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

Abstract

The effects of anthropogenic emissions of nitrous oxide (N 2 O), carbon dioxide (CO 2 ), methane (CH 4 ) 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 N 2 O and CO 2 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 CH 4 increase during the twentieth century reduced the ozone losses owing to halocarbon increases, and the N 2 O chemical destruction of O 3 is buffered by CO 2 thermal effects in the middle stratosphere (by approx. 20% for the IPCC A1B/WMO A1 scenario over the time period 1900–2100). Nonetheless, N 2 O is expected to continue to be the largest anthropogenic emission of an O 3 -destroying compound in the foreseeable future. Reductions in anthropogenic N 2 O 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, N 2 O, CO 2 and CH 4 , and thus may not be a good choice of a benchmark of O 3 recovery.