An ultrafine dust air pollution advisory was lifted for all of Seoul at 3 p.m. Friday after 43 hours, the metropolitan government said.

The city-run Research Institute of Public Health and Environment announced the termination of the advisory, saying the capital's hourly average concentration of ultrafine dust particles fell to 33 micrograms per cubic meter, lower than the advisory clearance level of 35 micrograms.

The institute issued the ultrafine dust advisory for all of Seoul at 8 p.m. Wednesday, when the hourly average density of ultrafine particles smaller than 2.5 micrometers in diameter, known as PM 2.5, soared to 96 micrograms per cubic meter.

"The latest onset of heavy ultrafine dust concentrations was caused by the combination of stagnant local air and influx of air pollutants from abroad," an official from the institute said.

"It is estimated that inflows of easterly wind caused by the development of a low-pressure system Friday morning may have temporarily weakened the ultrafine dust concentrations," the official explained.

The weather authorities here categorize concentrations of PM 2.5 between zero and 15 micrograms as "good," between 16 and 35 as "normal," between 36 and 75 as "bad" and more than 76 as "very bad."

The ultrafine dust advisory has also been lifted in Incheon and parts of Gyeonggi Province, which surrounds Seoul, but the PM 2.5 density will remain at bad levels in other parts of the central region for the time being, according to the state-run National Institute of Environmental Research.

It forecast that the central region will continue to be affected by the sporadic concentrations of ultrafine particles until Monday. (Yonhap)