THIS PROPOSAL WILL UTILIZE AN ARRAY OF NASA EARTH OBSERVATIONS TO ADVANCE OUR COLLECTIVE KNOWLEDGE OF THE ATMOSPHERIC CHEMISTRY CONDITIONS AND EMISSIONS THAT DRIVE AIR POLLUTION DISPARITIES IN U.S. CITIES. THE RESEARCH WILL ADDRESS UNCERTAINTIES DUE TO A GENERAL LACK OF OBSERVATIONS OF (A) FINE-SCALE SPATIAL PATTERNS IN ATMOSPHERIC COMPOSITION (B) TEMPORAL VARIATIONS THAT REFLECT SOURCES AND TRANSIENT EXTREME EVENTS (C) SPATIOTEMPORAL VARIABILITY IN CHEMICAL MIXTURES AND (D) THE LINKED EFFECTS OF CHEMISTRY AND EMISSIONS ON INEQUALITY. THE PROPOSAL WILL DEMONSTRATE THAT NASA EARTH OBSERVATIONS ARE PARTICULARLY WELL-POSITIONED TO TEST HYPOTHESES RELATED TO THESE UNCERTAINTIES. METHODOLOGICALLY THE RESEARCH WILL TAKE AN OBSERVATIONAL APPROACH LEVERAGING A RANGE OF DATASETS INCLUDING: NOVEL HIGH-SPATIAL-RESOLUTION NASA NITROGEN DIOXIDE (NO2) AIRBORNE SPECTROMETER OBSERVATIONS IN SITU AIRCRAFT MEASUREMENTS OF NUMEROUS TRACE SPECIES FROM THE DISCOVER-AQ SARP LMOS AND LISTOS CAMPAIGNS TROPOMI NO2 COLUMNS GROUND-BASED MONITORING NETWORKS EMISSIONS INVENTORIES AND THE U.S. CENSUS DATABASE. THE RESEARCH WILL EXPAND AND ADVANCE THE APPLICATION OF SATELLITE REMOTE SENSING TO STUDY CONTROLS OVER INTRA-URBAN SPATIOTEMPORAL VARIABILITY GENERALLY AND AS IT RELATES TO POLLUTION INEQUALITY SPECIFICALLY. THE RESEARCH WILL BE MOST RELEVANT TO THE NASA EARTH SCIENCE ATMOSPHERIC COMPOSITION QUESTION HOW IS THE ATMOSPHERE CHANGING AS IT WILL IMPROVE OUR FUNDAMENTAL UNDERSTANDING OF CONTROLS OVER SPATIOTEMPORAL VARIABILITY IN INTRA-URBAN AIR QUALITY INCLUDING THOSE ATMOSPHERIC CONTROLS LINKED TO FUTURE CHANGES IN ATMOSPHERIC COMPOSITION. IN ADDITION THE PROPOSAL WILL DIRECTLY RESPOND TO TWO NASA DISCOVER-AQ MISSION GOALS INVESTIGATING RELATIONSHIPS BETWEEN COLUMN AND SURFACE TRACE SPECIES VARIABILITY AND THE HORIZONTAL DISTRIBUTION OF TRACE SPECIES AS RELATED TO SATELLITE-BASED AIR QUALITY ANALYSES.