WE PROPOSE A STUDY TO QUANTIFY OZONE AND CLIMATE IMPACTS ASSOCIATED WITH THE ROLLOUT OF A FLEET OF ADVANCED SUPERSONIC N+2 GENERATION AIRCRAFT. WE WILL USE STATE-OF-THE-ART ATMOSPHERIC MODELING AND ADJOINT METHODS TO ESTIMATE BOTH ABSOLUTE IMPACTS AND SENSITIVITIES TO PARAMETERS INCLUDING FLEET SIZE AIRCRAFT PERFORMANCE AND EMISSIONS FUEL PROPERTIES AND ROUTE SELECTION. THE MODELS WE WILL DEVELOP IN ORDER TO ASSESS THESE IMPACTS WILL COMPRISE A SUITE OF FLEXIBLE AND POWERFUL RAPID DESIGN AND ASSESSMENT TOOLS ALLOWING FURTHER INVESTIGATION OF THE ENVIRONMENTAL IMPACTS OF SUPERSONIC AIRCRAFT AS WELL AS MORE GENERAL ATMOSPHERIC IMPACT ASSESSMENT. IN ORDER TO ACHIEVE THESE OBJECTIVES WE HAVE GATHERED A TEAM WITH INTERNATIONALLY-RECOGNIZED EXPERTISE IN ATMOSPHERIC SCIENCE CLIMATE SCIENCE AVIATION S ENVIRONMENTAL IMPACTS AND THE MODELS REQUIRED TO EFFICIENTLY STUDY THESE SYSTEMS. ASSESSING THE OZONE AND CLIMATE IMPACTS OF SUPERSONIC AIRCRAFT REQUIRES AN INTEGRATED APPROACH THAT INVOLVES INTERACTIONS AMONG SEVERAL COMPONENT MODELS WHICH WE HAVE PREVIOUSLY USED TO ASSESS AVIATION S ENVIRONMENTAL IMPACTS. FOR THIS STUDY WE WILL IMPROVE THESE TOOLS TO REPRESENT THE EFFECTS OF SUPERSONIC STRATOSPHERIC FLIGHT AND IMPLEMENT EFFICIENT NUMERICAL METHODS TO ASSESS MODEL SENSITIVITIES TO INPUT PARAMETERS. WE WILL USE OUR EXPERIENCE MODELING AND IMPLEMENTING STRATOSPHERIC CHEMISTRY IN THE GEOS-CHEM UCX 3D CHEMICAL-TRANSPORT MODEL TO FURTHER ADVANCE MODELING OF THE IMPACT OF AIRCRAFT FLYING IN THE STRATOSPHERE. SPECIFIC FOCUS AREAS WILL INCLUDE IMPROVING THE TREATMENT OF WATER INTRODUCED IN THE STRATOSPHERE BY HIGH-ALTITUDE AIRCRAFT AND EXTENDING HETEROGENEOUS REACTION MECHANISMS TO INCLUDE CHEMISTRY ON HYDROPHILIC CARBONACEOUS AEROSOLS. IN ADDITION TO THE DIRECT INTERACTIONS OF AVIATION NOX WITH THE OZONE CYCLE WE ANTICIPATE ADDITIONAL OZONE EFFECTS DUE TO INTERACTIONS BETWEEN AVIATION EMISSIONS AND CHLORINE ACTIVATION AND INDIRECT CLIMATE EFFECTS DUE TO OXIDATION OF ATMOSPHERIC METHANE. WE WILL IMPLEMENT AN ADJOINT MODEL OF GEOS-CHEM UCX IN ORDER TO EFFICIENTLY ASSESS A WIDE RANGE OF EMISSIONS AND ROUTE SELECTION SCENARIOS. A SINGLE ADJOINT MODEL RUN WILL PROVIDE THE SENSITIVITY COEFFICIENTS NEEDED TO COMPUTE FIRST-ORDER ESTIMATES FOR CHANGES TO MEAN OZONE CONCENTRATION POPULATION EXPOSURE TO UV AND GLOBAL RADIATIVE FORCING FOR ANY FLEET AND EMISSIONS SCENARIO INCLUDING THE EVALUATION OF IMPACTS FROM INDIVIDUAL ROUTES AND THE EFFECT OF INDIVIDUAL DESIGN DECISIONS. WE WILL ALSO INCORPORATE THE CLIMATE IMPACT RESULTING FROM DIFFERENCES IN CONTRAIL FORMATION BETWEEN HIGH-ALTITUDE SUPERSONIC AIRCRAFT AND CONVENTIONAL AIRCRAFT BY EXTENDING OUR EXISTING CONTRAIL MODEL TO STRATOSPHERIC ALTITUDES AND INTRODUCING MICROPHYSICAL MODELS FOR HETEROGENEOUS NUCLEATION OF MIXED WATER/SULFURIC ACID VAPOR AND HOMOGENEOUS NUCLEATION OF ICE CRYSTALS. SIMPLIFIED CHEMICAL KINETIC MODELS OF SUPERSONIC CRUISE AIRCRAFT ENGINES WILL BE EMPLOYED TO ESTIMATE EMISSIONS PROFILES FOR BLACK CARBON NOX SOX AND OTHER SPECIES AFFECTING ATMOSPHERIC CHEMISTRY AND RADIATIVE TRANSFER. THE POTENTIAL IMPACTS OF ALTERNATIVE JET FUELS INCLUDING LOW-SULFUR LOW AROMATICS FUELS PRODUCED BY HEFA AND FISCHER-TROPSCH PROCESSES WILL BE MODELED BY INCORPORATING DATA FROM EXPERIMENTAL MEASUREMENTS WITH THE ENGINE MODEL. WE WILL ALSO CONSIDER SCENARIOS FOR POSSIBLE LNG-FUELED AIRCRAFT WHICH COULD OFFER SIMILAR EMISSIONS BENEFITS. THE IMPACT OF SUPERSONIC CRUISE AIRCRAFT WILL DEPEND ON THE ROUTES AND SCHEDULES OF THOSE AIRCRAFT. WE WILL IDENTIFY A SET OF PHYSICALLY AND ECONOMICALLY FEASIBLE ROUTES BASED ON INSIGHTS FROM FLEET ASSIGNMENT MODELS IN WHICH AIRCRAFT ARE ASSIGNED TO ROUTES SO AS TO MAXIMIZE NETWORK PROFITABILITY. WE WILL DEVELOP AND ASSESS SCENARIOS FOR CHANGES IN FLEET ASSIGNMENTS IN WHICH PROPORTIONS OF FLIGHTS ARE REPLACED WITH SUPERSONIC AIRCRAFT AS WELL AS SCENARIOS IN WHICH SUPERSONIC AIRCRAFT SERVE AS A SUPPLEMENT TO THE SUBSONIC FLEET.