http://www.nearingzero.net (nz288.jpg)

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Physics 6 Schedule
Feb. 13 Ozone Depletion Video (104 Phys.) Feb. 15 Video Discussion Energy Ozone
Feb. 20 Ozone II Feb. 22 Cool Activity
Feb. 27 Ozone III Issue Topic Due March 1 Energy Thermodynamics
March 6 Video (104 Physics) March 8 Video Discussion Thermodynamics
Lab meets Friday!
Only two things are infinite, the universe and
human stupidity, and I'm not sure about the
former.A. Einstein
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Announcements

• Homework 7 let the Wayback Machine take you to
  January 17, 1999.
• Homework 7 can be turned in Wednesday.

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Reviewing the last few slides from the previous
lecture
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Yes, I see the 1973-1993 decreasing trend, but
lets go back to 1984 (and try to remove the
possibly misleading trend line).
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Sending myself back to 1984, I say this needs
watchedstill.
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Why does this situation need watched?
We have a dangerous situation.
We have a mechanism causing the situation.
We have taken steps to correct the situation.
(Banning of trivial CFC uses, such as
propellants.)
Are our steps working?
We must watch and wait.
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Many resources show the Arosa data (which I also
showed you) because it represents the longest
continuously-monitored series of ozone
measurements.
Remember, the Arosa spectrometer measures the
total column of ozone above the observing
station, so it is sensitive to stratospheric
ozone.
Ozone-monitoring stations were also established
in Antarctica, and satellite measurements began
in the 1970s.
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As we monitored the ozone layer during the late
1970s and early 1980s, new research suggested
it was premature to believe there was a problem.
Large amounts of nitrogen oxides, such as NO2,
have been released by the combustion of fossil
fuels. Nitrogen oxides also participate in
catalytic reactions that should destroy ozone.
Early calculations (ca. 1970) showed that ozone
depletion should have been far more severe than
was then observed.
Clearly, some aspect of atmospheric chemistry was
not well understood.
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Another puzzle is the neutralization of chlorine
by nitrogen oxides.
Chlorine and nitrogen oxides react and
short-circuit the ozone-destroying process. The
interaction reduces, but does not completely
eliminate, the ability of chlorine to destroy
ozone.
As research continued, more chlorine reactions
were discovered.
These reactions result in chlorine reservoirs,
in which chlorine is tied up for long periods of
time, reducing the destructive power of chlorine.
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Examples of reactions that produce chlorine
reservoirs
ClO NO2 ? ClONO2 Cl- CH4 ? HCl
(For the chemists in the audience, these are not
meant to be balanced reactions!)
After the chlorine reservoirs were discovered, it
was concluded that CFCs should have minimum
effect on the ozone.
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But in 1984, British Antarctic Survey scientists
Jonathon Shanklin, Joseph Farman, and Brian
Gardiner reported the alarming discovery that
Antarctic ozone levels were 35 below the 1960s
average.
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Their report was initially dismissed.
Your data are clearly wrong. Go back and measure
it again.
Their data were not supported by satellite
measurements.
Shanklin and co-workers double-checked. They were
right.
The satellite data were also right.
The analysis of the satellite data was flawed!
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The computer programs that analyzed the satellite
ozone data were programmed to discard outliers.
Actual ozone levels were so low that they were
treated as outliers and neglected!
The 1985 discovery of the ozone hole was such a
shock that it triggered incredibly rapid
international reaction.
The actual story is a bit more complicated. See
here and here for starters.
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In 1987 the Montreal Protocol required CFC
production to be cut by 50 by 1998.
As the evidence for ozone depletion mounted, so
did the response in 1990 the London Amendment to
the Montreal Protocol required CFC production to
cease by 2000.
The 1992 Copenhagen amendment required CFC
production to cease by 1996.
I think it is safe to say that most of those who
have been following the ozone situation believe
the ozone layer will recover if the nations of
the world abide by these protocols.
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A look ahead Global Warming.
Define Global Warming.
What will be necessary to convince you that
global warming is happening?
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Click here for a link to the full-sized picture.
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(No Transcript)
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It is easy to find skeptics who believe there is
no ozone hole, or that there is no reason to be
alarmed by ozone depletion.
I suggest that it is healthy to practice
skepticism.
I suggest that it is unhealthy to practice
skepticism in the face of data to the contrary.
Some ozone depletion myths
See the link for details.
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Volcanoes and sunspots are the cause of ozone
depletion.
The claim is not supported by data!
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CFCs are heavier than air, and cant reach the
stratosphere.
The claim might be valid if there were no motion
in the atmosphere (which is untrue), and is not
supported by data!
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Ozone depletion occurs only over Antarctica.
False. Period.
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There is no link between ozone depletion and
higher uv levels.
False!
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There is a massive amount of data showing ozone
depletion.
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The British Antarctic Survey is an excellent
source of data.
You can also read NASAs Ozone Watch.
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One more subject before I go back to Energy.
Why is the ozone hole over Antarctica? What
about the Arctic?
The chemistry of polar atmospheric clouds is
complex and still not fully understood. However,
enough is known to understand the mechanism for
ozone depletion.
Polar stratospheric clouds are not like the
tropospheric clouds that we all know.
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The unique geography of Antarctica results in the
formation of a polar vortex. During the
Antarctic winter, the cold air circulates like a
giant bathtub vortex.
Polar stratospheric clouds do not form by
uplifting of warm, moist air. Rather, they form
slowly, during the long polar winters, and
require long periods of isolation of their air
masses before temperatures become low enough for
them to form.
Here is a movie. Here is an external link (if you
are viewing this lecture from a computer other
than mine).
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Although much remains to be learned, it is
evident that large quantities of the ClOOCl dimer
(notice it is made of two molecules of ClO) build
up during the Antarctic winter.
When spring returns and sun shines on the
Antarctic, the ClOOCl is rapidly converted into
chlorine ions
ClOOCl UV ? Cl- ClO2 ClO2 ? Cl- O2.
These reactions rapidly produce huge
concentrations of Cl-, which triggers massive
destruction of ozone.
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As spring proceeds and the polar vortex breaks
down, the stratospheric clouds vaporize, and the
ozone-destroying reactions slow down.
The ozone hole dissipates as ozone-containing
air from the warmer latitudes mixes with the
polar air.
Because this mixing dilutes ozone concentrations
from the rest of the atmosphere, and carries
ozone-destroying chlorine away from the polar
regions to the rest of the atmosphere, the
antarctic ozone hole can effect the atmosphere
elsewhere.
You can find hundreds of images illustrating the
Antarctic ozone hole. (Birth and death of the
1997 Ozone Hole.)
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We got a wake-up call when an Arctic hole
appeared.
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More animations.
Arctic, 2000.
Antarctic, 2003.
(External link.)
(External link.)
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Final thoughts
Where are we now?
The years Antarctic hole recently closed. This
years Arctic hole is likely growing.
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Wild Cards for the future?
Global Warming?
Ozone depletion and global warming are two
different issues, except
The same greenhouse gases that may (or may not)
cause global warming may (or may not) have caused
a measurable decrease in stratospheric
temperatures.
Decreasing stratospheric temperatures enhances
the formation of stratospheric clouds, and leads
to increased ozone depletion.
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Why all this time spent on Ozone depletion?
The Process is interesting.
The Process is important.
Human choices will determine who lives, and under
what conditions.
We were lucky this time. Will we be lucky next
time?