Background: COVID-19 is mainly transmitted from person to person through droplets and direct contact. The roles of air pollutants and meteorological factors in the occurrence of COVID-19 remain controversial so far.

Objectives: The purpose of the study was to conduct a meta-analysis of recent findings to assess the associations of air pollution and meteorological factors with risk of COVID-19.

Methods: We systematically searched three electronic literature databases (PubMed, EMBASE, and Web of Science) to identify studies published up to July 2020 which reported the associations of air pollution, meteorological factors with COVID-19. We assessed the risk of bias in all studies and meta-analyzed the associations of air pollutants and meteorological factors with COVID-19 using random-effects models, and conducted various sensitivity analyses.

Results: We identified 724 records in the initial search, and included 10 studies in the final analysis. Except for O₃ and PM_2.5, the other air pollutants and meteorological factors were all associated with the occurrence of COVID-19. NO₂ and relative humidity (%) were positively associated with the occurrence of COVID-19 [relative risk (RR) and 95% confidence interval (CI) were 1.045 (95% CI: 1.009, 1.082) and 1.013 (95% CI: 1.000, 1.026), respectively]. In contrast, temperature (℉) was negatively associated with the occurrence of COVID-19 [RR: 0.998 (95% CI: 0.996, 1.000)].

Conclusions: High NO₂ concentration, high relative humidity, and low temperature may facilitate the transmission of COVID-19.