South Korea was one of the five countries with the worst air pollution in the world in 2017,.
That's according to a report from the OECD on fine dust pollution.
Number one was India, followed by China, Vietnam, South Africa and South Korea.
The cause of the pollution is coal used for power generation.
The report says South Korea burns coal to generate 46 percent of its electricity,... far higher than the average among OECD countries of 27 percent.
The global average is 38 percent.
A South Korean industry official said the problem is that China and Korea will continue to increase their reliance on coal, so it's unlikely that air quality will improve in the next few years.