6Stuart P Naegele, William D Sellers. A study of visibility in eighteen cites in the western and southwestern United States[J]. Monthly Weather Review, 1981, 109(10) : 234- 240.
7Kim Young J, Kyung W, Kim Shin D, et al. Fine particulate matter characteristics and its impact on visibility impairment at two urban sites in Korea: Seoul and Incheon [J]. Atmospheric Environment, 2006, 40: S593- S605.