Iran shut primary schools in Tehran and other parts of the country on Sunday as thick smog blanketed the capital despite curbs on road traffic and industrial activity.
Local authorities late Saturday announced the closure of all primary schools in the province of Tehran, which is home to 14 million residents, except in two towns.
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 its more than eight million cars and motorbikes.
Airborne concentration of fine particles（PM2.5） hit 185 microgrammes per cubic metre in the south of Tehran and 174 in its centre on Sunday morning, local authorities said. That is far above the World Health Organization 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. Authorities ordered mines and cement factories in Tehran province to close and reinforced traffic restrictions in the capital’s centre. They called on the elderly, children, pregnant women and people with heart problems to stay indoors.
Source article: http://iservice.ltn.com.tw/Service/english/english.php?engno=1161756&day=2017-12-20