SAPRC Atmospheric Chemical Mechanisms and VOC Reactivity Scales

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Please note: Several errors were found in the SAPRC-07 mechanisms, including one that has small but non negligible effects on ozone and other predictions and VOC reactivity scales. The documentation and files implementing the mechanism have been updated. Please replace all documentation reports and files dated prior to January 25, 2010. See below for a description of the updates.

Click here for the files implementing this mechanism for CMAQ and SAPRC modeling systems. Click here for files and programs implementing the mechanism in the SAPRC box and chamber modeling software

The updated version of the SAPRC-99 mechanism, designated SAPRC-07, was completed in August, 2007, and made available on this site at that time. Since then the mechanism and documentation have been updated several times. Given below are the current versions of the available documentation of this mechanism and and its associated reactivity scales.

Peer reviewed manuscripts documenting the full and condensed SAPRC-07 mechanism have been accepted for publication in Atmospheric Environment and are now in press. Although the publication issues have not yet been determined, they are available at the Atmospheric Environment Issues web site through the "Articles in Press" link. The titles and DOI numbers of the manuscripts are: "Development of the SAPRC-07 chemical mechanism," doi:10.1016/j.atmosenv.2010.01.026, and "Development of a condensed SAPRC-07 chemical mechanism," doi:10.1016/j.atmosenv.2010.01.024.

Final report documenting the mechanism, its evaluation, and the updated reactivity scales. Available in Microsoft Word (saprc07.doc) and PDF (saprc07.pdf) formats. The current version is dated January 27, 2010.

Tables in the Appendices to the report Excel format (saprc07.xls). This includes the large tables not in the main body of the report, the VOC reactivity tabulation (MIR and other scales) and uncertainty classifications in Table B-1 of the report, and other tables. The current version is dated May 11, 2011.

The table with the MIR and other reactivity data is also available in a separate Excel file (scales07.xls) that contains only this table and the associated footnotes. This includes the data in (saprc07.xls) that may be more useful for those only interested in the reactivity data, and is also more up-to-date. It also contains reactivity values for individual city-specific MIR, MOIR, and EBIR scenarios that are not in saprc07.xls. Note: The current version is dated May 11, 2011. It includes new VOCs added for the 2009-2010 MIR update discussed in the MIR10 report discussed below. The only change relative to the version dated March 31, 2010, concerns the reactivity of ethyl methyl ketone oxime (EMKO), which was revised based on new data in a recent report to the CARB.

A report discussing the update to the MIR values resulting from the use of the SAPRC-07 mechanism and describing the revised method used to calculate MIR values for the 24 hydrocarbon "bins" used in some CARB reactivity-based regulations is available in Microsoft Word (MIR10.doc) and PDF (MIR10.pdf) formats. The spreadsheet (HCcalc.xls) used to derive the compositions used to calculate the reactivities of the 24 hydrocarbon bins, which is referenced in the report, is also available. This can also be used to estimate compositions and reactivities of other hydrocarbon mixtures given type distributions and boiling point ranges. The current versions of the spreadsheet and report are Jaunary 28, 2010. They incorporate the updates in the SAPRC-07 mechanism and reactivity scale as of this date, and should replace earlier versions.

The CARB contracted Merched Azzi, Richard Derwent, Robert Harley, and William Stockwell to conduct peer reviews of the SAPRC-07 mechanism.  These reviews are available at the CARB RSAC website. My response to these reviews is available in Microsoft word (RespRev.doc) and PDF (RespRev.pdf) formats. This document is dated March 20, 2009.

The final report documenting the condensed versions of the SAPRC-07 mechanism is available. Available in Microsoft Word (csaprc07.doc) and PDF (csaprc07.pdf) formats. The report, which was revised to incorporate recent updates to the base mechanism,  is dated January 28, 2010 and supersedes earlier versions. The SAPRC-07 condensed mechanisms have been updated to be consistent with the current (1/25/10) version of SAPRC-07 and the files implementing these updated mechanisms are available on the "SAPRC-07 Chemical Mechanism and Emissions Speciation Files for CMAQ" page. The revised versions after July 13, 2009, were modified to retain methane, so it can be used for cleaner air simulations.

The maximum ozone impacts of NO, NO2, and HONO, which have their highest positive impacts on ozone under very low NOx conditions, have been added to the reactivity tabulation in scales07.xls. These are more appropriate to use than MIR values for these NOx species for applications, such as life cycle analyses, where maximum ground-level ozone impacts of NOx are compared to those for VOCs. A report documenting the derivation of these NOx Maximum Incremental Reactivity (NMIR) values is available in Microsoft Word (NOxMIR.doc) and PDF (NOxMIR.pdf) formats. This report has not been updated to the current version of the mechanism, but the NMIR the values tabulated in scales07.xls have been updated.

A version of the distributed files and programs have been prepared, including files for the various versions of the SAPRC-07 mechanism (including condensed versions) and files to conduct chamber simulations and test calculations. This contains the corrected version of the mechanism and should replace any versions of the mechanism downloaded prior to January 25, 2010. Some of the programs have been updated as well. See the SAPRC mechanism files distribution page to download the files and for more information. 

