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

摘要

The effects of anthropogenic emissions of nitrous oxide (N_2O), 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_2O 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_2O 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_2O is expected to continue to be the largest anthropogenic emission of an O_3-destroying compound in the foreseeable future. Reductions in anthropogenic N_2O 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_2O, CO_2 and CH_4, and thus may not be a good choice of a benchmark of O_3 recovery.