The Hole in the Ozone Layer
Threads:
The Hole in the Ozone Layer, Ozone Hole(2002), Ozone Hole(2006)
Sam Lentini, on 26/8/2002 wrote:
I am a student and I have a question
about the ozone layer. I hope you can help me. Why is the hole in the
ozone layer in Antarctica, it practically has no people to create
pollution?
Podargus replied:
The
quick answer is that warm air (including the pollutants) rises over the
tropics and then moves polarwards.
The Arctic also
has a thinning, but Antarctica is an isolated continent and is
meteorologically isolated.
During the
winter there are very low temperatures in the stratosphere that lead to
stratospheric clouds, these clouds provide conditions that promote
chemicals that can destroy ozone. The destruction occurs when the
sun returns.
In the Arctic
similar conditions can exist but are more likely to be disturbed
because it is not isolated (weatherwise) as is Antarctica.
John Winckle added
Not only no population but 95% of all
the aerosols supposedly causing the ozone depletion are released in the
Northern hemisphere. Yet there is no hole in the arctic
Can anyone comment here?
Peter Macinnis
replied:
The
Arctic "hole" is always smaller, but it is there, nonetheless.
Arctic ozone
depletion, to give the ''hole'' its correct name, has always been less
than ozone depletion in the Antarctic, but a report in the Journal of
Geophysical Research in January 1999 said ozone losses reached record
high levels during the northern winters of 1995-96 and 1996-97. The
second winter also featured a very long-lived Arctic polar
stratospheric vortex. This is a low pressure system occurring between
14 and 35 kilometres (9-22 miles) above the Earth. The vortex forms
during the polar winter, when the lack of sunlight lowers the
temperature and produces a circular wind system. The vortex is almost
certainly a key step in setting up the chemical conditions which lead to
ozone loss.
Typically, the
Antarctic is colder than the Arctic, so the stratospheric clouds which
initiate ozone loss, are more common there. The vortex in 1996-7
produced low temperatures and ozone losses at levels similar to those
of the Antarctic in the early 1980s. Up to half the ozone was lost,
compared with long term averages. The vortex lasted into May, keeping
the ozone hole going until then, and raising ground-level ultraviolet
radiation in northern Europe.
Two chemical
processes were involved. The better-known chlorine activation (mainly
from CFCs) in the polar stratospheric clouds in winter was replaced by
other reactions powered by nitric oxide (NO) and nitrogen dioxide
(NO2), thanks to the persistent vortex.
The researchers
say that the long-lasting winter vortices may persist, if they are
caused by changing climatic conditions. This would lead to ever greater
low-ozone air masses, driven by early spring halogen chemistry or by
summertime nitrogen oxide (NOx) chemistry, leading to significant
effects in the northern hemisphere.
The note of
alarm being sounded by these better-informed authors contrasts
interestingly with the complacent attitudes I encountered at a
conference in Edinburgh in 1993, when the ozone hole was dismissed by a
geologist as something that need only worry a few penguins in
Antarctica.
This
information is largely drawn from a reputable Australian online
encyclopedia, where it was published first in January 1999.
On the
29/9/2003, Helen Murley wrote:
<snip>
A few years ago,
as an extremely mature age Law student, I had to write an 8,000 word
essay on Environmental Law. I opted for the Ozone layer.
Didn't understand half of what I read, remember even less.
Ok. I now a bit about Rio, Montreal Protocol(?) and Kyoto -
including which countries are dragging their heels in signing,
ratifying, etc. No prizesfor guessing which countries.
I roughly know
causes for ozone - CFCs, flatuent cows, gas emissions, etc.
What I don't
know, is why the size of the hole keeps varying, why it split, and if
it moves location.
Ray
replied:
CFCs
are the primary cause of the hole in the ozone layer, due I believe, to
the chemical reactivity of chlorine and fluorine dissociated ions with
the covalent resonance of O3
(ozone) gas, and producing ordinary oxygen gas, chlorate and
fluorites. Old fridges and hair spray scenario....
Something
like that.
