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Ozonesonde launch from South Pole Station

Nick Morgan/NOAA

For more than twenty-six years, scientists have been measuring stratospheric ozone above the South Pole to track the severity of the ozone hole. The loss of ozone in the stratosphere, attributed mainly to the use of chlorofluorocarbons and similar compounds, allows more ultraviolet solar radiation to reach lower levels of the atmosphere. That can lead to in creased incidence of skin cancer, eye damage and other health and environmental problems. The 1987 Montreal Protocol requires its signatory nations (197 to date) to reduce and eventually eliminate ozone depleting substances,especially chlorofluorocarbons.

The crucial South Pole measurements are made year round by ozone detection instruments known as ozonesondes, carried aloft by rubber balloons, which rise to an altitude of about twenty-two miles and report data on ozone quantities along with altitude, pressure, temperature, and relative humidity. The data from about sixty soundings per year from 1986 to 2010 show seasonal changes of the ozone layer and the annual development of the ozone hole, according to a report by Birgit Hassler of the National Oceanic and Atmospheric Administration and the University of Colorado in Boulder, together with four colleagues. The fastest ozone loss occurs during the Antarctic late winter and early spring from late August to late September. The ozone then recovers by early summer.

Over the long term, the ozonesonde measurements show a stabilization in the rate of ozone loss since 2000, which the team attributes to implementation of the Montreal Protocol. Asked about what that might mean for the future, Hassler notes that chlorofluorocarbons are very long lived in the atmosphere. Nevertheless, the current stabilization and the projected slowdown of ozone loss by the end of the current decade can be seen as a first sign of ozone recovery, which is expected to continue over the coming decades. (Journal of Geophysical Research Atmospheres)