Delhi's AQI improves after consistent winds, may worsen after Oct 15

The share of stubble burning in the total pollution marginally rose to 0.8% on Sunday from 0.4% a day before, as per the Centre’s Decision Support System (DSS).

The air quality in the Capital improved on Sunday, a day after it nearly entered the “poor” category. Average air quality index (AQI) was recorded at 167 (moderate) on Sunday, against 199 on Saturday, due to consistent winds of 10-15km per hour.

Delhi saw a pleasant evening with the minimum temperature at 19.6°C on Sunday. (Arvind Yadav/HT Photo)

However, the share of stubble burning in the total pollution marginally rose to 0.8% on Sunday from 0.4% a day before, as per the Centre’s Decision Support System (DSS).

“Delhi’s air quality is very likely to be in the ‘moderate’ category from October 13 to 14 and in the ‘poor’ category on October 15,” as per the air quality Early Warning System (EWS) for Delhi, which comes under the ministry of Earth sciences. It added that the AQI is likely to stay “poor” after October 15, for another six days.

The Central Pollution Control Board (CPCB) classifies air quality on a scale where 0-50 is good, 51-100 satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor, and 401-500 severe.

The AQI generally starts worsening in October – following the withdrawal of the southwest monsoon and a dip in air temperature. This is coupled with both the start of stubble burning in northwest India, combining with the festival season when firecrackers are burst, and a drop in the temperature or wind speed.

According to experts, low wind speeds, combined with low temperature lead to “inversion” – where cooler air becomes trapped beneath warm air. This creates a lid that concentrates pollutants near the surface. Further, northwesterly winds during this season also carry smoke from stubble burning in Punjab and Haryana, with its peak contribution to Delhi’s particulate matter often going up to 40% around early November.

The DSS, which estimates the contribution of sources of pollution to Delhi’s PM 2.5, estimated that Delhi’s transport sector was the biggest contributor on Sunday, with an estimated emission load of 19.8%. This was followed by emissions from Sonipat (9.2%) and Jhajjar (5.1%). The contribution of stubble burning on Sunday was 0.8%, with a similar contribution load forecast for Monday too.

Farm fires are comparatively lower this year, so far, as compared to last year. Between September 15 and October 11, Punjab recorded 116 fires as compared to 533 last year during the same period. For Haryana, the count till October 11 is 11 as compared to 280 fires last year.

Meanwhile, Delhi’s maximum temperature on Sunday was recorded at 31.5degrees Celsius (°C) , three degrees below normal and a notch higher than Saturday. The minimum was 19.6°C – a notch below normal. Forecast indicates cool northwesterly winds to keep the minimum between 18-20°C till Tuesday, even as the maximum will marginally rise by 1-2°C. The maximum is forecast to touch 34°C by Wednesday, the India Meteorological Department (IMD) has said.

“We will see clear skies persist, with the wind direction gradually shifting to easterly in the second half of the week. Winds of 5-10 km/hr are likely in the next two to three days,” said an IMD official.

Further, Delhi environment minister Manjinder Singh Sirsa shared the CPCB data on Sunday, stating that the Capital has already recorded 199 days of AQI lower than 200 this year. “This was nearly double than the 110 days recorded in 2016. Delhi’s air is improving because there is work happening on the ground,” he said.