The history of ozone layer research dates back to 1930, when the first theory of how the ozone layer is formed was presented. Kowalok (1993) gives a brief synopsis of important discoveries and events leading to an understanding of stratospheric ozone and the discovery of destructive capabilities of chlorofluorocarbons (CFCs) on ozone in his paper "Common Threads: Research Lessons from Acid Rain, Ozone Depletion, and Global Warming."
Despite its low concentration, ozone plays a critical role in chemical and biological processes by filtering ultraviolet radiation in the 220-320 nm wavelength range (1 nm = 10[-9]m). The region of concern for biological effects is the ultraviolet-B (UV-B) range from 280 to 320 nm. The effectiveness of ozone absorption decreases exponentially as the wavelength of radiation increases. All radiation consisting of wavelengths shorter than 280 nm is absorbed in the upper atmosphere; wavelengths longer than 320 nm are not significantly absorbed by ozone. Therefore, biological systems are vulnerable to wavelengths in the transitional region of 280 to 320 nm due to ozone losses. Lower ozone amounts result in greater amounts of UV-B reaching the surface, which can lead to damaging effects on humans, plants, and animals. Thus, ozone located in the stratosphere is crucial to life on Earth, but ironically, ozone found at the surface of the Earth can be harmful to humans, plants, and animals. For example, high ozone amounts at ground level are known to cause respiratory problems in humans and can lower yields of certain crops. The location of ozone defines whether ozone is beneficial or harmful to humans and the environment.
Natural variations in ozone do occur, but recent levels of ozone loss over the poles and lower latitudes cannot be explained by natural variability alone. Manmade CFC compounds were developed in the early 1930s for a variety of industrial and commercial applications, but it was not until the 1970s that these and other chlorine-containing substances were suspected of having the potential to destroy atmospheric ozone. In 1985 a team of British researchers first reported unusually low ozone levels over Halley Bay, Antarctica, which were caused by chemical reactions with chlorine and nitrogen compounds. Research was initiated that found CFCs to be largely responsible for the anomalously low levels during the polar springtime. This polar ozone depletion at lower stratospheric altitudes is what has been termed the "ozone hole." For example, the "Time Progression of Springtime Ozone Depletion" over the South Pole in 1993 is shown in a diagram provided by D. J. Hofmann of the Climate Monitoring and Diagnostics Laboratory of the National Oceanic and Atmospheric Administration (1994).
The primary concern over ozone depletion is the potential impacts on human health and ecosystems due to increased UV exposure. Increases in skin cancer and cataracts in human populations are expected in a higher UV environment. Lower yields of certain cash crops may result due to increased UV-B stress. Higher UV-B levels in the upper ocean layer may inhibit phytoplankton activities, which can impact the entire marine ecosystem. In addition to direct biological consequences, indirect effects may arise through changes in atmospheric chemistry. Increased UV-B will alter photochemical reaction rates in the lower atmosphere that are important in the production of surface layer ozone and urban smog.
Concern over these potential effects has prompted the international community to enact policies aimed at reducing the production of ozone-depleting chemicals. An important event in the history of international ozone policy was the Montreal Protocol on Substances That Deplete the Ozone Layer (1987), which called for the phaseout and reduction of certain substances over a multiyear time frame. Discoveries of more extensive ozone loss and rapid formulation of replacement substances for chlorine-containing compounds have led to refinements of the original Protocol. Updates set forth at London (1990) and Copenhagen (1992) have called for accelerated phaseout and replacement schedules. The following publications provide a good introduction to the issues and effects related to ozone depletion: