صادق کریمی

INTRODUCTION: Urban air pollution, especially in densely populated metropolises such as Tehran, has become one of the most serious environmental and health challenges. Nitrogen dioxide (NO₂), as one of the most important pollutants resulting from human activities, accumulates persistently in the surface layers of the atmosphere, especially in the cold seasons and under temperature inversion conditions. This study conducts an integrated hazard analysis of the spatiotemporal distribution of NO₂ in Tehran County over a seven-year period (2018–2024), with a focus on the interplay between anthropogenic and natural factors in shaping this hazard. METHODS: In this descriptive-analytical study with an integrated approach, daily NO2 concentration data were extracted from Sentinel-5P satellite images (TROPOMI sensor) during the winter seasons from 2018 to 2024 in Tehran. Using spatial extraction tools in the GIS environment, data were processed, seasonal averages were calculated, and raster-to-vector conversion was performed, and spatiotemporal distribution patterns of NO2 were plotted and analyzed. FINDINGS: The findings showed that the distribution pattern of NO2 has undergone significant spatial and temporal changes over the seven years. In 2018 and 2019, the highest concentrations were observed in central Tehran and the northeastern districts. A marked decline occurred in 2020 and 2021, coinciding with mobility restrictions imposed during the COVID-19 pandemic. However, from 2022 onward, NO₂ levels began to rise again, with a notable increase in southern and eastern areas by 2024. These shifts reflect a transition in pollution hotspots—from the city center toward peripheral zones—followed by a partial return to a more centralized pattern, indicative of extensive urban expansion and intensified human activities in suburban areas. CONCLUSION: According to the research results, NO₂ pollution in Tehran constitutes a “compound hazard,” resulting from the complex interaction of anthropogenic drivers (e.g., traffic, industry, and urban development) and natural conditions (e.g., temperature inversions and topography). The observed changes in NO₂ spatial patterns mirror transformations in urban morphology, land use, and environmental management policies.