Pollutants Return to Haunt Tehran’s Skies

EghtesadOnline: After several consecutive months of air quality improvement, the skies of Tehran once again were tainted with pollution in June.

News ID: ۷۴۷۷۴۱

02 July 2019

According to data released by Tehran Air Quality Control Company, residents of the capital breathed more polluted air in the month, compared with the same period of last year.

Charts published on TAQCC’s website, Airnow.tehran.ir show that clean blue skies were not seen at all in June, meaning that the air quality index never went below 50 showing "good" condition.

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), Financial Tribune reported.

"Moderate" status dominated the month, as in 19 days the Air Quality Index hovered between 51 and 100.

TAQCC data show that in June, sensitive groups in the capital were strongly recommended to limit their outdoor activities for one-third of the month. The AQI entered the threshold of 101-150 for 11 days, showing the condition as “unhealthy for sensitive groups”.

Children, the elderly, pregnant women and those with respiratory and cardiovascular conditions fall in the above group.

Things Getting Worse

Figures indicate that people in Tehran are breathing less clean air these days, as the number of summer days with air pollution has increased over the past few years, at least during the period under review.

June 2018 had a bit more satisfactory resume, as bright blue skies appeared at least for one day with the index remaining between 0 and 50, which indicates a "good" status.

“Moderate” air condition was recorded for 24 days in the month, with AQI standing between 51 and 100.

Sensitive residents were advised to limit their outdoor exertion for only six days, with the index remaining “unhealthy” for the group.

Pollutants measured to determine air quality include carbon monoxide, nitrogen dioxide, sulfur dioxide, ground-level ozone and particulate matter (PM2.5 and PM10). AQI figures are calculated as per the concentration of pollutants.

An analysis of AQI illustrates that the pollutant responsible for the 11 and six unhealthy days for sensitive groups in June 2019 and 2018 respectively was ground-level ozone.

Bad Ozone

Besides ozone, which occurs naturally in the Earth's troposphere, forming 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.

Scientific definitions say that 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.

The ground level ozone 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

Hossein Shahbazi, director of modeling and forecast at TAQCC, earlier told ISNA 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.

The Growing Problem

According to the official, over the last several days, the concentration of ozone among air pollutants has increased, especially in the neighborhood of Tarbiat Modarres in Tehran.

Shahbazi maintained that remedial measures to alleviate this kind of pollution are similar to those regularly suggested for other sorts 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," he said.

Experts believe that although the contaminant has not turned into a serious issue in Iran yet, measures are needed 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 the high levels of pollution.

Further information on the sources of NOx and VOC is available in Tehran's first emission inventory report for 2015, provided by researchers at the Fuel, Combustion and Emission group at Sharif University of Technology in collaboration with experts of AQCC.

Risks and Measures

Poor air quality has long troubled all urban residents in Iran, causing over 12,000 pollution-related deaths in the fiscal 2016-17.

Thanks to Nature's help and healing measures introduced by municipal bodies, Tehran passed a large number of days with good air quality last year, especially when Tehran Municipality started anti-air pollution measures in autumn 2018.

One of the latest measures is the air pollution reduction scheme implemented in the metropolis in November 2018.

As per the scheme, dilapidated vehicles are banned from the roads and violators are fined.

All four- and two-wheelers must undergo mandatory technical inspections and acquire conformity cards showing that the vehicles are roadworthy.