Fig. 3.

Direction of the relationship between air pollution and COVID-19 cases/spread, hospitalizations, and deaths split by pollutant. The relationship was coded separately for each pollutant and COVID-19 outcome pair for each study. Pollutants included: particulate matter less than 10 and 2.5 μm in diameter ($P{M}_{10}$ and $P{M}_{2.5}$ respectively); ozone ($O_3$); nitrogen dioxide ($N{O}_2$), nitrogen oxides $(N{O}_X)$, sulfur dioxide ($S{O}_2$), carbon monoxide ($CO$) and a more general multiple-pollutant air quality index, AQI. The category “other” includes other measures of air pollution such as ammonia ($N{H}_3$), benzene, benzidine, acetaldehyde SO4, aerosol optical depth (AOD), and other non-methane volatile organic compounds (NMVOC).