Scattering albedo as a function of frequency for different MW dust mixtures, together with observational estimates of the dust albedo in various regions. The values are from the following sources, as indicated in the figure: Witt et al. (1982, 1990, 1992, 1993, 1997), Murthy & Henry (1995), Murthy et al. (1991, 1993, 1994), Hurwitz et al. (1991), Lillie & Witt (1976), Morgan et al. (1976), Henry (2002), Schiminovich et al. (2001), Laureijs et al. (1987), Mattila (1970), Lehtinen & Mattila (1996), Haikala et al. (1995), Gibson & Nordsieck (2003), Burgh et al. (2002), Calzetti et al. (1995), and Gordon et al. (1994).