DEVELOPMENT OF REVISED SAPRC AROMATICS MECHANISMS

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MECHANISM DESCRIPTION General Mechanism The starting point for the mechanisms developed in this work is the SAPRC-07 mechanism as documented by Carter (2010a,b). For this work, all portions of the mechanism were unchanged except as described in the following sections. Except for revisions to the general acyl peroxy + HO 2 reactions made as a result of an updated IUPAC recommendation (IUPAC, 2009), all of the revisions concerned the reactions of aromatics and model species used to represent aromatic photooxidation products. For simulations of chamber data, including the simulations used for adjusting the aromatics mechanisms, the reactions of each of the aromatic compounds present in the experiments were represented explicitly, rather than by a lumped model species (i.e., using TOLUENE rather than ARO1). This is the same approach as used when evaluating the SAPRC-07 mechanism against chamber data (Carter, 2010a,b). A complete listing of the SAPRC-11 mechanisms used for the chamber and ambient simulations are given in Appendix A, where Table A-1 lists the model species and Table A-2 lists the reactions and rate constants. Table A-1 also indicates which species had changes to their mechanisms as part of this work, and footnotes to Table A-2 indicate which reactions were changed. If there is no footnote for a species or reaction in these tables then the mechanism is the same as given by Carter (2010a,b). The absorption cross sections and wavelength-dependent quantum yields are also the same as given by Carter (2010a,b), and are therefore not duplicated here. Revisions to Base Mechanism Table 1 lists the model species whose mechanisms were revised, added, or removed for this version of the base mechanism, and Table 2 lists the reactions involved. Footnotes to the table document the reasons for the changes or additions to the mechanisms, and additional discussion of these changes is given below. Note that except for the removed species listed in Table 1, the information on these two tables is a subset of the information in the complete mechanism listing given in Table A-1 and Table A-2 in Appendix A. Note that these tables do not include species and reactions that were added for the purpose of modeling aromatic SOA formation that are discussed by Carter et al (2012), since they do not affect the gas-phase that are the subject of this report. See Carter et al (2012) for a complete discussion of the revisions of the aromatics mechanism for SOA predictions. Although a complete update of the mechanism based on a thorough review of current evaluations and data was beyond the scope of the present project, during the course of this project we became aware of revised evaluations that made changes to the base mechanism appropriate. These are summarized below. Reaction of OH radicals with acetylene. The temperature dependence parameters used for acetylene in SAPRC-07 was based on the NASA (2006) evaluation, which is unchanged in the most recent NASA (2011) evaluation, should have had k 0 =5.5x10 -30 cm 3 molec -1 s -1 , independent of temperature, and k ∞ =8.3x10 -13 (T/300) 2 cm 3 molec -1 s -1 . However, the (T/300) 2 temperature dependence was erroneously associated with k 0 in the mechanism. This has been corrected. This will not affect model performance for chamber simulations for this compound and have very little effect on atmospheric simulations at ambient temperatures. 8
Table 1. List of model species in the base mechanism that were added or deleted or whose mechanisms were changed in the current mechanism update. Species added by Carter et al (2012) that affect only SOA predictions are not included. Species Description Discussion Errors Corrected ACETYLEN Acetylene (represented explicitly) Error in temperature dependence parameters corrected. Does not affect evaluation against chamber data or atmospheric MIR predictions. Mechanisms or Lumping Revised MECO3 RCO3 BZCO3 MACO3 All model species in the mechanism used to represent acyl peroxy radicals that react to form PAN or PAN analogues 9 Mechanism for reaction with HO 2 radicals revised based on new IUPAC (2009) evaluation. GLY Glyoxal Mechanism for reaction with OH and NO 3 revised based on new IUPAC (2008a) evaluation. CRES Cresols Now used to represent only cresols and not phenol or C 8+ phenolic compounds, which are represented by separate model species. Mechanism revised to improve simulations of O 3 reactivity and SOA formation in o-cresol - NO x chamber experiments. AFG1 AFG2 AFG3 Model Species Added Photoreactive monounsaturated dicarbonyl aromatic ring opening products and other unknown photoreactive aromatic ring opening products. Used to represent di-unsaturated dicarbonyl ring opening products. HCOCO3 [a] Peroxy radical formed from H- abstraction reactions from glyoxal PHEN XYNL Phenol and Xylenols and other C 8+ phenolic compounds, respectively Yields reoptimized based on model simulations of aromatic - NO x chamber experiments, including new experiments not available when SAPRC-07 was developed. Mechanisms are not changed other than removing