This year's summer is reaching its end while the capital has seen no "good" air quality during the first two months of the hot season.
This is clearly illustrated if the air quality in the 62-day period is analyzed based on the national Air Quality Index, which divides the 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).
AQI standards in Iran were determined by the High Council for Environmental Protection in 2012. Reportedly, the system is a translation of the 2012 version of standards set by the United States Environmental Protection Agency, which is no longer in use today.
However, based on the detailed report published by Tehran Air Quality Control Company, the capital, which has long been notorious for air pollution, passed 49 days with "moderate" AQI.
Furthermore, the sensitive groups in Tehran have breathed 13 days in "unhealthy" conditions, with the index standing between 101 and 150. Children, the elderly, pregnant women and those with respiratory and cardiovascular problems, which are all categorized under the sensitive group, were advised to avoid prolonged or heavy outdoor exertion.
Pollutants measured to determine air quality include carbon monoxide, nitrogen dioxide, sulfur dioxide, ground-level ozone and particulate matter (PM2.5 and PM10). The AQI figures are calculated based on the concentration of these pollutants.
Accordingly, air conditions in the capital have been unhealthy (for sensitive groups) in two of the 13 days due to the density of PM 2.5 and one day for the presence of PM10.
Nevertheless, the causes of air pollution were not limited to the above-mentioned particles. High concentration of ozone near ground level has also worsened the air quality in 12 days during the period under study.
Ozone is described as "bad" ozone, which is a secondary pollutant formed in the earth's lower atmosphere, near ground level, when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants and other sources react chemically in the presence of sunlight's ultraviolet rays.
Past Records
Taking a glance at the TAQCC's data, even a layman can say the air conditions have deteriorated through time, as the Air Quality Index during the first two months of last year's summer indicates a clearer sky in the capital.
Tehran experienced 51 days with "moderate" (51-100) AQI and 11 days with "unhealthy for sensitive groups" AQI.
According to the data, in five of the total unhealthy days, the dominance of PM2.5 was evident. Furthermore, ozone polluted the weather for only six days that is half the number of days with high ozone levels during the current year's period of study.
This is while two years ago, during July 22 to August 22, , the air quality in the capital experienced unhealthy conditions only in 8 days and there were no tracks of PM10 or ozone pollution.
Reportedly, Tehran saw 54 days of "moderate" quality in the summer of 2016.
The capital's pollution often reaches unhealthy levels in the cold season when the phenomenon of inversion occurs and PM2.5 is chiefly responsible for poor air quality in winter.
In the warm season, which is rather a relief from smog, ozone and dust particles are to be blamed for high levels of pollution. Seemingly, though, their role in the state of the capital's air quality is becoming more prominent.
The troubled skies of Tehran and other metropolises in the country are in dire need of effective mitigation efforts, while, unfortunately, the officials continue to adopt the same old stopgap solutions such as school closures or traffic restrictions to improve the capital's air quality without achieving any lasting success.
