Delhi had the highest PM (Particulate Matter) 2.5 levels in the country in the month of October and has been experiencing a consistent upward trend since 2021, according to the Respirer Report. The report, on analysis of air quality over the past five years, said that while air pollution has increased in the country's four major cities, it has fallen in state capitals like Lucknow and Patna, according to a recent report.

It indicates that while Delhi, Mumbai, Hyderabad and Kolkata saw PM 2.5 levels higher in October 2023, compared to a year ago, Chennai saw a fall of over 23 per cent compared to a year ago. The study analysed PM 2.5 concentrations between 2019 and 2023 in eight of India's major state capitals-- Delhi, Mumbai, Chennai, Kolkata, Bengaluru, Lucknow and Patna.