Winter pain: How Delhi’s pollution spikes are mirroring traffic hours

NEW DELHI: A new analysis of early winter trends in Delhi-NCR by Centre for Science and Environment (CSE) revealed that particulate matter 2.5 rose and fell almost in tandem with nitrogen dioxide during morning (7-10 am) and evening (6-9 pm) hours, as both pollutants surged with traffic emissions before being trapped near the surface by shallow winter boundary layers.

While carbon monoxide showed sharper, more immediate peaks linked to vehicular plumes, PM2.5 displayed broader peaks as fine particles accumulated and dispersed more slowly. Carbon monoxide, another highly toxic pollutant that curdles the blood and is predominantly emitted by vehicles, showed widespread exceedances across Delhi this winter, said CSE.




Nearly 22 monitoring stations in Delhi recorded carbon monoxide levels above the 8-hour standard on more than 30 out of 59 days, beginning Oct 1, indicating persistent traffic-linked emissions. Dwarka Sector 8 was the worst affected, with 55 exceedance days, followed by Jahangirpuri and DU North Campus (50 days each).

This synchronised pattern clearly demonstrates that the daily particulate pollution spikes are closely reinforced by traffic-related emissions of both nitrogen dioxide and carbon monoxide, especially under low-dispersion winter conditions. "This cocktail of pollutants also makes the air more toxic to breathe. Yet, every winter, anti-pollution efforts are dominated by dust-control measures with feeble action against polluting vehicles and industry as well as burning of waste and solid fuel," said Anumita Roychowdhury, executive director, research and advocacy, CSE.

Since the contribution of farm fires to Delhi's pollution has decreased this year, it means local sources are adding to the foul air, the organisation said. Peak levels of pollution during early winter were lower compared to the previous year due to less farm fires, but average winter trends have remained nearly the same.

"Since 2022, the annual trend in PM2.5 levels plateaued and even took an upward turn, showing plateauing of pollution at an elevated level. Between 2018 and 2020 (start of the pandemic), there was a steady decline in year-on-year PM2.5 levels in Delhi. But from 2021-22, the levels have remained largely elevated and stable with slight variations," said CSE, adding that Delhi continues to breathe extremely polluted air throughout the year, with no sustained downward trend.

The report found that several NCR cities remained just as polluted, and often worse. A region-wide smog episode affected NCR towns, but it was Bahadurgarh that endured the most persistent conditions, with the episode lasting a full 10 days — from Nov 9 to 18. "Smaller towns in the region display more intense and longer smog build-up. Even though peak pollution spikes are lower this winter due to lesser contribution of farm fires, the airshed is getting increasingly more saturated," said Sharanjeet Kaur, deputy programme manager, urban lab, clean air unit, CSE.

To deal with pollution, the report recommends meeting electrification targets for all segments of vehicles in a time-bound manner and replacing older vehicles. It proposes upscaling integrated public transport with last-mile connectivity and walking and cycling infrastructure, restraining the use of personal vehicles with the help of parking caps and congestion tax. It recommends encouraging the industry to switch over to affordable cleaner fuels, closing the waste loop to stop burning, ensuring access to clean fuels for households and decomposing or ploughing straw back into the soil to increase soil carbon.

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