lightning and atmospheric chemistry - taucolin/courses/atmoselec/nox.pdf · • 1785 cavendish...
TRANSCRIPT
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• 1785 Cavendish performed the first experiments with a
spark discharge in glass tube. Discovered that oxidized
nitrogen (NOx=NO + NO2) compounds resulted from
the “burning” of air.
•1827 von Liebig discovered nitric acid (HNO3) in rain water and
related it to Cavendish’s experiments. NOx oxidized in drops.
• Nitric acid (HNO3) provides an important source of nitrate for
biosphere. Important in evolution of life.
•1970 Crutzen showed that tropospheric ozone (O3) was strongly
influenced by the amounts of atmospheric NOx.
•Ozone is poisonous to people, animals, plants, and is harmful to
perishable materials such as rubber, plastics, etc.
•1990’s led to a dramatic increase in the study of lightning
produced NOx since O3 is a strong greenhouse gas.
Lightning and Atmospheric Chemistry
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OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell a9 oxidation states from –3 to +5
-3 0 +1 +2 +3 +4 +5
NH3
Ammonia
NH4+
Ammonium
R1N(R2)R3
Organic N
N2 N2O
Nitrous
oxide
NO
Nitric
oxide
HONO
Nitrous acid
NO2-
Nitrite
NO2
Nitrogen
dioxide
HNO3
Nitric acid
NO3-
Nitrate
N2O5
Nitrogen
pentoxide
Decreasing oxidation number (reduction reactions)
Increasing oxidation number (oxidation reactions)
Nitrogen: Nitrogen is a major component of the atmosphere, but an essential nutrient in short
supply to living organisms.
free radical free radical
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•is the third most important greenhouse
gas
•impacts the Earth’s radiation budget and
can cause changes in atmospheric
circulation patterns.
•is toxic to humans, plants and animals.
TROPOSPHERIC OZONE:
NOx [NO+NO2]:
•is a primary pollutant found in photochemical smog
•is a precursor for tropospheric ozone formation
Why is NOx important?
NOx indirectly affects our local air quality and global
climate Has a strong influence on Ozone (O3) and hydroxyl
radical (OH) concentration
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EULINOX
Observational Evidence of LNOx
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New Mexico Colorado
(Germany)
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Tg N / yr Theoretical estimates
4 Tuck (1976)
18-41 Chameides et al. (1977)
47-100 Chameides (1979)
3 Dawson (1980)
0.9 Hill et al. (1980)
1.2 Bhetanabhotla et al. (1985)
Laboratory estimates
35-47 Chameides et al. (1977)
1.8 Levine et al. (1981)
9.4 Peyrous and Lapeyre (1982)
2.6 Borucki and Chameides (1984)
2.5-8.3 Wang et al. (1998)
Field Measurements
37 Noxon (1976, 1978)
2-4 Kowalczyk and Bauer (1982)
30 Drapcho et al. (1983)
220 Franzblau and Popp (1989)
3 Huntrieser (1999)
Lightning-Produced NOx
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Lightning: An Important Source of NOx
~50 Total
0.1-1 (0.4) N2O Degradation
0.7-1 (0.7) Aviation
1-16 (5.5) Soil Emissions
1-20 (5-7) Lightning
4-24 (10) Biomass Burning
28-32 (28) Fossil Fuel Burning
Tg N/yr Current Annual NOx Source
[Schumann and Huntrieser 2007]
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Why such large uncertainties?
To get a global number one has to answer 3 questions:
• What is the energy of a “typical” lightning discharge?
• How much NOx is produced per unit energy?
• How do we extrapolate to the globe?
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1. Energy of a lightning discharge
E1 = L ------------------ dt I(t)2
(t) r(t)2
E2 = V I(t) dt = V Q
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Wang et al. (1998)
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How long is a “typical”
lightning channel?
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0 100
5 103
10 103
15 103
20 103
25 103
30 103
35 103
40 103
I(t) = Io [exp
-at-exp
-bt+exp
-ct]
Cu
rren
t (A
mp
eres
)
Time (microseconds)
0 20 40 60 80 100
Io = 35 kA
Io = 10-60 kA
V ~ 3x108 Volts
E = 109 – 1010 Joules
<E> = 6.7 x 109 J
(Price et al., 1997)
E2 = V I(t) dt = V Q
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2. How much NOx is produced per unit energy?
O2
N2
T~30,000 K
O
O
N
N
NO
NO2
NO
NO
NO
NO
NO2
~1mm ~5 cm
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Temperature of Lightning
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How much air
is processed by
lightning?
