THE RELATIVE IMPLICATIONS OF OZONE FORMATION BOTH IN THE STRATOSPHEREAND THE TROPOSPHERE

Although ozone (O-3) occurs in both the troposphere and the stratosphe re, mechanisms of O-3 formation and removal in both regions of the atm osphere are very different. Moreover, the presence of O-3 in the two l ayers has very different implications for the biosphere, especially ve getation. This introductory paper gives an overall appreciation of the two pools of O-3 and their relative influences upon plant life. In th e troposphere, natural and unburnt hydrocarbons (HCs) not only partici pate 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 tissue s. 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 chlorofluorocar bons (CFCs) has prompted urgent studies to assess the consequences of enhanced UV-B radiation on vegetation. Preliminary assessments of poss ible changes to UK crops are described in this paper.