Tehran suffering from extreme air pollution

New York Times : Air pollution in Tehran has reached new levels of severity. Although in 2009 the city experienced more than 300 “healthy” air days, by 2011 the number had fallen to fewer than 150. Tehran is now experiencing air pollution particulate levels that are four times the concentrations found in Los Angeles, and it has more severe pollution than Shanghai or Mexico City. Some residents who venture outdoors have taken to wearing masks, and recently, the government closed schools and businesses for five days to try to cut back on the pollution. One of the key contributors is likely the locally produced gasoline that Iran introduced following the imposition in 2010 of sanctions by the US on the sale of refined gasoline to Iran. The gasoline that Iran is producing is not of the same quality as the fuel it had been importing and produces more pollutants when burned. However, the Iranian government has not acknowledged the connection.