Biogenic emissions

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MEGAN

Updated annual emission factor for Isoprene

In GEOS-Chem v7-04-12 (as of Sep 2007), we use the older annual emission factors (AEF's) for isoprene.

However, Alex Guenther (personal communication) uses the current isoprene AEF's were obsolete and that we should be using updated isoprene AEF's. Dylan Millet has created an updated AEF file for isoprene but it has not been implemented into the standard GEOS-Chem code yet. (Some folks have already used the new AEF's in their research codes.) The new AEF's are currently scheduled to be implemented in GEOS-Chem beta release v8-01-02.

Reference: Guenther, A., T. Karl, P. Harley, C. Wiedinmyer, P.I. Palmer, and C. Geron (2006), Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature), Atmospheric Chemistry and Physics, 6, 3181-3210.

MEGAN Website: http://bai.acd.ucar.edu/Megan/index.shtml

--Bob Y. 11:57, 2 December 2008 (EST)

Impact on isoprene emissions

Here are some presentations which document the change in the MEGAN biogenic emissions of isoprene caused by switching to the new annual emission factor (AEF) file.

  1. HERE is a comparison (by Dylan Millet) of isoprene emissions from GEIA vs. old MEGAN (i.e. v8-01-03 and prior) vs. new MEGAN (v8-01-04 and later, with updated baseline annual emission factors from Alex Guenther). 2001, 2x2.5, v7-04-11, GEOS-4 met.
  2. HERE is a comparison (by Rynda Hudman) on the effects of MEGAN on the v7-02-04 benchmark.

NOTE: The newer AEF's for isoprene are now used in GEOS-Chem v8-01-04 and higher.

--Bob Y. 09:39, 3 March 2009 (EST)

MEGAN documentation

Dylan Millet (dbm@umn.edu) wrote: There was discussion at the 2009 GC User's Meeting about divergent implementations of MEGAN and the need to better document what we're doing in GEOS-Chem. Here is a description (current as of 5/1/2009) for people to use and modify in their publications.

We use the Model of Emissions of Gases and Aerosols from Nature (MEGAN) [Guenther et al., 2006] to derive isoprene emissions for each GEOS-Chem grid square [Palmer et al., 2006; Millet et al., 2008]. MEGAN computes emissions for plant functional types (PFTs) as a function of temperature, solar radiation, leaf area index (LAI), and leaf age. Fractional coverage for each PFT and vegetation-specific emission factors (EFs) are based on the MEGAN landcover data (PFT v2.0, EFs v2.0). The temperature effect on leaf emissions is computed as a function both of the current temperature and the average temperature over the previous 15 days [Guenther et al., 1999]. The implementation also includes a 5-layer canopy model [Guenther et al., 1999] to account for the effects of direct and diffuse PAR on sunlit and shaded leaves. We explicitly consider the effect of leaf age on emissions, with leaf age fractions for new, young, mature, and old leaves estimated for each model grid square from local LAI and temperature changes according to Guenther et al. [2006]. We drive MEGAN in GEOS-Chem with assimilated surface air temperature and photosynthetically active radiation (direct and diffuse) observations from the NASA Global Modeling and Assimilation Office (GMAO). Monthly mean LAI values are based on AVHRR satellite data [Buermann et al., 2002].
References
Buermann, W., Wang, Y.J., Dong, J.R., Zhou, L.M., Zeng, X.B., Dickinson, R.E., Potter, C.S., and Myneni, R.B.: Analysis of a multiyear global vegetation leaf area index data set, J. Geophys. Res., 107, 4646, doi:10.1029/2001JD000975, 2002.
Guenther, A., Baugh, B., Brasseur, G., Greenberg, J., Harley, P., Klinger, L., Serca, D., and Vierling, L.: Isoprene emission estimates and uncertainties for the Central African EXPRESSO study domain, J. Geophys. Res., 104, 30625-30639, 1999.
Guenther, A., Karl, T., Harley, P., Wiedinmyer, C., Palmer, P.I., and Geron, C.: Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature), Atmos. Chem. Phys., 6, 3181-3210, 2006.
Millet, D.B., Jacob, D.J., Boersma, K.F., Fu, T.M., Kurosu, T.P., Chance, K., Heald, C.L., and Guenther, A.: Spatial distribution of isoprene emissions from North America derived from formaldehyde column measurements by the OMI satellite sensor, J. Geophys. Res., 113, D02307, doi:10.1029/2007JD008950, 2008.
Palmer, P.I., Abbot, D.S., Fu, T.M., Jacob, D.J., Chance, K., Kurosu, T.P., Guenther, A., Wiedinmyer, C., Stanton, J.C., Pilling, M.J., Pressley, S.N., Lamb, B., and Sumner, A.L.: Quantifying the seasonal and interannual variability of North American isoprene emissions using satellite observations of the formaldehyde column, J. Geophys. Res., 111, D12315, doi:10.1029/2005JD006689, 2006.

--Dbm 14:48, 1 May 2009 (EDT)

GEIA

Clarification about isoprene from grasslands

Prasad Kasibhatla (psk9@duke.edu) wrote:

In emissdr.f, there are the following 2 lines: 
              ! Isoprene emissions from grasslands (use GEIA always)
              GRASS = EMISOP_GRASS(I, J,IJLOOP, SUNCOS, TMMP, XNUMOL_C)
But it looks like further down when emissions of isoprene are saved into an array, the value stored in GRASS is not used: 
              IF ( IDTISOP /= 0 ) THEN
                 ! NOTE: Don't save into EMISRR for the tagged CO
                 ! simulation (jaf, mak, bmy, 2/14/08)
                 IF ( NO_TAGCO ) THEN
                    EMISRR(I,J,IDEISOP) = EMISRR(I,J,IDEISOP) +  &
                                         ( EMIS / DTSRCE )
                 ENDIF
              ENDIF
I am a bit confused as to what the grassland isoprene emissions are in relation to non--grassland emissions.

May Fu (cetmfu@polyu.edu.hk) replied:

For GEIA, emisop.f calculates the total isoprene emission, including those from grassland. emisop_grass.f calculates the isoprene emission ONLY from grassland and stores it into variable GRASS. You can see this in emisop_grass.f, where the grassland grids are picked out, and then emission factors for grassland is used to calculate the emission. The reason we need to call emisop_grass.f is because the grassland acetone emission is scaled from the grassland isoprene emission.
In MEGAN, routine GET_EMISOP_MEGAN in megan_mod.f calculates the total isoprene emission. But because the MEGAN emission factors were given as a gridded map, not as a function as land types, there is no easy way to determine the emission from grassland. So we use the GEIA isoprene emission for grassland to calculate acetone emission ONLY, regardless of whether you choose GEIA or MEGAN for isoprene itself.
In short, the call to function emisop_grass.f indeed should NOT be counted as additional isoprene source.

--Bob Y. 12:04, 2 December 2008 (EST)

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