A comprehensive approach for assessing synergistic impact of air quality and thermal conditions on mortality: The case of Thessaloniki, Greece

The present paper introduces a novel approach for investigating the synergistic effect of thermal stress (maximum apparent temperature, Tapp(max)) and air pollutant concentrations (PM10, NO2, and O-3) on daily mortality in Thessaloniki, Greece. We examine Tapp(max) effects on all-cause mortality, analyzing variations at low, medium, and high levels of pollutants using a prototype modeling framework capable of accounting for multiple lagged exposures. We find J-shaped Tapp(max)-mortality relationships with increasing pollutant levels, indicating that high thermal stress levels (Tapp(max) > 33 degree celsius) favor pollution build-up, subsequently increasing mortality. Heat effects surpass cold effects, with PM10, NO2, and O-3 associated with 47.7%, 38.7%, and 32% increases in heat-related mortality, respectively, compared to 13.6%, 19.2%, and 2.1% increases in cold-related mortality. Detailed temporal lag structure analysis, conceptualized and conducted for the first time in the present study, unravels different dose-response patterns for the various predictors. PM10 shows the highest mortality risk on the exposure day, whereas NO2 risk is more pronounced a week after exposure. The temporal pattern of O-3 differs significantly, as the risk increases with lag until a threshold, followed by decrease. These outcomes underline the importance of holistic planning for public health mitigation and adaptation measures, especially in cities.