The Hole in the Ozone

[Pymander]

Ozone is O3, a powerful oxidising agent. What is the cause of northern leaching. Why the southern hole, when over two thirds of humanity is in the northern hemisphere? It has been blamed on halogenated carbon compounds like freon, a refrigerant, which now attracts a tax like carbon tax for CO2 emissions. Yet carbon tetrachloride, once used extensively as a dry cleaning fluid, was also used in fire extinguishers, being non-combustible, and creating a heavy vapour to smother fires. That was until it became known that, with alcohol in the system, breathing the vapour caused instant fatal renal failure. These substances do not occur naturally, to my knowledge. Why are they blamed?

[D H]

Ozone is O3, a powerful oxidising agent. What is the cause of northern leaching. Why the southern hole, when over two thirds of humanity is in the northern hemisphere? It has been blamed on halogenated carbon compounds like freon, a refrigerant, which now attracts a tax like carbon tax for CO2 emissions. Yet carbon tetrachloride, once used extensively as a dry cleaning fluid, was also used in fire extinguishers, being non-combustible, and creating a heavy vapour to smother fires. That was until it became known that, with alcohol in the system, breathing the vapour caused instant fatal renal failure. These substances do not occur naturally, to my knowledge. Why are they blamed?

Chlorofluorocarbons are blamed for the creation of the ozone holes because they are the key culprit. That they do not occur naturally means we are the cause.

 

Ozone chemistry 101:

The ozone-oxygen cycle starts with high energy ultraviolet light splitting an ordinary oxygen molecule into a pair of free oxygen atoms. These free oxygen atoms quickly combine with other ordinary oxygen molecules to form ozone. Ultraviolet light, even low energy UV light, can cause an ozone molecule to split into a free oxygen atom and an ordinary oxygen molecule. The free oxygen atom once again quickly combines with ordinary oxygen to reform an ozone molecule. Ozone can also combine with a free oxygen atom to form two ordinary oxygen molecules. The rates at which these reactions occur drives the balance of ordinary oxygen, ozone, and free oxygen in the ozone layer. The free oxygen + ordinary oxygen reaction is very fast. This means that an ozone molecule will effectively hang around for a long time before recombining with a free oxygen atom to form a pair of O₂ molecules.

 

There are other sinks besides the O₃+O -> 2O₂ path. Ozone is very reactive. It can oxidize just about anything. This means that even under natural conditions, the ozone concentration in summertime will reach a steady state level in which ozone production balances ozone destruction. Now let's turn out the lights (i.e., wintertime). This removes the source of those free oxygen atoms. The ozone concentration will naturally deplete in wintertime.

 

The problem with chlorofluorocarbons is that they greatly enhance the depletion of ozone. Sunlight can split off a free halogen radical from a chlorofluorocarbon molecule. It is that free halogen radical that does the damage. It can react with ozone, stealing a oxygen atom to form a halogen monoxide molecule and an ordinary oxygen molecule. This halogen monoxide molecule in turn reacts with a free oxygen atom to form a halogen radical and an ordinary oxygen molecule. Neither of these reactions requires sunlight. Note that the end result is halogen+O₃+O->halogen+2O₂. The halogen catalyzes the depletion of ozone and free oxygen, and it does it without sunlight. This reduces the peak ozone level in summertime but more importantly exacerbates the wintertime depletion (which peaks in early spring).

 

So why is it worse in the southern hemisphere? The first thing to realize is that while the sources of chlorofluorocarbons are mostly in the northern hemisphere, the atmosphere is fairly well mixed at the top of the troposphere, even more so in the stratosphere. It doesn't matter where the sources are on the ground. Concentrations aren't the answer. The answer lies in the very different winter weather patterns over the Arctic and Antarctic regions. Antarctica is an isolated continent, completely surrounded by ocean. The Arctic is an isolated ocean, mostly surrounded by continents. A long-lived southern polar vortex sets up every winter over Antarctica. Air doesn't flow in, doesn't flow out. This vortex extends up into the stratosphere. The lack of mixing means that even under natural conditions, wintertime ozone depletion over Antarctica is much greater than it is over the Arctic. Add the enhanced depletion caused by chlorofluorocarbons and this natural depletion becomes severe. The northern hemisphere does occasion see ozone holes form because the northern polar vortex does set up every once in a while.

