Trends in PM10 and PM2.5 air pollution and related health risk in Tehran over the last two decades

In this study, we have analyzed PM₁₀ and PM_2.5 mean concentrations over 20-year (2003−2022) and 16-year (2007–2022) period, respectively obtained from air quality monitoring stations installed in 22 districts across Tehran, one of the most populated cities in the world. By applying the Mann-Kendall test, the results showed that the annual PM₁₀ mean concentrations increased by 0.27 % per year, while the annual PM_2.5 mean concentrations declined by −1.27 % per year. The annual PM₁₀ and PM_2.5 mean concentrations have largely exceeded, on average 2 times, the 2021 World Health Organization (WHO) air quality guidelines for human health protection (i.e., 15 and 5 μg m⁻³ for PM₁₀ and PM_2.5). During the study period, the daily PM₁₀ concentrations <50 μg m⁻³ were 4.3 % of time, 95.5 % of time between 50 and 200 μg m⁻³, and 0.2 % of time exceeding 200 μg m⁻³. The hazard quotient (HQ) values of non-carcinogenic risk due to PM₁₀ and PM_2.5 exposure for all age groups were > 1, showing potential health risk for children and adults. The local authorities should consider implementing measures, such as blue and green infrastructure, to reduce the levels of air pollution and mitigate related human health risks.