1. MAPPING OF VOLATILE ORGANIC COMPOUND (VOC) EMISSIONS USING SATELLITE OBSERVATIONS OF FORMALDEHYDE COLUMNS Daniel J. Jacob
with Paui I. Palmer, Tzung-May Fu, Dylan B. Millet, Dorian S. Abbot
and Kelly V. Chance, Thomas Kurosu (Harvard SAO/CFA)
supported by NASA Atmospheric Chemistry Modeling and Analysis Program

2. SATELLITE OBSERVATIONS OF TROPOSPHERIC COMPOSITION …a rapidly growing resource!
Sensor
TOMS
GOME
IMG
MOPITT
MISR
MODIS
AIRS
SCIA-MACHY
TES
OMI
Platform (launch)
multi
(1979-)
ERS-2 (1995)
ADEOS
(1996)
Terra Aqua
(1999) (2002)
Envisat (2002)
Aura
(2004)
ozone
X (tropics) X
aerosol CO
NO2
HNO3
HCHO
SO2
BrO

3. IMPORTANCE OF NON-METHANE VOC EMISSIONS FOR ATMOSPHERIC CHEMISTRY
Precursors of tropospheric ozone
Precursors of organic aerosols
Sinks of OH
Isoprene, terpenes,
oxygenates…
Alkenes, aromatics,
oxygenates…
Alkanes, alkenes,
aromatics…
~ 200 Tg C yr-1
~ 600 Tg C yr-1
~ 50 Tg C yr-1
Vegetation
Biomass burning
Industry

4. SPACE-BASED MEASUREMENTS OF HCHO COLUMNS AS CONSTRAINTS ON VOC EMISSIONS
solar
backscatter
340 nm
hn (l < 345 nm), OH
Oxidation (OH, O3, NO3)
VOC
HCHO
lifetime of hours
many steps
Emissions

5. SPACE-BASED MEASUREMENTS OF ATMOSPHERIC COLUMNS BY SOLAR BACKSCATTER
Examples: TOMS, GOME, SCIAMACHY, MODIS, MISR, OMI, OCO
Applications to retrievals of O3, NO2, HCHO, BrO, CO, CO2, aerosols…
absorption
Backscattered
intensity IB l1 l2
wavelength
Slant optical depth
Scattering by
Earth surface
and by atmosphere
“Slant column”
Vertical column
The air mass factor (AMF) depends on viewing geometry and radiative transfer

6. THE GOME INSTRUMENT
Instrument in polar sun-synchronous orbit, 10:30 a.m. observation time
320x40 km2 field of view, three cross-track scenes
Complete global coverage in 3 days
Operational since 1995
HCHO column is determined from backscattered solar radiance in 340 nm absorption band
Concurrent retrievals of cloud fractions, tops, optical depths

7. FITTING OF HCHO SLANT COLUMNS FROM GOME SPECTRA
ts = 1.0 ± 0.3 x1016 cm-2
Fitting uncertainty of
4x1015 molecules cm-3
corresponds to ~ 1 ppbv HCHO in lowest 2 km
ts = 3.0 ± 0.4 x1016 cm-2
ts = 8.4 ± 0.7 x1016 cm-2
Chance et al. [2000]

8. HCHO SLANT COLUMNS MEASURED BY GOME (JULY 1996)
2.5x1016
molecules
cm-2 2
1.5 1
detection
limit
0.5
South
Atlantic
Anomaly
(disregard)
-0.5
High HCHO regions reflect VOC emissions from fires, biosphere, human activity

9. AIR MASS FACTOR (AMF) CONVERTS SLANT COLUMN WS TO VERTICAL COLUMN W
“Geometric AMF” (AMFG) for non-scattering atmosphere: q
EARTH SURFACE

10. IN SCATTERING ATMOSPHERE, AMF DEPENDS ON VERTICAL DISTRIBUTION OF ABSORBER
340 nm
HCHO
EARTH SURFACE
Use GEOS-Chem chemical transport model to specify shape of vertical profile for given scene

11. AMF FOR A SCATTERING ATMOSPHERE
AMFG = 2.08
actual AMF = 0.71
GOME
sensitivity
w(z)
HCHO mixing ratio
profile S(z) (GEOS-Chem)
what
sees
Palmer et al. [2001]

12. QUANTIFYING AMF ERRORS USING AIRCRAFT PROFILES
ICARTT mission over North America (summer 2004)
0-10 km spirals and profiles during ICARTT:
In situ HCHO, clouds, aerosol extinction
Mean HCHO profiles in ICARTT
Observed (Fried)
Observed (Heikes)
GEOS-Chem model
(n = 89)
Dylan B. Millet, Harvard
Clouds are the principal source of error

13. FORMALDEHYDE COLUMNS FROM GOME: July 1996 means
…compare to GEOS-Chem including GEIA biogenic VOC emissions
and U.S. EPA anthropogenic VOC emissions
GEOS-Chem vs. GOME: R = 0.83, bias = +14%
Palmer
et al. [2003]

