Estimates of the mass of dust suspended in the Martian atmosphere are derived from global and regional 9-μm opacity maps produced from Viking Infrared Thermal Mapper data. During the peak of the 1977b storm, a total dust mass of approximately 4.3¿1014 g was suspended, equivalent to 4.3¿10-4 g/cm2, or a layer 1.4 μm thick. During a local dust storm near Solis Planum at Lg 227¿, approximately 1.3¿1013 g of dust were lofted, equal to about a 6-μm layer in that vicinity. ¿ American Geophysical Union 1995