Environmental Issues & Problems
ENV 150
Ozone Depletion
Guillaume Mauger
Today: Ozone
Climate Change
Reminders
Thursday: Quiz #3, Rough Draft of SLRP
Atmospheric Layers
What is ozone?
ozone “layer”
Ozone significantly reduces
harmful UV radiation in sunlight
What is ozone?
! O3
…without it, our health and ecosystems would suffer.
Why is ozone tracked as a pollutant???
Answer:
tropospheric vs. stratospheric ozone
• Ozone forms at the Earth’s
surface due to pollutants,
and is toxic to humans.
• Ozone in the stratosphere
forms for different reasons.
• We don’t breathe the
ozone that’s in the
stratosphere, we just
benefit from its absorption
of UV
http://www.pscleanair.org/
Stratospheric Ozone creation:
Stratospheric Ozone creation:
Sunlight is more intense in the stratosphere,
and can “photodissociate” oxygen:
Sunlight is more intense in the stratosphere,
and can “photodissociate” oxygen:
1)
O2 + UV photon " O + O
molecular
oxygen
atomic
oxygen
1)
O2 + UV photon " O + O
2)
O2 + O + M " O3 + M*
So much energy is released in the formation of
ozone that another molecule is needed to
absorb the excess.
Stratospheric Ozone creation:
Reaction #1 requires intense sunlight, which
is more prevalent higher up
1)
O2 + UV photon " O + O
2)
O2 + O + M " O3 + M*
Reaction #2 requires denser air, and air is
more dense at lower altitudes.
Stratospheric Ozone creation:
COMPROMISE: ozone found btw 15-40 km
Stratospheric Ozone removal:
(natural)
Stratospheric Ozone
before human intervention
O2 + UV photon " O + O
O3 + UV photon " O2 + O
This is how ozone shields us from UV!
O2 + O + M " O3 + M*
O3 + UV photon " O2 + O
(creation)
(removal)
in balance (equilibrium):
rate of creation = rate of destruction
Stratospheric Ozone
Stratospheric Ozone
Sydney Chapman, Oxford, 1930
Paul Crutzen, 1970
Discovered new reactions involving
Nitrous Oxide.
(produced by soil microbes)
Result: Can correctly explain
stratospheric concentrations!
Molina & Rowland
CFCs
= Chlorofluorocarbons
Nature 249, 810-812 (28 June 1974)
Stratospheric sink for chlorofluoromethanes: chlorine
atom-catalysed destruction of ozone
• Originally seen as a “triumph of
technology”
! the very non-reactiveness of CFCs turns
out to be a problem:
Stable, nonreactive, long-lived, nonflammable, &
safe (much safer than ammonia, which they
replaced)
…also cheap to manufacture
• 1950s/60s: rapid increases in production
Molina & Rowland
Molina & Rowland
Nature 249, 810-812 (28 June 1974)
Stratospheric sink for chlorofluoromethanes: chlorine
atom-catalysed destruction of ozone
Nature 249, 810-812 (28 June 1974)
Stratospheric sink for chlorofluoromethanes: chlorine
atom-catalysed destruction of ozone
! the very nonreactiveness of CFCs turns
out to be a problem:
! the very nonreactiveness of CFCs turns
out to be a problem:
Cl + O3 " ClO + O2
ClO + O " Cl + O2
NET:
O3 + O " 2O2
= removal of ozone
Cl + O3 " ClO + O2
ClO + O " Cl + O2
NET: O3 + O3 " 2O2
= removal of ozone
The Cl atoms are
not used up!
= catalyst
Molina & Rowland
note: not just CFCs
Nature 249, 810-812 (28 June 1974)
Stratospheric sink for chlorofluoromethanes: chlorine
atom-catalysed destruction of ozone
CFCs
“chlorofluorocarbons”
HBFCs
“hydrobromofluorocarbons” - fire extinguishers
CH3Br
“methyl bromide”
HCl
“hydrogen chloride”
- fumigant (pesticide)
! warned of serious damage to life on
earth due to increasing UV to surface:
decreases in food production & fisheries,
decreases in human immune system,
increases in cataracts, skin cancer, …
! no direct evidence: all theoretical
Response:
Ozone in switzerland
• Both environmental groups AND
industry spurred the creation of an UN
treaty to prevent the destruction of the
ozone layer
• Montreal Protocol, 1987
• Copenhagen Protocol
ban CFCs and other
ozone-depleting
chemicals