution is a threat to human health, in particular since it aggravates
respiratory diseases. Early COVID-19 outbreaks in Wuhan, China and Lombardy,
Italy coincided with high levels of air pollution drawing attention to a
potential role of particulate matter and other pollutants in infections and
more severe outcomes of the new lung disease. Both air pollution and COVID-19
outcomes are driven by human mobility and economic activity leading to spurious
correlations in regression estimates. We use district-level panel data from
Belgium, Brazil, Germany, Italy, the UK, and the US to estimate the impact of
daily variation in air pollution levels on COVID-19 infections and deaths.
Using random variation in air pollution generated by thermal inversions, we
rule out that changes in mobility and economic activity are driving the
results. We find that a 1%-increase in air pollution levels over the three
preceding weeks leads to a 1.5% increase in weekly cases. A 1%-increase in air
pollution over four weeks leads to 5.1% more COVID-19 deaths. These results
indicate that short-term measures to reduce air pollution can help mitigate the
health damages of the virus.
