Can soot particles emitted by airplane exhaust contribute to the formation of aviation contrails and cirrus clouds?

[1] Flame soot samples taken as surrogates for aviation soot have been generated under two limiting conditions of combustion in a rich and lean flame resulting in grey and black soot, respectively. Absolute mean surface residence times tau(s) of H2O adsorbed on soot ranging from 400 to 150 ms have been measured for black soot at 243 K and for grey soot at 193 K, respectively. The kinetic parameters for desorption of H2O adsorbed on grey and black soot are E-a = 7 +/- 0.5 and 9 +/- 0.6 kcal/mol, logA/ s(-1) = 8.8 +/- 0.5 and 8.5 +/- 0.5, respectively. We conclude that soot aerosol may be coated with H2O molecules in a sulfur-free pathway once the particles have cooled down to 500 K in the plume of aviation exhaust

Kinetic model for non-sticky collisions in pulsed molecular diffusion tube experiments

A kinetic model for molecular flow is developed to simulate the escape rate profiles that result when molecules are pulsed into the top of a cylindrical tube, experience non-reactive collisions with the tube surface and are detected after exiting at the base. The model includes time-dependent rate coefficients for formation of a pseudo steady-state spatial distribution and for escape. The mean distance traveled down the tube per collision is estimated by applying a cosine directional distribution. Under molecular flow conditions and for non-sticky gas/surface interactions this model allows for the determination of the average number of collisions per molecule before detection. Simulations were carried out on SF6, Ar, N2, Ne, He colliding with Pyrex and Teflon-coated surfaces at temperatures ranging from 25 to 64`C and in tubes with a range of dimensions. Mean collision numbers are in agreement with those calculated from Monte Carlo simulations