Dangerous air quality as pollution engulfs Tehran

Dangerous poor air quality in the Iranian capital of Tehran has led to school closures once again, the country's state television reported on Tuesday.

Tehran’s air is among the most polluted in the world. Authorities also urged the elderly, those who are sick and children to take precautions. The smog is mostly caused by heavy traffic as well as factory pollution and typically worsens during the cold season.

Inversions commonly hover over Tehran in the winter. As cold, stagnant air settles in the valley, it traps car and other emissions that have no way of escaping. Similar measures were announced for Tehran's neighboring Alborz province.