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 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 similar to 0.1 to 10 Torr (similar to 13-1,300 Pa) at a discharge voltage of 5 kV and discharge current of 1,500 mu A was collected and measured by isotope ratio mass spectrometry. Experiments were also conducted by varying the discharge current from 75 to 1,500 mu A at similar to 0.5 Torr (similar to 67 Pa) and 5 kV. The results show enrichments in N-15 in product N2O of up to 32 relative to the reactant N-2 and even larger enrichments in N-15 of up to 77 at the central nitrogen atom. Depletions in O-18 as large as -71 relative to reactant O-2 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. Key Points N2O produced in a 5 kV corona discharge in 10 Torr N-2/O-2 is enriched in N-15 and depleted in O-18 relative to the initial air mixture Isotopic composition measurements can help constrain mechanisms of N2O formation and destruction in a corona discharge The influence of local lightning activity on N2O in the upper tropical troposphere may be identifiable by its distinct isotopic signature

Automated summary

The study found that N2O produced under specific conditions has a unique isotopic composition, which can be used to determine the different sources of N2O through isotope measurements. Isotopic composition research helps to further understand the formation and destruction mechanisms of N2O and can be used to identify the sources of changes in atmospheric N2O concentrations.