Students and civil servants in several parts of Iran have been instructed to stay home on Wednesday and Thursday due to dangerously high levels of air pollution, state media reported.

Tehran, which frequently faces pollution issues, has been blanketed in smog in recent days. The city, located in the southern foothills of the Alborz Mountains, is particularly prone to poor air quality as the mountains trap polluted air. 

This phenomenon, known as thermal inversion, is especially problematic during winter, when cold air and a lack of wind can leave hazardous smog lingering for days.

On Wednesday, local media reported that Tehran’s air quality had reached “unhealthy” levels, with an average air quality index (AQI) of 170. In response, museums and banks in the capital, except for select branches, were closed.

The Milad Tower, standing at 435 meters, was nearly invisible on Wednesday morning due to the thick smog. Pollution levels were also high in other major cities, including Isfahan in central Iran, Tabriz in the northwest, and Ahvaz in the southwest, according to state television.

The pollution has been attributed to several factors, including outdated industrial infrastructure, an aging vehicle fleet, and poor-quality gasoline. In recent weeks, the government has also pointed to the fuel used in certain power plants as a key contributor to pollution.

Iranian Health Minister Mohammad-Reza Zafarghandi has stated that air pollution is responsible for the premature deaths of around 50,000 people across the country each year. In response to the growing concerns over air quality, Iranian authorities have repeatedly closed schools in Tehran, including a week-long closure in 2019.