[Pymander]

Chlorofluorocarbons are blamed for the creation of the ozone holes because they are the key culprit. That they do not occur naturally means we are the cause.

 

Ozone chemistry 101:

The ozone-oxygen cycle starts with high energy ultraviolet light splitting an ordinary oxygen molecule into a pair of free oxygen atoms. These free oxygen atoms quickly combine with other ordinary oxygen molecules to form ozone. Ultraviolet light, even low energy UV light, can cause an ozone molecule to split into a free oxygen atom and an ordinary oxygen molecule. The free oxygen atom once again quickly combines with ordinary oxygen to reform an ozone molecule. Ozone can also combine with a free oxygen atom to form two ordinary oxygen molecules. The rates at which these reactions occur drives the balance of ordinary oxygen, ozone, and free oxygen in the ozone layer. The free oxygen + ordinary oxygen reaction is very fast. This means that an ozone molecule will effectively hang around for a long time before recombining with a free oxygen atom to form a pair of O₂ molecules.

 

There are other sinks besides the O₃+O -> 2O₂ path. Ozone is very reactive. It can oxidize just about anything. This means that even under natural conditions, the ozone concentration in summertime will reach a steady state level in which ozone production balances ozone destruction. Now let's turn out the lights (i.e., wintertime). This removes the source of those free oxygen atoms. The ozone concentration will naturally deplete in wintertime.

 

The problem with chlorofluorocarbons is that they greatly enhance the depletion of ozone. Sunlight can split off a free halogen radical from a chlorofluorocarbon molecule. It is that free halogen radical that does the damage. It can react with ozone, stealing a oxygen atom to form a halogen monoxide molecule and an ordinary oxygen molecule. This halogen monoxide molecule in turn reacts with a free oxygen atom to form a halogen radical and an ordinary oxygen molecule. Neither of these reactions requires sunlight. Note that the end result is halogen+O₃+O->halogen+2O₂. The halogen catalyzes the depletion of ozone and free oxygen, and it does it without sunlight. This reduces the peak ozone level in summertime but more importantly exacerbates the wintertime depletion (which peaks in early spring).

 

So why is it worse in the southern hemisphere? The first thing to realize is that while the sources of chlorofluorocarbons are mostly in the northern hemisphere, the atmosphere is fairly well mixed at the top of the troposphere, even more so in the stratosphere. It doesn't matter where the sources are on the ground. Concentrations aren't the answer. The answer lies in the very different winter weather patterns over the Arctic and Antarctic regions. Antarctica is an isolated continent, completely surrounded by ocean. The Arctic is an isolated ocean, mostly surrounded by continents. A long-lived southern polar vortex sets up every winter over Antarctica. Air doesn't flow in, doesn't flow out. This vortex extends up into the stratosphere. The lack of mixing means that even under natural conditions, wintertime ozone depletion over Antarctica is much greater than it is over the Arctic. Add the enhanced depletion caused by chlorofluorocarbons and this natural depletion becomes severe. The northern hemisphere does occasion see ozone holes form because the northern polar vortex does set up every once in a while.

 

Okay. And now that regulation is in place, and CFC's are regulated, are these phenomena becoming less pronounced?

[swansont]

Yes, it appears that the ozone layer is recovering.

 

http://www.scientificamerican.com/article.cfm?id=first-signs-of-ozone-hole-recovery-spotted

http://mb.com.ph/articles/356324/study-ozone-layer-slowly-recovering

[Pymander]

Okay. And now that regulation is in place, and CFC's are regulated, are these phenomena becoming less pronounced?

 

Enlightening. Thanks D H for your thorough reply to my question. It complements the Wiki material well. My speculations were otherwise but I am disallowed to continue with these. Will be studying the psychology and logic of all participants in my discussions. My own psychology seems suspect. Sorry I couldn't answer more directly, but the tree of enquiry mixed with other extraneous input presented too difficult a task to have any hope of success or conclusion, and forced me to remain general in focus. Then, enquiry into our evolution from whatever source must cross all subject boundaries and specialities of science, that none can conquer alone. Thanks also for the links from Swansont. This Forum gives an oportunity for people to express themselves which normal social interactions tend to exclude an obscure.