The Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE) made in situ observations of the composition of the lower stratosphere from the NASA ER-2 aircraft at latitudes from 15¿N to 60¿N, during November 1992 and April, May, and October 1993. SPADE followed the Airborne Arctic Stratospheric Expedition II (AASE-II, September 1991 to March 1992) by 8 months. Together the two missions provide a record of stratospheric trace species and aerosols at middle and high latitudes spanning the input and decay of debris from the eruption of Mt. Pinatubo. New instruments deployed for SPADE include sensors to measure OH, HO2, H2O, CO2, NO2, and the UV/visible radiation field, complementing sensors previously developed on the ER-2 (ClO, BrO, NO, NOy, N2O, O3, H2O, HCl, CH4, CFC-11, CFC-113, and aerosol number and size distribution). The data provide the first simultaneous in situ measurements of radicals and reservoir species to include representatives from all the important families of stratospheric reactants, observed as functions of time of day (at ~18 km), latitude and altitude (15--20 km). The results place strong new constraints on models of stratospheric photochemistry. For example, measurements of the radicals HO2, NO2, ClO, and BrO allow for a nearly completely empirical evaluation of local rates for photochemical removal of ozone (by known catalytic cycles). Highly precise observations of the seasonal cycle and interannual changes in CO2, combined with data for N2O and other tracer species, provide new insights into rates for transport in the lower stratosphere. High resolution data obtained during SPADE by the ER-2 (in its own wake) and in AASE-II by the DC-8 (in wakes from commercial aircraft) provide support for engineering models of NOx emissions from subsonic jet aircraft at cruise conditions. Observations from the DC-8 during AASE-II, defining global distributions of NOx and NOy near the tropopause, and of HF, HCl, ClNO3, and HNO3 column abundances, provide new information on the processes influencing polar ozone loss. ¿ American Geophysical Union 1994