Лекция: Ozone layer reduction

Ozone (O3) is distributed very unevenly with height and latitude as a result of the complex photochemistry involved in its produc­tion. Since the late 1970s, dramatic declines in springtime total ozone have been detected over high southern latitudes. The normal increase in stratospheric ozone associated with increasing solar radiation in spring apparently failed to develop. Observations in Antarctica show a decrease in total ozone in September-October from 320 Dobson units (10-3cm at standard atmos­pheric temperature and pressure) in the 1960s to around 100 in the 1990s. The results from one specific location illustrate the presence of an 'ozone hole' over the south polar region. Similar reductions are also evident in the Arctic and at lower latitudes. Between 1979 and 1986, there was a 30 per cent decrease in ozone at 30-40 km altitude between latitudes 20 and 50 °N and S; along with this there has been an increase in ozone in the lowest 10 km as a result of anthropogenic activities. These changes in the vertical distribution of ozone concentration are likely to lead to changes in atmospheric heating, with implications for future climate trends. The global mean column total decreased from 306 Dobson units for 1964-80 to 297 for 1984-93. The decline over the last 25 years has exceeded 7 per cent in middle and high latitudes. The effects of reduced stratospheric ozone are particularly important for their potential biological damage to living cells and human skin. It is esti­mated that a 1 per cent reduction in total ozone will increase ultraviolet-B radiation by 2 per cent, for example, and ultraviolet radiation at 0.30 µm is a thousand times more damaging for the skin than at 0.33 µm. The ozone decrease would also be greater in higher latitudes. However, it should be noted that the mean latitudinal and altitudinal gradients of UV-B radiation imply that the effects of a 2 per cent UV-B increase in mid-latitudes could be offset by moving poleward 20 km or 100 m lower in altitude! Recent polar observations suggest more dramatic changes. Stratospheric ozone totals in 1990 over Palmer Station, Antarctica (65°S), were found to have maintained low levels from September until early December, instead of recov­ering in November. Hence, the altitude of the sun was higher and the incoming radiation much greater than in previous years, especially at wavelengths ≤0.30 µm. It remains, however, to determine the specific effects of increased UV radiation on marine biota, for instance.