Changes and additions to mechanism, reactivity scales, or documentation:

5/11/11: The reactivity scale in scales07.xls and saprc07.xls has been updated to include new reactivity values for ethyl methyl ketone oxime (EMKO), which was revised based on new data in a recent report to the CARB. The reactivity values for all other VOCs are unchanged.

2/4/11: SAPRC-07 box modeling programs and files updated and programs and files needed to do reactivity scale calculations were added. See SAPRCfiles.pdf for a discussion of the files and their installation and use.

4/20/10: Duplicate entries of several perfluoro ethers, with incorrect MIR and other reactivity values, have been deleted from the reactivity tabulations in Table B-1 in saprc07.xls and in scales07.xls. The deleted entries, with incorrect reactivity values, were for "methyl-nonafluoro-butyl ether", "methyl-nonafluoro-isobutyl ether", "ethyl nonafluorobutyl ether", and "ethyl nonafluoroisobutyl ether". These are the same compounds as methoxy-perfluoro-n-butane, methoxy-perfluoro-isobutane, ethoxy-perfluoro-n-butane, and ethoxy-perfluoro-isobutane, which are also on the reactivity list but with the correct reactivity values. The correction to the table was made on 3/31/10 but not uploaded to the website until 4/20/10. Note that the reactivity tabulations in saprc07.doc, saprc07.pdf, MIR10.doc, MIR10.pdf, and in the supplementary material for the Atmospheric Environment journal article have not been corrected and still contain these erroneous duplicate entries.

2/2/10: Web pages distributing the SAPRC-07 mechanism files and the SAPRC modeling software were reorganized and a spreadsheet giving the calculated photolysis rates for the solar actinic fluxes used for the reactivity scale calculations is now included in the distribution if mechanism files.

1/28/10: An error in the files implementing the mechanism that caused in the rate constant for the O1D+H2O reaction to be low by ~18% was found and corrected. This resulted in slightly increased O3 predictions in ambient simulations, though still lower than calculated using SAPRC-99, and also resulted in MIR values being somewhat closer to those for SAPRC-99. The effects of this change on the chamber simulations used to evaluate the mechanism are negligible. All versions of the mechanism are affected. The mechanism documentation reports, reactivity scales, and mechanism implementation files have been updated to incorporate this correction.

1/22/10: A minor error in the procedure used to output.MEC files where the "N" parameter in falloff reactions was not being given when it was different than 1.0 was corrected. This affects only the files for CMAQ and not the calculations using the SAPRC software, which are the basis of the calculations and reactivity tables in the reports.

1/20/10: The report to the CARB documenting the MIR and hydrocarbon bin MIR update has been updated to the current mechanism version and renamed from MIR09 to MIR10. The spreadsheet HCcalc.xls for calculating hydrocarbon bin and mixture reactivities has also been updated.

1/15/10: A number of errors were found in the base SAPRC-07 mechanism and corrected, and the reactivity scales, documentation, and files have been updated accordingly. A number of edits were also made to the documentation not only to correct the errors but to make editorial changes and corrections noticed as part of preparing journal articles documenting the mechanisms. The corrections and updates are described in Appendix E in saprc07.doc or saprc07.pdf. Most of the errors concern low NOx reactions that do not significantly affect O3 predictions, though an error was found that affected MIR values for tertiary amines. The changes affect all versions of the mechanism, and all files and reports downloaded prior to this date should be replaced by the current versions.

11/13/09: Minor corrections made to "C" versions of SAPRC07 and SAPRC07T. (This is the version that uses explicit reactions for peroxy radical operators to be consistent with most airshed model software. The correction involved adding 0.5 PROD to reactions of the xPROD operator with MEO2, RO2C, and RO2XC, for consistency with the treatment of these reactions in the "B" version. The effect on most model simulations should be negligible.) See distributions of mechanism files for CMAQ and the SAPRC software.

11/12/09: Input and data files for simulations of chamber experiments for modeling using SAPRC software have been corrected and updated. A few experiments had errors in model simulation input files that were updated, and some experimental data files are missing. Input files and chamber data files should be current and complete for all experiments listed in Table C-1 in saprc07.xls.

9/9/09 and 8/26/09: The report documenting the MIR update (MIR09.pdf, now renamed MIR10.pdf) has been updated and several VOCs and mixtures have been added. These new VOCs have also been added to scales07.xls

7/28/09: Files implementing SAPRC-07A, the otherwise uncondensed version of the mechanism using the SAPRC-99 peroxy radical operators, have been added to the files implementing the mechanism in CMAQ and the SAPRC software.

7/13/09: The condensed mechanism was revised to retain methane so it can be used in cleaner air simulations. The condensed mechanism documentation report (csaprc07.doc and csaprc07.pdf) was revised accordingly, and several corrections were made to the report. In addition, several corrections and updates were made to the files implementing the mechanism for SAPRC software.

