The South Korean government has updated its recommendations for when pollution is bad enough to wear a face mask.
In the guidelines released today, it says healthy people can go out without a mask even on days when pollution is considered bad that is, when fine dust concentrations are up to 50 micrograms per cubic meter.
But for the elderly, pregnant women and people with certain health conditions, masks are recommended when fine dust is higher than 36 micrograms.
At home, the government advises opening the windows at least three times a day for 10 minutes, even when the air is bad.
As for light exercise outdoors, it's recommended when dust is under 75 micrograms, but in or near a park rather than on the roadside.