Scientists have spotted the largest hole yet in the ozone layer over Antarctica, a depleted region three times the area of the United States in size.

Measurements from a NASA satellite-mounted spectrometer showed the hole expanded to a record 11 million square miles (28 million square kilometers) in size on September 3. That bests, albeit not by much, a previous record set in September 1998.

"These observations reinforce concerns about the frailty of Earths 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," said Michael Kurylo, manager of NASAs Upper Atmosphere Research Program.

"Due to their long persistence in the atmosphere, it will be many decades before the ozone hole is no longer an annual occurrence."

The United Nations World Meteorological Organization (WMO) called the ozone decrease in the region "remarkable" for so early in September, according to a bulletin it issued September 7.

"A large crescent-shaped area contains exceptionally low ozone for so early in the season and nearly circles the continent," the bulletin read in part.

The ozone holes size has since stabilized, but low levels in its interior continue to fall, according to NASA. The lowest readings are typically recorded in late September or early October each year.

"At this point, we can only wait to see how the ozone hole will evolve in the coming few months and see how the years hole compares in all respects to those of previous years," said Jack Kaye, director of NASAs Office of Earth Sciences Research.

Ozone molecules, made up of three atoms of oxygen, form a thin, yet crucial layer in the atmosphere, absorbing otherwise harmful ultraviolet radiation from the sun. Excessive amounts of UV radiation can boost skin cancer rates and harm plant life.

The latest results were gathered by NASAs Total Ozone Mapping Spectrometer (TOMS) on its Earth Probe (EP) satellite. The American space agency will soon launch QuickTOMS and Aura to continue its ozone data-gathering efforts.