Pollution Darkens Tehran Skies

The residents of Iranian capital breathed in more polluted air in March compared with the corresponding month of last year, data released by Tehran Air Quality Control Company show. 
Charts published on TAQCC’s website, Airnow.tehran.ir, show that in March, clean blue skies were seen on only four days with the air quality index 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, keeping the index between 51 and 100 in 20 days.