Delhi was the most polluted city in terms of air pollution in the last one year, between October 1, 2022, and September 30, 2023. Patna is the second-most polluted city, followed by Muzaffarpur, Faridabad, Noida, Ghaziabad, Meerut, Nalbari, Asansol, and Gwalior, according to a report by Respirer Living Sciences, a sensor-based network providing real-time information on different aspects including air quality, and Climate Trends, a research-based initiative focusing on climate change and environment.
The report said that while there was a marginal improvement in Delhi's air quality, the national capital maintained its position as India's most polluted city. The PM2.5 concentration, or the concentration of particulate matter whose size is 2.5 micrometres, is 100.1 micrograms per cubic metre in Delhi. The World Health Organization's (WHO's) upper safe limit of annual PM2.5 is five micrograms per cubic metre. This means that the PM2.5 concentration in the last one year was more than five times WHO's safe level.
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The Central Pollution Control Board's 'good' PM2.5 level is 30 micrograms per cubic metre. This means that the PM2.5 concentration in Delhi in the previous year was more than three times the 'good' PM2.5 level.
The PM2.5 concentration in Patna in the last one year was 99.7 micrograms per cubic metre. There has been a 24 per cent deterioration in air quality over the last one year.
As many as seven cities are in the list of top 10 polluted Indian cities. Bihar is also a part of the list. Both Delhi-NCR and Bihar are part of the Indo-Gangetic plain, and so many cities situated on this plain being among the list of top 10 polluted cities is indicative of the poor air quality over the plain.
Mumbai's air quality has worsened
October to March are the peak pollution months. Air quality measurements of six major capitals – Delhi, Mumbai, Bengaluru, Kolkata, Lucknow, and Patna – between 2019 and 2023 have shown that the air quality of Mumbai has steadily worsened over the years, while that of Delhi and Lucknow has improved.
A revised version of the Graded Response Action Plan (GRAP), a government air pollution control programme, was brought into force in Delhi-NCR from October 1, 2023.
Indian cities with the cleanest air
Aizawl in Mizoram has the cleanest air in India. The PM2.5 concentration in Aizawl is 11 micrograms per cubic metre.
Aizawl is followed by Chikkamagaluru in Karnataka, Mandikhera in Haryana, and Chamarajanagar, Madikeri, Vijayapura, Raichur, Shivamogga, Gadag, and Mysuru in Karnataka.
As many as eight cities in Karnataka have clean air.