Chapter 2 (CIC) and Chapter 18 (CTCS)

• Read in CTCS Chapter 18.1-3

• Problems in CTCS: 1, 7, 9, 11, 13

The Ozone Hole

• Ozone varies with the seasons– Sun’s star spot cycles 11-12 years– Winds that are seasonal and 28 month cycles

Average [O3] over Northern US = 320 DUEquator = 250 DUAntarctica (’57) = 320 DUAntarctica (’97) = 120 DU

Why is it Disappearing?• Generation of radicals destroys ozone

– H2O + h H. + . OH– NO. – CCl2F2 + h Cl. + . CClF2 220 nm

O3 + 2 Cl. 2 ClO. + O2

2 ClO. Cl2O2

Cl2O2 + UV photon .ClO2 + Cl. .ClO2 + UV photon Cl. + O2

2 O3 3 O2 with Cl. as a catalyst (105 turnovers)

Why Use CFC’s?

• Correct b.p.• Not flammable• Not poisonous• Cheap• Inert

– Allows them to make their way into the stratosphere where UV light can attack them (average lifespan is 120 years)

What Evidence is There That CFC’s are

Guilty?“Smoking Gun”

*Stanitski, D.L.; Eubanks, L.P.; Middlecamp, C.H.; Stratton, W.J. Chemistry in Context: Applying Chemistry to Society, 3rd Edition, McGraw-Hill, Boston, MA, 2000, pg 78.

Why over Antarctica and Not the North Pole?

• Coldest spot at -90ºC

• Water freezes into frozen clouds providing a surface

• We’re seeing decreases in the north, but it is not classified as a “hole”

• Winds in the north are much more significant

What’s Being Done About it?

• Montreal Protocol 1987– Reduce CFC’s to ½ 1986 levels by 1998

• London 1990– Ban CFC’s by 2000 (done by 1996)

• Copenhagen 1992– Use HCFC’s but must stop these by 2030

• HCFC’s are 5% as efficient as CFC’s at destroing ozone

• Montreal 1997– Elimination of CCl4, CH3Br between 2000 and 2005