GEOS-Chem chemistry mechanisms
On this page, we provide an overview of the chemistry mechanisms used in GEOS-Chem.
Contents
Overview
GEOS-Chem can perform many different types of chemical simulations, including:
- Several detailed ozone chemistry mechanisms
- Specialty simulations for tracers with simpler chemistry, including
- Radon-Lead-Beryllium
- Carbon gases (CO, CO2)
- Mercury
- Methane
- etc.
You may find more information about each of these mechanisms in the subsections below.
--Bob Y. 10:08, 1 October 2013 (EDT)
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 these updates in this section.
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 tropospheric chemistry mechanisms:
| Mechanism | Description | Nickname | Solvers |
|---|---|---|---|
| standard |
|
Full-chemistry, fullchem |
|
| SOA |
|
SOA |
|
| Dicarbonyls |
|
Dicarbonyls |
|
| isoprene |
|
Caltech isoprene scheme, Paulot isoprene scheme |
|
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 tropospheric chemistry mechanisms in GEOS-Chem v9-02, as listed below:
| Mechanism | Description | Nickname | Solvers |
|---|---|---|---|
| standard |
|
Full-chemistry, fullchem |
|
| SOA |
|
SOA |
|
| Dicarbonyls |
|
Dicarbonyls |
|
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)
Stratospheric chemistry
GEOS-Chem was historically developed as a model of tropospheric chemistry and composition. The above-mentioned chemistry mechamisms in GEOS-Chem v9-01-03 and in GEOS-Chem v9-02 only solve the chemical reaction matrix within the troposphere. In order to prevent tropospheric species from accumulating in the stratosphere and being transported back into the troposphere, we have implemented the following simple stratospheric chemistry schemes:
- Linoz stratospheric ozone chemistry
- Application of monthly-mean prod/loss rates archived from the GMI model
Linoz only applied to ozone. The simple linearized stratospheric chemistry, which uses production and loss rates archived from the GMI model, is applied to all other species. (NOTE: The user has the option to disable Linoz and use the archived GMI prod/loss rates for ozone, but this is typically not done.)
In the near future, we will be adding the UCX chemistry mechanism into GEOS-Chem. UCX combines both stratospheric and tropospheric reactions and species into a single unified mechanism.
--Bob Y. 12:11, 1 October 2013 (EDT)
Planned updates
The following chemistry updates are slated for inclusion to GEOS-Chem following the v9-02 release.
Mechanisms in GEOS-Chem v10
We propose adding the Unified tropospheric-stratospheric Chemistry eXtension (UCX) mechanism into the release following GEOS-Chem v9-02. UCX, which was developed by Steven Barrett's group (the MIT Laboratory for Aviation and the Environment), 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)
Flexchem
We also propose to add a cleaner implementation of KPP into GEOS-Chem. This implementation, which we have named Flexchem, will allow users to customize the chemical mechanism according to their research interests. Flexchem will remove the existing SMVGEAR and KPP infrastructure, and all related input files (i.e. globchem.dat, mglob.dat, etc.)
As of this writing (Oct 2013), Flexchem is still under development. We hope to have it installed in a version of GEOS-Chem sometime in 2014.
--Bob Y. 10:17, 1 October 2013 (EDT)
Mechanisms for aerosol microphysics
GEOS-Chem contains two different aerosol microphysics packages: TOMAS and APM.
TOMAS
As of this writing (Oct 2012), the TOMAS aerosol microphysics scheme has been more tightly integrated into GEOS-Chem v9-02. It adds several size-resolved aerosols (you may select from 12, 15, 30, or 40 size bins) to the standard GEOS-Chem "full-chemistry" simulation.
--Bob Y. 11:34, 1 October 2013 (EDT)
APM
The APM aerosol microphysics is currently being re-integrated into GEOS-Chem. APM needs to be brought up to date with the recent update for secondary organic aerosols with semi-volatile primary organic aerosols. The work is ongoing as of October 2012.
--Bob Y. 11:32, 1 October 2013 (EDT)
Specialty simulations
GEOS-Chem can also perform "specialty simulations" (aka "offline simulations"). These are simulations for species having simpler chemistry mechanisms that do not require the use of a full chemical solver such as SMVGEAR or KPP. Many of these simulations rely on oxidant fields (O3, OH) saved out from a previous "full-chemistry" simulation.
List of specialty simulations
The following table provides links to information about the available specialty simulations in GEOS-Chem. Please note that some of these simulations are out of date and will require some work in order to be brought back to the state-of-the-science. Contact the relevant GEOS-Chem Working Group for more information.
| Category | Simulation | Status | Contact |
|---|---|---|---|
| Aerosols | Aerosol-only simulation (can be customized to include only the aerosol species you want) |
Up-to-date | Aerosols Working Group |
| Carbon Gases | C2H6 simulation | Needs attention | Carbon Cycle Working Group |
| Carbon Gases | CH3I simulation | Needs attention | Carbon Cycle Working Group |
| Carbon Gases | CH4 simulation | Up-to-date | Carbon Cycle Working Group |
| Carbon Gases | Tagged CO simulation | Up-to-date | Carbon Cycle Working Group |
| Carbon Gases | CO2 simulation | Up-to-date | Carbon Cycle Working Group |
| Carbon Gases | OCS simulation | Under development | Carbon Cycle Working Group |
| Hg and POPs | Hg simulations
|
Up-to-date | Hg and POPs Working Group |
| Hg and POPs | Persistent Organic Pollutants (POPs) simulation | Up-to-date | Hg and POPs Working Group |
| Ozone | Tagged Ox simulation | Needs attention | Chemistry Working Group |
| Radionuclides | Rn-Pb-Be simulation | Up-to-date | Transport Working Group |
| Radionuclides | H2-HD isotope simulation | Needs attention | Transport Working Group |
Note to developers
The GEOS-Chem Support Team will be happy to assist you with technical issues (i.e. debugging, or answering questions about coding) pertaining to specialty simulations. However, we expect the GEOS-Chem user community to be responsible for the scientific content and validation of offline simulations, and shall:
- Provide the appropriate code, data, and documentation for offline simulations to the GEOS-Chem Support Team
- Benchmark and evaluate GEOS-Chem offline simulations
- Notify the GEOS-Chem support team of any bugs or technical issues.
--Bob Y. 10:59, 1 October 2013 (EDT)
Analytical tools
Process analysis diagnostics
Barron Henderson (U. Florida) has created a software package for process analysis diagnostics. He writes:
Process-based Analysis examines the change in each species due to each process and reaction. Models predict atmospheric state, which in a time-series can be used to create net-change of each species. What this cannot tell us, is which processes led to that change. To supplement state (or concentration), GEOS-Chem has long archived emissions and employed advanced diagnostics to predict gross chemical production or loss. Process Analysis goes a step further archiving grid-cell budgets for each species, and decomposing gross production/loss into individual reaction contributions. Process Analysis extensions are currently available in CAMx, WRF-Chem, CMAQ, and now GEOS-Chem. This allows for direct comparisons of models at a fundamental, process level.
To obtain this software, please contact Barron Henderson directly.
--Bob Y. 12:26, 1 October 2013 (EDT)
