This letter presents experimental data and their interpretation that lend support to earlier speculations concerning the formation of nitrous oxide (N2O) by excited ozone (O3) chemistry. This is a significant new development because the discovery of an atmospheric source of N2O has important implications for its global budget and because this process may account for the mass independent N2O isotope anomaly recently observed in the troposphere and lower stratosphere. ¿ 1998 American Geophysical Union