SATELLITE INSTRUMENTS HAVE MADE MULTI-YEAR OBSERVATIONS OF TROPOSPHERIC NO2 COLUMNS WHICH PROVIDE TOP-DOWN CONSTRAINTS ON THE AMOUNTS CHANGES AND TREND OF NOX EMISSIONS OVER THE UNITED STATES. A NUMBER OF RESEARCH ISSUES IN THE APPLICATIONS OF SATELLITE OBSERVATIONS OF NO2 HAVE EMERGED FROM PUBLISHED STUDIES AND OUR PREVIOUS AND ONGOING RESEARCH INCLUDING PROPER REPROCESSING OF SATELLITE DATA FOR INVERSE MODELING AND TREND ANALYSIS RESOLUTION RE-MATCHING IN THE VALIDATION OF SATELLITE OBSERVATIONS USING IN SITU AND GROUND-BASED REMOTE SENSING MEASUREMENTS AND INVERSE MODELING SOURCE-DEPENDENT EMISSION INVERSION AND HIGH-RESOLUTION EMISSION INVERSION. WE WILL ANALYZE IN THIS PROJECT MULTIPLATFORM REMOTE SENSING AND IN SITU OBSERVATIONS OF TROPOSPHERIC NOX INCLUDING COLUMN NO2 MEASUREMENTS FROM SATELLITES AND GROUND-BASED PANDORA INSTRUMENTS DISCOVER-AQ DC3 AND SEAC4RS IN SITU MEASUREMENTS AND SURFACE MEASUREMENTS AT EPA AQS SITES TO ADDRESS THESE RESEARCH ISSUES. THE OVERARCHING GOAL OF THIS PROJECT IS TO MAKE BETTER USE OF SATELLITE (SUCH AS OMI GOME-2 AND TROPOMI) OBSERVATIONS IN UNDERSTANDING AIR QUALITY AND ITS CHANGES OVER THE UNITED STATES. THE SPECIFIC RESEARCH OBJECTIVES ARE AS FOLLOWS. (1) INTEGRATE IN SITU GROUND-BASED AND SATELLITE OBSERVATIONS USING MODEL SIMULATIONS AND CONDUCT DETAILED COLUMN NO2 PRODUCT INTERCOMPARISON. (2) UNDERSTAND BETTER THE LEVEL OF REPROCESSING REQUIRED FOR TREND ANALYSIS OF NOX EMISSIONS AND CONDUCT INVERSE MODELING OF NOX EMISSIONS FROM 2005. (3) DEVELOP INVERSIONS OF SOURCE-DEPENDENT NOX EMISSIONS BASED ON SATELLITE OBSERVATIONS. ASSESS THE EFFECTS OF SOURCE-DEPENDENT NOX ON SURFACE O3 CONCENTRATIONS. (4) DEVELOP HIGH-RESOLUTION INVERSIONS IN WHICH URBAN-SCALE NOX EMISSIONS (UP TO 4 KM) CAN BE RELIABLY DERIVED BASED ON RELATIVELY COARSE RESOLUTION SATELLITE OBSERVATIONS (~50 KM) IN ORDER TO UNDERSTAND HIGH-RESOLUTION (URBAN SCALE AND HIGHER) NOX EMISSION TRENDS. THE PROPOSED RESEARCH ADDRESSES THE FIRST EARTH SCIENCE RESEARCH OBJECTIVE IN THE 2014 SCIENCE PLAN FOR NASA S SCIENCE MISSION DIRECTORATE I.E. (TO) ADVANCE THE UNDERSTANDING OF CHANGES IN THE EARTH S RADIATION BALANCE AIR QUALITY AND THE OZONE LAYER THAT RESULT FROM CHANGES IN ATMOSPHERIC COMPOSITION . (T)HE ANALYSIS OF SATELLITE REMOTE-SENSING DATA OF THE EARTH S ATMOSPHERE AS DESCRIBED BY THE ACMAP CALL WILL BE INTEGRATED WITH GROUND-BASED REMOTE SENSING MEASUREMENTS AND MULTIPLATFORM IN SITU MEASUREMENTS USING CHEMICAL TRANSPORT MODEL SIMULATIONS. THE PROJECT WILL ADDRESS THE ACMAP SCIENCE ISSUE OF TROPOSPHERIC AIR QUALITY AND OXIDATION EFFICIENCY . WHILE WE WILL NOT DEVELOP DATA PRODUCTS FROM THE EOS AURA INSTRUMENTS USING LEVEL 2 DATA WE WILL FURTHER DEVELOP THE INVERSE MODELING METHODOLOGY TO IMPROVE THE SCIENCE APPLICATIONS OF SATELLITE COLUMN NO2 MEASUREMENTS. THE SPECIFIC ACMAP PROGRAM ELEMENTS THAT WILL BE ADDRESSED IN THIS PROJECT ARE (U)SING 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 AND (U)SING THE ABOVE-DESCRIBED DATA SETS TO STUDY TROPOSPHERIC AIR QUALITY AND OXIDIZING CAPACITY OF THE TROPOSPHERE .