Composite distributions of measured total reactive nitrogen (NOy) from the NASA ER-2 during the Airborne Arctic Stratospheric Expedition (AASE) are presented. The observed features of these distributions are discussed in terms of the controlling dynamical, chemical, and microphysical processes. In the latitudinal profile from 58¿N to within about 4¿ poleward of the polar vortex boundary, NOy conforms closely to predictions of NOy based on N2O measurements. The features of the distribution are apparently dynamically controlled. Poleward of 5¿ of latitude within the boundary, the average NOy decreases sharply and is significantly lower than that predicted from N2O. This feature is consistent with loss of NOy through sedimentation of particles containing NOy in polar stratospheric clouds. The observed loss is not as systematic as in the Antarctic, consistent with the observed differences in season and meteorological conditions between the two campaigns. ¿ American Geophysical Union 1990