Delhi set to see most polluted December in four years: Here’s why | Delhi News

The average AQI for the month is worse than it has been in recent years – in 2022, the average for December was 319, while it was 336 in 2021, 332 in 2020, and 337 in 2019. The last time a higher average was recorded was in 2018 – 360.

This comes on the heels of November this year being the second most polluted November in Delhi in six years.

The national capital has recorded three days of ‘severe’ (401 to 500) AQI this month, with the figure hitting a high of 450 on December 23, a day after Stage III or the ‘severe’ category of the Graded Response Action Plan (GRAP) was imposed in Delhi-NCR, bringing with it a ban on BS III petrol and BS IV diesel four-wheelers.

Inversion conditions in winter as the temperature falls – cold air remaining trapped close to the surface of the earth by a lid of warm air above it – prevents the dispersion of pollutants since the cold air does not rise. But, Anumita Roychowdhury, Executive Director, Research and Advocacy, at the Centre for Science and Environment, pointed out that this happens every winter and does not explain the higher pollution levels.

“Overall, pollution levels this winter have been high. The first phase of winter, where everyone is talking about stubble burning, is over now. Despite that, pollution levels are high, which is clearly an indicator that pollution in the local and surrounding regions is high. Inversion and slow winds are normal winter phenomena. The volume of activities — vehicles, industrial activities and waste burning in the entire region – all of this is contributing to the trend, showing us that in the coming year, round-the-year action will have to be scaled up significantly to be able to address this issue. As activities increase, action has to keep pace with that change,” Roychowdhury said.

Gufran Beig, founder project-director SAFAR, and chair professor, National Institute of Advanced Studies, pointed to another factor that could be keeping pollution levels higher – large-scale circulation patterns.
“In general, large-scale circulation patterns have reduced the surface wind speed. Last year, these patterns – the La Nina phenomenon – resulted in an increase in wind speed that dispersed pollutants and brought cleaner-than-usual air to Delhi in December,” he said.