CONTEXT: WILDFIRES EMIT VAST QUANTITIES OF ORGANIC GASES AND PARTICULATES. QUANTIFYING ORGANIC AEROSOL CONCENTRATIONS AND PROPERTIES IS IMPORTANT FOR ASSESSING THE VARIOUS ENVIRONMENTAL IMPACTS OF FIRES. SOME FRACTION OF THE ORGANIC AEROSOL FROM FIRES ABSORBS LIGHT. THE OPTICAL SIGNIFICANCE AND IMPACTS OF THIS SO-CALLED BROWN CARBON (BRC) ARE LARGELY UNKNOWN INCLUDING ITS INFLUENCE ON DIRECT RADIATIVE FORCING AND OVERALL CLIMATE IMPACT RELATIVE TO BLACK CARBON. IN CERTAIN CASES UV LIGHT ABSORPTION BY BRC MAY ALSO REDUCE PHOTOCHEMICAL REACTIONS RATES THAT AFFECT FORMATION OF SECONDARY POLLUTANTS SUCH AS OZONE. A KEY TO ASSESSING THE INFLUENCE OF BRC ON CLIMATE IS ITS EMISSIONS AND SUBSEQUENT PROCESSING AS IT AGES WHICH DETERMINES THE BRC DISTRIBUTION THROUGHOUT THE ATMOSPHERIC COLUMN. OUR PREVIOUS STUDIES OVER THE CONTINENTAL UNITED STATES INVOLVING DIRECT IN-SITU MEASUREMENTS OF BRC FROM NASA RESEARCH AIRCRAFT SHOW THAT BRC IS EMITTED FROM WILDFIRES BUT MUCH OF IT IS RAPIDLY DEPLETED BY PHOTOCHEMICAL PROCESSES SUCH AS BLEACHING AND YET IT IS FOUND DISPERSED THROUGHOUT THE TROPOSPHERE. PART OF THIS REDISTRIBUTION WAS FOUND TO BE DUE TO TRANSPORT TO THE UPPER TROPOSPHERE BY DEEP CONVECTION AND THAT IN-CLOUD HETEROGENEOUS PROCESSING MAY PRODUCE BRC. RADIATIVE TRANSFER CALCULATIONS SUGGEST THAT BRC ACCOUNTS FOR ABOUT 24% OF COMBINED BLACK AND BRC WARMING AT THE TROPOPAUSE UNDER CLEAR SKY CONDITIONS. THE OVERALL MASS OF WILDFIRE ORGANIC AEROSOL IS ALSO NOT WELL CHARACTERIZED DUE TO PARTICLE SIZE DETECTION LIMITATIONS WITH CURRENTLY UTILIZED INSTRUMENTATION. ACCURATE KNOWLEDGE OF THE TOTAL AEROSOL ORGANIC MASS IS NEEDED TO ASSESS ORGANIC AEROSOL BUDGETS. OBJECTIVE: THE MAJOR OBJECTIVE OF THIS PROPOSAL IS TO EXTEND THE DATA SETS ON BRC LEVELS TO ASSESS BRC SOURCES DISTRIBUTIONS AND OPTICAL IMPORTANCE. THIS PROJECT BUILDS ON OUR PAST DC8 AIRCRAFT MEASUREMENTS AND EXTENDS THE MEASUREMENT CAPABILITIES THROUGH THE FIRST DEPLOYMENT OF AN ONLINE DIRECT BRC MEASUREMENT SYSTEM. A SECONDARY OBJECTIVE IS TO INVESTIGATE THE SOURCES OF WATER-SOLUBLE ORGANIC CARBON (WSOC) AEROSOL AND CHARACTERIZE WSOC CONCENTRATIONS OVER A LARGE PARTICLE SIZE RANGE (ALL SIZED BELOW NOMINALLY 4 M DIAMETER) TO CONTRAST WITH CURRENT ORGANIC AEROSOL MEASUREMENTS THAT ARE LIMITED TO SUB-1 M PARTICLES. WSOC LEVELS WILL BE ASSESSED OVER BROAD SPATIAL SCALES OF THE CONTINENTAL TROPOSPHERE. METHOD: BRC AND WSOC WILL BE MEASURED FOLLOWING THE SAME METHOD EMPLOYED ON THE PREVIOUS NASA MISSIONS (DC3 AND SEAC4RS). FILTERS WILL BE SEQUENTIALLY EXTRACTED IN WATER AND METHANOL AND THE LIGHT ABSORPTION SPECTRA OF THE EXTRACTS DETERMINED WITH A LONG PATH SPECTROPHOTOMETER. WSOC WILL BE DETERMINED VIA A DISSOLVED ORGANIC CARBON MEASUREMENT OF THE FILER WATER EXTRACT. IN ADDITION THIS PROJECT WILL PROVIDE A SPECTROPHOTOMETER AND SUPPORT FOR COUPLING IT TO THE UNIVERSITY OF NEW HAMPSHIRE MIST CHAMBER SAMPLING SYSTEM FOR ONLINE MEASUREMENT OF BRC. THE DEPLOYMENT OF THIS NEW BRC SYSTEM WILL NOT INTERFERE WITH THE EXISTING USE OF THIS COLLECTOR FOR NITRIC ACID MEASUREMENTS. PERFORMANCE ASSESSMENT WILL BE BASED ON COMPARISONS TO FILTERMEASURED BRC. IMPACT: THIS PROJECT WILL PROVIDE QUANTITATIVE DATA ON IMPORTANT AEROSOL PROPERTIES RELATING TO WILDFIRE EMISSIONS INCLUDING INVESTIGATE THEIR OPTICAL IMPACTS AND AFFECT ON THE ORGANIC AEROSOL BUDGET.