Friday, September 28, 2007

The Earth’s Ozone Layer: Safe at Last?

The Montreal Protocol might be working since scientists had observed a steady decline of ozone destroying chemicals in our atmosphere since the 1990’s, is this good news for the ozone layer?

By: Ringo Bones

Compared to the Kyoto Protocol’s mandate of reducing greenhouse gas emissions to limit the harm that could be caused by climate change. The Montreal Protocol’s mandate (mission?) of eliminating existing chemicals then in use in the industry and in domestic situations that are harmful to the Earth’s ozone layer was perceived as an insurmountable task – by both critics and proponents alike- 20 years ago.

The Montreal Protocol, whose full official title is the Protocol on Substances That Deplete the Ozone Layer is a treaty that was established on September 16, 1987 at Montreal, Canada by a 25 nation body who first signed on. Presently, 168 nations are now parties to the accord. The Montreal Protocol’s mandate was to set limits on the production of ozone depleting chemicals like chlorofluorocarbons (CFCs), halons, and related substances that release chlorine or bromine to the ozone layer of the Earth’s atmosphere. But first, a brief description on how the ozone layer of our planet works.

The Earth’s ozone layer –or the part that filters harmful UV rays out- is found in the upper part of the stratosphere at 40 to 50 kilometers up. The ozone found at ground level is a pollutant. Ozone is an allotrope of oxygen. Allotrope is an element in two or more different forms usually in the same phase like the element carbon that can both exist as coal, or a diamond depending on how it’s atoms are arranged. Unlike the ordinary atmospheric i.e. diatomic oxygen that we breathe whose molecular structure is composed of two oxygen atoms, while ozone has three. Even though both are composed of the same elemental oxygen, ozone can irritate –even damage- our lungs in long term exposure. While monatomic oxygen i.e. gaseous oxygen existing as single atoms plays a part in providing color in the aurora borealis and australis as it gets hit by charged particles from the sun. Every time an ozone molecule gets hit by an energetic ultraviolet radiation from the sun like UV-B (cancer causing), UV-C (chromosomal and immune system damage) and UV-A (tans the skin but still harmful in excess), it breaks apart into a diatomic oxygen molecule and a monatomic oxygen. Oddly enough, the same harmful UV rays allow the ripped oxygen molecules to recombine into ozone thus the cycle continues. This is how ozone absorbs UV radiation. While ozone destroying chemicals that reach the stratosphere also break ozone molecules apart, the bad part is the ozone molecule broken by this method didn’t perform it’s duty of absorbing UV rays. If enough ozone is broken apart chemically, levels of harmful UV rays reaching to the Earth’s surface could increase.

The biggest hurdle in the total manufacture and utilization ban of ozone destroying chemicals is that the “miracles” of contemporary society like refrigerants / keeping things cool and putting out “technical” fires will be seriously affected by the ban. The haloalkane / BCF fire suppressant halon had saved countless fighter pilots that served during the Vietnam War. An F-105 Thunderchief survived being hit by a Soviet made surface-to-air missile to return to her home air base thanks to the halon fire suppression system. Next to the modern ejection seat, halon is the modern jet pilot’s “other best friend.”

Under the Montreal Protocol, the ozone depleting potential or ODP, of any substance is measured with respect to an equal molecular mass of CFC-11, which is assigned a value of 1.0. Most other CFC’s have an ODP rating that ranges from 0.5 to about 1.3. Hydrochlorofluorocarbons, which are being used as transitional replacements until 2020 for CFC’s in refrigeration, have ODP’s that are generally less than 0.5. The problem with hydrochlorofluorocarbons or HCFC’s is that HCFC’s are a very efficient greenhouse gas because of its high specific heat rating. Thus it’s use could contribute to global warming while it’s molecular structure is still under investigation if it chemically breaks down fast enough before it reaches into the stratospheric regions to affect the ozone layer. Hydrofluorocarbons, which are also replacing CFC’s as refrigerants, have an ODP of zero. The molecular structure of HFC’s allows it to chemically break down before it drifts high into the ozone layer. The caveats of hydrofluorocarbons or HFC’s is that the refrigeration system that use HFC’s as a refrigerant are inefficient compared to ones that use CFC or HCFC i.e. it consumes more electricity. Also, ozone-depleting potentials are based on existing scientific knowledge and are to be reviewed and revised periodically. Thus the ODP rating of HFC's could change in the future.

An article published in the March 5, 2007 edition of Science Now about the findings that chlorine based ozone destroying agents are in decline. But the scientists conducting the study are still wary about the future recovery status of our ozone layer because bromine based ozone destroying agents can not yet be tracked with certainty as easily as chlorine based agents using current procedures. The good news is that the preliminary findings suggest that if current preventive measures on ozone depleting chemicals continue, there will be a marked improvement on the status of the Earth’s ozone layer 50 years from now. All of humanity now lives in hope.

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