Seoul is covered with fine dust, Jan. 7. Yonhap

Air quality in Korea reached its worst level this winter Saturday due to high levels of fine and "yellow" dust, according to the weather authorities.

As of 10 a.m., the daily average concentration of ultrafine dust particles smaller than 2.5 micrometers in diameter, known as PM2.5, was 86 micrograms per cubic meter, while that of fine dust known as PM10 was 143 micrograms per cubic meter nationwide, said Air Korea that is run by the environment ministry.

These figures were much higher than the yearly average concentration of ultrafine and fine dust in 2021 ― 18 and 36 micrograms per cubic meter, respectively.

The weather authorities have issued an ultrafine dust advisory in all areas except for the southern resort island of Jeju, and a fine dust advisory in Gyeonggi Province that surrounds Seoul, and the central Chungcheong, and South Jeolla and South Gyeongsang provinces.

As of 5 p.m. Friday, a yellow dust warning has been in effect in the South Chungcheong and Jeolla provinces, the southwestern city of Gwangju and Jeju Island.

On Sunday, the fine dust level is also expected to be "bad" across most parts of the country, including the greater Seoul area and Gangwon Province in the east.

The Korea Meteorological Administration categorizes concentrations of fine dust between 81 and 150 micrograms as "bad" and more than 151 as "very bad."

The authorities have advised people to refrain from leaving their homes on such days and to wear a face mask if they have to go outside. (Yonhap)