A new instrument, the Forward Scattering Spectrometer Probe (FSSP) 300, was used on the NASA ER-2 during the Airborne Arctic Stratospheric Expedition (AASE) to count and size particles in the size range of approximately 0.4 to 24 &mgr;m diameter. A brief description of the instrument is presented and observations for each ER-2 flight are summarized. Measurements were made in both type I and type II polar stratospheric clouds as well as in the background sulfuric acid particles. Total particle concentrations up to 16 cm-3 with total particle volumes up to 10 &mgr;m3 cm-3 were observed in some of the polar stratospheric cloud events. ¿ American Geophysical Union 1990