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.
The national capital’s air quality fluctuated between “poor” and “very poor” categories on Friday, and was expected to decline sharply over the weekend owing to changing weather and “significant” stubble burning. The overall air quality index (AQI) in the city stood at 306 at 9 am on Friday. It improved by 64 points and was recorded at 242 at 9 pm.
At the start of the day, the overall AQI at DTU, Dwarka Sector 8, Narela, Wazirpur and Bawana was 312, 316, 310, 312, and 341 respectively, which falls in the “very poor” category. Only Bawana recorded its AQI (320) in the “very poor” category in the evening.
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.
The Ministry of Earth Sciences’ air quality research and forecast service, SAFAR, said, “Under the influence of a western disturbance, surface wind speed has increased. Increased ventilation coefficient has lead to improvement in air quality.”
“These conditions are likely to prolong until tomorrow and hence, in spite of increased intrusion of stubble (burning), only marginal deterioration (of air quality) is predicted on Saturday,” it said in a report.
However, it said, transport-level wind direction is likely to become northwesterly by October 20 and Delhi’s surface winds will also slow down. “Under this scenario, faster intrusion and deterioration of air quality to the middle of the very poor category is predicted. Stubble burning incidents in Haryana, Punjab, and nearby border regions are only moderate and hence, even if winds are favourable, drastic deterioration (of air quality) is not expected,” the SAFAR report said.
The share of stubble burning to Delhi’s PM2.5 concentration was 7 per cent on Friday. It is predicted to increase to 17 per cent on Saturday, according to SAFAR data. The period between October 15 and November 15 is considered critical as maximum number of stubble burning incidents take place in this span in Punjab and adjoining states and is one of the main reasons for alarming spike in pollution in Delhi-NCR.
Stubble burning in Punjab, Haryana
Despite a ban on stubble burning in Punjab and Haryana, farmers continue to defy it amid lack of financial incentives. State governments are providing 50 to 80 per cent subsidy to farmers and cooperative societies to buy modern farm equipment for in-situ management of paddy straw and running a massive awareness campaign against stubble burning.
While the Delhi government has repeatedly stressed that stubble burning was the major reason for Delhi’s deteriorating air quality, the Supreme Court-mandated Environment Pollution (Prevention and Control) Authority has said local sources of pollution was the primary concern.
“It is not that local pollution has increased, it is that weather has turned adverse and so, air pollution is again on the rise. If we keep focusing on external reasons, we will not fix our problems,” EPCA member Sunita Narain said on Thursday.
Kuldeep Srivastava, a senior scientist at the India Meteorological Department (IMD), said predominantly slow easterly winds are blowing in the region. Slow wind speed is not favourable for dispersion of pollutants. There is an active western disturbance over parts of Jammu and Kashmir, Uttarakhand, Punjab and Haryana. It is expected to reduce the impact of stubble burning slightly, he said.
“After October 20, the wind speed is likely to increase and as a result the city’s air quality is expected to improve,” Srivastava said.
IMD officials said that due to the occurrence of mist and high concentration of pollutants, the visibility levels at Safdarjung and Palam decreased to 1,500 metres at 8:30 am from 2,500 metres at 5:30 pm on Thursday.