The average level of PM10 -- fine airborne particles smaller than 10 micrometers in diameter -- was 125 micrograms per cubic meter as of 8 a.m. in 25 districts across Seoul, according to the National Institute of Environmental Research.
The heavily polluted air is the result of yellow dust from northeastern China and southern Mongolia, the agency said. The particles are now moving southwest, it said.
Fine dust advisories are issued when the level of PM10 exceeds 150 micrograms per cubic meter for two consecutive hours.
The level of PM2.5 -- ultrafine airborne particles smaller than 2.5 micrometers in diameter -- was average, 23 micrograms per cubic meter, as of 8 a.m.
Those suffering respiratory and heart problems are advised to stay indoors and dust masks are recommended when going outside.
Korea saw a high level of particulate pollution last week for the first time this autumn.
Typically, high levels of PM2.5 affect Korea from autumn through spring as wind blows from west to east. Pollutants traveling from China as well as domestic emissions from old diesel cars and coal-fired power plants are believed to be major contributors.
By Ock Hyun-ju (firstname.lastname@example.org)