Seoul City has issued an ultrafine dust advisory as of noon Saturday.

The advisory is issued when the density of fine dust in the air exceeds an average 90 micrograms per cubic meter per hour and this continues for at least two hours.

Ultrafine dust levels in 25 Seoul districts averaged 99 micrograms per cubic meter at Saturday noon.

When advisories are in effect, people with respiratory or cardiovascular diseases as well as children and seniors should refrain from leaving home, but if they must go out, they are advised to wear masks.

Seoul City temporarily closed the outdoor skating rink at Seoul Plaza from 1 p.m. as the air pollution registered a level of “poor.”

The skating rink also shut down briefly in the late afternoon also on Friday due to poor air quality.