Only 14% of cities worldwide met the World Health Organization's (WHO) air quality recommendations in 2025, according to Swiss company IQAir, cited by Report.
IQAir found that just 14% of cities complied with WHO guidelines, limiting the annual average concentration of PM2.5 particles to 5 micrograms per cubic meter. In 2024, the figure was 17%.
The study analyzed data from 9,446 cities across 143 countries and territories. Only 13 countries and territories met the recommended PM2.5 levels: Australia, Andorra, Bermuda, US Virgin Islands, Grenada, Iceland, New Caledonia, Panama, Puerto Rico, Barbados, Réunion, French Polynesia, and Estonia.
Nieuwoudtville, South Africa, was ranked the cleanest city with the lowest PM2.5 concentration.
Countries with the highest air pollution included India, Bangladesh, Tajikistan, Chad, and the Democratic Republic of Congo. Loni, in India"s Uttar Pradesh state, was the world's most polluted city, with PM2.5 levels 22 times above WHO guidelines.
The report noted that 54 countries saw increases in annual PM2.5 levels, 75 countries saw decreases, two countries remained unchanged, and 12 countries added new data.
Wildfires, worsened by climate change, were a major factor in the global decline in air quality in 2025.
"New data shows global air quality progress stalling as wildfire smoke and climate change intensify global air pollution. Despite some regional improvements, major data gaps remain, with only a fraction of the global population having access to hyper-local, real-time air quality information," IQAir said
PM2.5 particles are tiny pollutants produced by burning fossil fuels. They can enter the bloodstream through the lungs and affect nearly every organ, and have been linked to a wide range of health issues, including diabetes and cancer.