Beginning Monday, Seoul officials waived public transport fees during commuter hours as the daily average density of ultra-fine dust remained above 50 micrograms per cubic meter — a level that's widely considered harmful. Authorities have also limited car use for public employees, closed 360 parking lots and reduced construction work on government-funded projects.

Those policies were first introduced last year when Seoul's air quality index exceeded 179 micrograms per cubic meter of fine dust, the highest level among global metropolitan cities after New Delhi in India. Experts say the country's use of coal and diesel has resulted in increasing air pollution, exacerbated by smog from China.

The latest anti-pollution operations will likely stay in place for several days but aren't expected to negatively impact private company operations, Miha Hribernik, senior Asia analyst at Verisk Maplecroft, said in a note.

Asia's fourth-largest economy is the eighth-worst performing country in Verisk Maplecroft's 2018 Air Quality Index. India and Bangladesh took first and second place, respectively.