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style="position:absolute; left:0; text-align:left; margin-left:-4px; margin-top:8px; width:5in; height:0; z-index:251662336" type="#_x0000_t32"> <w:wrap type="square"> </w:wrap></v:shape><span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="line-height:1;"><b><span style="color:black">Background:</span></b><span style="color:black"> The largest capital of the Middle East, with 8000 Km² and a population of 13 million people, has about 40% of Iran&#39;s industrial units in its suburbs. The purpose of this study was to investigate the trend of air quality in Tehran between 2018 and 2024.</span></span></span></span></span></span></span><br> <span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="line-height:1;"><b><span style="color:black">Methods:</span></b> <span style="color:black">Daily air quality index (AQI) data were collected from 16 monitoring stations in Tehran province over three time periods: 2 years before, 2 years during, and 2 years after the COVID-19 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.</span><span style="color:black"></span><br> <b><span style="color:black">Results:</span></b> <span style="color:black">PM_2.5was the dominant pollutant across all seasons, peaking at 99.4% in autumn and remaining above 90% in winter. The AQI for PM</span>_{<span style="color:black">2.5 </span>}<span style="color:black">increased from 109 pre-pandemic to 143 post-pandemic. Seasonal trends revealed significant increases in pollutants such as O₃ and </span><span style="color:black">PM_2.5</span><span style="color:black">in spring, summer, and autumn, while NO₂ levels fluctuated. The Kruskal-Wallis test indicated significant seasonal variations, with </span><span style="color:black">PM_2.5</span><span style="color:black">showing the most substantial increase (H = 262.43, <i>p</i> < 0.001). O₃ and PM₁₀ also showed significant post-pandemic growth, whereas SO₂ and NO₂ had smaller but significant fluctuations (<i>p</i> < 0.05).</span><span style="color:black"></span><br> <b><span style="color:black">Conclusion:</span></b><span style="color:black"> 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.</span></span></span></span></div> Air Pollution, O3, PM2.5, Tehran, Iran, 76 84 http://jhehp.zums.ac.ir/browse.php?a_code=A-10-102-8&slc_lang=en&sid=1 Koorosh Kamali drkamali@zums.ac.ir 100319475328460016577 100319475328460016577 No Department of Public Health, School of Public Health, Zanjan University of Medical Sciences, Zanjan, Iran. Fatemeh Masaebi fatemeh.masaebi71@gmail.com 100319475328460016578 100319475328460016578 No Department of Statistics, Faculty of Health, Zanjan University of Medical Sciences, Zanjan, Iran. Zohre Farahmandkia zfarahmand@zums.ac.ir 100319475328460016579 100319475328460016579 Yes Social Determinants of Health Research Center, Institute of Health and Metabolic Diseases, Zanjan University of Medical Sciences, Zanjan, Iran; Department of Environmental Health Engineering, Faculty of Health, Zanjan University of Medical Sciences, Zanjan, Iran.