According to Tehran Air Quality Control Company, air pollution monitoring stations of the metropolis have recorded fewer days with ground-level ozone in August, letting the citizens breathe fresh air more frequently.
TAQCC charts show that during the month under review, the ozone pollutant pushed the Air Pollution Index up to the “unhealthy” threshold for the sensitive group in seven days. Children, pregnant women, cardiovascular and respiratory patients and the elderly form the group.
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 main culprit behind the pollution was ground-level ozone, with the highest density of 128 recorded on August 15.
In the remaining 24 days, the index hovered in the range of 51 to 100, which indicates the moderate condition.
Comparative data analysis of ozone pollution in the year-ago month shows air quality has worsened these days.
In August 2019, moderate status almost dominated the month, such that AQI stood between 51 and 100 for 27 days.
The health-wise vulnerable people were warned to limit their outdoor activities in the four remaining days, as the index hit the unhealthy status for the sensitive group.
The pollutant pushing up the index in all bad air quality days was ground-level ozone, with a maximum rate of 140 and 102 respectively in August 2019 and 2018.
Good air quality condition was not recorded even for one day during the periods under review.
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.
Growing Concerns
Mohammad Rastegari, an official with the Department of Environment, believes that although the contaminant in Iran has not turned into a serious issue, Tehran is experiencing the highest levels of ground-level ozone over the past several years.
TAQCC data show that in the first five months of the current Iranian year (started March 20), ground-level ozone was the culprit on 38 polluted days, climaxing on July 19 with ozone density reaching 161.
In the year-ago period, ozone density was high on 25 days, reaching a maximum of 160 on June 30.
In 2018, things were a lot better as only 16 days recorded ozone pollution from March 20 to August 21. The highest level of ozone was 150 on July 1.
This is while in 2017, ozone was responsible for air pollution on only seven days, reaching its peak (128) on June 28.
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 increasing 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.
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, "bad" ozone in the lower atmosphere 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 said, "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 have a harmful effect on 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.
In the warm season, which offers relief from smog, ozone and dust particles are to be blamed for the high levels of pollution.
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.