J. CHEM. SOC. FARADAY TRANS., 1994, 90(15), 2159-2169
FARADAY RESEARCH ARTICLE
A. R. Ravishankara"? and Edward R. Lovejoy
Aeronomy Laboratory, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder
CO 80303, USA
"Lastly, the question is raised: Should atmospheric lifetime be used as an index of acceptability ? "
HCFC's were promoted as a replacement for CFC's because the don't last as long. Who cares how long they last they're all going to react, they'll react long before they expire. That's like being given a poison that expires in 100 years. So what if it lasts that long that damage is done now, not 100 years after not reacting for that long. If chlorine is being pumped into the atmosphere from CFC's and it's not reacting for 100 years how is it depleting the ozone layer? It is of course, it's all reacting neatly instantly.
"CFCs were hailed as the most stable and non-toxic compounds
ever produced by mankind"
"Measurements by Lovelock in the 1970s3 established
the ubiquity of CFCs in the atmosphere. This pioneering
work prompted Rowland and Molina to suggest that,
because of their inertness, CFCs could transport chlorine to
the stratosphere and promote ozone depletion. "
This is the James Lovelock that recanted when it stopped warming.
"The majority of species emitted by natural processes into the
atmosphere have lifetimes of less than a few years. The
hydrocarbons emitted from trees, for example, live for a few
hours or possibly a few days. Methane, which has significant
natural sources, has an atmospheric lifetime of about 10
years. CO, and N,O are exceptionally long-lived natural
emissions which have lifetimes of nearly a century. The main
sink for CO, is conversion into carbonates in the oceans
while N,O is removed primarily by photolysis in the stratosphere.
All the natural species are short-lived compared to
some of the compounds produced by humans. The most
stable gases emitted by humans appear to be the perfluoro
compounds. These molecules, which are very potent greenhouse
gases, have atmospheric lifetimes of thousands of years.
As mentioned earlier, the time it takes to cleanse the atmosphere
increases proportionately with the atmospheric lifetime.
Therefore, even though there may be no currently
identified harm to the atmosphere due to the emissions of a
very long-lived species, one cannot be certain that they are
benign. When CFCs were invented and released into the
atmosphere, their deleterious effects were not known. Fortunately,
CFCs are relatively short lived, compared to PFCs,
and it will take only about a century for CFCs to be removed
from the atmosphere once their emissions are curtailed. The
release of any very long-lived species in the atmosphere
should be viewed with the greatest concern. The PFC lifetimes,
though long on historical timescales, are short compared
to the evolutionary timescales. Hence, life on Earth
may not be able to adopt to the changes these emissions may
cause. Thus, it seems prudent to ask if the long-lived... "