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Atmosphere
reading: Chapter 18, sections 18.1 – 18.4
Course pack: pp. 4 – 32 (Ozone hole, Effects of acid rain, Global warming,
Greenhouse effect)
As you read ask yourself …
What kinds of chemistry take place in the different regions of the
atmosphere? What are the reactions involved?
In what ways is this chemistry harmful or protective for humans?
How h
H
have human
h
activities
ti iti affected
ff t d the
th chemical
h i l reactions
ti
that
th t
naturally take place in the atmosphere?
What is the greenhouse effect? Is it natural, protective, harmful? Can
you explain what happens at a molecular level?
Chem 102
divided into 4 regions based on T
troposphere
P (torr)
(we live there)
Altitude (km)
Earth’s atmosphere
1
stratosphere
rxns between atoms and
solar uv radiation
mesosphere
ionosphere
reactions absorb hν
Chem 102
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Composition
temperature extremes form
boundaries between layers
mixing slow at the boundaries
between layers
non-uniform composition
concentrations expressed in ppm
V  n from the ideal gas law
1ppm 
1 volume
10 6 volumes total

1mol
10 6 moles total
Chem 102
 mol fraction
3
What is the
concentration of H2
in ppm?
Chem 102
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Outer regions of atmosphere
outer defense against radiation and
high energy particles
Ph t di
Photodissociation
i ti
molecule absorbs photons and bonds are
broken
O2 + hν
+
In the molecule CF3Cl the C-Cl bond has a bond dissociation energy of
339 kJ/mol. What wavelength of light has enough energy per photon to
break this bond?
need energy per bond = 339 X 103 J mol-1/ 6.023 X 1023 bonds mol-1
Chem 102
5
Photoionization
molecule absorbs a photon and loses an
electron
occurs at high elevation
before they reach the earth’s surface, photons with
ionizing energy
Chem 102
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Ozone in the upper atmosphere
O3 absorbs photons (240-310 nm)
Energy intensity (JJ)
100
10-2
10-4
10-6
280
300
320
340
360
λ (nm)
Chem 102
main reaction:
7
Ozone is formed and decomposed naturally in the atmosphere
3 x 108 tons are formed and decompose daily
formed between 30 km and 90 km
Why?
need higher altitude to get high
energy photons for
O2 + hν  O(g) + O(g)
need
d llower altitude
ltit d tto h
have
sufficient O2(g)
Chem 102
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O2 + hν  O(g) + O(g)
O2(g) + O(g)  O3*(g)
O3*(g) + M(g)  O3(g) + M*(g) + heat
OO
3(g)
2(g)
( +
) +h hν νOO
( +
) +O(g)
O(g)
O( )
3(g)
2(g)
O(g) +O(g) +M(g)  O2(g) + M*(g) + heat
Chem 102
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Ozone concentrations vary naturally
not uniform , higher concentration at the poles
vary with
seasonal – maximum in
Canada in March
Chem 102
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Depletion of the ozone is also natural
H2O + h ν  H + OH
Crutzen identified the nitrogen
oxide role in 1970.
N2O is a byproduct of fertilization,
fossil fuel combustion and
industrial processes like biomass
and biofuel burning.
Chem 102
11
Ozone depletion
potential (ODP)
global warming
potential (GWP)
Chem 102
from 2 October 2009 VOL 326 SCIENCE, pp. 123-125
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Ozone depletion
1995 Nobel prize Rowland, Molina and Crutzen
over southern Canada ozone is 6%
decreased since 1970’s
as high as 10-20% in the summer in
high Arctic
Chem 102
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Destruction caused by chlorofluorocarbons (CFCs)
CFCs (tradename: Freon)
persist in stratosphere for 120 years
react with high energy uv <220 nm:
CFCs in spray cans banned in
North America in 1978, in world
by Montreal Protocol in 1987
Chem 102
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Ozone depletion in Antarctica
Dobson unit : One DU is is
0.4462 millimoles of ozone
per square metre
hole
appears
each
spring
Chem 102
15
unique process in Antarctica
atmosphere contains inactive
molecules containing Cl :
cold dark winter forms
polar stratospheric clouds (PSCs)
PSCs contain ice crystals,
crystals catalyze release of Cl2
Cl2 is trapped by drop in
pressure due to cold temperatures
in spring, sunlight activates the Cl2
May 2004
Oct. 2004
catalytic destruction of ozone
until all Cl2 is consumed
Chem 102
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spring,
dark blue is greatest destruction
Chem 102
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Chemistry of the troposphere
There is so much pollution in the air now that if it
weren’t for our lungs there’d be no place to put it all.
