Atmospheric production of nitrous oxide from excited ozone and its potentially important implications for global change studies



[1] Nitrous oxide (N2O) is a greenhouse gas included in the Kyoto Protocol. Its production from excited ozone (O3) may potentially influence inverse modeling, future growth projection, and the use of mass-independent Δ17O anomaly of N2O for probing paleoatmospheric O3. On the basis of the three-component model of N2O quantum yield in photolysis of O3 in air, the globally averaged atmospheric production of N2O from O3 electronically excited by the Hartley-Huggins band and from highly vibrationally excited ground-state O3 are 1.01 and 0.26 Tg N a−1, respectively. The sum of the two productions is 9.4 and 7.7%, respectively, of the N2O from microbial and anthropogenic activities estimated by Global Emissions Inventory Activity and by the Intergovernmental Panel on Climate Change (2001). Uncertainties in these results are discussed. Subject to those uncertainties, inverse modeling of N2O that neglects productions from O3 could yield artificially magnified (by about 7%) globally averaged emission of N2O from microbial and anthropogenic activity and introduce distortion in the regional and seasonal pattern in that emission. Experiments that could narrow the uncertainties are discussed. Production from highly vibrationally excited O3 reduces the steepness in the decrease of N2O volume-mixing ratios (VMR) above 35 km. Modeled and observed VMR comparisons show latitude- and season-dependent overestimation and underestimation of the N2O VMR by models. Globally averaged comparison suggests possible N2O source deficit in the stratosphere. Limitations, uncertainties, and need for experiments associated with this possibility are also discussed. If proven real, the possible missing N2O source could influence the atmospheric affects of solar UV variability, subject to conditions that are discussed.