Chapter 7 - Environmental Photobiology

Abstract

Occurrence of a hole in the ozone layer is observed and attributed to the presence of man-made chlorofluorocarbons (CFCs). The CFCs contained in many coolants, electronic solvents, and foam are slowly released into the atmosphere, where they can exist for up to 100 years. In the stratosphere, via short-wavelength Ultra Violet (UV) radiation, they produce free chlorine, which destroys the ozone. Each CFC molecule acts in a catalytic fashion to destroy about 100,000 ozone molecules. Even if harmless chemicals are now substituted for CFCs, the long lifetimes of CFCs already present in the environment mean that the ozone layer continues to be adversely affected until the middle of the 21st century. The resulting increase in the UV spectrum reaching the earth's surface is largely confined to the wavelength region 295–315 nm. Ozone consumption is believed to be a result of photochemical reactions, such as the photodissociation of chlorofluoromethane resulting in the release of chlorine.