A day after entering the red zone for the first time this season, Delhi’s air quality continued to remain in the ‘severe’ category on Friday for the second consecutive day, despite a marginal improvement in the measurement index because of a slight increase in wind speed.
Scientists at the India Meteorological Department (IMD) said the rising number of stubble burning cases in the neighbouring states of Punjab and Haryana has been the primary factor behind the Capital’s foul air — contributing to 21% of Delhi’s PM 2.5 levels on Friday.
Central Pollution Control Board (CPCB) data recorded the overall air quality index (AQI) of Delhi on Friday at 406, in the ‘severe’ category. Even though the wind speed over Delhi improved to around 8-10kmph through the day, it was not enough to bring about much improvement from Thursday’s AQI recording of 450.
This is the second consecutive day when the AQI in the national capital crossed the severe mark.
According to CPCB data, last year, the air quality plunged into the ‘severe’ category on 24 occasions. In 2018, there were 20 such days and in 2017, there were nine days when the AQI levels remained in the red zone.
VK Soni, head of IMD’s environment monitoring research centre, said there was a marginal improvement in the air quality because of higher wind speed in the day. However, the levels started dipping again after 4pm. He said stubble burning in Punjab and Haryana is negatively impacting Delhi’s air.
“Yesterday fire counts only over Punjab was over 5,000, and even today the number has been around 4,000-5,000. Even though the wind speed picked up during the day, the improvement in air quality was not very significant only because of a high share of farm fires,” Soni said.
The average wind speed on Friday was 8-12kmph, but blowing from the north-westerly direction, carrying plumes of smoke from the agrarian states of Punjab and Haryana, where the stubble burning activities is at its peak now.
Scientists explained that a similar situation was seen in Delhi last week, on October 30, when an improvement in wind speed was supposed to have resulted in a reduction in pollution levels. But despite wind speed remaining above 12kmph through the weekend, its impact on the AQI was marginal because of a high stubble burning count.
The Union ministry of earth sciences’ air quality monitoring centre, System of Air Quality and Weather Forecasting and Research (Safar), recordings show that 3,225 farm fires were reported from Punjab and Haryana, contributing to 21% of Delhi’s PM 2.5 levels.
IMD monitoring data shows that late Thursday night, the PM 2.5 levels (ultrafine particulate matter with diameter less than 2.5 micrometres) had started improving and had reached below the 300ug/m3 mark. This means that the risk of Delhi entering the ‘severe plus’ category on Saturday had reduced.
According to the winter segment of the Supreme Court-approved Graded Response Action Plan (Grap), Delhi will enter the ‘severe plus’ or ‘emergency’ zone if the PM 2.5 levels constantly remains above the 300ug/m3 mark and the PM 10 levels (particulate matter with diameter less than 10 micrometres) remains above the 500ug/m3 mark for at least 48 hours.
According to Grap, under the ‘severe plus’ category, the CPCB task force can direct state governments in Delhi and NCR to stop the entry of trucks, except those carrying essential commodities, into Delhi, halt construction activities and implement the odd-even road rationing policy.
Kuldeep Srivastava, head of IMD’s regional weather forecasting centre, said no significant improvement in the pollution level is likely during the weekend. “The wind will slow down through Friday night, which might lead to deterioration in the air quality early Saturday. The wind direction will also continue to be north-westerly, which will transport smoke from farm fires,” he said.
IMD said that on Sunday, the wind might slow down, spelling trouble for Delhi.
“We expect that from Monday, the wind direction will become easterly, but before that, the wind speed will slow down. However, everything will depend on the state of stubble burning in Punjab and Haryana now,” said Soni.
