The percentage of population exposed to a fine particulate matter (PM2.5) concentration greater than 10 micrograms (μg) per cubic meter (m3).

The World Health Organization (WHO) provides air quality guidelines based on scientific evidence and expert advice. 10 μg/m3 is the air quality guideline (AQG): These are the lowest levels at which total, cardiopulmonary and lung cancer mortality have been shown to increase with more than 95% confidence in response to long-term exposure to PM2.5.