Only seven countries in the world – less than 4% – had air pollution levels at or below the healthy annual level in 2023, a new report has found. Bangladesh, historically among the most polluted countries in. the world and the worst in 2022, with PM2.5 levels more than 15 times higher than WHO standards. Tajikistan and Burkina Faso followed closely. World Health Organization (WHO) issued new, more stringent guidelines on air pollution in September 2021.