According to the data published by Tehran Air Quality Control Company, in the past three weeks starting July 1, Tehran’s residents have been exposed to high levels of ground-level ozone, an uncommon air pollution that becomes a regular phenomenon as temperature rises.
Based on TAQCC charts, during the period under review, high ozone level pushed Air Pollution Index into the “unhealthy” threshold for the sensitive group on 11 days.
The group comprises people with cardiovascular and respiratory diseases, pregnant women, children and the elderly. In the remaining six days, the index hovered in the moderate range.
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.
The maximum ozone density registered during the unhealthy days was 149 on July 1.
A comparative data analysis of ozone pollution during the past few years shows that things have recently become worse.
In the year-ago period (July 1-18, 2019), ground-level ozone was responsible for eight days of air pollution in the capital city.
The concentration of the pollutant reached its highest level on July 4, 2019, pushing up the Air Quality Index to 134, showing an "unhealthy" status for the sensitive group.
The remaining 10 days were in moderate air condition.
A year earlier, in July 1-18, 2018, air quality status was much more approving, as the ozone density pushed API into the threshold of unhealthy for the sensitive group for only six days with a maximum figure of 150 on July 1.
Moderate status was registered in the remaining 12 days.
Growing Concerns
Mohammad Rastegari, an official with the Department of Environment, believes that although the contaminant has not turned into a serious issue in Iran yet, Tehran experienced the highest level of ground-level ozone last year for the first time.
With the coronavirus gaining strength in the country, health experts caution that the pollution can increase the risk of Covid-19 spreading further.
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.
In the last fiscal 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 sensitive groups”.
According to an earlier TAQCC report, the temporary waiver of traffic restrictions in Tehran had a negative effect on the generation of ground-level ozone.
Traffic rules in the capital city were suspended for two months 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 emit more 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), which occur 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 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.
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.