Grey. Toxic. Noxious: The choke is on again

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.

- Jasjeev Gandhiok

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 levels.