Short-Term Associations Between Temperature, Air Pollutants (SO₂, NO₂, SPM, Ox), and Mortality in Hiroshima and Sapporo, Japan (2012–2019): Age and Gender-Specific Differences Across Seasons

The health impacts of air pollution and temperature variations are of increasing concern, particularly in urban environments where emissions and population densities are high. Short-term exposure to pollutants such as sulfur dioxide (SO₂), nitrogen dioxide (NO₂), suspended particulate matter (SPM), and oxidants (Ox) has been linked to adverse health outcomes, including increased rates of cardiovascular and respiratory diseases. Additionally, temperature fluctuations, especially during extreme weather conditions, exacerbate the vulnerability of populations to these pollutants, contributing to excess mortality.

Japan, with its diverse climate and urban landscape, presents a unique case for studying the interactions between air pollution, temperature, and mortality. Hiroshima, located in a temperate climate, and Sapporo, in a colder region, offer contrasting environments to examine the seasonal and regional variations in these associations. This study investigates the short-term associations between temperature, air pollutants (SO₂, NO₂, suspended particulate matter (SPM), and oxidants (Ox)), and mortality in Hiroshima and Sapporo, Japan, from January 1, 2012, to December 31, 2019. Using a time-stratified case-crossover study design, we examine the impacts on cardiovascular, respiratory, and general mortality, focusing on gender- and age-specific differences. Seasonal variations, comparing summer and winter periods, and different emission levels across the study period are also considered. By analyzing these interactions, this study aims to deepen the understanding of how short-term environmental factors and pollution levels influence health outcomes in urban populations, contributing to targeted public health interventions in Japan.