Nationwide and regional evidence on PM2.5-mortality in a tropical climate: Risks persist below standard and under climate extremes.
BACKGROUND Thailand has recorded daily PM2.5 up to 414 µg/m³ , nationwide, and region-specific evidence on short-term associations with cardiorespiratory mortality remains limited under tropical climate extremes, diverse climate regions, or below standard levels. Prior studies emphasized temperate settings. This nationwide tropical study assessed region-specific risks and effect modifiers. METHOD We analyzed 4.3 million hourly pollutant and meteorological data (2014-2022) from 87 stations, aggregated to daily exposures for 6584 sub-districts. Cardiovascular (259,463) and respiratory (153,170) deaths were examined using a time-stratified case-crossover with logistic regression to estimate adjusted odds ratios (AORs: 95% CIs) per 10 µg/m³ PM2.5. RESULTS PM2.5 correlated with O3 in the north and with NO2 in Bangkok, p < 0.001. Cardiovascular was significant at lag01 with AOR of 1.016 (95% CI: 1.009-1.022) nationwide, higher in Bangkok, northeast, and north, and elevated in females 1.022 (95% CI: 1.011-1.032); elderly 1.017 (95% CI: 1.008-1.025); winter 1.023 (95% CI: 1.012-1.033); and vein diseases 1.153 (95% CI: 1.028-1.294). Respiratory was significant at lag02, 1.022 (95% CI: 1.013-1.031), highest in east, central, Bangkok, and north, and stronger in females 1.034 (95% CI: 1.019-1.048); elderly 1.025 (95% CI: 1.014-1.036); winter 1.031 (95% CI: 1.017-1.046); and lung diseases 1.134 (95% CI: 1.064-1.208). Risks persisted under Thailand's PM2.5 standard, cardiovascular 1.016 (95% CI: 1.001-1.030) and respiratory 1.031 (95% CI: 1.010-1.051); extreme cold 1.055 (95% CI: 1.030-1.082) and 1.055 (95% CI: 1.022-1.090); and extreme dry 1.014 (95% CI: 1.003-1.026) and 1.017 (95% CI: 1.002-1.033). Sensitivity, temperature, and COVID-19 analyses confirmed robustness. CONCLUSION This nationwide tropical study identified regional variation and subgroup-specific short-term associations between PM2.5 exposure and cardiovascular and respiratory mortality. offering evidence that may inform and guide region-specific abatement, strengthen standards, and inform protective health policies.