Delhi: In first for the season, temp below 15°C as AQI worsens

The mercury fell below the 15-degree Celsius mark on Wednesday morning for the first time this winter, with the minimum temperature recorded at 14.6 degrees Celsius — two notches below normal — as Delhi’s air quality deteriorated sharply in the last 24 hours, and was expected to get over the rest of the week.

Delhi’s overall Air Quality Index (AQI) was recorded at 232 (poor), from Tuesday’s reading of 139 (moderate), largely owing to a rise in farm fires across the northern plains as the contribution of stubble burning in Delhi’s overall PM 2.5 concentration touched a season high of 16%, data from the System of Air Quality and Weather Forecasting and Research (Safar) showed.

Safar, which comes under the Union ministry of earth sciences, has forecast that the air quality will further deteriorate “rapidly” in the next 24 hours to touch “very poor” by Thursday, and then hit the higher end of the “very poor” category by Friday.

“Delhi’s AQI is in the ‘poor’ category. The effective fire count of stubble burning in the northwest region of Delhi is 656 and its share in PM2.5 is 16% as transport level winds are north westerly. AQI is now forecasted to deteriorate rapidly and slip to the ‘very poor’ category by Thursday and deteriorate further to the higher end of the ‘very poor’ category by Friday,” SAFAR said on Wednesday, stating that calm local winds, along with highly favourable transport-level winds (northwesterly winds that will bring pollution from Punjab and Haryana towards Delhi) are expected to enhance stubble-burning related intrusion.

“Any increase in fire counts in the next three days would increase the finer particle levels of Delhi,” it added.

Prior to Wednesday, the highest contribution of stubble burning in Delhi’s air was 15% on October 21.

Two stations – Shadipur and Anand Vihar were in the “very poor” category, with readings of 316 and 313 respectively.

An AQI between 51 and 100 is classified as “satisfactory”, between 101 and 200 is “moderate”, between 201 and 300 is “poor”, and between 301 and 400 is “very poor”. An AQI over 401 is meanwhile classified as “severe” by the Central Pollution Control Board. The Capital’s air quality deteriorates to hazardous levels every winter, plunging the city into a public health emergency.

Anumita Roy Chowdhury, executive director, research and advocacy at the Centre for Science and Environment (CSE) says while a delayed monsoon has helped control pollution spikes, historical data shows an episodic smog event is generally seen in late-October and early November, coinciding with stubble burning peaks and Diwali.

“With the current meteorological conditions, we may see another such event before or around Diwali and the exposure to air pollution during this period is at its peak. With Covid-19 still around, as a community, we may have to avoid exposure to outside air and this is generally seen each year when regulatory agencies ask people to avoid stepping out or exercising during smog events,” she said.

Safdarjung,Delhi’s base station recorded a maximum temperature of 28.2 degrees Celsius on Wednesday – three notches below normal, while the minimum was recorded at 14.6 degrees. Mayur Vihar recorded the lowest maximum temperature on Wednesday at 26.8 degrees, while the lowest minimum across Delhi was 14.1 degrees Celsius at Mungeshpur.

A Met official says local winds are becoming calm at night, which coincides with a drop in temperature, leading to a spike in pollution late at night and in the morning. “Following the rain, there is also moisture in the air and you are now seeing a slight haze at night. Calm winds mean the contribution from stubble burning and local pollutants are now becoming trapped and similar conditions are expected in the next few days,” said the official who asked not to be named.

IMD has forecast the minimum temperature to remain around 14 degrees Celsius for the next two days, and said it could dip to 13 degrees by Saturday.

The maximum temperature, meanwhile, is expected to remain below 30 degrees till the end of the week.