NEW DELHI: Delhi was the most polluted city in the country this winter from Oct 1, 2024, to Feb 28, 2025) for the second consecutive year.
The average PM2.5 concentration throughout this period was 159 micrograms per cubic metre, according to a new analysis by the Centre for Research on Energy and Clean Air (CREA). Byrnihat in Meghalaya was the second most polluted city after Delhi with an average PM2.5 of 157 micrograms per cubic metre.
Four National Capital Region cities — Ghaziabad, Gurgaon, Noida and Charkhi Dadri — were among the top 10 most polluted cities in India in the winter season. The analysis covered 238 cities in the country and is based on the Continuous Ambient Air Quality Monitoring Stations (CAAQMS) data from the Central Pollution Control Board, which was available for 80% of the days.
The previous winter (2023-24) too, Delhi had topped the list of polluted cities with a higher average of 171 micrograms per cubic metre. The daily national ambient air quality standard (NAAQS) for PM2.5 is 60 micrograms per cubic metre, while WHO’s daily safe limit is 15 micrograms per cubic metre.
Of the 151 days when Delhi’s average PM2.5 concentration was monitored this winter season, the capital met the NAAQS norm on just eight days. The average PM2.5 levels surpassed 250 micrograms per cubic metre (categorised as severe) on 20 days. The PM2.5 concentration was in the range of 121-250 micrograms per cubic metre on 74 days and 91-120 micrograms per cubic metre on 23 days.
According to the analysis, over the 151-day winter period, 100 cities featured in the top 10 most polluted cities at least once. Of these, 44 cities appeared at least 10 times. Byrnihat had the highest recurrence (111 days), followed by Delhi (105 days), Hajipur (80 days) Ghaziabad (52 days), and Bahadurgarh (47 days).
Aizawl in Mizoram recorded the lowest winter-average PM2.5 level at 7 micrograms per cubic metre, making it the cleanest city in the analysis. The other top 10 least polluted cities had six cities from Karnataka and three from Tamil Nadu.
Manoj Kumar, an analyst at CREA, said, “With all Delhi-NCR cities exceeding NAAQS benchmarks, the persistent severity of winter pollution in the region is evident. The upcoming National Clean Air Programme revision must prioritise source-wise emission load reduction with effective implementation and monitoring to ensure measurable improvements in air quality across the region.”
