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A Tale of Two Models: A Comparison of the Biogenic Emission Inventory System (BEIS3.14) and Model of

Emissions of Gases and Aerosols from Nature (MEGAN 2.04)

George Pouliot7th Annual CMAS Conference

7 October 2008

What are the major differences in these two models that estimate emissions from biogenic sources?

It was the best of times, it was the worst of times, it was the age of wisdom, …

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1. Brief introduction to MEGAN and BEIS

• Biogenic Emissions Inventory System (BEIS v3.14)

• Model of Emissions of Gases and Aerosols from Nature (MEGAN v2.04)

2. Spatial differences between two models for an annual simulation

3. Temporal differences between the two models

4. Future Work

Topics to be Discussed

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Details about BEIS3.14

• Based on BELD3 vegetation database (limited to North America)

• Emission factors derived for USGS land use types, crops, and specific tree

types

• Soil NO algorithm is a function of temperature, rainfall, and growing season

(Yienger and Levy, 1995)

• Simple canopy model for Light adjustment• Summer/Winter factors based on freeze dates

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Details about MEGANv2.04

• Gridded emission factors based on global datasets for 11 species

• Emission factors for all other species based on 4 functional plant types

(broadleaf, needles, shrubs, etc)

• NO emission estimates are a function of temperature only

• Simple parameterization of canopy light attenuation in Version 2.04; Version

2.10 will have an explicit canopy model

• Monthly gridded leaf area indices (LAIs) used for seasonal variation

Guenther, A., T. Karl, et al. (2006). "Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)." Atmos. Chem. Phys. 6(11): 3181-3210.

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Isoprene Emissions(MG/yr)BEIS MEGAN

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Monoterpenes Emissions (Mg/yr)BEIS MEGANHot spot

decrease

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Sesquiterpenes Emissions (Mg/yr)BEIS MEGAN

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Methanol Emissions (Mg/yr)BEIS MEGAN

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Formaldehyde Emissions (Mg/yr)BEIS MEGAN

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Soil Nitric OxideBEIS MEGAN

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Summary of Spatial Differences

• Isoprene: Relative to BEIS, MEGAN generates higher isoprene in all areas, especially the southern U.S.

• Monoterpenes: MEGAN is lower in Canada, southwestern U.S., and northwestern U.S.

• Sesquiterpenes: MEGAN is lower in midwestern U.S. • Methanol: MEGAN is higher in all areas• Formaldehyde: MEGAN is lower in all areas, especially the

southwestern U.S.

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Percent Difference BEIS and MEGAN(based on 2003 annual emissions saprc99)

+ MEGAN is higher

- BEIS is higher

isoprene 60%

methanol 139%

monoterpenes -40%

acetone 12%

sesquiterpenes -19%

Nitric Oxide -72%

Formaldehyde -71%

OLE1 -63%

OLE2 -37%

RCHO -93%

ALK1 -92%

ALK2 -95%

ALK3 -63%

ethene 23%

carbon monoxide -14%

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Isoprene 36km daily domain totals 2003

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Monoterpenes 36km daily domain totals 2003

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Sesquiterpenes 36km daily domain totals 2003

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Methanol 36km daily domain totals 2003

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Formaldehyde 36km daily domain totals 2003

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Soil Nitric Oxide 36km daily domain totals 2003

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Summary

• Comparison of BEIS3.14 and MEGAN2.04 made for 2003 for SAPRC99 mechanism species

• MEGAN is higher for Isoprene, methanol, acetone, ethene

• BEIS is higher forMonoterpenes, sesquiterpenes, formaldehyde, other VOCs, soil NO

• BEIS has a more detailed soil NO algorithm• MEGAN and BEIS have different spatial patterns

(different normalized emission inputs)

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Future Work

• Compare CMAQ results for BEIS3.14 and MEGAN2.04 for 3 week period in 2003

• Incorporate MEGAN into CMAQ as an option compared to BEIS

• MEGANv2.10 is expected by the end of the year (will include updated canopy model)

• Eventually may replace BEIS with MEGAN

• Disclaimer: Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy