Photolysis mechanism
Here we link to pages describing the various versions of the FAST-J and FAST-JX photolysis mechanisms used in GEOS-Chem.
Photolysis mechanisms used in standard GEOS-Chem versions
The following photolysis mechanisms have been implemented in official releases of GEOS-Chem:
FAST-J
The FAST-J photolysis mechanism was used in GEOS-Chem versions prior to GEOS-Chem v10-01.
FAST-J is being currently being replaced by the FAST-JX v7.0 photolysis mechanism, which will ship with the standard GEOS-Chem v10-01 public release (slated for late 2014).
--Bob Y. 11:58, 20 May 2014 (EDT)
FAST-JX v7.0
The FAST-JX v7.0 photolysis mechanism is the newest version of the FAST-J software. It is being incorporated into GEOS-Chem v10-01 by Sebastian Eastham (MIT) and the GEOS-Chem Support Team. This is being done concurrently with the introduction of the UCX stratospheric-tropopsheric chemistry mechanism into GEOS-Chem.
--Bob Y. 11:58, 20 May 2014 (EDT)
VOC photolysis
Here I summarize VOC photolysis in Fast-JX v7.0
| Old reaction | Old rate | New reaction | New rate | Note |
|---|---|---|---|---|
| CH2O = HO2 + HO2 + CO | same | Significant increase by 10% to 20% | channel a | |
| CH2O = H2 + CO | same | increase by 6% to 15% | channel b | |
| PAN = 0.6MCO3 + 0.6NO2 + 0.4MO2 + 0.4NO3 | same | JPL2010 suggests two channels, in contrast to FastJX-v7.0, branching ratio follows IUPAC | ||
| ALD2 = MO2 + HO2 + CO | same | |||
| ALD2 = CH4 + CO | same | |||
| GLYX = 0.5H2 + CO + 0.5CH2O + 0.5CO | GLYX = H2 + 2CO GLYX = CH2O + CO |
Pressure dependence is now included | now 3 channels | |
| GLYX = 2.0CO + 2.0HO2 | same | Pressure dependence is now included | ||
| MACR = CO + HO2 + CH2O + MCO3 branching ratio = 0.5 |
same | |||
| MACR = MAO3 + HO2 branching ratio = 0.5 |
remove this channel | suggested by IUPAC, also consistent with Fast-JX v7.0 | ||
| MVK = PRPE + CO branching ratio = 0.6 |
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| MVK = MCO3 + CH2O + CO + HO2 branching ratio = 0.2 |
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| MVK = MO2 + MAO3 branching ratio = 0.2 |
MVK = MO2 + RCO3 | this channel was removed in FJX v7.0, but it shouldn't according to IUPAC. MAO3 is changed to RCO3 for carbon balance. | ||
| GLYC = CH2O + 2.0HO2 + CO | same | |||
| GLYC = CH3OH + CO | two more channels were added in FJX v7.0, but IUPAC only recommends this one | |||
| MEK = 0.85MCO3 + 0.85ETO2 + 0.15MO2 + 0.15RCO3 | same | two channels are merged into one reaction |
--Jmao 15:54, 20 May 2014 (EDT)
Photolysis mechanisms used in research versions of GEOS-Chem
The following photolysis mechanisms have been used in non-standard research versions of GEOS-Chem:
FAST-JX v6.2
The FAST-JX v6.2 photolysis mechanism was implemented into several research versions of GEOS-Chem by Jingqiu Mao (Princeton). But this version of FAST-J was never incorporated into the standard GEOS-Chem model.
--Bob Y. 11:58, 20 May 2014 (EDT)