Ozone
Depletion, History and politics
Ground
based measurements of Ozone were first started in 1956, in at Halley
Bay, Antarctica. Satellite measurements of ozone started in the
early 70's, but the first comprehensive worldwide measurements started
in 1978 with the Nimbus-7 satellite. Nimbus-7 carried a TOMS (total
ozone mapping spectrometer, and a SBUV(solar backscatter UV meter).
The TOMS finally broke on May 7th,1993, but today there are several
different satellites measuring concentrations of ozone and other
atmosheric gases. Gases in the troposphere and lower stratosphere
are sampled by weather balloons or by airplanes such as the ER-2
managed by NASA.
Chloroflourocarbons were first created in 1928 as non-toxic, non-flamable
refrigerants, and were first produced commercially in the 1930's
by DuPont. The first Chlorofluorocarbon was CFC-12, a single carbon
with two chlorines and two Fluorines attached to it. Today many
different CFC's are produced and
worldwide consumption in 1988 was estimated at over billion kilograms.
In 1974 M.J.Molina and F.S.Rowland published a laboratory study
demonstrating the ability of CFC's to catalytically
breakdown Ozone in the presence of high frequency UV light. Further
studies estimated that the ozone layer would be depleted by CFC's
by about 7% within 60yrs and based on such studies the US banned
CFC's in aerosol sprays in 1978. Slowly various nations agreed to
ban CFC's in aerosols but industry fought the banning of valuable
CFC's in other applications. A large shock was needed to motivate
the world to get serious about phasing out CFC's and that shock
came in a 1985 field study by Farman, Gardinar and Shanklin. Published
in _Nature_, May 1985, the study summarized data that had been collected
by the British Antartic Survey showing that ozone levels had dropped
to 10% below normal January levels for Antarctica. The authors had
been somewhat hesitant about publishing because Nimbus-7 satellite
data had shown no such drop during the Antarctic spring. But NASA
soon discovered that the spring-time ''ozone hole'' had been covered
up by a computer-program desiged to discard sudden, large drops
in ozone concentrations as ''errors''. The Nimbus-7 data was rerun
without the filter-program and evidence of the Ozone-hole was seen
as far back as 1976.
It is important to note that the description of the discovery of
the ozone hole presented above is not accurate. Dr Richard D. McPeters,
Principal Investigator, Earth Probe TOMS at Goddard Space Flight
Center explains "Ozone is derived on a FOV-FOV basis and there has
never been a filter applied as described. The explanation I usually
see is that we "threw out" the low values. This is not correct either.
Our software had flags for ozone that was lower than 180 DU, a value
lower than had ever been reliably reported prior to 1983. In 1984,
before publication of the Farman paper, we noticed a sudden increase
in low value from October of 1983. We had decided that the values
were real and submitted a paper to the conference the following
summer when Joe's paper came out, showing the same thing. As the
first one in print, he gets full credit for discovery of the ozone
hole. It makes a great story to talk about how NASA "missed" the
ozone hole, but it isin't quite true."
Numerous studies since then have confirmed both the Anartic hole,
as well as an overall global decrease in Ozone. One major study
calculates that the global ozone has decreased 2.5% from 1969 to
1986 and another 3% drop from 1986 to 1993(Science:260:1993), above
and beyond what natural
factors could account for.
ChloroFluorocarbons
Chlorfluorocarbons
are a family of non-reactive, nonflamable gases and volatile
liquids. Because of their properties they are used in a multitude
of applications; $28 billion of industrial goods and service last
year in the US alone.
The non-reactivity of CFC's, so desirable to industry, allows them
to drift for years in the environment until they eventually reach
the stratosphere. High in the stratosphere intense UV solar radiation
severs chlorines off of the CFC's, and it is these unattached chlorines
that are able to catalytically convert Ozone molecules into Oxygen
molecules:
- Cl
+ O3 ---> ClO + O2 ClO + O3 ---> 2 O2 + Cl.
The
term ''catalyst'' is applied to compounds which can be used repeatedly
in a reaction without being consumed. This means that a small amount
of catalyst can break down a very large amount of Ozone. It is estimated
that one Chlorine atom can convert 100,000 molecules of Ozone into
Oxygen before that chlorine becomes part of a less reactive compound,
such as HCl, and eventually is precipitated out of the stratosphere
by water vapor.
For more information, see CFC-Ozone chemistry
or Chlorofluorcarbons.
Current
Goverment regulations
The impact of United Nations sponsored resolutions depend a great
deal on the willingness of individual goverments to back those resolutions
with laws, preferably laws which offer meaningful punishments and
rewards to their respective industries. Although collective UN interest
in preserving the enviroment is high, individual ambassadors must
return to their countries with agreements that their goverments can
live with.
The most recent world resolution regarding the problem of ozone
depletion is the Montreal Protocol. The original Montreal Protocol
was signed in the fall of 1987, based on negotiations started between
european-scandinavian countries and the US over CFC's in aerosol
sprays in 1983. The protocol has gone through a series of revisions
(each one named after the city where the revision committee met)
as new information from science and industry has become available.
The latest one, held in Copenhagan in November of 1992, laid down
the most stringent CFC phase-out schedule for CFC's for the world
to date; and was signed by over 100 nations representing 95% of
the world's current CFC consumption. Trade sanctions on CFC's, Halons
and products that contain them, were imposed as of April 1993 on
nations not signing the protocol, and in May 1993 this ban was extended
to the export of halocarbon solvents such as Methyl chloride and
Carbon tetrachloride. This protocol laid out a schedule for the
phase-out of CFC's and related halocarbons by the year 2030. A additional
impact of the protocol was to mandate the sharing of technology
between countries in order to speed the replacement and recycling
of CFC's.
In November of 1990 an amended federal Clean Air Act was signed
into law. This legislation included a section (Title IV) entitled
Stratospheric Ozone Protection which directs the EPA to write regulations
affecting every industry using Class 1 and 2 halocarbons. Compounds
are included in either class 1 or 2 based on their ODP. The act
lays out a U.S. schedule for the phaseout of all class 1 compounds
by the year 2000 and tightens regulations dealing with documentation
and recycling of class 2 compounds. In addition congress; in the
1989, 1990 Omnibus Reconciliation Acts and the 1990 Floor Stocks
Tax; imposed taxes on the use, storing and importation of listed
CFC's and halons. The Omnibus Acts tax is based on both the amount-used
of the compounds and the compounds ODP, so companies are encouraged
to stock and use halocarbons less hrmful to the ozone layer.
In 1988, Sweeden was the first country to legislate the complete
phase-out of CFC's, with a scheduled phase-out of CFC's in all new
goods by 1994. In March 1989 environmental ministers of the EEC
announced a total phase-out of CFC's by the year 2000.
Victoria freenet has a very nice summary of global, national and
provencial goverment actions regarding the ozone layer, showing
the Canadian interest in combating ozone depletion.
Author: Brien Sparling
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