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Author Topic: patency of UV light through glass  (Read 8987 times)

Offline MatejBrada

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patency of UV light through glass
« on: 07/09/2005 21:00:01 »
Can someone maybe explain me, why can visible light go through glass,whereas UV light cannot? (on atomic level of course).
As I see it, it should be the other way around, because UV light has bigger energy.
Another, rather Chemist question is, how comes, that ozon absorbs Uv light and normal oxygen does not. Does it have something to do with hybridization of orbitals?


 

Offline David Sparkman

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Re: patency of UV light through glass
« Reply #1 on: 08/09/2005 04:05:51 »
It has to do with the energy levels of the outer electrons of the material in question. These electrons can adsorbe and reemit photons that are energitic enough to boost these electrons to higher energy levels. Say you had an orbit that was 1.2 electron volts above the ground state of an electron. A photon of 1.3 ev passes by and is captured by the electron boosting it into its new orbit. The electron immedately sheds the excess energy in the form of a photon with 0.1 ev, and then when the electron tires of its joy ride, sheds the rest of the energy in the form of a photon of 1.2 ev.

This is a simple quantium explaination of what happens. I am sure there are more complecations as well. I sat in on a presentation of some crystal designs that could be vibrated to pass (be transparent to) certain wavelenghts depending on the frequency (a narrow band of wavelengths). They were being developed to detect when a plane was being targeted by a certain kind of radar instead of just general energy.

David
 

Offline MatejBrada

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Re: patency of UV light through glass
« Reply #2 on: 08/09/2005 21:20:57 »
Well thanks, I got it. But still, I donno about this oxygen-ozon mystery. I cannot find any difference for light in bonding of ozon and oxygen.
 

Offline David Sparkman

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Re: patency of UV light through glass
« Reply #3 on: 09/09/2005 00:18:35 »
It is a simple energy level thing. O3 is unstable and will degenerate into O2. So there has to be an energy source forming the O3. There are two sources in nature, Lightening (that clean fresh smell after a storm is Ozone) and the radiation from the sun. They both boost the energy levels of the oxygen to higher levels where they can react to form O3.

The idea the enviromental people put forth is that freon and certain other chemicals act like a catalyst to change 2(O3) to 3(O2). This could be a reason for the increase in the ozone depletion zone over the south pole if you can show how a heavy freon molecule can easily be transported high above the earth to react with this layer in any quanity.

It could also be caused by a reduction in solar radiation. The hole grows larger during the time that the south pole points away from the sun and smaller when it points at the sun (our winter up north).

Of course the logical thing to do is for all earthlings to stop buying cheap chemicals and buy expensive chemicals to try to off set the lack of solar radiation and let the ozone hole heal thereby profiting chemical manufactors, and research scientists, and lowering our standard of living just a little. Oh and we feel so much better about the good things we have done for mother earth.

David
 

Offline MatejBrada

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Re: patency of UV light through glass
« Reply #4 on: 09/09/2005 21:03:22 »
Well, I have to thank You, because You explained me quite a lot.
Isn't it possible for freons to get there by normal Brown's movement?
 

Offline ukmicky

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Re: patency of UV light through glass
« Reply #5 on: 09/09/2005 22:28:04 »
MatejBrada
I was gooing to comment on normal brown movements, but fortunately for you and everyone else on this forum i'm going through a grown up phase.:D
Hopfully it will end tommorow
« Last Edit: 10/09/2005 04:44:41 by ukmicky »
 

Offline David Sparkman

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Re: patency of UV light through glass
« Reply #6 on: 10/09/2005 07:48:12 »
From
http://www.junkscience.com/may99/freon.htm


Freon superstitions
Editorial
Copyright 1999 Washington Times
May 18, 1999

    There's nothing like scorching hot vinyl seats and rolled down windows to remind one of the dangers of junk science.

    Back in 1995, Congress outlawed future U.S. production of the CFC-based refrigerant R-12 (also know by the trade name Freon), on the theory that reactive chlorine molecules escaping from leaking automobile air conditioners were attacking and degrading the Earth's protective ozone layer, creating holes that allowed dangerous ultraviolet (UV) radiation to reach the planet's surface unfiltered.

    The problem with this theory is that the chlorine molecules in Freon are heavier than air; they settle to the ground upon release - many tens of thousands of feet below the ozone layer.

