Reactor 3 (Mox, a blend of Pu, and U fuel) after explosion - Reactor 1 at
bottom - Reactor 2 in between which is said to be in full melt down.
Copyright © 2010 R. R. Dickerson
1
Do Japanese Reactor Breakdowns pose a
threat to us?
• Chernobyl released massive amounts of
radioactive material:
–
131I
halflife 8 d
• Mixed gaseous and particulate phases.
• Particles 0.1 – 1.0 mm last the longest.
• Bioaccumulates in milk and caused thyroid cancer
in the Ukraine.
• Treatable with 150 mg KI (RDA 150 mg)
–
137Cs
halflife 30 yr
Copyright © 2010 R. R. Dickerson
• Particulate Phase
2
– One Bq is defined as the activity of a quantity of
radioactive material in which one nucleus decays
per second.
– Plutonium (239Pu), an a emitter, and toxic.
• Unknown amounts emitted.
• Ingestion. bio clearance time: months.
– Annual Limit of Intake = 3E5 Bq (8mCi)
• Inhalation. Small particles stick to the lung alveolae.
– Annual Limit of Intake = 300 Bq = 0.0081 mCi = 0.13 mg 239Pu.
Ultimately, Chernobyl caused only local problems.
Copyright © 2011 R. R. Dickerson
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Gamma Ray Spectrometers.
Copyright © 2011 R. R. Dickerson
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Forward Trajectories from Japanese Nuclear
Reactor Fires
Copyright © 2011
5
Chernobyl Results
• Barely detectable over N. Dakota after 10 d.
• 1% of release deposited (wet and dry) onto
UK. Not a major health threat.
• Local effects serious.
• 6000 cases of thyroid cancer in Ukraine.
Copyright © 2011 R. R. Dickerson
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Forward Trajectories today, 17 March.
Copyright © 2010 R. R. Dickerson
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Stratospheric Ozone Lecture
AOSC/CHEM 637
Atmospheric Chemistry
Russell R. Dickerson
Copyright © 2010 R. R. Dickerson
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Copyright © 2010 R. R. Dickerson
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Cholesterol photolysis to Vitamin D
hn
→
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Folate, vitamin B-9
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Copyright © 2010 R. R. Dickerson
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VII. STRATOSPHERIC POLLUTION
Without ozone in the atmosphere there could be no life as we know it on
the surface of the Earth. All of the atmospheric ozone, that is the “ozone
column” is only about 0.3 atm cm. In other words, if all the air were
squeezed out of the atmosphere, and the remaining ozone were brought to
STP, it would be only 0.3 cm thick.
– Murphy’s Law is strictly obeyed by NOx pollution in the atmosphere.
– Chemistry of the stratosphere different from troposphere.
(VIEWGRAPH)
See
Limb Image
Table 15.1 Solar intensity at the Earth’s surface assuming 0.30 atm cm
(300 D.U.) ozone. Note that the maximum flux is about 7x10¹⁵
(photons/(cm²s)/10 nm).
Copyright © 2010 R. R. Dickerson
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Actual depth of atmospheric layers.
Copyright © 2010 R. R. Dickerson
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λ
(nm)
σ
(atm⁻¹cm⁻¹)
I/Io
250
305
1.0x10⁻⁴⁰
275
162
1.0x10⁻²¹
300
9.5
6.0x10⁻²
325
0.27
9.2x10⁻¹
Where O₃ stops absorbing, sunlight begins to reach the surface of the
Earth. Hartley (1880) measured the ozone spectrum. Fabry and Buisson
(1913) measured the solar spectrum at the Earth’s surface and concluded
that the UV radiation reaching the surface of the Earth must be controlled
by ozone in the upper atmosphere, they even made an accurate estimate of
the amount of ozone!
Today we will examine the various catalytic cycles that control the
level of ozone in the stratosphere. We will calculate the O₃ abundance for
a highly simplified atmosphere containing only O₂ and N₂.
Copyright © 2010 R. R. Dickerson
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Copyright © 2010 R. R. Dickerson
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VII. A) OZONE CATALYTIC CYCLES
1)
Chapman Reactions (1931)
O₂ + hn → 2O
O + O₂ + M → O₃ + M†
O₃ + hn → O₂ + O
O + O₃ → 2O₂
(1)
(2)
(3)
(4)
By way of qualitative analysis, Reactions (1) plus (2) produce ozone.
O₂ + hn → 2O
(1)
2 x ( O + O₂ + M → O₃ + M )
(2)
3 O₂ + hn → 2 O₃ NET
Copyright © 2010 R. R. Dickerson
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While Reactions (3) plus (4) destroy ozone.
O₃ + hn → O₂ + O
O + O₃ → 2O₂
2O₃ + hn → 3 O₂
(3)
(4)
NET
Reactions (3) plus (2) add up to a null cycle, but they are responsible for
converting solar UV radiation into transnational kinetic energy and
thus heat. This cycle causes the temperature in the stratosphere to
increase with altitude. Thus is the stratosphere stratified.
