Mortality burden attributed to the synergy between human-bioclimate and air quality extremes

This study investigates the synergistic effects of air pollution (PM10, NO₂, O₃) and thermal conditions, based on modified Physiologically Equivalent Temperature (mPET), on human mortality in Thessaloniki, Greece, stratified by age (adults vs. seniors), season (warm vs. cold), and urban regions (North, Central-East, West). Leveraging data from 2001 to 2019, our analysis, which focuses on attributable fractions (AFs), reveals distinct patterns of vulnerability across demographic and climatic contexts. Seniors specifically, consistently exhibit higher AFs under both heat and cold stress, particularly when combined with elevated PM10 and NO₂ levels during colder periods. Seasonal disparities are evident, with ozone-related AFs being higher during warmer months, especially under elevated mPET values that correspond to strong and extreme heat stress. Regional analyses further highlight variations in risk profiles, with the Central-East urban area experiencing the most pronounced effects due to higher air pollutant concentrations and a greater number and intensity of extreme temperature events. These findings underscore the critical need for tailored early health warning systems that integrate age-specific vulnerabilities, seasonal variability, and regional/local dynamics. Our results provide actionable insights for heat-health action plans, emphasizing the importance of mitigating compounded risks from heat and air pollution to safeguard urban populations effectively.