Solar Nebular Theory
The Earth’s Atmosphere
• Composition of the atmosphere
–
–
–
–
N2 : 78%
O2 : 21%
Ar : 1%
CO2 : ~400 ppmv
• Tell me about the evolution of the Earth's
atmosphere… from the beginning
Solar Radiation
• The structure and chemistry in our atmosphere is
driven by solar radiation.
The Earth’s
Atmosphere
Martian and Venusian Atm
• Temperature
profiles
separate the
layers
• the layers filter
out the most
energetic
damaging solar
radiation
thermodynamic and kinetic
concentrations
1
Thermospheric Reactions
The Thermosphere
• temperature  as altitude 
(1200 ºC to -90 ºC)
• b/c solar radiation is most
intense at the high altitudes
• as altitude  less of the
high energy light (<100
nm) is available for
absorption (much of it has
already been absorbed)
• The radiation is ionizing
and breaks bonds.
• What is the ionosphere?
Converting DHrxn to l
• What photon is required to break the triple bond of N 2
(using bond enthalpies)?
the 127 nm
absorption
• Convert reaction enthalpy from per mole to per molecule
• Then determine the l max from the energy per molecule
• Bond enthalpies are
often an
underestimate of the
energy needed
• What happens to the extra energy when the photon
l<79.59 nm?
Mesospheric Reactions
• breaking bonds, generating exited states
2
Night Glow
• exited states store
energy and then
release it as light
and heat
Thermo- and Mesospheric Actinic Flux
The Mesosphere
• temperature as
altitude 
• gas pressure increases
by 105 so more gas to
absorb
• Absorption crosssections are less
intense, so more
molecules are required
• This is only possible in
lower layers of the atm
The Stratosphere
• temperature  as altitude  (-2 ºC to -60 ºC)
• most of the 200-300 nm gets absorbed at the top, so
less absorption at bottom = less heat
mesosphere top = 85 km
mesosphere bottom = 50 km
Actinic ≡ able to cause
photochemical reactions
Stratospheric Actinic Flux
absorption
here due to
O2
a major
absorption
here due to
ozone
Note that this
is only
happening
below 50 km in
the
stratosphere.
• M is a chaperone
molecule
– most likely O2 or N2
– absorbs the excited state
energy
3
Photolytic Reactions: Chapman 1
Lifetime Calculations
• In cycles (such as the Chapman), species are
formed and then participate in other reactions
• The rate of the reaction can determine how long
a species persists (t).
Photolytic Reactions: Chapman 3
The Formation of Ozone
• What is the rate law for ozone formation?
• What is the lifetime equation for atomic
oxygen?
• Calculate the lifetime of atomic O at 100 km,
90 km, 80 km, 70 km, 60, km, 50 km, & 40
km.
The Formation of Ozone
Lifetime of [O] Results
4
Ozone Efficacy
Biologically Damaging Radiation
UV-C
UV-A
UV-B
UV-C
UV-B
The Troposphere
UV-A
Albedo
• Cold at the top and warm at the bottom
• The visible light heats the Earth’s surface and
warming the bottom of the troposphere.
• Brown dirt: high or low albedo?
• 70% of the light
hitting the surface get
absorbed. 30% reflects
back into space.
• The 30% reflected is
called the albedo.
• White snow: high or low albedo?
Reflected vs. Emitted Light
• Reflected light from the surface…
– Maintains the same wavelength (visible in, visible out)
– This is the albedo.
• The Earth is warm, so it acts as a blackbody
radiator.
– The surface temperature determines the emitted
radiation.
• White sand: high or low albedo?
• If a planet’s albedo increases, it will get warmer or
colder?
Blackbody Radiation
• If the sun
emits
visible,
what does
the Earth
emit?
• Define atmospheric window.
• If the UV absorbed in the atm. layers involves
breaking bonds and ionizing mcs, what does the
light emitted by Earth do to mcs?
5
A tale of 3 siblings
based on distance from the sun (scientist calculate)
• Venus (atm = 96% CO2, 90 atm, avg T= 840 °F)
– 67 million miles from sun
– average temperature should be 210 °F colder
• Earth (atm = 0.3% CO2, 1 atm, avg T= 59 °F)
– 93 million miles from sun
– average temperature should be 60 °F colder
• Mars (atm = 95% CO2, 0.01 atm, avg T= -45°F)
– 128 to 155 million miles from sun
– average temperature should be about 10 °F colder
What makes the difference between actual and calculated?
What makes a greenhouse gas?
• gases with a changing dipole moment
• Its ability to absorb infrared radiation
• When the right wavelength of light hits the
molecule, it will absorb it
demo: IR tutor
• what about?
»
»
»
»
N N
O=O
O=C=O
CH4
out-of-plane
bend
asymmetric
stretch
symmetric
stretch
Greenhouse Gases
Molecular Vibrations of Water
vibrations
Los Angeles Basin
Beijing Smog
• What causes
this?
