The authorities shuttered primary schools in the province of Tehran, home to 14mn residents, before ordering them to remain closed today.
All sports competitions set for today were also cancelled, as restrictions on road traffic were stepped up, including a ban on trucks.
Airborne concentration of fine particles (PM2.5) hit 185 microgrammes per cubic metre in the south of Tehran and 174 in its centre yesterday morning, local authorities said.
That is far above the World Health Organisation recommended maximum of 25 microgrammes per m3 over a 24-hour period.
The microscopic particles lodge deep in the lungs and are harmful to human health.
“Tehran is suffocating (but) hundreds of thousands of cars are built each year,” said Hossein, a man in his sixties who did not give his surname.
“They’re building in the mountains, they’re destroying our forests. We don’t want any more oil, we don’t want any more petrol,” he added.
Every year, Iran’s sprawling capital 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 its more than 8mn cars and motorbikes.
Authorities also ordered mines and cement factories to close, and called on the elderly, children, pregnant women and people with heart problems to stay indoors.
Residents who ventured out wore face masks while others chose to remain at home.
Ali Ebrahimian, a retiree, said he only stepped outside to sort out “an urgent matter”.
Fatemeh Assadi, a woman in her sixties, accused the authorities of failing to prevent the pollution. “The government’s not doing anything,” she said.
Iran is expected to produce 1.5mn new vehicles by the end of this Persian year which ends in March, according to official figures, in a country where some 20mn cars and trucks are already on the roads.
In October, Tehran mayor Mohamed Ali Najafi said he wanted to develop public transport and help reduce traffic in the capital, which lies at between 1,400 and 1,800 metres above sea level.
But he warned that a solution would take time.
In the northwestern cities of Tabriz and Urmia, schools remained closed for the second day straight yesterday, official news agency IRNA said.
While atmospheric pollution in Iran is not as severe as in India or China, it endangers the health of its residents.
