The air quality index (AQI) reached 422, with 12 of Delhi's monitoring stations recording severe readings.
A familiar grey shroud fell over Delhi on Thursday morning and draped it for the rest of the day, as pollution stations flashed deep red and the air quality index (AQI) spiralled into the “severe” zone for the first time this season, flinging the Capital headlong into its annual bad air nightmare.
While Delhi recorded a 24-hour average AQI of 392 (just short of the “severe” mark) in the Central Pollution Control Board’s (CPCB) official bulletin at 4pm, this number tipped into the severe category just an hour later, with a recording of 402. At 10pm, this number barrelled up to 422. In fact, even at 4pm, 12 of Delhi’s 34 monitoring stations clocked severe readings, with usual suspects Mundka (453) and Anand Vihar (449) topping the grim charts.
The air emergency prompted authorities to roll out — if belatedly and reactively — a plethora of pollution mitigation measures, including a ban on private constructions and on the use of older BS-3 petrol and BS-4 diesel vehicles across NCR.
Meanwhile, Delhi chief minister Arvind Kejriwal said no in-person lessons will be conducted for students in Classes 5 and below for two days (Friday and Saturday).The CPCB bulletin also showed a significant variation in AQI across the National Capital Region. Greater Noida was the worst off, with a reading of 402 (severe) at 4pm, while Faridabad (368) and Noida (351) followed suit. The AQIs in Gurugram and Ghaziabad were, oddly, in the “poor” category at 297 and 286, respectively.
Delhi’s AQI deteriorated rapidly on Thursday and was significantly worse than 362 (very poor) a day ago, as still surface-level winds exaggerated the impact of local sources of pollution. In fact, Delhi’s bad air on Thursday was largely down to pollutants emitted within the city, underlining a possibly increasing baseline pollution level,even as farm fires in Punjab and Haryana continued to tick up and played a role in driving up PM2.5 (ultra-fine particulate matter) levels.
The direction of long-range transport winds is a key factor in Delhi’s air quality. A northwesterly current — like the one the Capital was experiencing on Thursday — brings smoke from farm fires in Punjab and Haryana into Delhi.
The two states together recorded 1,543 farm fires on Wednesday, nearly identical to the 1,556 on Tuesday, but nearly double the 827 blazes that satellites tracked a week ago. These numbers are still lower than historical numbers. For instance, the two states clocked 1,978 fires on November 1 last year, 2,477 in 2021 and 3,500 in 2020.
Since October 1, Punjab and Haryana together have logged 10,228 farm fires this year, as against 19,716 in the same period last year and 20,428 in 2021. To be sure, year-on-year data on stubble fires is not always comparable due to differences in cropping and harvest patterns.Mahesh Palawat, vice president at Skymet, a private weather forecaster, said that even though surface-level winds were calm, the upper-level transport winds blew in at around 8km/hr, from the northwest.
“This may have possibly brought some stubble smoke. A portion of this is likely to have accumulated over Delhi,” he said, stating while surface level local winds are normally 10-100 metres high, transport-level winds blow much higher, at heights of around 1,000 metres.
The CPCB bulletin said PM2.5 was the prominent pollutant in Delhi’s air, which is a byproduct of combustion sources. This is likely to include contributions from the vehicular sector, industries, and stubble burning.
Delhi’s PM2.5 levels peaked at 242.7µg/m³ at 10pm and the PM10 peaked at 412µg/m³, also at 10pm, both over four times India’s safe standards. And this when India’s pollution norms are less stringent than global thresholds. For instance, the Indian safe standard for PM2.5 is 60µg/m³, while the World Health Organization’s (WHO) standard is a fourth of that at 15 µg/m³. Similarly, India’s PM10 standard is 100µg/m³ and the WHO’s is 45µg/m³. Delhi’s PM2.5 levels peaked at 173.3µg/m and PM10 at 327.8µg/m on Wednesday.
Sunil Dahiya, analyst at the Centre for Research on Energy and Clean Air (CREA), said Delhi is now at the mercy of meteorological conditions — and the AQI reading deteriorates rapidly if winds become calm.
“We have been seeing this for the past few days too, but on Thursday, we did not see an increase in wind speed after noon either. This led to pollutants stagnating completely,” he said.
The toxic air prompted the Delhi government on Thursday to announce a two-day break for primary schools (classes 5 and below). “In light of the rising pollution levels, all govt and private primary schools in Delhi will remain closed for the next 2 days,” CM Kejriwal said in a post on X (formerly Twitter).
Meanwhile, the Commission for Air Quality Management (CAQM) stepped up anti-pollution curbs in the city, setting into effect Stage 3 of the city’s Graded Response Action Plan (Grap).
The restrictions include a ban on the use of BS-3 petrol and BS-4 diesel vehicles, private constructions and demolitions (excluding non-polluting work like plumbing, interior decoration, electrical work and carpentry), as well as curbs on the use of hot-mix plants.
Grap Stage 3 is designed to kick in when the AQI is likely to touch the “severe” category and be between 401 and 450, and experts criticised the agency for reacting to the spike in pollution rather than pre-empting it.
“The whole idea behind revising Grap was to make it pre-emptive. Earlier, we would wait for the air quality to touch a certain mark, before the measures were imposed. Now, we need not do that and can do it based on forecasts, but these need to be accurate too,” said Dahiya, criticising the Early Warning System (EWS) for Delhi, an air quality forecasting tool developed by the Indian Institute of Tropical Meteorology (IITM).
And the air is only likely to get worse.
With farm fires nowhere near their peak, temperatures set to plummet further, and Diwali 10 days away, the city’s grey shroud is likely to stay, and may only get thicker, experts warned.
Delhi on Thursday clocked a minimum temperature of 16.3°C, a degree above normal and nearly identical to a day ago. The India Meteorological Department (IMD) said it predicts no change in temperatures over the next couple of days.