• What are the
chemical
components?
6
4 Stroke Engine
Four-Stroke Engine
• cylinder fires every other cycle
• exhaust is vented separately from fuel intake
– there is no mixing, so less HC emissions
• lubrication is separate from fuel
1) intake
2) compression
3) power
4) exhaust
– oil has higher MW so it combusts less
• must run right-side up (b/c of lubrication)
Two-Stroke Engines
Two Stroke Engine
• the piston acts as the valves by covering or uncovering
the intake and exhaust
– simpler construction
– the piston also is its own fuel injector as it compresses and
injects the fresh fuel in the downstroke and pulls in fresh fuel
for the next cycle in the upstroke
– fresh fuel forces out exhaust; fuel leaks out with exhaust
– less fuel efficient than 4 stroke
1) intake/compression
1) power/pressurize
fresh fuel
• cylinder fires once every cycle
– more power than four-stroke engine (every other cycle)
• lubrication and fuel are mixed
– engine can operate upside down
– engines don’t last long because of poor lubrication
– lubricant does not combust well  HC emissions
2) transfer/exhaust
Key Engine Differences
Diesel Engine
• higher compression so higher efficiency
1
efficiency  1   
 rc 
R
Cv
• Diesel engines
–
–
–
–
–
similar to the 4-stroke gas engine
high temperature and high compression
more efficient than 4-stroke gas
uses lower grade, less flammable fuel
emissions include NO and soot
animation
7
Key Engine Differences
• 4-stroke
– exhaust and intake of fresh fuel occur in different steps, thus
fresh fuel is not exhausted to the same degree
– lubricant and fuel are separate
– operated at high temperatures (leads to high NO levels)
– emissions are higher in NO and relatively low in HCs
Emission
Comparisons
• 2-stroke
– exhaust and intake occur in the same step, so fresh fuel can
be sent out with the exhaust
– lubricant and fuel are mixed; lubricant does not burn as
cleanly
– operated at lower temperatures (leads to low NO levels)
– emissions are low in NO and high in HCs
Diesel vs. Biodiesel Fuel
Diesel vs. Biodiesel Fuel
• biodiesel does not require an oxygenator
because it is oxygenated (fatty esters –COOR)
Ethanol as a Fuel Additive
Other Fuels
8
Measurements
• Pollutants: NO2, CO2, CO, and C8H18
– Are they GHG’s?
– What radiation can we use to detect them?
Form
DG°f
(kJ/mol)
NO2
51.3
N2
0.0
NO
87.6
CO
-137
CO2
-394
CH4
-50.8
octane
16.4
O2
0.0
O3
163
Types of Smog
• Photochemical smog
– Consists of NOx, O3, CO, HCs or VOCs
– Formed from petroleum combustion (usually).
– Primary pollutants (NO, CO, HC) produced at high
temperatures and by (relatively) clean fuel.
• Classical Smog
– Consists of smoke, soot, SOx (can include NOx)
– Trace levels of Hg, and other toxic metals
– Formed from coal combustion (usually), a relatively
dirty fuel.
Photochemical Smog Generates
Ground-level Ozone
Why Does NO Form If It is So
Unfavorable???
• What is the sign of DGrxn for this reaction?
• What is the sign of DGrxn for this reaction?
DGrxn = +175.2 kJ
• What does this mean?
Form
DG°f
(kJ/mol)
NO
87.6
N2
0.0
O2
0.0
9
The Hydroxyl Radical
• OH• (the hydroxyl radical)
Ground-level Ozone
from CO
– this is the “detergent” of the atmosphere
– our atmosphere is an oxidizing environment
– gases tend to react with the hydroxyl radical to
form their highest oxidation state (most stable)
• CO forms NO2
and regenerates
OH
• NO2 forms O3
• Since OH has
been regenerated,
it catalyzes the
production of O3
for each CO
l = 300 nm
Hydroxyl Radical Reactions
Hydroxyl Radical Reactions
One O2 was consumed, forming NO2. Each NO2 forms a O3.
Two O2 units were consumed, forming NO2 and HOO. Each can
form a O3.
Photochemical Smog Generates
Ground-level Ozone
• For every HC, NO, CO, and other pollutants
(sulfur compounds) the OH catalytic cycle
turns each into additional O3 molecules.
• Photochemical smog leads to massive O3
production.
So, one O3 → 2 OH; one OH → 2 O3, the other OH → O3.
A net gain of 2 O3.
Smog Chemistry
• Nitrogen cycles
– Production of one NO2 results in one O3
• Carbon cycles
– CO + OH eventually yields…
– alkane + OH eventually yields…
• Sulfur cycles
– RSH + OH eventually yields…
+ OH + O3
(½ additional O3)
+ 3 O3 per C atom
(2 additional O3)
+ 3 O3 per C atom
+ 1 H2SO4
(2 additional O3)
• Can you summarize the main point to all of
this?
