The national capital's air quality was recorded in the “moderate” category on Sunday morning, and it is likely to turn “poor” on Monday due to lowering temperatures and slow wind speed.
The city recorded an air quality index (AQI) of 174 at 10:30 am which falls in the “moderate” category. On Saturday, the 24-hour average AQI was 189.
An AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.
"As predicted, the PM2.5 contribution (in pollution) is increasing, which is a characteristic of winters. The air quality is likely to deteriorate to the lower end of poor quality on Monday," the System of Air Quality and Weather Forecasting and Research (SAFAR) said.
PM2.5 is tiny particulate matter less than 2.5 microns in diameter. It can enter deep into the lungs and even into the bloodstream.
It said an increase in farm fires was observed around Punjab, Haryana and neighbouring border regions and it is likely to impact Delhi in the coming days.
Pawan Gupta, a senior scientist at Universities Space Research Association, NASA, said farm fires were observed in more districts of Punjab. Fires in Uttar Pradesh have also started showing up, he said.
Also, there is a marked dip in minimum temperatures recorded in Delhi. On Sunday, it settled at 18.5 degrees Celsius, three notches below normal.
The minimum temperature is likely to drop to 18 degrees Celsius by Wednesday.
Low temperatures and stagnant winds help in accumulation of pollutants near the ground, affecting air quality.