Short-term effects of particulate matter during desert and non-desert dust days on mortality in Iran

Background: Increased atmospheric particulate matter (PM) concentrations are commonly observed during desert dust days in Iran, but there is still no evidence of their effects on human health. We aimed to evaluate the association between daily mortality and exposure to PM 10 and PM 2.5 during dust and non-dust days in Tehran and Ahvaz, two major Middle Eastern cities with different sources, intensity, and frequency of desert dust days. Methods: We identified desert dust days based on exceeding a daily PM 10 concentration threshold of 150 g/m 3 between 2014 and 2017, checking for low PM 2.5 /PM 10 ratio typical of dust days. We used a time-stratified casecrossover design to estimate the short-term effects of PM 10 and PM 2.5 concentrations on daily mortality during dust and non-dust days. Data was analyzed using conditional Poisson regression models. Results: Higher concentrations of PM and frequency of desert dust days were observed in Ahvaz rather than Tehran. In Ahvaz, the effect of PM 10 at lag 0 was much higher during dust days, an increment of 10 g/m 3 was associated with 3.28% (95%CI = 2.42, 4.15) increase of daily mortality, than non-dust days, 1.03% (95%CI = -0.02, 2.08), while in Tehran, was slightly higher during non-dust days, 0.72% (95%CI = 0.23, 1.23), than in dust days, 0.49% (95%CI = -0.22, 1.20). No statistically significant associations were observed between PM 2.5 and daily mortality in Ahvaz, while in Teheran the effect of PM 2.5 increased significantly during non-dust days at lag 2, 1.89% (95%CI = 0.83, 1.2.95 and lag 3, 1.88% (95%CI = 0.83, 1.2.95).