O₃ + hn → O₂ + O
(3)
O + O₂ + M → O₃ + M*
(2)
NULL
NET
By way of quantitative analysis, we want [O₃]ss and [O]ss and [Ox]ss
where “Ox” is defined as odd oxygen or O + O₃. The rate equations
are as follows.
Copyright © 2010 R. R. Dickerson
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d [O3 ] / dt  R2  R3  R4
d [O] / dt  2 R1  R2  R3  R4
d [O3  O] / dt  d [Ox ] / dt  2 R1  2 R4
(a)
(b)
(a+b)
From the representation for O atom chemistry:
[O]SS 
j (O3 )[O3 ]  2 j (O2 )[O2 ]
k 2 [O2 ][ M ]  k 4 [O3 ]
In the middle of the stratosphere, however, R₃ >>2 R₁ and R₂ >> R₄ thus:
[O]SS 
j (O3 )[O3 ]
k 2 [O2 ][ M ]
(I)
This does not mean that R₄ is unimportant, but it can be ignored in an
approximation of [O]ss at the altitude of the ozone layer.
The ratio of [O] to [O₃] can also be useful:
Copyright © 2010 R. R. Dickerson
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[O]SS
j (O3 )

[O3 ]SS k 2 [O2 ][ M ]
(II)
Reactions 2 and 3 set the ratio of O to O₃, while Reactions 1 and 4 set the
absolute concentrations. Now we will derive the steady state ozone
concentration fro the stratosphere. From the assumption that Ox is in
ready state we know:
R₁ = R₄
Thus
j(O₂)[O₂] = k₄[O][O₃]
Substituting from (I), the steady state O atom concentration:
k 4 j (O3 )[O3 ]2
j (O2 )[O2 ] 
k 2 [O2 ][ M ]
or
Copyright © 2010 R. R. Dickerson
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[O3 ]SS 
j (O2 )[O2 ]2 k 2 [ M ]
k 4 j (O3 )
SAMPLE CALCULATION
At 30 km
j (O2 )  6  10 11 s 1
j (O3 )  1  10 3 s 1
k 2  4.5  10 34 cm6 s 1
k 4  1  10 15 cm3 s 1
[O ]  30 ppm
3 ss
(VIEWGRAPH)
Copyright © 2010 R. R. Dickerson
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• In any good experiment you check ratios of
variables first, to avoid errors or bias. Lets
look at the O/O3 ratio. Then we’ll consider
the absolute concentration of ozone.
Copyright © 2010 R. R. Dickerson
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Copyright © 2010 R. R. Dickerson
& Z.Q. Li
23
Copyright © 2010 R. R. Dickerson
& Z.Q. Li
24
O/O3 = j(O3)/(k2 M O2)
Beautiful agreement!
Copyright © 2010 R. R. Dickerson
& Z.Q. Li
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What is the observed O3 mixing ratio?
2x1012 molecules cm-3/2.7x1019 (P30/P0*298/T)
P30 ~ P0exp(-30/7) = 0.014 atm
[O3] = (2E12/3E19)/0.014 ~ 5E-6 = 5 ppm
Copyright © 2010 R. R. Dickerson
& Z.Q. Li
26
We calculated almost a factor of ten above the true concentration! What
is wrong? There must be ozone sinks missing.
2) Bates and Nicolet (1950) “HOx”
Odd hydrogen “HOx” is the sum of OH and HO₂ (sometimes H and H₂O₂
are included as well).
HO₂ + O₃ → OH + 2O₂
OH + O₃ → HO₂ + O₂
2O₃ → 3O₂
The following catalytic also destroys ozone.
OH + O₃ → HO₂ + O₂
HO₂ + O → OH + O₂
O + O₃ → 2O₂
Copyright © 2010 R. R. Dickerson
(5)
(6)
NET
(6)
(7)
NET
27
The second catalytic cycle speeds up Reaction 4, that is it effectively
increases k₄. Note that any loss of odd oxygen is the same as loss of
ozone. These catalytic losses are still insufficient to explain the
observed ozone concentration.
3) Crutzen (1970); Johnston (1971) “NOx”
Odd nitrogen or “NOx” is the sum of NO and NO₂. Often “NOx” is used
as “odd nitrogen” which includes NO₃, HNO₃, 2N₂O₅, HONO, PAN
and other species. This total of “odd nitrogen” is better called “NOy” or
“total reactive nitrogen.” N₂ and N₂O are unreactive.
NO + O₃ → NO₂ + O₂
O + NO₂ → NO + O₂
O + O₃ → 2O₂
NET
This is the major means of destruction of stratospheric ozone. The NOx
cycle accounts for about 70% of the ozone loss at 30 km. We will
calculate the implied steady ozone concentration later.
