Despite a ban on the sale of crackers, the evening after Deepavali saw the Delhi record its sharpest dip in air quality this year. Air quality plummeted to ‘severe’, the worst rating on the air quality index (AQI), according to the Central Pollution Control Board’s (CPCB) updated report of Friday.
Regions surrounding Delhi — Ghaziabad and Noida — also posted similar ‘severe’ levels of pollution on the AQI, a 6-rung, colour-coded scale that indicates average concentrations of the most threatening pollutants hovering over the city.
The AQI registered 402 on the scale — the uppermost being 500 — according to data from 14 monitoring stations in Delhi.
These numbers buck a historical trend in which smog and pollution peak in the 24 hours following Deepavali, though it still remains to be seen if the pollution will clear in the next few days. This year, according to the CPCB, the concentration of pollutants was significantly lower than last year, when cracker-burning and unfavourable weather saw pollution levels spike above the maximum readings at several monitoring stations.
Dipankar Saha, who heads the air quality division at CPCB, said moisture levels were high the morning after Deepavali and a rain-bearing depression in the Bay of Bengal had stalled winds, stopping the dispersal of pollutants. “We expect better air quality after 24 hours, provided there is no further addition of pollutants,” he added.
The severe smog, which built up in the days leading to Deepavali last year, triggered a directive by the Supreme Court to implement a comprehensive pollution management plan. A consequence of this plan was that, over the last week, the Badarpur Thermal Power Station was shut down, diesel generators in Delhi banned, and brick kilns that did not employ the latest technology were clamped.
The AQI on Deepavali day in 2015 was 327, 426 in 2016 and 327 this year, according to the agency’s Deepavali report. Concentrations of most categories of pollutants — sulphur dioxide, particulate matter 10 and 2.5 — saw a fall this year across most stations, except for nitrous oxide. Air quality this year was slightly better than last time, even though meteorological conditions, such as average wind speeds and mixing heights (a swathe of the atmosphere that facilitates the dispersal of pollutants) were almost as unfavourable last year.