Nitrous Oxide Formation by Corona Discharge: Isotopic Composition Measurements and Atmospheric Applications

Abstract

AbstractThe expanding use of nitrogen‐containing fertilizers in agriculture has led to an increase in N2O, an important greenhouse gas and ozone‐depleting substance, since preindustrial times. Isotopic measurements are a valuable tool to distinguish the contribution of different sources of N2O, but the isotopic composition of N2O formed in the low temperature plasma regimes in lightning has not previously been measured. Here, a corona discharge was generated in flowing or static zero air, and the N2O formed at discharge cell pressures from ∼0.1 to 10 Torr (∼13–1,300 Pa) at a discharge voltage of 5 kV and discharge current of 1,500 μA was collected and measured by isotope ratio mass spectrometry. Experiments were also conducted by varying the discharge current from 75 to 1,500 μA at ∼0.5 Torr (∼67 Pa) and 5 kV. The results show enrichments in 15N in product N2O of up to 32‰ relative to the reactant N2 and even larger enrichments in 15N of up to 77‰ at the central nitrogen atom. Depletions in 18O as large as −71‰ relative to reactant O2 were also measured. The isotope‐isotope relationships of the N2O produced in the corona discharge are distinct from those of other sources of N2O, suggesting that isotope measurements can be used to determine whether local or regional variations in the atmospheric concentration of N2O – such as the enhanced N2O levels measured in the upper tropical and subtropical troposphere during the HIPPO mission – can be attributed to lightning activity, soil emissions, or biomass burning.