The source of PM2.5 pollution is typically combustion, including car engines, power plants, construction projects, fires, and wood burning. Long-term exposure to PM2.5 air pollution has been linked to premature death as well as a number of chronic conditions such as lung disease, reduced lung function, asthma, and heart problems.
Heavy industrialization and rapid growth of developing cities are among the most common causes of high concentrations of air pollution. In some cases, high concentrations of fine particulates in the air are the result of lacking or non-existent public works infrastructure, such as sewage systems.
The vast majority of the cities on this list can be found in either China or India. The high number of cities from the two countries might seem to suggest these nations have especially poor regulations, infrastructure, or industries that tend to pollute — or a combination of these factors.
Addressing environmental issues costs money, and many countries lack the resources necessary to tackle even the most pressing environmental problems. In some nations, the government is simply not making it a priority — these are countries doing the most and least to protect the environment.
To identify the most polluted places on Earth, 24/7 Tempo reviewed the most recent measured annual average of PM2.5 for 2,602 cities across the globe. Most recent measure of PM2.5 and PM10 (also whether the figure for PM10 is measured or converted), and the number and type of weather station reporting pollution for each city are from the World Health Organization (WHO) Global Ambient Air Quality Database for 2018. All other data for each country came from the World Bank for the most recent year of data available.