Robert Orben
carbon monoxide
source – incomplete combustion of
hydrocarbons
colourless, odourless,
most abundant pollutant gas
hazard:
0.1% can bind 60% of
hemoglobin in a few hours
Chem 102 http://www.ec.gc.ca/soer-ree/English/Indicators/Issues/Urb_Air/Tech_Sup/uasup5_e.cfm
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sulfur compounds and acid rain, mostly SO2
arise from decay of organic matter and
from fossil fuel combustion
production 3:1 human activities to natural
health hazard, even at low concentrations
Average levels of sulfur
dioxide in Canadian
cities
Note: The annual
maximum acceptable
National Ambient Air
Quality Objectives for
sulfur dioxide is 23 ppb
http://www.ec.gc.ca/soer-ree/English/Indicators/Issues/Urb_Air/Tech_Sup/uasup5_e.cfm
Chem 102
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Chemistry
Reduction of SO2
http://wapedia.mobi
 remove from coal & oil before it is burned
 remove from gases produced when fuels are burned:
Inject powdered limestone:
lime reacts with sulfur
dioxide:
Chem 102
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oxides of nitrogen
natural sources: volcanos, oceans, biological decay
human activities: internal combustion engine, other high
heat processes run in air
human activities
produce 4 times
natural
mixture of oxides, called NOx, source of acid rain and smog
Chemistry
at high T: N2(g) + O2(g)  2 NO(g) endothermic reaction
Chem 102
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NOx contributes to photochemical smog
O
CH
H 3C O
O
+ NO2
CH3C O ONO2
PAN
Chem 102
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Reduction of presence of NOx
catalyze the conversion of NOx to safer
gases
catalytic converter
oxidize CO and hydrocarbons to CO2 and H2O
reduce Nox to N2
gases are adsorbed on a surface to facilitate the
reaction
Chem 102
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Acid Rain
acid rain typical pH is 4.0
natural pH of rain is 5.6,
Chem 102
www.ec.gc.ca
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Most aquatic life disappears
Freshwater lakes
Many fish disappear
pH of lakes dependant
on soil and rock around lake
Normal
aquatic life
Lakes
are dead
pH
1
2
3
4
5
f limestone:
for
li
t
6
7
8
9
10
11
12
13 14
increasing acidity
leaching
nutrients are more soluble and wash out of soil
elevated levels of Al3+
fish and plants vary in ability to tolerate high Al3+
concentrations
Chem 102
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forests:
damage from acid
fog and clouds especially bad
damage from ozone
loss of nutrients from leaching
Chem 102
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structural damage
limestone:
metal structures
increased rusting
Chem 102
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Greenhouse gases and climate
Global changes in climate
Warming
Except for nuclear war or collision with an asteroid,
no force has more potential than global warming
to damage our planet’s web of life.
Time Magazine April 2001
evidence from
ice cores over 160
millenia
cores from ocean
floor
greater at the poles
than elsewhere
Chem 102
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climate change, cont’d
winters are shorter
ice cover shrinking  sea level rise
corals are dying ( warm water and increased CO2)
precipitation pattern is changing
increased frequency of extreme weather
Chem 102
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Earth balances energy from sun
earth is warmed by solar radiation
(all wavelengths)
λ = 4000 to 50,000 nm
thermal IR region
Greenhouse effect
molecules in atmosphere
p
absorb IR radiation and
re-emit radiation
Chem 102
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Natural greenhouse effect
keeps Earth’s average T at +15°C rather than -15°C (based on
distance from sun)
greenhouse
h
gases absorb
b b
radiation at the λ the earth
emits
has 5 – 200 year lifetime in atm.
from natural sources: organic
decay, combustion of plants
other greenhouse gases are:
Chem 102
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What makes a molecule a greenhouse gas?
must absorb infrared radiation
infrared radiation provides the energy
to cause molecules to vibrate
not single atoms
diatomics
μ = Qr
triatomics
e.g CO2
Chem 102
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A. fossil fuel burning 5.3
D. plant respiration 40 – 50
B. land use 0.6 – 2.6
E. decay of residues 50 – 60
C. photosynthesis 100-120
F. sea – surface gas exchange 100 – 115
G. net ocean uptake 1.6 – 2.4
A
B
C
D
E
units are
billions of
tons of
carbon
F
G
Chem 102
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N2O
Human activity producing
excess greenhouse gases
Concentrations
CO2 sources
CH4
CFCs
CO2
30% rise
i iin CO2
Methane sources
N2O sources
Chem 102
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IPCC: enhanced greenhouse effect increasing the average temperature
– producing climate change
reduce gas production
mitigation
(geoengineering)
NASA Goddard Institute for Space Studies,
http://data.giss.nasa.gov/gistemp/graphs/
Chem 102
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There are no passengers on
spaceship earth.
We are all crew.
Marshall McLuhan
Chem 102
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