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Dylan Millet, Daniel Jacob, and May Fu Harvard University Thomas Kurosu and Kelly Chance Harvard-Smithsonian Astrophysical Observatory Alex Guenther NCAR.

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Presentation on theme: "Dylan Millet, Daniel Jacob, and May Fu Harvard University Thomas Kurosu and Kelly Chance Harvard-Smithsonian Astrophysical Observatory Alex Guenther NCAR."— Presentation transcript:

1 Dylan Millet, Daniel Jacob, and May Fu Harvard University Thomas Kurosu and Kelly Chance Harvard-Smithsonian Astrophysical Observatory Alex Guenther NCAR Colette Heald UC Berkeley OMI HCHO measurements to test isoprene emissions and land cover GEOS-Chem Meeting April 11, 2007

2 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

3 Relating HCHO Columns to Isoprene Emission VOCs HCHO OH, h k i, Y i OH, h k HCHO Local Ω HCHO -E i Relationship VOC source Distance downwind Ω HCHO Isoprene a-pinene propane 100 km detection limit Palmer et al., JGR (2003,2006) Millet et al., JGR (2006) HCHO vertical columns measured by OMI (Summer 2006)

4 Relating HCHO Columns to Isoprene Emission What drives variability in column HCHO? Measured HCHO production rate vs. column amount Isoprene dominant source when Ω HCHO is high Ω HCHO variability over N. America driven by isoprene Other VOCs give rise to a relatively stable background Ω HCHO  Not to variability detectable from space INTEX-A Millet et al., JGR (2006).

5 Measuring HCHO from Space 1995-2001 40 x 320 km footprint global coverage: 3 days GOME 2002-present 30 x 60 km footprint global coverage: 6 days SCIAMACHY 2004-present 13 x 24 km footprint global coverage: 1 day OMI SBUV instruments in low Earth orbit

6 OMI HCHO Columns over North America

7 OMI (2006) vs. GOME (1996-2001) OMI: better counting statistics, cloud filtering  less retrieval noise 10-20% lower than GOME (accounting for interannual climate differences) June-August GOMEOMI

8 Relating HCHO Columns to Isoprene Emissions Uniform Ω HCHO -E isoprene relationship Variable Ω HCHO -E isoprene relationship Ω HCHO = SE isoprene + B [10 15 molecules cm -2 ] [10 13 atomsC cm -2 s -1 ] OMI Isoprene Emission

9 Model of Emissions of Gases and Aerosols from Nature G2006 Guenther [2006] (MODIS) CLM Community Land Model (AVHRR) [10 13 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 Emissions w/ G2006 vegetation MEGAN Isoprene Emissions w/ CLM vegetation Guenther et al., ACP (2006) 12.2 TgC Broadleaf trees

10 Spatial Patterns in Isoprene Emissions OMI – MEGAN Isoprene Emissions June-August, 2006 Large sensitivity to surface database used MEGAN higher than OMI over dominant emission regions MEGAN OMI – MEGAN Isoprene Emissions June-August, 2006 MEGAN with CLM vegetationMEGAN with G2006 vegetation OMI

11 G2006 Broadleaf Trees MEGAN w/ CLM Land Cover MEGAN w/ G2006 Land Cover OMI – MEGAN Isoprene Emissions June-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

12 OMI – MEGAN Isoprene Emissions June-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 CLM Fineleaf Evergreens CLM Crops [10 13 atomsC cm -2 s -1 ]

13 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 EFs Broadleaf tree emissions need to be uniformly decreased by 44% Constant EFs More consistent with OMI Optimum broadleaf tree EF: 13.1 x 10 12 atomsC/cm 2 /s similar to MEGAN mean rejects MEGAN’s use of 3-4x higher EFs in certain locations

14 The End

15 OMI vs. Aircraft Data & GEOS-Chem

16 MEGAN isoprene emissions using 2 land cover databases Guenther [2006] (MODIS) – G2006 Community Land Model (AVHRR) - CLM G2006 CLMEF [%] [10 10 atomsC/cm 2 /s] [10 13 atomsC cm -2 s -1 ] PFT Coverage and Isoprene Emission Factors (EFs) Isoprene Emission

17 OMI Isoprene Emission vs. MEGAN-CLM Uniform Ω HCHO -E isoprene relationship Variable Ω HCHO -E isoprene relationship OMI - MEGAN MEGAN w/ CLM vegetation [10 13 atomsC cm -2 s -1 ] OMI isoprene emission (uniform slope) OMI isoprene emission (variable slope)

18 OMI Isoprene Emission vs. MEGAN-G2006 Uniform Ω HCHO -E isoprene relationship Variable Ω HCHO -E isoprene relationship OMI - MEGAN MEGAN w/ G2006 vegetation [10 13 atomsC cm -2 s -1 ] OMI isoprene emission (uniform slope) OMI isoprene emission (variable slope)

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