Delhi Minister for Environment Gopal Rai launches the ‘Patake Nahi, Diya Jalao’ [Light up lamps, not crackers] campaign to motivate people to embrace tradition and eliminate pollution, in New Delhi. Image Credit: ANI

New Delhi: Favourable weather conditions led to a rare drop in pollution in India’s capital New Delhi, with residents last month breathing the cleanest air in at least four years but the authorities are warning that air quality is set to drop sharply in November.

A delayed end to the monsoon, intermittent rains and a sharp pick-up in wind speeds ensured that the concentration of hazardous, small airborne particles known as PM2.5 in a cubic metre of air averaged 72 in October when air quality typically takes a turn for the worse.

That was sharply down from an average concentration of 126 recorded in October 2020 - 25 times over the World Health Organization’s safe limit - according to data gathered by the state-run Central Pollution Control Board.

But a confluence of factors, including falling temperatures, a drop-off in winter wind speed and farmers preparing to torch farm waste of the previous rice crop to ready the field for planting the wheat crop, is likely to turn the air hazardous.

“Because of frequent rains, most farmers didn’t get to burn crop stubble, and now they have an even shorter window to dispose of crop waste,” said Anumita Roychowdhury, an executive director at the Centre for Science and Environment think tank.

“As rains ebb, more and more farmers will rush to burn rice stubble, and that will happen when broader weather patterns will allow pollutants to hang in the air, resulting in a thick smog,” Roychowdhury said.

Adding to the concerns, the Diwali festival of lights falls on Thursday when Indians will set off firecrackers as part of an ancient Hindu tradition.

Delhi has banned the sale of firecrackers, but authorities rarely get to enforce such curbs.

“The October air was clean, but we’re really worried about November,” said a senior government official involved in framing policies to curb air pollution. “Stubble burning could peak right after Diwali.” Crop waste burning accounts for about a quarter of air pollution in October and November.

In its outlook for the subsequent five days, the Air Quality Early Warning System for Delhi, that comes under the Ministry, said that the air quality is likely to deteriorate on November 5 and 6 significantly and may reach the upper end of the “very poor” category. PM2.5 to be the predominant pollutant.

“From November 4 onwards, the wind direction will change from the present easterly to north-westerly which are highly favourable to the intrusion of stubble burning,” System of Air Quality and Weather Forecasting And Research (SAFAR) founder and project director Gufran Beig told IANS.

“Even if 50 per cent of the firecrackers burst in 2020 happen to be lit this Diwali, then the air quality will deteriorate to ‘severe’, and without crackers, the air quality will settle at upper end of ‘very poor’ on November 5 and 6,” he added.

Delhi’s air quality on Monday morning was pegged at the “very poor” category with its AQI settling at 302 and by evening, it increased to 306.

The level of PM 2.5 and PM 10 pollutants in the air this morning stood at 122 and 256, respectively, whereas by evening, the level of PM 2.5 pollutants increased to 128, according to the SAFAR.

“Delhi’s AQI is in the ‘very poor’ category and likely to improve to upper end of ‘poor’ for Monday (November 1) and Tuesday (November 2) due to expected change in wind direction to westerly/south-westerly reducing transport of emissions from stubble burning. Isolated rainfall is likely in upwind region that would improve air quality. Share of crop residue burning emissions in PM2.5 is about 8per cent (Effective fire count 1,734). Prevailing shallow mixing layer height reduces dispersion of pollutants,” SAFAR stated this morning.

Air quality of Delhi starts deteriorating as winter approaches the national capital due to stubble burning in the state of Uttar Pradesh, Haryana, and Punjab. It often leads to a rise in toxicity by increasing the level of PM 2.5 and PM 10 pollutants in the city’s air.