According to data published by Tehran Air Quality Control Company, Tehran’s residents have been exposed to high levels of ground-level ozone in the month, a source of air pollution that becomes conspicuous when temperature rises.
Based on TAQCC charts, during the period under review, ozone pollutant hit emergency levels and Air Pollution Index entered the “unhealthy” threshold for all citizens on two days, as API stood between 151 and 200.
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).
In addition, the index hovered in the range of 101 to 150 in 18 days, which indicates unhealthy condition for sensitive groups.
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.
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 remaining 11 days passed with moderate air quality status.
Comparative data analysis of ozone pollution in the year before shows air quality is having poorer quality these days.
In July 2019, moderate status almost dominated the month, such that AQI stood between 51 and 100 for 22 days.
The health-wise vulnerable people were warned to limit their outdoor activities in 10 remaining days, as the index hit unhealthy status for the sensitive group.
A monthly analysis also delivers similar results.
TAQCC data show that in June, AQI showed moderate air condition in 22 days and the index entered the threshold of unhealthy for sensitive groups for 10 days.
The pollutant particle pushing up the index in all bad air quality days have been ground-level ozone.
Good air quality condition was not recorded even for one day during the reviewed periods.
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.
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.
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 used their private cars for commutation and emitted more toxic pollutants in the air, the report says.
After traffic restrictions were eased, the rate of Covid-19 transmissions started rising. As a result, it has been reimposed for a week.
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 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 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.