Experts have repeatedly emphasized that burning fossil fuels, factories operating within city limits, the excessive use of private cars and the growing number of low-quality motorcycles are the main culprits.
However, Tehran Air Quality Control Company recently conducted a study on the nature and sources of pollutants, which changes the long-presumed share of these culprits in the chronic air pollution.
The study names pollutants affecting air quality as carbon monoxide, carbon dioxide, nitrogen monoxide, nitrogen dioxide, sulfur dioxide, ground-level ozone and particulate matters (PM2.5 and PM10). These pollutants are classed as primary and secondary, according to Financial Tribune.
Pollutants directly emitted into atmosphere are considered primary, such as SO2, NO2, NO, CO and PMs. Through their exposure to atmospheric elements like sunlight and high temperature, these pollutants can be converted into other carcinogens like nitrate (NO3) and sulfur trioxide (SO3), which are called secondary pollutants.
However, the study shows that among all pollutants, particulate matters, especially PM2.5, are the most harmful due to their ability to penetrate deep into the lungs and blood streams unfiltered, causing heart attacks, respiratory disease and premature death.
Focusing on the primary origins of these microscopic killers, the study provides a new configuration of their contributing to PM2.5 emission.
Share of Pollution Sources
The sources are mainly divided into stationary and mobile modes. Stationary sources, which include industrial units, generate 24% of the total PM2.5 in Tehran’s air.
Mobile sources are responsible for the remaining 76%, including private cars, taxis, motorcycles, minibuses, buses, heavy duty vehicles and airplanes.
Until now, almost all analyses are compatible with the previous data. But the interesting part is the share of each source in the category.
According to the new data, the highest level of emission is spewed by passenger buses, equal to 31%, even more than all the stationary sources of pollution in the city.
Heavy duty vehicles are the next most polluting source with 23.7%, followed by motorcycles with 10%, airplanes with 5% and minibuses with 4.3%.
The data illustrate that the least polluting groups are private vehicles and taxis with a respective contribution of 1.6% and 0.4%.
This is while not only have the capital’s urban managers always censured passenger vehicles for their detrimental effects on air pollution, but they have also set several traffic regulations, schemes and fines to curb the use of private cars.
Weak efforts to relocate 300 industrial units in Tehran have been to no avail.
Over the past many years, city councilors and mayor have failed to address the issue effectively, blaming others for the worsening air pollution.
Smog in Tehran takes the lives of over 3,500 people every year, the Ministry of Health reported.
AQI on Highs
Charts published by TAQCC’s website, Airnow.tehran.ir, show that in December, Tehran’s residents were exposed to more polluted air, as clear blue skies were not to be seen at all, meaning that the air quality index did not fall under 50.
The index categorizes conditions dictated by a measure of polluting matters into good (0-50), moderate (51-100), unhealthy for sensitive groups (101-150), unhealthy (151-200), very unhealthy (201-300) and hazardous (301-500).
TAQCC data show that in December, "moderate" status was the prevailing air condition, as the index hovered between 51 and 100 on 13 days.
Besides, sensitive groups in the capital were warned to limit their outdoor activities on 14 days, as the index stood at the threshold of 101-150 that categorizes the condition as “unhealthy for sensitive groups”.
Children, the elderly, pregnant women and those with respiratory and cardiovascular conditions fall in the above group.
The AQI crossed emergency levels in three days with the index showing "unhealthy" status for all and causing the closure of numerous kindergartens, schools and universities.
Analyses illustrate that the pollutant responsible for the toxic index recorded in the month was PM2.5 0 (atmospheric particulate matters that have a diameter of less than 2.5 and 10 micrometers respectively).
TAQCC data illustrate that air quality condition was significantly better during the same period of last year. In December 2018, AQI had three "good", 17 "moderate" and 10 "unhealthy" days.