Why
the hole moves, expands and shrinks I have no idea (with you waiting
for answers and a better explanation than mine), but it is likely that
the intense ionisation at the magnetic poles produces a natural hole in
the ozone layer which human activity has increased unnaturally.
I
can say that bovine and domestic flatulence is part of the global
warming scenario and not part of ozone depletion. At least, not
directly. Methane and CO2, are greenhouse gases.
Sandie Stockwell
commented:
I thought
the carbon-fluorine bond strength was too great to be broken by UV
light, which is what happens with the carbon-chlorine bond.
Fluorine
compounds tend to be particularly stable which is part of the reason
why 3M withdrew their waterproofing spray products (name escapes me).
They, 3M, tried to get baseline levels in blood of these fluorocarbons
but found that they occurred even in blood kept for over forty years.
The compounds hadn't broken down and there seemed to be no
physiological effects but 3M decided to be safe rather than sorry.
Sandie answered:
the
UV breaks the bond, producing free radicals (any species with unpaired
bonding electrons)
CCl3F +UV --> oCCl2F + oCl
where o = unpaired electron
and CCl2F2 + UV --> oCClF2 + oCl
oCl + O3 -->oClO + O2
oCLO + oO --> oCl + O2
it is the
chlorine free radical (in this case an atom of chlorine) that does the
damage and because it is regenerated in the reaction with ozone one
chlorine atom may destroy thousands of ozone molecules
http://www.cci.net.au/ConqChem/HSCmod3frameset.htm
and look at
ozone destruction
and to be
totally pedantic (have to be, I'd never let my students get away with
it) ions have a charge, most free radicals don't.
David Maddern
added:
snip'd from below
<What
I don't know, is why the size of the hole keeps varying, why it split,
and if it moves location.
end
spin'n
Look
at the weather, it varies a lot.
The
ozone hole is high up and the area is centred over the pole in the warm
months and shrinks markedly in winter. The 'hole' is an area of thin
ozone = O3
The
rest of the atmosphere around there circulates around the pole and
expands and contracts and is just as chaotic as our weather here.
So
the whole thing is a dynamic moving system and that is why it changes
shape, splits and so on.
Hope
that helps
Podargus
commented:
Snip>
>
I roughly know causes for ozone - CFCs, flatuent cows, gas emissions,
etc.
> What I don't know, is why the size of the hole keeps varying, why
it
split, and if it moves location.
Because of
weather patterns the ozone depleting gases tend to end up over both the
Arctic and Antarctic in the upper atmosphere. In the northern
hemisphere this 'hole' is not so stable as the weather patterns tend to
include the Arctic. Antarctica on the other hand is to a certain
extent weather self contained largely because of the west wind that
circles the continent.
The URLs below
will give a fuller, and therefore better understanding.
http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/ozone_hole.html
http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/ATM_CHEM/ozone_atmosphere.html
Peter
Macinnis responded:
<snip>
>So the whole
thing is a dynamic moving system and that is why it changes
>shape, splits and
so on.
While
that is an element of the generation of the hole, I don't think that
is
the whole story -- there are chemical changes, (possibly driven by sunlight?)
that mean there is a large area over Antarctica, sometimes beyond,
with virtually no ozone in summer, the so-called "hole". I am no expert,
but I am certain that part of the problem in summer is beause there IS
a hole that grows in size -- THEN the chaotic bit cuts in as David described,
so the hole can pass over us in bad years.
To
confuse matters, some gases are involved in both greenhouse effects and ozone
depletion. For example, nitrous oxide N2O (levels of which vary with global
warming) interacts with the ozone. The N2O mostly comes from bacteria,
according to a paper I skimmed from Nature the other day -- I can say
more on that tomorrow.
So
my question is: given the absolute fact (I believe it to be such) that there
is less ozone over the south pole in our summer, and that this is the "ozone
hole" in question, what drives the removal/destruction of the ozone?
Toby Fiander
replied:
> So my question
is: given the absolute fact (I believe it to be such) that
> there is
less ozone over the south pole in our summer, and that this is the
> "ozone
hole" in question, what drives the removal/destruction of the ozone?
