Estimating chemical errors in large-scale simulations of aircraft emissions

Calculations of a relatively comprehensive chemical reaction mechanism appl ied to individual parcels of aircraft emissions under upper tropospheric co nditions show that over a typical residence time of air in the upper tropos phere, each aircraft-emitted NOx molecule produces about 2-3 molecules of O -3 per day as long as the reactive NOy remains in the upper troposphere. In the upper tropospheric environment characterized by low ambient turbulence and appreciable vertical wind shear, aircraft plumes grow slowly during in itial stages, and take several days to diffuse to a size comparable to the grid volume used by global-scale Eulerian models. By assuming aircraft emis sions are immediately diluted into a larger grid cell volume, larger-scale models will overestimate the calculated O-3 production by 20 to 30%, This o verestimate depends on the vertical diffusion efficiency, vertical wind she ar, and NO concentrations in the ambient environment. This overestimate can be compensated for in larger scale models by reducing the reaction coeffic ient of the NO + HO2 reaction by less than 3% under typical upper troposphe ric conditions.