Objective To evaluate the association between ambient ozone exposure and mortality from respiratory and circulatory system diseases in Beijing, and to explore the potential modifying effect of heatwaves on this relationship.

Methods Daily data on air pollutants, meteorological factors, and causes of death in Beijing from 2019 to 2023 were collected. A time-series analysis was used to assess the single-day and cumulative lag effects of daily maximum 8-hour ozone concentration (O_{3-8 h}) exposure on mortality from respiratory and circulatory system diseases. Stratified analyses were conducted by gender, age, and region. Furthermore, a generalized linear model was applied to explore the impact of heatwave exposure on the association between O_{3-8 h} and mortality from respiratory and circulatory system diseases during the warm season.

Results The single-day lag effect of O_{3-8 h} exposure on respiratory disease mortality was the strongest at lag 3 d (RR=1.06, 95%CI: 1.02-1.10), and the cumulative lag effect peaked at lag 07 d (RR=1.36, 95%CI: 1.11-1.66). For circulatory disease mortality, the single-day lag effect of O_{3-8 h} exposure was maximized at lag0 d (RR=1.07, 95%CI: 1.03-1.12), with the cumulative lag effect reaching its peak at lag 07 d (RR=1.19, 95%CI: 1.06-1.34). Stratified analyses indicated that the elderly, males, and urban residents were significantly more affected. Moreover, the risk of O_{3-8 h}-related circulatory mortality became more pronounced during heatwave exposure.

Conclusion Short-term ozone exposure is associated with an increased risk of mortality from respiratory and circulatory system diseases in Beijing. The elderly, males, and urban residents exhibit higher susceptibility, and this association is further strengthened when combined with heatwave exposure. These findings suggest that public health protection measures for vulnerable populations should be emphasized and enhanced when ozone exposure coincides with high-temperature weather.