Air quality monitoring stations around the capital city show residents took an easier breath in November compared with the corresponding month of 2019.
Based on data published by Tehran Air Quality Control Company on its website, Airnow.tehran.ir, the capital experienced fewer polluted days in November compared to a year earlier.
During the month, the air quality chart was dominated by ‘moderate’ status, with Air Quality Index hovering between 51 and 100 on 22 days.
The index categorizes air conditions according to 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).
Charts published by TAQCC show that sensitive groups in Tehran were advised to limit their outdoor activities on eight days, since AQI hovered between 101 and 150, marking an unhealthy status for the group.
Children, the elderly, pregnant women and those with respiratory and cardiovascular problems, all of whom fall in the sensitive group, are classed as sensitive.
Month-on-month comparisons, however, show that Tehran air has been cleaner in November compared to the past October.
The charts illustrate that AQI did not enter the range of good air quality even for a day. Air condition was unhealthy for the sensitive group on 14 days, as it hovered between 101 and 150.
In the 17 remaining days, the index remained in moderate state.
Comparisons
The AQI review during the year-ago month shows air quality in Tehran has improved.
In November 2019, moderate air quality condition was registered on 11 days, but the index went up in the range of unhealthy for the sensitive group on 18 days, compelling the authorities to warn them of outdoor exposures.
Furthermore, AQI hit the emergency button on Dec. 29, 2019, entering the threshold of “unhealthy” status for all, that is between 151 and 200.
November 2018, however, experienced good air quality only on two days. Moderate air quality dominated the month, as AQI lingered between 51 and 100 for 20 days.
Outdoor activities were banned for the sensitive group in the remaining eight days, as the index entered the threshold of unhealthy for the group, that is between 101 and 150.
Analyses revealed that as is usual for the cold season, the pollutant responsible for the toxic index recorded on all polluted days in the month under review was PM2.5- atmospheric particulate matters that have a diameter of less than 2.5 micrometers.
Every year when the cold season arrives, the mercury dips and pollution is trapped closer to the ground suffocating residents in the ever-expanding metropolis. Scientists call the phenomenon “temperature inversion”.
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.
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 traffic restrictions 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, 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 stringent traffic schemes, for it can disperse pollution and change air stability within 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.
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%.
