BBC News
Public offices, banks, schools and universities will remain shut throughout Wednesday and Thursday, officials said.
It follows a similar move last Wednesday, when state TV announced the closures because of “polluted and unhealthy” atmospheric conditions.
Critics say the holidays are costly for Iran’s economy.
Iran’s weekend begins on Friday, meaning the weekend has been extended by two days.
Tehran’s population has greatly increased in recent decades, and there are high number of cars on the roads – many of them old.
The city is wedged between mountains, meaning dirty air can get trapped when there is no wind or rain.
Iranian health experts say thousands of deaths a year are caused by heart attacks and respiratory illnesses brought on by smog.
