With the early onset of hot days, ozone pollution is once again blanketing the skies of Tehran that has long been notorious for high levels of toxic emissions.
According to the data published by Tehran Air Quality Control Company, over the past two days, residents in the capital city were exposed to high levels of ground-level ozone, an uncommon type of air pollution that becomes a regular phenomenon as temperature rises, ISNA reported.
Based on TAQCC charts, on Saturday and Sunday, high ozone level pushed Air Pollution Index into the threshold considered “unhealthy” for the sensitive group. The group comprises people with cardiovascular and respiratory diseases, pregnant women, children and the elderly.
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).
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.
Although this is the first trace of ozone recorded by air pollution monitoring stations in Tehran since the beginning of the current Iranian year (March 20), comparative data analysis of ozone pollution during the past few years shows that things have recently become worse.
In the first half of the last Iranian year (March 19-Sept. 21, 2019), ground-level ozone was responsible for 25 days of air pollution in the capital city.
The concentration of the pollutant reached its highest on July 1, 2019, pushing up the Air Quality Index to 160, showing an "unhealthy" status for all groups.
The traffic rules in the capital city have been temporarily suspended since late March, when the rapid spread of novel coronavirus compelled officials to make changes in favor of social distancing, the most effective way of cutting the infection chain
Mohammad Rastegari, an official with the Department of Environment, believes that although the contaminant has not turned into a serious issue in Iran yet, last year was the first time Tehran experienced the highest levels of ground-level ozone.
In the previous year (ended March 20, 2019), bad ozone was recorded on 16 days. The highest level of the pollutant was recorded on July 1, with the index standing at 150, within the range of “unhealthy” for the sensitive group.
According to a recent TAQCC report, the waiver of traffic restrictions in Tehran has had a negative effect on the generation of ground-level ozone.
Traffic rules in the capital city have been temporarily suspended since late March, when the rapid spread of novel coronavirus compelled officials to make changes in favor of social distancing, the most effective way of cutting the infection chain.
To avoid the public means of transportation, citizens use their private cars for commutation and increase the toxic pollutants in the air, the report says.
As the ground level ozone (also called bad ozone results from the chemical reaction between other emitted particles in the presence of sunlight, its density is expected to go higher with the rise in air temperature.
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), created in high concentration 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 have harmful effects on sensitive vegetation and 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 is rather a relief from smog, ozone and dust particles are to be blamed for the high levels of pollution.
