Association and interaction of O3 and NO2 with emergency room visits for respiratory diseases in Beijing, China: A time-series study

Background: Ozone (O 3 ) and nitrogen dioxide (NO 2 ) are the two main oxidative gaseous pollutants in the atmosphere. Their short-term effect and interaction on emergency room visits (ERVs) for respiratory diseases remain unclear. Methods: : We conducted a time-series study based on 144,326 ERVs for respiratory diseases of Peking University Third Hospital from 2014 to 2019 in Beijing, China. Generalized additive models with quasi-Poisson regression were performed to analyze the associations of O 3 , NO 2 and their composite indicators (O x and O x wt ) with ERVs for respiratory diseases. An interaction model was further performed to evaluate the interaction between O 3 and NO 2 . Results: : Exposure to O 3 , NO 2 , O x and O x wt was positively associated with ERVs for total respiratory diseases (TRDs) and acute upper respiratory infection (AURI). For instance, a 10 μg/m 3 increase in O 3 and NO 2 were associated with 0.93% (95%CI: 0.05%, 1.81%) and 5.87% (95%CI: 3.92%, 7.85%) increase in AURI at lag0-5 days, respectively. More significant linear exposure-response relationships were observed in O x and O x wt over the entire concentration range. In stratification analysis, stronger associations were observed in the group aged < 18 years for both O 3 and NO 2 , in the warm season for O 3 , but in the cold season for NO 2 . In interaction analysis, the association between O 3 and ERVs for respiratory diseases was significantly stronger at high concentrations of NO 2 in the <18 years group. Conclusions: : Short-term exposure to O 3 and NO 2 was positively associated with ERVs for respiratory diseases, particularly in younger people (<18 years). This study for the first time demonstrated the synergistic effect of O 3 and NO 2 on respiratory ERVs, and O x and O x wt may be potential proxies.