Delhi’s air quality nosedived on Sunday as calm local winds trapped pollutants close to the surface and pushed the air quality index (AQI) back into the “very poor” zone after just two days, with forecasters warning that the Capital may have its first try with “Severe” air this season on October 30, a day before Diwali.
The city clocked a 24-hour average AQI of 356 at 4pm on Sunday, according to Central Pollution Control Board (CPCB) data, a reading significantly worse than 255 (classified as “poor”) a day ago.
The air worsened despite long-range transport winds, which typically blow 5-10 feet above the surface, changing direction on Saturday and blowing in from the east-southeast (from Uttar Pradesh and southern Haryana), instead of the northwest (from Punjab and northern Haryana).
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Hence, Delhi’s AQI tanked even without the impact of smoke from stubble fires in north India’s paddy fields.
The Decision Support System (DSS), a central government tool that identifies pollution sources, said the contribution of stubble burning to Delhi’s PM2.5 levels was 5.5% on Saturday, down from 14.6% on Friday. The system reflects the previous day’s numbers.
Officials with the India Meteorological Department (IMD) said the pollution spike was largely due to local pollutants.
“There has been a change in wind direction from northwesterly to southeasterly, but winds in Delhi were calm throughout Saturday evening and the early hours of Sunday,” said an IMD official who asked not to be named.
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CPCB classifies an AQI between 0-50 as “good”, between 51 and 100 as “satisfactory”, between 101 and 200 as “moderate”, between 201 and 300 as “poor”, between 301 and 400 as “very poor”, and over 400 as “severe”.
Delhi’s AQI tipped into “very poor” on October 21 and fell out of that range for just two days, Friday and Saturday — an aberration for the city’s notoriously polluted winters.
A thick dome of smog, fueled by a lethal cocktail of dipping temperatures and smoke from farm fires, sheathes Delhi from mid-October till December in what has come to be known as the Capital’s pollution season.
During this time, Delhi’s AQI is among the worst in the world, routinely spiraling past the 450 mark. Last year, Delhi’s AQI peaked at 468, and in 2022, it hit 450.
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Three of the 37 pollution-monitoring stations in Delhi logged readings in the “deep-red” on Sunday — Bawana (411), Burari (405) and Jahangirpuri (404).
Forecasts by the Centre’s Early Warning System (EWS) for Delhi warned that the air is unlikely to improve soon.
“Delhi’s air quality is likely to be in the very poor category from October 28 till October 30. The air quality may reach the ‘severe’ category on October 30 in case of additional emissions from firecrackers and stubble fire. The meteorological conditions are unfavorable for effective dispersion of pollutants,” EWS said in its Sunday bulletin.
Delhi’s AQI often spikes to “severe” after Diwali, when polluting firecrackers go off across the city for hours, plunging the region into an air emergency that threatens even healthy people with severe respiratory and cardiac ailments.
CPCB data since 2015 shows that there has been a spike in the AQI the day after Diwali in seven of the last eight years, barring 2022 – when strong winds on Diwali day helped disperse firecracker emissions.
Last year, Delhi’s AQI on Diwali day (November 12) was just 218 (poor), the lowest since AQI data is available. However, rampant violations of the ban on firecracker-use pushed the AQI to 358 (very poor) the next day.
Delhi also woke up to a haze, with IMD the minimum visibility dipping to 1,000 meters at Palam at around 7.30am. It was 1,500 meters at Safdarjung. Visibility below 1,000 meters is classified as a shallow fog. “Calm wind conditions meant visibility was low between 7 and 8 am. This then started to improve as the sun came out,” said an IMD official.
