Oxygen Isotope Dynamics of Atmospheric Nitrate and Its Precursor Molecules

Abstract

The stable oxygen isotopic composition of atmospheric nitrate is a powerful proxy for assessing what oxidation pathways are important for converting nitrogen oxides into nitrate. Large 18O enrichments and excess 17O (i.e. mass independent composition) are observed in atmospheric nitrate collected across the globe. These isotope enrichments and their variability in space and time have been linked to the magnitude of ozone oxidation. Attempts to model the oxygen isotope enrichments using simplified isotope mass balance assumptions and photochemical models have yielded reasonably good agreement between observations and simulations. However, there is a lack of atmospheric nitrate isotope measurements across a range of different atmospheric environments. Isotopes of oxygen in atmospheric nitrate can be utilized to assess changes in atmospheric chemistry, applied as tracers in nitrate deposition studies, and used to assess the atmosphere’s chemical response to environmental change over time using ice core nitrate.