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

BACKGROUND: Ozone (O3) and nitrogen dioxide (NO2) are the two main gaseous pollutants in the atmosphere that act as oxidants. Their short-term effects 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 association of O3, NO2 and their composite indicators (Ox and Oxwt) with ERVs for respiratory diseases. An interaction model was further performed to evaluate the interaction between O3 and NO2. RESULTS: Exposure to O3, NO2, Ox and Oxwt was positively associated with ERVs for total respiratory diseases and acute upper respiratory infection (AURI). For instance, a 10 µg/m3 increase in O3 and NO2 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. Significant linear exposure-response relationships were observed in Ox and Oxwt over the entire concentration range. In stratification analysis, stronger associations were observed in the group aged < 18 years for both O3 and NO2, in the warm season for O3, but in the cold season for NO2. In interaction analysis, the effect of O3 on total respiratory emergency room visits and AURI visits was the strongest at high levels (> 75% quantile) of NO2 in the < 18 years group. CONCLUSIONS: Short-term exposure to O3 and NO2 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 O3 and NO2 on respiratory ERVs, and Ox and Oxwt may be potential proxies.