Post on 20-Dec-2015
Dylan Millet, Daniel Jacob, and May FuHarvard University
Thomas Kurosu and Kelly ChanceHarvard-Smithsonian Astrophysical Observatory
Alex GuentherNCAR
Colette HealdUC Berkeley
OMI HCHO measurements to test isoprene emissions and land cover
GEOS-Chem MeetingApril 11, 2007
HCHO Columns Map Isoprene Emissions from Space
Formaldehyde (HCHO) is a major breakdown product in the oxidation of isoprene
Giving us an isoprene emission proxy that can be measured from space
Relating HCHO Columns to Isoprene Emission
VOCs HCHOOH, h
ki, Yi
OH, h
kHCHO
iiEYk
iHCHOHCHO
1Ω
Local ΩHCHO-Ei Relationship
VOC source Distance
downwind
ΩHCHO
Isoprene
a-pinenepropane
100 km
detectionlimit
Palmer et al., JGR (2003,2006)Millet et al., JGR (2006)
BES isoprene HCHOΩ
HCHO vertical columns measured by OMI(Summer 2006)
Relating HCHO Columns to Isoprene Emission
What drives variability in column HCHO?
Measured HCHO production rate vs.
column amount
Isoprene dominant source when ΩHCHO is high
ΩHCHO variability over N. America driven by isoprene
Other VOCs give rise to a relatively stable background ΩHCHO
Not to variability detectable from space
INTEX-A
Millet et al.,JGR (2006).
Measuring HCHO from Space
1995-200140 x 320 km footprint
global coverage: 3 days
GOME
2002-present30 x 60 km footprint
global coverage: 6 days
SCIAMACHY
2004-present13 x 24 km footprint
global coverage: 1 day
OMI
SBUV instruments in low Earth orbit
OMI HCHO Columns over North America
OMI (2006) vs. GOME (1996-2001)
OMI: better counting statistics, cloud filtering less retrieval noise10-20% lower than GOME (accounting for interannual climate differences)
June-AugustGOME OMI
Relating HCHO Columns to Isoprene Emissions
UniformΩHCHO-Eisoprene relationship
VariableΩHCHO-Eisoprene relationship
ΩHCHO = SEisoprene+ B
[1015 molecules cm-2] [1013 atomsC cm-2 s-1]
OMI Isoprene Emission
Model of Emissions of Gases and Aerosols from Nature
G2006Guenther [2006]
(MODIS)
CLMCommunity Land
Model(AVHRR)
[1013 atomsC cm-2 s-1]
Environmental drivers (T, h, LAI, leaf age, …)
Vegetation-specific baseline emission factors
Drive MEGAN with 2 land cover databases
MEGAN Isoprene Emissionsw/ G2006 vegetation
MEGAN Isoprene Emissionsw/ CLM vegetation
Guenther et al., ACP (2006)
12.2 TgC
Broadleaf trees Broadleaf trees
Spatial Patterns in Isoprene Emissions
OMI – MEGAN Isoprene EmissionsJune-August, 2006
Large sensitivity to surface database used
MEGAN higher than OMI over dominant emission regions
MEGAN MEGAN
OMI – MEGAN Isoprene EmissionsJune-August, 2006
MEGAN with CLM vegetation MEGAN with G2006 vegetation
OMI OMI
G2006 Broadleaf Trees
MEGAN w/ CLM Land Cover
MEGAN w/ G2006 Land Cover
OMI – MEGAN Isoprene EmissionsJune-August, 2006
Bottom-Up Emissions Too High in Dominant Source Regions
MEGAN emissions >70% too high over much of the Ozark Plateau, Upper
South, Upper Midwest
Large regional emissions driven by oak tree cover, high temperatures
Broadleaf tree isoprene emissions overestimated
OMI – MEGAN Isoprene EmissionsJune-August, 2006
CLM-Driven Emissions Too Low in Deep South
Bias in modeled emissions: >100%
Underestimate of broadleaf tree or shrub coverage
-or-
Modeled emissions from evergreen trees or crops too low
CLMFineleaf Evergreens
CLMCrops
[1013 atomsC cm-2 s-1]
Constraints on Emission Factors
Possible explanation for OMI-MEGAN discrepancy:Fast chemical loss within forest canopies?
Farmer and Cohen [2007]
Regress OMI isoprene emissions against G2006 PFTs
Variable EFsBroadleaf tree emissions need to be
uniformly decreased by 44%
Constant EFsMore consistent with OMI
Optimum broadleaf tree EF:• 13.1 x 1012 atomsC/cm2/s• similar to MEGAN mean
• rejects MEGAN’s use of 3-4x higher EFs in certain locations
The End
OMI vs. Aircraft Data & GEOS-Chem
MEGAN isoprene emissions using 2 land cover databases
Guenther [2006] (MODIS) – G2006Community Land Model (AVHRR) - CLM
G2006 CLM EF
[%] [1010 atomsC/cm2/s] [1013 atomsC cm-2 s-1]
PFT Coverage and Isoprene Emission Factors (EFs)
Isoprene Emission
OMI Isoprene Emission vs. MEGAN-CLM
UniformΩHCHO-Eisoprene relationship
VariableΩHCHO-Eisoprene relationship
OMI - MEGAN OMI - MEGAN
MEGAN w/ CLM vegetation
[1013 atomsC cm-2 s-1]
OMI isoprene emission (uniform slope) OMI isoprene emission (variable slope)
OMI Isoprene Emission vs. MEGAN-G2006
UniformΩHCHO-Eisoprene relationship
VariableΩHCHO-Eisoprene relationship
OMI - MEGAN OMI - MEGAN
MEGAN w/ G2006 vegetation
[1013 atomsC cm-2 s-1]
OMI isoprene emission (uniform slope) OMI isoprene emission (variable slope)