Delhi's pre-Diwali PM2.5 levels in 2026 reached a three-year high, with an average concentration of 236 µg/m³, marking a 97% increase from 2025.
CSE analysis highlights transport as the largest local pollution contributor, while stubble burning's impact declined closer to Diwali.
Nitrogen dioxide levels peaked during evening rush hours and stayed elevated until midnight, reflecting the impact of traffic congestion.
CSE called for coordinated action across Delhi-NCR to address persistent pollution challenges.
Delhi recorded an average PM2.5 concentration of 236 micrograms per cubic metre (µg/m³) in the week before Diwali this year, the highest for the corresponding period in three years, according to an analysis released by Delhi-based think tank Centre for Science and Environment (CSE) on November 11. The concentration was 97 per cent higher than the 120 µg/m³ recorded in 2025 and 32 per cent above the 179 µg/m³ recorded in 2024.
According to the analysis, Delhi's pre-winter pollution in 2026 was generally higher than in 2025, except for a brief late-September drop caused by rain. In both years, pollution surged in the days leading up to Diwali.
"Diwali pollution is an annual tipping point, but elevated particulate levels before the festival this year show that baseline pollution is higher than in previous years," said Anumita Roychowdhury, executive director, Research and Advocacy, CSE.
Eleven of Delhi's 13 officially designated pollution hotspots recorded lower PM2.5 concentrations between October 1 and November 8 compared with the same period in 2025. Anand Vihar registered the largest decline, at 49 per cent, followed by Wazirpur (41 per cent), Ashok Vihar (40 per cent) and Bawana (22 per cent).
Jahangirpuri and Punjabi Bagh, however, recorded increases of 2 per cent and 1 per cent, respectively. Jahangirpuri remained the most polluted designated hotspot, with an average PM2.5 concentration of 163 µg/m³.
Several areas outside the designated hotspot network also recorded high pollution levels. Vivek Vihar had an average PM2.5 concentration of 144 µg/m³, followed by Sonia Vihar (139 µg/m³), ITO (137 µg/m³) and Delhi Technological University (135 µg/m³). NIH Narela and NSUT Jaffarpur recorded 122 µg/m³ and 111 µg/m³, respectively.
The rise in pollution extended across the National Capital Region (NCR), with Delhi, Gurugram, Faridabad, Noida, Ghaziabad and Greater Noida recording a sharp increase in PM2.5 levels in early November after a relatively less polluted September.
An analysis of data from the Indian Institute of Tropical Meteorology's (IITM) Decision Support System (DSS) for November 1-8 found that pollution transported from neighbouring National Capital Region (NCR) districts accounted for 54.43 per cent of Delhi's PM2.5 burden. Local sources accounted for 33.06 per cent, while stubble burning contributed 14.29 per cent.
In fact, the contribution of stubble burning declined as Diwali drew closer. On November 1, stubble burning accounted for 11.5 per cent of Delhi's PM2.5 levels, falling to 8.6 per cent the following day. The contribution peaked at 16.2 per cent on November 4.
On November 6, when the city's air quality index (AQI) reached 382 and Stage III of the Graded Response Action Plan (GRAP) was invoked, farm-fire smoke accounted for around 8 per cent of PM2.5 pollution.
Among Delhi's local pollution sources, transport was the largest contributor, accounting for 52 per cent. Residential activities contributed 13 per cent, followed by peripheral industries at 11 per cent. Construction accounted for 7 per cent, while energy use and waste burning contributed 5 per cent each. Road dust and other sources accounted for 4 per cent each.
"Among local sources, transport remains the largest contributor," said Roychowdhury.
Emergency traffic restrictions introduced in Delhi in early November did not significantly reduce weekday congestion, the CSE analysis found.
During November 2-6, the average daily Travel Time Index (TTI) stood at 2.40, compared with 2.38 on October 30, the last working day before the restrictions came into effect. The evening peak TTI was also almost unchanged at 3.49, against 3.48 on October 30. TTI compares travel times during congested periods with those under free-flow conditions. Commuters continued to take 13 per cent longer to complete journeys than on standard weekdays between January and April 2026. During evening rush hours, journeys took 13-31 per cent longer.
The hourly congestion pattern during the restriction period also remained similar to that before the curbs. Morning peak congestion was 1 per cent higher, while evening peak congestion remained unchanged. The Planning Time Index (PTI), which measures the additional time commuters need to allow to complete 95 per cent of their journeys, improved only marginally during evening hours, from 6.36 to 6.16.
The analysis also compared traffic patterns during Holi and Diwali in 2026. While congestion fell 46 per cent below a normal weekday on Holi, Diwali traffic was 29 per cent below a typical Sunday, with afternoon congestion remaining higher due to last-minute shopping and social visits.
Shubham Srivastava, deputy programme manager, Clean Air and Sustainable Mobility, CSE, said the restrictions had failed to flatten rush-hour peaks.
Nitrogen dioxide (NO2), nearly 80 per cent of which is emitted by vehicles, also rose during the evening rush hour and remained elevated until midnight, according to the analysis of October 30-November 9 data.
NO2 levels peaked at 67 µg/m³ at 7 pm and remained above 55 µg/m³ until midnight. The daily average increased by about a third from November 2, even as traffic congestion remained largely unchanged.
"In effect, the evening rush loads the air and the still night air keeps it there," said Sharanjeet Kaur, deputy programme manager, Urban Lab, CSE.
Roychowdhury said Delhi-NCR needed sustained emission reductions across all major sectors and coordinated action across the region's airshed. She said the continued reliance on emergency GRAP restrictions reflected the failure of routine pollution-control measures.
Srivastava said clean-air plans also needed to address the volume of vehicles on roads rather than focus primarily on tailpipe technology and traffic management. Vehicles emit more pollutants per kilometre when they idle or move slowly through congestion, he said. CSE called for greater investment in mass public transport, mandatory trip-reduction measures and stricter restraints on private vehicle use.