One country has half of the world's 20 most polluted cities - and it’s not China

New Delhi is no longer the world’s most polluted city, but India continues to afflicted by air pollution, being home to four of the 10 cities with the worst air pollution levels, according to new data from the World Health Organisation.

Zabol in Iran had the dirtiest air in the world in terms of PM2.5 levels, followed by four Indian cities: Gwalior, Allahabad, Patna and Raipur. Overall, 10 Indian cities figured in the list of world’s 20 most polluted cities. In contrast, China, which has also been plagued by air pollution, only had four cities in the top 20, including Xingtai, Baoding, Shijiazhuang and Handan.

WHO’S global urban air pollution database measures the levels of fine particulate matter (PM10 and PM2.5) from 3,000 cities in 103 countries. WHO described particulate matter as the “greatest environmental risk to health”, causing over three million premature deaths every year.

Iran’s Zabol had PM2.5 levels of 217 micrograms per cubic metre, followed by India’s Gwalior at 176 and Allahabad at 170, and Saudi Arabia’s Riyadh at 156 and Al Jubail at 152. Nigeria’s Onitsha had the highest PM10 levels at 594.

New Delhi, which was the most polluted city in terms of PM2.5 levels in 2014, is now ranked 11th, with PM2.5 levels of 122.

Overall, outdoor air pollution had grown 8% globally in the last five years. The survey revealed that more than 80% of people living in urban areas that monitored air pollution were exposed to air quality levels that were higher than WHO’s limits. Urban air pollution levels were the lowest in high-income countries in Europe, the Americas and the Western Pacific region. The residents of low-income countries were the worst affected, with 98% of cities in low and middle-income countries unable to meet WHO guidelines.

“Most sources of urban outdoor air pollution are well beyond the control of individuals and demand action by cities,” WHO states in its report, “as well as national and international policymakers to promote cleaner transport, more efficient energy production and waste management.”