Delhi’s respite from deteriorating air quality was short-lived, as the Capital clocked an air quality index of 303, classified as “very poor” on Saturday—a day after it clocked a 150-point improvement in 24-hour average AQI on Friday, according to the Central Pollution Control Board’s (CPCB’s) daily bulletin.
The AQI on Friday was 218, classified as “poor” by the CPCB.
Experts attributed the dip to a change in the wind direction, which led to a higher contribution of stubble burning as well.
According to the CPCB, an AQI of 51–100 is classified as “satisfactory”, 101–200 is “moderate”, 201–300 is “poor”, 301–400 is “very poor”, and a reading above 400 is “severe”.
Data from the Centre’s Decision Support System (DSS) for Air Quality Management in Delhi showed that the contribution of stubble burning to Delhi’s air pollution had increased from 1.6% on Friday to 9.03% on Saturday. The contribution of stubble burning, however, is expected to go down to 3.45% by Sunday, according to forecasts by DSS.
Sunil Dahiya, founder and lead analyst at the think-tank, Envirocatalysts, said, “The wind speed did not see any significant change on Saturday, but the wind direction did. The wind a day before was mostly coming from the north but on Saturday, the primary wind direction was northwest and west, which is why the contribution of stubble burning from states like Haryana and Punjab went up.”
DSS data showed that the contribution of pollution from Jhajjar in Haryana adversely impacted the Capital’s AQI, as it increased from 4.89% a day before to 10.66% on Saturday. In contrast, it only accounted for 0.22% on Thursday.
The forecasts predicted the contribution to increase to 11.24% by Sunday.
“Jhajjar has two coal-based power plants; so, naturally, with the increase in contribution from the district, Delhi’s air quality has deteriorated,” Dahiya said.
The Centre’s Air Quality Early Warning System (AQEWS) for Delhi has forecasted the city’s AQI to remain in the “very poor” category for the next few days.
“The air quality is very likely to be in the very poor category from Sunday to Tuesday. The outlook for the subsequent six days is that the air quality is likely to be in the very poor category,” the AQEWS said in its bulletin on Saturday evening.
Mahesh Palawat, vice president at Skymet Meteorology, said, “The wind speed has remained somewhat variable throughout Saturday, with an average of about three to five kilometres per hour (kmph). The impact of slight rain in the neighbouring areas of Delhi that had helped clear up some of the pollution on Friday due to the wash-out effect has also faded and with the pollution sources working consistently, the air pollution levels have gone up in the Capital again.”
“The wind direction has changed and is now primarily coming from the west, with some influence from the southwest and northwest direction as well, leading to a greater contribution to air pollution from neighbouring areas. The wind speed needs to be at least around 10-15kmph for it to properly help the dispersion of pollutants, “ Palawat said.
On Saturday, the city recorded a minimum temperature of 19.4 degrees Celsius (°C), which was 3.3°C above normal but lower by 2.2°C from the day before. The maximum temperature was 30.5°C, which was 0.5°C below normal.
“Mainly clear skies are expected to persist on Sunday. A smog or shallow fog is likely to prevail at many places on Sunday morning. Moderate fog might also be seen at isolated places of the city in the early hours,” an IMD official said.
The IMD has also forecasted a fresh western disturbance to influence the western Himalayan region from Monday night.
According to forecasts by the department, the maximum temperature of Delhi is expected to remain around 29-31°C till Wednesday and then dip further. The minimum is expected to stay around 16-18°C.