Delhi’s air slips back into severe zone as wind changes direction

Delhi’s air quality slipped into the ‘severe’ zone on Saturday, as winds changed direction and slowed down considerably making dispersion of pollutants difficult.

Delhi’s air quality slipped into the ‘severe’ zone on Saturday, as winds changed direction and slowed down considerably making dispersion of pollutants difficult. The air quality is likely to remain in the lower end of ‘severe’ to the upper end of ‘very poor’ zone over the next two days, government agencies forecast.

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According to the Central Pollution Control Board’s (CPCB) 4pm bulletin, the AQI was 404 on Saturday. It was 382 in the ‘very poor’ zone on Friday. The last time air quality was in the ‘severe’ category was on November 25, with an AQI reading of 413.

On a scale of 0-500, an AQI value between 301-400 is considered ‘very poor’ while 401-500 is ‘severe’.

According to scientists at the India Meteorological Department (IMD), with stubble burning incidents being negligible at present, local accumulated pollutants have not been able to disperse because of unfavourable meteorological conditions.

V K Soni of IMD’s environment monitoring research centre, said that winds at present are blowing from the east, which have increased the moisture content in the air. “High moisture content and calm winds trap pollutants close to the ground resulting in an increase in the PM 2.5 and PM 10 concentrations. The air quality is likely to improve slightly on Sunday and may remain in the upper end of the ‘very poor’ zone,” said Soni.

IMD scientists said that the average wind speed on Saturday was less than 5 kmph. Also, at Safdarjung Observatory, the official marker for city weather, shallow fog was observed in the early morning hours with visibility being 600 metres.

“While there was an increase in the night temperature, the air quality deteriorated because of winds being calm. Whenever there is a change in wind direction, it impacts the air quality. From December 7-10, air quality may improve considerably, as northwesterly winds will return to Delhi. Also, the wind speed is likely to remain around 12-15kmph at that time,” said Kuldeep Srivastava, head of IMD’s regional weather forecasting centre.

On Saturday, the minimum temperature was 11 degrees Celsius, two notches above normal. The maximum settled at 27.8 degrees Celsius, three notches above normal.

The System for Air Quality and Weather Forecasting and Research (SAFAR), the union ministry’s air quality forecasting wing, said the share of stubble burning to the city’s PM 2.5 levels was just 1%. “The air quality is likely to improve slightly to the ‘very poor’ zone on Sunday. However, significant improvement may take place only from December 7 onwards,” the SAFAR bulletin stated.

According to experts, every year after peak pollution in November, which is mostly attributed to contribution from stubble burning, bad air episodes are seen towards December-end and early January. This is mainly because as compared to November, meteorological conditions are even more unfavourable during this time while the baseline pollution (local emission from Delhi and neighbouring regions) stays the same. This includes local waste burning, industrial fumes, vehicular emissions and dust suspension, among others.

D Saha, former head of CPCB’s air lab, said that during December-January, with colder days and calm winds, the meteorological conditions are tougher and slows down dispersion. “Also, at this time because of the geographical position of Delhi, dust and other emissions from the Indo-Gangetic plains settle here. Enforcement agencies need to ensure that local emissions are minimised to prevent the peaks in pollution,” said Saha.