Plume-scale and regional-scale modeling studies of uncertainties associated with calculated impacts of aircraft emissions on upper tropospheric ozone

Both plume- and regional-scale models are used to quantify aircraft impacts on upper tropospheric O3 and the sensitivity of calculated impacts to numerous uncertain physical and chemical processes. A Lagrangian plume chemistry model shows that realistic aircraft plumes grow slowly during initial stages, and take several days to diffuse to a size comparable to the grid volume used by global-scale Eulerian models. By assuming aircraft emissions are immediately diluted into a grid cell air volume, larger-scale models will overestimate the calculated O3 production by 20 to 30%. The overestimate of O3 production depends on the vertical diffusion efficiency, vertical wind shear, and NOx concentrations in the ambient environment. This overestimate can be compensated for in a larger scale model by reducing the reaction coefficient of the NO + HO 2 reaction by less than 6%.;Regional scale studies of 5-day simulations show that at flight altitudes near 250 hPa averaged over the Eastern United States, aircraft induced NO x perturbations are about 7% and O3 perturbations are 0.01 to 0.02% relative to typical background NOx and O3 concentrations of 165 ppt and 150 ppb respectively. The maximum NOx and O 3 perturbations can be as large as 30% and 0.2% respectively over local areas downwind of major flight corridors.;Over a typical residence time of air in the upper troposphere, the plume scale model suggests that on average, each aircraft-emitted NOx molecule produces about 1--3 molecules of O3 per day as long as the reactive NOy remains in the upper troposphere. In the regional simulations, the aircraft-emitted pollutants only remain in the model domain for 2--20 hours, during which about 4 molecules of additional O 3 are produced per aircraft NOx molecule emitted.;Calculated larger scale aircraft impacts on O3 in the upper troposphere will be extremely sensitive to the proper specification of tropopause height, lightning-NOx emissions, convective mixing, and to model vertical resolution, all of which introduce about 10 to 60% uncertainties in calculated O3 perturbations. All of these processes are highly variable and uncertain in current large-scale atmospheric chemistry models.