Introduction

There are currently two prominent problems in atmospheric and environmental science that have received much attention: the possibility of widespread ozone depletion and the potential for global warming. The primary concerns of public debate and scientific research have focused on (i) to what extent ozone depletion and global warming are, in fact, occurring and (ii) if so, to what extent these phenomena are due to natural rather than anthropogenic causes. There is growing evidence relating ozone depletion directly to the release of man-made trace gases, notably chlorofluorocarbons used in the refrigeration industry and as propellants in spray cans. Since ozone provides an effective shield against damaging ultraviolet radiation from the Sun, there is indeed good reason to be concerned, because a thinning of the ozone layer could have serious biological ramifications. The most harmful ultraviolet radiation reaching the Earth's surface, commonly referred as UV-B, lies in the wavelength range between 280 and 320 nm (see Table 1.1). UV-B radiation, which has enough energy to damage the DNA molecule, is strongly absorbed by ozone. Radiation with wavelengths between 320 and 400 nm, referred to as UV-A, is relatively little affected by ozone. UV-A radiation can mitigate some of the damage inflicted by UV-B (this is known as “photo-repair”), but it causes sunburn and is therefore believed to be a partial cause of skin cancer. In addition to the harmful effects on humans, too much ultraviolet radiation has deleterious effects on terrestrial animals and plants, as well as aquatic life forms.