Vertical profiles of aerosol concentration were measured on 8 occasions from McMurdo Station, Antarctica (78¿S), between late August and early October 1992. Polar stratospheric clouds (PSCs) were observed on 6 of these soundings. The characteristics of PSCs, and ozone, were quite different above and below about 16 km. Above 16 km PSCs were variable in time, with particles >1.0 &mgr;m radius contributing significantly to the surface area, generally <8 &mgr;m2 cm-3. Below 16 km PSCs were much more stable and were dominated by high concentrations of smaller particles, <1.0 &mgr;m, with surface areas of 20--30 &mgr;m2 cm-3. This lower layer coincided with the altitude of the primary Pinatubo volcanic aerosol as measured in mid September and October, and with the 4 km region of the atmosphere where ozone was virtually completely destroyed over Antarctica in 1992.