Delhi’s air improves, may turn severe again during Diwali

RELIEF Increased wind speed helps disperse pollutants trapped in air; AQI improved to 340 NEW DELHI:

Traces of rain and increased wind speed marginally lifted Delhi’s air quality index (AQI) on Saturday but the respite may be short-lived as pollution levels are likely to spike to the ‘severe’ category from November 5, scientists managing the capital’s early warning system said.

The AQI improved to 340 from Friday’s 370 but remained in the ‘very poor’ category.

Officials at the Central Pollution Control Board (CPCB) said wind speed improved to 12kmph because a western disturbance passing through the northern plains helped disperse pollutants trapped in the air.

Officials said traces of rain(0.2mm) recorded at the Safdarjung observatory – which is representative of Delhi’s weather -- helped clear the air.

“Wind speed was good on Saturday. The air quality could start dipping again from November 5 due to a change in wind direction,

Delhi Ghaziabad Gurugram Noida Faridabad which will start blowing from the northwest. Winds from the northwest could bring pollutants from stubble burning in neighbouring states,” said a senior CPCB official, who did not wish to be named.

The levels of particulate matter – PM 2.5, PM 10, primary pollutants in Delhi’s air — which had shot up to four times the safe limit on Thursday, also improved on Saturday.

The concentration of PM 2.5 is likely to increase sharply from November 5 owing to a change in wind direction and crop stubble burning.

“If significant stubble burning continues over the weekend in the northwest regions of Punjab and Haryana, its impact is likely over Delhi, which may push the air quality to the ‘severe’ category. The northwest wind direction will continue to impact air quality on November 6-7 during Diwali days,” one of the scientists cited above said, not wishing to be named.

According to experts, DelhiNCR needs a wind speed of more than 10 km per hour and a ventilation index (which determines how fast pollutants get dispersed) of at least 6,000 square metres/ second. Anything below this will fail to disperse the pollutants.

Conditions are, however, likely to worsen again on Sunday as the ventilation index is likely to drop to around 4,000 square metres/second, the scientist said.

The mercury could dip on Sunday because of the cold northwesterly winds.

The maximum and minimum temperatures could dip over the next few days and drop to around 13 degrees Celsius on Diwali on account of a western disturbance, which triggered snowfall in the high altitudes of Himachal Pradesh and Jammu and Kashmir.

PM2.5