The Centre for Research on Energy and Clean Air (CREA) in its report, highlighted the severity of winter air pollution in India, revealing that 173 out of 238 cities recorded PM2.5 levels exceeding the National Ambient Air Quality Standards (NAAQS) of 40 µg/m³. Aizawl, Mizoram recorded the lowest winter-average PM2.5 level at 7 µg/m³, making it the cleanest city in the analysis.
Not a single city met the World Health Organisation (WHO) guideline of 5 µg/m³, underscoring the widespread air quality crisis, the report said.
According to the report, Delhi was the most polluted city in India during winter 2024-25, with an average PM2.5 concentration of 159 µg/m³ throughout the season. During the previous winter (2023-24), Delhi also topped the list with a higher average of 171 µg/m³.
Byrnihat in Meghalaya followed closely in winter 2024-25, recording a PM2.5 concentration of 157 µg/m³. Other cities among the top 10 most polluted included Hajipur, Ghaziabad, Gurgaon, Noida, Patna, Asansol, Durgapur, and Charkhi Dadri. The top 10 most polluted cities are located in Bihar, Uttar Pradesh, Haryana, West Bengal, and Assam along with Delhi.
Moreover, none of the 238 cities analysed met the World Health Organisation's (WHO) guideline of 5 µg/m³, emphasising the scale of air quality challenges. Winter refers to the period from October 1, 2024, to February 28, 2025 (winter 2024-25).
On a broader state level, Rajasthan (34 cities), Bihar (24 cities), and West Bengal (7 cities) had all monitored cities exceeding NAAQS. Similarly, Maharashtra (30 out of 31 cities), Odisha (15 out of 16 cities), and Uttar Pradesh (15 out of 20 cities) had a high proportion of cities with winter PM2.5 levels above the national standard.
The report said over the 151-day winter period, 100 cities featured in the top 10 most polluted cities are listed 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, Mizoram recorded the lowest winter-average PM2.5 level at 7 µg/m³, making it the cleanest city in the analysis. The top 10 least polluted cities included six cities from Karnataka, three from Tamil Nadu, and one from Mizoram.
Among the 98 NCAP (National Clean Air Programme) cities with Continuous Ambient Air Quality Monitoring Stations (CAAQMS) data, 78 recorded winter-average PM2.5 levels above NAAQS, while all 98 exceeded the WHO's recommended limit. Similarly, in 140 non-NCAP cities, 95 surpassed NAAQS, and all remained above WHO guidelines. This highlights that air pollution is not limited to NCAP cities but extends to a wider set of urban areas.
"Data gaps remain a challenge in assessing air pollution trends comprehensively. During winter 2024-25, no CAAQMS data was available for any day from stations in Darbhanga, Ernakulam, Hosur, Kochi, Kozhikode, Pathardih, and Thoothukudi. Additionally, 44 cities had less than 80 per cent data coverage, including 21 cities in Haryana. While all 24 cities in Haryana initially had data available at the start of winter, several monitoring stations stopped reporting by December. By the end of the season, only Charkhi Dadri, Faridabad, and Gurgaon met the 80 per cent data coverage threshold, while data from the remaining 21 cities, crucial for assessing winter pollution, was unavailable," the report said.