Amid bad air, Delhi’s mercury at 11.8°C, season’s lowest

The colder mornings and calm conditions are likely to make high levels of air pollution recorded after Diwali celebrations tougher to disperse.

Delhi on Monday recorded the season’s lowest minimum temperature at 11.8 degrees Celsius – two notches below normal for this time of the year, the India Meteorological Department (IMD) said, and predicted winds will be weak for the next couple of days.

A man covers himself with warm clothes as heavy smog blankets Dwarka on Monday. (Vipin kumar/HT Photo)

The colder mornings and the relatively calm conditions are likely to make the high levels of air pollution recorded in the aftermath of Diwali celebrations tougher to disperse, experts said.

“Delhi saw a similar spell between November 2 and 9, where calm winds at night and fairly mild winds during the day were not allowing pollutants to disperse freely. We may see a similar scenario now, with all the gains seen over the weekend – from rains and strong winds – being lost due to firecracker emissions,” said IIT Delhi professor Mukesh Khare.

Before Monday, the season’s lowest minimum temperature was recorded a day earlier at 12.4 degrees Celsius.

Met officials said with the northwesterly winds to continue over the next few days, the minimum is likely to hover around 11-12 degrees, and a dip below 10 degrees is expected only towards the last week of the month.

“Strong northwesterly winds were blowing towards Delhi on Saturday and Sunday, and even though the wind speed has dropped in the last 24 hours, the wind direction is still northwesterly and should continue in this direction for the next three days. No substantial dip is expected further, but it should hover between 11 and 12 degrees Celsius during this period,” said Kuldeep Srivastava, a scientist at IMD.

He said the wind speed across the capital remained strong – averaging 8-10km per hour during the day on Sunday but dropped to 6km per hour by the evening and became calm overnight. “It remained calm throughout the day on Monday at Safdarjung, but the winds picked up at Palam only around 3pm,” said Srivastava. This meant visibility at Safdarjung was between 300 and 800 metres, and between 700 to 1,800 metres at Palam, he added.

“Similar conditions are expected over the next two days too, with calm winds to be seen overnight and in the early hours, followed by an average wind speed of 5-6km per hour in the afternoon,” he added.

Usually, winds with speeds of upwards of 8km per hour are needed to disperse pollution.

Delhi’s maximum temperature was recorded at 27.3 degrees Celsius on Monday, a degree below normal. The forecast for Tuesday said Delhi is likely to see shallow to moderate fog during the day, with the maximum and minimum likely to hover around 27 and 12 degrees Celsius respectively.