PROPOSAL SUMMARYWE PROPOSE TO CONTINUE OUR STUDIES OF ATMOSPHERIC ORGANIC TRACE GAS COMPOSITION FROM DIFFERENT ATMOSPHERIC REGIONS TO ADDRESS SCIENTIFIC QUESTIONS RELATED TO UNDERSTANDING AND IMPROVING PREDICTIVE CAPABILITY FOR CHANGES IN THE OZONE LAYER CLIMATE FORCING AND AIR QUALITY ASSOCIATED WITH CHANGES IN ATMOSPHERIC COMPOSITION. THE PROPOSED RESEARCH WILL MAINTAIN AND FURTHER STRENGTHEN THE CAPABILITIES OF OUR GROUP TO DEPLOY WHOLE AIR SAMPLING INSTRUMENTS FROM AIRBORNE AND SHIP-BASED PLATFORMS AND TO MEASURE A WIDE RANGE OF ORGANIC TRACE GASES RELEVANT TO STUDYING CHEMISTRY OF THE UT/LS REGION. BECAUSE OF ITS UNIQUE CAPABILITIES WE WILL KEEP UR BALLOON BORNE SAMPLER IN A STANDBY MODE FOR POTENTIAL USE AS NEEDED TO ADDRESS SPECIFIC PROBLEMS. IN PAST CAMPAIGNS WE HAVE MEASURED HALOCARBON SOURCE GASES AND A RANGE OF TRACERS THAT PROVIDE NEEDED INFORMATION ON TEMPORAL TRENDS IN ATMOSPHERIC TRACE GASES IN THE UT/LS ON REACTIVE HALOGEN BUDGETS AND ON AIR MASS SOURCES AND CHEMICAL PROCESSING. THESE MEASUREMENTS WERE DONE WITH A WHOLE AIR SAMPLER DEPLOYED AS PART OF DIFFERENT AIRBORNE INSTRUMENT PAYLOADS INCLUDING THE ER-2 WB-57 GLOBAL HAWK AND NSF GV. DURING THIS PROJECT WE WILL FOCUS ON SYNTHESIS OF DATA COLLECTED FROM PREVIOUS CAMPAIGNS AND WE WILL MAINTAIN THE WHOLE AIR SAMPLING AND ANALYTICAL CAPABILITIES FOR FUTURE UT/LS FIELD MISSIONS. DURING THE FINAL YEAR OF THE PROJECT WE PLAN TO ENGAGE OTHERSCIENTIFIC GROUPS OR INSTITUTIONS TO BEGIN A TRANSITION OF STRATOSPHERIC WHOLE AIR SAMPLING CAPABILITIES FROM THE CURRENT PI TO A NEW LEADERSHIP GROUP (WITH DETAILS TO BE DEFINED AT AN APPROPRIATE LATER TIME).FOR THE CURRENT PROPOSAL THE MAJOR OBJECTIVES OF OUR PROJECT ARE: - UNDERSTANDING THE ROLE OF SHORT-LIVED HALOGEN SPECIES ON REACTIVE CHEMISTRY IN THE UT/LS THROUGH MEASUREMENTS OF A BROAD RANGE OF HALOGENATED SOURCE GASES FROM WHOLE AIR SAMPLES. - USE OF TRACE GASES FROM MARINE AND CONTINENTAL REGIONS TO DIAGNOSE TRANSPORT PATHWAYS SOURCE REGIONS AND THE ROLE OF CONVECTION IN SHAPING THE CHEMISTRY AND MICROPHYSICAL PROPERTIES OF THE UT/LS AND THE TTL REGION. - USE OF MODEL RESULTS FROM CAM-CHEM (AND OTHER MODELS) TO SYNTHESIZE THE WEALTH OF DATA FROM PAST CAMPAIGNS AND TO TEST VARIOUS MODEL PERFORMANCES E.G. EMISSIONS ETC. - CONTINUATION OF LONG-TERM MEASUREMENT OF CFC REPLACEMENT GASES IN THE STRATOSPHERE (HCFCS HFCS ETC.) PERFLUOROCARBON GASES ETC. TO BETTER UNDERSTAND THEIR TRANSPORT AND FATE IN THE ATMOSPHERE. - MAINTENANCE AND ENHANCEMENT OF CURRENT SAMPLING AND ANALYTICAL TECHNIQUES IN PREPARATION FOR FUTURE FIELD MISSIONS.