Tehran logs 63 clean-air days in best five-year start
Tehran has recorded 63 clean-air days since March 21, 2026, the highest figure for the same period in five years, while ozone pollution has risen more slowly than in previous years, the Tehran Air Quality Control Company said on June 2.
The capital registered 63 clean-air days and 10 days with acceptable air quality through June 1, marking its strongest start to a year since 2021, according to data from the city’s air-monitoring network, ILNA reported.
The figures point to a notably cleaner opening to the year for Tehran, where ground-level ozone typically becomes the dominant pollutant during the warmer months. Monitoring data show that the seasonal increase in ozone concentrations has started later and progressed more gradually than in recent years.
A comparison of hourly ozone levels during the first 10 days of June found lower concentrations than those recorded over the same period in 2025. No ozone-related air-quality readings exceeded acceptable limits in either year, though daytime levels were generally higher last year.
The company said more favorable weather conditions, including milder temperatures and increased atmospheric instability, may have contributed to the slower build-up of ozone, alongside a possible reduction in ozone-forming pollutants.
Ground-level ozone is formed when pollutants from traffic and urban activities react under strong sunlight and high temperatures. Unlike the protective ozone layer in the upper atmosphere, it can pose risks to respiratory health, particularly during hot, sunny and low-wind conditions.
Officials cautioned that ozone concentrations could increase in the coming weeks as summer temperatures rise and solar radiation intensifies across the Iranian capital.