Simultaneous effects of CO₂ and chlorofluoromethanes on stratospheric ozone

Abstract

THE amount of ozone in the stratosphere is determined by a dynamic balance between processes from three disciplines: photochemical kinetics, radiative transfer and dynamical meteorology. These processes are interactively coupled, principally through the temperature of the air molecules; because of the low pressure and solar UV light a chain reaction is possible by which the composition of the stratosphere, and particularly its ozone content, may be affected by comparatively small quantities of trace species. Calculations have indicated that oxides of nitrogen from high-flying aircraft and nuclear weapons, nitrous oxide from artificial fertilisers and various chlorine-containing derivatives of methane and ethane (mainly CF₂Cl₂, CFCl₃, CCl₄ and CH₃CCl₃) could be large enough to act in this way. Reductions in ozone column density could lead to increases in the amount of solar UV light transmitted to the planetary surface in the wavelength region 290–320 nm, with possible effects on human health and biological activity. We have already shown that projected increases in carbon dioxide amounts in the atmosphere would lead to cooling and thus to ozone enhancement in the stratosphere, particularly at the upper levels. Here we extend these calculations to include simultaneous perturbations of CO₂ and chlorofluoromethanes.