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

Abstract

Nitrous oxide (N 2 O) is a greenhouse gas included in the Kyoto Protocol. Its production from excited ozone (O 3) may potentially influence inverse modeling, future growth projection, and the use of mass-independent Δ 17 O anomaly of N 2 O for probing paleoatmospheric O 3. On the basis of the three-component model of N 2 O quantum yield in photolysis of O 3 in air, the globally averaged atmospheric production of N 2 O from O 3 electronically excited by the Hartley-Huggins band and from highly vibrationally excited ground-state O 3 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 N 2 O 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 N 2 O that neglects productions from O 3 could yield artificially magnified (by about 7%) globally averaged emission of N 2 O 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 O 3 reduces the steepness in the decrease of N 2 O volume-mixing ratios (VMR) above 35 km. Modeled and observed VMR comparisons show latitude- and season-dependent overestimation and underestimation of the N 2 O VMR by models. Globally averaged comparison suggests possible N 2 O source deficit in the stratosphere. Limitations, uncertainties, and need for experiments associated with this possibility are also discussed. If proven real, the possible missing N 2 O source could influence the atmospheric affects of solar UV variability, subject to conditions that are discussed. Copyright 2008 by the American Geophysical Union.