A re-investigation of the ultraviolet absorption spectrum of nitrous oxide (N2O) agrees with previous results in the range 210 to 235 nm, but contrary to previous results it indicates a vanishingly small cross section above 260 nm. The absence of the relatively long wave length absorption implies a negligible rate of photolysis of nitrous oxide in the troposphere. These results plus the previously estimated atmospheric mean residence times of N2O indicate that there is a large, unknown tropospheric sink for nitrous oxide.