Investigation of the Atmospheric Ozone Formation Potential of Methyl Pivalate
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INVESTIGATION OF THE ATMOSPHERIC OZONE FORMATION POTENTIAL OF METHYL PIVALATE Report to ExxonMobil Chemical Company by William P. L. Carter, Dongmin Luo, and Irina L. Malkina November 17, 2000 College of Engineering Center for Environmental Research and Technology University of California Riverside, California 92521 00-AP-RT2R-001-FR ABSTRACT A series of environmental chamber experiments and computer model calculations were carried out to assess the atmospheric ozone formation potentials of methyl pivalate. The experiments consisted of determining the effects of this compound on NO oxidation, ozone formation, OH radical levels, and other measures of reactivity when added to varying simulated model photochemical smog systems. Methyl pivalate was found to slightly enhance O3 formation under conditions most representative of the atmosphere, but to inhibit radical levels and inhibit O3 in experiments that are sensitive to effects on radical levels. A mechanism for the atmospheric reaction for methyl pivalate was developed that is consistent with available laboratory data and current estimation methods, and that could simulate the results of these experiments after only minor adjustments of the overall nitrate yield to within its range of uncertainty. This mechanism was then incorporated in the overall SAPRC-99 mechanism and used to predict the atmospheric ozone impacts of this compound under various atmospheric conditions. The ozone formation potentials of methyl pivalate on a mass basis was found to be about 10-20% that of the mixture used to represent reactive VOC emissions from all sources. Its ozone formation potentials were found to be very similar to those of ethane, the compound used by the EPA as the basis for determining exemptions of compounds from regulation as ozone precursors. ii ACKNOWLEDGEMENTS The authors acknowledge Mr. Dennis Fitz for assistance in administering this program, Mr. Kurt Bumiller with assistance in carrying out the environmental chamber experiments, and Dr. Roger Atkinson for helpful discussions. Although this work was funded by ExxonMobil Chemical Company, the opinions and conclusions expressed in this report are entirely those of the primary author, Dr. William P. L. Carter. Mention of trade names or commercial products do not constitute endorsement or recommendation for use. iii TABLE OF CONTENTS INTRODUCTION.........................................................................................................................................1 EXPERIMENTAL AND DATA ANALYSIS METHODS..........................................................................3 Overall Experimental Approach .............................................................................................................3 Environmental Chamber.........................................................................................................................4 Experimental Procedures ........................................................................................................................5 Analytical Methods.................................................................................................................................5 Characterization Methods.......................................................................................................................6 Temperature .....................................................................................................................................6 Blacklight Light Source ...................................................................................................................7 Dilution ............................................................................................................................................7 Reactivity Data Analysis Methods .........................................................................................................7 CHEMICAL MECHANISMS AND MODELING METHODS ................................................................10 Chemical Mechanism ...........................................................................................................................10 General Atmospheric Photooxidation Mechanism.........................................................................10 Atmospheric Reactions of Methyl Pivalate....................................................................................10 Modeling Methods................................................................................................................................15 Environmental Chamber Simulations ............................................................................................15 Atmospheric Reactivity Simulations..............................................................................................15 EXPERIMENTAL RESULTS AND MECHANISM EVALUATION ......................................................17 Summary of Experiments and Characterization Results ......................................................................17 Methyl Pivalate Reactivity Experiments ..............................................................................................21 ATMOSPHERIC REACTIVITY CALCULATIONS ................................................................................24 Scenarios Used for Reactivity Assessment...........................................................................................24 Base Case Scenarios.......................................................................................................................25 Adjusted NOx scenarios .................................................................................................................27 NOx Conditions in the Base Case Scenarios ..................................................................................27 Quantification of Atmospheric Reactivity .....................................................................................28 Results...................................................................................................................................................29 CONCLUSIONS.........................................................................................................................................34 REFERENCES............................................................................................................................................35 APPENDIX A. ............................................................................................................................................39 MECHANISM LISTING AND TABULATIONS .....................................................................................39 iv LIST OF TABLES Table 1. Detailed mechanism for the reactions of methyl pivalate with OH radicals in the presence of NOx. Predicted products are shown in bold font. .................................................12 Table 2. Chronological listing of the environmental chamber experiments carried out for this program....................................................................................................................................18 Table 3. Summary of conditions and selected results of the environmental chamber reactivity experiments with methyl pivalate............................................................................................20 Table 4. Summary of the conditions of the scenarios used for atmospheric reactivity assessment................................................................................................................................26 Table 5. Atmospheric incremental calculated for the base ROG mixture, ethane, methyl pivalate, and acetone................................................................................................................30 Table 6. Atmospheric relative calculated for ethane, methyl pivalate and acetone...............................31 Table A-1. Listing of the model species in the mechanism used in the model simulations discussed in this report.............................................................................................................40 Table A-2. Listing of the reactions in the mechanism used in the model simulations discussed in this report. See Carter (2000) for documentation. ...................................................................43 Table A-3. Listing of the absorption cross sections and quantum yields for the photolysis reactions...................................................................................................................................52 Table A-4. Chamber wall effect and background characterization parameters used in the environmental chamber model simulations for mechanism evaluation...................................61 LIST OF FIGURES Figure 1. Selected results of the low NOx mini-surrogate side equivalency test experiment, and comparison with comparable data obtained in low NOx mini-surrogate experiments with added methyl pivalate......................................................................................................20 Figure 2. Selected experimental and calculated results of the incremental reactivity experiments with methyl pivalate. (Effects of nitrate yield variation are not shown for simulated formaldehyde and acetaldehyde data.) ....................................................................22 Figure 3. Distribution plots of relative reactivities of ethane, methyl pivalate, and acetone in the base case scenarios.............................................................................................................33