6/22/09: The report to the CARB describing the update to the MIR scale and bin calculation method for their regulatory purposes (MIR09.pdf, now renamed MIR10.pdf) was revised. This included revisions to the methods used to calculate the hydrocarbon Bin MIR's, so the reactivity and composition tabulations in the SAPRC-07 documentation report (saprc07.pdf or saprc07.doc and saprc07.xls) were revised accordingly.

6/8/09: The report and reactivity tabulations have been updated to include several new compounds and minor additions have been made to the mechanism documentation tabulations for a few other compounds.

4/9/09: The files implementing the SAPRC-07 mechanisms on SAPRC software, available on the SAPRC mechanism files page, have and the condensed SAPRC-07 mechanism report, been updated to be consistent with the current mechanisms as of this date.

4/8/09: The condensed and "toxics" versions of SAPRC-07 have been revised to be consistent with the 3/19/09 version of SAPRC-07, and the files implementing the various versions of SAPRC-07 have been prepared and are available on the "SAPRC-07 Chemical Mechanism and Emissions Speciation Files for CMAQ" page. The report documenting condensed SAPRC-07 still and the files implementing the mechanism in the SAPRC modeling software still need to be updated. Please contact me if you need the updated versions sooner.

3/19/09: Changes have been made to the base SAPRC-07 mechanism to correct some errors found in the previous versions. The documentation report (saprc07.doc and saprc07.pdf) and the reactivity scales tabulations (saprc07.xls and scales07.xls) have been updated accordingly. The changes are summarized in Appendix E of the documentation report. (The condensed and "toxics" versions of SAPRC-07 and the available files not implementing the mechanisms were not updated until 4/8/09 -- see above.) These changes do not affect the emissions speciation assignments.

12/17/08: The final report for the condensed version of SAPRC-07 has been finalized and made available. Available in Microsoft Word (csaprc07.doc) and PDF (csaprc07.pdf) formats. Other than being finalized, the version is dated July 4, 2008 was unchanged.

7/7/08: Several corrections have been made to the mechanism and the documentation, reactivity scales, and mechanism files have been updated accordingly.

7/7/08: Files for the preliminary "toxics" version of of SAPRC-07, designated SAPRC07T have been added. This is being developed for the EPA for implementation in CMAQ. See the readme file for the current SAPRC-07T distribution.

6/3/08: The CARB hydrocarbon bins have been added to the reactivity tabulation in Table B-2 (scales07.xls). The compositions used to derive the reactivities of the bins have been added to Table B-10, which is included in saprc07.xls. Footnotes to Table B-2 references how these bin compositions were derived.

5/28/08: A number of corrections were made to the mechanism, the documentation report was updated, and the reactivity scales were recalculated. Any versions of the documentation, mechanism files, or reactivity tabulations uploaded prior to this date need to be replaced by the current versions. See Appendix E in the documentation report (e.g., saprc07.pdf). The changes in reactivity values compared to the 12/31/07 version were small except for 1,1-dichloroethene, where there was an error in the rate constant that was corrected.

1/22/08: The maximum ozone impacts of NO, NO2, and HONO, which have their highest positive impacts on ozone under very low NOx conditions, have been added to the reactivity tabulation in scales07.xls. A report documenting the derivation of these values is available in Microsoft Word (NOxMIR.doc) and PDF (NOxMIR.pdf) formats. Also, the tabulations in scales07.xls also give the reactivities in the individual MIR, MOIR and EBIR as well as base case scenarios.

12/31/07. Documentation report and mechanism and reactivity tabulations updated to incorporate results of recent studies of the mechanism of methyl iodide (Carter, 2007) and of amines and several other consumer product VOCs (Carter, report on CARB Contract 06-408,  in preparation). The mechanism and reactivity values for methyl iodide have been added, the mechanisms and reactivity values have changed for all amines, and several consumer product VOC have been added. The amine reactivities in previous tabulations should not be used. Reactivities have not changed for any other previously tabulated compounds.

6/28/07. Error in Table B-1 in saprc07.xls and scales07.xls corrected. The previous version had incorrect standard deviations for the "Base" reactivities.

8/31/07. A number of errors in the report have been corrected when preparing the final (8/31/07) version. See the summary of revisions.

8/31/07. The mechanism as listed in the June 15 version of the report had two errors. Reaction BR08 should be changed from "RO2C + HO2 = HO2" "RO2C + HO2 =" and reaction BR13 should be changed from "RO2XC + HO2 = HO2" to "RO2XC + HO2 =". This has been corrected in the current (8/31) version of the report and reactivity scales. The change has only small effects on O3 and reactivity scales, but a non-negligible effect on calculations of HO2 in low NOx scenarios.

Carter main web page

Current version of files implementing SAPRC-07 for CMAQ and other modeling software systems.

Current version of the programs and files implementing the mechanisms using the SAPRC box and chamber modeling software.

Emissions speciation project containing assignments of emissions categories to model species in SAPRC and other mechanisms

The following links give information about SAPRC-99:

SAPRC-99 mechanism documentation report

Latest VOC Reactivity tabulations for SAPRC-99 Mechanism

Files implementing SAPRC-99 Chemical Mechanism and Associated Software

Current Information on Emissions Speciation Database Work