The phenomenon creates a layer of warm air above the city that traps pollution from some 10 million cars and motorbikes.

Pollution in Tehran has hit a dangerous level on the Air Quality Index, with airborne particles considered “unhealthy” for the general public.

Kindergartens and primary schools in the Iranian capital were ordered to stay closed Sunday, according the state run television.

Every year, Tehran suffers some of the worst pollution in the world when cool temperatures cause an effect known as “temperature inversion.”

The phenomenon creates a layer of warm air above the city that traps pollution from some 10 million cars and motorbikes.

Pollution has become a political football in recent years, with conservatives and reformists blaming each other for the problem.

[vuukle]