All schools, universities, and businesses in Tehran and other cities of the province were closed Wednesday, some for the second day, due to air pollution.

Tehran Governor Mohsen Mansouri announced the measure following a decision by the Tehran Province Air Pollution Emergency Committee. The neighboring province of Alborz, the southern province of Khuzestan, East Azarbaijan province in the north west, and Esfahan province in central Iran also reported shut-downs due to air pollution including severe sandstorms.

The air quality index in many Iranian cities, including Tehran and Kermanshah, has reached a maximum level, making it hazardous for people to leave their homes. While Tehran’s air is among the world’s most polluted, many large Iranian cities face similar problems, especially when power stations use heavy diesel fuels as demand for electricity runs ahead of the supply of natural gas.

Dust storms, originating in both Iran and neighboring countries, have also increased markedly in recent years in several Iranian provinces, notably Khuzestan, Kermanshah, and Sistan-Baluchestan. While there have been efforts to reduce such storms through more effective management of water resources and planting drought-resistant trees in arid areas, these have so far proved inadequate.