The Global Modeling Initiative assessment model: Application to high-speedcivil transport perturbation

The NASA Atmospheric Effects of Aviation Project (AEAP) Global Modeling Ini tiative (GMI) three-dimensional (3-D) chemical transport model (CTM) was ap plied to assess the impact of a fleet of high-speed civil transports (HSCTs ) on abundances of stratospheric ozone, total inorganic nitrogen (NOy), and H2O. This model is specifically designed to incorporate a diversity of app roaches to chemical and physical processes related to the stratosphere in a single computing framework, facilitating the analysis of model component d ifferences, modeling intercomparison and comparison with data. A proposed H SCT fleet scenario was adopted, in which the aircraft cruise in the lower s tratosphere, emitting nitrogen oxides (NOx) and water (H2O). The model calc ulated an HSCT-induced change in Northern and Southern Hemisphere total col umn ozone of +0.2% and +0.05%, respectively. This change is the result of a balance between an increase in local ozone below approximately 25 km and a decrease above this altitude. When compared to available NOy observations, we find that the model consistently underestimates lower stratospheric NOy . This discrepancy is consistent with the model bias toward less negative o zone impact, when compared to results from other models. Additional analysi s also indicates that for an HSCT assessment it is equally important for a model to accurately represent the lower stratospheric concentrations of ozo ne and H2O. The GMI model yields good agreement In comparisons to ozone dat a For present-day conditions, while H2O is constrained by climatology as mu ch as possible; thus no further biases would be expected from these compari sons. Uncertainties due to discrepancies in the calculated age of ail compa red to that derived from measurements, and of the impact of emissions on he terogeneous and polar chemistry, are difficult to evaluate at this point.