Only seven countries met the World Health Organisation’s (WHO) air quality standards in 2024, according to new data released on Tuesday. 

Researchers have warned that the fight against air pollution is set to become even more challenging following the United States’ decision to halt its global air quality monitoring efforts.

Chad and Bangladesh recorded the highest pollution levels last year, with average smog concentrations exceeding WHO guidelines by more than 15 times, according to Swiss air quality monitoring firm IQAir.

According to IQAir, only Australia, New Zealand, the Bahamas, Barbados, Grenada, Estonia, and Iceland maintained air quality within the WHO’s recommended limits.

Significant data gaps, especially in Asia and Africa, cloud the worldwide picture, and many developing countries have relied on air quality sensors mounted on US embassy and consulate buildings to track their smog levels.

However, the State Department has recently ended the scheme, citing budget constraints, with more than 17 years of data removed last week from the US government’s official air quality monitoring site, airnow.gov, including readings collected in Chad.

“Most countries have a few other data sources, but it’s going to impact Africa significantly, because oftentimes these are the only sources of publicly available real-time air quality monitoring data,” said Christi Chester-Schroeder, IQAir’s air quality science manager.

Data concerns meant Chad was excluded from IQAir’s 2023 list, but it was also ranked the most polluted country in 2022, plagued by Sahara dust as well as uncontrolled crop burning.

Average concentrations of small, hazardous airborne particles known as PM2.5 hit 91.8 micrograms per cubic metre (mg/cu m) last year in the country, slightly higher than 2022.

The WHO recommends levels of no more than 5 mg/cu m, a standard met by only 17% of cities last year.

India, fifth in the smog rankings behind Chad, Bangladesh, Pakistan and the Democratic Republic of Congo, saw average PM2.5 fall 7% on the year to 50.6 mg/cu m.

But it accounted for 12 of the top 20 most polluted cities, with Byrnihat, in a heavily industrialised part of the country’s northeast, in first place, registering an average PM2.5 level of 128 mg/cu m.

Climate change is playing an increasing role in driving up pollution, Chester-Schroeder warned, with higher temperatures causing fiercer and lengthier forest fires that swept through parts of South East Asia and South America.

Christa Hasenkopf, director of the Clean Air Program at the University of Chicago’s Energy Policy Institute (EPIC), said at least 34 countries will lose access to reliable pollution data after the US programme was closed.

The State Department scheme improved air quality in the cities where the monitors were placed, boosting life expectancy and even reducing hazard allowances for US diplomats, meaning that it paid for itself, Hasenkopf said.

“(It) is a giant blow to air quality efforts worldwide,” she said.