Loni, a city on the northeastern edge of Delhi, recorded the world’s highest average PM2.5 concentration in 2025, according to IQAir. Its annual average was 112.5 micrograms per cubic metre (µg/m³), about 23% higher than the previous year and 22 times the World Health Organization’s recommended annual guideline of 5 µg/m³.

IQAir assessed data from more than 9,400 cities across 143 countries, drawing on measurements from over 40,000 air-quality monitoring stations. The rankings cover PM2.5, fine particles smaller than 2.5 micrometres that can penetrate deep into the respiratory system and enter the bloodstream. The report cautions that readings come from specific monitoring points, so they do not provide a complete picture of pollution across an entire city or region. They also do not account for other types of air pollution.

The five cities with the highest reported annual PM2.5 levels were Loni, India (112.5 µg/m³); Hotan, China (109.6); Byrnihat, India (101.1); Delhi, India (99.6); and Faisalabad, Pakistan (98.8).

Loni is described as a commuter and low-wage manufacturing centre, with small businesses producing textiles, leather goods, plastics, packaging and car parts. Local media reports cited by the article identify the burning of electronic waste to recover metals, open rubbish fires, illegally used coal, diesel generators, and dust from unpaved roads and construction sites as contributing factors.

In Byrnihat, an industrial town in the northeastern Indian state of Meghalaya, a national environmental research institute identifies industry and road dust as major sources of fine-particle pollution. The town’s location among hills also makes air circulation more difficult, the report says. Faisalabad, meanwhile, is a major textile hub, with local industry also including chemicals, fertilisers, paper and food processing.

In Europe, IQAir recorded the highest PM2.5 level in the Turkish city of Iğdır, at 64.4 µg/m³. Authorities point to its position in a low-lying basin near Mount Ararat and the area’s dry climate as disadvantages for air quality. Within the European Union, the highest reported reading was in Slavonski Brod, Croatia, at 27.2 µg/m³. Local authorities identify household heating with solid fuels such as wood as a key source, alongside traffic and industry.

Sources: Handelsblatt.