**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** NITROGEN INPUTS, ESPECIALLY SYNTHETIC FERTILIZER AND MANURE, ARE CRITICAL TO CROP PRODUCTIVITY IN THE US.THE YIELD RESPONSEEFFECTS ACROSS DIFFERENT CROPS, CLIMATES AND SOILS HASBEEN STUDIED FOR DECADES. HOWEVER, THESE SAME N INPUTS CAN ALSO EMIT NITROGEN OXIDES, A CENTRAL PRECURSOR TO TROPOSPHERIC OZONE, WHICH SUPPRESSES CROP GROWTH AND NEGATIVELY IMPACTS HUMAN HEALTH. THE LINK BETWEEN NITROGENINPUTS, OZONE FORMATION AND CROP YIELD REDUCTIONS HAS RARELY BEEN EVALUATED, ESPECIALLY IN A REGION WITH HIGH NITROGEN USE. A BETTER UNDERSTANDING OF THIS CRITICAL YIELD DAMPENER IS CRUCIAL AS US CROP PRODUCTION FACES A RANGE OF MOUNTING PRESSURES. CONSEQUENTLY, THE RESEARCH QUESTION DRIVING THIS PROJECT IS: HOW MUCH ARE THE POSITIVE EFFECTS OF NITROGENINPUTS DIRECTLY OFFSET BY ONE OF ITS MAJOR NEGATIVE EFFECTS?OUR APPROACH FOCUSES ON THE US CORN BELT AS A HOTSPOT OF NITROGENUSE AND COMBINES PLOT-SCALE EMPIRICAL MEASUREMENTS WITH SOIL-COLUMN TO REGIONAL-SCALE MODELING. THE FIVE MAJOR OBJECTIVES ARE: (1) DIRECTLY MEASURE SOIL AGRICULTURAL NITROGEN OXIDES EMISSIONS IN EXPERIMENTAL PLOTS; (2) USE NEW MODEL DEVELOPMENTS TO SIMULATE THE IMPACT OF AGRICULTURAL NITROGENINPUTS ON NITROGEN OXIDES EMISSIONS AT THE PLOT SCALE; (3) EVALUATE THE TROPOSPHERIC NITROGEN OXIDES AND OZONE RESPONSE TO AGRICULTURAL SOIL NITROGENEMISSIONS AT THE REGIONAL SCALE; (4) ESTIMATE THE DAMAGE TO CROP YIELDS AND HUMAN HEALTH FROM NITROGENINPUT-INDUCED OZONEFORMATION; AND (5) ASSESS HOW DIFFERENT NITROGENMANAGEMENT AND CLIMATE SCENARIOS IMPACT FUTURE CROP PRODUCTIVITY AND TROPOSPHERIC OZONEDAMAGE. OUR COMBINATION OF DATA GENERATION AND MODEL DEVELOPMENT WILL LEAD TO INNOVATIVE SUSTAINABLE SOLUTIONS THAT COULD UNDERPIN POLICIES TO COMBAT THE THREAT OF TROPOSPHERIC OZONEON CROP PRODUCTIVITY AND NITROGENPOLLUTION WRIT LARGE.