An improvement in weather conditions brought a slight respite to the people in Delhi as the overall air quality was no longer in the ‘severe’ category Thursday, after the Capital was gripped by one of the worst streaks seen in a decade. A week after Delhi saw its first dense smog day, the weather conditions also became clear Thursday morning over much of the plains in North India.
After its Air Quality Index (AQI) remained in the ‘severe’ or ‘severe plus’ category for six consecutive days, Delhi’s average air quality was 376 or in the ‘very poor’ category at 10 am Thursday, as per the Central Pollution Control Board (CPCB).
However, a few air quality monitoring stations in Delhi reported ‘severe’ air quality levels. Out of the 37 such stations, 11 reported ‘severe’ air quality and the remaining ‘very poor’. The most polluted place was Wazirpur with an AQI of 437, followed by Jahangirpuri with an AQI of 436, both in the ‘severe’ category.
Fog formation is aided by low wind speed and high moisture content in the atmosphere. With wind speeds picking up over the past two days, this has helped clear the dense fog conditions. “Stronger lower tropospheric north-northwesterly winds have decimated the fog layer from plains of Northwest India… Due to stronger north-northwesterly winds the maximum and minimum temperatures have also fallen close to their normal values against the situation a week ago when temperatures were 4-6°C above normal due to prevailing easterlies,” said Krishna Mishra, Senior Scientist, India Meteorological Department (IMD).
The wind speed was 6 to 12 kmph on Wednesday, after which calm winds prevailed in the night. The Westerlies wind continued to be at 6 to 8 kmph on Thursday morning. According to the Indian Institute of Tropical Meteorology (IITM), an average wind speed above 10 kmph is favourable for the dispersal of pollutants.
While dense fog was reported only over East Uttar Pradesh on Wednesday, as per IMD officials, the condition improved by Thursday morning and no significant dense fog conditions were reported over the northern plains.
Mercury levels dipped further and the minimum was 10.2 degree Celsius on Thursday. Lower temperatures keep the pollutants trapped in the atmospheric layers closer to the surface.
In the next seven days, as per the IMD forecast, the minimum temperature and the maximum temperature in Delhi will be 10-12 degree Celsius and 24-27 degrees Celsius, respectively. These are around normal as they are close to the long-period temperature range (11.3 minimum, 26.7 maximum) for the next seven days.
The Early Warning System, developed by IITM, said in its forecast the air quality will be in the ‘very poor’ category for the next six days. Cold, dry strong winds will blow from the Northwest, reaching up to 10 to 12 kmph in the next four days, according to the IMD forecast. This is expected to help in the dispersal of pollutants.
