Black Carbon in Tehran Air Declines

Data from Tehran Air Quality Control Company (affiliated to Tehran Municipality) showed the ban on dilapidated and polluting heavy vehicles in the city has reduced the amount of black carbon in the capital's air by half.

Since December 2017, polluting trucks and those lacking a technical inspection license have been banned from plying the streets of Tehran. The measure is aimed at moderating the effects of inversion that occurs during the cold season when polluted air is trapped close to the ground.

The company has conducted tests to assess the effects of the ban on air quality, ISNA reported.

According to Ahmad Taheri, director of air quality measurement system at the company, the new law has not directly reduced the concentration of PM2.5 (particulate matter 2.5 micrometers in diameter or smaller that includes black carbon) but has brought down the amount of black carbon by 50%.  

Black carbon is the sooty black material emitted from gas and diesel engines, coal-fired power plants and other sources that burn fossil fuel. It is the main type of emission generated by the heavy-duty fleet.

The official said that in places frequented by trucks in Tehran, black carbon comprised more than 60% of PM2.5.

"Black carbon is a primary pollutant emitted from the exhaust pipe, but once in the atmosphere, it reacts with other pollutants such as nitrates and sulfates, and creates secondary particulate matters," he said, adding that preventing the emission of primary pollutants will stop the formation of secondary types.

Taheri noted that although the prohibition on heavy vehicles does not directly affect PM2.5, it can reduce their toxic nature to a considerable degree.