Background: The largest capital of the Middle East, with ۸۰۰۰ Km۲ and a population of ۱۳ million people, has about ۴۰% of Iran's industrial units in its suburbs. The purpose of this study was to investigate the trend of air quality in Tehran between ۲۰۱۸ and ۲۰۲۴. Methods: Daily air quality index (AQI) data were collected from ۱۶ monitoring stations in Tehran province over three time periods: ۲ years before, ۲ years during, and ۲ years after the COVID-۱۹ pandemic. Descriptive statistics were calculated for each pollutant during these periods, and box plots were used to visualize AQI distributions. The Kruskal-Wallis test was applied to assess significant differences in AQI across the three time periods. Results: PM۲.۵ was the dominant pollutant across all seasons, peaking at ۹۹.۴% in autumn and remaining above ۹۰% in winter. The AQI for PM۲.۵ increased from ۱۰۹ pre-pandemic to ۱۴۳ post-pandemic. Seasonal trends revealed significant increases in pollutants such as O۳ and PM۲.۵ in spring, summer, and autumn, while NO₂ levels fluctuated. The Kruskal-Wallis test indicated significant seasonal variations, with PM۲.۵ showing the most substantial increase (H = ۲۶۲.۴۳, p < ۰.۰۰۱). O۳ and PM۱۰ also showed significant post-pandemic growth, whereas SO₂ and NO₂ had smaller but significant fluctuations (p < ۰.۰۵). Conclusion: The results show that reducing traffic and preventing the use of Mazut fuel in power plants have had significant effects on reducing air pollutants, and the sharp decrease in precipitation in recent years has increased the dispersion and emission of particles.

کلیدواژه ها:

Air Pollution ، O۳ ، PM۲.۵ ، Tehran ، Iran