HETEROGENEOUS CHEMISTRY IN AIRCRAFT WAKES - CONSTRAINTS FOR UPTAKE COEFFICIENTS

Recent in situ measurements in subsonic and supersonic aircraft plumes show the presence of high aerosol abundances. Given the large initial surface areas of the exhaust particles (volatile aerosols, soot, and ice) of 10(3) - 10(5) mu m(2) cm(-3) or more, heterogeneous processing can potentially become important. Based on an analytical model to pre dict the temporal evolution of the surface areas, the potential for he terogeneous chemistry during the lifetime of single aircraft wakes is investigated. The model surface areas are constrained by plume observa tions and compared to numerical simulations of aerosol formation and g rowth. Efficient heterogeneous processing on volatile aerosols and soo t on timescales below I day generally requires uptake coefficients gre ater than or similar to 0.003 - 0.007, depending on the specific surfa ce area of soot. For low available surface areas and slow reactions, t he lifetime of emitted exhaust species sensitively depends on the wake mixing properties. Shutting off uptake by volatile particles inhibits heterogeneous processing unless high soot surface areas and reaction probabilities are prescribed. Depending on the lifetime of ice contrai ls, uptake coefficients greater than or similar to 0.1 are required fo r rapid uptake of exhaust species on the ice particles. This lower lim it becomes relaxed if contrails are long-lived or develop into persist ent cirrus or polar stratospheric clouds, rendering activation of chlo rine potentially important. The model is applied to investigate the up take of gaseous HNO2 and SO2 by the observed particles in the plume of the Concorde in the lower stratosphere.