Each year, most of Japan's prefectures are affected by what is known as yellow dust, which appears as a yellow fog in the atmosphere for a few days, often in late winter and early spring. A mixture of des ert sand, arid topsoil and man-made pollutants from Central Asia, China and Mongolia, the annual yellow dust storms are a growing health hazard that have canceled or delayed flights in Japan and South Korea and, when mixed with rain, muddy the streets, creating an environmental headache for governments and individuals.

Q: What, exactly, are yellow dust storms and where do they come from?

A: Yellow dust and sandstorms originate mostly in Central Asia, China and Mongolia. The Takla Makan desert and the Gobi desert, as well as the Loess Plateau, are the main sources. The sand, dust and particles rise into the air and are driven across the Korean Peninsula to Japan by prevailing westerly winds. However, yellow dust from the storms has been found as far away as the U.S. Rocky Mountains.