Abstract
Calculations of a relatively comprehensive chemical reaction mechanism applied to individual parcels of aircraft emissions under upper tropospheric conditions show that over a typical residence time of air in the up. per troposphere, each aircraft-emitted NOx molecule produces about 2-3 molecules of O3 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 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 larger grid cell volume, larger-scale models will overestimate the calculated O3 production by 20 to 30 %. This overestimate depends on the vertical diffusion efficiency, vertical wind shear, and NOx concentrations in the ambient environment. This overestimate can be compensated for in larger scale models by reducing the reaction coefficient of the NO + HO2 reaction by less than 3% under typical upper tropospheric conditions.
Highlights
With the increased demand for aircraft transportation, pollution resulting from aircraft emissions has been identified as a potential problem to ambient environment
Since this study considers the impacts of aircraft plumes under typical flight corridor conditions, the density of the aircraft emissions is the major concern regardless of the size of the larger air volume considered
Realistic aircraft plumes grow slowly in the initial few hours to day after emission, and the emitted aircraft pollutants remain confined to relatively small plume vol
Summary
With the increased demand for aircraft transportation, pollution resulting from aircraft emissions has been identified as a potential problem to ambient environment. Over half of the subsonic aircraft emissions are released at flight altitudes between 9 to 13 km, where aircraft spend most of their air time (Baughcum 1997). At these altitudes, both tropospheric and stratospheric conditions are TAO, Vol 12, No 1, March 2001 common, and the photochemical properties are distinctively different from those of the lower troposphere. Chemical removal proceeds rapidly through dynamic processes such as turbulent mixing and dry deposition. In the upper troposphere and lower stratosphere, little turbulent mixing occurs, and the atmosphere is highly stable
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