10
Radical Reactions
• Most reaction have a high Ea
• Radical reactions do not
• The daytime radical reactions are driven by the
sun (starts the formation of the first radical)
• At night, reactions continue until the radicals
are gone.
What Happens
at Night
×
×
O3  hv  O*  O2
Ultimate Fate of Smog
–
–
–
–
NOx becomes HNO3
Carbon → CO2
SOx becomes H2SO4
Metals enter the food web
Texas
Texas
(acid deposition)
(climate change)
(acid deposition)
(bioaccumulation)
Sources of Hg
11
Smog Chemistry
Modes of
Pollution
• Nitrogen & NOx worksheet
• All driven by light and the hydroxyl radical
most pollution
goes into the
air
Worksheet
• pH of natural rain
• pH of acid rain
Acid Rain Production
• SOx and NOx are the principle culprits
night time production (involves smog 2ndaries):
NO2 + O3  NO3 + O2
Form
DG°f
(kJ/mol)
NO2 + NO3  N2O5
NO2
51.3
N2O5 + H2O  2 HNO3
N2
HNO3
-111.25
day time production:
HNO2
-50.6
NO2 + OH  HNO3
NH3
-16.5
0.0
Acid Rain Production
(dry conditions)
SO2 + OH + M  HSO3 + M
HSO3 + O2 + M  HOO + SO3
SO3 + H2O  H2SO4
HOO aids the production of HNO3:
NO + HOO  NO2 + OH
NO2 + OH + M  HNO3 + M
12
Atmospheric Oxygen
Ozone Destruction
• O2 (molecular oxygen)
–
–
–
–
necessary for aerobic organisms
atmospheric content is ~20% by volume
produced by photosynthesis
consumed by combustion, respiration
• O3 (ozone)
– in the troposphere it is a lung irritant
– in the stratosphere it blocks UV radiation (along with O2)
– produced by O2 and UV-C radiation (Chapman cycle)
• Ozone reacts with many other reactive atmospheric
species.
• These reactions reduce the level of steady-state ozone
in the stratosphere.
• Many of the reactive species are catalytic, and destroy
ozone faster than the Chapman cycle can replenish it.
• Some catalysts are natural and some are
anthropogenic.
• They all participate in the destruction of ozone in the
following manner.
• good ozone = stratospheric ozone
• bad ozone = tropospheric ozone
Ozone Destruction
• These catalysts simulate the last
step in the Chapman cycle.
• Reduce ozone two ways.
Ozone Destruction
Chapman Cycle
• Natural catalysts
– N2O from soil bacteria (enhanced by
anthropogenic fertilizer)
– OH produced from ozone reacting with water and
from photolysis of methane
1) Breaks O3 into O2
2) Prevent O from forming O3
• First step doesn’t require UV-B
• Anthropogenic Catalysts
• Write a mechanism
for Cl, Br, OH, NO
– Cl from CFCs
– Br from halons
• What are the
characteristics of a
catalyst? (4 things)
CFC’s or Freons
Cl
F
C
F
Cl
Freon-12
• non-flammable
• very stable
Halons make good fire extinguishers
Cl
• non-toxic
F
C
Cl
extinguish time : from hours to minutes
Cl
• non-conductive
• cheap to make
Freon-11
• CFC’s were considered a “perfect” chemical
• they revolutionized food storage and climate control
• CFC’s replaced sulfur dioxide and ammonia, which
are toxic
13
General Ozone Loss Comparison
Something Special About Antarctica
South Pole movie
North Pole movie
60°
Antarctic Ozone Hole
• Polar Vortex
– Isolates the south
pole and prevents
dilution of Cl
compounds.
– Keep warm air out
and allows
temperatures to drop
to -90 °C.
– Cold temps favor
PSCs.
Antarctic Ozone Hole
• Polar Stratospheric Clouds (PSC)
– Cl and ClO are very reactive
– NOx helps to convert these to ClONO2 , relatively
stable and requires rare UV-C to activate it
14
Antarctic Ozone Hole
• Polar Stratospheric Clouds (PSC)
–
–
–
–
PSCs combine water and NOx to form NAT
NAT: nitric acid trihydrate or HNO3·3H2O
Less NOx means more Cl and ClO
PSCs also provide a reactive surface to convert less
reactive Cl to more reactive Cl
Antarctic Ozone Hole
• Dark Winter
– Allows for very cold temperatures at tropopause
and stratosphere.
– The absence of light allows the Cl2 levels to build up
until spring arrives.
– Ditto for Br2.
