CSE study: Vehicles key culprit behind pollution load

While Delhi remains highly polluted, the analysis said many NCR cities performed just as poorly or worse.

Gases such as nitrogen dioxide (NO2) and carbon monoxide (CO) have shown significant spikes in Delhi-NCR in a new analysis of early winter trends, surging with traffic emissions trapped under shallow winter boundary layers. These findings, experts said, point to the strong influence that traffic-related emissions have on Delhi’s daily pollution spikes.

Dense early-morning fog seen in Dwarka on Monday. (Vipin Kumar/HT Photo)

The analysis by the Centre for Science and Environment (CSE), released Monday, also noted that while peak pollution levels have been lower this early winter compared to previous years, the average pollution levels remain largely unchanged.

The study, covering the period from October 1 to November 15, found PM2.5 rising and falling almost in tandem with NO2 during morning (7-10am) and evening (6-9pm) hours – a clear indication of the impact of traffic emissions and congestion.

CSE said NO2 displayed sharper, more immediate peaks linked directly to vehicular plumes, while PM2.5 showed broader peaks as fine particles accumulated and dispersed more slowly. CO, which is also predominantly emitted from vehicles, showed widespread exceedances across Delhi this winter. More than half (22) monitoring stations recorded CO levels above the eight-hour standard on more than 30 of the 59 study days, pointing to persistent traffic-linked emissions. Delhi has a total of 40 air quality stations.

Experts said the synchronised pattern across pollutants demonstrates that daily particulate spikes are closely reinforced by traffic-generated emissions – especially at a time when government action, and public attention appears to gravitate towards other factors such as farm fires etc.

“This cocktail of pollutants also makes the air more toxic to breathe. Yet, every winter, pollution control efforts are dominated by dust control measures with feeble action on vehicles, industry, waste, and solid fuel burning,” said Anumita Roychowdhury, executive director for research and advocacy at CSE.

The analysis found lower peak levels this year but cautioned that this was largely because the contribution of farm fires was reduced, meaning local sources continued to play a major role.

“Both the average and the peak levels are less compared to the previous three winters. The October-November PM2.5 average is about 9% lower than the previous year, and even the worst peaks appear slightly lower,” the study noted.

CSE also observed that since 2022, Delhi’s annual PM2.5 levels have plateaued or risen slightly after earlier declines. Between 2018 and 2020 – including the pandemic year – Delhi recorded steady year-on-year drops in PM2.5. Since 2021-22, however, pollution levels have remained elevated and largely unchanged. “But when compared to the three-year baseline for early winter, the average hasn’t changed at all, it has plateaued at the same unhealthy level. Winter looks better only when compared to last year’s extreme; in real terms, pollution remains consistently high,” said Sharanjeet Kaur, deputy programme manager at CSE’s Urban Lab.

Dipankar Saha, former head of CPCB’s air laboratory, said vehicles and road congestion are year-round sources of pollution in Delhi, with their impact exacerbated during the winter months due to unfavorable meteorological conditions. “This leads to accumulation particularly around traffic intersections,” he said.

While Delhi remains highly polluted, the analysis said many NCR cities performed just as poorly or worse. A region-wide smog episode affected several towns, with Bahadurgarh recording significantly higher smog intensities.

To address the persistent crisis, CSE recommended time-bound electrification of all vehicle segments, scrapping and replacing older vehicles, expanding integrated public transport with strong last-mile connectivity, and building walking and cycling infrastructure. It also called for measures to restrain personal vehicle use through parking caps, pricing, and congestion taxes; switching industries to cleaner fuels; ending waste burning; improving access to clean household fuels; and managing crop residue by decomposing or ploughing straw back into the soil.