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The health impacts of increasing heat exposure are alarming, especially in a climate change era. The role of ozone in the extreme temperature-mortality association remains unclear. We examined the mechanisms through which ozone influences extreme temperature-mortality association in Greater London, UK, from 2010 to 2018. Employing a time-series analysis with generalized linear quasi-Poisson models, we quantified the effects of daily 8-h maximum ozone concentrations, heatwaves, and extreme temperature on all-cause, respiratory and cardiovascular mortality. Interaction analyses were applied to assess the synergistic effects of ozone and heat-related exposures. A causal mediation analysis was utilised to decompose the total effect of high temperature/heatwave on mortality into direct and indirect effects. The risk of all-cause mortality during the warm season (May to September) increased by 1.3 % (95 % Confidence Interval (CI): 1.1 %, 1.6 %) for each 1 °C increment in daily mean temperature. Heatwave days (two or more days with unusually high temperatures) were associated with an 8.6 % (95 % CI: 6.9 %, 10.4 %) increase in all-cause mortality compared to non-heatwave days. These effects were more pronounced for respiratory mortality, i.e. 1.6 % (95 % CI: 1.0 %, 2.2 %) increase per 1 °C increment in temperature and 9.6 % (95 % CI: 4.6 %, 15.0 %) increase during heatwaves. The risk of heat-related mortality increased on high ozone days, and high temperatures amplified the risk of ozone-related mortality. The proportion of the total effect of extreme temperature and heatwaves on all-cause mortality mediated by ozone was 8.5 % and 8.8 %, respectively. For respiratory mortality and heatwaves, the proportion mediated was 14.9 %. Our findings show synergistic effects of ozone and extreme temperature on mortality, as well as mediating effects of ozone in the heat-mortality associations.
Gao et al. (Wed,) studied this question.