Financial Tribune- Indices used to calculate Tehran�s air quality have not been updated for six years, as a result of which globally recognized high levels of pollution are considered healthy and do not call for precautionary measures.

General specifications of air quality index (AQI) used in Tehran match those of international standards, but the levels of pollutant density considered to determine AQI are noticeably different, the Persian daily Donya-e-Eqtesad reported. Based on AQI, conditions are divided into Good (0-50), Moderate (51-100), Unhealthy for Sensitive Groups (101-150), Unhealthy (151-200), Very Unhealthy (201-300) and Hazardous (301-500).

Pollutants measured to determine air quality include carbon monoxide, nitrogen dioxide, sulfur dioxide, ground-level ozone and particulate matter (PM2.5 and PM10). The AQI figures are calculated based on the density of these pollutants and here is where Iranian standards have failed to catch up with the world. Based on international standards, when the density of PM2.5 is higher than 12 micrograms per cubic meter, AQI passes 50 and conditions are described as Moderate. This is while in Tehran, the threshold level is higher than 15.5 mg/cm.

In other words, air quality having a density of between 12 and 15.4 mg/cm of PM2.5 is considered Good in the Iranian capital whereas it is regarded Moderate in the world.

Also, PM2.5 levels of higher than 55.4 mg/cm are regarded Unhealthy in the world but the threshold in Tehran is 65.4 mg/cm. This means that a wide range of between 55.4 and 65.4 mg/cm is considered Unhealthy for Sensitive Groups in Iran�s highly polluted metropolis.

The AQI standards in Iran were determined by the High Council for Environmental Protection in 2012. Reportedly, the system is a translation of the 2012 version of standards set by the United States Environmental Protection Agency, which is no longer in use today.

Since then, the international threshold level of particulate matters has been regularly lowered so that the minimum amount of particulate matter would be defined as Good. The policy is also aimed at hardening the responsibilities of urban and environmental authorities. Over the past 196 days, Tehran has experienced 10 Good days, 21 USG days and no Unhealthy days based on the current outdated standards.

Obviously, the figures would have been different if the indices had been assessed on the basis of current international standards. The current optimistic results do not necessitate control measures such as restriction on vehicle use and closure of schools. Experts believe that the standards must be updated as soon as possible, especially as the more polluted half of the year has already begun.

The move is also required today, as Japan�s International Cooperation Agency is involved in projects to control Tehran�s air pollution. Activists have also called on Tehran Air Quality Control Company, a subsidiary of Tehran Municipality, to increase the number of monitoring stations. The company currently has only 21 stations with some districts having two stations and others such as the much crowded 5, 17 and 12 districts having none. Besides, certain districts are too vast for a single station to determine their air quality precisely.