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Updated: Oct 11, 2019 00:05 IST

Delhi-NCR’s air quality deteriorated on Thursday to its worst level in nearly three months as winds slowed down, the temperature dipped and an increasing number of farm fires took place in nearby states — recreating a combination of factors that has been turning pollution during winter months into a public health crisis in recent years.

According to Central Pollution Control Board (CPCB) data, the 24-hour average air quality index (AQI) till 4pm was at 211 — considered ‘poor’. By evening, the blue sky in the morning had turned hazy and by 10pm, the AQI had risen to 223 — a level not seen since July 14 when the AQI was 235. The spike took place a day after Delhi saw its cleanest post-Dussehra air in five years.

Weather officials said the immediate change is due to climatic conditions typical of pre-winter period: As the monsoon withdraws, an anti-cyclone wind pattern has formed over Rajasthan. “This result in stagnant weather conditions such as low wind speed that does not allow pollutants to disperse,” said Kuldeep Srivastava, head, regional weather forecasting centre (RWFC), India Meteorological Department (IMD).

The System of Air Quality and Weather Forecasting and Research (SAFAR), a unit of the Union ministry of earth sciences, said air quality will deteriorate further over the next 48 hours.

The most prominent impact from slowing winds is the trapping of local pollutants — vehicle exhaust gases, road dust and industrial emissions. But it is pollution from neighbouring states, in the form of smoke from farm fires, that pushes the air quality into hazardous levels.

According to data from the United States’s National Aeronautics and Space Administration (Nasa), the number of fires spotted in states of Haryana and Punjab recorded a significant spike over the last two days. The total number of fires spotted in these two states on Monday was at 45. On Wednesday, the latest till which data from Nasa was available, the number had climbed to 178.

To be sure, at least 1,000 instances of farm fires have been recorded daily in the last couple of years during the peak crop burning period, which begins in mid-October and lasts for about three weeks. Paddy farmers in Haryana and Punjab set fire to their fields to clear it of stubble, which is left behind after mechanised harvesting.

“Most of these fires are reported from farms, even though some are accidental as well. We have been monitoring farm areas over satellite,” said A Narayan, member secretary Haryana Pollution Control Board.

K Garg, member secretary Punjab Pollution Control Board, said that this year the most numbers of fires till now have been reported from Amritsar and Tarn Taran districts.

With the air quality deteriorating, the pollution watchdog CPCB has asked the Delhi government and other agencies to ensure there is no open storage of construction material, dumping or burning of waste. The Supreme Court-mandated Environment Pollution (Prevention and Control) Authority had also predicted a rise in the pollution levels in the city from October 12, and ordered that the Graded Response Action Plan (GRAP) to combat ‘very poor’ and ‘severe’ levels of pollution will come into force from October 15.

(With inputs from Abhishek Jha in New Delhi)