Air pollution in Tehran, Iran

Problems

• Tehran, the capital of the Islamic Republic of Iran (IRI), is located in the north of
  the country with a population of about 8.5 million. The population can reach over 12.5 million during the day, with people from nearby cities commuting daily to Tehran for work (Shahbazi et al. 2016). 
  
  There are more than 17 million vehicular trips per day in Tehran (Hosseini and Shahbazi 2016), and many of the vehicles have outdated technology. Thus, the air in Tehran is amongst the most polluted in the world.
  
  Topography and climate add to the pollution problem. Tehran is at a high altitude and is surrounded by the Alborz Mountain Range, which traps polluted air. Temperature inversion, a phenomenon particularly occurring during the winter months, prevents the pollutants from being diluted. Several recent trends indicate that reducing air pollution will not be straightforward: rapid population growth (partially due to migration from other cities), industrial development, urbanization, and increasing fuel consumption are pressure points for clean air in Tehran

• Causes of air pollution in Tehran

  Pollutants from heavy-duty vehicles, motorbikes, refineries, and power plants are Tehran's primary air pollution sources. 80% of air pollution in Tehran is due to vehicles, and the remaining 20% is due to factories and industry emissions.
  
  Iranian refineries are also outdated, leading to high levels of mazut production, reaching 50 percent in most refineries compared to 5-10 percent in other countries. This low-quality mazut cannot be sold on the world market, and due to storage difficulties, it must be consumed domestically. When burned by power plants and industries, mazut generates much more pollution than natural gas.

• Health and environmental impacts of air pollution

  Air pollution in Tehran has serious health and environmental impacts, such as respiratory diseases, cardiovascular problems, reduced visibility, acid rain, and soil degradation. Between March 2021 and March 2022, the deaths attributed to sustained exposure to PM2.5 particles rose by at least 87% from the previous year.
  
  Tehran continues to suffer from severe air pollution, especially in winter, when temperature inversion traps the pollutants in the lower atmosphere. The city is particularly vulnerable to smog due to its high altitude and the surrounding Alborz mountains that trap polluted air. Winter temperatures can exacerbate the problem as cold air prevents the smog from rising.