Sources of the oxygen isotopic anomaly in atmospheric N_2O

Abstract

One-dimensional and two-dimensional models are used to investigate the isotopic composition of atmospheric N_2O. The sources of N_2O in the atmosphere are based on recent laboratory measurements of the N_2O quantum yield in the mixture of O_3/O_2/N_2 (Estupiñán et al., 2002). Two recently proposed pathways (Estupiñán et al., 2002; Prasad, 2005) are evaluated in the model. We find that the new atmospheric sources constitute a few percent of the total N_2O source, but can account for ∼50–100% of the Δ^(17)O anomaly observed in N_2O. The essence of the mechanism is to transfer a heavy oxygen atom originally in O_3 to N_2O. The magnitude of Δ^(17)O in N_2O is a linear function of the strength of these new N_2O sources. Laboratory and atmospheric measurements are proposed to confirm the chemical pathways. The potential of Δ^(17)O in N_2O for providing a new tool to probe ozone levels in paleoatmospheres is discussed.

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