Grantee Research Project Results
Final Report: A New Application of the Fundamental Physics of Atmospheric Pressure Ionization Mass Spectrometry to Ozone and Fine Particulate Formation Mechanisms
EPA Grant Number: R828179Title: A New Application of the Fundamental Physics of Atmospheric Pressure Ionization Mass Spectrometry to Ozone and Fine Particulate Formation Mechanisms
Investigators: O'Brien, Robert J. , Hard, Thomas M. , Atkinson, Dean B.
Institution: Portland State University
EPA Project Officer: Hahn, Intaek
Project Period: July 1, 2000 through June 30, 2002
Project Amount: $223,574
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Water , Land and Waste Management , Air , Safer Chemicals
Objective:
This objective of this research project was to determine the applicability of real-time ion-trap mass spectrometry (ITMS) to the elucidation of atmospheric-pressure oxidation mechanisms as they occur in polluted air for the formation of oxidants and particles.
Summary/Accomplishments (Outputs/Outcomes):
This study successfully applied ITMS to the identification and characterization of the reaction mechanisms of ozone and hydroxyl radicals with atmospheric alkenes, which are important in the formation of polluted air oxidants and particles. ITMS is a relatively new, inexpensive, but powerful form of mass spectrometry that has not previously been applied to the study of atmospheric oxidation mechanisms as they occur in polluted atmospheres. The products of typical oxidation mechanisms were identified and their time evolution studied by analyzing processes in two types of atmospheric reactors. In a static reactor, primary and secondary oxidation products were identified by their characteristic parent ion masses and fragmentation patterns. In a flowing reactor, the time dependence of their evolution was followed as well.
There are numerous approaches available to investigate the kinetics and mechanisms of gas-phase reactions, including Fourier transform infrared (FTIR) spectroscopy (Niki, et al., 1987), fast flow tube/mass spectrometers (Li, et al., 2002), turbulent flow tube high-pressure chemical ionization mass spectrometry (Seeley, et al., 1996; Scholtens, et al., 1999), atmospheric chambers coupled with a gas chromatography-flame ionization detector (GC-FID), and atmospheric pressure ionization-mass spectrometer (Arey, et al., 2001; Foster, et al., 1999) . In this study, we introduced a method where atmospheric pressure reactors are coupled to an ITMS. The ITMS is potentially valuable as a detector for gas phase reaction experiments because it provides various clean chemical ionization modes, and mass spectrometry/mass spectrometry experiments that can be performed for structure determination. In addition, the ITMS is an inexpensive bench-top instrument.
Alkenes are an important class of volatile organic compounds (VOCs) that have natural and industrial sources (Seinfeld and Pandis, 1998). In the atmosphere, the main sinks for alkenes are chemical reactions with ozone, OH, and NO3 (Seinfeld and Pandis, 1998; Atkinson, 1997). The mechanism of gas phase reactions of ozone with alkenes in the troposphere has been studied over the last few decades (Atkinson, 1997; Tuazon and Pandis, 1998; Hasson, et al., 2001). Major overall features of ozone-alkene reactions have been established for simple alkenes, but little verifiable information is available for reactions with large alkenes (either open-chain or ring compounds), especially the nature and yields of their products (Atkinson, 1997; Tuazon, et al., 1998; Hasson, et al., 2001).
The accepted mechanism of gas phase reaction of ozone with alkenes proceeds via the addition of O3 to the double bond, which rapidly dissociates to a carbonyl product and a biradical "Criegee" intermediate (Niki, et al., 1987; Atkinson, 1997; Martinez and Herron, 1987):
The biradical intermediate is an energy-rich species, which rapidly undergoes complex bimolecular and unimolecular rearrangement and/or fragmentation to yield a set of secondary products, including hydroxyl radicals (OH) (Atkinson, 1997). Typical OH/alkene reaction rate coefficients are several orders of magnitude larger than those for the corresponding O3/alkene reaction; therefore, OH reacts rapidly with the alkene to produce a secondary set of gas phase products. The reactivity of OH causes problems for studying the primary products of ozonolysis; therefore, OH scavengers such as cyclohexane (Shu and Atkinson, 1994) and 2-butanol (Chew and Atkinson, 1996) are commonly used to suppress the OH formed from the reactions of O3 with alkenes.
In this paper, 2,3-dimethyl-2-butene (tetramethylethylene, TME) was used as a reagent because the 2,3-dimethyl-2-butene (TME)/O3 reaction has been studied intensively (Niki, et al., 1987; Martinez and Herron, 1987). The major features of the reaction's products and kinetic data are well established (Niki, et al., 1987; Foster, et al., 1999; Tuazon, et al., 1998; Hasson, et al., 2001; Olzmann, et al., 1997; Kroll, et al., 2001; Johnson, et al., 2001; Greene and Atkinson, 1992; Schaefer, et al., 1997; Richard, et al., 1999; Siese, et al., 2001; Grosjean, et al., 1996). The reaction is quite fast. Reported primary stable products of the TME/O3 reaction are acetone ([CH3]2CO), methylgloxal (CH3C[=O]CHO), and hydroxyacetone or acetol (CH3C[=O]CH2OH).
