AS A MIX OF BOTH DIRECTLY EMITTED PARTICLES ALONG WITH SPECIES FORMED SECONDARILY IN THE ATMOSPHERE AEROSOL DISTRIBUTIONS ARE GOVERNED BY A COMPLEX INTERPLAY OF EMISSIONS METEOROLOGY TRANSPORT AND CHEMISTRY. MODELS THUS PLAY A SIGNIFICANT ROLE IN INTERPRETATION OF AEROSOL REMOTE SENSING MEASUREMENTS BUT THIS INTRODUCES POTENTIAL ERRORS FROM MODEL REPRESENTATION OF AEROSOL PROCESSES AS WELL AS SIGNIFICANT UNCERTAINTIES IN EMISSIONS. DATA ASSIMILATION AND INVERSE MODELING CAN BE USED TO INCORPORATE OBSERVATIONS OF AEROSOLS AND THEIR PRECURSORS INTO AIR QUALITY AND WEATHER FORECAST MODELS. HOWEVER MOST EFFORTS TO DATE HAVE FOCUSED ON INVERTING FOR A PARTICULAR SUBSET OF AEROSOL SOURCES MEASUREMENTS E.G. DUST OR HAVE ASSIMILATED INTEGRAL QUANTITIES PM2.5 AOD WITHOUT EXTRACTING INFORMATION RELATED TO COMPOSITION AND SOURCES RELYING ON MODEL ASSUMPTIONS WHICH MAY BE SYSTEMATICALLY BIASED. GIVEN THESE CHALLENGES HERE WE PROPOSE TO ADVANCE THE USE OF BOTH TRACE-GAS AND AEROSOL REMOTE SENSING DATA FROM MULTIPLE OBSERVATIONAL PLATFORMS E.G. OMI MODIS AND AERONET TO IMPROVE OUR UNDERSTANDING OF THE PROPERTIES AND SOURCES OF ATMOSPHERIC AEROSOLS. WE FOCUS ON CHALLENGES RELATED TO HARMONIZATION AND UTILIZATION OF BOTH GAS-PHASE AND AEROSOL-PHASE MEASUREMENTS AND THE SIMULTANEOUS NEED FOR BOTH DETAILED HIGH-RESOLUTION STUDIES OF REGIONAL AIR QUALITY ALONG WITH BROADER EVALUATION OF TRENDS THROUGHOUT THE GLOBE. SPECIFICALLY WE AIM TO ADDRESS THE FOLLOWING RESEARCH QUESTIONS: (1) WHAT IS THE BENEFIT OF MULTI-SPECIES MULTI-PHASE DATA ASSIMILATION OVER SEQUENTIAL SINGLE SPECIES INVERSIONS AND WHAT CAN THIS TELL US ABOUT OUR AEROSOL MODEL AND SOURCE ESTIMATES? (2) HOW CAN COMBINATIONS OF EXISTING AND UPCOMING REMOTE SENSING TOOLS BE USED SYNERGISTICALLY TO REFINE MONTHLY ANTHROPOGENIC EMISSIONS TO FACILITATE IMPROVED AIR QUALITY FORECASTING? (3) WHAT ARE THE GLOBAL SPATIOTEMPORAL TRENDS OF AEROSOL AND AEROSOL PRECURSOR EMISSIONS THROUGHOUT THE LIFETIME OF AURA? (4) HOW DO TRENDS IN AEROSOL SOURCES AFFECT ATMOSPHERIC COMPOSITION AND WHAT ARE THE RESIDUAL LOCAL AND LONG-RANGE IMPACTS ON AIR QUALITY CLIMATE AND REACTIVE NITROGEN DEPOSITION? TO ANSWER THESE QUESTIONS WE WILL UTILIZE THE GEOS-CHEM ADJOINT MODEL TO PERFORM THE FIRST EVER MULTI-SPECIES MULTI-PHASE 4DVAR INVERSIONS. THESE WILL BE DRIVEN THROUGH ASSIMILATION OF SO2 AND NO2 FROM OMI AND TROP-OMI EVENTUALLY AOD FROM MODIS OMI AND AERONET AND SINGLE SCATTERING ALBEDO ACROSS MULTIPLE WAVELENGTHS FROM AERONET; ADDITIONAL REMOTE SENSING MEASUREMENTS WILL BE USED FOR CROSS-VALIDATION. THE USE OF TRACE-GAS AND AERONET DATA WILL ALLOW US CORRECT ERRORS IN MODEL AEROSOL COMPOSITION AND MICROPHYSICAL DESCRIPTION. A NEW HYBRID MASS BALANCE / 4DVAR TECHNIQUE WILL BE USED TO EFFICIENTLY EVALUATE TRENDS OF TRACE-GAS EMISSIONS. REGIONAL STUDIES AT HIGHER RESOLUTION 0.25 0.3125 WILL BE USED TO CONSTRAIN CURRENT MONTHLY ANTHROPOGENIC EMISSIONS INVENTORIES THAT COULD BE USED FOR IMPROVED AIR QUALITY FORECASTING. THE BROADER IMPACTS OF THESE RESULTS WILL BE EVALUATED THROUGH ASSESSMENTS OF MULTIPLE ENVIRONMENTAL IMPACTS SUCH AS AIR QUALITY CLIMATE AND ECOSYSTEMS. THIS PROPOSAL THUS SUPPORT THE SOLICITED AURA-ACMAP RESEARCH GOALS OF USING AURA DATA ALONG WITH OTHER SATELLITE TRACE GAS DATA SETS TO QUANTIFY AND MAP EMISSIONS AND QUANTIFY THE IMPACT OF LONG-RANGE TRANSPORT AND EXPORT OF TRACE GASES IMPORTANT TO AIR QUALITY THE EFFECTS OF AIR QUALITY ON CLIMATE TO STUDY ATTRIBUTION OF CHANGES IN AIR QUALITY OVER THE PAST 20 YEARS AND TO STUDY AEROSOL CHARACTERISTICS WITH RESPECT TO THEIR IMPACTS ON TROPOSPHERIC CHEMICAL PROCESSES. ALL OF THESE ACTIVITIES SUPPORT THE BROADER ACMAP RESEARCH ISSUE OF INVESTIGATING LONG-TERM TRENDS IN ATMOSPHERIC COMPOSITION WHERE CAUSE AND EFFECT AS WELL AS ATTRIBUTION AND PREDICTION ARE ELUCIDATED THROUGH THE USE OF MODELS AND OBSERVATIONS FROM MULTIPLE INSTRUMENTS.