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.