Soot aerosol in the lower stratosphere: Pole‐to‐pole variability and contributions by aircraft

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.