STATE AND FEDERAL AGENCIES HAVE DEVOTED SIGNIFICANT RESOURCES TO UNDERSTAND AND MITIGATE SURFACE O3 FORMATION AND THE EMISSION OF ITS CHEMICAL PRECURSORS. WHILE SUCCESSFUL LEGISLATION HAS LED TO REDUCTIONS IN THE NUMBER OF AIR POLLUTION EPISODES THERE ARE STILL LOCATIONS OFTEN HIGH-POPULATION URBAN CORRIDORS THAT STRUGGLE TO ATTAIN THE FEDERAL AMBIENT AIR QUALITY STANDARDS. THE ROOT CAUSES OF AIR QUALITY EVENTS ARE NOW MORE VARIED AND SOMETIMES HIGHLY LOCALIZED. SURFACE MONITORING NETWORKS PROVIDE DETAILED OBSERVATIONS OF ATMOSPHERIC CONDITIONS AT THESE LOCATIONS BUT THE DENSITY OF MEASUREMENT SITES LIMITS HOW THESE DATA ARE USED TO INFER EMISSIONS SOURCES. SATELLITE OBSERVATIONS OF POLLUTANTS CAN PINPOINT PERSISTENT EMISSIONS SOURCES WHICH BETTER INFORM THE INTERPRETATION OF SURFACE MONITOR DATA. IN ADDITION TECHNIQUES HAVE BEEN DEVELOPED USING SATELLITE DATA TO DETERMINE THE ATMOSPHERIC PHOTOCHEMICAL REGIMES THAT LEAD TO O3 FORMATION. WHILE SATELLITES PROVIDE GLOBAL OBSERVATIONS OF AIR POLLUTANTS OFTEN THEY ARE NOT ABLE TO RETRIEVE THE VERTICAL DISTRIBUTION OF O3 PRECURSORS REQUIRE CLEAR SKIES ONLY PROVIDE DATA AT THE TIME OF THE OVERPASS AND ARE NOT COMPLETELY SENSITIVE TO ATMOSPHERIC CONDITIONS AT OR NEAR THE SURFACE. DIURNAL AND VERTICAL VARIATION OF THE O3 PRODUCTION REGIME WILL INFLUENCE THE ONSET AND PERSISTENCE OF SURFACE O3 EPISODES. TO ASSESS THESE FACTORS AIRCRAFT FIELD MISSIONS ARE REQUIRED. SINCE 2011 THERE HAVE BEEN SEVERAL FEDERAL AND STATE SPONSORED FIELD MISSIONS IN THE MID-ATLANTIC REGION. WE PROPOSE TO USE AIRCRAFT OBSERVATIONS FROM RESEARCH FLIGHTS IN THIS AREA PRIOR TO THE 2011 DISCOVER-AQ MISSION THROUGH THE RECENT OWLETS AND LISTOS CAMPAIGNS TO CHARACTERIZE THE VERTICAL NATURE OF O3 PRODUCTION CHEMISTRY WITHIN THE BOUNDARY LAYER AND LOWER FREE TROPOSPHERE ALONG WITH THE TEMPORAL EVOLUTION BOTH DIURNAL AND LONG-TERM OF AIR QUALITY IN THE MID-ATLANTIC REGION. OBSERVATIONS FROM THE NASA AND UNIVERSITY OF MARYLAND (UMD) AIRCRAFT AND SURFACE INSTRUMENTS WILL ALLOW US TO MORE ACCURATELY QUANTIFY CHANGES AND TRENDS IN NEAR-SURFACE ATMOSPHERIC COMPOSITION. THE UMD RESEARCH AIRCRAFT HAS BEEN FLYING SINCE 1996 PARTICIPATED IN THESE NASA MISSIONS AND HAS ALSO FLOWN IN THE INTERVENING YEARS SOMETIMES INCLUDING NASA INSTRUMENTS ALONG WITH THE STANDARD INSTRUMENT PAYLOAD. VERTICAL PROFILES OF NO2 AND HCHO WILL ALLOW US TO IDENTIFY ALTITUDES WHERE O3 CHEMISTRY SWITCHES FROM VOC SENSITIVE TO NOX SENSITIVE AND TO DETERMINE THE ALTITUDES THAT MOST INFLUENCE THE COLUMN NO2 AND HCHO RETRIEVALS (I.E. THE INTEGRAL OF THE PROFILES). THESE WILL BE COMPARED TO ARCHIVED OUTPUT FROM AIR QUALITY MODEL SIMULATIONS PERFORMED BY OUR TEAM. OBSERVATIONS FROM MORNING AND AFTERNOON FLIGHTS ALONG WITH SURFACE DATA WILL QUANTIFY DIURNAL VARIATIONS IN THE CHEMICAL COMPOSITION OF THE ATMOSPHERE. DERIVED QUANTITIES SUCH AS NOX/NOY WILL ALLOW US TO IDENTIFY FRESH EMISSIONS FROM LOCAL SOURCES AND AGED AIR CARRYING POLLUTION FROM SOURCES FURTHER UPWIND. WE WILL DETERMINE HOW TRENDS IN PRECURSOR SPECIES ARE ATTRIBUTED TO EFFECTIVE AIR QUALITY LEGISLATION IMPLEMENTATION VARYING ECONOMIC ACTIVITY AND CHANGES IN LAND USE. A CHEMICAL BOX MODEL CONSTRAINED TO AIRCRAFT DATA WILL BE USED TO CALCULATE THE NOX OR VOC SENSITIVITY OF THE O3 PRODUCTION REGIME AND TO TEST COMMONLY USED CHEMICAL MECHANISMS FOR THEIR ABILITY TO REPRODUCE ATMOSPHERIC CONDITIONS. THIS ANALYSIS OF OBSERVATIONS AND MODELS WILL PROVIDE A MORE COMPLETE UNDERSTANDING OF THE TEMPORAL AND REGIONAL NATURE OF AIR QUALITY EVENTS THAT EFFECT MILLIONS OF PEOPLE. IN THIS WAY THE BEST AVAILABLE SCIENCE WILL BE ACCESSIBLE TO STATE AND REGIONAL POLICY MAKERS TO DEVELOP POLLUTION MITIGATION STRATEGIES.