Two-Dimensional Description of the Natural Atmosphere Including Active Water Vapor Modeling and Potential Perturbations due to NO(x) and HO(x) Aircraft Emissions.

The status of the Aerospace time-dependent two-dimensional photochemical model of the atmosphere as developed under contract to the FAA High Altitude Pollution Program HAPP is presented, together with the significant findings obtained during this study. Model improvements are described, as are the chronological effects of recent hydroperoxyl reaction rate measurements on the state of the natural and perturbed atmosphere. Comparisons with available data are made to elucidate our current ability to calculate the distribution of many trace species in the natural atmosphere. The most serious problem is the significant overprediction of stratospheric HNO3 concentration. When the most recent chemical reaction rates are used and ClOx is included, estimates of the effect of combined NOx and HOx emissions from projected future fleets of subsonic and supersonic aircraft indicate a resulting increase in ozone level in both the stratosphere and troposphere, with the significant change occurring in the troposphere. Peak increases in total ozone column are currently estimated to be 3.5 percent during summer-fall. The effect of HOx emissions on the total ozone column has been found small in comparison to the corresponding effect of NOx emissions.