Sandstorms and/or duststorms that are affecting the Korean peninsula occur most frequently in the spring season in the arid and semi-arid area of sand deserts including Badainjaran, Tengger, Mu Us, Hunsandakue and Keoeolchin, Gobi region and Loess Plateau in the Asian continent. The area of Asian dust source regions cover most of northern China and Mongolia. Warning is issued when the hourly averaged dust(PM10) concentration is expected to exceed 800 ㎛/㎥ for over 2hours.