Directions for running MEGAN v2.04 online in WRF-Chem

Compiling

1) Compile real.exe and wrf.exe like normal.

2) Compile bioemiss_conv_megan2.exe by issuing the command from the WRFV2.2 directory:

>compile bioemiss_conv_megan2

This will create the file chem/bioemiss_conv_megan2.exe

“Preprocessing”

3) Obtain a file named MEGAN_input_WRFchem_form3.txt from Christine Wiedinmyer; change the file name to MEGAN_input_WRFChem.txt. This file is domain/grid dependent; therefore, you’ll need to provide her the information (a sample wrfout_d01_<date> or wrfinput_d01 file would suffice).

4) Run real.exe with bio_emiss_opt =1 (in namelist.input) (from 00:00:00 UTC for 23 hours – not sure if this part matters). This step will create a file named wrfinput_d01 that does not contain any input for MEGAN.

5) Run bioemiss_conv_megan2.exe in the directory where the files MEGAN_input_WRFChem.txt (from step 3) and wrfinput_d01 (from step 4) are located. This step will create a file named wrfbiochemi_d01, which only needs to be created once for each simulation domain.

Running WRF-Chem

6) Run real.exe like normal in a directory that contains the file wrfbiochemi_d01 (from step 5), but with bio_emiss_opt=3. With bio_emiss_opt=3, real.exe will create wrfinput_d01 containing inputs required for running MEGAN online. (Note: wrfbiochemi_d01 and wrfinput_d01 will also include variables for running BEIS3.13, but the values for BEIS variables will all be all zero; you’ll need to create a different wrfbiochemi_d01 file if you want to use bio_emiss_opt=2.)

7) Now, you can run wrf.exe with MEGAN emissions calculated online using bio_emiss_opt=3.

Output Variables for Biogenic Emissions

• The following variables were added to the Registry/registry.chem to output emissions rates calculated by MEGAN v2.04:

Variable Name Species

mebio_isop isoprene

mebio_apin a-pinene

mebio_bpin b-pinene

mebio_bcar b-caryophyllene

mebio_acet acetaldehyde and ethanol

mebio_mbo MBO ( (2-methyl-3-ene-2-ol)-methylbutenol)

mebio_no NO, NH₃, and N₂O

These variables are in units of mol km^-2 hr^-1. The species classification follows Table 2 of the MEGAN v2.0 Documentation.

• The variable e_bio was originally used for the Guenther biogenic emissions scheme (bio_emiss_opt=1). For bio_emiss_opt=3, e_bio is “borrowed” by the MEGAN emissions module as diagnostic variables to output biogenic emission rates for mechanism species. For example, e_bio(i,j,p_iso-1) is the emission rate for isoprene; for CBMZ, e_bio(i,j,p_iso-1) includes emissions of isoprene, 2xmonoterpenes, 3xsesquiterpenes, etc. When bio_emiss_opt=3, e_bio is strictly a diagnostic variable and is not used outside of SUBROUTINE bio_emissions_megan2. e_bio is in units of ppm m min^-1.

The use of e_bio is unchanged from previous WRF-Chem versions if bio_emiss_opt=1 or bio_emiss_opt=2.

• The following variables were originally used for the BEIS3.11 biogenic emissions scheme (bio_emiss_opt=2):

ebio_iso

ebio_oli

ebio_api

ebio_lim

ebio_hc3

ebio_ete

ebio_olt

ebio_ket

ebio_ald

ebio_hcho

ebio_eth

ebio_ora2

ebio_co

ebio_no

For bio_emiss_opt=3, these variables are “borrowed” by the MEGAN emissions module as diagnostic variables to output biogenic emission rates for mechanism species. For example, ebio_iso is the emission rate for isoprene; for CBMZ, ebio_iso includes emissions of isoprene, 2xmonoterpenes, 3xsesquiterpenes, etc. When bio_emiss_opt=3, ebio_???’s are strictly diagnostic variables and are not used outside of SUBROUTINE bio_emissions_megan2. ebio_???’s are in units of mol km^-2 hr^-1.

Note: ebio_xyl is not used because there are no biogenic emissions for xylene.

The use of ebio_???’s is unchanged from previous WRF-Chem versions if bio_emiss_opt=1 or bio_emiss_opt=2.