The Iranian capital’s residents inhaled more polluted air in October compared with the same period of last year, data from Tehran Municipality show.
Charts regularly published by Tehran Air Quality Control Company’s website, Airnow.tehran.ir, illustrate that Air Quality Index did not enter the range of good air quality even for a day.
AQI 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).
According to the data, air quality was unhealthy for the sensitive group for 14 days in the month, hovering between 101 and 150.
This vulnerable group of people, including the elderly, cardiovascular and respiratory patients, pregnant women and children, was advised to limit their outdoor activities and stay home.
In the 17 remaining days, the index remained in moderate state; AQI did not enter the 50 threshold even for a day. Analyses illustrate that the pollutant responsible for the toxic index recorded in the 14 polluted days was PM2.5—particulate matters smaller than 2.5 micrometers.
The AQI review during the year-ago months shows air quality in Tehran is getting worse year by year.
In October 2019, "moderate" status was recorded on all 31 days. A year earlier, the rarely-seen good air quality was recorded on three days of October. The remaining 28 days were moderate.
Carbon monoxide, nitrogen dioxide, sulfur dioxide, ground-level ozone, PM2.5 and PM10 (atmospheric particulate matters that have a diameter of less than 2.5 and 10 micrometers respectively) are measured to determine air quality. AQI figures are calculated as per the concentration of pollutants.
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 added that these old cars emit 579,000 tons of toxins into the air annually, which means 1,586 tons a day.
Giving more specific information, Shahidzadeh noted that of all the pollutants spewed into Tehran’s air annually, these dilapidated cars are responsible for 82% of sulfur oxide, 23% of PM2.5 and PM 10, 46% of carbon monoxide and 45% of nitrogen monoxide.
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. He also warned urban managers on the danger of canceling traffic rules for any reason.
However, comparisons have shown that the implementation of traffic schemes have not had much effect on curbing air pollution in the city.
With the outbreak of Covid-19 in the country, municipal bodies in Tehran lifted the traffic limits in late March and early August, to discourage people from using public transportation to curb the spread of the virus. But the measure led to clogged roads and heavy traffic in the city.
According to Mohammad Rastegari, the head of the Department of Environment, told reporters that in both rounds, the resumption of traffic schemes in the capital has had close to zero effect on air pollution.
“Air quality data recorded daily by TAQCC show no decline in air pollution levels after the resumption of traffic restrictions in the city,” he said.
Pointing to the decisive effect of environmental phenomena, such as wind, on air quality, the DOE official said wind can be much more effective than the most strict traffic schemes, for it can disperse pollution and change air stability in a few hours.
This is why, he added, traffic schemes alone cannot reduce air pollution levels and can only cause minor changes.
Share of Pollutants
Rastegari’s words are supported by a study conducted by TAQCC on the share of different sources in Tehran’s air pollution.
The study divides the sources 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 new data, the highest level of emission is spewed by passenger buses by 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%.
