Long-term PM_2.5 exposure in Bangladesh: identification of pollution hotspots, trends, sources and health risk assessment

Fine particulate matter (PM_2.5) represents a significant global challenge due to its severe effects on human health, climate, and the environment, and is identified as the leading cause of premature mortality and morbidity worldwide. The limited availability and distribution of ground-based measurements hinder long-term studies on the impacts of air pollution in Bangladesh. Therefore, in this study, global estimates of monthly PM2.5 developed by Washington University were used to analyze the spatiotemporal distribution and variability of PM2.5, trends, health risk (HR), control zones, and potential source contribution function (PSCF) in Bangladesh from 2001 to 2020. The 20-year average spatial distribution shows PM_2.5 hotspots across Bangladesh, particularly in the urban areas of Dhaka, Mymensingh, Chittagong, Barisal, Khulna, Rajshahi, and Rangpur, with higher pollution in the winter than in other seasons. In winter, PM_2.5 ranged from 55.12 to 159.42 µg/m³ across 64 cities in Bangladesh, which is 11 to 32 times higher than the World Health Organization Air Quality Standards (WHOAQS; annual mean: ≤ 5 µg/m³) and 4 to 11 times higher than the Bangladesh National Ambient Air Quality Standards (BNAAQS; annual mean: ≤ 15 µg/m³). Moreover, PM₂.₅ levels significantly increased in 63 cities across Bangladesh, with rates ranging from 0.54 to 1.38 µg/m³/year between 2000 and 2020. PM₂.₅ components in Bangladesh show an increasing trend for Sea Salt (SS), Organic Carbon (OC), Sulfate (SO₄), Black Carbon (BC), and Nitrate, except for Dust, which exhibits a negligible decreasing trend. Weather conditions, industrial emissions, vehicle exhaust, and biomass burning significantly influence PM₂.₅ concentrations. The HR assessment showed that the percentage of extremely high-risk areas in Bangladesh rose significantly from 14.57 to 39.29% between 2001 and 2020. Finally, PSCF analysis shows that air quality in Bangladesh is mainly affected by external sources of PM_2.5 originating from the Indo-Gangetic Plain (IGB), India, Nepal, Bay of Bengal, Sri Lanka, Gulf of Mannar, Arabian Sea, and Laccadive Sea, with the strongest impact in the winter, followed by spring, autumn, and summer. It is recommended that policymakers utilize the findings of this study to implement targeted strategies for reducing PM_2.5 concentrations and improving air quality across Bangladesh.