CLOUD-RELEVANT AEROSOL CHEMISTRY AND PHYSICS: OVERCOMING THE CLEAR SKY BIAS .A. CARLTON UNIV. OF CALIFORNIA IRVINE V. GHATE ARGONNE NATIONAL LAB. .AT ANY GIVEN TIME CLOUDS COVER ABOUT 60% OF EARTH S SURFACE. BOUNDARY LAYER CUMULUS CLOUDS ARE THE PRIMARY CHANNELS BY WHICH CHEMICALS FROM THE POLLUTED BOUNDARY LAYER ARE LOFTED TO THE FREE TROPOSPHERE. CUMULUS CLOUDS A COLLECTION OF ATMOSPHERIC AQUEOUS PHASE REACTORS SCAVENGE SOLUBLE GASES AND SUSTAIN OXIDATION REACTIONS YIELDING LOWER VOLATILITY PRODUCTS WHICH CONTRIBUTE TO AND CHEMICALLY MODIFY AEROSOL MASS ALOFT WHEN DROPLETS EVAPORATE. BOUNDARY LAYER CUMULUS REFLECT A GREATER AMOUNT OF SOLAR RADIATION BACK TO SPACE COMPARED TO THE UNDERNEATH LAND SURFACE. DESPITE THE ABUNDANCE AND IMPORTANCE OF CLOUDS APPROACHES TO UNDERSTAND TROPOSPHERIC COMPOSITION GENERALLY HAVE A CLEAR SKY BIAS THAT HINDERS KNOWLEDGE OF AEROSOL PHYSICOCHEMICAL PROPERTIES AND THEIR DISTRIBUTION DURING CLOUDY PERIODS. FOR EXAMPLE ATMOSPHERIC CHEMISTRY AIRCRAFT CAMPAIGNS OFTEN AVOID CLOUDS. RETRIEVAL TECHNIQUES ARE SENSITIVE TO SCATTERING DUE TO CLOUDS AND GENERALLY PROVIDE AEROSOL RADIATIVE PROPERTIES IN CLOUD-FREE REGIONS. AEROSOL WATER UPTAKE FOR A GIVEN CHEMICAL COMPOSITION INCREASES WITH INCREASING BOUNDARY LAYER RELATIVE HUMIDITY (RH) AND HIGHER RH RESULTS IN GREATER CUMULUS CLOUD COVER. HENCE WHEN PARTICLE CHEMICAL PROPERTIES THAT GOVERN WATER UPTAKE ARE MOST CRITICAL THEY ARE LEAST UNDERSTOOD. .THIS IS A KEY KNOWLEDGE GAP. .THROUGH THE PROPOSED WORK WE WILL EVALUATE THE RELATION OF CLOUDS TO THE PHYSICOCHEMICAL PROPERTIES OF FINE PARTICLE MASS OVER THE U.S. USING AN INTEGRATED OBSERVATIONAL STRATEGY INVOLVING SPACE- AND SURFACE-BASED PLATFORMS IN ADDITION TO ATMOSPHERIC MODELING. WE SEEK TO UNDERSTAND TROPOSPHERIC FORMATION PROPERTIES AND VERTICAL DISTRIBUTION OF AEROSOLS AS WELL AS AEROSOL INTERACTION WITH CLOUDS. WE HYPOTHESIZE THAT PRIMARILY IN THE CENTRAL AND EASTERN U.S. A CLEAR SKY BIAS IN UNDERSTANDING OF ATMOSPHERIC COMPOSITION OBSCURES CYCLES IN AEROSOL HYGROSCOPICITY THAT INFLUENCE WATER UPTAKE IN WAYS IMPORTANT FOR REGIONAL RADIATION BUDGETS. THE SPECIFIC QUESTIONS THAT WILL HELP US TEST THE ABOVE HYPOTHESIS ARE: 1) HOW DO AEROSOL PHYSICAL AND CHEMICAL PROPERTIES DIFFER DURING CLOUDY AND CLEAR-SKY PERIODS OVER THE U.S.? AND 2) HOW DO THE VERTICAL PROFILES OF CLIMATE-RELEVANT RADIATIVE PROPERTIES OF TROPOSPHERIC FINE PARTICLE MASS VARY DURING CLOUDY AND CLEAR-SKY PERIODS IN THE CENTRAL AND EASTERN U.S.? .WE PROPOSE TO EMPLOY A COMBINATION OF NASA DATA PRODUCTS FROM MODIS CALIPSO AND AERONET SURFACE OBSERVATIONS FROM ROUTINE NETWORKS AND INTENSIVE FIELD CAMPAIGNS IN ADDITION TO CLOUD CHEMISTRY MODELING WITHIN AN ATMOSPHERIC MODEL. WE FOCUS ON THE CENTRAL AND EASTERN U.S. UNIQUE LOCATIONS THAT EXPERIENCE A WIDE RANGE OF WEATHER PHENOMENA AND REMOTELY SENSED AEROSOL OPTICAL PROPERTIES. OUR OBJECTIVES ARE TO: 1) CHARACTERIZE PARTICLE HYGROSCOPICITY AND AEROSOL LIQUID WATER (ALW) CONTENT FROM THE SURFACE TO THE TOP OF THE BOUNDARY LAYER DURING CLOUDY AND CLEAR SKY PERIODS OVER THE U.S. FOR THE LAST ~20 YEARS 2) CHARACTERIZE NGSTR M EXPONENTS DURING CLOUDY AND CLEAR SKY PERIODS TO EVALUATE AND DEVELOP DETAILED RADIATIVE ESTIMATION TECHNIQUES 3) EXPLORE HOW INCLUSION OF DETAILED CLOUD CHEMISTRY CHANGES AEROSOL VERTICAL PROFILES AT LOCATIONS WHERE THE PREDICTED RADIATIVE IMPACTS CAN BE EVALUATED. .THIS PROPOSED RESEARCH DIRECTLY ADDRESSES NASA S STRATEGIC OBJECTIVE 1.1 TO UNDERSTAND THE EARTH SYSTEM. THIS PROPOSAL DIRECTLY RESPONDS TO AREAS A AND B OF THE A19 SOLICITATION BY INVESTIGATING TROPOSPHERIC AIR QUALITY OVER THE PAST 20 YEARS WITH A FOCUS ON ALOFT COMPOSITION INTERACTION WITH THE SURFACE AND RELATED SOURCE ATTRIBUTION . WE PROPOSE TO STUDY AEROSOL CHARACTERISTICS WITH RESPECT TO THEIR IMPACTS ON TROPOSPHERIC CHEMICAL PROCESSES IN ADDITION TO UNDERSTANDING THE EFFECTS OF CLOUDS ON AEROSOL RADIATIVE PROPERTIES AND AS AN AQUEOUS MEDIUM FOR CHEMICAL REACTIONS. .