The ozone hole over the Antarctic is the second smallest it has been in the last 20 years, according to data from NASA and National Oceanic and Atmospheric Administration satellites.
Scientists who work on the ozone-monitoring project believe slightly warmer temperatures in the lower stratosphere contributed to the smaller hole in the ozone layer this fall, but the results also indicate progress in reducing harmful chlorine compounds in the atmosphere.
"It shows that we're on the right track," said Bryan Johnson, an atmospheric chemist for NOAA in Boulder and project manager for ozonesonde, the program that measures ozone over Antarctica. "We're going to be getting smaller and smaller ozone holes for the next 30 or 40 years until, in 50 years, we won't have any ozone hole to speak of."
The ozone measurements this year were made using a satellite and instruments designed and built by Boulder-based Ball Aerospace under contract to NASA. The Suomi National Polar-orbiting Partnership satellite launched Oct. 28, 2011, with the Ozone and Mapping Profiler Suite on board.
The measurements continue a satellite record dating back to the early 1970s. The satellite and its instruments are expected to continue to provide environmental observations into the 2030s, Ball Aerospace said in a news release.
Johnson said the satellite data is supplemented with localized data collected from instruments on balloons.
The extremely cold temperatures above Antarctica during the winter, combined with certain atmospheric conditions, cause chlorine compounds to accumulate in polar stratospheric clouds, Johnson said. When the sun hits those chlorine compounds in September, at the start of spring in the Southern Hemisphere, they break up into free chlorine that immediately destroys ozone.
Scientists expect to see ozone levels drop precipitously every September, and they did this year, too, but much less than in previous years.
Johnson said scientists expect to find areas with no ozone at all, but this year "we never reached what we call complete destruction of ozone in the specific layer."
Johnson said scientists believe two factors came into play. Temperatures were a few degrees warmer in the lower stratosphere due to natural fluctuations. That inhibited the formation of polar stratospheric clouds. Also, a weather system known as the "vortex" that normally keeps conditions very stable over Antarctica moved off the continent, breaking up the concentration of chlorine compounds.
However, scientists expect the hole to continue to shrink due to international agreements regulating the production of certain chemicals that release chlorine compounds into the atmosphere.
The ozone layer acts as a shield against ultraviolet radiation, which can cause skin cancer. The ozone hole first appeared in the early 1980s. It reached its largest size ever on Sept. 6, 2000, at 11.5 million square miles, NOAA said.
In 2012, the average size was 6.9 million square miles, and the ozone hole reached its largest size for this year on Sept. 22, when it covered 8.2 million square miles.
That is the second smallest the hole has been in the last 20 years, NOAA said. However, the ozone layer is not expected to return to its early 1980s state until 2065.
Contact Camera Staff Writer Erica Meltzer at 303-473-1355 or firstname.lastname@example.org.