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 less than 10 µm (PM10), may modify temperature-related mortality in tropical urban settings. 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 PM10.
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 PM10 category using a cut-off based on the World Health Organization 24-hour Air Quality Guideline (WHOAQG) 2021 (45 µg/m3). Heat and cold effects were evaluated by comparing the 99thvs. 90th percentile and 1stvs. 10th percentile temperatures, respectively.
Results: Approximately 33% of days exceeded the WHOAQG level. Non-accidental mortality increased at both heat [relative risk (RR): 1.07; 95% confidence interval (CI): 1.04–1.11] and cold extremes (RR: 1.11; 95% CI: 1.06–1.17) without clear modification by PM10. Cardiovascular mortality was more strongly associated with cold, rising by 17% (RR: 1.17; 95% CI: 1.07–1.27); however, this association diminished under both PM10 levels. In contrast, respiratory mortality increased at high temperatures (RR: 1.35; 95% CI: 1.22–1.50), with risks significantly elevated across PM10 categories.
Conclusions: Temperature extremes significantly impact mortality in Klang Valley, with varying effects by cause of death. PM10 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.
