ANALYSIS OF TROPOSPHERIC OBSERVATIONS
FROM GOME AND TOMS
Randall Martin, Daniel Jacob,
Jennifer Logan, Paul Palmer
Harvard University
Kelly Chance, Thomas Kurosu
Harvard-Smithsonian Center
for Astrophysics
HOW DO COLUMNS OF TROPOSPHERIC NO2 FROM
GOME COMPARE WITH TRADITIONAL BOTTOM-UP NOx
INVENTORIES?
GOME/SCIAMACHY
Tropospheric NO2 column ~ ENOx
~ 2 km
BOUNDARY
LAYER
hn (440 nm)
NO2
NO
NO/
NO2

O3, RO2
NOx lifetime 1 day
Emission
HNO3
Deposition
NITROGEN OXIDES (NOx)
WITH ALTITUDE
RETRIEVAL OF TROPOSPHERIC NO2 FROM GOME
(errors e in 1015 molecules cm-2)
GOME SPECTRUM (423-451 nm)
Fit spectrum
e1 = 0.6-0.8 O3, O4, H2O, Ring, Undersampling,
Common Mode
SLANT NO2 COLUMN
Remove stratospheric contribution,
diffuser plate artifact
e2 = 0.4
Use Central Pacific GOME data with:
•HALOE to test strat zonal invariance
•PEM-Tropics, GEOS-CHEM 3-D
model to treat tropospheric residual
TROPOSPHERIC SLANT NO2 COLUMN
Apply AMF to convert slant column
to vertical column
Quantitative retrieval in
partly cloudy scene
e3 = 0.5-3.2
Use radiative transfer model with:
•local surface albedos from GOME
•local vertical shape factors from
GEOS-CHEM global model
• local cloud info from GOMECAT
TROPOSPHERIC NO2 COLUMN
GEOS-CHEM MODEL
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•
•
•
•
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Assimilated Meteorology (GEOS)
2ox2.5o (4ox5o) horizontal resolution, 26 layers in vertical
24 tracers, 120 solved species, ~400 reactions describe tropospheric O3-NOxhydrocarbon chemistry
Heterogeneous chemistry (with off-line aerosol fields)
Photolysis: Fast-J including aerosol scattering
Emissions:
– Fossil fuel: GEIA (NOx), Logan (CO), Piccot (NMHCs)
– Biosphere: modified GEIA (hydrocarbons) & Yienger/Levy (soil NOx)
– Lightning: Price/Rind/Pickering, GEOS convective cloud tops
– Interannually varying biomass burning (Logan, Duncan et al. 2002)
Deposition: modified Wesely (dry), Liu/Mari (wet)
Cross-tropopause transport: SYNOZ
RECENT AND CURRENT APPLICATIONS:
• Tropospheric ozone : global budget, Asian outflow, U.S. air quality, Middle East,
transatlantic transport, tropics (TOMS)
• Carbon monoxide: budgets, interannual variability
• Studies of Aerosols, Carbon dioxide, and Organics
• Satellite retrievals, inversions, data assimilation: CO, CO2, O3, HCHO, NO2
• Chemical forecasting: TRACE-P, NOAA 2K2
GEOS-CHEM MODEL CAPTURES REGIONAL
VARIATION IN NO
GEOS-CHEM
Aircraft
Observations
NO2 number
density
RETRIEVAL OF TROPOSPHERIC NO2 FROM GOME
GOME SPECTRUM (423-451 nm)
SLANT NO2 COLUMN
Remove stratospheric contribution,
diffuser plate artifact
Use Central Pacific GOME data with:
•HALOE to test strat zonal invariance
•PEM-Tropics, GEOS-CHEM 3-D
model to treat tropospheric residual
TROPOSPHERIC SLANT NO2 COLUMN
TROPOSPHERIC NO2 COLUMN
GEOS-CHEM MODEL IDENTIFIES FAVORABLE
REGIONS TO DETERMINE STRATOSPHERIC COLUMN
BIAS THAT WOULD RESULT FROM THE ASSUMPTION
OF ZERO TROPOSPHERIC NO2 OVER THE PACIFIC
GEOS-CHEM
Aircraft Observations
Comparison with PEM-T
observations of NO from aircraft
suggests small model bias
NO2 number
density
TROPOSPHERIC NO2 COLUMN FROM GOME AFTER
REMOVING STRATOSPHERE AND DIFFUSER PLATE
ARTIFACT, AND CORRECTING FOR THE PACIFIC BIAS
1996
RETRIEVAL OF TROPOSPHERIC NO2 FROM GOME
GOME SPECTRUM (423-451 nm)
SLANT NO2 COLUMN
TROPOSPHERIC SLANT NO2 COLUMN
Apply AMF to convert slant column
to vertical column
Quantitative retrieval in
partly cloudy scene
Use radiative transfer model with:
•local surface albedos from GOME
•local vertical shape factors from
GEOS-CHEM global model
• local cloud info from GOMECAT
TROPOSPHERIC NO2 COLUMN
IN SCATTERING ATMOSPHERE, AMF CALCULATION
NEEDS EXTERNAL INFO ON SHAPE OF VERTICAL PROFILE
RADIATIVE TRANSFER MODEL
Io
sigma ()
IB
ATMOSPHERIC CHEMISTRY MODEL
dt()
“a-priori”
Shape factor
S ( ) = C NO2 ( )
 air
 NO2
EARTH SURFACE
Scattering weight w( ) =
-1  ( )  ln I B
AMFG  e
t
() is temperature dependent cross-section
Tabulate w() as function of:
• solar and viewing zenith angle
• surface albedo, pressure
• cloud optical depth, pressure
AMF =
NO2 mixing ratio CNO2()
INDIVIDUAL
GOME SCENES
1
slant
= AMFG  w( ) S ( )d
vertical
T
CLOUDS SIGNIFICANTLY AFFECT SENSITIVITY OF GOME
Cloudy-sky
scattering
weights
Clear-sky
scattering
weights
Shape factor
CLOUD REFLECTIVITY (Rc) AND CLOUD FRACTION (f)
HAVE A LARGE INFLUENCE ON THE AMF
AMFa Ra (1 - f )  AMFc Rc f
AMF =
Ra (1 - f )  Rc f
Solar Zenith Angle
Cloud Optical Thickness
JULY 1996
Clear-sky
AMF
Fraction of I
From Clouds
(GOMECAT
and LIDORT)
Actual AMF
accounting
for clouds
VERTICAL COLUMNS LARGELY CONFINED TO
REGIONS OF SURFACE EMISSIONS
NO/
NO2

WITH ALTITUDE
NOx lifetime
~1day
GOME RETRIEVAL OF TROPOSPHERIC NO2
vs. GEOS-CHEM SIMULATION (July 1996)
GEIA & Logan
emissions
scaled to 1996
MODELS AND SATELLITE OBSERVATIONS:
THE ODD COUPLE
SATELLITE SPECTRA
“L1 DATA”
IN SITU OBSERVATIONS
(“L1 DATA”)
A PRIORI INFORMATION
profile shape,
Concentration range,
Correlations…
RETRIEVAL
ATMOSPHERIC
CONCENTRATIONS
“L2 DATA”
MODELS
INCEST?
