DEVELOPMENT OF REVISED SAPRC AROMATICS MECHANISMS

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Figure 34. Figure 35. Figure 36. LIST OF FIGURES (continued) Plots of model errors for simulations of the integrated OH levels in the trimethylbenzene - NO x experiments with the SAPRC-11 mechanism. ................................ 64 Plots and tables of selected model performance results for the phenol - NO x experiments using the SAPRC-11 mechanism....................................................................... 65 Plots and tables of selected model performance results for the o-cresol - NO x experiments using the SAPRC-11 mechanism....................................................................... 65 Figure 37. Plots and tables of selected model performance results for the 2,4-dimethyl phenol - NO x experiments using the SAPRC-11 mechanism. ............................................................. 66 Figure 38. Figure 39. Plots of selected incremental reactivity evaluation results for the m-cresol. Results are shown for both SAPRC-11 (solid lines) and SAPRC-07 (dashed lines).......................... 66 Selected experimental and model calculation results for the cresol - NO x experiments carried out using different chambers and light sources with similar reactant concentrations........................................................................................................... 68 Figure 40. Plots of ∆([O 3 ]-[NO]) model error against initial ROG/NO x ratios for the surrogate - NO x experiments. ...................................................................................................................69 Figure 41. Figure 42. Figure 43. Figure 44. Figure 45. Figure 46. Figure 47. Maximum daily O 3 calculated for the various 1-day scenarios used for reactivity assessments using the SAPRC-11 mechanism, and relative changes in maximum O 3 for SAPRC-11 compared to SAPRC-07. ............................................................................... 71 Comparisons of MIR values calculated using the SAPRC-11 and SAPRC-07 mechanisms calculated using the “Averaged Conditions” scenario. ..................................... 73 Quantum yields for radical formation and yields of uncharacterized photoreactive products that photolyze to form radicals (AFG1) derived to fit the chamber data for the various aromatic compounds............................................................................................ 76 Comparison of radical formation quantum yields for compounds predicted to form unsaturated 1,4-diketones relative to those of isomers that cannot form these products.................................................................................................................................. 77 Experimental and calculated concentration-time plots for O 3 in the Euphore benzene - NO x and benzene - NO x - HONO experiments. (From Goliff , 2012)................................. 78 Comparison of model errors for SAPRC-11A simulations of Euphore and UCR benzene experiments. ............................................................................................................. 78 Experimental and calculated concentration-time plots for ozone and phenol for the UCR EPA chamber experiments for which phenol data are available................................... 81 viii
EXECUTIVE SUMMARY Background and Problem Statement The chemical mechanism is the portion of the model that represents the processes by which emitted primary pollutants, such as volatile organic compounds (VOCs) and oxides of nitrogen (NO x ), interact in the gas phase to form secondary pollutants such as ozone (O 3 ) and other oxidants. The SAPRC- 07 mechanism is the latest in the SAPRC series of gas-phase chemical mechanisms that are used for various airshed model applications. Simulations of environmental chamber data are important to mechanism development because mechanisms for many emitted VOCs are complex and have uncertainties, and available data, theories, and estimates are not sufficient to fully constrain the mechanism. For this reason, the predictive capabilities of the mechanisms need to be evaluated by determining if the mechanism can simulate the results of appropriate environmental chamber experiments, and in some cases uncertain portions of the mechanism may need to be adjusted for the mechanisms to give satisfactory simulations of these data. If a mechanism cannot adequately simulate results of well-characterized chamber experiments, it cannot be relied upon to give accurate predictions in airshed model applications. Appropriate representation of the reactions of aromatic hydrocarbons is a priority for airshed models because of their high reactivity combined with their relatively large emissions. The need to evaluate and adjust mechanisms based on simulations of chamber data is particularly important for aromatics because of the complexities and significant uncertainties in their mechanisms, and the fact that much of their relatively high atmospheric reactivity is due to secondary reactions of poorly characterized products. Although results of a large number of environmental chamber experiments with aromatics were used in developing the aromatics mechanisms for SAPRC-07, most of these experiments were carried out at NO x levels much higher than typically observed ambient NO x levels, and comprehensive mechanism evaluation data were available for only a few representative compounds. Since SAPRC-07 was developed, a large number of additional aromatic environmental chamber experiments were conducted, including experiments for additional compounds and many experiments at lower NO x levels than previously available. Most of these were carried out to provide data to develop mechanisms for prediction of secondary organic aerosol (SOA) formation from aromatics, but they can also be used for gas-phase mechanism evaluation. It was found that SAPRC-07 did not perform well in simulating O 3 formation in many of the new experiments, particularly experiments at lower NO x levels and also experiments with phenolic compounds that are important aromatic oxidation products. These new data indicate that the SAPRC-07 aromatics mechanisms do not give the best fits to the currently available chamber dataset, and need to be revised to take the new data into account. Accomplishments Although this work did not represent a complete update of SAPRC-07, a number of updates and revisions were made to SAPRC-07 to derive the updated version that is designated SAPRC-11. Almost all of the revisions concerned reactions of aromatics or aromatic oxidation products, with mechanisms updated for benzene, toluene, ethylbenzene, and all xylene, trimethylbenzene, ethyltoluene and propyl benzene isomers, as well as phenol, o-cresol, and 2,4-dimethylphenol. Mechanisms for other aromatics are derived based on those for these 17 representative compounds. 1
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: LIST OF FIGURES (continued) Figure
Page 11 and 12: However, this issue is probably not
Page 13 and 14: significant uncertainties in their
Page 15 and 16: New UCR EPA Experiments New CSIRO E
Page 17 and 18: Table 1. List of model species in t
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
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Ethyl Benzene (Model "A") Number of
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n-Propyl Benzene Number of Runs 4 5
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m-Xylene Number of Runs 128 Average
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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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