Grantee Research Project Results
Final Report: The Chemical Kinetics and Mechanisms of Hydrocarbons Contributing to Ozone Production in the Atmosphere
EPA Grant Number: R825258Title: The Chemical Kinetics and Mechanisms of Hydrocarbons Contributing to Ozone Production in the Atmosphere
Investigators: Demerjian, Kenneth L. , Anderson, James G.
Institution: The State University of New York , Harvard University
EPA Project Officer: Hahn, Intaek
Project Period: November 25, 1996 through November 24, 1999
Project Amount: $534,939
RFA: Air Quality (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The objective of this research project was to perform laboratory chemical kinetic and mechanistic studies of hydrocarbon oxidation by ozone (O3) and hydroxyl radical (OH) using a high-pressure flow system. The specific objectives were: (1) direct measurement of OH formation yields in ozone-olefin reactions; and (2) kinetic rate constant and mechanistic pathway studies of the OH-isoprene and OH- α-, β-pinene reactions.
Summary/Accomplishments (Outputs/Outcomes):
The reaction of ozone with unsaturated hydrocarbons in the gas phase is believed to be an important source of HOx radicals in the troposphere. However, because the reaction mechanism involves vibrationally excited intermediate species, and most yield measurements are indirect, the exact mechanism and product branching ratios remain uncertain. Direct pressure-dependent measurements of radical yields for a number of ozone-alkene reactions have been performed. OH and H radicals are detected using laser induced fluorescence (LIF) and resonance fluorescence (RF), and are measured at steady state, formed from the ozone-alkene reaction, and lost to reaction with the alkene. Short reaction times (always < 100 ms, usually 10 ms) ensure minimal interference from secondary reactions. Measurements from 1 torr to hundreds of torr cover a set of simple symmetric alkenes: ethane; trans-2-butene; 2,3-dimethyl-2-butene; 3-hexene; and 3,4-dimethyl-3-hexene. OH yields for the smaller alkenes are pressure independent and consistent with results from previous indirect measurements at 1 atm. However, yields for the larger alkenes decrease rapidly with pressure, resulting in 1 atm yields significantly lower than current recommendations. This pressure dependence is caused by the large number of nonreactive modes of the carbonyl oxide (Criegee) intermediate. Larger intermediates have longer lifetimes with respect to unimolecular reaction, and therefore are more susceptible to collisional stabilization; we motivate this effect more quantitatively using statistical theory. Therefore, while radicals are produced directly in the ozone-alkene reaction, yields measured in environmental chambers may be overestimates due to interferences by secondary reactions.
Isoprene, 2-methyl-1,3-butadiene, is one of the most abundantly emitted biogenic hydrocarbons in the atmosphere. Its loss in the atmosphere is dominated by reaction with the OH, and can be a significant factor in the OH budget in rural environments, and in the production of ozone on the regional scale. Understanding the oxidation mechanism for isoprene is of great importance to the tropospheric and air pollution chemistry communities, and while it has received substantial experimental attention, major uncertainties remain. Laboratory studies have been performed in a unique chemical kinetic flow reactor to elucidate the reaction mechanisms for OH oxidation of isoprene and 1,3-butadiene in the presence of nitric oxide. The studies were performed under "wall-less" flowing conditions with products observed a few seconds after reaction by infrared spectroscopy. The use of reaction modulation spectroscopy permits the accurate measurement of a percent change in high alkene concentration and of 1013 molecules/cm3 concentrations for products. Since only approximately 1 percent of the alkene is reacted, any secondary chemistry is negligible. Measured carbonyl species agreed well with previous studies, while alkyl nitrate yields were consistent with upper values reported in the literature. Nitric oxide sensitivity studies performed excluded the possibility of competing chemistry. Isoprene is not observed to form 3-methyl furan, indicating that this is not a prompt oxidation product. However, furan was observed in oxidation studies with butadiene. In addition, peroxy radicals in the second stage of butadiene oxidation are fully converted to peroxynitrates, and the average cross sections for integrated peroxynitrate bands have been determined. The research performed under this grant, and collaborated cofunded research with the National Science Foundation, has resulted in eight published peer-reviewed papers.
Journal Articles on this Report : 8 Displayed | Download in RIS Format
Other project views: | All 17 publications | 8 publications in selected types | All 8 journal articles |
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Donahue NM, Kroll JH, Anderson JG, Demerjian KL. Direct observations of OH production from the ozonolysysis of olefins. Geophysical Research Letters 1998;25(1):59-62. |
R825258 (1997) R825258 (Final) |
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Donahue NM, Anderson JG, Demerjian KL. New rate constants for ten OH alkane reactions from 300 to 400 K: An assessment of accuracy. Journal of Physical Chemistry A 1998;102(18):3121-3126. |
R825258 (Final) |
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Dransfield TJ, Perkins KK, Donahue NM, Anderson JG, Sprengnether MM, Demerjian KL. Temperature and pressure dependent kinetics of the gas-phase reaction of the hydroxyl radical with nitrogen dioxide. Geophysical Research Letters 1999;26(6):687-690. |
R825258 (Final) |
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Dransfield TJ, Donahue NM, Anderson JG. High-pressure flow reactor product study of the reactions of HOx + NO2: The role of vibrationally excited intermediates. Journal of Physical Chemistry A 2001;105(9):1507-1514. |
R825258 (Final) |
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Kroll JH, Hanisco TF, Donahue NM, Demerjian KL, Anderson JG. Accurate, direct measurements of OH yields from gas-phase ozone-alkene reactions using an in situ LIF instrument. Geophysical Research Letters 2001;28(20):3863-3866. |
R825258 (Final) |
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Kroll JH, Clarke JS, Donahue NM, Anderson JG, Demerjian KL. Mechanism of HOx formation in the gas-phase ozone-alkene reaction. 1. Direct, pressure-dependent measurements of prompt OH yields. Journal of Physical Chemistry A 2001;105(9):1554-1560. |
R825258 (Final) |
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Kroll JH, Sahay SR, Anderson JG, Demerjian KL, Donahue NM. Mechanism of HOx formation in the gas-phase ozone-alkene reaction. 2. Prompt versus thermal dissociation of carbonyl oxides to form OH. Journal of Physical Chemistry A 2001;105(18):4446-4457 |
R825258 (Final) |
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Sprengnether M, Demerjian KL, Donahue NM, Anderson JG. Product analysis of the OH oxidation of isoprene and 1,3-butadiene in the presence of NO. Journal of Geophysical Research-Atmospheres 2002;107(D15):art. no. 4269. |
R825258 (Final) |
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Supplemental Keywords:
air, natural hydrocarbons, oxidation, reactivity., RFA, Scientific Discipline, Air, tropospheric ozone, Atmospheric Sciences, rate constant determinations, high pressure flow system, fate and transport, ozone occurrence, Reaction Modulation Spectroscopy, spectroscopic studies, ambient air, ozone formation, hydrocarbon oxidation, chemical kinetics, atmosphereRelevant Websites:
http://www-kinetics.harvard.edu Exit
http://www.asrc.cestm.albany.edu Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.