Sensitivity of two‐dimensional model predictions of ozone response to stratospheric aircraft: An update

The Goddard Space Flight Center two‐dimensional model of stratospheric photochemistry and dynamics has been used to calculate the O 3 response to stratospheric aircraft (high‐speed civil transport (HSCT)) emissions. The sensitivity of the model O 3 response was examined for systematic variations of five parameters and two reaction rates over a wide range, expanding on calculations by various modeling groups for the NASA High Speed Research Program and the World Meteorological Organization. In all, 448 model runs were required to test the effects of variations in the latitude, altitude, and magnitude of the aircraft emissions perturbation, the background chlorine levels, the background sulfate aerosol surface area densities, and the rates of two key reactions. No deviation from previous conclusions concerning the response of O 3 to HSCTs was found in this more exhaustive exploration of parameter space. Maximum O 3 depletions occur for high‐altitude, low‐latitude HSCT perturbations. Small increases in global total O 3 can occur for low‐altitude, high‐latitude injections. Decreasing aerosol surface area densities and background chlorine levels increases the sensitivity of model O 3 to the HSCT perturbations. The location of the aircraft emissions is the most important determinant of the model response. Response to the location of the HSCT emissions is not changed qualitatively by changes in background chlorine and aerosol loading. The response is also not very sensitive to changes in the rates of the reactions NO + HO 2 → NO 2 + OH and HO 2 + O 3 → OH + 2O 2 over the limits of their respective uncertainties. Finally, levels of lower stratospheric HO χ generally decrease when the HSCT perturbation is included, even though there are large increases in H 2 O due to the perturbation.