EVALUATION
ASSIMILATION
INCREASED
KNOWELDGE
SCIENTIFIC ANALYSIS
“L4 DATA”
DIAGNOSE MODEL CONTAMINATION OF RETRIEVAL
BY CORRELATING AMF WITH VERTICAL COLUMN
Little relationship between AMF and
enhanced NO2 columns
r = -0.65
r = -0.14
Negative correlation implies that AMF conversion to vertical columns will
modify the slant column patterns to better fit the model
CAN WE USE GOME TO ESTIMATE NOx EMISSIONS?
TEST IN U.S. WHERE GOOD A PRIORI EXISTS
Comparison of GOME retrieval (July 1996) to GEOS-CHEM model fields
using EPA emission inventory for NOx
GOME
GEOS-CHEM
(EPA emissions)
GOME
BIAS = +18%
R = 0.78
NO2 COLUMN FROM LIGHTNING SMALL COMPARED
TO RETRIEVAL ERROR
Tropospheric NO2 Column Enhancement from Lightning (6 Tg N yr-1) for July
(GEOS-CHEM)
Error in Tropospheric NO2 Column Retrieval 7-33x1014 molecules cm-2
We conclude that GOME is consistent with bottom-up NOx
emissions inventories, but interesting differences remain …
What can we learn from TOMS about the relative
roles of biomass burning, lightning, and dynamics in
the distribution of tropical tropospheric ozone?
?
Lightning
?
Nitrogen oxides (NOx)
CO, Hydrocarbons
hn
?
Ozone (O3)
hn, H2O
Hydroxyl (OH)
TROPICAL TROPOSPHERIC
OZONE LARGELY DETERMINES
OXIDIZING POWER OF
ATMOSPHERE
Fires
Biosphere Human
activity
Ocean
MOST LIGHTNING ACTIVITY IS OVER LAND
INTENSE BIOMASS BURNING OVER
NORTHERN AFRICA DURING DJF
TROPOSPHERIC OZONE COLUMNS (Sep’96-Aug’97)
GEOS-CHEM
TOMS (CCD)
DJF
MAM
JJA
SON
R = 0.66
MODEL BIAS = -0.5 DU
EL NINO INTERANNUAL VARIABILITY IN OZONE:
DIFFERENCE BETWEEN OCT 97 AND OCT 96
Chandra et al. [2002]
OZONE ENHANCEMENT FROM LIGHTNING (GEOS-CHEM)
largely explains observed wave-1 pattern in TOMS ozone
SIMULATED OZONE CONCENTRATIONS AND FLUXES
AT 300 hPa IN JAN 97
Incursion of northern hemispheric ozone over the South Atlantic
through the “westerly duct” contributes to the wave-1 pattern
OZONE VERTICAL PROFILES OVER ABIDJAN
North African Dec-Feb ozone enhancement from biomass burning
Is seen by aircraft observations but not by TOMS
GEOSCHEM
TOMS
(distributed
w/assumed
standard
profile)
MOZAIC
aircraft
data
RAYLEIGH SCATTERING LIMITS SENSITIVITY OF TOMS TO
SEASONAL VARIATION IN LOWER TROPOSPHERE
TOMS sensitivity to ozone
(LIDORT radiative
transfer model)
TOMS
standard
profiles
S. Atlantic
profile
Abidjan profile
TOMS UNDERESTIMATES OZONE OVER BIOMASS
BURNING REGIONS AND OVERESTIMATES OZONE
OVER THE PACIFIC
CORRECTION FOR TOMS RETRIEVAL EFFICIENCY
CANNOT EXPLAIN DISCREPANCY OVER ABIDJAN
What do GOME and SCIAMACHY observe?
TOMS (MR)
TOMS (CCD)
Corrected CCD
Tropopause
GEOS-CHEM
200 hPa
MOZAIC
(200 hPa)
Month
SUMMARY
WAVE-1 from Lightning
Surface NOx from GOME
What does GOME show?
Accurate a-priori vertical
profile and cloud info
essential for nadir retrievals