THIS PROPOSAL IS IN RESPONSE TO THE NASA ROSES 2016 A.19 SOLICITATION (NNH16ZDA001N-ACMAP) ON ATMOSPHERIC COMPOSITION: AURA SCIENCE TEAM AND ATMOSPHERIC COMPOSITION MODELING AND ANALYSIS PROGRAM . IN PARTICULAR WE PROPOSE TO USE EOS AURA (OMI) AQUA (MODIS) AND TERRA (MOPITT MODIS) DATA PRODUCTS WITHIN A MULTI-SPECIES DATA ASSIMILATION AND INVERSE MODELING SYSTEM TO ANALYZE SPATIOTEMPORAL PATTERNS OF ANTHROPOGENIC COMBUSTION IN MEGACITIES AROUND THE GLOBE. INCREASING POPULATION AND RAPID GROWTH AND DEVELOPMENT OF URBAN AREAS AROUND THE WORLD PRESENT A COMPELLING AND URGENT NEED TO UNDERSTAND ASSESS AND PREDICT THE ACCELERATING STRESSES ON OUR CHANGING ENVIRONMENT. THIS IS ESPECIALLY TRUE IN MEGACITIES WHERE HUMAN ACTIVITIES ARE MOST INTENSE ACCOMPANIED BY IMMENSE ENERGY CONSUMPTION MAINLY IN THE FORM OF FOSSIL-FUEL COMBUSTION. THESE DIRECTLY LEAD TO ENHANCED EMISSIONS OF AIR POLLUTANTS GREENHOUSE GASES AND WASTE ENERGY LARGELY IMPACTING AIR QUALITY CLIMATE AND ECOSYSTEMS. AT PRESENT THERE IS A GAP IN OUR UNDERSTANDING OF HOW COMBUSTION ACTIVITY AND EFFICIENCY IN MEGACITIES EVOLVE IN SPACE AND TIME ESPECIALLY AS WE INEVITABLY MOVE TOWARDS FINER SCALES AND MORE COMPLEX INTERCONNECTED SYSTEMS. IT IS IMPERATIVE THAT WE PROVIDE A MORE ACCURATE AND CONSISTENT ANALYSIS AND ASSESSMENT OF THE CHANGES IN ATMOSPHERIC COMPOSITION DUE TO ANTHROPOGENIC COMBUSTION AT SCALES THAT IS RELEVANT TO AIR QUALITY ENERGY AND ENVIRONMENTAL POLICY. HERE WE PROPOSE A 3-YEAR PROGRAM OF RESEARCH TO CHARACTERIZE AND QUANTIFY THE BULK COMBUSTION ACTIVITY AND EFFICIENCY OF MAJOR MEGACITIES WITHIN THE RECENT DECADE USING AN ENSEMBLE APPROACH TO CHEMICAL DATA ASSIMILATION. WE FOCUS ON JOINTLY ANALYZING COEMITTED COMBUSTION PRODUCTS SUCH AS NO2 CO SO2 AND AEROSOLS (FROM OMI MOPITT AND MODIS). EACH OF THESE CONSTITUENTS EXHIBITS DISTINCT ATMOSPHERIC SIGNATURES THAT DEPEND ON FUEL TYPE COMBUSTION TECHNOLOGY PROCESS PRACTICES AND REGULATORY POLICIES. DISTINGUISHABLE PATTERNS AND RELATIONSHIPS BETWEEN THE INCREASES IN CONCENTRATIONS ACROSS THE MEGACITY (OR ENHANCEMENTS) DUE TO EMISSIONS OF THESE CONSTITUENTS ENABLE US TO: A) IDENTIFY TRENDS IN COMBUSTION ACTIVITY AND EFFICIENCY AND B) RECONCILE DISCREPANCIES BETWEEN STATE- TO COUNTRY-BASED EMISSION INVENTORIES AND MODELED CONCENTRATIONS OF THESE CONSTITUENTS. WE HAVE CONDUCTED THREE PROOF-OF-CONCEPT STUDIES ON THE POWER OF CHEMICAL ENHANCEMENT RATIOS (CO/CO2 CO/NO2/AOD AND BC/CO) IN IDENTIFYING COMBUSTION PATTERNS ACROSS 46 MEGACITIES CONTINENTAL UNITED STATES AND MAJOR FIRE REGIONS. HERE WE WILL FULLY EXPLOIT THIS CONCEPT WITHIN A COUPLED WEATHER-ATMOSPHERIC-CHEMISTRY-CLIMATE CDAS (I.E. NCAR WRF-CHEM AND CAM-CHEM/DART) THAT WE DEVELOPED AND IMPLEMENTED. IN PARTICULAR WE AIM TO ADDRESS THE FOLLOWING SCIENCE QUESTIONS: 1) WHAT ARE THE OBSERVED AND MODELED RELATIONSHIPS AND TRENDS OF CO NOX SO2 AND AEROSOL ENHANCEMENTS IN THESE MEGACITIES AS CAN BE DERIVED FROM MULTIPLE PLATFORMS AND SENSORS AND ENSEMBLE OF MODEL SIMULATIONS? 2) WHAT ARE THE KEY FACTORS CONTRIBUTING TO THE ERRORS IN OUR ESTIMATES OF EMISSIONS AND ABUNDANCE AS CAN BE DIAGNOSED FROM CHEMICAL REANALYSIS AND INVERSE MODELING STUDIES INCLUDING A FIRST-OF-A-KIND CDAS INTERCOMPARISON PROJECT WHICH WE WILL INITIATE AND LEAD? 3) WHAT ARE THE LOCAL-REGIONAL-GLOBAL CONTRIBUTIONS OF MEGACITY COMBUSTION TO OBSERVED CHANGES IN ATMOSPHERIC COMPOSITION AS CAN BE INFERRED AND ESTIMATED FROM CDAS? FINALLY WE NOTE THAT WE ARE WELLPOSITIONED TO TAKE ADVANTAGE OF THE INCREASING AVAILABILITY OF MULTI-SPECIES ATMOSPHERIC OBSERVATIONS (ESPECIALLY FROM OMI) TOGETHER WITH RECENT ADVANCES IN COUPLED MODELING AND DATA ASSIMILATION TOWARDS IMPROVING OUR ABILITY TO ACCURATELY ASSESS KEY DRIVERS OF ANTHROPOGENIC COMBUSTION AND ITS IMPACTS ON ATMOSPHERIC COMPOSITION.