High concentrations of ozone near ground level along with dust particles will diminish the capital's air quality over the coming summer days, officials at Air Quality Control Company have forecast.
Besides ozone, which occurs naturally in the earth's upper atmosphere, forming a protective layer that shields the earth from the sun's harmful ultraviolet rays, there is "bad" ozone in the earth's lower atmosphere, near ground level, which is considered a harmful air pollutant.
"The 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," ISNA quoted Hossein Shahbazi, director of modeling and forecast at Tehran's AQCC as saying.
Elaborating on the ground level ozone, the official said it is a result of chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC), created in high concentration in the presence of sunlight.
Major Sources
"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 children, the elderly and people of all ages who have lung diseases such as asthma. Ground level ozone can also have harmful effects on sensitive vegetation and ecosystems.
Hot Spot
According to the official, over the last several days, the concentration of ozone among the air pollutants has increased, especially in Tarbiat Modarres neighborhood in Tehran.
"Ozone concentration has been recorded at 'unhealthy level for all groups' in the area," Shahbazi said.
The official maintained that remedial measures to alleviate this kind of pollution are quite similar to those regularly suggested for other sorts of pollution, namely "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," Shahbazi said.
The official stressed that although the contaminant has not turned into a serious issue in Iran yet, measures are essential to prevent it from exacerbating Tehran's already poor air quality.
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 high levels of pollution.
Further information on the sources of NOx and VOC is available in Tehran's first emission inventory report (2015), provided by researchers at the Fuel, Combustion and Emission group at Sharif University of Technology in collaboration with experts at AQCC.
