Irradiating CFC's in aqueous environments destroys them.

[NNadir]

X-rays destroy chlorofluorocarbons (CFC's) when suspended in water.

From the Journal of Physical Chemistry B, 107 (46), 12740 -12751, 2003.

Abstract:

"Chemical Reactions in CF2Cl2/Water (Ice) Films Induced by X-ray Radiation

C. C. Perry, G. M. Wolfe, A. J. Wagner, J. Torres, N. S. Faradzhev, T. E. Madey, and D. H. Fairbrother*

Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, and Laboratory for Surface Modification and Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854-8019

Received: April 25, 2003

In Final Form: July 3, 2003

Abstract:

The chemical reactions initiated by high-energy radiation (Mg or Al K X-rays) in amorphous CF2Cl2/H2O(ice) films have been studied using a combination of reflection absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Following deposition, the structure of the CF2Cl2/H2O(ice) film resembles an amorphous ice phase having CF2Cl2 molecules caged within the film, and a smaller number of CF2Cl2 molecules adsorbed on the ice surface. X-ray irradiation produces a broad distribution of low-energy secondary electrons whose interactions with CF2Cl2/H2O(ice) films are associated with the production of H3O+, CO2, and COF2 (carbonyl fluoride) as detected by RAIRS. COF2 is identified as an intermediate species whose electron-stimulated decomposition leads to CO2 production. The product partitioning is dependent on the film's initial composition; in water rich films, CO2 and COF2 production is favored, whereas a more thermally stable, partially halogenated polymeric CFxCly film is detected by XPS in CF2Cl2 rich films. Chloride and fluoride anions are also produced and solvated (trapped) within the ice film. During the early stages of X-ray irradiation, the dominance of Cl- anions formed in the film by reaction with low-energy secondary electrons is consistent with the suggestion that C-Cl bond cleavage of CF2Cl2 via dissociative electron attachment (CF2Cl2 + e- ·CF2Cl + Cl-) is the dominant initial process. "

The intermediate described in the abstract, COF2, is also known as fluorophosgene. This toxic compound is an intermediate as well in the slow, ozone destroying, decomposition of these same compounds in the stratosphere.

[prodigal_green]

1. I know I sound as dumb as a freeper

but, is this a good thing or a bad thing? I'm referring to the intermediates.

[no_hypocrisy]

2. I think it's a good thing. Chlorofluorocarbons are the elements that

are released into the atmosphere that rise and collect. This in turn destroys the ozone layer surrounding this planet. Without the ozone, protection against ultraviolet light from the sun is lost and this speeds up global warming, especially when added to the build-up of carbon dioxide.

Are you with me so far?

Anther source of chloroflurocarbons is freon from refrigerators and freezers, home and car air conditioners (the latter less so as motor vehicles have converted to less destructive coolants in the recent past).

http://www.virtualglobe.org/en/info/env/02/ozone02.html

[prodigal_green]

3. I understand the dangers of CFCs

It was this line that confused me:

The intermediate described in the abstract, COF2, is also known as fluorophosgene. This toxic compound is an intermediate as well in the slow, ozone destroying, decomposition of these same compounds in the stratosphere.

[NNadir]

4. Not a dumb question at all: It depends on the circumstances.

The formation of fluorophosgene in the upper atmosphere from CFC's effectively breaks the chain reaction leading to the formation of chlorine radicals that catalyze the destruction of ozone. The reaction forming fluorophosgene probably occurs when a CF2Cl radical interacts with a hydroxyl radical (from the splitting of water) to form an intermediate (difluorochloromethanol) that rapidly decomposes to fluorophosgene and hydrochloric acid. This effectively prevents the CF2Cl radical from recombining with a chlorine radical and repeating the cycle of ozone destruction all over again. In this sense, it is a good thing, since a molecule of CFC is no longer available to destroy ozone.

Fluorophosgene however is even more toxic than its cousin phosgene, which was used as a war gas in World War I (and is still used today in many industrial processes). Still, since this reaction is slow, since the stratosphere is remote and since the concentrations very low, I very much doubt that fluorophosgene has much physiological or health effect in actual practice.

What is interesting about this work is that it suggests a relatively easy process to remove (industrially) rogue CFC's from the atmosphere.

[prodigal_green]

5. Thanks!

I wasn't sure when I read it if the solution was possibly more dangerous than the problem, but it looks like it isn't so that IS good news.

[Massacure]

6. Either way, once they are up you can't take them down

That means we have cut down on how much we put up using the technology.

How long does it take for CFC's to break down the ozone?

