17 



ozonesonde balloons throughout 1986 and, most importantly, we were able to get a 

 team of researchers to McMurdo Station in late austral winter of 1986 to make 

 measurements of the details of the chemistry in the depleted region. The first Na- 

 tional Ozone Expedition (NOZE-1) was put together by NSF, NASA and NOAA and 

 included both government laboratory and academic researchers. The results of 

 NOZE-1 (and NOZE-2 the following year) established beyond doubt the dominant 

 role that chlorine plays in the destruction of ozone and, in turn, provided the basis 

 for the Montreal Protocol, the first multinational treaty concerning environmental 

 protection. Without the preexisting facilities and capabilities of USAP it would have 

 been impossible to develop the data necessary for the policy makers to forge this 

 landmarK treaty and, much more importantly, mankind would have delayed actions 

 that have protected the ozone layer from more extreme damage. 



Since the days of NOZE, NSF and our sister agencies have been working hard 

 to elucidate the details of the causes of the ozone hole and to look for effects of ex- 

 cess ultraviolet radiation on the biota which live in Antarctic waters and the sur- 

 rounding land areas. In support of this there is a coordinated program consisting 

 of several continuing monitoring activities as well as a number of research projects 

 aimed both at biological effects and atmospheric chemistry and dynamics. 



In response to the discovery of the Antarctic ozone hole, the USAP initiated the 

 NSF UV-Radiation Monitoring Network to directly measure UV-radiation reaching 

 the earth's surface. Instruments are located at the three U.S. Antarctic stations as 

 well as in southern Argentina and in Alaska. Data from the Antarctic clearly show 

 increases in UV radiation during ozone hole events. 



The international scientific community, through periodic United Nations Environ- 

 mental ProgrammeAVorld Meteorological Organization "state-of-the science" assess- 

 ments, has established beyond a doubt that tne main cause of the ozone hole is cata- 

 lytic chemistry involving chlorine from manmade chemicals. The reactions proceed 

 very rapidly above Antarctica because of the presence of polar stratospheric clouds 

 (PSC), a polar phenomena caused by the very low stratospheric temperatures 

 reached during the winter. These PSCs provide surfaces on which chemical reac- 

 tions occur that increase the amount of chlorine that occurs in the active, ozone- 

 destroying form. It has also been shown that in addition to the PSCs, aerosols from 

 volcanoes accelerate the chlorine chemistry that destroys ozone. This makes the 

 need to reduce the chlorine burden of the atmosphere particularly urgent because 

 it demonstrates that there is a potential for dramatic ozone depletion above non- 

 polar regions. Indeed, rather severe reductions in total column ozone were measured 

 above the US following the 1991 eruption of Mt. Pinitubo. 



The effect of increased UV-radiation on Antarctic organisms has been a major 

 focus of research. It has been shown that the growth of microscopic marine plants, 

 called phytoplankton, inside the ozone hole decreased 6% to 12% compared to 

 phytoplankton growth under normal UV-radiation concentrations. The 

 phytoplankton form the base of the marine food web. Even small decreases in 

 growth rate due to increased UV-radiation could adversely affect invertebrate lar- 

 vae, fish, crabs, birds and mammals, which could in turn affect the global food sup- 

 ply- 



During the next decade, if there is full compliance with the international agree- 

 ments of the Montreal Protocol, the abundances of atmospheric chlorine and bro- 

 mine will reach the highest levels that the planet will have to endure. Over the next 

 ten years the Earth's ozone layer will be at its most vulnerable. Ozone research, like 

 any scientific endeavor, has encountered and will continue to encounter the unex- 

 pected. For example, the Antarctic ozone hole was not predicted, and its discovery 

 and explanation revealed a new process that was previously unknown to atmos- 

 pheric researchers. There may well be others. For example, studies of the 1991 

 eruption of Mt. Pinitubo have shown that volcanic particles served to enhance, by 

 an additional 2% for a few years, the ozone depletion caused by manmade chlorine 

 compounds. What would be the effects of a major volcanic eruption during the 'Vul- 

 nerable decade?" Another issue for the future is the fact that at mid-latitudes, 

 where most of the world's human population resides, the observed downward trends 

 in ozone concentrations are twice as large as those predicted. The reasons for this 

 difference, and what it could mean for our understanding of future ozone losses, are 

 not yet clear. As another example, Antarctic research has shown that bromine from 

 anthropogenic chemicals (methyl bromide and the Halon class of fire suppressants) 

 is also responsible for some of the ozone hole, though the quantitative aspects are 

 not yet clear. Understanding the long term development of the phenomena requires 

 continuing research as does the effect of external drivers such as the solar cycle and 

 the quasibiennial oscillation, a tropical, stratospheric phenomena which exhibits re- 

 versals of high altitude winds on an approximate 26 month cycle and which is well 

 know to affect global ozone levels. 



