Chad and Bangladesh were the world’s most polluted countries in 2024. Average smog levels more than 15 times higher than WHO guidelines. Only Australia, New Zealand, the Bahamas, Barbados, Grenada, Estonia and Iceland made the grade. The WHO recommends levels of no more than 5 mg/cu m, a standard met by only 17% of cities last year. The U.S. State Department has recently ended the scheme, citing budget constraints, with more than 17 years of data removed last week from airnow.gov, including readings collected in Chad. The data gaps, especially in Asia and Africa, cloud the worldwide picture, and many developing countries have relied on air quality sensors mounted on U.s. embassy and consulate buildings to track their smog Levels. The State Department scheme improved air quality in the cities where the monitors were placed, boosting life expectancy and even reducing hazard allowances for U.N. diplomats, meaning that it paid for itself, experts say.