Stratospheric Ozone Depletion

Taylor Westphal

What is Ozone? What is a DU?

• Ozone is O3, created by disassociation of O2 by UV light, one molecule of which joins a nearby O2 molecule to form ozone.

• From NASA’s ozonewatch: “One Dobson Unit is the number of molecules of ozone that would be required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and a pressure of 1 atmosphere”.

Chlorofluorocarbons (CFC)

Used for many refrigerants, aerosols, and solvents. Chlorine from CFCs is not soluble like Cl from natural sources, and is able to get into the stratosphere. The Cl reacts with O3

and during which reaction, the ozone is destroyed and the Cl is freed to react with more ozone. A single Cl molecule can reside in the stratosphere for decades and destroy as many as 100,000 ozone molecules

Ozone “Hole”• Formed seasonally during the southern

hemisphere winter due to Polar Stratospheric Clouds (PSCs), which are complex, and have to do with the extreme air temperature and circulation.

• These unusual clouds (sometimes water, sometimes acids) provide a surface for CFCs to react with ozone, speeding the reaction and significantly reducing the amount of ozone in the atmospheric column.

The Ozone Hole: Winter vs. Summer

Montreal Protocol• Passed in 1987.• Similar agreements were attempted starting in

the 70’s.• If followed, ozone layer could potentially recover

by 2050.• Sometimes cited as the most successful

international agreement ever, being ratified by 196 states.

• No trouble from chemical industry, CFC patents had expired anyway, good chance to find a profitable replacement.

Who cares, right?

Some Potential Effects• Skin cancer.• Damages to various aspects of plant health.• Damages to Phytoplankton health. Being the

foundation of the ocean food chain: damage to the ocean ecosystem.

• Direct damage to reproductive development of various fish, crustaceans, amphibians, etc.

• Colorful shirts will fade faster.

Anecdote.

Protect Yourself from UV

References:Wikipedia:http://en.wikipedia.org/wiki/Ozone_depletion

EPA:http://www.epa.gov/ozone/strathome.html

NASA:http://ozonewatch.gsfc.nasa.gov/facts/ozone.html