The effect of air pollution when modified by temperature on respiratory health outcomes: A systematic review and meta-analysis.

BACKGROUND:Respiratory diseases are a leading cause of mortality and morbidity, and are exacerbated by air pollution and temperature. AIM:To assess published literature on the effect of air pollution modified by temperature on respiratory mortality and hospital admissions. METHODS:We identified 26,656 papers in PubMed and Web of Science, up to March 2021, and selected for analysis; inclusion criteria included observational studies, short-term air pollution, and temperature exposure. Air pollutants considered were particulate matter with a diameter of 2.5 μg/m3, and 10 μg/m3 (PM2.5, and PM10), ozone (O3), and nitrogen dioxide (NO2). A random-effects model was used for our meta-analysis. RESULTS:For respiratory mortality we found that when the effect PM10 is modified by high temperatures there is an increased pooled Odds Ratio [OR, 95% Confidence Interval (CI)] of 1.021 (1.008 to 1.034) and for the effect of O3 the pooled OR is 1.006 (1.001-1.012) during the warm season. For hospital admissions, the effects of PM10 and O3 respectively, during the warm season found an increased pooled OR of 1.011 (0.999-1.024), and 1.015 (0.995-1.036). In our analysis for low temperatures, results were inconsistent. CONCLUSIONS:Exposure to air pollution when modified by high temperature is likely to increase the odds of respiratory mortality and hospital admissions. Analysis on the interaction effect of air pollution and temperature on health outcomes is a relatively new research field and results are largely inconsistent; therefore, further research is encouraged to establish a more conclusive conclusion on the strength and direction of this effect.