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Size of lightning channel
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Zel’dovich Reactions
O2 O + O
O + N2 NO + N
N + O2 NO + O
When the lightning channel cools below T ~ 2500 K
NOx remains “fixed” or “frozen” in the atmosphere
(fixed nitrogen)
~85% of NOx is in form of NO
With volume mixing ratios of 1-4%
P (NO) = 1017 molecules/Joule
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Wang et al. (1998)
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~cm
~ meters
Region of coronae and
streamers due to high electric
fields surrounding channel
Hot channel
O+ + N2 NO+ + N
NO+ + e- NO
NO+ + N N2O+
N2O+ + e- N2O
Much larger volume of air
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3. Global Extrapolation
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Flashrate Parameterization
Z_IC
Z_CG
CTH
CC
Flashrate parameterization of
Price and Rind [1992]
Fcontinental CTH4.9
Fmarine CTH1.73
IC/CG Ratio parameterization
of Price and Rind [1993]
IC-CG Ratio CC4.0
0C
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Using ISCCP
clouds from
1983-1990
Annual mean
NOx production
is 12 Tg N/yr
Price et al. (1997)
Using Satellite Observations of Clouds
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0
0.5
1
1.5
Global estimates of monthly NO production (Tg)
Mon
thly
NO
x p
rod
uct
ion
(T
g)
Month
J F M A M J J A S O N D
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Using Modelled Clouds
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GCM simulations using lightning parameterizations
Total Lightning:
F ~ H5 over land
F ~ H 1.7 over oceans
(Price & Rind, 1992)
Fraction of CG vs. IC lightning:
IC/CG ~ cold cloud thickness
(Price and Rind, 1993)
How do we model lightning in GCMs?
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Observations Model
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Levy et al.
(1999)
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TOP-DOWN ESTIMATES OF GLOBAL LIGHTNING
NOx EMISSIONS
[Martin et al., 2007]
Using SCIAMACHY (NO2), OMI (O3), ACE-FTS (HNO3):
Target locations/times where NO2 column is dominated by
lightning source
Global source of 6 ± 2 TgN/yr from lightning
Obs (satellite)
Model (6 TgN/yr)
Model (4-8 TgN/yr)
Model (no lightning)
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Formation of Ozone (O3)
OH + CO H + CO2
H + O2 + M HO2 + M
Low NOx High NOx
HO2 + O3 OH + 2O2
Net: CO + O3 CO2 + 2O2
Ozone destruction
HO2 + NO OH + NO2
NO2 + h NO + O
O + O2 + M O3 + M
Net: CO + 2O2 CO2 + O3
Ozone production
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Simplified Chemistry of Nitrogen Oxides
Exploit Longer Lifetimes in Upper Troposphere
NO NO2
NOx lifetime < day
Nitrogen Oxides (NOx)
Boundary
Layer
NO/NO2
with altitude
hv
NO NO2
O3, RO2
hv
HNO3
NOx lifetime ~ week
lifetime ~ weeks
Ozone (O3)
lifetime ~ month
Upper
Troposphere
Ozone (O3)
lifetime ~ days
HNO3
O3, RO2
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July 21, 1998
12UT at 400mb
Maximum NOx production of 1 ppb
Total NOx Lightning NOx
(Flatoy and Hov, 1997)
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Ozone production : max of 1 ppb/hour
July 21, 1998 9-12UT
Total Ozone
Production
Ozone Production
Due to Lightning
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NOx from lightning Ozone from lightning
July 1998 mean at 400mb
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NASA Goddard Institute for Space Studies (GISS)
General Circulation Model (GCM)
2xCO2 climate - Control = ~ 4o C global warming
+30%
Price & Rind
(1994)
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CHANGING LNOX?
Warmer climate = more thunderclouds = more lightning
Impact:
(1) increasing UT ozone formation (positive forcing)
(2) Increasing OH leads to small reductions in CH4
(negative forcing)
Models predict
+ 4-60 % LNOx
per °K
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Summary and Conclusions
•Lightning is a major source of NOx in the troposphere
and is likely the largest source in the upper troposphere.
•Lightning produces between 5-10 Tg N/yr.
•While NOx production by lightning is a minor contributor
to surface O3 concentrations, and is likely the largest
contributor in the tropical upper troposphere.
•75% of the lightning-NOx and O3 is produced in the tropics
•The highest global production of LNOx occurs during JJA and the
lowest production occurs during DJF.
•Due to this natural imbalance, the northern hemisphere had a
natural bias in tropospheric ozone, even in pre-industrial times.
•Future climate change may increase global lightning activity
resulting in an increase in tropospheric O3 (positive feedback).