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 (µg/m3). That level is far above the World Health Organization’s recommended annual guideline of 5 µg/m3.
IQAir’s 2025 rankings placed three Indian cities among the four most polluted globally: Loni, Byrnihat in the northeast and the national capital, New Delhi. Byrnihat had been the top city in IQAir’s 2024 list. The report also found that the world’s 25 most polluted cities are concentrated across India, Pakistan and China.
At the national level, Pakistan ranked as the most polluted country in 2025, with average PM2.5 concentrations up to roughly 13 times the WHO guideline. India ranked sixth among countries. Only 13 countries and territories met the WHO annual PM2.5 guideline, underscoring how widespread hazardous air quality remains in the hardest-hit regions.
PM2.5 — fine particulate matter smaller than 2.5 micrometers — is associated with a range of serious health effects, including respiratory and cardiovascular disease. IQAir’s findings reinforce growing evidence and public concern about air pollution in South Asia, where urban and industrial emissions, vehicle exhaust, crop burning, construction dust and meteorological conditions combine to produce persistent smog.
The report calls for stronger pollution controls, tighter emissions standards and coordinated policy responses at local, state and national levels to reduce exposures and protect public health.