Spatiotemporal distribution of tropospheric NO2 column density over Iran using the OMI sensor data

One of the most important issues related to climate is air pollution. Today, due to the increasing use of fossil fuels, the concentration of air pollutants, especially nitrogen dioxide (NO2), has increased and has caused many problems for human health. The study investigated the temporal-spatial study of tropospheric NO2 column density using the OMI sensor data during the study period of 2005-2020 over the Iranian territory. In the long-term, the average NO2 was estimated to be 1.57e + 15 molecules/cm2, with the highest amount over Tehran (1.5e + 16 molecules/cm2) and the lowest amount over suburban areas (1e + 14 molecules/cm2). In addition to the metropolis of Tehran, cities such as Isfahan, Ahvaz, Shiraz, Tabriz, Rasht, Sari, Mashhad, Qom, Qazvin, and the industrial areas of the southern coast had high concentrations. The time-series analysis of the tropospheric NO2 column density during the 5823 consecutive day study period showed an increasing trend over Iran considering the averages change from 1.36e + 15 molecules/cm2 in 2005 to 1.78e + 15 molecules/cm2 in 2020. The seasonality results also showed that the maximum and minimum NO2 values occur in winter (1.57e + 15 molecule/cm2) and summer (1.31e + 15 molecule/cm2), respectively. As such, November, December, and January had the highest, and the months of June, July, and August had the lowest monthly mean NO2 column densities. The higher concentrations of NO2 during the cold seasons are mainly due to the higher activity of emission sources in addition to the specific weather conditions at this period of the year. Besides, its harmful effects will intensify in the future referring the increasing trend of NO2 pollutants. Therefore, before the further increase, preventive measures should be taken by the relevant authorities.