IT IS WELL KNOWN THAT HETEROGENEOUS HALOGEN CHEMISTRY ON AND IN POLAR STRATOSPHERIC PARTICLES (PSCS) PLAYS A DOMINANT ROLE IN DRIVING CHANGES IN POLAR CHEMICAL COMPOSITION AND OZONE DEPLETION. WHILE SUCH PROCESSES COULD ALSO BE IMPORTANT OUTSIDE THE POLAR REGIONS THEIR IMPACTS THERE ARE SMALLER AND THEREFORE MORE DIFFICULT TO IDENTIFY. THE FUNDAMENTAL OBJECTIVE OF THIS PROPOSAL IS TO BETTER CHARACTERIZE AND QUANTIFY HETEROGENEOUS HALOGEN CHEMISTRY OUTSIDE THE POLAR REGIONS BY EXPLOITING THE EXTENSIVE SAMPLING PROVIDED BY DIFFERENT SATELLITE DATASETS COUPLED WITH INSIGHTS FROM A NUMERICAL MODEL. WE WILL MAKE USE NOT JUST OF AVERAGE VALUES BUT ALSO WILL EMPLOY OBSERVED AND MODELED PROBABILITY DISTRIBUTION FUNCTIONS. SIGNIFICANT ACTIVATION OF INORGANIC HALOGENS OUTSIDE THE POLAR REGIONS MAY POTENTIALLY RESULT IN THE FOLLOWING: (I) DEPLETION OF OZONE INCLUDING POSSIBLE CHEMISTRY-CLIMATE COUPLING (II) CHANGES IN THE CHEMICAL BUDGETS NOT ONLY OF CHLORINE AND BROMINE SPECIES BUT ALSO THOSE OF NITROGEN COMPOUNDS IN THE UPPER TROPOSPHERE AND LOWER STRATOSPHERES; AND (III) ALTERATION OF THE LOCAL LOSS RATES AND LIFETIMES OF SOME ORGANIC MOLECULES DUE TO ENHANCED ATOMIC CHLORINE CONCENTRATIONS E.G. ETHANE AND METHANE NEAR THE TROPOPAUSE. THESE CONSIDERATIONS BROADEN THE SCOPE OF POTENTIAL IMPACTS ASSOCIATED WITH THE CHEMISTRY TO BE EVALUATED IN THIS PROPOSAL. AMONG THE FACTORS GOVERNING HETEROGENEOUS PROCESSING ARE THE DETAILED DISTRIBUTIONS OF AEROSOLS AND WATER VAPOR. THE PROPOSED WORK WILL ANALYZE THIS CHEMISTRY USING THE RICH DATABASE OF SATELLITE PRODUCTS FROM AVAILABLE LONG RECORDS PROVIDED BY OCCULTATION AND EMISSION INSTRUMENTS USING A SUITE OF MEASUREMENTS OF TEMPERATURE NITROGEN DIOXIDE (NO2) HYDROGEN CHLORIDE (HCL) CHLORINE NITRATE (CLONO2) WATER VAPOR (H2O) OZONE (O3) AEROSOLS AND CLOUD INFORMATION. THE OBSERVATIONS WILL BE PROBED IN CONJUNCTION WITH THE NATIONAL CENTER FOR ATMOSPHERIC RESEARCH COMMUNITY EARTH SYSTEM MODEL VERSION 2 (CESM2) WHOLE ATMOSPHERE COMMUNITY CLIMATE MODEL (WACCM). THE CESM2 (WACCM) IS THE LATEST VERSION OF THIS MODELING FRAMEWORK. THE OBSERVATIONS WILL PROVIDE A CRITICAL AND QUANTITATIVE TEST OF THE MODEL AND PHOTOCHEMICAL UNDERSTANDING AND THE COMPARISONS OF DIFFERENT DATASETS TO EACH OTHER AND TO THE MODEL CAN BE EXPECTED TO ILLUMINATE POSSIBLE MEASUREMENT UNCERTAINTIES AND SENSITIVITIES. THE CESM2 (WACCM) MODEL WILL BE RUN IN SPECIFIED DYNAMICS MODE USING THE NASA GLOBAL MODELING AND ASSIMILATION OFFICE MODERN-ERA RETROSPECTIVE ANALYSIS FOR RESEARCH AND APPLICATIONS VERSION 2 (MERRA2) METEOROLOGICAL FIELDS. THIS WILL ALLOW SYNOPTIC COMPARISON OF MODEL AND OBSERVATIONS FOR THE PARTICULAR CONDITIONS OF EACH MISSION. WACCM ALREADY HAS A PURPOSE-BUILT CAPABILITY TO OUTPUT CHEMICAL CONSTITUENT AND OTHER INFORMATION AT THE SPECIFIC LONGITUDE LATITUDE AND LOCAL TIME OF THE GIVEN SATELLITE INSTRUMENTS MAKING IT WELL SUITED FOR EXAMINING A BROAD RANGE OF SATELLITE DATASETS INCLUDING THOSE FOR DIURNALLY VARYING SPECIES.