THE OBJECTIVE OF THIS PROPOSAL IS TO DETERMINE IF THE LOWER LIMIT FOR 14N/15N IN PLUTO S HCN CAN BE USED TO CONSTRAIN THE ORIGIN OF PLUTO S NITROGEN. IN PREVIOUS STUDIES WE HAVE USED STABLE ISOTOPE RATIO MEASUREMENTS COMBINED WITH MODELING OF ISOTOPIC FRACTIONATION TO EVALUATE THE EVOLUTION OF TITAN S ATMOSPHERE AND HAVE FOUND THAT NITROGEN IN TITAN S ATMOSPHERE ORIGINATED AS NH3 IN THE PROTOSOLAR NEBULA (PSN). IT IS UNCLEAR AT THIS TIME IF THE NITROGEN IN PLUTO S ATMOSPHERE ORIGINATED AS NH3 IN THE PSN LIKE TITAN S OR IF THE FORMATION CONDITIONS FOR PLUTO WERE COLD ENOUGH TO TRAP AND RETAIN SUFFICIENT N2 IN THE PSN TO ACCOUNT FOR THE TOTAL INVENTORY OF NITROGEN ACQUIRED BY PLUTO DURING ITS FORMATION. THE RECENT NON-DETECTION OF HC15N IN PLUTO S ATMOSPHERE BY ALMA SUGGESTS THAT THE INFLUENCE OF CHEMISTRY ON THE EVOLUTION OF THE ISOTOPE RATIO IS LESS SIGNIFICANT AT PLUTO THAN IT HAS BEEN FOUND TO BE AT TITAN. IN ORDER TO BETTER UNDERSTAND THIS WE SEEK TO ADDRESS THE FOLLOWING THREE SCIENCE QUESTIONS: 1. HOW DOES NITROGEN ISOTOPE FRACTIONATION BETWEEN N2 AND HCN AT PLUTO COMPARE TO WHAT IS OBSERVED AT TITAN? 2. HOW DO CONDENSATION AEROSOL TRAPPING AND SUBLIMATION INFLUENCE THE ISOTOPIC COMPOSITION OF HCN AND N2 IN PLUTO S ATMOSPHERE? 3. HOW DOES THE ESCAPE OF 15N FROM PLUTO S ATMOSPHERE COMPARE TO THE ESCAPE OF 14N? WE WILL ADDRESS THESE OBJECTIVES THROUGH A SYSTEMATIC STUDY THAT WILL EXPLORE THE INFLUENCE OF DIFFERENT PRODUCTION AND LOSS PROCESSES OF HCN ON THE ISOTOPE RATIOS IN N2 AND HCN AND THE IMPLICATIONS FOR THE EVOLUTION OF THE ATMOSPHERE. THE PROPOSED WORK IS DIRECTLY RELEVANT TO THE NASA NFDAP PROGRAM BECAUSE IT MAKES USE OF THE RECENT ATMOSPHERIC OBSERVATIONS MADE BY THE NEW HORIZONS ALICE ULTRAVIOLET SPECTROGRAPH OF THE ALTITUDE PROFILES OF N2 CH4 AND THE C2 HYDROCARBONS TO VALIDATE OUR PHOTOCHEMICAL MODEL OF PLUTO S ATMOSPHERE. THIS OBSERVATION-VALIDATED MODEL WILL BE USED TO ADDRESS SCIENCE QUESTIONS OUTSIDE OF THE SCOPE OF THE NEW HORIZONS MISSION THUS BROADENING SCIENTIFIC PARTICIPATION IN THE ANALYSIS AND INTERPRETATION OF DATA RETURNED BY THESE MISSIONS.