CMAQ v5.1 SAPRC07 changes

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Brief Description

Minor updates and additions were made to the v5.0.2 released version of SAPRC07TB and TC, in order to remain consistent with important updates in reaction rates and to enable consistency with aerosol updates.

SAPRC07 Mechanism Updates

Description of changes

Updates from SAPRC11 and IUPAC

  1. Implemented the nonaromatic changes found in the supplementary material from Carter and Heo (2013),
    1. Modified reaction BR22, BR32, BR43, and BR55, the MECO3, RCO3, BZCO3, and MACO3 reactions with HO2 based on IUPAC recommendations for HO2 + acyl radical reactions (
    2. Corrected reaction BE10, ACETYLENE + OH, by setting the temperature power for k0 to zero and setting temperature for kinf to -2
    3. Corrected reaction BE04, ETHENE + OH, by setting the temperature power to zero
    4. Revised GLY reactions with OH and NO3 based IUPAC (2008) recommendation, requiring addition of a new peroxy radical species HCOCO3 (
  2. Revised N2O5 + H2O heterogeneous reaction to yield HNO3 and ClNO2 (see CMAQv5.1 ClNO2 chemistry)
  3. Changed the OH + NO2 reaction based on the recommendation of the IUPAC datasheet (
  4. Removed species NO2EX, excited NO2, and its reactions.

Isoprene modifications

The high HOx pathways for isoprene oxidation have been modified to explicitly account for production of isoprene epoxydiol, which can form SOA and modify the gas phase concentrations. The high NOx pathways have only one change.

high HOx pathway:

  1. Explicitly represent isoprene hydroperoxide by changing yR6OOH to yISOPOOH in reaction of isoprene+OH
  2. Added reactions to form ISOPOOH from yISOPOOH (reaction rates based on yR6OOH)
  3. Added reactions of ISOPOOH to make IEPOX - copied reactions IS88, IS89,and IS92 from saprc07tic here with the following changes to make species compatible:
    1. Changed HC5 to RCHO
    2. Changed HACET to MEK
    3. Changed model species ISOPO2 (rxn IS89) to the products from ISOPO2, based on Xie et al (2013)
  4. Produced 100% ISOPOOH from reaction ISOPO2+HO2 (no acyl peroxy radical)
  5. Added reactions of IEPOX from saprc07tic (IS90, IS91, IS96, IS112-IS114, left reactions unchanged except to substitute HACET with MEK)
  6. Added species IEPOXOO

high NOx pathways:

  1. Added ISOPRXN to represent SOA formation from isoprene+NO3 (rxn BE08)

Modifications for SOA and other changes

  1. Added species and reactions to better represent SOA from alkanes and PAHs (as described in SOA updates):
    1. Added reaction SOAALK + OH = OH + ALKRXN (removed ALK5RXN and added ALKRXN)
    2. Changed BL15 to (ARO2MN+OH) and added BL15b (NAPHTHAL+OH) to separate napthalene (which now makes PAHRO2) from ARO2 (which makes XYLRO2; removed ARO2 and added ARO2MN. Added NAPHTHAL and PAHRO2)
    3. Changed <BC09> to <BC09> (ARO2MN+CL) and <BC09b> (NAPHTHAL+CL)
    4. Added reactions of model species PAHRO2 with NO and HO2 to make PAHNRXN and PAHHRXN.
  2. Shortened some species names to 12 characters to make compatible with CMAQ tools:
    1. TRIMETH_BENZ124 changed to TMBENZ124

New Species

New Species Description
ISOPOOH, yISOPOOH isoprene hydroperoxide and its SAPRC07 operator
IEPOX isoprene epoxydiol
IEPOXOO peroxy radical from isoprene epoxydiol
HCOCO3 acylperoxy radicals from glyoxal (from SAPRC11)
ARO2MN model species ARO2 without naphthalene
NAPHTHAL explicit naphthalene
PAHRO2 tracer for SOA precursor from NAPHTHAL
SOAALK tracer for alkanes that react produce SOA in significant amounts
ALKRXN tracer for SOA precursor from SOAALK
CLNO2 nitrylchloride

Removed Species

NO2EX: Excited NO2

ALK5RXN: replaced by ALKRXN

Significance and Impact

SAPRC07TB and TC are compatible with new representation of SOA production (SOA updates) and heterogeneous changes (Integration of gas and heterogeneous chemistry; CMAQv5.1 ClNO2 chemistry); little change in ozone or other oxidants.

Affected files

  • gas/ebi_saprc07tb_ae6_aq (new ebi solver files)
  • gas/ebi_saprc07tc_ae6_aq (new ebi solver files)
  • MECH/saprc07tb_ae6_aq
  • MECH/saprc07tc_ae6_aq


Carter, W.P.L., Heo, G., 2013, Development of revised SAPRC aromatics mechanisms, Atm. Env. 77: 404-414.article

Xie, Y. F. Paulot, W. P. L. Carter, C. G. Nolte, D. J. Luecken, W. T. Hutzell, P. O.Wennberg, R. C. Cohen, and R.W. Pinder, 2013. Understanding the impact of recent advances in isoprene photooxidation on simulations of regional air quality. Atmos. Chem. Phys., 13, 8439–8455.article


Deborah Luecken, National Exposure Research Laboratory, U.S. EPA