Abstract:Background: Extreme temperatures and air pollution are well-established environmental risk factors for mortality. While the independent effects of temperature have been extensively studied, less is known about how air pollution, particularly particulate matter (PM 2.5), may modify temperature-related mortality in tropical urban settings. Objectives: This study aims to assess the short-term effects of ambient temperature on non-accidental, cardiovascular, and respiratory mortality in Klang Valley, Malaysia, and to examine the modifying role of PM 2.5. Methods: A time-series analysis was conducted using daily mortality, temperature, and air pollution data from 2008 to 2023. Distributed lag non-linear models (DLNMs) with quasi-Poisson regression were used to estimate cumulative temperature mortality associations across a 21-day lag period. Analyses were stratified by PM 2.5 category using a cut-off based on the WHO 24-hour guideline (45 µg/m³). Heat and cold effects were evaluated by comparing the 99th vs 90th percentile and 1st vs 10th percentile temperatures, respectively. Results: Temperature exhibited non-linear associations with mortality, with cold effects more pronounced for cardiovascular deaths and heat effects strongest for respiratory deaths. Stratified analyses revealed that PM 2.5 modified these associations: heat-related respiratory mortality risks were amplified under the high PM 2.5 exposure category, while temperature-related cardiovascular risks appeared flatter. The strongest heat-related effect was observed for respiratory mortality at 30°C, regardless of PM 2.5 category. Non-accidental mortality showed elevated risks at both extremes, though modification by PM 2.5 was less evident. Conclusion: Temperature extremes significantly impact mortality in Klang Valley, with varying effects by cause of death. PM 2.5 modifies these associations, particularly enhancing heat-related respiratory mortality. These findings highlight the need for integrated public health strategies that address both temperature and air pollution to protect vulnerable populations in tropical urban environments.
Keywords: Climate Change and Planetary Health, ambient temperature, air pollution, mortality, cardiovascular, respiratory