[NNadir]

7. Not exactly.

This effect if technologically applied, would be used to shorten the atmospheric half-life of CFC's, which typically are measured in centuries. This would not be a means of removing new CFC's, but a means of removing those that remain from the period of the second half of the twentieth century.

I have been interested in whether this type of reaction would take place for some time, as a possible means of eliminating ground level ozone. Although the present work took place using ice, there is no reason to suspect that a similar effect might not be found with steam/air mixtures.

Early on in my consideration of how to use fission products productively, I thought that radiocerium oxide (Ce-144), would be an excellent product for use in this kind of process. Ceric oxide, the catalyst used in self cleaning ovens, is completely insoluble and has the added benefit of oxidizing hydrocarbons and carbon particulates to CO2.

Unfortunately, I later understood that there is a limit to how large a system you could build. The longest lived radioisotope from fission is Ce-144, with a half life of only 284.89 days. This means that there are very definite low limits to how much of this isotope will be available at any given time. If the world's energy demand doubled, and all of it were obtained by nuclear means, once the amount of Ce-144 on the planet reached 440 MT, it would approach equilibrium (it approaches with grams of such equilibrium in about 16 years) and be decaying as fast as it could be produced.

A similar situation applies for Ruthenium-106, (half life = 367 days) which could theoretically be used to decompose not only CFC's but nitrogen oxides as well.

One has to be very careful irradiating air, because under some circumstances, you can have a positive NOx flux. This is why some Ruthenium (which decays to Palladium) is desirable. Ruthenium and Palladium both catalyze the decomposition of NO and NO2.

[struggle4progress]

8. Actually, from the abstract, this article appears to be a technical ...

... contribution to the study of the mechanisms by which CFCs destroy ozone. CFCs are known to dissociate photochemically; there have also been discussion of dissociation by cosmic rays; and there is evidence that important reaction steps occur on ice crystals, as well as questions about why greater ozone loss occurs at lower temperatures. The abstract indicates these authors are concerned with the irradiation chemistry of CFCs in thin films on ice crystals, with some attention to the issue of how much water is in the film; this would, of course, be exactly the sort of feature that might be expected to vary with temperature. Use of X-rays seems to be a way to simulate the radiation environment of the upper atmosphere.


Effects of cosmic rays on atmospheric chlorofluorocarbon dissociation and ozone depletion.
Phys Rev Lett. 2001 Aug 13;87(7):078501. Epub 2001 Jul 30.

Lu QB, Sanche L.

Group of the Canadian Institutes of Health Research in Radiation Sciences, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada, J1H 5N4.

Data from satellite, balloon, and ground-station measurements show that ozone loss is strongly correlated with cosmic-ray ionization-rate variations with altitude, latitude, and time. Moreover, our laboratory data indicate that the dissociation induced by cosmic rays for CF(2)Cl(2) and CFCl(3) on ice surfaces in the polar stratosphere at an altitude of approximately 15 km is quite efficient, with estimated rates of 4.3 x 10(-5) and 3.6 x 10(-4) s(-1), respectively. These findings suggest that dissociation of chlorofluorocarbons by capture of electrons produced by cosmic rays and localized in polar stratospheric cloud ice may play a significant role in causing the ozone hole.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11497927&dopt=Abstract


2002-05-29
Ozone Losses May Be Speeding Up At Higher Latitudes, According To University Of Colorado Study

New findings by University of Colorado at Boulder researchers indicate ozone losses due to the breakdown of chlorofluorocarbons, or CFCs, occur much faster than previously believed at higher latitudes roughly 10 miles above Earth.

Associate Professor Darin Toohey of the Program in Atmospheric and Oceanic Sciences said scientists have known for several decades that chlorofluorocarbon-derived compounds can deplete stratospheric ozone. More recently, some have proposed that adverse chemical reactions caused by man-made compounds occurring just seven to 10 miles in altitude could lead to additional ozone losses. <snip>

PAOS researchers and students have used balloons and aircraft to show that ozone-gobbling chlorine “free radicals” produced by the breakdown of CFCs are more concentrated at high latitudes than previously believed. During winter and spring, the reactions appear to be accelerated from about 50 degrees to 60 degrees in latitude – roughly from Vancouver, B.C., north to Great Slave Lake in the Northwest Territories –all the way to the North Pole.

These chemical reactions occur in regions where there are ice clouds, based on measurements of CU-Boulder Professor Linnea Avallone of PAOS and the Laboratory for Atmospheric and Space Physics, said Toohey. <snip>

http://www.sciencedaily.com/releases/2002/05/020529071845.htm