Short-term heat effects and effect modification by ambient air pollution on cardiovascular and respiratory mortality across 148 cities from 13 European countries – Results of the EXHAUSTION project

Abstract

Background and Aim: Epidemiological evidence on the potential interactive effects of high air temperature and air pollution on cause-specific mortality remains inconclusive and limited to selected locations. We investigated the effects of temperature on cardiovascular and respiratory mortality and its effect modification by particulate matter with a diameter ≤ 2.5 µm [PM₂.₅] and ozone [O₃] during summer months (May-September) in 148 cities across 13 European countries. Methods: For these cities, we obtained daily counts of cardiovascular and respiratory mortality and daily exposure data between 2000 and 2018. We used location-specific confounder-adjusted Quasi-Poisson regression with a tensor product between air temperature and the air pollutant. We extracted temperature estimates at low, medium, and high levels of pollutants defined as the 5th, 50th, and 95th percentile of location-specific air pollutant concentrations. A random-effects multilevel meta-analytical model was used to derive the country-specific and overall estimates. Results: High summer temperatures were associated with increased cardiovascular and respiratory mortality. We further observed modification of the heat effects by elevated levels of PM₂.₅ and O₃ in most locations, with stronger effects for respiratory than cardiovascular mortality. For example, the percent increase in respiratory mortality per increase in the 2-day average summer temperature from the 75th to the 99th percentile was 9.2% (95% Confidence Interval [CI] 8.9-9.4), 13.0% (95% CI 12.8, 13.2), and 19.8% (95% CI 19.5, 20.2) at low, medium, and high levels of PM₂.₅, respectively. Conclusion: We observed significant modification of the heat effects by elevated levels of PM₂.₅ and O₃ leading to an increased risk of cardiovascular and respiratory mortality. With both temperature and air pollutant concentrations foreseen to increase considering climate change, targeted adaptation and mitigation measures are crucial to enhance resilience and sustainable development in alignment with EU climate change policies. Keywords: Air temperature, air pollution, cause-specific mortality, effect modification, Europe