Satellite-Based Investigation of Total Column Ozone (O₃) and Nitrogen Dioxide (NO₂) over Iran during 2019–2023

Air pollution is one of the most important environmental hazards, affecting more than 90% of the world's population and posing significant direct and indirect impacts on human health and quality of life. This study investigates the annual and monthly variations in total column O₃ and NO₂ over Iran using TROPOMI/Sentinel-5P and OMI/Aura satellite data. The results from both satellite datasets indicate high NO₂ concentrations over Tehran Province (near 40 DU) and the northern coasts of the Persian Gulf (more than 80 DU) during most months of the year. In contrast, total column O₃ is generally higher at higher latitudes (more than 300 DU) throughout most of the year, with the highest values occurring between July and October. However, the satellite-derived ozone concentrations are not consistent with measurements from more than 90 ground-based air quality monitoring stations across Iran. It should be noted that the number of air quality monitoring stations measuring surface O₃ and NO₂ concentrations is considerably lower in the southern and eastern regions of Iran than in the northern and western regions, primarily because the majority of the country's population is concentrated in the north and west. Consequently, comparing satellite-derived total column O₃ and NO₂ with ground-based surface measurements is challenging due to the limited spatial coverage of air quality monitoring stations across Iran. This study therefore highlights the need to establish additional air quality monitoring stations, particularly in eastern Iran and the country's desert regions, to improve the spatial coverage and reliability of satellite validation. Composite reanalysis fields for 27 July 2024 further demonstrate that the event occurred within a broader amplified Rossby-wave pattern, featuring a blocking ridge over Iran, anomalously strong jet streaks at 200 hPa, and a companion trough over northern Europe.