Stratospheric ozone depletion due to nitrous oxide: influences of other gases

The effects of anthropogenic emissions of nitrous oxide (N2O), carbon dioxide (CO2), methane (CH4) and the halocarbons on stratospheric ozone (O-3) over the twentieth and twenty-first centuries are isolated using a chemical model of the stratosphere. The future evolution of ozone will depend on each of these gases, with N2O and CO2 probably playing the dominant roles as halocarbons return towards pre-industrial levels. There are nonlinear interactions between these gases that preclude unambiguously separating their effect on ozone. For example, the CH4 increase during the twentieth century reduced the ozone losses owing to halocarbon increases, and the N2O chemical destruction of O-3 is buffered by CO2 thermal effects in the middle stratosphere (by approx. 20% for the IPCC A1B/WMO A1 scenario over the time period 1900-2100). Nonetheless, N2O is expected to continue to be the largest anthropogenic emission of an O-3-destroying compound in the foreseeable future. Reductions in anthropogenic N2O emissions provide a larger opportunity for reduction in future O-3 depletion than any of the remaining uncontrolled halocarbon emissions. It is also shown that 1980 levels of O-3 were affected by halocarbons, N2O, CO2 and CH4, and thus may not be a good choice of a benchmark of O-3 recovery.