SINGAPORE — Pakistan was ranked the world’s smoggiest country in 2025, with concentrations of hazardous small particles known as PM2.5 up to 13 times higher than the recommended World Health Organization level, research showed Tuesday.
Swiss air quality monitoring firm IQAir said in its annual report that 13 countries and territories kept average PM2.5 levels at the WHO standard of less than 5 micrograms per cubic meter last year, up from seven in 2024. The other 130 out of 143 monitored countries and territories, including the United States, failed to meet the WHO guideline.
Bangladesh and Tajikistan were second and third on the most polluted list. Chad, statistically the smoggiest country of 2024, ranked fourth in 2025, but the decline in PM2.5 concentrations last year is likely to be the result of data gaps.
Last March, the United States shut down a global monitoring program that compiled pollution data collected from its embassy and consulate buildings, citing budget constraints.
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“The loss of the data in March made it appear there was a significant drop in PM2.5 levels (in Chad), but the fact of the matter is that we don’t know,” said Christi Chester Schroeder, lead author of the IQAir report.
The U.S. decision eliminated a primary data source for many smog-prone countries, and Burundi, Turkmenistan and Togo were excluded from the 2025 report because of information gaps.
India’s Loni was the world’s most polluted city in 2025, with average PM2.5 levels of 112.5 micrograms, followed by Hotan in the northwestern Chinese region of Xinjiang at 109.6 micrograms.
The world’s top 25 most polluted cities were all in India, Pakistan and China.
Only 14% of the world’s cities met the WHO standard in 2025, down from 17% a year earlier, with Canadian wildfires driving up PM2.5 across the United States and as far as Europe.
Among the countries that met the standard in 2025 were Australia, Iceland, Estonia and Panama.
Laos, Cambodia and Indonesia all reported significant PM2.5 reductions compared with the previous year, thanks mainly to wetter and windier La Niña weather. Mongolia saw average concentrations fall 31%, to 17.8 micrograms per cubic meter.
In all, 75 countries reported lower PM2.5 levels in 2025 compared with a year earlier, with 54 recording higher average concentrations, IQAir said.
