NEW DELHI: Delhi’s air quality sharply worsened on Sunday as calm winds and low mercury impacted the dispersion of pollutants.
Within 24 hours, the Air Quality Index (AQI) rose from 316 on Saturday to 382, placing it in the higher end of the ‘very poor’ category. This was the worst AQI in over nine months. A higher AQI than this was last recorded at 392 on Jan 31, shows Central Pollution Control Board data.
The highest AQI in Oct was 364 in the ‘very poor’ category on Oct 23. The air quality is likely to hover within the ‘very poor’ category till Wednesday.
IMD has predicted that mist or smog conditions during the early hours of Monday to Wednesday. Experts said the wind direction has been changing from north-westerly to southeasterly on Sunday, and wind speed dropped to zero during the transition phase. Even the night temperature, which mostly remained at least 3-4 degrees above normal in Oct, has now started dipping in November. On Sunday, the city recorded the season’s lowest minimum temperature at 16.5 degrees Celsius, one degree above normal. It was a dip of around four degrees as the minimum temperature settled at 21.1 degrees Celsius on October 31.
“As the wind direction is changing to south-easterly, winds turned calm during the daytime, causing accumulation of pollutants. Variable winds blew in the city in the last 24 hours, but south-easterly winds are expected to prevail on Monday and Tuesday. Though south-easterly winds are unfavourable for the transport of emissions from stubble burning to Delhi, local winds are expected to be calm during the night and light during the daytime. Since local winds will not pick up in the next two days, it is likely to impact the air quality,” Mahesh Palawat, vice-chairman of Skymet Meteorology, said.
As the winds turned calm during the daytime, the AQI spiked from 366 at 8 am to 382 at 4 pm based on the average calculated by CPCB of 39 stations out of a total of 40. The AQI reading surpassed 400 at 14 stations, placing them in the ‘severe’ category. This included Anand Vihar, the most polluted with an AQI of 436, followed by Nehru Nagar at 430 and Punjabi Bagh at 425.
“Meteorological conditions are likely to be extremely unfavourable for the dispersion of pollutants,” the Air Quality Early Warning System for Delhi (EWS) said on Sunday. The EWS added that the air quality is likely to remain in the very poor range till Wednesday, but it is forecast to stay in the ‘very poor’ to ‘severe’ category during the subsequent six days from November 6 onwards.
The share of stubble burning in Delhi’s PM2.5 was 14.96% on Saturday, according to the Decision Support System. However, as southeasterly winds are likely to blow in the city, the contribution of stubble burning is expected to decrease. Satellites detected 351 residue burning events on Sunday. Of these, 216 were in Punjab, 19 in Haryana, 16 in UP, 36 in Rajasthan, and 67 in MP, according to satellite data compiled by the Indian Agricultural Research Institute.