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)

What are the major 

differences in these two 

Office of Research and Development

National Exposure Research Laboratory | Atmospheric Modeling and Analysis Division| 

George Pouliot

7

th Annual CMAS Conference

7 October 2008 

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, ...
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

Topics to be Discussed

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3. Temporal differences between the two models 

4. Future Work
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)

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• Simple canopy model for Light adjustment

• Summer/Winter factors based on freeze dates
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; 

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• 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.
Isoprene Emissions(MG/yr)

BEIS MEGAN

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Biogenic Isoprene

Anthropogenic Isoprene

Other Biogenic VOCs

Other Anthropogenic VOCs
Monoterpenes Emissions (Mg/yr)

BEIS Hot spot MEGAN

decrease

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Biogenic Monoterpenes

Anthropogenic

monoterpenes

Other Biogenic VOCs

Other Anthropogenic VOCs
Sesquiterpenes Emissions (Mg/yr)

BEIS MEGAN

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Biogenic sesquiterpenes

Anthropogenic

sesquiterpenes

Other Biogenic VOCs

Other Anthropogenic VOCs
Methanol Emissions (Mg/yr)

BEIS MEGAN

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Biogenic Methanol

Anthropogenic Methanol

Other Biogenic VOCs

Other Anthropogenic VOCs
Formaldehyde Emissions (Mg/yr)

BEIS MEGAN

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Biogenic formaldehyde

Anthropogenic formaldehyde

Other Biogenic VOCs

Other Anthropogenic VOCs
Soil Nitric Oxide

BEIS MEGAN

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Anthropogenic Nox

Biogenic Nox
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. 

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• 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. 
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%

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Formaldehyde -71%

OLE1 -63%

OLE2 -37%

RCHO -93%

ALK1 -92%

ALK2 -95%

ALK3 -63%

ethene 23%

carbon monoxide -14%
Isoprene 36km daily domain totals 2003

2500

3000

3500

4000

4500

ISOPRENE (Mmol/day)

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0

500

1000

1500

2000

1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361

DAY OF THE YEAR

ISOPRENE (Mmol/day)

MEGAN BEIS
Monoterpenes 36km daily domain totals 2003

300000

400000

500000

600000

MONOTERPENES (kmol/day)

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0

100000

200000

300000

1 22 43 64 85 106 127 148 169 190 211 232 253 274 295 316 337 358

DAY OF YEAR

MONOTERPENES (kmol/day)

MEGAN BEIS
Sesquiterpenes 36km daily domain totals 2003

20000

25000

30000

35000

40000

45000

50000

SESQUITERPENE (kmol/day)

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0

5000

10000

15000

20000

1 22 43 64 85 106 127 148 169 190 211 232 253 274 295 316 337 358

DAY OF YEAR

SESQUITERPENE (kmol/day)

MEGAN BEIS
Methanol 36km daily domain totals 2003

1500

2000

2500

3000

Methanol (Mmol/day)

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0

500

1000

1500

1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361

DAY OF YEAR

Methanol (Mmol/day)

MEGAN BEIS
Formaldehyde 36km daily domain totals 2003

150

200

250

300

FORMALDEHYDE (kmol/day)

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0

50

100

150

1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361

DAY OF THE YEAR

FORMALDEHYDE (kmol/day)

MEGAN BEIS
Soil Nitric Oxide 36km daily domain totals 2003

150000

200000

250000

NO FLUX (kmol/day)

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0

50000

100000

1 22 43 64 85 106 127 148 169 190 211 232 253 274 295 316 337 358

DAY OF THE YEAR

NO FLUX (kmol/day)

MEGAN BEIS
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, 

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• 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)
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 

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• 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