'Delhi's location makes it vulnerable': Study says 65% of city's air pollution in 2025 came from outside

About two-thirds of Delhi's air pollution in 2025 came from outside the city, largely from nearby NCR areas and neighbouring states, news agency PTI reported, citing an analysis by the Centre for Research on Energy and Clean Air (CREA). 

Data for the winter months showed that around 65% of Delhi's PM2.5 pollution originated outside the national capital, while about 35% came from sources within the city.

"Transboundary pollution from NCR districts and neighbouring states plays a major role in Delhi's air pollution. Delhi's location makes it vulnerable, as winds from the north and north-west carry polluted air from nearby regions into the city. Addressing Delhi's pollution crisis, therefore, requires coordinated, airshed-level action rather than city-specific measures alone," Manoj Kumar N, an analyst with CREA, was quoted as saying.

Although pollution from outside Delhi was the main contributor overall, the study found that vehicles were the biggest source of pollution generated within the city during winter. Vehicular emissions made up nearly half of Delhi’s local PM2.5 pollution, more than pollution from industries, construction activity and other combustion sources combined.

The analysis also showed a clear fall in pollution from crop-residue burning during the 2025 winter season. Compared with 2024, the contribution of stubble burning to PM2.5 levels dropped by about 10.6%.

During the crop-residue-burning period from October 15 to November 30, stubble burning contributed an average of 4.9% to Delhi’s PM2.5 pollution in 2025. This was much lower than the 15.5% recorded during the same period in 2024.

Daily data showed that the highest stubble-burning contribution in 2025 was 22.47% on November 12. This was followed by 16.48% on November 15 and 16.14% on November 17.

In 2024, the figures were much higher, with stubble burning contributing 37.52% on November 15, 35.18% on November 1 and 33.33% on November 14.

Among NCR areas, Bahadurgarh was the biggest external contributor to PM2.5 pollution in 2025. It recorded the highest levels in January, October, November and December, with an annual average PM2.5 concentration of about 173 micrograms per cubic metre.

Within Delhi, November was the most polluted month in 2025 for fine particulate matter. The city recorded an average PM2.5 concentration of 215 micrograms per cubic metre during the month. In November 2024, PM2.5 levels were even higher, with a monthly average of 249 micrograms per cubic metre.

Over the full year, Delhi’s average PM10 concentration dropped to about 197 micrograms per cubic metre in 2025 from 211 micrograms per cubic metre in 2024. This marked a decline of about 6.6%.

Air Quality Index data showed some improvement in 2025. Delhi’s annual average AQI stood at 201, and the city did not record a single ‘good’ air quality day.

During the year, Delhi recorded 79 satisfactory days, 121 moderate days, 86 poor days, 71 very poor days and eight severe days. In comparison, 2024 had 66 satisfactory days and 17 severe days, while the number of very poor days remained almost the same at around 70. According to the analysis, the small improvement seen in 2025 was mainly due to better air quality during June and July, which helped bring down the annual average AQI.

(With inputs from PTI)