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Sea salt seasons chemical brew that destroys Arctic ozone

January 18, 2001-Purdue University WEST LAFAYETTE, Ind. – Sunlight, snow and sea salt are sometimes used to illustrate nature at its best. But new scientific evidence shows that, when combined, these forces provide a potent mixture for destroying ozone.

Purdue University researchers, working with scientists from Battelle and the University of California, Irvine, discovered that bromine and chlorine, two chemicals found in sea salt, may initiate a series of chemical events that destroy ozone in the Arctic troposphere, the lowest part of the atmosphere.

The findings, published in the Jan. 19 issue of the scientific journal Science, describe the role that bromine and chlorine play in a complex series of chemical reactions that occur each spring when, after several months of darkness, sunlight interacts with the snow in the Arctic region.

The study traces the source of those chemical precursors to the salty minerals found in sea water that is carried into the snow-pack in the form of tiny salt particles by wind and waves.

"Bromine and chlorine have long been suspected as major players in this series of chemical events, but until now the source of these chemicals was unknown," says Paul Shepson, professor of atmospheric chemistry at Purdue. "Our findings indicate that this near-surface ozone depletion in the Arctic is a naturally occurring event."

Ozone, a beneficial component of the earth's upper atmosphere, is a pollutant at the ground level but is essential to the health of the atmosphere, Shepson says.

The findings may help scientists develop better models to simulate and predict longterm changes in the composition of the earth's atmosphere, he says. "Because three-quarters of the earth's surface is covered by ocean, we've uncovered a process we need to understand much better in terms of our ability to model ozone in the atmosphere."

All that is true, as well as Mt. Erebus as a source of the Cl and Br.

But, also remember that diatomic oxygen absorbs the highest-energy ultraviolet radiation from the sun, namely, all radiation with wavelengths shorter than 240 nm. However, there is a great deal of ultraviolet radiation between 240 nm and 290 nm that is not absorbed by O2 molecules. This radiation is absorbed by ozone.

The ozone in the stratosphere is produced by photochemical reactions involving O2. When diatomic oxygen in the stratosphere absorbs ultraviolet radiation with wavelengths less than 240 nm, it breaks apart into two monotonic oxygen atoms.

The resulting oxygen atoms combine with O2 molecules to form ozone.

O(g) + O2(g)=>>O3(g)

This reaction is exothermic, and the net effect of the previous two reactions is the conversion of three molecules of O2 to two molecules of ozone with the simultaneous conversion of light energy to heat. Ozone absorbs ultraviolet radiation with wavelengths as long as 290 nm. This radiation causes the ozone to decompose into O2 molecules and oxygen atoms.

This, too, is an exothermic reaction. The overall effect of this reaction and the previous reaction is the conversion of light energy into heat. Thus, ozone in the stratosphere prevents highly energetic radiation from reaching the Earth's surface and converts the energy of this radiation to heat, and as long as there is oxygen(O2) and sunlight you will have ozone(O3) in short order.

The Freon ban used ozone destruction as a scaretactic. It wasn't about ozone as much as it's about greenpeace's war on chlorine, technology, and man.