GEOS-Chem chemistry mechanisms

On this page, we provide an overview of the chemistry mechanisms used in GEOS-Chem.

NOx-Ox-hydrocarbon-aerosol chemistry and variants

The NOx-Ox-hydrocarbon-aerosol (aka "full-chemistry") simulations have undergone several updates in recent GEOS-Chem versions. We provide a summary of recent updates made to the various mechanisms.

Mechanisms in GEOS-Chem v9-01-03 and prior versions

In GEOS-Chem v9-01-03, users could select from one of four pre-defined chemistry mechanisms:

Mechanism	Description	Nickname	Solvers
standard	NOx-Ox-hydrocarbon-aerosol species PLUS bromine species	Full-chemistry or fullchem	SMVGEAR KPP
SOA	NOx-Ox-hydrocarbon-aerosol species PLUS secondary organic aerosol species	SOA	SMVGEAR KPP-
Dicarbonyls	NOx-Ox-hydrocarbon-aerosol species PLUS dicarbonyl species	Dicarbonyls	SMVGEAR only
isoprene	NOx-Ox-hydrocarbon-aerosol species PLUS isoprene oxidation products	Caltech isoprene scheme, Paulot isoprene scheme	SMVGEAR KPP

The bromine tracers and species were added to the standard mechanism just prior to the release of GEOS-Chem v9-01-03.

-Bob Y. 17:00, 30 September 2013 (EDT)

Mechanisms in GEOS-Chem v9-02 and later versions

Several modifications were made to the above-mentioned chemistry mechanisms in GEOS-Chem v9-02, as listed below:

Mechanism	Description	Nickname	Solvers
standard	NOx-Ox-hydrocarbon-aerosol species PLUS bromine species PLUS Updates to inorganic chemistry reactions (cf. JPL 10-6) PLUS Methyl peroxy nitrate chemistry PLUS Isoprene oxidation species chemistry (aka "Caltech isoprene scheme") PLUS Fix RO2+HO2 rate constant PLUS Increase of NO3 uptake by aerosol PLUS Removal of NOx and Ox partitioning PLUS Inhibition of N2O5 uptake by nitrate aerosol PLUS Improved HO2 uptake by aerosol	Full-chemistry or fullchem	SMVGEAR KPP
SOA	Everything in the "standard" simulation listed above PLUS Updated SOA species PLUS Semi-volatile primary organic aerosol (OPTIONAL)	SOA	SMVGEAR KPP-
Dicarbonyls	NOx-Ox-hydrocarbon-aerosol species PLUS dicarbonyl species	Dicarbonyls	SMVGEAR only

Starting with v9-02, family tracers (NOx, Ox) have now been removed from all GEOS-Chem mechanisms. The individual family members (NO, NO2, O3, etc.) are now carried as individual advected tracers and chemical species. Also, the isoprene mechanism from v9-01-03 now has been folded into the standard mechanism.

--Bob Y. 09:56, 1 October 2013 (EDT)

Chemistry mechanisms in GEOS-Chem v10

We propose adding the Unified tropospheric-stratospheric Chemistry eXtension (UCX) mechanism into the release following v9-02. UCX, which was developed by Steven Barrett's group (the Lab for Aviation Environment at MIT), combines the existing GEOS-Chem "standard" mechanism (based on v9-01-03) with several new stratospheric species and reactions.

Because UCX will be a major update to GEOS-Chem, we propose naming the version in which it ships to GEOS-Chem v10-01. This will make it easier to denote versions that contain UCX from versions that do not.

--Bob Y. 10:04, 1 October 2013 (EDT)