THE RELATIVE IMPLICATIONS OF OZONE FORMATION BOTH IN THE STRATOSPHERE AND THE TROPOSPHERE

Although ozone (O-3) occurs in both the troposphere and the stratosphere, mechanisms of O-3 formation and removal in both regions of the atmosphere are very different. Moreover, the presence of O-3 in the two layers has very different implications for the biosphere, especially vegetation. This introductory paper gives an overall appreciation of the two pools of O-3 and their relative influences upon plant life. In the troposphere, natural and unburnt hydrocarbons (HCs) not only participate in the formation of atmospheric O-3 but are also involved in the formation of free radicals from O-3 which go on to injure plant tissues. In the stratosphere, O-3 absorbs significant amounts of ultraviolet radiation (285-315 nm, UV-B) from sunlight which would otherwise harm biological systems. Depletion of stratospheric O-3 by chlorofluorocarbons (CFCs) has prompted urgent studies to assess the consequences of enhanced UV-B radiation on vegetation. Preliminary assessments of possible changes to UK crops are described in this paper.