A NASA ER-2 high-altitude research aircraft intercepted the exhaust wake of a supersonic Concorde aircraft in the stratosphere near New Zealand on October 8, 1994. Black carbon (soot) aerosol (BCA) was sampled by wire impactors during the first five of 12 short-duration wake intercepts. BCA concentration in Concorde exhaust at 16.3 km altitude was 0.2 particles cm-3, the size distribution peaked at a geometric mean radius of 0.09 μm, and the mass loading was 2.0¿1.4 ng m-3. With a plume dilution factor (DF) of 1.0¿10-5, determined by the ratio of CO2 measured in the plume (above the ambient stratospheric background level) to CO2 in the engine exhaust plane, the Concorde BCA emission index was EI(BCA)=0.07¿0.05 g BCA per kg fuel burned. Applying this EI to estimates of aircraft fuel burned by the current subsonic fleet in the stratosphere yields average stratospheric BCA loadings of 0.5 ng m-3, commensurate with observations in the northern stratosphere. Applying the Concorde EI to fuel consumption by a projected future fleet suggests a twofold-threefold increase of stratospheric BCA by the year 2015. A strong gradient in BCA concentration exists between the northern and the southern hemispheres, indicating interhemispheric mixing times longer than stratospheric residence times.¿ 1997 American Geophysical Union