Thick smog keeps schools closed for fourth day in Iran

Schools were closed for a fourth straight day in Tehran yesterday as dangerous air pollution covered the Iranian capital and traffic restrictions failed to clear the thick smog.

Average airborne concentration of the finest and most hazardous particles (PM2.5) was "unhealthy" at 160 microgrammes per cubic metre, slightly worse than Tuesday, authorities said.

That is more than six times higher than the World Health Organization recommended maximum of 25 microgrammes per m3 over a 24-hour period.

Authorities extended traffic restrictions so that only one in two cars could go on the street, depending on their number plates.