Biggest Antarctic ozone hole ever

(September 2000)

In early September, a NASA spectrometer detected an Antarctic ozone hole (or more formally, an ozone depletion area) that is 28.3 million square kilometers larger than the entire combined land mass of Australia, the United States and Canada. The previous record was approximately 27.2 million square km on Sept. 19, 1998.

The ozone hole's size currently has stabilized, but the low levels in its interior continue to fall. The lowest readings in the Antarctic ozone hole are typically observed in late September or early October each year, according to NASA.

Dr. Michael J. Kurylo, manager of NASA's Upper Atmosphere Research Program, comments: "These observations reinforce concerns about the frailty of Earth's ozone layer. Although production of ozone-destroying gases has been curtailed under international agreements, concentrations of the gases in the stratosphere are only now reaching their peak. Due to their long persistence in the atmosphere, it will be many decades before the ozone hole is no longer an annual occurrence."

Most atmospheric ozone is found between 9.5 km and 29 km above the Earth's surface, and the chemistry behind the annual ozone holes is now fairly clear, but scientists are somewhat surprised by the size of this one. The reasons behind the large hole this year seem to involve both early-spring conditions in the southern hemisphere and an extremely intense Antarctic vortex. The Antarctic vortex is an upper-altitude stratospheric air current that sweeps around the Antarctic continent, confining the ozone hole.

The measurements were obtained using the Total Ozone Mapping Spectrometer (TOMS) aboard NASA's Earth Probe (TOMS-EP) satellite. NASA instruments have been measuring Antarctic ozone levels since the early 1970s. Since the discovery of the ozone 'hole' in 1985, TOMS has been a key instrument for monitoring ozone levels over the Earth, and soon NASA will launch QuickTOMS and Aura, two spacecraft that will continue to gather these important data.