THE SAPRC-99 CHEMICAL MECHANISM
AND UPDATED VOC REACTIVITY SCALES
Broken links corrected or removed 3/31/10
Final Mechanism Documentation Report dated May 8, 2000
Updated and Corrected Data as of February 5, 2003
Software and Mechanism Files now Available (Last updated September 25, 2001)
Prepared for the California Air Resources
Contracts No. 92-329 and 95-308
William P. L. Carter
Air Pollution Research Center and
College of Engineering, Center for Environmental Research and Technology
University of California, Riverside, CA, USA
Mailing Address: CE-CERT, University of California, Riverside CA 92521
Phone: (909) 781-5797. FAX: (909) 781-5790
The SAPRC-99 detailed atmospheric chemical mechanism for VOCs and NOx represents a complete update of the SAPRC-90 mechanism of Carter (1990), and incorporates recent reactivity data from a wide variety of VOCs. It has assignments for ~400 types of VOCs, and can be used to estimate reactivities for ~550 VOC categories. A condensed version was developed for use in regional models. A unique feature of this mechanism is the use of a computerized system to estimate and generate complete reaction schemes for most non-aromatic hydrocarbons and oxygenates photochemical smog systems. The mechanism has been evaluated against test ozone reactivity predictions for over 80 types of VOCs.
The mechanism was used to update the various ozone reactivity scales developed by Carter (1994a), including the widely used Maximum Incremental Reactivity (MIR) scale. However, the reactivity estimates for many VOC classes are uncertain, which must be taken into account when using these data for regulatory applications. To aid this, uncertainty classifications have been assigned to all VOCs for which MIR's have been calculated. In addition, a method to derive upper limit MIRs for VOCs with uncertain mechanisms is described, and upper limit MIRs are presented for all VOCs in the mechanism.
NOTE: Some corrections and modifications had to be made to the mechanism since the draft report dated September 1999 was prepared. In particular, the previous version had an error in the ozone cross sections, and there were some minor changes to the mechanism generation system that caused small changes in parameter values. Anyone who downloaded the report prior to April 3, 2000 and the reactivity data prior to January 30, 2000 should download the report and/or the data again. Also, the April 3, 2000 data tabulation includes VOC classes that were not in the January 30 data set.
May 8, 2000 revision: Additional VOC classes requested by the CMA were added. This affects the reactivity listings in Appendix C and the listing of the reactions of the individual model species in Table A-6. Some minor corrections were made to the mechanism documentation. The most significant is adding the reactions of aromatics and other assigned mechanism species to the detailed model species reaction listing on Table A-6, which were omitted from the April 11 version. Some reference citations in footnotes to Table B-1 were also corrected. The base mechanism and the reactivities of all the compounds listed in the April 11 version are the same.
November 13-29, 2000 revisions: Additional VOC classes requested by the CARB and others were added. A minor correction was made to the way mechanisms were estimated for some types of esters and a corrections were made for a few other compounds. These corrections are summarized in a separate report to the CARB.
October 26, 2002 revisions: The CARB requested the most recent
MIR values for use in their regulatory
programs. Although no substantive changes were made to the mechanism or reactivity calculation methodology or scenarios since the time the previous scales were calculated in May-November of 2000, some corrections have been made to some mechanism and emissions assignments for certain types of VOCs, and modifications or corrections have been made to some of the files and software programs. In addition, a number of VOCs or VOC classes have been added as a part of preparing mechanism assignments for emissions inventories and for other projects. Therefore, estimated mechanisms were re-generated for all VOCs whose mechanisms are based on the computerized mechanism generation system, and all reactivity scales were re-calculated using the existing mechanism files and software. This has resulted in resulting in non-negligible MIR changes for a small number of VOCs and very small changes for many others, and the addition of ~95 new VOC classes. Tables giving the changed or added MIRs are given in a separate letter to the CARB.
January 23, 2003 revisions: Several classes of VOCs were added for inclusion the CARB list as a result of a consulting project. These are incorporated in an expanded list of MIR values provided to the CARB. In addition, the MIRs for some of the new VOC classes added in the October 26 revision were recalculated using the more detailed estimated mechansism derived using the adjusted product approach. Tables giving the changed or added MIRs are given in a separate letter to the CARB. Note that this letter supercedes the one dated October 26, 2002.
January 27, 2003 revisions: Same data as the January 23 list, but CAS numbers are now included in the table where known and applicable. These CAS number assignments were taken from my emissions database work.
January 31, 2003 revisions: Same MIR data as January 23 list, but upper limit MIR estimates were added for the new model species.
February 5, 2003 revisions: Molecular weights for diethylbenzenes corrected. This resulted in a slight decrease in MIRs for those compounds. Otherwise, no changes or additions.
Files and software to implement this mechanism are now available
Information Available and Related Links