For the first time in over four months, Delhi’s air turned ‘poor’ on Tuesday with the 24-hour average Air Quality Index (AQI) reading 211 at 4 pm. Delhi's AQI was 'poor' last on June 11. According to the Central Pollution Control Board, the main pollutant for the last three days has been ground-level ozone and Particulate Matter (PM) 10. The dip in AQI had prompted the Commission for Air Quality Management (CAQM) in National Capital Region and Adjoining Areas to activate Stage 1 of the Graded Response Action Plan (GRAP) to tackle pollution. (See box). There are two types of ozone – one in the upper atmosphere, which creates a shield against harmful ultraviolet rays and ground-level ozone, exposure to which may increase frequency of asthma attacks, can aggravate lung diseases such as emphysema, and chronic bronchitis, and inflame airways. Ground-level ozone is not emitted directly but is formed on warm and sunny days when oxides of nitrogen (NOx) and volatile organic compounds (VOC) react with each other. Both are emitted because of vehicular pollution by cars, power plants and industries. Ground-level ozone pollution is primarily an urban affair. PM 10, meanwhile, is most likely a result of road dust, said Delhi Pollution Control Committee officials, as rain has dried up. India Meteorological Department (IMD) officials said clear sky and a dip in wind speed have led to the accumulation of pollutants. According to the Centre's Air Quality Early Warning System forecast, the six days at least will record 'poor' AQI. Delhi has seen a long spell of clean air this year, with July getting 29 days of satisfactory AQI. Heavy rain over the past three months has been a major contributory factor. While the bad air is inevitable as temperatures dip, winds still and rain dries up, the Delhi government is expecting the relief to last a little longer. A senior government official pointed to the delay in the rice harvest in Punjab and Haryana this year because of late rain and flooding. “As in many areas, the harvest has not even started, by Diwali, it will still be underway. This means that the farm fires might peak in November, instead of October end. So, even as the meteorological conditions deteriorate, the AQI may not dip as rapidly as it usually does in the last two weeks of October,” the official said. “Diwali in Delhi is expected to be better than the past few years because stubble burning may not start in a big way till the end of the month,” he added. Farms are set on fire by farmers to get rid of the long stubble left behind after paddy is harvested using machines. Rice stubble, unlike wheat stubble, is not fed to cattle because it is high in silica. The number of farm fires recorded in Punjab, Haryana, UP, Madhya Pradesh and Rajasthan are the lowest so far this year. UP has recorded more than half of the cases, official data shows. Between September 15 and October 14, 552 incidents of farm fires have been detected in Punjab, Haryana, UP, Delhi, Rajasthan and MP. UP topped the chart with 225 fires in this duration, followed by 165 fires in Punjab.
