Weak winds are forecast to trap pollution, with forecasts suggesting air quality could reach the severe category by Monday.
Delhi wakes up to Diwali on Sunday after its most polluted festival eve in a decade, with a perfect storm gathering over the night to come.
Farm fires in Punjab and Haryana climbed to their highest this season on Saturday — and the Isro satellite’s count rose for a 10th straight day, the ground wind fell calm after sunset, and within two hours of the first evening window for firecrackers opening at 8pm, the city’s air was 30% dirtier than a night earlier.
All of that came before the festival night itself, when most of the city’s firecrackers are burst, and light winds are forecast for Sunday.
The 4pm air quality index (AQI) on Saturday was 369, “very poor” on the Central Pollution Control Board’s (CPCB) 0-500 scale and the highest for the day before Diwali since 2016, when it was 404. The index, an average of the past 24 hours, has climbed from 261 on November 1. Measured pollution first peaked on Saturday morning: between 10am and 11am, PM2.5 — the fine particulate matter small enough to lodge deep in the lungs — averaged 295 micrograms per cubic metre across Delhi’s 59 monitoring stations, and 36 of them were above 250, where CPCB’s “severe” band for PM2.5 begins.
Saturday afternoon was the best-ventilated afternoon of the week, with the layer of air that pollution mixes into returning to its usual depth after four days at about half that. A shallower mixing layer means less room for pollutants to disperse into. Yet every hour from 11am to 5pm was dirtier than on Friday.
Then the evening window for bursting opened. PM2.5 jumped from 177 micrograms per cubic metre at 7.45pm, to 208 at 8pm, and climbed every 15 minutes to 289 at 10pm across the 55 stations that had reported, HT’s analysis of CPCB’s 15-minute readings shows.
Over the same hours on Friday, the air moved only from 202 to 229. Saturday evening’s trends will show up in Sunday’s bulletin.
The surge was sharpest in residential neighbourhoods such as Punjabi Bagh, where PM2.5 nearly tripled in an hour, from 208 at 7pm to 593 at 8pm, and RK Puram, which read 621 at 9pm, more than double its level at that hour on Friday. By 9pm nine stations were above 400, against none on Friday, and from 10pm even the median station was above 250. Mundka read 718.