    And even if they didn't, natural processes release exponentially more chlorine into the surrounding air than anything done by the hand of man. For example, the eruption of Mount Pinatubo in the Philippines generated more chlorine in a few short hours than if all the man-made CFCs in the world were vented en masse.

    But junk science prevailed; Freon was banned. The automakers quickly switched over to a replacement refrigerant (R-134a) beginning with their 1995 and newer models. This new refrigerant is not nearly as efficient as Freon, however, and does not cool as well, particularly on extremely hot days.

    In the meanwhile, federal taxes on the remaining stocks of Freon, combined with the effects of scarcity, have driven per-pound costs of the stuff from around $2 to more than $40. A routine top-off that once cost less than $50 now can cost $200 or more. What's more, Freon is no longer legally available to private individuals; one must be a certified air-conditioning mechanic with all the necessary EPA say-sos before one may lawfully buy R-12.

    But in a few short years, even certified technicians may not be able to get their hands on any Freon; supplies are rapidly dwindling and import prohibitions prevent repair shops from bringing Freon into the U.S. from countries where it is still legal to produce it.

    Sometime soon, those who own older cars will face having to do without air conditioning - or pony up for an expensive retrofit kit to convert their car to the new refrigerant, R-143a. The cost for the changeover is typically $500-$1,000 or more.

    All because of junk science purveyed by reportorial know-nothings in the media who prefer a good scare story to checking out their facts. Remember that next time you burn your behind on those hot vinyl seats. http://

David
 

Offline daveshorts

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Re: patency of UV light through glass
« Reply #7 on: 10/09/2005 17:49:37 »
I think that the point is that all the natural processes that release chlorine do so in a state that is reactive with water/ junk lying around in the lower atmosphere so they don't get very far. Chloroflourocarbons however are increadably stable so they will last for ages in the lower atmosphere and a small proportion of them will make it into the upper atmosphere. Here the intense UV can break them down releasing the Chlorine which will catalyze the decomposition of large quantities of ozone.

If your theory was correct why wasn't there an ozone hole 50 years ago if natural sources of chlorine dominate ozone destruction, and why has the ozone hole stopped growing since chloroflourocarbons were banned?
 

Offline gsmollin

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Re: patency of UV light through glass
« Reply #8 on: 10/09/2005 18:50:53 »
Huaaaaaahahahah, soon I shall be rich, selling my hoarded stockpile of R-12 on e-bay for $200/lb.

"F = ma, E = mc^2, and you can't push a string."
 

Offline David Sparkman

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Re: patency of UV light through glass
« Reply #9 on: 10/09/2005 20:27:15 »
Well I googled Ozone hole and found 7 pages of links. Moving though them all, I just found the same story told over and over again: how the hole was going to be very large this winter (northern winter), but that they expected the hole problem to get better since florocarbons have been banned.

What I did not find was a table of hole sizes for several years. Nor did I find any research on the Clorine content of the upper atmosphere, nor anything to suggest how florocarbons have been proven to reach the upper atmosphere.

I did read an artical concerned about a possible Artic ozone hole that might open up if a volcano erupted in the NORTHERN hemisphere. That got me to wondering. The hole problem is in the southern hemesphere. Most of the industralize world is in the northern hemespheree. Most Freon useage would therefore be in the northern hemesphere, but there is no hole in the northern hemesphere.

Could the main source of upper atmosphere chlorine be vocanos? The southern hemesphere does have most of the active vocanos. hmmm

I think we need to spend 1 trillion dollars to make a portable volcano cap that will capture and elimanate clorine emmissions. If I write it up nicely, do you think I can get the money from the guilt ridden industralized countries? i could say it would take 30 years to build, and then go live in luxery for the next 29 years before anouncing that it was not practical.

David
 

Offline MatejBrada

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Re: patency of UV light through glass
« Reply #10 on: 11/09/2005 21:43:07 »
So, what you say, is that in southern hemisphere, there are more volcanos, and therefore, there is bigger ozon hole. the problem, could be, that the biggest ozon hole is above anatarctica, and I don't expect there to be many volcanos on antarctica.
 

