Data released by Tehran Air Quality Control Company show residents of Tehran breathed more polluted air in the month, compared with the same period of several past years.
On many days, air temperature hovered around 40 degrees Celsius midday and fell to 26 degrees early mornings.
According to Iran Meteorological Organization data, the average temperature in July was 32.94 degrees that is 1.26 degrees higher than the average in July 2016. The average temperature had declined slightly from 33.9 degrees in 2018, Financial Tribune reported.
Charts published on TAQCC’s website, Airnow.tehran.ir show that clean blue skies were not seen at all in July, 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).
"Moderate" status dominated the month, as in 22 days the Air Quality Index hovered between 51 and 100.
TAQCC data show that in July, sensitive groups in the capital were strongly recommended to limit their outdoor activities for one-third of the month. AQI was between 101 and 150 for eight days, making the condition “unhealthy for sensitive groups”.
Children, the elderly, pregnant women and those with respiratory and cardiovascular conditions fall in the above group.
The citizens of Tehran breathed in high levels of pollutants on the first day of the month, with the index crossing 150 and showing "unhealthy" status for all groups.
Worsening Conditions
Figures indicate that people in Tehran are breathing more toxic air these days, as the number of summer days with air pollution has increased compared to the past few years, at least during the period under review.
July 2018 had a bit more satisfactory resume, as the AQI did not cross the threshold of "unhealthy" for all groups and remained below 150 throughout the month-long period.
"Moderate" status was recorded for 22 days and the sensitive residents were advised to cut their outdoor activities on nine days, for the index remained "unhealthy" for the group.
No days with "good" air quality condition was recorded in the month.
Looking back at the corresponding period of the previous year, one can see a significant difference.
In July 2017, the sensitive group was warned of air quality pollution only for four days, with AQI standing between 101 and 150.
All the 27 remaining days in the month passed with the index showing "moderate" air quality.
The worsening condition is not only because of the number of polluted days, but also the type of dominant pollutants that seem to have changed.
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 in July 2017 the pollutant responsible for unhealthy days were PM2.5 in two days and ground-level ozone in one day.
This is while the effect of bad ozone becomes stronger in the following year, as in July 2018, out of nine polluted days the ground-level ozone was responsible for eight.
This year in July, the density of ozone was dangerously high in nine days.
Bad Ozone and Other Sources
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 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.
Hossein Shahbazi, director of modeling and forecast at TAQCC, earlier told ISNA, "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 past month, the concentration of ozone among air pollutants 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 the 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 remedial measures introduced by municipal bodies, Tehran passed a larger number of days with good air quality last year, especially when Tehran Municipality launched 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 two- and four-wheelers must undergo mandatory technical inspections and acquire conformity cards showing that the vehicles are roadworthy.