RACHEL MARTIN, HOST:
South Korea is one of the smoggiest countries in the world. It's common to hear that neighboring China is to blame for that, but a recent NASA study found there's a lot Korea can do on its own to clear the air. Here's NPR's Elise Hu.
ELISE HU, BYLINE: Seoul's towering mountains would be a sight to see if a thick industrial haze didn't blanket the city on so many days. The health effects can be seen in hospitals.
UNIDENTIFIED NURSE: (Speaking Korean).
HU: Patients at Hanyang University Hospital blow into plastic mouthpieces attached to a machine that measures their lung function.
KIM SANG-HEON: Let's see the results.
HU: It's a common test for those who come in complaining of chronic cough and difficulty breathing. Dr. Kim Sang-heon says since there's a clear link between pollution and respiratory illnesses, these days, he preaches a lot of dirty-air avoidance to his patients.
KIM: I usually say stay home if they hear it is high.
HU: High pollution is a common occurrence in Seoul, where the fine-particle pollution levels are among the highest in the world. Seoul's air-quality average was unhealthy for sensitive populations or worse on 78 days in 2016. By comparison, Los Angeles air quality only got that bad on two days of the year, and New York's air never hit those levels. Many Koreans are quick to blame neighboring China, whose notorious industrial dust does drift over. But the government wanted to know more about its own, pollution. Enter NASA, represented by its program manager and scientist, Barry Lefer.
BARRY LEFER: We can't fly over China. So this is a way to sample China and sample Korea, and the Koreans are very interested in working with us.
HU: South Korea's government teamed up with NASA for the most ambitious study of air quality here to date. Last year they flew planes at various altitudes above the peninsula, chasing dust and sampling it for a month. This summer...
UNIDENTIFIED MAN: It's nice to stand in front of a room and begin to tell you some of the things that we learned.
HU: ...Scientists began sharing preliminary results. The question dominating debates in South Korea is how much of the pollution here is homegrown. The answer is complicated. NASA sampled the air at a time when trans-boundary pollution was low, but even still, the results did help it model the atmosphere. Lefer.
LEFER: The models said that over half of the air pollution is coming from local sources and the rest is coming from other countries.
HU: Local sources include vehicle emissions, industrial sites and power plants. Lefer says news that a majority of the pollution here is homegrown is actually good in a key way.
LEFER: You can't do anything about the trans-boundary pollution whereas you can do something about your local sources.
HU: The government is taking some action now. President Moon Jae-in is overseeing a fine-dust task force, shuttering 10 of the country's oldest coal plants and the city of Seoul has begun issuing fine-dust alerts over mobile phones to better inform residents of dangerous days. Kim, the doctor, thinks growing public awareness of the pollution is working.
KIM: I expect some new change will be given to us.
HU: Armed with more data, the battle to curb South Korea's pollution problem comes from a new place of knowledge. Elise Hu, NPR News, Seoul.