Tehran's schools and kindergartens were closing for at least four days because of severe air pollution on Tuesday.

Authorities have also exempted many employees from attending governmental offices, Iran's state TV reported.

Tehran’s air quality is among the worst in the world.

The smog is mostly caused by heavy traffic due to millions of fuel-burning cars, motorbikes and factory emissions.

It worsens during the cold season because of a lack of wind and rain.

A taxi driver said domestically made cars as well as low-quality fuel are contributing to poor air quality.

"I as a citizen have to use such fuel, I have no choice, and my car consumes too much fuel.

The city is surrounded by tall hills and mountains on three sides.

Cold, stagnant air settles in the valley, trapping automotive and other emissions that cannot escape.

The phenomenon is called temperature inversion.

On Tuesday, the air quality index in the capital stood at 164, according to Iran's Air Quality Control department.

A range of 151-200 is considered unhealthy for all citizens.

In July 2022, schools and government offices closed in Iran’s capital and several other cities in the country, after a sandstorm blanketed Tehran and the surrounding region.

AP video by Saeed Sarmadi