Ozone in Earth's thin blanket

Sunlight filtered by the atmosphere

Not all of the sunlight from the sun makes it to the surface of Earth.

What's in air?

The Ozone layer

The SHIELD that protects us from ultra-violet (high energy) light from the sun...

90% of Earth's air mass is within 10 km of the surface of Earth.

History of 'Freon'

Around 1900 - Refrigerators use toxic gases as coolants: methyl chloride, ammonia, sulfur dioxide.

Cracked pipes in your refrigerator? $\Rightarrow$ You die.

1928 - GM chemists synthesize a chlorofluorocarbon (CFC), brand-named "Freon" used first in Frigidaire refrigerators: non-toxic, non-corrosive, chemically inert.

Breathe it, and nothing happens to you! [This is CFC-12: dichlorodifluoromethane].

1932 - Carrier uses Freon in its "Atmospheric Cabinet" - world's first self-contained home air-conditioner unit.

1945 - Freon used as the propellant in paints, hair sprays, health care products. Later, foam bubbling agent.

Where do the CFC's go?

1974 - Mario Molina and Sherwood Rowland suggested that CFCs could be broken apart by high energy UV light, freeing chlorine, which can then do this...

$Cl + O_3 \rightarrow ClO + O_2$

A second reaction frees the Cl to destroy anew...

$ClO + ClO + [UVl i g h t] \rightarrow Cl+Cl+O_2$

1978 - Consumer boycott leads to U.S. ban on CFCs in spray propellants.

Measuring ozone

Nowadays, there's a satellite that orbits Earth with the main purpose of measuring ozone. Go to ozonewatch.gsfc.nasa.gov. Watch together with someone else one of the mp4 movies.

• At what time of year is the amount of ozone lowest? (blue is low, purple is lower)
• Where is the ozone the lowest?

Before anyone was worried about ozone... English researchers at the Halley Bay research station in Antarctica had been measuring ozone since the late 1950s. They couldn't quite believe the drop after ~1975, checked and re-checked, and published in 1985.

They also noticed a new seasonal effect: Each spring (October), the ozone would suddenly drop precipitously, and then recover a few months later.

Effects of elevated UV radiation

Hazards of elevated UV radiation include

• Phytoplankton (sunlight-absorbing plankton) are vulnerable to UV, and are at the bottom of food webs in the oceans near Antarctica.
• Increased risk of skin cancer and cataracts in humans.
• Genetic damage to plants and animals.

The smoking gun

1986 - Susan Solomon organized an expedition to measure ClO.She proposes that stratospheric ice breaks up enclosed CFCs, releasing Cl when heated by springtime sunlight.

Montreal Protocol

1987 - 24 nations signed the Montreal Protocol.

Republican President Ronald Reagan recommended the treaty for U.S. Senate approval.

As of Sept 2009, all 196 member states of the UN had signed on to the treaty to phase out ozone-destroying chemicals.

1995 - Nobel prize in Chemistry goes to Paul Crutzen, Mario Molina and Sherwood Rowland. The committee commends them for "contribut[ing] to our salvation from a global environmental problem that could have catastrophic consequences."

(NASA's The World We Avoided website modelled unregulated, 3% annual growth in CFC emissions, and concluded that Earth would have lost 67% of our ozone, and UV radiation at Earth's surface would have doubled by 2065).