Swiss air-quality monitor IQAir named Loni in Uttar Pradesh the world’s most polluted city in 2025, reporting an annual average PM2.5 concentration of 112.5 micrograms per cubic meter. The figure far exceeds the World Health Organization’s recommended annual guideline of 5 µg/m3.
IQAir’s 2025 data showed three Indian cities among the four most polluted globally: Loni, Byrnihat in the northeast, and the national capital, New Delhi. Byrnihat had previously topped IQAir’s 2024 rankings. The report also noted that the world’s 25 most polluted cities were concentrated across India, Pakistan and China.
At the country level, Pakistan was ranked the most polluted in 2025, with average PM2.5 levels as much as 13 times higher than the WHO guideline. India ranked sixth among countries. Only 13 countries and territories met the WHO annual PM2.5 guideline, underscoring the widespread nature of hazardous air quality in the most affected regions.
PM2.5 — fine particulate matter smaller than 2.5 micrometers — is linked to a range of serious health outcomes, including respiratory and cardiovascular disease. The IQAir findings add to growing evidence and public concern over air pollution in South Asia, where urban and industrial emissions, vehicle exhaust, crop burning, construction dust and meteorological factors combine to produce persistent smog episodes.
The report highlights the need for stronger pollution control measures, stricter emissions standards, and coordinated policy responses at local, state and national levels to reduce exposures and protect public health.