Ozone is a natural trace gas in Earth’s atmosphere. In the lower atmosphere, ozone helps trap heat to keep the earth warm. In the upper atmosphere, it plays an even more important role by filtering harmful ultra-violet (UV) rays from the sun. Overexposure to UV rays destroys skin cells, causes cancer and cataracts, and can lead to macular degeneration. Without a protective ozone layer, there would not be life on earth as we know it. For this reason, scientists and environmentalists the world over were extremely concerned to discover a large hole in the ozone over Antarctica.
Man-made chlorofluorocarbon (CFC) compounds, chlorine, and bromine are attributed with creating the hole in the ozone. CFCs, used in aerosol products, air conditioners, and refrigeration units, were banned in 108 countries in the 1980s; however, they continue to be released into the atmosphere from older products still in use. Additionally, experts estimate that about half of the bromine in the atmosphere is from human use, along with nearly all of the chlorine.
CFCs rise into the atmosphere and, through exposure to other compounds, extreme cold, and sunlight, convert to chlorine atoms. Chlorine atoms change ozone molecules into oxygen. The problem here is that oxygen, while good to breathe in the lower atmosphere, doesn’t filter UV rays. CFCs effectively “open a window” in our protective atmosphere. This window in the ozone builds over Antarctica.
This remote region might seem like an odd place for a hole in the ozone. Antarctica is unpopulated by any permanent human beings and remains pristine. Why isn’t the hole over highly populated areas where CFCs and other greenhouse emissions are known to be high? It turns out the answer has to do with the earth’s rotation and other climatological factors.
First, the earth’s spinning motion ensures that all gasses or emissions released into the air, whether natural or manmade, spread more or less evenly throughout the troposphere, or lower atmosphere, over the period of about a year. According to the Environmental Protection Agency (EPA), it then takes anywhere from two to five years for these gasses to spread into and throughout the stratosphere, or upper atmosphere. From here, climate comes into play in the changing chemistry of the CFCs and their role in creating the hole in the ozone.
In winter, the earth’s tilted axis prevents sunlight from shining on the South Pole. This causes temperatures in the atmosphere over Antarctica to plummet as low as -108° Fahrenheit (-78° Celsius). Cool air descending from the South Pole creates a “winter vortex” of circulating winds in the middle latitudes over Antarctica, acting like a huge whirlpool. This effectively cuts off the ozone over Antarctica from mixing with the planet’s larger atmospheric pool.
As temperatures continue to drop in the sunless winter, Polar Stratospheric Clouds (PSCs), or clouds of nitric acid ice-crystals, begin to form over Antarctica. CFC compounds collect on these ice-crystals, combining with the nitric acid compounds that convert the CFCs to more active forms of chlorine. These compounds build over the long winter season.
When spring comes and sunlight strikes the clouds, UV radiation splits the motherlode of chlorine molecules into highly active chlorine atoms. Each single chlorine atom can destroy a massive amount of ozone molecules, converting them to oxygen. The result is a runaway process that eats up the protective gasses, creating a huge hole in the ozone.
Each year, scientists monitor the hole as it seasonally expands and contracts. In 2005, the hole in the ozone measured a startling 10-million square miles (25,899,881 sq. km), or roughly three times the size of the United States. Only the year 2003 beat this dubious record, with a hole that measured 11-million miles.
As seasons change and the vortex subsides, the upper area ceases to be isolated, temperatures rise, and the opening in the ozone shrinks. However, scientists now believe that the hole may not fully repair itself until the year 2065. The lesser-damaged ozone over the North Pole is expected to heal by about 2040.
While it may be encouraging that we have a predictive scale for recovery of the hole in the ozone, there is another concern. Ozone depletion is taking place at a rate of a few percent per year, most noticeably at the mid-latitudes of the planet. While scientists struggle to understand this phenomenon, humans are at risk of increased cases of cancer due to greater UV exposure, both through a thinner protective atmospheric blanket and because of the ozone hole. These complex conditions are also closely associated with global warming.