Tropospheric ozone in Tehran: integrated assessment of inhalation health risk over the last decade

This study assessed long-term trends of tropospheric ozone (O₃) concentrations in Tehran, Iran, over the time period 2015-2024, and quantified the non-carcinogenic health risks across different age groups by applying the United States Environmental Protection Agency (U.S. EPA) human health risk assessment methodology. The O₃ data from 22 air-quality monitoring stations and satellite-retrieved columnar from Copernicus Sentinel-5P were analyzed. Annual O₃ mean concentrations exhibited a slight non-statistically significant decreasing trend (-0.11% year^-1). Peak concentrations were recorded in 2021, corresponding to post-COVID-19 socio-economic recovery and rising precursor emissions. Age-specific Hazard Quotients (HQ) remained <1.0 in all years, indicating acceptable non-carcinogenic risk for any single life stage. However, the cumulative lifetime Hazard Index (HI), obtained by summing age-specific HQs, ranged from 5.48 to 8.10 and consistently exceeded the U.S. EPA safe threshold of 1.0, showing potential adverse non-carcinogenic health effects from chronic O₃ exposure over a full lifetime. These results underline the importance of controlling O₃ precursors in densely populated cities and demonstrate the value of combining ground and satellite observations with lifetime exposure modeling for urban air-quality management.