As I understand
it, the ozone hole grows at the end of winter as ultra-violet
radiation activates the ozone depletion process. The polar vortex previously
mentioned contains the area affected, until the polar
vortex is
affected by the increasing radiation.
As the vortex
breaks down, typically in November, ozone depleted air passes of over parts of the
southern land masses, notably Tasmania. Diffusion lessens the problem
of reduced protection from radiation, but there is still
an increased
risk of sunburn and worse in most years, if the stratospheric conditions push the
hole over land. I was tempted to use the word, "weather" for these
conditions, but in the stratosphere, I don't think this is strictly accurate
- others may have a view.
For some time,
Tasmanian schools (well, those of which I know) have been telling children they
should stay indoors in late spring and early summer and to wear a hat
when outdoors in daylight throughout the year, which seems pretty extreme for
Tasmania, until you realise the effect of the ozone hole as it breaks up.
The level of UV
radiation reaching the surface of the earth is affected by a range of
factors. There is a UV forecasting service:
http://www.bom.gov.au/weather/national/charts/UV.shtml
The Bureau also
has some education activity sites about UV, the ozone hole and a (w)hole lot
more.... I have not been following this thread closely due to the pressure of
work. Perhaps this was mentioned earlier.
Jann
O'connor added:
<snip>
> For some
time, Tasmanian schools (well, those of which I know) have been
> telling
children they should stay indoors in late spring and early summer
> and to wear
a hat when outdoors in daylight throughout the year, which seems
> pretty
extreme for Tasmania, until you realise the effect of the ozone hole
> as it
breaks up.
A
few months ago there was discussion that Tas kids should not wear their hats
outdoors all the time as they are becoming deficient in Vitamin D
http://aca.ninemsn.com.au/stories/1453.asp
The
relevent section on Tassie children (Burnie - where Toby's kids did most
of their growing up) appears below my signature.
Nick
commented:
While discussing
the Ozone Hole, there was a report in today's Courier Mail (titled
ozone hole nearly at record size) claimed that "the ozone hole over
Antartica is at near record size this spring" and that the ozone
hole is currently 27 million sq km (4 times the size of Aust).
Steve
added:
I
have never been able to find out why "domestic flatulence" should be so
much worse for the environment than the flatulence of the millions of natural
occurring animals. See the massive herds of buffalos or antelopes
or any other animals occupying the prairies and savannas. I
know that cows are much more economical in digesting grass than a lot of
other animals, but is the difference that great? And do the numbers stack
up?
Kevin Phyland
responded:
Been chewing
this topic over for a while now (cud that I am...)
Coupla things
occur to me and I'll need any of the following *postulates* put to bed
before any conclusions can be reached...
[1]
The height of the troposphere is wayyyy lower at the poles than at the
equator (I'd be guessing maybe 60% lower?)
[2] This is because it gets quite cold (even in the stratosphere) at
the poles.
[3] Not much in the way of CFCs gets emitted in either of the polar
regions.
[4] The ocean temperatures lag by about 2 to 3 months from the ambient
air temperatures.
So...I
*postulate* that the reason that the ozone hole(s) (thinning really)
occur at the poles is that the Universes's
weakest (but
most all pervasive) force may be at work. Picture the globe, not
as it is as a solid but including a very thin layer of atmosphere
(which is wayyy more fluid btw) which is *lower* at the poles...
Might not
gravity start to drive the heavier gases slowly towards the poles for a
start, (as well as the obvious
polarward
movement just due to differential heating) then the polar vortex gets
it entangled (to use a quantum and rather raunchy word) and
tightens its grip on said gases?
Then perhaps the
onset of sunlight in early spring causes the breakdown of 0-3 into 0-2?
The lag of ocean
temperatures is reflected in upper-tropospheric /lower-stratospheric
temperatures hence the *late* appearance of the ozone thinning (as
opposed to mid-winter) perhaps?
I'm doing this
from first principles...upper atmospheric physics is not my forte (if
anything is)...