Offline David Sparkman

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Re: patency of UV light through glass
« Reply #11 on: 11/09/2005 23:07:53 »
Each hemisphere has its own atmospheric system without much blending between them. Chlorine produced in the southern hemisphere tends to remain there. The buffer zone between the two systems is where these hurricanes are coming from.

The ozone is generated by solar radiation in the upper levels of our atmosphere. The poles receive the least amount of radiation as they face the sun at very oblique angles. And so that is where the ozone is the thinnest. When the pole is pointed away from the sun as it is during the winter season in whichever hemisphere, the ozone gets it thinnest. So the southern hole should begin to get smaller in the next few months as we head into southern hemisphere summer. There is no hole in the northern hemisphere where all the Freon was being released.

It is just a matter of degree. If advanced countries release a 100 tons of contaminates into the air a year, and one volcano releases 10,000 tons into the air, should we go to great expense to cut down on the man made pollution? or just say it is insignificant?

Watch the news stories on volcanoes, they are the main polluters of the earth, but they have been around for a long time. Some one ought to come up with a way of capping volcanoes and cleaning up their emissions. How about all industrial countries give up 10% of their income to build a volcano Capper! :D


David
 

Offline daveshorts

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Re: patency of UV light through glass
« Reply #12 on: 12/09/2005 14:55:17 »
quote:
Originally posted by David Sparkman

Well I googled Ozone hole and found 7 pages of links. Moving though them all, I just found the same story told over and over again: how the hole was going to be very large this winter (northern winter), but that they expected the hole problem to get better since florocarbons have been banned.



urr try this:
http://www.theozonehole.com/ozoneholehistory.htm

It would appear that the hole has got really significantly worse between 1982 and 2003 looking at some of the other pages though 2004 looks a bit better, but this could just be some freak of the weather.

The ozone hole is a recent phenomenum which increases the chance that it is a man made effect... Global warming is something we could adapt to, a loss of ozone would seriously screw us up in comparison, so I feel that having to adapt a few air conditioning systems in cars is a very small price to pay!!!
 

Offline ukmicky

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Re: patency of UV light through glass
« Reply #13 on: 13/09/2005 01:39:18 »
to daveshorts

How recent is recent, when did we first take measurements of the holes. I would of thought in order to say it is a recent phenomenum we would have to go back 50, 100's even thousands of years in order to prove that fact.

As far as we know the holes in the ozone layer are just part of the natural cycle of the earth. I understand its better to be safer than sorry. So yes its a good idea to ban the use of certain gases etc just in case we are having an adverse effect on the ozone layer.

But surely the possibility has got to exist that the holes could be something that happens from time to time, just like the times in the past when the earth went through  periods of  warming & cooling.
Maybe the holes are a natural forerunner before the earth goes through a period of heating up or freezing:)

« Last Edit: 18/09/2005 19:09:50 by ukmicky »
 

Offline daveshorts

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Re: patency of UV light through glass
« Reply #14 on: 13/09/2005 14:37:22 »
True our data does only last about 50 years and it could just be natural variation but:

There is definitely CFC in the stratosphere:
http://www.cmdl.noaa.gov/noah/publictn/elkins/cfcs.html

There is definitely a mechanism for this CFC to turn into chlorine in the stratosphere

There is a mechanism for this chlorine to destroy ozone

Ozone has been dissappearing in the period that there has been CFCs in the atmosphere.

and I think the quantities involved tie up reasonably well...

seeing as the science is a lot better than global warming (which ain't bad), the consequences of not doing anthing are a lot worse, and the costs of doing something are pretty trivial, I think banning CFCs was pretty sensible.
 

Offline robbojnr

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Re: patency of UV light through glass
« Reply #15 on: 16/09/2005 14:14:18 »
so tell me with regards to ozonation 03 therapy does it work for healing or is it another scam...i see ppl in london like one place offers ozonation therapy for healing all sorts of ailments
 

Offline daveshorts

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Re: patency of UV light through glass
« Reply #16 on: 16/09/2005 15:41:41 »
I would worry, as ozone is an increadibly reacive gas which is used to kill bacteria in some water treatment works and likely to oxidise all sorts of bits of you that are not meant to be oxidised... (a bit like bleach). If you are very lucky and they are not using much ozone, it may not be doing you any harm...
 

