Delhi is poised to end 2025 with a slightly lower annual average concentration of PM2.5 pollutants compared to the last few years owing largely to a prolonged and abundant monsoon, showed data from the Central Pollution Control Board (CPCB).
However, this statistical figure masks the extremes in pollution levels that the city has encountered this year. This means that the gains delivered by an exceptionally wet monsoon were entirely undone by a brutally polluted winter.
CPCB data from January 1 to December 28 shows the city’s average PM2.5 concentration at 95.31 micrograms per cubic metre (µg/m³). While this figure is marginally better than the consistent 100+ µg/m³ averages of recent years – and marks the lowest since the Covid-19 lockdown year of 2020 (94.93 µg/m³) – it remains alarmingly high. It is more than 2.5 times India’s annual safe standard of 40 µg/m³ and nearly six times the World Health Organization’s stricter guideline of 15 µg/m³.
The annual average for 2024 was 104.51 µg/m³. Prior to that, the averages were 100.48 µg/m³ in 2023, 98.27 µg/m³ in 2022, and 105.24 µg/m³ in 2021. Before the pandemic, Delhi’s air was consistently worse, with averages like 108.54 µg/m³ in 2019 and a peak of 135.22 µg/m³ in 2016.
Experts, however, unanimously attribute the slight dip in the annual number not to transformative policy action, but to favourable meteorology. And that too, they said, was undone when the city experienced hazardous air in November and December.
“Meteorological conditions have largely been favourable in several months, including the early summer period. May was the wettest ever on record for Delhi,” said Mahesh Palawat, vice president at Skymet. “We saw excess rains in October and an early Diwali, which may have reduced the overall impact – typically seen in November when meteorological conditions are unfavourable,” Palawat said, adding while wind speeds were better through November, they have been unfavourable in December – making it a highly polluted month.
India Meteorological Department (IMD) records reveal an extraordinary streak of excess rainfall from May through October. This year’s May 2025 was the wettest ever recorded, with 186.4 mm of rain (over six times the normal). August, meanwhile, was the wettest in 15 years, with 400.1 mm (72% above normal). Even October, which is a post-monsoon month, saw nearly six times its usual rainfall.
This relentless rain scrubbed the air, settling dust and pollutants for months. The benefit is clearly seen in PM10 (coarse particle) levels, with the annual average falling to 196.51 µg/m³ from 212.08 µg/m³ last year, though it is still over three times the safe limit.
However, the clean-air reprieve ended abruptly. November and December recorded zero rainfall. With the arrival of winter and stagnant wind conditions, pollution skyrocketed. December is on track to be Delhi’s most polluted since 2018, with an average PM2.5 concentration of 207 µg/m³ for the first 27 days, according to the Centre for Research on Energy and Clean Air (CREA).
The modestly improved annual average, experts said, tells a deceptive story. It smooths over the extreme peaks that impact public health.
“While marginal improvements in the overall average indicate overall progress, the gains made possibly in the monsoon season… mean nothing when residents face extreme pollution levels,” said Dipankar Saha, former head of CPCB’s air laboratory.
He said that even in 2020, with drastically reduced emissions during lockdowns, pollution levels remained above national standards. “This shows our background emissions are high and we remain dependent on favourable meteorological conditions,” Saha stated, emphasizing that consistent, cross-NCR on-ground action needs to intensify.
Complicating the picture are questions about data accuracy. An HT analysis in November flagged missing data sets, suspicious measurement patterns, and algorithmic loopholes in calculating Delhi’s average AQI, suggesting reported values may not fully reflect worse ground-level conditions — meaning the actual air quality could be significantly worse.
More recently, HT had reported on December 30 how the capital is on track to record its most polluted December since 2018. The average AQI this month stands at 349. It was last higher in 2018, when the average AQI was 360. An analysis by the Centre for Research on Energy and Clean Air (CREA) for December 1-27 reveals Delhi has recorded an average PM2.5 concentration of 207µg/m³ – making it a highly polluted end to the year.