Concurrent exposure to heatwaves and high ozone pollution and cause-specific mortality: Findings from seven major...

The frequency and intensity of heatwaves have been increasing owing to rapid climate change, and ambient ozone concentrations have also markedly increased in recent years. We aimed to investigate the association between concurrent exposure to heatwaves and high ozone levels and cause-specific mortality in seven major cities in Korea.

We collected data on the daily cause-specific mortality counts from 2014 to 2023 across seven Korean metropolitan cities. Meteorological data, including the daily maximum temperature and mean humidity, were obtained from the Korea Meteorological Administration, and air pollution data (maximum 8-h average [MDA 8] ozone and PM₁₀) were obtained from AirKorea. We applied a two-stage time-series regression analysis restricted to May-September, adjusting for long-term trends, day of the week, humidity, and PM₁₀.

During the warm seasons of the study period, a total of 474,369 all-cause deaths were identified across seven major Korean cities. The mean daily maximum temperature and MDA8 ozone concentration were 27.8°C and 0.050 ppm, respectively. Concurrent exposure to heatwaves and high ozone pollution was associated with increased risks of all-cause, non-accidental, and cardiovascular mortality. However, no additive interaction between heatwaves and high ozone exposure was observed. Mortality risk progressively increased with the number of consecutive days of concurrent exposure events, with stronger associations observed under more stringent heat-wave definitions.

Concurrent exposure to heatwaves and elevated ozone concentrations during the warm season was associated with increased risks of all-cause, non-accidental, and cardiovascular mortalities in Korea's seven major cities. Although additive interaction effects were modest, mortality risks tended to increase as the duration of concurrent heatwave and high-ozone exposure increased and under more extreme heat-wave conditions.