The first day of winter began will heavy pollution in Tehran, Mashhad and a number of other major cities across Iran.

Khabar-on-line reports that the city of Tehran’s air quality reached warning levels on Sunday December 22.

The report adds that all parts of Greater Tehran including the suburbs are under an air pollution advisory.

The report indicates that the falling temperature in the final days of autumn has led to a spike in air pollution in big industrial cities.