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City’s air slightly better, western disturbance may bring more relief
New Delhi
New Delhi
Delhi’s air improved slightly to ‘very poor’ on Saturday, after remaining in the ‘severe’ zone for over 24 hours.
A change in wind direction, leading to a rise in mercury, allowed room for better ventilation. This in turn helped improve the air quality, said weather experts.
The Air Quality Index (AQI), as calculated by the Central Pollution Control Board’s (CPCB) 4pm bulletin on Saturday was 371, as against 404 the previous day. CPCB officials said the situation is not likely to improve much in the coming days with the air quality likely to reel under ‘very poor’ zone till at least December 10.
According to scientists at the India Meteorological Department (IMD), Saturday’s improvement in air quality was mainly on account of wind direction changing to northeasterly (because of an approaching western disturbance) that resulted in a rise in night temperature. So far, a fog cover, cold and slow surface winds had been pushing up pollution levels.
On Saturday, the minimum temperature was 9.3 degrees Celsius, which was higher than 8.4 degrees Celsius on Friday. The city had recorded its coldest day of the season so far on Thursday with the minimum temperature dipping to 7.6 degrees Celsius.
Also, the day temperature rose to 24.8 degrees Celsius, a notch above the season’s normal.
“A rise in day temperature helps heat up the earth’s surface and bring up the mixing height (atmospheric boundary layer), allowing better ventilation. When this boundary layer is compressed, it allows concentration of pollutants. It’s just like the ceiling of a room, if it’s brought too close to the surface, it will only result in suffocation,” said a senior IMD scientist.
Besides, while there was fog in the morning hours, reducing the visibility to 200 metres, the duration was too small and hence it did not have much impact on the air quality.
“A significant improvement in the air quality is likely on December 12-13, when the approaching western disturbance is expected to bring thunderstorm and rain. Also, strong surface wind of up to 20-25 kmph are likely around this time, that will blow the pollutants away,” said Kuldeep Srivastava, head, IMD’s regional weather forecasting centre.
