Double trouble: The interaction of PM2.5 and O3 on respiratory hospital admissions

The co-occurrence of fine particulate matter (PM2.5) and ozone (O-3) pollution during the warm season has become a growing public health concern. The interaction between PM2.5 and O-3 and its contribution to disease burden associated with co-pollution has not been thoroughly examined. We collected data on hospital admissions for respiratory diseases from a city-wide hospital discharge database in Beijing between 2013 and 2019. City-wide 24-h mean PM2.5 and daily maximum 8-h mean O-3 were averaged from 35 monitoring stations across Beijing. Conditional Poisson regression was employed to estimate the interaction between warm-season PM2.5 and O-3 on respiratory admissions. A model incorporating a tensor product term was used to fit the non-linear interaction and estimate the number of respiratory admissions attributable to PM2.5 and O-3 pollution. From January 18, 2013 to December 31, 2019, 1,191,308 respiratory admissions were recorded. We observed multiplicative interactions between warm-season PM2.5 and O-3 on upper respiratory infections (P = 0.004), pneumonia (P = 0.002), chronic obstructive pulmonary disease (P = 0.041), and total respiratory disease (P < 0.001). PM2.5-O-3 co-pollution during warm season exhibited a super-additive effect on respiratory admissions, with a relative excess risk due to interaction of 1.65% (95%CI: 0.46%-2.84%). There was a non-linear pattern of the synergistic effect between PM2.5 and O-3 on respiratory admissions. Based on the World Health Organization global air quality guidelines, 12,421 respiratory admissions would be reduced if both daily PM2.5 and O-3 concentrations had not exceeded the target (PM2.5 15 mu g/m(3), O-3 100 mu g/m(3)). The number of respiratory admissions attributable to either PM2.5 or O-3 pollution decreased by 48.7% from 2013 to 2019. Prioritizing O-3 control during the warm season is a cost-effective strategy for Beijing. These findings underscore the significance of concurrently addressing both PM2.5 pollution and O-3 pollution during the warm season to alleviate the burden of respiratory diseases.