Exposure to air pollution and COVID-19 mortality in the United States: A nationwide cross-sectional study.

A small increase in long-term exposure to PM 2.5 leads to a large increase in the COVID-19 death rate. Despite the inherent limitations of the ecological study design, our results underscore the importance of continuing to enforce existing air pollution regulations to protect human health both during and after the COVID-19 crisis. The data and code are publicly available so our analyses can be updated routinely.