14. SEASONALITY OF GOME HCHO COLUMNS (9/96-8/97) largely reflects seasonality of isoprene emissions
GOME GEOS-Chem (GEIA) GOME GEOS-Chem (GEIA)
MAR
JUL
APR
AUG
SEP
MAY
JUN
OCT
Abbot et al. [2003]

15. INTERANNUAL VARIABILITY OF GOME HCHO COLUMNS
Augusts : correlation with temperature anomaly explains some but not all of the HCHO column variability
GOME HCHO Temp. anomaly
GOME HCHO Temp. anomaly
1995
1999
1996
2000
2001
1997
Abbot
et al.
[2003]
1998

16. RELATING HCHO COLUMNS TO VOC EMISSION
oxn.
hn (<345 nm), OH
VOCi
HCHO
yield yi
k ~ 0.5 h-1
Emission Ei
smearing, displacement
In absence of horizontal wind, mass balance for HCHO column WHCHO:
Local linear relationship
between HCHO and E
… but wind smears this local relationship between WHCHO and Ei depending on the lifetime of the parent VOC with respect to HCHO production:
Isoprene
WHCHO
a-pinene
propane
100 km
Distance downwind
VOC source

17. TIME-DEPENDENT HCHO YIELDS FROM VOC OXIDATION
Box model simulations with state-of-science MCM v3.1 mechanism
methylbutenol
High HCHO signal from isoprene with little smearing,
weak and smeared signal from terpenes;
GEOS-Chem yields may be too low by 10-40% depending on NOx
Palmer et al, [2005]

18. HCHO COLUMN vs. ISOPRENE EMISSION RELATIONSHIP IN GEOS-Chem MODEL
Results for U.S. quadrants in July 1996 simulation w/ 2ox2.5o horizontal resolution show: (1) dominance of isoprene emission as predictor of WHCHO variability;
(2) linear relationship between the two
Standard simulation NW NE
R2 = 0.43
HCHO from simulation
w/o Isoprene emission
R2 = 0.51
Model HCHO column [1016 molec cm-2]
R2 = 0.65 SW SE
R2 = 0.49
We use this relationship to derive “top-down” isoprene emissions from the GOME HCHO column observations
Isoprene emission [1013 atomC cm-2 s-1]

19. GOME vs. MEGAN ISOPRENE EMISSION INVENTORIES (2001)
MEGAN is a new inventory of isoprene emissions developed by Alex Guenther
[Guenther et al., 2005]
Good accord for seasonal variation, regional distribution of emissions;
GOME 10-34% higher than MEGAN depending on month, differences in hot spot locations
Palmer et al. [2005]

20. EVALUATING GOME ISOPRENE EMISSION ESTIMATES vs
EVALUATING GOME ISOPRENE EMISSION ESTIMATES vs. IN SITU FLUX MEASUREMENTS (2001)
PROPHET forest site in northern Michigan (M. Pressley, WSU):
also shown are local MEGAN isoperene emission inventory values
Palmer et al. [2005]

21. YEAR-TO-YEAR VARIABILITY OF GOME HCHO OVER SOUTHEAST U.S.
Amplitude and phase are highly reproducible
GOME HCHO Column [1016 molec cm-2]
Southeast US average N; W
P. I. Palmer (Harvard)

22. WHAT DRIVES GOME HCHO TEMPORAL VARIABILITY OVER SOUTHEAST U. S
WHAT DRIVES GOME HCHO TEMPORAL VARIABILITY OVER SOUTHEAST U.S. DURING MAY-SEPTEMBER?
Monthly mean GOME HCHO vs. surface air temperature;
MEGAN parameterization shown as fitted curve
Temperature drives ~80% of the variance of monthly mean HCHO columns
P.I. Palmer (Harvard)

23. GOME HCHO COLUMNS OVER EAST ASIA (1996-2001)
JAN
APR
JUL
OCT
FEB
MAY
AUG
NOV
MAR
JUN
SEP
DEC
Relationship to VOC emissions far more complex than for N. America; biomass burning, isoprene, anthropogenic VOCs, direct HCHO emission all contribute
Tzung-May Fu (Harvard)

24. GOME vs. GEOS-Chem HCHO COLUMNS OVER EAST ASIA
MEGAN biogenic emission inventory is far too low
APR
MAY
JUN
JUL
AUG
SEP
T. M. Fu (Harvard)

25. VOC CONTRIBUTIONS TO HCHO PRODUCTION IN CHINESE CITIES (JAN-FEB 2001)
Vehicle-generated xylenes could make a large contribution to HCHO columns NC CC
Ethane 0.3 % Benzene 0.4 %
Propane 0.3 % Toluene 2.4 %
ALK4 5.1 % Xylene 20.2 %
Ethene 19 % Isoprene 8.2 %
PRPE 43 % WC SC
B. Barletta (UCI), T.-M. Fu (Harvard)

26. PRELIMINARY HCHO COLUMN DATA FROM OMI (launched on Aura in July 2004)
26 Day Average: 24 September – 19 October 2004
K. Chance and T. Kurosu (Harvard CFA)

27. OMI HCHO RETRIEVALS AND MODIS FIRE COUNTS
Chongqing (Red Basin)
Jakarta