The city of Seoul got cleared of ultrafine dust coming from China on Friday, leading the Seoul government to lift the warning against the pollutant.

Concerns, however, persist, as China still has a high level of the "particulate matter (PM) 2.5," a nanoscale particulate matter that is 2.5 micrometers or less in diameter and largely made up of sulphate and nitrate particles.

The city and the surrounding areas experienced unprecedentedly thick layers of ultrafine pollutants on Thursday, prompting the Seoul Metropolitan Government to issue its first-ever advisory as its PM-2.5 level reached 93 micrograms per cubic meter.

It is far higher than the 85 micrograms per cubic meter threshold for issuing the advisory, according to the city.

High-density fine dust was created in Shanghai and Qingdao of China, and moved westward toward the Korean Peninsula. Thick smog and still air in the country combined with the dust to worsen the situation, the city said.

"As of 12 a.m., Friday, we lifted the advisory, as the PM-2.5 level dropped to around 47 micrograms per cubic meter at that time and has been on a decrease," said Kang Hee-eun, a chief weather official in the city government.

The expansion of cold, high pressure pushed away the pollutants from the atmosphere, he added.

But China continued to experience a high level of fine dust, with Beijing having 77 micrograms per cubic meter and Shanghai 437 micrograms per cubic meter as of 11 p.m, Thursday.

"If a west wind blows, we will once again be affected by the dust," Kang said, asking citizens to pay close attention to their health. 

Exposure to the ultrafine particles can cause several serious health effects such as cardiac and respiratory problems, as they penetrate the respiratory system further than larger particles, according to experts. (Yonhap News)