Copyright © 2010 R. R. Dickerson
28
4) Stolarski & Cicerone (1974) “ClOx”
Cl + O₃ → ClO + O₂
ClO + O → Cl + O₂
O + O₃ → 2O₂
NET
This reaction scheme is very fast, but there is not much ClOx in the
stratosphere … yet. Today ClOx accounts for about 8% of the ozone
loss at 30 km. If all these catalytic destruction cycles are added
together, they are still insufficient to explain the present stratosphere
O₃ level.
The general for of a catalytic ozone destruction cycle is:
X + O₃ → XO + O₂
XO + O → X + O₂
O + O₃ → 2O₂
NET
Copyright © 2010 R. R. Dickerson
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Molina, M.J., and Rowland F. S., Stratospheric sink for chloroflurormethanes –
chlorine atomic-catalyzed destruction of ozone, Nature, 249 (5460): 810-812
1974.
CClxFy + hn → CClx-1Fy + Cl
CFC’s do not decompose in the troposphere.
Copyright © 2010 R. R. Dickerson
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Table 15.2 Stratospheric ozone destruction cycles
Cycle
Sources
Sinks
Reservoirs
HOx
H₂O,CH₄,H₂
HNO₃ · nH₂O H₂O,H₂O₂
H₂SO₄ ·
nH₂O
NOx
N₂O + O(¹D)
HNO₃
HO₂NO₂,ClO
NO₂
ClOx
CH₃Cl,CFC
HCl
HCl, HOCl
The sinks involve downward transport to the troposphere and rainout or
other local loss. Note that some sinks are also reservoirs:
HCl + OH → H₂O + Cl
Copyright © 2010 R. R. Dickerson
31
Antarctic Ozone Hole
In the Antarctic winter there is no sunlight and even in the spring there is
too little UV to generate enough O atoms to destroy ozone. The
annual loss of ozone over Antarctica is driven by heterogeneous
chemistry and visible radiation. A good current review Is provided by
Solomon Nature, 1990, and “Scientific Assessment of Ozone
Depeation :1991” (WMO). The destruction of ozone is usually
moderated by the production of chlorine nitrate, an important reservoir
species.
NO₂ + ClO + M → ClONO₂ + M
In the Antarctic winter, heterogeneous reactions “denitrify” the
stratosphere (Molina et al., Science, 1987).
ice
HCl  ClONO2 
Cl2 (gas)  HNO3 (aq.) *
Cl2  hν  2Cl
Molecular chlorine is only weakly bound, and can be dissociated by
visible radiation.
Copyright © 2010 R. R. Dickerson
32
Cl + O₃ → O₂ + ClO
ClO + ClO + M → (ClO)₂ + M
(ClO)₂ + hv → Cl + ClOO
ClOO + M → Cl + O₂ + M
2O₃ → 3O₂
NET
Two types of Polar Stratospheric Clouds (PSC’s) exist.
Type I = HNO₃ · 3H₂O Nitric acid trihydrate, formed at T ≤ 195K
Type II = H₂O Ice formed at T ≤ 190K
• They move NOy species from the vapor phase to the condensed phase
as HNO₃.
• The are involved in catalytic cycles with chlorine and bromine
compounds that speed the reaction of ozone with itself to form oxygen.
• They move chlorine from the reservoir species HCl and ClONO₂ to
ClOx.
Copyright © 2010 R. R. Dickerson
33
OTHER STUFF
McElroy et al. (1986)
Cl + O₃ → ClO + O₂
Br + O₃ → BrO + O₂
ClO + BrO → Cl + Br + O₂
2O₃ → 3O₂
NET
twice (Cl + O₃ → O₂ + ClO)
ClO + ClO + M → (ClO)₂ + M
(ClO)₂ + hv → Cl + ClOO
ClOO + M → Cl + O₂ + M
2O₃ → 3O₂
NET
Copyright © 2010 R. R. Dickerson
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ClO + ClO + M → Cl₂O₂ + M
Cl₂O₂ + M → Cl₂ + O₂ + M
Cl₂ + hv → 2Cl
etc.
Note HCl is a reservoir, not a stable sink:
HCl + OH → H₂O + Cl
Solomon et al. (1986)
OH + O₃ → HO₂ + O₂
Cl + O₃ → ClO + O₂
HO₂ + ClO → HOCl + O₂
HOCl + hv → OH + Cl
2O₃ → 3O₂
NET
(6)
Crutzen and Arnold (1986)
Copyright © 2010 R. R. Dickerson
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1.
2.
3.
4.
Remove NOx via reactions on particles
Condensation of HNO₃  3H₂O at higher temperatures than pure
H₂O.
Cosmic ray induced OH – not a big deal.
HCl + OH → ClOx
HBr + OH → BrOx
Copyright © 2010 R. R. Dickerson
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