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
MVK = MCO3 + CH2O + CO + HO2 branching ratio = 0.2
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)