AN INNOVATIVE COUPLED MODELING-SATELLITE STUDY IS PROPOSED TO CHARACTERIZE TRENDS IN SUMMERTIME ATMOSPHERIC COMPOSITION OVER NORTH AMERICA IN THE PERIOD 2000-2020 AT HIGH SPATIAL RESOLUTION AND TO EVALUATE HOW WELL WE CAN EXPLAIN THESE REGIONAL CHANGES. UNDERSTANDING THE RESPONSE OF ATMOSPHERIC COMPOSITION TO CHANGES IN ANTHROPOGENIC EMISSIONS IS CRITICAL TO DEVELOPING COST-EFFECTIVE POLICIES DESIGNED TO REDUCE THE IMPACTS OF POLLUTANTS SUCH AS O3 AND PM2.5 ON HUMAN HEALTH. SATELLITE DATA WILL HELP INFORM EMISSIONS IN THE MODEL SIMULATIONS AND MODEL INFORMATION WILL BE UTILIZED TO RE-PROCESS THE SATELLITE RETRIEVALS. NEW SATELLITE RE-PROCESSING TECHNIQUES WILL BE USED TO TAKE A FRESH LOOK AT REGIONAL TRENDS OF AIR POLLUTION IN NORTH AMERICA BETWEEN 2000 AND 2020. THESE TECHNIQUES ALLOW USERS TO RE-PROCESS THE SAME SPECTRAL RADIANCE INFORMATION GATHERED DURING THE ORIGINAL SATELLITE OVERPASS AND BETTER ALIGN IT WITH THE CURRENT STATE OF THE SCIENCE. WE HYPOTHESIZE THAT TOP-DOWN EMISSION ESTIMATES TRENDS AND NOX-VOC SENSITIVITIES WILL BE DIFFERENT IN MAGNITUDE USING THESE NEW ALGORITHMS. WE WILL ALSO BEGIN TO UTILIZE TROPOMI DATA WHICH HAS SMALLER PIXEL SIZES AND LOWER SIGNAL-TO-NOISE RATIOS TO FURTHER ENHANCE OUR UNDERSTANDING OF THE CHANGING ATMOSPHERE. A SERIES OF MODELING EXPERIMENTS ARE DESIGNED TO STUDY THE EXTENT TO WHICH RESPONSES OF ATMOSPHERIC COMPOSITION TO CHANGES IN US ANTHROPOGENIC EMISSIONS ARE INFLUENCED BY UNCERTAINTIES IN OFFICIAL BOTTOM-UP EMISSION ESTIMATES AND THEIR PROJECTED CHANGES WITH POLICIES AND CHEMICAL FEEDBACKS (E.G. DUE TO CHANGES IN OXIDIZING CAPACITY CAUSED BY RELATIVE CHANGES IN NOX AND VOC EMISSIONS). WE WILL ALSO EVALUATE THE EXTENT TO WHICH RADIATION FEEDBACKS (E.G. DUE TO REGIONAL CHANGES IN AOD AND RESULTING CHANGES IN SOLAR RADIATION REACHING THE LOWER TROPOSPHERE) AND CHANGES IN NON-ANTHROPOGENIC EMISSIONS (E.G. BIOMASS BURNING) CONTRIBUTE TO REGIONAL CHANGES IN ATMOSPHERIC COMPOSITION. THE ANALYSES WILL BE DONE OVER THE CONTINENTAL US (CONUS) AT 12 KM RESOLUTION WITH MORE DETAILED (4 KM RESOLUTION) ANALYSIS OVER THE MID-ATLANTIC LAKE MICHIGAN AND THE PACIFIC NORTHWEST; REGIONS THAT HAVE EXPERIENCED DIFFERENT DECADAL TRENDS IN EMISSIONS AND WHERE EXTENSIVE FIELD CAMPAIGNS HAVE BEEN CONDUCTED. THIS STUDY WILL MAKE USE OF NASA DATA COLLECTED DURING SUMMER CAMPAIGNS IN CONUS. THE PROJECT TEAM INCLUDES EXPERTS IN SATELLITE AND EMISSIONS DATA FROM ARGONNE NATIONAL LABORATORY (ANL) AND COUPLED AIR QUALITY AND METEOROLOGY MODELING EXPERTS FROM UNIVERSITY OF IOWA (UI) AND UNIVERSITY OF CALIFORNIA-LOS ANGELES (UCLA). AIR QUALITY SCIENTISTS FROM LAKE MICHIGAN AIR DIRECTORS CONSORTIUM (LADCO) AND MARYLAND DEPARTMENT OF THE ENVIRONMENT (MDE) WILL HELP GUIDE THE ANALYSES WITH THE GOAL OF MAXIMIZING THE VALUE OF THE STUDY TO REGIONAL AIR QUALITY MANAGERS. THE BROADER IMPLICATION OF THIS STUDY IS AN IMPROVED PROGNOSTIC CAPABILITY TO DETECT AND ATTRIBUTE REGIONAL CHANGES IN ATMOSPHERIC COMPOSITION THROUGH UTILIZATION OF CONTEMPORARY MODELS AND HIGH SPATIAL RESOLUTION REMOTE SENSING OBSERVATIONS. THIS IMPROVED CAPABILITY SHOULD INCREASE THE CONFIDENCE IN PROJECTIONS OF ATMOSPHERIC COMPOSITION AND BETTER INFORM EMISSION REDUCTION STRATEGIES TO SUPPORT PROTECTION OF PUBLIC HEALTH AND REGULATORY GOALS OF THE STATES AND PROVIDE A MUCH-NEEDED PERSPECTIVE ON THE HISTORIC LINKAGES BETWEEN EMISSIONS SOURCES AND AMBIENT AIR POLLUTION.