Ozone Recovery

Ozone Comeback

We've been hearing for years about mankind's detrimental effects on the Earth's atmosphere, notably the depletion of the Ozone Layer and formation of an unprotected "hole" allowing higher-than-normal levels of radiation through. Earlier this week, however, I heard some good news: the Ozone Layer is showing signs of recovery!  Good news in the environmental field is a rarity, especially for something so globally influential, so this is very exciting indeed!

How does this Ozone stuff work?

Notice the resonance structure!

Ozone is a molecule with three oxygen atoms, or O3, that makes up about .1 parts per million of the Earth's atmosphere at any given time.  In the specific band, shown above, known as the Stratospheric Ozone Layer, the concentration can get up to 10 parts per million.  Ozone is formed by the collision of a free oxygen atoms with its diatomic form, O2.  The energy absorbed from UV radiation breaks this bond and releases the free oxygen once again to repeat the process.  In this way, UV energy is absorbed before entering the lower atmosphere.  This UV energy would otherwise be extremely damaging to our plants and animals. The extra oxygen atom makes the molecule very unstable, accounting for its low abundance, and it fairly readily dissociates into O2 and O so it is naturally kept at that certain concentration. Lately, however, humans have thrown off the balance in a very bad way.

Some History

Significant drops in Ozone levels were first detected in the 1970's.  The Ozone depletion has been associated with a rise in certain radiation-related health issues, such as skin cancer and cataracts.  In 1995, the Nobel Prize in Chemistry went to scientists who realized that CFCs (chlorofluorocarbons) were the main perpetrators.  These CFCs (such as CFCl3 or CF2Cl2) were widely used in insulators and coolants in refrigeration and air conditioning units.  When released into the atmosphere, energy from the UV radiation broke the bonds to free one of the chlorines, which then associated with one of the oxygen atoms in ozone to form ClO and O2.  A free oxygen can then collide with the ClO molecule to free the Cl again and form another O2, allowing the halide to continue this process, devastating the ozone concentrations.  Once word got out, CFC use was drastically reduced and controlled, with permits now being required to handle them.

The Ozone "Hole"

The effect of CFCs, as well as some other chemicals in the atmosphere, have led to a severe depletion of historic ozone levels.  However, the idea that there is a giant hole in the atmosphere sitting over Antarctica is a little misleading. The truth is a bit more complicated.  There is a "hole" over Antarctica, but it isn't always there and it isn't what it sounds like. 

Not exactly....

Winters in Antarctica are long, dark, and very, very cold.  This lack of direct energy allows a polarization in the stratospheric clouds, which is not favorable to the polar O3 molecules.  When the sunlight returns, the energy jump-starts the ozone destruction reaction and drastically lowers the concentration of ozone in that area for a few months between August and November (we're talking a 10million square mile "hole" here).  This does, however, let in a lot more radiation than is normal and that causes the problems we have already discussed.  The hole was first noticed in a 1985 British survey and raised the alarm about ozone depletion.  Once CFCs were identified as a problem compound, a coalition was formed to phase it out before it was too late. 

On our way to recovery...

The good news is: we're not doomed!  We've been almost 20 years without profuse amounts of CFCs and the intensive cooperation, through the Montreal Protocol, between a number of countries together has been slowing the growth of the "hole" and finally stopping it.  Recently, after an assessment by a group of scientists under the United Nations Environment Programme and the World Meteorological Organization, we finally saw a decrease in size of the Ozone "hole" (shown below).

 

As you can see, this is by no means solved.  The "hole" is still bigger than the continent of Antarctica itself, for goodness sake.  But it does mean that our efforts are helping and that, over the next few decades, we should continue to see improvement.  This has large, world-wide implications when you consider the effects of climate change; we definitely don't need anything else going on to throw off global temperatures.  An unfortunate side note: the chemicals that have been developed to replace the use of CFCs are still pumped into the atmosphere and are exceedingly effective greenhouse compounds.  Another note: ozone is starting to build up in the lower Troposphere and causing lung damage and other health problems in some areas..You can just never win.

Citations:

United Nations Environment Programme. (2014, September 10). Earth's ozone layer on track to recovery, scientists report. ScienceDaily. Retrieved September 16, 2014 from www.sciencedaily.com/releases/2014/09/140910162324.htm

Earth System Research Laboratory. Disappearing ozone. National Oceanic and Atmospheric Association. Retrieved September 16, 2014 from http://www.esrl.noaa.gov/gsd/outreach/education/samii/SAMII_Activity3.html

Science on the Edge: Arctic and Antarctic Discoveries. Ozone hole over Antarctica. National Science Foundation. Retrieved September 16, 2014 from http://www.nsf.gov/about/history/nsf0050/arctic/ozonehole.htm

(Photo Only) : http://www.ozone-services.com/what-is-ozone/