Mortality burden of air pollution in an Iranian industrial city: a 10-year multi-pollutant time-series study

Abstract

Air pollution remains a major public health concern in highly polluted industrial cities, particularly in low- and middle-income countries. This study quantified the short-term associations between ambient air pollution and cause-specific mortality in Arak, Iran, a representative industrial urban setting with chronically elevated pollutant levels. A 10-year time-series analysis (January 2015–November 2025) was conducted using daily concentrations of PM₂.₅, PM₁₀, SO₂, NO₂, NO, O₃, and CO and daily counts of all-cause, cardiovascular, and respiratory mortality. Generalized linear models with a negative binomial distribution were applied in single- and multi-pollutant frameworks, adjusting for meteorological variables, long-term trends, and temporal confounders. The strongest mortality associations were observed within a lag window of 0–3 days. In single-pollutant models, PM₂.₅ and SO₂ showed significant positive associations with total mortality per interquartile range increase (PM₂.₅ RR = 1.112, 95% CI: 1.082–1.142; SO₂ RR = 1.102, 95% CI: 1.074–1.131), with the largest effects observed for respiratory mortality. Multi-pollutant models confirmed independent associations for PM₂.₅ (RR = 1.086) and SO₂ (RR = 1.092), while the NO₂ association was attenuated after adjustment for co-pollutants—likely reflecting its role as a marker of traffic-related mixtures rather than an independent toxicant. Seasonal analyses revealed stronger PM₂.₅-related mortality risks during summer months, possibly due to enhanced photochemical activity. An estimated 527 excess deaths annually (5.0% of total mortality) were attributable to ambient air pollution exposure, with respiratory mortality showing the highest vulnerability. These findings demonstrate a substantial and preventable mortality burden associated with air pollution in industrial urban environments and highlight the importance of prioritizing emission control strategies targeting particulate matter and sulfur-containing pollutants.