Vertical profiles of aerosol have been measured approximately biweekly since June 1991 at Laramie, Wyoming (41¿N). Both the total number concentration and concentration of particles >0.15 to 10.0 &mgr;m were measured using balloonborne instruments. The aerosol size distributions were best represented when bimodal lognormal distributions were fit to the data. After an early short-lived intense aerosol layer, the stratospheric maximum surface area and mass (40 &mgr;m2 cm-3, 160 ppbm) was observed to occur approximately 180 days after the eruption. The aerosol was then observed to remain relatively homogeneous both in altitude and time during 1992, with the maximum surface area and mass remaining relatively constant between 20 to 30 &mgr;m2 cm-3 and 30 to 60 ppbm. ¿ American Geophysical Union 1993