SAPRC atmospheric chemical mechanisms are used in airshed models to
model the gas-phase, ground-level atmospheric photochemical reactions
of organic compoundsd in the presence of oxides of nitrogen, for the
purpose of predicting formation of secondary pollutants such as
ozone and toxic organic products. Versions of this mechanism have also
been used to derive ozone reactivity scales that quantify the relative
amounts of ozone formed when different volatile organic compounds
(VOCs) are emitted under various conditions. This page gives links
to versions of the mechanism and its reactivity scales.
The SAPRC-22 Mechanism is now available.
latert version of the SAPRC mechanisms is SAPRC-22
which was updated on September, 2023 to incorporate improvements in
estimates for peroxy radical isomerization reactions and an improved
peroxy lumping method. It should now be finalized
unless correctable problems are found. Like previous SAPRC mechanisms,
it uses the SAPRC mechanism
generation system (MechGen
to derive explicit mechanisms for
atmospheric reactions of organic compounds, which are then processed
using various reduction methods to produce a lumped mechanism for
airshed modeling. Its
development is consistent with the systematic mechanism
development approach outlined by Kaduwela et al (2015)
SAPRC-22 incorporates the latest updates MechGen, which are being
documented in a journal article to be submitted for peer review.
SAPRC-22 is similar to SAPRC-18 in chemical detail, but uses a more
efficient method to reprsent peroxy radical reactions that requires use
of fewer model species and reactions. Since SAPRC-22 is more
up-to-date and has somewhat greater chemical detail than SAPRC-07 or 11
but has similar computer demands, it is an appropriate update for
models that currently use SAPRC-07 or 11.
The SAPRC-18 mechanism is superceded by SAPRC-22.
SAPRC-18 mechanism is first complete update of all aspects of the SAPRC
series of mechanisms since the development of SAPRC-07. The objective
was to provide an up-to-date mechanism with chemical detail needed for
model applications that need it, but not more than necessary or
appropriate given current knowledge. It uses the SAPRC mechanism
generation system (MechGen) to derive explicit mechanisms for
atmospheric reactions of organic compounds, and its
development is also consistent with the systematic mechanism
development approach mentioned above.
Although the mechanism has been evaluated against available
environmental chamber data and is considered finalized, it has not been
implemented in 3D models, in part because it is much larger than other
available mechanisms. SAPRC-22 was developed to address the size issue,
and should be used rather than SAPRC-18 if size is an issue. The full version of SAPRC-22 is comparble to SAPRC-18 in size.
The preliminary SAPRC-16 mechanism is no longer supported.
The SAPRC-16 mechanism is a preliminary version of SAPRC-18 that was used in the study of Venecek et al, titled "Analysis
of SAPRC16 chemical mechanism for ambient simulations," Atmos
Environ, 192, 136-150, 2018.
It is similiar to SAPRC-18 but is based on an earlier version of the
SAPRC mechanism generation system. Because it was used in a
publication, the SAPRC-16 web site containing its preliminary documentation and files is being retained for archival purposes.
The SAPRC-11 mechanism is an incremental update to SAPRC-07
SAPRC-11 mechanism is an update to SAPRC-07 that has a new version of
aromatic chemistry that performs better in simulations of environmental
chamber data. The representation of non-aromatic chemistry and the
degree chemical detail has not been signficiantly modified. This
mechanism is documented by Carter and Heo "Development
of Revised SAPRC Aromatics Mechanisms," Atmos. Environ. 77, 404-414, 2013.
It has been implemented in various airshed models and used to update
the SAPRC-07 VOC reactivity scale, though the reactivity changes are
not signficant for most compounds, and the SAPRC-07 scale (see below)
is still the most widely used. The SAPRC-11 mechansim has also been
used to develop a preliminary, chemicaly-based model for secondary
organic aerosol (SOA) formation.
The CSAPRC-07 mechanism is a condensed version of SAPRC-07
CSAPRC-07 mechanism is a condensed version of SAPRC-07 that is
described by Carter, "Development of a Condensed SAPRC-07 Chemical
Environment, 44, 5336-5345, 2010.
It was developed by examining effects of various reduction approaches
on predictions of ozone and other measures of reactivity, and adopting
those that have the least effects on ozone predictions.
Its development is consistent with the systematic mechanism reduction approach outlined by Kaduwela et al (2015)
gives essentally the same ozone predictions desspite its much smaller
size. The level of condensation is similar to that used in the latest
Carbon Bond mechanisms. Files for this version of the mechanism are
available on request.
The SAPRC-07 mechanism is the most widely used version of SAPRC
SAPRC-07 mechanism is a complete update to SAPRC-99 and is described by
Carter, "Development of the SAPRC-07 Chemical Mechanism," Atmospheric
Environment, 44, 5324-5335, 2010. It is
used in airshed modeling studies and was used to develop the SAPRC-07
reactivity scale that is used or has been considered for use in California's reactivity-based VOC regulations
It is the first version of the SAPRC mechanisms that utilized a
mechanism generation system to help derive mechanisms for reactions of
some organics. Links to information about this mechanism and its
reactivity scales are given below.
- Final report documenting the mechanism. “Development
of the SAPRC-07 Chemical Mechanism and Updated Ozone Reactivity
Scales". This report also has an Appendix in the form of an Excel file (saprc07.xls), including tables that are too large for the main body of the text. Contains detailed information not in the Atmospheric Environment
paper, including detailed results of the evaluations against chamber
data, reactivity listings, and preliminary documentation of the
mechanism generation system used.
- Latest listing of SAPRC-07 MIR and other reactivity scales: Documentation report (MIR10.pdf) and Reactivity values in an Excel file (scales07.xls). Supercedes the reactivity listings given in the report documenting the mechanism and saprc07.xls.
- The spreadsheet HCcalc.xls
was used to derive the compositions used to calculate the reactivities of
the 24 hydrocarbon bins, and can also be used to estimate compositions and
reactivities of other hydrocarbon mixtures given type distributions and
boiling point ranges. This method is described in the report on updating the SAPRC-07 reactivity scale (MIR10.pdf).
- Link to the web site for where the SAPRC box modeling software and input files for SAPRC-07 and other versions of SAPRC mechanisms.
- Archive web page with links to various files for implementing SAPRC-07 in CMAQ and other airshed modeling software. Last updated December, 2011
- The California Air Resroucres Board 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 given in RespRev.pdf. This document is dated March 20, 2009.
SAPRC-99 mechanism is a complete update to the SAPRC-90 and
incorporates mechanisms for a wide variety of VOCs. It has been
superceded by SAPRC-07 or SAPRC-11 for airshed model applications, and
its reactivity scale is superceded by the SAPRC-07
The SAPRC-90 is the first published version of the SAPRC mechanisms and is described in the journal article “A
Detailed Mechanism for the Gas-Phase Atmospheric Reactions of Organic
Compounds,” Atmos. Environ., 24A, 481-518, 1990.
It is the first version of the mechanism that provides for reactions of
individual organic compounds to be added to the condensed mechanism for
atmospheric mixtures for deriving a reactivity scale, and is the basis
for the first version of the MIR and other VOC reactivity scales
described in the original paper “Development
of Ozone Reactivity Scales for Volatile Organic Compounds,” J. Air & Waste
Manage. Assoc., 44, 881-899, 1994. This mechanism, and its reactivity scale, have been superceded by the later versions described above.