The result is an insidious haze of mixed pollutants, mainly carbon monoxide and suspended particles. Levels of both of them have now reached well above the crisis point. Many Tehranis have resorted to wearing face masks while breathing through wads of cloth. Breathing problems and irritations of the skin and eyes have become common. The elderly and those with lung or heart problems are now being urged to stay at home.
Motor vehicles are the main culprit.
For some years now, a scheme has been in operation whereby cars need a special pass to enter the city centre on weekdays, but that is clearly not enough. A temporary measure resorted to recently, with some success, was the closure of all primary schools, but that is hardly a solution. It will not get underway for another two months and officials warn it will take time for the benefits to be felt. The BBC is not responsible for the content of external internet sites Links to other Middle East stories are at the foot of the page.