A Lagrangian simulation of supersonic and subsonic aircraft exhaust emissions

To estimate the effect of subsonic and supersonic aircraft exhaust on the s tratospheric concentration of NOy, we employ a trajectory model initialized with air parcels based on the standard release scenarios. The supersonic e xhaust simulations are in good agreement with two-dimensional (2-D) and 3-D model results and show a perturbation of about 1-2 ppbv of NOy in the stra tosphere. The subsonic simulations show that subsonic emissions are almost entirely trapped below the 380 K potential temperature surface. Our subsoni c results contradict results from most other models, which show exhaust pro ducts penetrating above 380 K, as summarized by Danilin et al. [1998] and I ntergovernmental Panel on Climate Change (IPCC) [1999]. The disagreement ca n likely be attributed to the excessive model diffusion of the strong verti cal gradient in NOy that forms at the boundary between the emission zone an d the stratosphere above 380 K. Our results suggest that previous assessmen ts of the impact of subsonic exhaust emission on the stratospheric region a bove 380 K should be considered to be an upper bound.