Antarctic ozone hole stands steady: study

The Antarctic ozone hole reached its peak size in September, stretching to 24.1 million square kilometres, almost the same size as last year's peak, scientists say.
The ozone hole, which forms annually in the August to October period, had peaked to 24 million square kilometres in September last year.
In comparison, the largest ozone hole area recorded to date on a single day was on September 9, 2000, at 29.9 million square kilometres.
The ozone layer helps shield life on Earth from potentially harmful ultraviolet (UV) radiation that can cause skin cancer, damage plants and phytoplankton - the top of the oceanic food chain.

"The good news is that our measurements show less thinning of the ozone over the South Pole during the past three years," said Bryan Johnson, a researcher with The National Oceanic and Atmospheric Administration (NOAA)'s Earth System Research Laboratory in Boulder, Colorado.
"However, the rate at which ozone thins during the month of September has remained about the same for the past two decades. A decrease in this rate will be an important sign of recovery," said Johnson.

South Pole balloon-borne ozonesonde observations measured a minimum amount of 120 Dobson Units of ozone this year on September 29.
Ozonesonde measurements of 250 Dobson Units in August are common just before the rapid destruction of ozone in September, researchers said.

NOAA releases about 50-60 ozonesonde balloons per year since 1986 to measure the ozone layer at the South Pole.
Over the last 50 years, satellite and ground-based records over Antarctica show ozone column amounts ranging from 100 to 400 Dobson units, which translates to about 1 millimetre to 4 millimetres of ozone in a layer if all of the ozone were brought down to the surface.
The Antarctic ozone hole began making a yearly appearance in the early 1980s, grew in size through the 1980s and has been consistently large since 1990, with annual variability attributed to stratospheric meteorological conditions over Antarctica, researchers said.

The hole is caused by chlorine released by man-made chemicals called chlorofluorocarbons or CFCs that were extensively used as aerosol sprays and in refrigerators.
These chlorine compounds lead to ozone depletion in certain upper atmospheric conditions. These conditions are at their peak over Antarctica as the dark cold winter gives way to the Antarctic spring in September.