Researcher Ahn Joon-young says cold weather has promoted a rise in coal-burning to heat homes in China, and expects the haze to become a more frequent problem for Korea. Warnings of the smog have sent sales of face masks soaring six-fold, along with detergents that claim to wash away bacteria and heavy metals. Dustproof windshield wipers and air filters are popular. China's official media outlets have been complaining about coal pollution for months - a sign the Communist government is beginning to take air quality more seriously (see also ).