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NEW DELHI: The air quality in Delhi sharply deteriorated to the ‘severe’ category on Saturday as a toxic greyish haze blanketed the city. The 24-hour average overall AQI released at 4pm was 431, as opposed to 349 a day earlier. However, the AQI subsequently slipped into the ‘severe plus’ category for the first time this year, reaching 452 at 8pm.This prompted CAQM to impose stringent measures under GRAP, first under stage 3 and then stage 4 as the air worsened, on the same day. No respite from hazardous air quality is expected on Sunday. Experts said the AQI spiked due to high emission loads and unfavourable meteorological conditions. The farm fire season is over, while an increase in moisture due to the formation of fog, calm winds, and inversion trapped the pollutants.Among the measures invoked are a ban on construction and demolition, no entry of non-essential trucks, hybrid mode for schools, and a ban on BS-III petrol and BS-IV diesel vehicles.The Delhi govt has directed that all govt and private offices operate at 50% strength, with the rest working from home. Data from the Central Pollution Control Board showed that the AQI rose rapidly on Saturday. It was 397 at 9am, in the higher end of the ‘very poor’ category, but reached the severe range at 10am at 401. According to the India Meteorological Department, the lowest visibility at Safdarjung, the city’s base station, was observed at 400 metres at 8am. It improved to 500 metres at 9.30am.Anumita Roychowdhury, executive director (research and advocacy), Centre for Science and Environment, said, “As the atmospheric conditions are turning unfavourable with low wind speed and poor dispersion of pollutants, high emissions from local sources are getting trapped, spiking the peak levels.”CAQM said a feeble western disturbance is approaching north-west India, and the prevailing meteorological condition has marked a reduction in wind speed, at times becoming calm, a shift in wind direction from westerly to easterly, and an increase in moisture content in the lower atmosphere. “Such conditions during the winter season are conducive to the formation of smog,” it said.
