Short‐Term Exposure to Fine Particulate Matter (PM _2.5 ), Cause Specific‐Mortality, and High‐Risk Populations: A Nationwide Time‐Stratified Case‐Crossover Study

Numerous studies have reported that short-term exposure to fine particulate matter (PM_2.5) is associated with mortality risk; however, results on high-risk populations and regions have been mixed. This study performed a nationwide time-stratified case-crossover study to assess the association between short-term PM_2.5 and mortality in South Korea (2015-2019) by each cause of death and age group. A machine-learning ensemble PM_2.5 prediction model was used to cover unmonitored districts. We estimated the excess mortality and Years of Life Lost (YLL) attributable to PM_2.5 and non-compliance with the 2021 WHO guidelines (>15 μg/m³). We examined the effect modifications by district-level accessibility to green spaces and medical facilities in the living sphere. In the total population, PM_2.5 was positively associated with mortality for non-accidental causes (OR: 1.008 with 95% CI: 1.006-1.010), circulatory diseases (1.007, 95% CI: 1.003-1.011), and respiratory diseases (1.007, 95% CI: 1.001-1.013). Based on the point estimates, the association was generally greater in younger age groups (0-59 or 60-69 years) than in older age groups (70-80 and 80 years or older), and this pattern was pronounced in mortality for cerebrovascular diseases and pneumonia. The excess mortality fraction and YLL due to non-compliance with WHO guidelines were 0.80% and 186,808.52 years. Our findings suggest high risk populations and benefits for establishing stricter PM_2.5 standards and action plans.