Delhi's air quality dips to worst level since December last year

Delhi's air quality on Thursday dropped to its worst level since December last year, with farm fires accounting for 42 per cent of its pollution, the maximum in this season so far, according to data from central government agencies.

Experts said unfavourable meteorological conditions -- calm winds and low temperatures -- and smoke from farm fires in neighbouring states led to a dense layer of haze on Wednesday night as the air quality index entered the 'severe' zone.

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The haze thinned on Thursday with higher wind speed helping in dispersion of pollutants. However, the 24-hour average air quality index (AQI) was recorded at 450, the highest since December 30 last year, when it was 446.

All the 36 monitoring stations in Delhi recorded air quality in the 'severe' category. The neighbouring cities of Faridabad, Ghaziabad, Greater Noida, Gurgaon and Noida also recorded 'severe' air pollution.

An 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".

PM10 levels in Delhi-NCR stood at 563 microgram per cubic metre (µg/m3) at 10 am, the highest since November 15 last year, when it was 637 µg/m3. It came down to 497 µg/m3 by 5 pm, according to CPCB data.

PM10 is particulate matter with a diameter of 10 micrometers and can get into the lungs. These particles include dust, pollen and mold spores. PM10 levels below 100 µg/m3 are considered safe in India.

The level of PM2.5 -- finer particles which can even enter the bloodstream -- were 360 µg/m3 at 12 noon. PM2.5 levels up to 60 µg/m3 are considered safe.

The Ministry of Earth Sciences’ air quality monitor, SAFAR, said the farm fire count in Punjab, Haryana, Uttar Pradesh, Uttarakhand and neighbouring areas increased significantly and stood at 4,135 on Wednesday, the highest in this season so far.

SAFAR said the boundary layer wind direction was northwesterly, favourable for the transport of pollutants from farm fires. It predicted conducive conditions for dispersion of pollutants over the next two days.

"The share of stubble burning in Delhi's PM2.5 pollution was estimated at 42 per cent on Thursday,” it said.

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"Better dispersion condition and not so low daytime boundary layer height is predicted for the next two days which is likely to improve AQI unless more than estimated fire-related emission takes place."

Stubble burning accounted for five per cent of Delhi's pollution on Wednesday, 10 per cent on Tuesday, 16 per cent on Monday and 40 per cent on Sunday. Last year, the stubble contribution to Delhi's pollution had peaked to 44 per cent on November 1, according to SAFAR data.

On Wednesday evening, the noxious haze reduced visibility to merely 600 metres at the Safdarjung Observatory, smudging landmarks from view. It was 1,200 metres on Thursday morning. On top of that, a large number of people across Delhi-NCR burst firecrackers to mark the Karwa Chauth festival.

"People are bursting crackers, it is not even Diwali yet. The city has already become a gas chamber. This happens every year. For how long will this continue?" asked Shiv Shrivastava, a resident of south Delhi.

"I can feel the pollutants in my throat despite wearing a mask. My eyes are burning. It is going to make the pandemic worse. I am scared," said Piyush Vohra, a resident of Jangpura.

Health experts said during the Covid-19 pandemic, air pollution has become a serious health concern for about the two crore residents of the national capital.

According to a doctor at the Sir Ganga Ram Hospital, intake of every 22 micrograms per cubic metre of polluted air is equivalent to smoking a cigarette.

Ajit Jain, the nodal officer for Covid-19 at Rajiv Gandhi Super Specialty Hospital, said air pollution was turning the pandemic catastrophic.

IMD officials said sudden change in the wind pattern on Wednesday had led to "subsidence", the downward movement of air over a large area when it cools and becomes heavier.

"The wind speed slowed down suddenly in the Delhi-NCR region. The temperatures have dipped alarmingly over the last few days," V K Soni, the head of IMD’s environment monitoring research centre, said.

The haze was primarily smoke from stubble burning in Punjab and Haryana. Unfavourable meteorological conditions trapped it in Delhi-NCR, he said.