This spring, Korea has been choking under very high concentrations of fine dust pollution.
Expert analysis now suggests that up to 69 percent of that dust was blown over from China.
The National Institute of Environmental Research and the city of Seoul released the results of a study on Monday using ground and satellite data and atmospheric modeling.
It found that while high dust levels in January were primarily from local sources, that was not the case in March.
On the 23rd last month, foreign dust, as a proportion, reached a peak of 69 percent.
On the days when it was highest -- the 25th and 26th, when emergency measures were taken near Seoul -- the foreign and domestic dust was just about 50-50.