Offline gsmollin

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Re: patency of UV light through glass
« Reply #17 on: 16/09/2005 18:46:11 »
I would like to give the explanation why the ozone hole is larger in Antarctica than at the north pole, even though almost all the CFCs were released in the northen hemisphere. The explanation is because Antarctica is over the south pole. The atmospheric conditions that destroy ozone are trapped over the south pole by the land mass of Antarctica. These conditions are largely mitigated by the ocean over the north pole, so the reduction of ozone is less. This is fortunate for us, since Antarctica is pretty sterile. If the ozone were that depleted over the northern hemisphere, we would be having many problems with agriculture, the ocean, and our own skins.

"F = ma, E = mc^2, and you can't push a string."
 

Offline David Sparkman

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Re: patency of UV light through glass
« Reply #18 on: 18/09/2005 18:46:12 »
I don't recall suggesting that the ozone hole was something new, just that we have just noticed it.

I am not sure I can accept GS view that the land mass of Antarctia has that much of an affect on the ozone layer which is in the upper boundries of our atmosphere. The jetstreams are below the ozone layer.

I think the fact that most volcanos are currently located in the southern hemisphere has much more to do with the ozone hole being large in the southern hemisphere, and being small to non-existant in the northern hemisphere.

David
 

Offline anthony

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Re: patency of UV light through glass
« Reply #19 on: 19/09/2005 04:49:27 »
It's not true to say that the hole in the oxone is non-existent in the northern hemisphere. It is significant, though not as pronounced as that in the south. The reason for the southern hole being more extensive was once given as being because the CFC's that degraded it came from one of the biggest CFC producers, ie. the US. Now this sounds like a traditional blame the Yanks type of thing. It is for example known that the mixing of the southern and northern atmospheres is slow. But, for reasons of the prevailing jet streams, I believe this is the accepted reason.
 

Offline daveshorts

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Re: patency of UV light through glass
« Reply #20 on: 19/09/2005 10:10:31 »
I thought the reason for the southern hemisphere ozone hole being bigger was that the ozone destruction is done on the surface of stratospheric ice crystals in sunlight. The crystals form during the winter and the destruction is done in the spring before they evaporate. The South pole has more stratospheric ice crystals (possibly because the ground is colder so there is less infra red emmitted to warm the stratosphere in the long winter) so more ozone depletion.
 

Offline anthony

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Re: patency of UV light through glass
« Reply #21 on: 03/10/2005 13:15:13 »
Dave, I didn't like you ice-crsytal photochemistry reason so I did some digging. and have found this:

The air of the Northern and Southern hemisphere is pretty much isolated into two
separate parcels.
About 90% of the CFCs released were in the Northern hemisphere.
Why then isn't the Ozone hole (the springtime depletion phenomenon) more
prominent in the North, and less prominent in the South?

It is true that the air parcels of the North and the South are largely isolated
from one another. But there is some mixing. The average mixing time for a
particular molecule released in the Northern hemisphere to get anywhere else in
the Northern hemisphere (e.g. Cernobyl fallout) is a matter of 2 or 3 weeks. This
compares with an average crossing time from North to South of between 6 months
and a year. There is always a little casual mixing at the equator, and twice a
year there is relatively major transfer associated with the monsoon seasons in
each hemisphere. The average time it takes for a molecule released at the Earth's
surface to reach the stratosphere is between 20 and 50 years. And most of the
molecules entering the stratosphere from below do so very close to the equator.
So as far as the molecules entering the stratosphere are concerned there is no
North/South difference -- there has been plenty of time for thorough mixing.

Remember that in order to help cause ozone destruction in the polar phenomenon, a
CFC molecule must rise from the surface into the stratosphere to at least 30 km
altitude, break up into smaller free radicals, and then be stored in the
stratosphere as hydrogen chloride or chlorine nitrate until it finds its way to
the polar regions in the stratosphere.

The reason that the ozone hole forms over the Antarctic rather than the Arctic
has to do with climatic differences which ultimately tie in with the different
surface geography in the two polar regions. The Antarctic lower stratosphere is
typically about 5 to 8 deg C colder than the Arctic.

This is from: http://www.madsci.org/posts/archives/mar2000/953164126.Es.r.html
The original source, I think, being the CRC for Southern Hemisphere Meteorology which is partially based at Monash University, Melbourne.
 

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Re: patency of UV light through glass
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