In this paper we present an analysis of the Mars Orbiter Laser Altimeter (MOLA) reflectivity measurements from the Mars Global Surveyor (MGS) spacecraft, during period of solar longitudes (Ls) 198¿→212¿. Reflectivity can be interpreted as a product of the surface geometrical albedo and the two-way atmospheric transmission. Relative surface albedos were obtained from the red filter of Viking Color Mars Digital Mosaics (MDIM) to derive opacities at the MOLA wavelength (1.064 &mgr;m). Opacity measurements are interpreted in terms of atmospheric aerosol loading in the canyons. We also observed sudden increase of opacity in the northern regions (65 ¿N), which we interpret as condensing ice clouds. ¿ 1998 American Geophysical Union