What causes depletion of the ozone layer?

Answer 1

Increases in the substances that decrease the amount of ozone present.

Free radicals, CFCs, chlorofluorocarbons (in aerosols and such).

ozone depletion occurs when the natural balance between the production and destruction of stratospheric ozone tipped in favor of destruction.

Ozone depletion is caused by the Ozone Depleting Substances(ODS) which are man-made chemicals and stay in the stratosphere causing the rate of depletion of ozone greater than its rate of formation.

CFCs

The release of CFCs into the atmosphere causes the ozone atoms to break down when warmed. Notably, the layer is depleted dramatically when the sun fails to rise over the polar regions, causing the hole in the ozone layer.

The most common factor is a lack of sunlight, although the greatest single event to cause ozone depletion has been noted as a solar mass ejection. These flares tear through the ozone layer and can take years to correct.

You can read the scientific description, below.

The main causes of ozone layer depletion are:

water vapor (Nature and Man),CFC's (ChloroFluoroCarbons, Man),halons (Man),carbon tetrachloride and methylchloroform (found so far in increasing amounts at lower altitudes, Nature and Man), andbromine oxide (volcanos), and bromine from manmade sources.

Manmade chemicals like chlorofluorocarbons, bromofluorocarbons and water vapor the major depleters of the ozone layer. There is evidence that natural sources of bromides and chlorides from ocean spray and volcanos can contribute to the depletion of the ozone as well as the Chloro- and Bromo- fluorocarbons. It is thought that these levels have been constant from the ocean and the "normal" ozone levels are in balance with this natural depletion. The simplified reactions are:

CFCl3 + hν -> CFCl2 + Cl

Cl + O3 -> ClO + O2

ClO + O3 + hv(?) -> Cl + 2 O2

In words: Chlorofluorocarbons undergo dissociation in the presence of sunlight to produce a chlorine ion molecule. This molecule combines with ozone to reduce it to oxygen and a ClO molecule.The ClO attacks another Ozone molecule producing atomic oxygen and a chloride ion. The recreation of the Cl ion and the reactive ClO lets the chlorine reform and participate through many cycles.

The role of water vapor is that it blocks one path of ozone formation (temporary storage of an oxygen atom on an N2 molecule, N2O*, becoming stable N2O which is mistakenly presented as an ozone depleter but is a water scavenger) and increases ozone decay (via production of hydrogen peroxide, H2O2). Noctilucent clouds show that water vapor has been increasing near the ozone layer over the last 100+ years.

Only ozone (not oxygen) in our current atmopshere can absorb UV-B radiation which is very very harmful for all the living organisms when it is at elevated levels. Potential impacts are death to algae and phytoplankton... all surface life in eventually, diseases and cancer.

The fluorine in some of these compounds does not contribute to the destruction of ozone. Ozone cannot displace fluorine from whatever molecule it is joined to.

The largest player of both Man's and Nature's depletion of ozone is water vapor.

The largest player of solely Man's efforts to the depletion of ozone is the CFCs used late in the 20th century, and still being made in the third world. These compounds are so stable, they are only removed from the air in the "ozone layer".

The concentration of ozone at any point in the atmosphere, is the result of a balance between reactions that make ozone, the natural decay of ozone, and destruction of ozone by other compounds.

With the Montreal protocol to ban ODS (ozone depleting substances) releases the present atmospheric load of brominated and chlorinated substances should decrease in time.

Global warming and ozone depletion are not the same problem.

Aside: In preparing for nuclear war the USA removed all Freon cooling systems from its atomic bomb carrying ICBMs so the the ozone layer would not be affected during a missile strike.

The amount of ozone at any point is a balance of those three processes. Production / decay / consumption.

"ozone depleting substances" is more generic, since other chlorine- and bromine-containing molecules, which are produced by Man, have been found "up there" too.

Note that CFCs are not "produced by aerosols", but were intentionally manufactured for the purposes of refrigerant or aerosol propellant. Not too many countries are still making / using CFCs.

The amount of ozone in the atmosphere in any given volume is the summation of: (+) photoproduction of oxygen into ozone.(+) photoactivation and decay of N2O* into N2 and ozone.(-) destruction of ozone with time.(-) increase in rate of destruction by increasing temperature.(-) destruction of ozone by water vapor.(-) destruction of ozone by other compounds / catalysts.(+/-) diffusion of ozone into or out of the volume being considered.

So thinning results from a reduction in 1 and/or 2, an increase in any of 3 thru 6, or 7 ozone bleeding out into other spaces (seen adjacent to the ozone hole).

Below is a link that talks about CFC chemistry, about halfway down the page.

The largest known thinning of ozone occurred in September of 1859 due to solar activity. Lack of sunlight is the known primary cause of the thinning area above each pole. No thinning has occurred over equatorial areas.

Answer 2

more and more pollution from burning fuel and fire and smoke

Answer 3

A lack of sunlight hitting the upper atmosphere during the winter months in the Antarctic has been the know cause of the "hole" in the ozone layer that has occurred for centuries.