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Old 10-18-2009, 04:34 PM   #1
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interesting read global warming


Global Warming Potential vs Ozone Depletion Potential
« on: June 26, 2007, 03:28:39 PM »

ODP Defined

The ODP, or Ozone Depletion Potential, is the potential for a single molecule of the refrigerant to destroy the Ozone Layer. All of the refrigerants use R11 as a calibration and thus R11 has an ODP of 1.0. The less the value of the ODP the better the refrigerant is for the Ozone Layer and the Environment.

GWP Defined

The GWP, or Global Warming Potential, is a measurement of how much effect the given refrigerant will have on Global Warming in relation to Carbon Dioxide. This is usually measured over a one hundred year period. In this case the lower the value of GWP the better the refrigerant is for the environment.

Refrigerants

R22 is a single hydro chlorofluorocarbon (HCFC) compound. It has a low chlorine content and ozone depletion potential and only a modest direct global warming potential.
ODP = 0.05, GWP = 1700

R410A is a binary blend of hydro fluorocarbon (HFC) compounds (50% = R32, 50% = R125) It has no chlorine content, no ozone depletion potential, and only a modest global warming potential.
ODP = 0.0, GWP 1890

We know R22 has an ODP, and R410A has none. R410A does however, have a higher GWP then R22. So what is actually worse for the environment?
We have always been told R22 has an effect on the ozone layer, and R410A does not...or does it?

Global Warming Can Increase Ozone Depletion

Scientist's are concerned that continued global warming will accelerate ozone destruction and increase stratospheric ozone depletion. Ozone depletion gets worse when the stratosphere (where the ozone layer is), becomes colder. Because global warming traps heat in the troposphere, less heat reaches the stratosphere which will make it colder. Greenhouse gases act like a blanket for the troposphere and make the stratosphere colder. In other words, global warming can make ozone depletion much worse right when it is supposed to begin its recovery during the next century.

Effects of Ozone Depletion and Global Warming

A lot of people think global warming and the ozone hole are the same thing. They aren’t.

At least, that’s the simple answer. Most people have only the most rudimentary understanding of how climate systems and atmospheric chemistry work – and many of them lump ozone depletion and climate change together simply out of confusion. They know that gases our industrial society pumps into the atmosphere are fouling up the entire planet – but the details are hazy.

The global warming which many scientists expect (and think they are observing) comes from release of certain gases which enhance the natural “greenhouse effect.” These “greenhouse gases,” carbon dioxide, methane, nitrous oxide, and the halocarbons, are produced by human activity and are building up in the atmosphere. They trap solar heat much as a greenhouse or blanket would, causing the temperature of the lower atmosphere to rise.

Scientists also know that a layer of ozone in the lower stratosphere protects Earth by shielding it from the sun’s ultraviolet radiation. Without that shield, life on land would be almost impossible. The problem is that halocarbons (such as the chlorofluorocarbons that were used as industrial solvents and spray-can propellants) were destroying the stratospheric ozone layer. The chlorine, fluorine, and bromine which these chemicals contain act as catalysts to kick off a chain reaction that destroys ozone. It is this process that has worsened the dramatic ozone hole that occurs over Antarctica at the end of every winter there. The worry is that a thinning ozone layer will mean more of the ultraviolet radiation which can harm living things (for example, by causing skin cancer in humans).

Global warming and ozone depletion are two different problems

The planet Earth is rarely as simple as it seems, and there are important cross-connections between the two problems which are worth understanding.

For example, the halocarbons which destroy the ozone layer also happen to be potent greenhouse gases. So there seem to be twice as many reasons to stop pumping them into the atmosphere. Their use is already being phased down under the 1987 Montreal treaty, and eventually (after decades) this phase down will help alleviate the human-caused enhanced greenhouse effect.

But the plot thickens. Another important greenhouse gas is ozone itself – at least, the ozone that is in the lower atmosphere (called the troposphere). So there is a paradox. The halocarbons increase global warming because they are greenhouse gases – but they also destroy another greenhouse gas, ozone, thereby reducing global warming.

Ultraviolet concerns alone may be enough to justify phasing out ozone-depleting chemicals. But from a climate perspective, what really matters is the net result of their direct warming and indirect “cooling” effects. We can say with some confidence that the overall net effect of the halocarbons is to warm the climate at Earth’s surface. But in actuality, whether the net effect is warming or cooling, strong or weak, depends on many things: the specific halocarbon, the location on the globe, etc.

The Truth

One “bad news” implication is that the climate-protection “windfall” scientists once thought would be reaped from the Montreal treaty will actually be smaller than expected. We will have to work harder than once expected to mitigate global warming.

Another “bad news” implication: the phase-out of the worst ozone-depleters (like CFC-11 and CFC-12) is being accomplished partly by substituting halocarbons whose ozone-depleting effects are much weaker (such as the hydrofluorocarbons). But these replacement chemicals are also greenhouse gases. And while their global-warming effect may be much less than that of the chemicals they replace, it is still many times that of carbon dioxide.

One further complexity: An important trace ingredient in the atmosphere is the hydroxyl radical – which consists of one oxygen and one hydrogen atom. The unstable hydroxyl radical tends to react quickly with other molecules in the atmosphere. In fact, hydroxyls and ultraviolet radiation seem to be responsible for much of the eventual destruction of methane, some halocarbons, and a number of other atmospheric pollutants.

Here’s the rub: the ultraviolet that reaches the troposphere plays a big role in creating hydroxyl radicals down there. So more ultraviolet reaching the troposphere could actually accelerate removal of greenhouse gases like methane. But this is hardly a reason to be complacent about stratospheric ozone depletion.

The above discussion actually gives only a hint of how complex atmospheric chemistry is – and how complex the climate-chemistry links and feedbacks are. It is a reminder than changing a system so complex could be fraught with perils.

Sources:
http://www.ess-home.com/news/global-...-depletion.asp
http://en.wikipedia.org/wiki/Global_warming_potential
http://www.nsc.org/EHC/climate/ccucla9.htm

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Old 10-18-2009, 04:48 PM   #2
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interesting read global warming


Was that your introduction, a question, or what?

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Old 10-18-2009, 10:34 PM   #3
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interesting read global warming


i thought i had posted it on the hvac section. sorry if i made a mistake here
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