Quick Dips

Ozone Chemistry

The DSIR Physical Sciences laboratory at Lauder, Central Otago, has been recognised as the southern hemisphere site in a five-station world network for the detection of stratospheric change. The network will see high-tech monitoring equipment, such as lasers to probe the upper atmosphere, put in place.

"The reason ozone depletion is so pronounced in Antarctica is the fact the chlorine gets stored during the winter-long polar night on stratospheric clouds that form because the temperatures are so low," says DSIR scientist Gordon Keys.

The ozone hole forms over Antarctica in early spring, when the chlorine stored in the clouds is converted to a reactive form by the arrival of the sun. The process involves a series of unusual chemical reactions taking place at temperatures as low as -85^oC. Normal ozone levels are restored in summer when ozone-rich air from other latitudes mixes with the Antarctic atmosphere.

Large amounts of nitrogen dioxide in the Antarctic stratosphere can cause active chlorine to be neutralised, preventing formation of the ozone hole.

"That is why we are interested in the oxides of nitrogen," says Keys. These gases are being monitored on Ross Island, using ground-based optical remote sensors. Preliminary results have shown a surprisingly high rate of nitric acid formation during autumn, and Keys speculates that this is involved with the unusual chemistry at work.

Yvonne Martin, Scott Base