Dylan Millet D.J. Jacob, D.R. Blake, K. Chance , A. Fried,
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Transcript of Dylan Millet D.J. Jacob, D.R. Blake, K. Chance , A. Fried,
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Dylan MilletD.J. Jacob, D.R. Blake, K. Chance, A. Fried,
B.G. Heikes, R.C. Hudman, T.P. Kurosu, H.B. Singh, S. Turquety, S. Wu, and the ICARTT Science Team
Variability of HCHO over North America: Implications for
satellite retrievals
ICARTT Data Analysis WorkshopUniversity of New Hampshire
August 10, 2005
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Space-based measurements of HCHO columns
Can we useHCHO as a proxy for VOC emissions?
OH, h, O3VOC HCHO
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HCHO slant columns measured by GOME(K. Chance, T.P. Kurosu et al.)
HCHO slant columns measured by OMI(K. Chance, T.P. Kurosu et al.)
-0.5
0
0.5
1
1.5
2
2.5
LOD
1016 molecules/cm2
Key Questions:
Measurement:1) What is the uncertainty and bias
in HCHO columns measured from satellites?
Interpretation2) What are the main precursors
contributing to HCHO columns and variability over North America?
3) What are the implications for retrieving VOC emissions from space?
Address using aircraft measurements
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Uncertainty in solar backscatter retrievals of HCHO
• Fitting uncertainty(~ 4 x 1015 molec/cm2)
• Relating slant columns to vertical columns– Air mass factor (AMF)
AMF depends on• HCHO vertical profile• Radiative transfer
– Cloud effects– Aerosol effects
HCHO
Model
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Computation of AMF
AMFG: Viewing geometry & SZAw(P): scatteringS(P): HCHO vertical distribution
Use DC-8 vertical profiles
Measured vs. modeled [HCHO], aerosol
“Satellite” clouds
T
s
P
Ps
G dPPSPwP
AMFAMF )()(
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AMF values
• Mean: 1.2 – 1.3• Range: 0.11 - 2.42• Model bias:
-5% over continents(-57+70%)+13% over ocean(-14+72%)
• 25% uncertainty for a single scene
• What drives the variability?
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Cloud and aerosol effects on AMF
Aerosol effectsIncrease the AMF (i.e. sensitivity to
HCHO) by ~15%Cloud effects
– Can ↑ or ↓ AMF– Major source of error– Double the uncertainty for a single
sceneRecommend cloud cutoff:
AMF error of 21% @ cloud fraction cutoff of 40%
Model AMF Bias
Mean
Individual profiles
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Interpretation of HCHO
• Methane, anthro. & biogenic VOCs
• What drives variability in HCHO?
OH, h, O3VOC HCHO
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Methane & OVOCs main HCHO precursors in most of the atmosphere
But variability in column production rate is low
Satellite LOD / HCHO: ~ 5x1011 molec/cm2 /s
isoprene OVOCs
NMHCs methane
terpenes
Measured column HCHO production rate
Pro
bab
ilit
y
HCHO sources & variability
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HCHO factors of variability
Isoprene dominant source when HCHO is high
Variability in HCHO over N.America driven by isoprene
NMHCs methane
terpenes
OVOCsisoprene
Measured column HCHO production rate
Co
lum
n H
CH
O
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HCHO production yield from isoprene
From measured (HCHO vs. i) &
modeled (ki/kHCHO):
Y = 1.61 ± 0.10
iiHCHO
iHCHO Y
k
k MOD MOD
MOD(flighttrack) OBS
HCHO column mass balance:
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ConclusionsAMF
Clouds major source of error
Increase AMF uncertainty by ~ 2x
Uncertainty in satellite HCHO columns due to the AMF:
Mean bias ~ -5% over continents
Uncertainty ~ 25% (1) for individual scene (less for time averages)
HCHO production & variability
Variability in HCHO over N. America driven by isoprene
Satellite retrievals of HCHO can be used as a proxy for isoprene emissions over N. America
Estimated average HCHO yield from isoprene oxidation: 1.61±0.10
Upper end of GEOS-Chem (0.9-1.9); lower end of MCM (1.6-2.4) yields
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Jakarta
Chongqing
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Note: bias from assuming constant HCHO & aerosol vertical profiles over land: +5%