South Korean officials say a seasonal phenomenon that scatters dust particles from China's Gobi Desert across East Asia every year is getting worse, as China rapidly industrializes.
It coats cars. It silhouettes entire cityscapes. And it can be hazardous to both public health and the economy.
"Yellow dust," or "hwangsa" in Korean, shows up on the Korean peninsula every spring. Seasonal winds carry billions of microscopic sand particles here, mainly from China's Gobi desert.
But experts say the yellow dust problem is worsening at the source in two ways. First, China's rapid economic growth has led to widespread clearing of vegetation, causing the Gobi and other desert areas to expand. Second, a robust increase in Chinese manufacturing is pouring industrial pollutants into the air, which bind together with the desert dust.
Son Tae-song of the Korean Meteorological Association says data from the past few days indicate the magnitude of the problem.
He says this Saturday's yellow dust readings were the highest in four years.
Scientific readings indicated more than 2,000 micrograms of dust per cubic meter of air in some areas, more than 27 times the normal average.
For South Koreans, that can mean a lot more than just a dirty car. Dr. Jang Geun-ho, an ear, nose and throat specialist here in Seoul, says there can be serious health effects.
He warns that even a few hours of exposure to unsafe yellow dust levels can cause bronchial, sinus, and eye irritation and infection.
Yeom Kyo-bong, an air quality policy advisor at Seoul's Environment Ministry, says yellow dust can also cause the economy to suffer.
He says the dust can harm crops by inhibiting their ability to process sunlight for food. He says the tiny particles can also clog the mechanism of high-tech manufactured products such as microchips.
South Korean officials and private organizations say China is taking its environmental problems seriously. Beijing is reportedly trying to limit desert growth, working with international groups to plant trees around the Gobi as a dust shield.
South Korea, meanwhile, is building a new facility on one of its northeastern islands to improve early detection of unsafe yellow dust levels. Authorities in Seoul say they are beginning to broadcast dust alerts to mobile phone users.
Meteorologists say there is likely to be at least one more alert in South Korea this week - and possibly several by the end of this month.