The chemical coupling between nitrogen oxides (NOx = NO + NO2) and biogenic volatile organic compounds (BVOCs) have important consequences for air quality and climate, playing a key role in the global budget for reactive nitrogen, ozone (O3), hydrogen oxide radicals (OH + RO2 + HO2) and secondary organic aerosols (SOA). Despite its significance for the climate system and human health, there are numerous uncertainties related to the chemical coupling of NOx and BVOC chemistry. These include a lack of understanding of the feedback of NOx and BVOC interactions on local/regional oxidation chemistry, the mechanisms responsible for SOA formation and NOx loss, and expected changes in NOx and BVOC oxidation chemistry in the future as anthropogenic NOx emissions are expected to decrease. Here we plan to conduct controlled laboratory chamber studies to further our understanding of the chemical coupling between NOx and BVOC utilizing oxygen stable isotopes (??17O and ??18O) of NO2, organic nitrate (both gas and particle phase), and inorganic nitrate. This will aid in evaluating the oxidation coupling between NOx and important BVOC molecules (isoprene, ?�- pinene, and ?�-pinene), and their role in organic nitrate formation pathways and NOx loss under varying conditions. Our specific objectives include to: (1) examine various organic nitrate formation pathways (OH, NO3, and O3) and their impact on NOx loss processes and oxidant budgets, (2) evaluate changes in the coupling of NOx and BVOC oxidation chemistry and the role this plays in reactive nitrogen chemistry cycling, and (3) probe the fate of peroxy radicals in the nighttime atmosphere and its role in NOx oxidation and organic nitrate formation. The combination of an established experimental chamber setup (GA Tech), suite of sensitive collection and measurement techniques, and isotope measurement facility (Brown Univ) put us in an excellent position to examine many of the major uncertainties in NOx-BVOC chemistry.