OVERVIEW - THE STRATOSPHERIC PHOTOCHEMISTRY AEROSOLS AND DYNAMICS EXPEDITION (SPADE) AND AIRBORNE ARCTIC STRATOSPHERIC EXPEDITION-II (AASE-II)

The Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (S PADE) made in situ observations of the composition of the lower strato sphere from the NASA ER-2 aircraft at latitudes from 15-degrees-N to 6 0-degrees-N, during November 1992 and April, May and October 1993. SPA DE followed the Airborne Arctic Stratospheric Expedition II (AASE-II, September 1991 to March 1992) by 8 months. Together the two missions p rovide a record of stratospheric trace species and aerosols at middle and high latitudes spanning the input and decay of debris from the eru ption of Mt. Pinatubo. New instruments deployed for SPADE include sens ors to measure OH, HO2, H2O, CO2, NO2 and the UV/visible radiation fie ld, complementing sensors previously deployed on the ER-2 (ClO, BrO, N O, NO(y), N2O, O3, H2O, HCl, CH4, CFC-11, CFC-113, and aerosol number and size distribution). The data provide the first simultaneous in sit u measurements of radicals and reservoir species to include representa tives from all the important families of stratospheric reactants, obse rved as functions of time of day (at approximately 18 km), latitude an d altitude (15-20 km). The results place strong new constraints on mod els 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 know n 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 l ower stratosphere. High resolution data obtained during SPADE by the E R-2 (in its own wake) and in AASE-II by the DC-8 (in wakes from commer cial aircraft) provide support for engineering models of NO(x) emissio ns from subsonic jet aircraft at cruise conditions. Observations from the DC-8 during AASE-II, defining global distributions of NO(x) and NO (y) near the tropopause, and of HF, HCl, ClNO3, and HNO3 column abunda nces, provide new information on the processes influencing polar ozone loss.