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)