On the Role of Contrail Ice in the Chemistry of Aircraft Exhaust Plumes

The formation of contrail ice particles has the potential to alter the chemistry occurring in aircraft exhaust plumes. A Gaussian plume model has been used to calculate the impact of contrail ice on plume chemistry as the exhaust emissions mix with the ambient atmosphere. Large Eddy Simulations (LES) were used to determine contrail ice surface areas for temperatures and relative humidities relevant to the mid-latitude upper troposphere. A method has been developed for analysing the results of the LES simulations to obtain both the dimensions of an expanding Gaussian plume representation and the ice surface area distribution within the plume. The method relies on mapping the LES tracer distribution onto an N-region equivalent Gaussian profile, with each region containing the same number of tracer molecules. Dimensions of the equivalent Gaussian plume can be estimated from the areas enclosed by these regions, and the ice surface area in each region can be obtained by averaging the surface area over the corresponding LES grid cells. Results will be presented for a number of LES scenarios, together with a discussion of the chemistry occurring in expanding plumes with and without the inclusion of the contrail ice particles.