Any thoughts?
Podargus
answered:
>
I have never been able to find out why "domestic flatulence" should be
> so much worse for the environment than the flatulence of the
millions of
> natural occurring animals. See the massive herds of buffalos or
> antelopes or any other animals occupying the prairies and savannas.
> I know that cows are much more economical in digesting grass than
a lot
> of other animals, but is the difference that great? And do the
numbers
> stack up?
This
has nothing to do with the ozone hole.
The
methane in the flatulence you refer to is of course the same in any
animal. Because ruminants carry around a methane digester as part
of their equipment they tend to produce more of it. A lot
more. There are now more domestic ruminants around than there
were wild ruminates in the past, even in USA. For instance it is
estimated that there were around 30,000,000 bison in North
America and sundry other ruminates. Somewhere I have the figures
for USA cattle, IIRC over 100,000,000. Then there is Canada,
Mexico and the South American countries. Plus a few sheep.
Australia and New Zealand
did not of course have any sheep or cattle.
Paul Williams
responded:
I have appended
below some weather bureau figures (for today) regarding the UV index
for Tasmania and Queensland (in part)
My understanding
is that figures will show less discrepancy (Qld -Tas) in Summer - I'm
unsure of this though. Certainly, - cover-up in Queensland
- pretty well all year. Taswegians: For most of the year, it seems,
must judge for themselves. -
I would hazard
that if one can stand the cold, running around naked would be a fine
and healthful thing to do at this time of year.
I would like to
see how much the (north to south) summer UV index figures converge?
Cheers
Paul
TASMANIA
UV Index Forecast
Thursday 25
September 2003
|
Clear/Scattered |
Broken |
Overcast |
| Burnie |
4 |
3 |
2 |
| Devonport |
4 |
3 |
2 |
| Hobart |
4 |
3 |
2 |
| Launceston |
4 |
3 |
2 |
| St Helens |
4 |
3 |
2 |
| Strahan |
4 |
3 |
2 |
| Swansea |
4 |
3 |
2 |
http://www.bom.gov.au/products/IDY05215.shtml
QUEENSLAND
UV Index Forecast
valid Thursday
25 September 2003
|
Clear/Scattered |
Broken
|
Overcast |
| Ayr/Home Hill |
13 |
9 |
5 |
| Biloela |
12 |
8 |
5 |
| Bowen |
13 |
9 |
5 |
| Brisbane |
11 |
8 |
4 |
| Bundaberg |
12 |
8 |
5 |
| Cairns |
14 |
10 |
6 |
http://www.bom.gov.au/products/IDY05213.shtml
Toby
Fiander added:
Perhaps
you like me wondered what the ozone hole was doing. This is about
the time that the ozone hole has started to break up in past years.
Sometimes part of the hole passes over Tasmania and other southern
parts.
Well,
there are other places to get this sort of data but have a look here:
http://www.theozonehole.com/ozonehole2003.htm
You
will need to go well down the page to get current information.
A
couple of interesting things have happened over the season:
- the hole formed more quickly than has been the case,
- technically the area affected has been no larger than last year,
but has had different characteristics,
- a second hole formed off the edge of the Antarctic continent at
one stage but seems to have coalesced with the main hole,
- the hole has extended over the southern part of South America and
the Falkland Islands, where depletion was intense in more than one
event of about a week,
- weather conditions are still suitable for further hole formation,
so it is not yet breaking up, although the peak of the area
affected has passed probably.
It
is not yet clear what this means for the future, but a large ozone hole
is not a great idea. The significance of the formation of a
second intense area of depletion off the coast of Antarctica will
require further analysis.
On 16/9/2006, Toby Fiander posted:
Here is a useful graph thingo, showing the diameter of the ozone hole. This
year is less, though not so different from previous years. Optimism may
have been premature.
http://www.theozonehole.com/ozonehole2006.htm
Gerald Cairns replied:
I
don't have time to dabble right now but the Dobson unit used to
describe the ozone hole is stated as the compressed value I presume at
sea level in terms of thickness. If the ozone hole which is in reality
a low density zone not a hole were compressed it should be compressed
in all directions not simply thickness. Anyone know the derivation of
the Dobson Unit.