reactions with O 3 , which were found to be negligible under all conditions of interest. The change concerned only the set of compounds this model species is used to represent, not its mechanism. Previously AFG3 was also used for monounsaturated diketones, but now a separate model species, AFG4, is used for these compounds. The mechanism for AFG3 was not changed because it was based on estimated mechanisms for the di-unsaturated dicarbonyls only. This was previously represented by the lumped acyl peroxy radical species RCO3 but the current evaluations indicate that its reaction with NO 2 does not form stable PAN analogues so RCO3 is not an appropriate representation. These are now represented separately from cresols in order to represented differences in ozone reactivity and SOA formation from various types of
Page 1 and 2: DEVELOPMENT OF REVISED SAPRC AROMAT
Page 3 and 4: ACKNOWLEDGEMENTS AND DISCLAIMERS Th
Page 5 and 6: TABLE OF CONTENTS (continued) APPEN
Page 7 and 8: LIST OF FIGURES (continued) Figure
Page 9 and 10: EXECUTIVE SUMMARY Background and Pr
Page 11 and 12: However, this issue is probably not
Page 13 and 14: significant uncertainties in their
Page 15: New UCR EPA Experiments New CSIRO E
Page 19 and 20: Table 2. Reactions that were modifi
Page 21 and 22: Table 2 (continued) Phot Set = name
Page 23 and 24: mechanism using the generic lumped
Page 25 and 26: Table 3 (continued) 4 Average of 5.
Page 27 and 28: Hydroperoxides (R6OOH) Phenolic Pro
Page 29 and 30: Table 5 (continued) 3 Yields of pro
Page 31 and 32: Table 6. Summary of yields of lumpe
Page 33 and 34: thus the model species AFG3 used to
Page 35 and 36: simulations of the chamber data usi
Page 37 and 38: separately primarily because they a
Page 39 and 40: the photoreactive α-dicarbonyls an
Page 41 and 42: MECHANISM EVALUATION Methods Chambe
Page 43 and 44: Table 9 (continued) ID TVA CSI Brie
Page 45 and 46: Modeling Methods The procedures use
Page 47 and 48: irradiation time would not yield a
Page 49 and 50: Adjustments to Mechanisms to Fit Da
Page 51 and 52: Compound ∆([O 3 ]-[NO]) Formation
Page 53 and 54: Benzene Number of Runs 14 Average M
Page 55 and 56: Toluene Plots and tables of selecte
Page 57 and 58: CTC108B ETC101 ETC103 CTC127B IR Su
Page 59 and 60: Ethyl Benzene (Model "A") Number of
Page 61 and 62: n-Propyl Benzene Number of Runs 4 5
Page 63 and 64: m-Xylene Number of Runs 128 Average
Page 65 and 66: m-Xylene (continued) o-Xylene p-Xyl
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IntOH Model Error 100% 50% 0% -50%
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p-Ethyl toluene Number of Runs 7 Av
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1,3,5-trimethylbenzene Model Error
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Phenol Number of Runs 5 50% Model E
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Although there is somewhat greater
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∆([O3]-[NO]) Model Error Full Sur
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constants and product yield paramet
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25 20 10 SAPRC-11 Reactivity 15 10
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there is an inconsistency between t
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e obtained from the AFG1 / (AFG1+AF
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higher NO x experiment. Note that t
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in this evaluation, as well as the
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develop chemically detailed or expl
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laboratory data and theories of atm
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REFERENCES Anderson, R.S., Czuba, E
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Carter, W. P. L. (2000a): “Docume
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IUPAC (2008e): http://www.iupac-kin
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White, S.J., M. Azzi, D. E. Angove,
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Table A-1 (continued) Type and Name
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Table A-1 (continued) Type and Name
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Table A-2. Listing of reactions and
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Table A-2 (continued) Label Reactio
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Table A-2 (continued) Phot Set = na
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Table B-1 (continued) Run New [a] C
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Table B-2. Summary of incremental r
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Table B-3 (continued) Run ID Surrog
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Table B-3 (continued) Run ID Surrog
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Table B-4. (continued) Cham. Set(s)
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Table B-4. (continued) Cham. Set(s)
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DEVELOPMENT OF REVISED SAPRC AROMATICS MECHANISMS

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