The discovery of the causation ozone hole from artificially made
chlorofluorocarbons (CFCs) has allowed developed countries around the world shift
to using more ozone friendly solvents in refrigeration, air conditioning, and
dry cleaning. The decline in usage of
these chlorofluorocarbons has allowed the ozone hole to slowly begin to
heal. The healing process, however, will
take much longer than the damaging process did, due to the long atmospheric
life of CFCs. It is expected to take
another 35 years (~ year 2050) for the ozone hole to completely heal.
This article written by Carolyn Gramling describes that carbon
tetrachloride, another ozone-depleting-substance (ODS), is not depleting from
the atmosphere as quickly as predicted (1% depletion per year rather than 4%),
unlike the other ODSs. This problem has
led to two proposed hypotheses. The
first being that there is still an unknown source of carbon tetrachloride contribution
into the atmosphere, and the second being that scientists might have
underestimated how long the molecule stays in the atmosphere. After many climate simulations were run, an
atmospheric chemist named Paul Newman was able to calculate that around 31,000
tonnes of carbon tetrachloride was still entering the atmosphere after it was
banned worldwide. This proposes a new
problem in finding these unknown sources of carbon tetrachloride.
This article does a nice job highlighting carbon tetrachloride
as the problematic pollutant by factoring out the other possible
pollutants. It also does explain many
different possibilities of how its presence in the atmosphere is not depleting
as predicted and cites very reliable sources within the atmospheric chemistry
field. Unfortunately, a lot of
unscientific jargon is used, such as "scientists have been underestimating
how long the molecule sticks in the
atmosphere," and that "it's kind of an usual molecule." It's understandable that this language is to
help readers without a background in atmospheric chemistry understand. Other than that, it's a very informative
article on a problem that needs to be known and dealt with.
Article: http://news.sciencemag.org/chemistry/2014/08/ozone-depleting-chemical-still-seeping-atmosphere
I would like to know more about the two hypotheses as to why CFC is not depleting out of the atmosphere as quickly as predicted. While the article did explain in some detail what unknown sources of CFC could be (illegal production, brownfields), I wanted to know more about the features of CFC that would led scientists to believe that CFC has a higher atmospheric lifetime than predicted.
ReplyDeleteSome emotion was also involved in the article, as in the description of CFC as nasty, but that was backed up nicely with specific adjectives such as carcinogenic. I think this was a good way how to get the reader to care about the article.
Overall, an informative read displaying information that may change how one views ozone hole recovery.
Throughout the above comment, what I mentioned as CFC should actually be carbon tetrachloride. Apologies for any confusion in the above comment resulting from this!
DeleteI think part of this might be my fault in the wording. They explained in the article that they were "possibilities" and not exactly hypotheses. It would, however, be nice to have a little more explanation on why they think it's possible for their predictions to have been wrong.
DeleteAccording to CFR 40 82.8, there is an exemption for essential laboratories and analytical uses to continue the use of ODS in small quantities. Maybe this exemption accounts for the excess ODS emissions. The exemption is up Dec. 31, 2014, assuming it is not renewed, this may account for some of the excess ODS emissions.
ReplyDeleteCFR: http://www.ecfr.gov/cgi-bin/text-idx?SID=fbe6f4d7d0b0e1983d8c332b99f8bb95&node=se40.18.82_18&rgn=div8
Does the article mention the exact process/model the scientist used to predict the how and how much CFC is removed from the atmosphere? How did they go from 4% depletion to 1%?
ReplyDeleteNo, unfortunately it does not go into specifics of how these conclusions were made. It only states them and cites the source.
DeleteIt seems unlikely to me that such a huge amount of CCl4 would enter the atmosphere solely from leaching out of old refrigerators. I understand that under the Montreal Protocol, countries were required to phase out the production of CCl4 and other ODSs, but how is this being regulated? If the guidelines of regulation aren't strict, especially in developing countries, CCl4 may very well still be in production. I would also be interested to see if the half-life of the compound is, indeed, much longer than originally expected.
ReplyDelete