Severe air pollution in Iran's capital, Tehran, has put nearly 400 people in hospitals with heart and respiratory problems.
Hassan Abbas, a Tehran emergency services official, said on December 30 that the city's dirty air had caused another 1,434 people to be treated in their homes for similar problems.
Tehran officials have urged sick and elderly people to stay indoors and away from heavy traffic areas.
The Iranian capital -- which has a population of some 12 million -- has some of the most-polluted air among the world's major cities.
Tehran's air quality worsens in the winter when an inversion traps cold air and pollutants above the city -- which has a high elevation and is surrounded by mountains.
Other Iranian cities, such as Isfahan and Mashhad, have also experienced high-pollution days in recent weeks.