Capital punishment: Delhi air now ‘severe’

Delhi AQI soared to 452 by 11pm, falling in comfortably “severe plus” – the worst possible category within the AQI range

City residents woke up on Wednesday to an all-too-familiar nightmare: a thick, choking haze of smog blanketing the city, laced with the acrid tang of pollution that signals the firm arrival of the Capital’s annual “severe” air crisis — slightly later than usual this year, but unrelenting as ever.

Even as residents struggled to breathe, the CAQM refrained from implementing Stage 3 of the Graded Response Action Plan, in which schools are shut and all private construction is halted, stating that the AQI will likely “improve” to the “very poor” zone by Thursday. (AFP)

The Capital recorded a 24-hour average air quality index (AQI) reading of 418 at 4pm, a sharp deterioration from 334 at the same time on Tuesday, according to data from the Central Pollution Control Board.

This rapid worsening showed no sign of stopping, with the AQI soaring to 452by 11pm, falling in comfortably “severe plus” – the worst possible category within the AQI range.

In fact, Delhi’s AQI reading on Wednesday was the worst for any city in the country.

But even as residents struggled to breathe, the Commission for Air Quality Management (CAQM) refrained from implementing Stage 3 of the Graded Response Action Plan (Grap) -- in which schools are shut and all private construction is halted -- stating that the AQI will likely “improve” to the “very poor” zone by Thursday.

The abrupt worsening in pollution was largely down to meteorological conditions: a cocktail of stagnant winds, sudden lowering of temperatures, and dense smog worked together to trap pollutants over the city.

These same factors had so far this season been favourable, and had thus helped the city avoid the brunt of post-Diwali pollution. For example, the bursting of firecrackers generally turns Delhi’s air severe in the days following Diwali. But it did not happen this year (Diwali was celebrated on October 31) because faster winds cleaned up the pollutants from firecrackers.

The first severe AQI in 2023 was recorded on November 3 and November 1 in 2022.

The annual air crisis returning in full force pointed also to a combination of administrative collapse and urban apathy, leaving all residents, but particularly children, the elderly and those with respiratory conditions, in the lurch.

CAQM attributed the deterioration to meteorological conditions.

“The CAQM... was informed by IMD//IITM [India Meteorological Department/Indian Institute of Tropical Meteorology] that an unprecedented extremely dense fog was reported over Delhi and adjoining regions, which had zero visibility during 0800 to 0930 hours... resulting in Delhi’s overall AQI move to ‘severe’ category,” the body said in a post on X.

“However, owing to stronger winds, the pollution concentration, thereby the AQI, is expected to start showing a declining trend...it was decided by the subcommittee to keep a close watch on the situation before invoking the stringent measures under Stage-III,” it added.

Grap stage 1 was invoked on October 15 and Grap stage 2 on October 22.

HT reached out to the Delhi government which did not respond to queries.

The AQI reading was 10pm on Tuesday night, but as the night got cooler, a dense layer of fog engulfed Delhi in the early hours of Wednesday, reducing visibility to near-zero and trapped the toxic cocktail of pollutants at the surface level. Experts attributed this to a change in wind direction, from easterly to westerly -- the latter being drier and colder, and bringing with it stubble fires from Punjab and Haryana.

Of the 36 working AQI monitoring stations in Delhi, only one recorded a “severe” reading at 8am on Wednesday. However, this deteriorated rapidly as the day progressed with at least 32 stations recording readings in this zone by 6pm.

Delhi’s AQI was at 361 (very poor) at 8am, 381 (very poor) at 12pm, 418 at 4pm, 439 at 6pm and 452 by 11pm. The Capital’s air has been in the “very poor” zone for nearly a fortnight. High surface winds and warmer temperatures through most of October and early November were the only factors keeping AQI in check, despite the rampant flouting of the ban on firecrackers during Dussehra and Diwali festivities and blazing farm fires.

To be sure, farm fires this year have accounted for an average of 16.23% of Delhi’s finer PM2.5 between October 22 and November 11 -- is lower than the contribution of 20.33% from the same period in 2023, according to the Centre’s decision support system. According to data from the Indian Agricultural Research Institute, till November 12, Punjab recorded 7,112 farm fires — lower than the 24,717 fires recorded in the same period last year and 43,144 fires recorded in 2022. In Haryana, the total fire count till November 12 was 1,020 — down from 1,813 fires in the same period last year and 2,979 fires in 2022. But experts have warned that this may be due to a late harvest, and that the worst on the stubble front may be yet to come.

Mahesh Palawat, vice president at Skymet, said that the main trigger for the sudden change in weather conditions was a change in wind directions on Tuesday and Wednesday. “We had observed easterlies for the last few days, which are warm and humid. From Tuesday night, westerlies and north-westerlies started affecting the region. The interaction between easterlies and the cold and dry westerlies led to a mixing of sorts, which further interacted with the humid atmospheric conditions to cause condensation of water vapour,” Palawat said.

He added that this heavy layer of condensed water molecules, factored in with calm winds of average speed of 3-4km/hour, led to a dense fog in the early hours of the day.

“High humidity conditions in the atmosphere leads to a higher density of clouds. This causes the wind velocity to go down and the natural ventilation of an area is severely impacted. The calm wind condition is incapable of dispersing pollutants,” said Mukesh Khare, an air pollution expert at Indian Institute of Technology, Delhi.

Meanwhile, Wednesday’s maximum temperature went down to 27.8°C, one degree below normal compared to 32.8°C a day before. The minimum was recorded at 17°C, three degrees above normal and 0.9°C lower than Tuesday’s.

According to IMD, Wednesday recorded the season’s first dense fog, which severely impacted visibility. Authorities from the Delhi airport said at least 10 flights were diverted from 7am, nine to Jaipur and one to Lucknow.

IMD data showed that the visibility at the Delhi airport was down to 300 metres at 4.30am from 900m at 12.30am. This dropped to 200m by 5.30am, and 100m at 6am, before hitting zero at 8am. By 9.30am, visibility at Palam increased to 50m and 400m at Safdarjung.

IMD classifies it as fog if the relative humidity is over 75% and visibility is less than 1,000m. However, as the day progressed, pollutants, dust and smoke mixed with the fog and created a murky film of smog. IMD classifies it as “shallow” fog when visibility is between 500 and 1,000 metres, “moderate” when it is between 200 and 500 metres, “dense” when it is between 50 and 200 metres and “very dense” when it is lower than 50 metres. Prior to Wednesday, the lowest visibility reported in Delhi this season was 700 metres at Safdarjung on Monday.

The Air Quality Early Warning System for Delhi has forecast the air quality to become “very poor” by Friday. “The air quality is likely to be in the severe category on Thursday and very poor category from Friday to Saturday. The outlook for the subsequent six days is that the air quality is likely to be in very poor category,” the AQEWS bulletin said.

Palawat added that the wind speed is expected to increase in the following days. “That might lead to dispersal of pollutants, despite the temperature dipping slightly,” he said.

“The fog cover might cut off heat from the sun during the day, leading to a decrease in the maximum,” said a senior IMD official.