Nitrogen isotope exchange between NO and NO2 and its implications for δ15N variations in tropospheric NOx and atmospheric nitrate

Abstract

AbstractThe nitrogen (N) isotope exchange between nitric oxide (NO) and nitrogen dioxide (NO2) has been previously suggested to influence N stable isotope compositions (δ15N) of these molecules. However, there is disagreement in the magnitude of the N isotopic fractionation ( ) resulting from this exchange process between previous experimental and theoretical studies. To this end, we measured associated with this exchange reaction at various temperatures. Our results indicate to be 1.0403 ± 0.0015, 1.0356 ± 0.0015, and 1.0336 ± 0.0014 at 278 K, 297 K, and 310 K, respectively. These measured values are within experimental error of the values we calculated using a modified version of the Bigeleisen‐Mayer equation corrected for accurate zero‐point energies, indicating an agreement between experiment and theory. Modeling of this exchange reaction demonstrates that δ15N‐NO2 may exhibit a diurnal and seasonal profile if N isotopic equilibrium is achieved.