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Even though Delhi has seen the cleanest pre-Diwali air in seven years on Sunday, calm winds in the city may push air quality into the ‘severe’ category over the next two days even if there is no emission load from burning firecrackers.
Delhi recorded an AQI of 259 (poor) on Sunday, the lowest in seven years for the day before Diwali. On November 3 last year, the AQI was 314 (very poor). It shot up to 382 on Diwali and was 462 (severe) the next day. In 2020, Delhi recorded an AQI of 296 a day before Diwali, and in 2019 it was 287.
AQI between zero 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”.
“For the next three days (October 24, 25, 26), peak surface wind speed is likely to be ‘calm to 5-10 km/h’ causing weak dispersion, and AQI is likely to be ‘very poor’ on Monday (Diwali daytime). It will likely worsen to ‘lower end of severe’ on Diwali night and the next day, October 25. Shallow mixing height during the night and early morning aids the accumulation of pollutants near the surface. However, moderate temperature (maximum 31-32; minimum 15-16 degrees Celsius) and mixing layer height (1.0-1.5km) during the day is expected to enhance vertical dispersion and dilution of near-surface pollutants,” according to a forecast issued by SAFAR (System of Air Quality and Weather Forecasting and Research) on Sunday.
The agency’s Diwali forecast, issued on Saturday, said if an additional firecracker load of 25% of long-term fire cracker load (as last year) is added along with background emissions, AQI is expected to worsen to ‘severe’ on Diwali and a day after Diwali.
SAFAR also said that with the number of fire counts increasing in neighbouring states, the impact is expected to be felt in Delhi soon. “Fire counts over the northwest region are gradually increasing (around 850) and its impact on Delhi’s air quality is likely to increase due to favourable transport level wind flow,” it said.
When does construction ban kick in
According to GRAP, if air quality turns “severe” authorities are required to enforce a ban on construction and demolition activities in Delhi-NCR, except on essential projects (like railways, metros, airports, ISBTs, national security/ defence-related projects of national importance) and non-polluting activities such as plumbing, carpentry, interior decoration and electrical works.
Paddy straw burning accounted for 25% of Delhi’s PM 2.5 pollution on Diwali last year.
Meanwhile, the local administration banned private construction in Anand Vihar and adjoining areas on Saturday until further orders after the AQI deteriorated.
According to officials, the decision to strictly impose restrictions based on the Graded Response Action Plan (GRAP) was taken in a meeting on Saturday. The order, which was issued after the meeting, said, “The air quality index at Anand Vihar and adjoining areas measured 410 on October 22. Hence, the Commission for Air Quality Management has taken serious note of it and instructed that necessary precautionary and dust-mitigation measures be taken to control the rising air quality index in the above areas… Therefore, it is directed to all concerned to stop private construction with immediate effect till further direction. Non-compliance with the direction will be viewed seriously.”
According to GRAP, if air quality turns “severe” authorities are required to enforce a ban on construction and demolition activities in Delhi-NCR, except on essential projects (like railways, metros, airports, ISBTs, national security/defence-related projects of national importance) and non-polluting activities such as plumbing, carpentry, interior decoration and electrical works.
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