Air quality monitoring stations in the capital city of Tehran showed that its residents were breathing fresh air in September compared to the year-ago month.
According to charts regularly published by Tehran Air Quality Control Company, during the month, moderate air quality status dominated the whole period.
In other words, the Air Pollution Index hovered between 51 and 100 throughout the month.
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).
The fluctuating AQI reached its highest level (97) on Sept. 9-10.
TAQCC comparative data show that September 2019 ended with a worsening of air quality. The company recorded 27 moderate days in the month and the remaining three days kept the vulnerable people inside their house, as AQI entered the range of 101 to 150, which translates into unhealthy status for the group.
A broader view, however, reveals that the city’s air quality in the first half of the current Iranian year (March 20-Sept. 21) had worsened compared to the same period of last year.
Citizens experienced 15 good air days and 133 days with moderate air quality. The health-wise vulnerable people were warned to limit their outdoor activities in 36 days, as the index hit the unhealthy status for the sensitive group.
AQI hit the emergency level, hitting the unhealthy status for all in the two remaining days.
The main culprit for the polluted days was PM2.5 (particulate matters smaller than 2.5 micrometers) and ground-level ozone.
TAQCC charts show that the first half of the last Iranian year passed with a higher air quality. Clear blue sky was seen on 25 days and 136 days were recorded as moderate.
The sensitive group was recommended to stay home on 24 days and only one day was recorded as unhealthy for all.
Pollutants responsible for the poor air quality in the period under review were NO2, PM2.5 and ozone, with the latter playing a strong role in making the air toxic.
Scientific studies have shown that ground-level ozone is a secondary pollutant, formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants and other sources react chemically in the presence of sunlight.
Ozone Formation and Risks
Besides ozone that occurs naturally in the Earth's troposphere and forms a protective layer that shields the earth from the sun's harmful ultraviolet rays, there is "bad" ozone in the lower atmosphere, near ground level, which is considered a harmful air pollutant.
The ground-level ozone results from chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC), which occur in high concentrations in the presence of sunlight.
Hossein Shahbazi, director of modeling and forecast at TAQCC, earlier told reporters that "emissions from industrial facilities, electric utilities and motor vehicle exhausts, gasoline vapors and chemical solvents are some of the major sources of NOx and VOC".
Ozone is a colorless gas, 1.5 times denser than oxygen.
Breathing ozone can trigger a variety of health problems, particularly for the children, the elderly and people of all ages who have lung disorders such as asthma. Ground-level ozone can also harm sensitive ecosystems.
Experts say remedial measures to alleviate this kind of pollution are similar to those regularly suggested for other types of pollution, such as "detecting and removing mobile or stationary sources of nitrogen oxides and hydrocarbon emissions”.
Vehicles burning diesel fuel and carburetor-equipped motorcycles are the most common producers of toxic emissions that lead to the emergence of ground-level ozone.
The capital's pollution levels often reach unhealthy levels in the cold season when the phenomenon of inversion occurs, but PM2.5 is chiefly responsible for poor air quality in this period.
In the warm season, which offers relief from smog, ozone and dust particles are to be blamed for the high levels of pollution.
Growing Concerns
Mohammad Rastegari, an official with the Department of Environment, believes that although ground-level ozone in Iran has not turned into a serious issue, Tehran is experiencing the highest levels of the contaminant over the past several years.
With the coronavirus gaining strength in the country, health experts caution that air pollution can increase the health risk of Covid-19.
The rapid outbreak of the new coronavirus in Iran since mid-February and the rising number of people with positive coronavirus tests have added to the risk of air pollution.
Some scientists and medical professionals argue that there is a potential link between long-term exposure to air pollution and compromised lung capacity, which could make an individual more likely to develop a severe form of Covid-19 and increase fatalities.
