This page provides files and documentation for the SAPRC-22 mechanism, which is the latest version of the the SAPRC series of gas-phase atmospheric mechanisms for airshed models. SAPRC-22 is an updated version of SAPRC-18, which in turn is an updated version of the widely used SAPRC-07
mechanism. As with previous SAPRC mechanisms, the representation of
reactions of almost all of the organics were derived using the SAPRC mechanism
generation system
(MechGen), which has been updated and documented prior to its use to
derive SAPRC-22, though the documenation is still under review. Therefore, SAPRC-22 incorporates some potentially
significant updates to the organic chemistry, which the underlying
chemistry incorporated in MechGen now being documented in a separate
paper that is being submitted for publication. The standard version of
SAPRC-22 is a suitable replacement to SAPRC-07, with more updated
chemistry, more tracking of toxic species, and comparable size and
computer demands, being significantly smaller in size than SAPRC-18 but representing similar chemical detail.
Please contact me
if you are interested in possibly using the mechanism and have
downloaded the documentation and files, so I can notify you if
corrections are needed or if there are new versions of the
documentation and associated files. However, this should be the final version unless needs for corrections are found.
Please note:
The current version of the SAPRC-22 mechanism reflects an update made in July, 2025 to reflect recent changes made to MechGen
in the process of completing its documentation. This differs from the
version uploaded in June, 2024 because the changes to MechGen causes
changes in some details of mechansims of model species representing
organic compounds. In addition, IEPOX, a secondary product formed from
Isoprene that may impact SOA formation, was added as a model species.
Note that this version is different from that described in the
available SAPRC22 documentation, dated September, 2023. Please
upload
new versions of these files if you have versions that were uploaded
before July 24, 2025. See the file dates on the table below. Note also
that only
the "standard" version of SAPRC-22 is now recommended for use in
airhsed models, are the "SAPRC22F" files are no longer available. This
version of SAPRC-22 is included with the distributed SAPRC software and files.
| Item | Description |
| SAPRC22.xls | A spreadsheet that can be used to create files implementing the current version of of SAPRC-22. It contains full listings of the model species and rate constant parameters and macros used to produce the distributed .RXN, .MEC, or .KPP files. Also contains inputs and outputs for a test calculating testing implementation of the mechanism, and tables giving assignments of model species to compounds and lists of compounds used to derived mechanisms of lumped species. Dated July 26, 2025. |
| SAPRC22.RXN | Reactions in standard SAPRC-22 for atmospheric simulations in SAPRC format. Created June 22, 2024.. |
| SAPRC22.mec | Reactions in standard SAPRC-22 for atmospheric simulations in CMAQ mech.def format. Created June 22, 2024 |
| SAPRC22.def SAPRC22.eqn SAPRC22.spcx | Files for implementing standard SAPRC-22 for test simulations using the KPP solver (gives photolysis rates calculated for Jeffries STD640 light model, Z=0, full sun). Note that the procedures used to create KPP files have not been tested to see if this was done properly and I'm unsure how to define photolysis reactions for KPP. Please contact me if you use these files and let me know how well they worked. Created June 22, 2024.. |
| PHF.zip | Absorption cross section and quantum yields for photolysis reactions. Zip file created July 6, 2019, which is when the file C2CHOabs.phf replaced C2CHO.phf when the mechanism was updated in July, 2023. Newest file other than that is dated October 14, 2016, but is still applicable to this version. |
| S22doc.pdf | Available documentation of the mechanism, dated September 29, 2023. Describes the versions of SAPRC-22 that were developed and how they differ from each other and previous versions, discusses how the mechanisms for the organics were derived from the mechanism generation system, documents the base mechanism for inorganics and common organics, discusses box model test calculations comparing versions of the mechanism, and provides information on how to implement the mechanism. Note that the current SAPRC-22 mechanism has some differences with the version listed in this report, but most of the documentation is still applicable. The version designated "standard" in the report is the starting point for the current SAPRC-22. The "full" version has not been updated because it is not recommended for use, since it gives essentially the same predictions as the standard version but it takes much more simulation time. |
| S22supp.xls S22Supp-23.xls | This is an electronic supplement to S22doc.pdf, containing the larger tables and complete mechanism listings that are not in the main document. It also includes inputs and outputs of a test calclation to verify correct implementation of this mechanism. The file S22Supp-23.xls is the original version that goes with the 2023 report, S22doc.pdf. The file S22supp.xls includes tables updated to the current version of the mechanism, and is dated July 25, 2025. |
Related Links | |
| MechGen web page | Web page with information about and a link to access the SAPRC mechanism generation system (MechGen) that was used to develop this version of SAPRC-22. The online version allows you to generate reactions for individual compounds and view the associated documentation for the data or estimation methods used. It also allows you to view detailed mechanisms for all compounds that were used to derive SAPRC-22, including components in mixtures used to derive mechanisms of lumped model species. It also gives documentation of the various estimation methods and assignments used. This page also has links to papers documenting MechGen, and links to obtain a basic web users guide, a complete users manual, and files to install the MechGen software. |
| SAPRC software and files website | Access to files for downloading SAPRC software and data files to conduct simulations and evaluate chamber experiments using various mechanisms, including SAPRC-22 files. Updated July 24, 2025. |
| Speciation website | Access to database and files giving assignmnets mapping categories used in emissions profile database to model species in various mechanisms. This now includes assignments for processing emissions for SAPRC-22 (they are the same for both versions). Updaed March 9, 2023. |
| Date | |
| July 26, 2025 | Updated SAPRC-22 files to the current version, which reflects recent changes made to MechGen in the process of completing its documentation, and the addition of an IEPOX model species. |
| July 7, 2024 | Updated link to information about MechGen |
| July 23, 2024 | New versions of the SAPRC-22 mechanisms, reflecting updates to the mechanism generation and lumping procedures and correcting errors, have been made available. |
| Nov. 4, 2023 Nov 14 | Available documentation for MechGen and the status of the manuscript describing the chemical estimates and assignments it uses were updated. Made available on Nov. 4 and updated Nov 14. |
| Sept. 9 | Mechanism was updated to incorporate an updated estimation method for autooxidation reactions of peroxy radicals that were implemented in MechGen since the last version was developed. These updates resulted in increased predicted importance of autooxidation reactions and resulted in a significant increase in size for "full" version of the mechanism, making itimpractical for use in most modeling applications. However, an improved method for lumping peroxy radical reactions was incorporated in the standard version, making use of the full version not necessary for most applications, so only the standard version is now recommended for use. |
| July 13 | Added new model species to better represent formation of non-volatile products from catechols. |
| July 7 | Corrected errors in treatment of aldehyde photolysis to make them more consistent with current recommendations. Also, corrected error in MechGen that resulted in underpredictions of formations of catechols from phenols. |
| July 1 | Corrected an error in MechGen that caused fast isomerization reactions of acyl peroxy radicals to be ignored. The version uploaded on July 1 should be the final version unless more needs for corrections are found. |
| April 7 | Updated version of the report and mechanism, that incorporates results of external reviews and some error fixes. These are superceded by later versions. |
| Mar. 8, 2023 | New version of the mechanism and documentation report were updated. These are superceded by later versions. |
| Dec. 30, 2022 | This page was created and the first versions of the mechanism and documentation files were uploaded. These are superceded by later versions. |