Delhi's air quality falls to ‘poor’ levels ahead of Diwali — Here’s why

After the withdrawal of the monsoon and ahead of the onset of winter, Air pollution in Delhi is again rising, breaching the ‘poor’ category on Tuesday with a reading of 201. In addition, the Centre’s Air Quality Early Warning System (EWS) predicted that the Air Quality Index will remain in the “poor” category till this week.

This marks the first instance where the air quality of the national capital has crossed the “poor” quality since June 11, when Delhi last recorded an AQI of 245. “Delhi’s air quality is very likely to be in the ‘poor’ category from October 14 till October 16. The outlook for the subsequent six days shows the air quality is likely to be between the ‘poor’ to ‘very poor’ categories,” EWS projections released on Monday said.

The Central Pollution Control Board (CPCB) said Delhi's AQI stood at 169 at 9 am on Monday, rising to a 24-hour average of 189 by 4 pm. This was a 22-point increase from Sunday's AQI of 167.

Why does air quality drop to the ‘poor’ category?

The air quality in Delhi typically deteriorates in October, following the retreat of the southwest monsoon, which brings lower temperatures and reduced wind speeds. This season shift also coincides with stubble burning in nearby states, festive firecracker use, and stagnant air conditions that trap pollutants near the surface.

Mahesh Palawat, vice president at Skymet meteorology, told HT that wind speeds dropped to between 6-10 km/hr on Monday, slowing the dispersion of pollutants. “Wind direction is westerly to northwesterly, and there will be marginal stubble intrusion. We don’t expect a significant change in terms of weather, with similar wind direction and low wind speed to persist,” Palawat said.

However, stubble burning is not yet a major contributor to the current spike. Data from the Decision Support System (DSS), which tracks the sources of Delhi’s PM2.5 pollution, indicated that farm fires contributed only 0.62 per cent to the city’s PM2.5 levels on Monday, a slight rise from 0.24 per cent the day before.