Fine dust has blanketed much of the country on Monday, the first day the masks are not required on public transit.

As of 8 a.m., levels of ultrafine dust, or particulate matter smaller than two-point-five micrometers in diameter, were considered "very bad" in Seoul, above 75 micrograms per cubic meter in density.

The levels were "bad," or between 36 and 75 micrograms per cubic meter, in Incheon, Sejong, Daejeon, Gwangju and the provinces of Gyeonggi, Gangwon, Chungcheong and Jeolla.

Ultrafine dust advisories were issued for Seoul, central Gyeonggi, parts of Incheon, South Chungcheong and North Jeolla provinces.

With the daily average expected to surpass 50 micrograms per cubic meter in the capital area for the second straight day, emergency reduction measures have been enforced as of 6 a.m., including adjusted operating hours and dust prevention measures for businesses and construction sites.