With all the news coming out about terrorist attacks, we tend to forget about our old nemesis, the ozone hole. How big is it this year, anyway?
Each year around August the ozone hole begins to open as light from the springtime Sun over the Antarctic triggers the chemistry of ozone destruction. It contracts again in December.
Predictions that the Antarctic ozone hole would begin to heal in the late 1990s have been wrong. Last year?s ozone hole set a record; it grew to be three times larger in area than the entire land mass of the United States. The hole was so big it exposed towns in southern Chile and Argentina to elevated levels of ultraviolet sunlight. This year?s hole appears to be another big one. The British Antarctic Survey reported that it covers an area more than twice the size of Europe. This equals the hole that opened up in 1999, and only the holes in 1998 and 2000 have been bigger.
In 2000, after growing to record proportions, the ozone vanished a month earlier than normal. Scientists don?t think the 2001 hole will do that, because it only happens once or twice in a decade.
Air temperature, as well as pollutants, influences the rate of ozone destruction. At very low temperatures, icy clouds form in the upper atmosphere. Ice crystals within these clouds provide a surface for chemical reactions that transform benign chlorine compounds into ozone destroyers. Therefore, colder winters cause greater springtime ozone destruction. Last year?s record hole followed a particularly frigid Antarctic winter (remember, the seasons are reversed south of the equator).
?Because of the overwhelming role of weather in the ozone hole, it means it?s really unpredictable,? says Richard McPeters, principal investigator for NASA?s Total Ozone Mapping Spectrometer. ?That?s what makes it fun to measure ozone - every year it surprises us.?
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Most of the world?s ozone-destroying pollutants come from the northern half of our planet. So why does the biggest ozone hole always opens up over the south pole, not the north?
New research confirms what scientists have long thought: Giant atmospheric waves that originate over land features such as the Himalayas help prevent the formation of a northern ozone hole. This means that Arctic cities remain safer from unwelcome doses of solar ultraviolet radiation, but global warming could change all that in the future. Small ozone holes have formed over the Arctic before, such as in the spring of 1997. But the chemistry of ozone destruction requires very cold air temperatures in the stratosphere, and the Arctic stratosphere isn?t as cold as the Antarctic.
The north-south difference is the result of the uneven way that land is distributed on the Earth. Most of our planet?s land and its highest mountains are in the northern hemisphere.High mountains generate large movements in the atmosphere that heat up polar air. These planetary waves displace air north and south as they travel around the planet. Stronger waves in the northern hemisphere warm the Arctic stratosphere and suppress ozone destruction. There are fewer tall mountain ranges and more open ocean around Antarctica, so it?s more vulnerable to ozone holes.
Stratospheric cooling can be the result of global warming. Greenhouse gases, which trap the heat radiating from Earth?s surface in the lowest level of the atmosphere, reduce the heat that reaches the stratosphere. Thus, greenhouse gases cool the stratosphere by insulating it from the warmer Earth below.
CFC molecules, which are ozone-destroying pollutants, peaked in 1994 and have now declined. However, computer simulations show that CFCs in the high stratosphere could return to pre-1980 levels in 30 to 50 years. It?s hard to say which trend will dominate: the cooling of the stratosphere, which would encourage an Arctic ozone hole, or the decline of CFCs, which would suppress it.
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Four chemicals being marketed as harmless to the ozone layer may actually be endangering it. As evidence grows that the ozone hole over the Antarctic is not healing as expected, an international coalition of governments is discussing whether to ban them.
Top of the list is n-propyl bromide, a new solvent approved in 1997 by the U.S. Environmental Protection Agency as an acceptable substitute for ozone-depleting substances such as CFCs. The chemical was known to be a potential ozone-eater, but it survives in the environment for less than 2 weeks, so it was assumed that it could not reach the ozone layer.
But Donald Wuebbles of the University of Illinois, warns that when the substance is released in the tropics, weather systems there can launch it into the stratosphere within days. So even if the chemical breaks down in the lower atmosphere, it could still be churning out by-products that react with ozone-depleting bromine and help transfer it into the stratosphere. n-propyl bromide?s potential for depleting ozone is 30 times more in the tropics than at northern latitudes. But China says it does not believe that n-propyl bromide depletes ozone.
UN scientists estimate that up to 10,000 tons of the chemical, marketed as ?environmentally friendly,? are made each year. That could rise to 50,000 tons a year by 2010.
Three other chemicals may also be banned. Hexachlorobutadiene is a solvent and by-product of the manufacture of PVC. Tens of thousands of tons of it are made each year. Halon-1202 is an older chemical still used to fight fires in military aircraft and tanks, and 6-bromo-2-methoxy-naphthalene is used in the manufacture of the agricultural fumigant methyl bromide.
And there are fears that there could be many other as-yet unidentified ozone-destroying chemicals in widespread use. ?Relatively small amounts of these new substances are being produced, but the levels of some of them are growing rapidly in the atmosphere,? says John Pyle of the Center for Atmospheric Science at the University of Cambridge.
?We cannot be complacent. If enough of these new chemicals are manufactured, we will delay the recovery of the ozone layer quite significantly,? warns Mario Molina of the Massachusetts Institute of Technology, who won the chemistry Nobel Prize in 1995 for his work on the thinning ozone layer.
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The thin layer of ozone in the atmosphere that we?re so worried about losing is capable of doing much more than absorbing harmful ultraviolet radiation.
According to Cyclopss Corp., a Salt Lake-based research company, ozone may become the next wonder decontaminant, that can even destroy Bacillus anthracis, the bacterium responsible for causing anthrax.
Ozone is a naturally occurring molecule composed of three oxygen atoms that quickly reacts with other substances, causing their decomposition. ?There are no microorganisms that are immune to it, nor can they build any resistance to it, because it literally takes them apart at their molecular level,? says William Stoddard, Cyclopss chief executive officer. ?It reacts with anything that has a double-carbon bond, so it reacts with any organic material on the Earth.?
They expect ozone to work better at decontaminating areas than traditional chemical methods. ?The traditional chemicals leave a residue behind that interferes with the drug. [However], ozone is unstable and reverts back to oxygen, and there is no chemical residue,? says Durand Smith, Cyclopss president.
The ozone would be delivered through a closed-loop system where an electrical current is run through water, generating ozone. The ozonated water will be sprayed over the area, destroying any pathogens present.
Ozone is already being used to sanitize water. ?Ozone is used extensively in the bottled water industry. It?s common for meat packing plants to use it to control microorganisms in the curing process,? says Jerry Nelson, owner of Salt Lake-based Nelson Laboratories.
Cyclopss has completed the installation of an ozone decontamination chamber for Nelson Laboratories. The chamber sterilizes by exposing equipment to ozone gas for 20 to 30 minutes. ?We are apparently the first to have done this particular application. And the preliminary data looks very good,? Nelson says.
We may soon see it used to remove anthrax from government and media offices and mail rooms. Spores like anthrax, which are the most difficult kind of pathogens to kill, are no match for ozone.
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