A thick layer of fine dust blanketed South Korea on Wednesday, prompting the capital Seoul to issue this year's first warning against the particles and urge people to stay indoors.

According to the data by the Korea Meteorological Administration, Seoul's atmospheric concentration levels of "particulate matter (PM)-10" pollutants recorded 227 micrograms per cubic meter as of 1 p.m., reaching the "very bad" level.

PM-10 refers to airborne particles 10 micrometers or less in diameter. Epidemiological evidence indicates that exposure to the pollutant causes several health effects such as cardiac and respiratory problems, according to experts. 

The weather agency categorizes the condition "very bad" when the PM-10 level rises beyond 201 micrograms per cubic meter, with the range of 121 to 200 micrograms defined as "bad."

As of 11 a.m., the level reached 172 micrograms per cubic meter, prompting the Seoul Metropolitan Government to issue the advisory, the first case of the year.

The city government issues the advisory when average pollutant levels of 170 micrograms per cubic meter persist for at least two hours. It is the first time that the warning was issued this year.  

Suwon city of Gyeonggi Province saw the level reach 201 micrograms per cubic meter, and the southern port city of Busan had

163 micrograms, according to data.

 "The density of the pollution will get thicker, as westerly wind will push fine dusts created in China toward the Korean Peninsula," a city official said, adding the condition is forecast to get better around the evening. 

"Elderly people, children and patients with respiratory and cardiovascular diseases should refrain from going outside. When going outside, citizens are advised to wear yellow-dust masks."  (Yonhap)