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EghtesadOnline: The residents of Iranian capital breathed in more polluted air in March compared with the corresponding month of last year, data released by Tehran Air Quality Control Company show.

Charts published on TAQCC’s website,, show that in March, clean blue skies were seen on only four days with the air quality index showing "good" condition. 

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).

Moderate status dominated the month, keeping the index between 51 and 100 in 20 days.

TAQCC data show that during the period, sensitive groups in the capital were warned to limit their outdoor activities on six days, as the index entered 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.

On March 17, AQI reached 153, hitting an emergency level because of the high density of toxic emissions.

Pollutants measured to determine air quality include carbon monoxide, nitrogen dioxide, sulfur dioxide, ground-level ozone and particulate matter (PM2.5 and PM10). AQI figures are calculated as per concentration of pollutants. 

Analyses illustrate that the element responsible for all polluted days recorded during the period under review was PM2.5 (atmospheric particulate matters that have a diameter of less than 2.5 micrometers).




Air quality in Tehran is getting worse year-on-year, since AQI was comparatively lower in March of last year.

A large number of people stayed home in self-quarantine, as the novel coronavirus raged across Iran. Data show Tehran’s residents were exposed to cleaner air in March 2020 compared to the month in the current year. 

TAQCC charts show that clear blue skies were seen for eight days of the month, meaning that the air quality index was below 50. 

During the month, “moderate” status was the most prevailing air condition, as the index hovered between 51 and 100 on 20 days. 

Besides, sensitive groups in the capital were warned to limit their outdoor activities on three days, as the index ranged between 101 and 150.

TAQCC data illustrate that air quality condition was significantly better during the same period of last year.

In March 2019, AQI had 13 “good” and 18 “moderate” days.



Main Culprits

While there are various debates on the causes of poor air quality in the metropolis, the head of TAQCC earlier blamed 100,000 dilapidated passenger cars in Tehran.

Hossein Shahidzadeh added that over 3.43 million passenger cars ply the capital’s streets every day, 100,000 of which are over 18 years old and have outlived their usefulness.

He noted that these old cars emit 579,000 tons of toxins into the air annually, which means 1,586 tons a day.

Shahidzadeh noted that of all the pollutants discharged into Tehran’s air annually, 82% of sulfur oxide, 23% of PM2.5 and PM 10, 46% of carbon monoxide and 45% of nitrogen monoxide are emitted by dilapidated cars.

He also said PM2.5 is the most harmful pollutant due to its ability to penetrate deep into the lungs and bloodstreams unfiltered, causing heart attacks, respiratory disease and premature death.

Shahidzadeh called the officials in charge to more seriously monitor the technical efficiency of cars plying Tehran’s streets. 



Substandard Vehicles

The low quality of brand new vehicles manufactured by domestic companies has also added to the problem. 

According to Hossein Moqaddam, CEO of Tehran Vehicle Technical Inspection Bureau, over one-third of vehicles used in Tehran failed to meet emission standards and pass technical inspection tests.

He said that in the last Iranian year (ended March 20, 2021), 1.66 million vehicles visited the capital's technical inspection centers, of which 1.19 million were under four years old and underwent their first technical check.

"Of the 597,600 new vehicles rejected, 17% did not receive the certificate due to high emission, 11% for wheel alignment, 4% for shock absorber failure, 13% for brake system problems and 16% for appearance issues,” he added.

The official noted that during the period, 1.13 technical certificates have been issued, of which 850,000 were regular and 283,000 were premium type.

The premium certificate has higher standards than that of the normal technical inspection certificates. While in normal tests, vehicles’ emissions are monitored in a low-speed performance but for receiving the premium certificate, the carbon monoxide emission of cars is assessed at 2,500 rpm.

Vehicles that do not meet local emission and safety standards spew poison into the air, threaten people’s lives and damage the environment.

Tehran Municipality’s Transportation and Traffic Organization has estimated that air pollution in the capital costs $2.6 billion annually.


Tehran Pollution Air Quality