After the previous review [ Brune, 1991] of the breadth of scientific activity following reports of an ozone hole over Antarctica and of similar photochemistry over the Arctic, it is surprising to find as rich a literature base for this review. Admittedly, some of the recent publications are new, but belated, reports of studies carried out before 1991, while some are results of ongoing studies. However, there have also been important new developments in stratospheric chemistry, many of which were initiated by the long-awaited launch of the Upper Atmosphere Research Satellite (UARS) [ Reber, 1993], the Second Airborne Arctic Stratospheric Expedition (AASE II) [ Anderson and Toon, 1993], the European Arctic Stratospheric Ozone Expedition (EASOE) [ Pyle et al., 1994], the NASA High-Speed Research Program (HSRP) [ Albritton et al., 1993], the eruption of Mount Pinatubo [ McCormick, 1992], and the Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE) [ Wofsy et al., 1994]. The review period was also highlighted by observations of the lowest global ozone abundances on record [ Gleason et al., 1993], detection of enhanced ultraviolet radiation at the earth's surface [ Frederick and Alberts, 1991], examinations of possible strategies for mitigating ozone losses [ Cicerone et al., 1991], and direct confirmation of the effectiveness of international agreements limiting the production of ozone-destroying substances [ Elkins et al., 1993].
Although in this review I will focus primarily on new results, I will also examine those that build upon the strong existing database. As with previous reviews, I will cite the work of US scientists, unless an international study involves a major contribution by a US researcher or is essential to illuminate an aspect of other work. There have been many advances in our understanding of stratospheric chemistry since the last review. As ground-based, aircraft and balloon in situ, and satellite observations continue to provide important data, the temporal and spatial distributions of more chemical species are being defined with higher resolution and accuracy [ Kolb, 1991]. Consequently, the field of stratospheric chemistry continues to be driven by laboratory studies and atmospheric observations. However, models remain the foundation for increasingly difficult assessments and predictions [ Prather and Remsberg, 1993]. As model descriptions have become more sophisticated, and as additional observational constraints are applied, the ties between models and measurements have grown stronger. I have chosen to highlight four issues that reflect this: polar ozone depletion, mid-latitude photochemistry, the effects of Mount Pinatubo, and the chemistry of bromine. It is becoming increasingly difficult to divide the research into separate intellectual topics, so the reader will find elements from each of these issues throughout the review.