Why does the air in Tehran become more polluted as the air cools?
▫ With the increase in air pollution in Tehran in recent days, suspended particles smaller than 2.5 microns (PM2.5) have once again become the dominant pollutant of the capital.
▫ Fatma Karimi, CEO of the Air Quality Control Company in Tehran, believes that the main factor for increasing the concentration of pollutants on cold days is more related to atmospheric conditions than to a change in emission sources.
▫ In the second half of the year, the stability of the air and the temperature inversion phenomenon cause pollutants produced from fixed and mobile sources to remain in the city's air for a longer period of time.
▫ According to him, the difference in weather conditions can be seen in the change in the air quality index; In less than a week, Tehran's index dropped from 49 on a clean day to 147 on an unhealthy day for sensitive groups.
Karimi also says that he does not have detailed information on the fuel burning of power plants, but he emphasizes that the production of suspended particles is not limited to diesel and that car fuel and steam also play a role in the creation of secondary pollutants.
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