AMMONIA IN THE ATMOSPHERE CONTRIBUTES TO THE FORMATION OF PARTICLES THAT DIMINISH HUMAN HEALTH. ADDITIONALLY DEPOSITION OF EXCESS AMMONIA CAN LEAD TO EUTROPHICATION OF ECOSYSTEMS. CURRENTLY ANTHROPOGENIC EMISSIONS OF AMMONIA PRIMARILY FROM AGRICULTURE CONTRIBUTE A SUBSTANTIAL PORTION OF THE BUDGET OF ATMOSPHERIC NITROGEN. NEVERTHELESS ESTIMATES OF AMMONIA EMISSIONS ARE QUITE UNCERTAIN SINCE A VARIETY OF NATURAL PROCESSES THAT PRODUCE AMMONIA AND EMISSIONS RATES FROM ANTHROPOGENIC SOURCES ARE POORLY CONSTRAINED. STRATEGIES FOR REDUCING CONCENTRATIONS OF PARTICLES ARE EVALUATED WITH MODELS OF THE ATMOSPHERE WHICH REPRESENT THE MOVEMENT OF AIR AS WELL AS THE CHEMICAL REACTIONS THAT TRANSFORM AMMONIA AND OTHER GASES SUCH AS OXIDES OF NITROGEN AND SULFUR DIOXIDE INTO PARTICLES. THE MODELS DEPEND ON ESTIMATED PARTICLE PRECURSOR EMISSIONS RATES WHICH ARE RELATIVELY UNCERTAIN COMPARED TO THE CHEMISTRY AND METEOROLOGY IN THE MODEL. IN THE U.S. PARTICLE CONCENTRATIONS HAVE DECLINED OVER THE LAST FOUR DECADES AS THE NATIONAL AMBIENT AIR QUALITY STANDARDS (NAAQS) HAVE BEEN TIGHTENED. EMISSIONS CONTROLS OF OXIDES OF NITROGEN AND SULFUR DIOXIDE ON FOSSIL FUEL COMBUSTION SOURCES ARE LARGELY RESPONSIBLE FOR THESE DECLINES. AS SUCH DEVELOPING EMISSIONS MITIGATION STRATEGIES TO REDUCE PARTICLES HAS BECOME MORE CHALLENGING AND HAS HIGHLIGHTED THE IMPORTANCE OF REDUCING AMMONIA CONCENTRATIONS WHICH HAD LARGELY BEEN NEGLECTED IN EMISSIONS CONTROL STRATEGIES. THE CROSS-TRACK INFRARED SOUNDER(CRIS) INSTRUMENT WHICH FLIES ON THE SUOMI NATIONAL POLAR-ORBITING PARTNERSHIP SATELLITE IN THE JOINT POLAR SATELLITE SYSTEM PROVIDES REGULAR OBSERVATIONS OF AMMONIA CONCENTRATIONS ACROSS THE GLOBE. THIS WORK WILL LEVERAGE THESE OBSERVATIONS AS A CONSTRAINT FOR IMPROVING AMMONIA EMISSIONS ESTIMATES IN A REGIONAL FOUR-DIMENSIONAL VARIATIONAL (4D-VAR) DATA ASSIMILATION FRAMEWORK. ADDITIONALLY THE AUGMENTED ATMOSPHERIC CHEMISTRY MODEL INTEGRAL TO THE 4D-VAR FRAMEWORK WILL ENABLE EFFICIENT CALCULATION OF SPATIALLY-HETEROGENEOUS INFLUENCES OF AMMONIA EMISSIONS ON CONCENTRATION-BASED METRICS SUCH AS THE DAMAGES PARTICLES CAUSE TO HUMAN HEALTH OR THE EUTROPHICATION INDUCED BY IT. THE REFINED ESTIMATES OF AMMONIA EMISSIONS FROM APPLICATION OF THE DATA ASSIMILATION APPROACH WILL PROVIDE TWO KEY PRODUCTS. FIRST WITH REFINED ESTIMATES OF AMMONIA EMISSIONS THE SCIENTIFIC COMMUNITY WILL HAVE A BETTER UNDERSTANDING OF ATMOSPHERIC COMPOSITION. SECONDLY THE EFFICIENT ADJOINT-BASED ESTIMATES OF THE HETEROGENEOUS IMPACTS OF AMMONIA EMISSIONS ON HEALTH AND ECOSYSTEM ENDPOINTS WILL BE MORE ACCURATE. IN CONCERT WITH ONE ANOTHER THESE REFINED ESTIMATES OF ATMOSPHERIC COMPOSITION AND EMISSIONS IMPACTS WILL SERVE ENVIRONMENTAL DECISION MAKERS WHO ARE SEEKING OPTIMAL ROUTES TO REDUCING DAMAGES FROM PARTICLES CONCENTRATIONS OR NITROGEN DEPOSITION. NASA HAS SUPPORTED SCIENTIFIC APPLICATIONS OF SATELLITE-BASED OBSERVATIONS THAT ENHANCE UNDERSTANDING OF ATMOSPHERIC COMPOSITION WHICH THIS WORK WILL ACCOMPLISH THROUGH IMPROVING MODELED VALUES OF ATMOSPHERIC AMMONIA BY REFINING THE MOST UNCERTAIN MODEL PARAMETERS EMISSIONS RATES. THROUGH THE HEALTH AND AIR QUALITY APPLIED SCIENCES TEAM (HAQAST) NASA HAS DEMONSTRATED AN INTEREST IN DEVELOPING MODELING TOOLS THAT DIRECTLY IMPROVE THE QUALITY AND EFFICIENCY OF THE ENDEAVORS OF AIR QUALITY AND HUMAN HEALTH STAKEHOLDERS. THIS WORK WILL SERVE ENVIRONMENTAL DECISION MAKERS BY TRANSFERRING THE USE OF THE CMAQ ADJOINT TO THIS COMMUNITY FOR EFFICIENT ELUCIDATION OF THE EMISSIONS MOST IMPACTING THE AREA OF INTEREST. FINALLY THIS EFFORT WOULD ESTABLISH A FRAMEWORK FOR LEVERAGING CRIS-BASED AMMONIA OBSERVATIONS WHICH COULD BE EXTENDED TO OTHER ATMOSPHERIC CONSTITUENTS IN THE FUTURE.