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

The expanding use of nitrogen‐containing fertilizers in agriculture has led to an increase in N 2 O, 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 N 2 O, but the isotopic composition of N 2 O 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 N 2 O 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 15 N in product N 2 O of up to 32‰ relative to the reactant N 2 and even larger enrichments in 15 N of up to 77‰ at the central nitrogen atom. Depletions in 18 O as large as −71‰ relative to reactant O 2 were also measured. The isotope‐isotope relationships of the N 2 O produced in the corona discharge are distinct from those of other sources of N 2 O, suggesting that isotope measurements can be used to determine whether local or regional variations in the atmospheric concentration of N 2 O – such as the enhanced N 2 O levels measured in the upper tropical and subtropical troposphere during the HIPPO mission – can be attributed to lightning activity, soil emissions, or biomass burning.