AERODYNE AEROSOL MASS SPECTROMETERS (AMS) ARE WIDELY USED TO QUANTIFY AND CHARACTERIZE THE COMPOSITION OF NON-REFRACTORY SUBMICRON PARTICLES WHICH ARE CENTRAL TO CLIMATE AND AIR QUALITY. AMSS HAVE BEEN DEPLOYED DURING MANY AIRCRAFT MEASUREMENT CAMPAIGNS INCLUDING ON NASA AIRCRAFT. THOSE DATASETS HOSTED AT NASA AND OTHER AGENCIES AROUND THE WORLD ARE NEEDED TO CONSTRAIN THE SOURCES AND PROPERTIES OF SUBMICRON AEROSOLS AND TO INFORM THEIR MODELING. THE QUANTIFICATION CAPABILITIES OF THE AMS HAVE RECENTLY BEEN DEBATED IN THE SCIENTIFIC LITERATURE ALTHOUGH THERE IS NO EVIDENCE SO FAR THAT REAL UNCERTAINTIES FOR AMBIENT DATA ARE LARGER THAN THE STATED ONES IN PARTICULAR FOR AIRCRAFT DATASETS. THE OBJECTIVE OF THIS PROPOSAL IS TO BETTER CONSTRAIN THESE UNCERTAINTIES IN AMS QUANTIFICATION IN PARTICULAR FOR NASA CAMPAIGNS. THESE GOALS WILL BE ACHIEVED THROUGH THE FOLLOWING SYNERGISTIC TASKS: (1) INVESTIGATION OF AMS QUANTIFICATION USING EXISTING NASA DATASETS. RIGOROUSLY CHARACTERIZING THE UNCERTAINTIES OF AMBIENT AMS DATA USING A COMBINATION OF AIRCRAFT DATASETS (FROM THE NASA MISSIONS INTEX-B ARCTAS DC3 SEAC4RS KORUS-AQ AND ATOM) AND KEY GROUND STUDIES. THESE DATASETS ARE IDEAL DUE TO OUR INTIMATE KNOWLEDGE OF THEM THE AVAILABILITY OF MULTIPLE HIGH-QUALITY SUPPORTING MEASUREMENTS ALLOWING REDUNDANT CONSTRAINTS AND THE WIDE RANGE OF AEROSOL TYPES SAMPLED. WE WILL EVALUATE MULTIPLE REDUNDANT INTERCOMPARISONS WITH COLLOCATED INSTRUMENTS INCLUDING COMPARISON TO AEROSOL VOLUME AND CHEMICAL MEASUREMENTS OPTICAL CLOSURE AND HYGROSCOPIC CLOSURE. THE LAST APPROACH IS UNIQUE IN SERVING TO CONSTRAIN THE ORGANIC / INORGANIC RATIO. THE UNCERTAINTIES IN ALL MEASUREMENTS WILL BE PROPAGATED RIGOROUSLY. IF ANY SYSTEMATIC BIASES ARE IDENTIFIED ACROSS ALL DATASETS A CORRECTION WILL BE PROPOSED. MORE ACCURATE UNCERTAINTY ESTIMATES WILL ARISE FROM THESE ANALYSES WHICH WILL ALSO ADD ANOTHER LAYER OF QUALITY CONTROL TO DATASETS ALREADY IN THE NASA ARCHIVE. (2) INVESTIGATION OF AMMONIUM SALT DETECTION WITH SOFT-IONIZATION. PERFORMING LABORATORY EXPERIMENTS COUPLING SOFT-IONIZATION TO THE AMS AT THE ADVANCED LIGHT SOURCE (ALS) TO SHED LIGHT ON THE VAPORIZATION AND THERMAL DECOMPOSITION MECHANISMS. AMMONIUM SALTS WILL BE INVESTIGATED TO CLARIFY THE REASONS BEHIND THE HIGH OBSERVED RELATIVE IONIZATION EFFICIENCY OF NH4 (RIE_NH4) WHICH HAS BEEN THE SUBJECT OF RECENT LITERATURE DISCUSSIONS. THIS WILL ALLOW AN IMPROVED UNDERSTANDING OF AMS DETECTION WHICH COULD TRANSLATE INTO IMPROVED QUANTIFICATION. (3) MEASUREMENTS OF RIE_OA AND CE*RIE_OA FOR AMBIENT ORGANIC AEROSOL PARTICLES. INVESTIGATING THE MOST UNCERTAIN PARAMETERS IN AMS QUANTIFICATION OF AMBIENT ORGANIC AEROSOLS (OA) THE RELATIVE IONIZATION EFFICIENCY (RIE_OA) AND PARTICLE COLLECTION EFFICIENCY (CE) BY DIRECT MEASUREMENTS OF AMBIENT OA AS WELL AS BY RE-AEROSOLIZING AMBIENT OA FROM FILTERS. THE FILTER MEASUREMENTS WILL UTILIZE A NEWLY DEVELOPED CALIBRATION METHOD AND SHOULD PROVIDE THE MOST DIRECTLY CONSTRAINED DETERMINATIONS OF RIE_OA FOR AMBIENT OA TO DATE. THE AMBIENT REAL-TIME MEASUREMENTS WILL EXPLORE POSSIBLE COMPENSATING EFFECTS OF RIE_OA AND CE AND THE EFFECT OF EXTERNAL MIXING. (4) EVALUATION OF CAPTURE VAPORIZER (CV) MEASUREMENTS OF OA SPECIES. RECENT LABORATORY AND FIELD MEASUREMENTS DEMONSTRATE THAT THE RECENTLY-DEVELOPED CV HAS THE POTENTIAL TO ELIMINATE THE EFFECT OF PARTICLE BOUNCE AND THUS SIGNIFICANTLY REDUCE AMS QUANTIFICATION UNCERTAINTY ESPECIALLY IN REMOTE ENVIRONMENTS TARGETED BY AIRCRAFT. HOWEVER THERE IS STILL A NEED FOR A MORE COMPLETE CHARACTERIZATION OF THE DEGREE TO WHICH THE CV CAN QUANTIFY IMPORTANT OA PROPERTIES THAT ARE OBTAINED FROM AMS SPECTRA. THE RESULTS FROM THE DIFFERENT TASKS WILL BE INTEGRATED AND IMPLEMENTED IN STANDARD AMS QUANTIFICATION PROTOCOLS. THE PROPOSED WORK WILL RESULT IN MORE ACCURATE UNCERTAINTIES AND IMPROVED CONFIDENCE ON THE QUANTIFICATION OF AMS DATA IN NASA AIRCRAFT CAMPAIGNS AND OTHER APPLICATIONS.