Antarctic Ozone Hole
• Onset of Spring
– when the first light comes, the catalysis of ozone
destruction begins
– because of the vortex, a fresh supply of ozone cannot
replace the loss
– ozone destruction continues until polar vortex
breaks up and warm air melts the PSCs
– because so little ozone is left there is less absorption
of UV and less heat, making cold last longer
– Cl· becomes bond up in HCl and ClONO2, which
are stable enough to stop the catalysis
Why
Not
The
North
Pole?
Animals in Danger
phytoplankton in the ocean
are a food source for many
species
15
CFC replacements & troubles
• HFC’s (hydrofluorocarbons)
– non-toxic and cheap
– fairly stable (doesn’t get into stratosphere as much)
– contributes to global warming
Outline:
3/20/2014
• Announcements
• HCFC’s (hydrochlorofluorocarbons)
–
–
–
–
not as stable as CFC’s (does not reach stratosphere as much)
flammable
Ozone Depleting Potential of about 5 %
not a long term solution (to be phased-out by 2030)
• Today: Ch. 3
– Climate Change
• HC’s (hydrocarbons)
– highly flammable
– contributes to global warming
Atmospheric Forms of Carbon
• CO2
–
–
–
–
greenhouse gas
product of respiration and combustion
nutrient for photosynthetic plants
long atmospheric lifetime (120 yrs)
• CH4
– greenhouse gas
– product of anaerobic digestion
– short atmospheric lifetime (12 yrs)
Forms of Carbon
• CO2 and CO32- are the two most stable forms of carbon
• in an aerobic environment CO2 and CO32- are the
ultimate fate of carbon in the absence of an external
input of energy (like photosynthesis)
• in an anaerobic
environment
hydrocarbons are the
ultimate fate of
carbon (fossil fuels)
Form
CO2
CH4
octane
CO32C6H12O6
graphite
DG°f DG°f per C atom
(kJ/mol)
(kJ/mol)
-394
-50.8
6.4
-528
-910
0.0
-394
-50.8
0.8
-528
-152
0.0
The Greenhouse Effect
mostly UV, visible,
infrared
another
version
16
Spectral Windows
Radiative Forcings
1. concentration
•
more gas = more absorption
GHG conc
movie
2. spectral window
•
•
does absorption overlap with another gas
no overlap = more absorption
3. strength of absorption
4. atmospheric lifetime
•
a small DpCFC is more important than a
large DpCO2
• each GHG has a semi-unique absorption
spectrum
• if two GHG’s absorb at the same wavelength,
when the % T approaches 0%, it does not
matter if the conc. of the gas increases
• if two GHG’s absorb in different spectral
windows, then the change in conc. of one gas
can be very significant
GHG spectral window
movie
A Timeline of Global Temperatures
the “Medieval Warm Period”
the “Little Ice Age”
what
happened?!?
from “Chemistry in Context” by Gilbert, Kirss, & Davies, p. 338
Increasing
GHGs
17
Ocean
pH
Sea Level Rise
• What is the primary reason, melting glaciers or rising
temperature?
(Earth Wobble!)
E cycles: 100,000 and 400,000 year cycles
T cycle: 41,000 years
P cycle: 20,000 years
18
How are Past Temps Measured?
increase of 50 ppm
or 30%
• Antarctic ice core samples
– the deeper the core, the older the sample
– measure the ratio between 18O and 16O in H2O
increase of 0.7 -1.0 °C
or 2.5%
Ice Core Temperatures
More Hurricanes?
(18O/16O)sample – (18O/16O)SMOW 
18O =

(18O/16O)SMOW
– SMOW = Standard Mean Ocean
Water
– SMOW = 1/500
• Evaporation: lighter 16O evaporates
more easily from a water body
resulting atmospheric H2O vapor is
poorer in 18O than oceanic water
• Condensation: heavier 18O are
precipitated faster than lighter 16O
19
Hurricane Intensity
Another Way of Looking at it
CD = the drag
coefficient
 is the surface air
density
r is the radius of the
storm
t is the lifetime of the
storm
Rising CO2 Levels
• Global Warming
– as partial press. CO2 & CH4, global temp. 
– as partial press. CO2 , dissolved CO2 
CO2 (aq) + H2O(l)  H2CO3(aq)  2 H+(aq) + CO32-(aq)
– dissolved CO2 , H2CO3 , pH , solubility of CaCO3 
• this will be disastrous for shellfish and coral
Cause or Correlation?
• does a rise in CO2 levels lead to a rise in temperature?
– Greenhouse effect says YES : more CO2, more greenhouse
gases, more trapped heat
• does a rise in temperature lead to a rise in CO2 levels?
– as T goes , trees grow more and absorb more CO2, CO2
levels go  (NO)
– as T goes , animal activity goes  and more CO2 is released,
CO2 levels go  (YES)
– as T goes , oceans warm and CO2 becomes less soluble,
atmospheric CO2 levels go  (YES)
• These are positive or negative feedback cycles
20