A recent analysis by the Centre for Research on Energy and Clean Air (CREA) shows that as of April 2025, over 90 percent (248 out of 273) of cities in India have already overshot the World Health Organization’s (WHO) annual PM2.5 guideline levels, based on pollution trends from January to April. This means that even if these cities recorded near-zero pollution levels for the rest of the year, they would still fail to meet the annual PM2.5 guideline of 5 µg/m³.
The “overshoot day” is defined as a day when the average pollution levels preceding that day are so high that even a 0.1 μg/m³ daily concentration of the pollutant for the remaining days of the year would ensure non-compliance of the city to the prescribed annual standard or guideline.
In January and February 2025, 109 cities each overshot the WHO annual PM2.5 standard, followed by 24 cities in March and six more cities in April. The sequential overshoot in different cities across the country emphasises that the issue is widespread rather than confined to a few regions in India. Despite several cities being among the most polluted in the country, only few are currently included in the National Clean Air Programme (NCAP). Thus, for other cities with persistent severe air quality issues, there are currently no action plans to reduce pollution levels.
However, when assessed against India’s National Ambient Air Quality Standards (NAAQS), only one city (Byrnihat) overshot the annual PM2.5 limit during January to April 2025 period. This contrast emphasizes the gap between national standards and global health-based guidelines.
Manoj Kumar, Analyst at CREA, said, “India must update its National Ambient Air Quality Standards to reflect the latest scientific findings and better align with the World Health Organization’s interim targets. The current standards, established more than a decade ago, are lenient and continue to contribute to significant health impacts and economic losses.”
April 2025 Monthly Snapshot:
Of the 248 cities with over 80 percent of data from Continuous Ambient Air Quality Monitoring Stations (CAAQMS), 227 cities met NAAQS for PM2.5, which is set at 60 µg/m³. However, only seven cities complied with the WHO daily safe guideline of 15 µg/m³.
Byrnihat in Assam/Meghalaya border emerged as the most polluted city in April 2025, with a monthly average PM2.5 level of 119 µg/m³, exceeding the NAAQS on 80 percent of the days. Byrnihat experienced 13 days in the ‘Very Poor’ PM2.5 AQI category, six days in ‘Poor’, five days in ‘Moderate’, and only six days in the ‘Satisfactory’ category.
Delhi ranked as the fifth most polluted city, with a monthly average PM2.5 concentration of 77 µg/m³. Throughout April, Delhi experienced 16 days in the ‘Moderate’ category, nine in ‘Poor’, and five in ‘Satisfactory’.
Other cities in the top 10 most polluted list include Siwan, Rajgir, Ghaziabad, Gurgaon, Hajipur, Baghpat, Aurangabad, and Sasaram. Bihar dominated the list with five entries, followed by Uttar Pradesh (two cities), and one city each from Assam, Haryana, and Delhi. Bihar also recorded the highest number of cities exceeding NAAQS with six cities, including five in the ‘Moderate’ and one in the ‘Poor’ category.
Gadag in Karnataka was India’s cleanest city, with a monthly PM2.5 average of just 6 µg/m³. The top 10 cleanest cities featured four from Karnataka, two from Tamil Nadu, and one each from Mizoram, Tripura, Andaman and Nicobar Islands, and Uttar Pradesh.