Transcript Earth`s Atmosphere

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 DU
Equator = 250 DU
Antarctica (’57) = 320 DU
Antarctica (’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.
.ClO + UV photon  Cl. + O
2
2
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