Ray Stephens commented:
Since 1996 it doesn't appear that the deviation has been significant enough
to quantify with any certainty anyway.
O3 breakdown is essentially halide caused isn't it? (something to do with
there strong -ve charge as free ions.)
We chlorinate our water as a matter of SOP, and I believe that chlorine
continually passes from solution in water to the atmosphere as a matter of
equilibrium, and if so, would this be a part of the equation?
In any case, there is still a huge number of old refrigerators and enough
freon afloat to still be significant for a while yet.
Toby Fiander added:
There is section at the same website on Dobson and his unit:
http://www.theozonehole.com/dobsonunit.htm
Dobson Units imply a thickness of ozone, but also a concentration, and,
either way, a DU value is a comparison with standard conditions, typically
about 500DU (the site says 300-500 - I suppose that must be right). The
Ozone Hole has a minimum value of about 100DU, which means that you need to
take precautions against sunburn and eye damage. At its worst, the Ozone
Hole was reaching out to the tip of South American and was in danger of
taking in part of Tasmania. This year's hole is less severe, but when it
breaks up probably in late October, the remains could still pass of southern
Australia and, on those days, it would be best not to have your people
working outdoors... which is, in part, my interest.
and:
There is section at the same website on Dobson and his unit:
http://www.theozonehole.com/dobsonunit.htm
Dobson Units imply a thickness of ozone, but also a concentration, and,
either way, a DU value is a comparison with standard conditions, typically
about 500DU (the site says 300-500 - I suppose that must be right). The
Ozone Hole has a minimum value of about 100DU, which means that you need to
take precautions against sunburn and eye damage. At its worst, the Ozone
Hole was reaching out to the tip of South American and was in danger of
taking in part of Tasmania. This year's hole is less severe, but when it
breaks up probably in late October, the remains could still pass of southern
Australia and, on those days, it would be best not to have your people
working outdoors... which is, in part, my interest.
Anthony Morton replied to Ray:
O3 breakdown is essentially halide caused isn't it? (something to do
with there strong -ve charge as free ions.)
We chlorinate our water as a matter of SOP, and I believe that
chlorine continually passes from solution in water to the atmosphere
as a matter of equilibrium, and if so, would this be a part of the
equation?
The reason the problem is with CFCs rather than ground-level halides
is, paradoxically, because CFCs are so chemically inert. Most halides
break down before they can reach the upper levels of the atmosphere,
but CFCs persist to these levels and only there do they encounter the
ionising radiation that knocks the halogen atoms off to wreak havoc
with atmospheric ozone.
Toby Fiander responded:
Ray said:
We chlorinate our water as a matter of SOP, and I believe that chlorine
continually passes from solution in water to the atmosphere as a matter of
equilibrium, and if so, would this be a part of the equation?
That is a good point... here is my understanding, someone else can provide
their greater understanding where mine is deficient.
Chlorine emitted at ground level generally attaches itself to non-volatile
compounds and does not get to the stratosphere where ozone can be damaged.
But ozone depleting chemicals come in several forms, and work by releasing
halide ions into the stratosphere where it can work to destroy ozone.
There are a bunch of things that have been released into the atmosphere over
the last century and are still working their way to the stratosphere where
sunlight will destroy their structure releasing the halide ions.
There is an explanation here, and long lists of ozone depleting substances:
http://www.theozonehole.com/odcs.htm
In any case, there is still a huge number of old refrigerators and enough
freon afloat to still be significant for a while yet.
The manufacture of new fridges in places whose trade we value, but who have
no real environmental conscience is still a problem, apparently.
Kevin Phyland noted:
afaik...ozone at the surface is considered a pollutant...at altitude a godsend...
also...the ozone *hole*
is not really a hole anyway...more a thinning...which is not to detract
from its importance...and i also believe it is a biennial
effect...fwiw...
