Abstract:

Since Farman et al. (1985) reported firstly the ozone depletion in the spring over An- tarctica, A great deal of research efforts has focussed on this unexpected phenomenon. The Antarctic ozone depletion occured in almost every springtime simce the earlier 1980s (Fig. 1), and maintains for about one month (Fig. 2). It reached its maximum and minimum in 1987 and 1988 respectively (Fig. 3). The height of ozone depletion is in the lower stratosphere about 10-22 km (Fig. 4). Based on the available literature on Antarctic ozone hole published, three interpretations on the ozone depletion are reviewed in this paper. (1) ATMOSPHERIC DYNAMICS In the winter when the sun does not shine directly on the southern hemisphere, the atmosphere over Antarctica cools by emission of longwave radiation and forms a circumpolar vortex. On the other hand, the activity of planetary wave from the southern hemisphere is weak which hardly transports heat, momentum and mass from middle latitudes to polar region. When the sunshine appears again over the Antarctic in the earlier springtime, the increasing diabat heating by the sun makes the air move upward, and carris the air with lower abundance of ozone in the troposphere into the stratosphere, resulting in the total ozone depletion. In the spring, the circumpolar vortex is brokendown by the final wrarming resulted from the increasing planetary wave activity from the southern hemisphere. Meanwhile, the mid-latitude air with high abundance of ozone flows rapidly onto Antarctica and results in increase of total ozone. In res-cent years the aerosol on Antarctica, which can absorb the solar radiation directly increased with the eruption of the volcanoes, and led the upwelling current to become stronger than ever before. A lot of observational facts shows that the temperature in the tratosphere over Antarctica also have decreased in the rescent years, there may be some relationships between these two phenomena (Fig. 5). (2) SOLAR ACTIVITY Yoshiro (1986) found that the year to year change in the three-year runnsng means of total ozone also has the same 11-year returning period as that of the wolf Sunspot number (Fig. 6). As the coming of the high solar activities, the concerntration of NO2 and odd nitrigen in the air increases which may play an role in appearence of the Antarctic ozone hole. (3) ANTHROPOGENIC ACTIVITIES Some of the authors suggested that the main cause for appearence of the ozone hole should be the increasing chlorine in the atmosphere which resulted from the solution of the man-made chloronuorocarbons by violet solar radiation. Solomon and others. (1986) and McElroy and others (1986a) concluded that large ozone decrease could occur at lower altitudes if most of the available total chlorine were in the reactive form of chlorine radical, or Clox. They suggested that total ozone variation might occur if the heterogeneous reactions (11) or (12) proceeded rapidly on the surface of polar stratospheric clouds (PSCs) which are frequently present in the Antarctic winter and spring. Solomon and his co-workers (1986) suggested that the loss of ozone might proceed at lower altitudes via the catalytic cycle (l3)-(16). EcElroy and others (1986a) emphasized the importance of synergy between bromine and chlorine that would exist under such conditions. In particular, the net reactions (17) - (19), as indicated by Molina and Molina (1986) in their studies of the Gl2O2 dimer chemistry, can proceed via the reaction (20) and subsequently destroyed by the cycle (21) - (23) or (23) - (26). The models suggest that about 75% of the computed ozone removal is associated with reactions involving the ClO dimer, and about 25% may be a reaction sequence involving ClO and BrO. The obtained results of studies on the Antarctic ozone hole till now indicate that the process of the formation and close of the ozone hole might be as follows. In the Antarctic winter, on the one hand, the planetary wave from the southern hemisphere acts weakly, which almost could not transport heat, momentum and mass to the antarctic