Long-term exposure to air pollution and severe COVID-19 in Catalonia: a population-based cohort study.

The association between long-term exposure to ambient air pollutants and severe COVID-19 is uncertain. We followed 4,660,502 adults from the general population in 2020 in Catalonia, Spain. Cox proportional models were fit to evaluate the association between annual averages of PM 2.5 , NO 2 , BC, and O 3 at each participant's residential address and severe COVID-19. Higher exposure to PM 2.5, NO 2, and BC was associated with an increased risk of COVID-19 hospitalization, ICU admission, death, and hospital length of stay. An increase of 3.2 µg/m 3 of PM 2.5 was associated with a 19% (95% CI, 16-21) increase in hospitalizations. An increase of 16.1 µg/m 3 of NO 2 was associated with a 42% (95% CI, 30-55) increase in ICU admissions. An increase of 0.7 µg/m 3 of BC was associated with a 6% (95% CI, 0-13) increase in deaths. O 3 was positively associated with severe outcomes when adjusted by NO 2 . Our study contributes robust evidence that long-term exposure to air pollutants is associated with severe COVID-19.