Byrnihat, Delhi Most Polluted Cities in First Half of 2025

A new analysis by the Centre for Research on Energy and Clean Air (CREA) has found that Byrnihat, on the Assam-Meghalaya border, was the most polluted city in India from January to June 2025, with Delhi following closely behind. The study is based on air quality data from the Continuous Ambient Air Quality Monitoring Stations (CAAQMS) across 293 Indian cities. The report highlights serious concerns about air pollution, especially in urban areas.

Report Highlights: Top Polluted Cities

According to the report, Byrnihat recorded an average PM 2.5 level of 133 micrograms per cubic metre (ug/m3), far exceeding the national safe limit of 40 ug/m3. Delhi followed with an average of 87 ug/m3, ranking it as the second most polluted city in the country.

Other highly polluted cities included Hajipur (Bihar), Ghaziabad (Uttar Pradesh), and Gurgaon (Haryana). The report also listed Sasaram, Patna, and Rajgir in Bihar, as well as Talcher and Rourkela in Odisha among the top 10 most polluted cities.

What is PM 2.5 and Why It Matters

PM 2.5 refers to tiny air particles that are 2.5 micrometres or smaller in size. These particles can go deep into the lungs and even enter the bloodstream, causing serious health issues such as asthma, heart disease, and respiratory infections. The National Ambient Air Quality Standards (NAAQS) recommend a safe level of 40 ug/m3 for PM 2.5, but many cities have far exceeded this limit.

Data Source and Monitoring Details

The CREA study used data from CAAQMS, which monitor air quality in 293 cities. Of these,

• 122 cities exceeded India’s national air quality standards.
• 117 cities stayed within the safe limit.
• 259 cities had already crossed the yearly PM 2.5 limit by June, indicating they will likely remain in the unsafe zone for the rest of the year.
• Under the National Clean Air Programme (NCAP), 131 cities are being monitored, and 98 of them have CAAQMS installed.

Cleanest Cities in India

On the brighter side, Aizawl, the capital of Mizoram, was named the cleanest city with an average PM 2.5 level of 8 ug/m3, though still slightly above the World Health Organization (WHO) safe level of 5 ug/m3.

Other clean cities included,

• Tirupur and Tirunelveli in Tamil Nadu
• Bareilly and Vrindavan in Uttar Pradesh
• Maihar in Madhya Pradesh
• Imphal in Manipur
• Chamrajanagar and Chikkamagaluru in Karnataka