A problem in these types of studies is that a multicomponent mass spectrum is obtained from the mixture of reactants and products. The approach investigated in this research project to mitigate this problem was to replace the electron ionization mode with a "softer" chemical ionization mode. Soft ionization refers to the ability to produce molecular ions or ions related to the original compound (e.g., protonated ions) from analytes with little or no fragmentation. Because the major products of the ozonolysis are easily protonatedoxygenated compounds, proton exchange chemical ionization reagents were used, including methane (CH4) and isobutane (C4H10).
The full final report describes the external reactor designs for the flow-tube and the static atmospheric pressure reactors and their operational procedures. The interface between the reactors and the low pressure mass spectrometer for each type is discussed. Experimental results for the TME/O3 reactions demonstrate the strengths and weaknesses of the two reactors. Table 1 illustrates agreement between traditional techniques and this new ITMS approach.
Table 1. Yields of Products From Reaction of Ozone With TME
| ITMS, this workstatic reactora | ITMS, this workflow-tube reactora | Niki, et al. (1987)b | Grosjean, et al. (1996) | Tuazon, et al. (1997) |
Acetone | 0.97 ± 0.05 | 1.01± 0.01 | 1.02 ± 0.13 | 1.006 ± 0.049 | 1.14 ± 0.19d |
Methylglyoxal | Not calibrated | Not calibrated | 0.09 | 0.314 ± 0.071c | Not observed |
Hydroxyacetone | 0.18 ± 0.1 | Not calibratede | 0.07 ± 0.01 | | Not observed |
a Static reactor and flow-tube reactors (yields relative to TME consumed, in presence of isobutane). b Absolute yields as cited in Calvert, et al., 2000. c Combined absolute yield of methylglyoxal plus hydroxyacetone. d Absolute yield with FTIR detection. e Absolute yield with GC-FID detection. |
It is demonstrated that atmospheric pressure reactors coupled with an ion trap mass spectrometer can be used to study gas phase reactions. The TME/ozone reaction was a sample case for the application of the new designs. The static and flow-tube reactors provide complementary information. The static reactor can be used to distinguish between different reaction products; the flow-tube can be used to study the kinetics of the products as well as the product yields. The new designs are convenient to use because they are interchangeable, and the loading of reactants and their release occur under conditions that permit continuous, sensitive, and specific monitoring by the ITMS. Future work will seek to study short-lived intermediate product behaviors at short distances. The method also can be used to investigate less well-studied biogenic alkene/ozone reactions. The instrument, in principle, may be used to study other oxidation reactions of hydrocarbons (e.g., reactions with OH and with NO3) relevant to atmospheric chemistry at realistic pressures and temperatures.
This research has developed a much simpler method of learning the oxidative fate of atmospheric VOC emissions. Such oxidative byproducts can show up both in the gas and the particulate phase. Both of these phases are inhaled by members of the general population and can be a significant potential health hazard. Future research using this technology will more economically and rapidly determine the status and distribution of such oxidation products.
References:
Niki H, Maker PD, Savage CM, Breitenbach LP, Hurley MD. Journal of Physical Chemistry 1987;94:941-946.
Li Z, Wuebbles RD, Pylawka NJ. Chemical Physics Letters 2002;354:491-497.
Seeley JV, Meads RF, Elrod MJ, Molina MJ. Journal of Physical Chemistry 1996;100:4026-4031.
Scholtens KW, Messer BM, Cappa CD, Elrod MJ. Journal of Physical Chemistry A 1999; 103:4378-4384.
Arey J, Aschmann SM, Kwok ESC, Atkinson R. Journal of Physical Chemistry A 2001;105:1020-1027.
Foster KL, Caldwell TE, Benter T, Langer S, Hemminger JC, Finlayson-Pitts B. Journal of Physical Chemistry 1999;1:5615-5621.
Seinfeld JH, Pandis SN. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. Second Edition. Wiley Interscience, January 1998.
Atkinson R. Journal of Physical and Chemical Reference Data 1997;26:215-290.
Tuazon EC, Aschmann SM, Arey J, Atkinson R. Environmental Science and Technology 1998;32:2106-2112.
Hasson AS, Orzechowska G, Paulson SE. Journal of Geophysical Research - Atmospheres 2001;106:3431-3442.
Martinez RI, Herron JT. Journal of Physical Chemistry 1987;91:946-953.
Shu Y, Atkinson R. International Journal of Chemical Kinetics 1994;26:1193.
Chew AA, Atkinson R. Journal of Geophysical Research 1996;101:28649.
Olzmann M, Kraka E, Cremer D, Gutbrod R, Andersson S. Journal of Physical Chemistry A 1997;101:9421-9429.
Kroll JH, Hanisco TF, Donahue NM, Demerjian KL, Anderson JG. Geophysical Research Letters 2001;28:3863-3866.
Johnson D, Rickard AR, Marston G, Fish DJ. Transport and chemical transformation in the troposphere. In: Proceedings of the 6th EUROTRAC Symposium, Garmisch-Partenkirchen, Germany, 2001, pp. 405-409.
Greene CR, Atkinson R. International Journal of Chemical Kinetics 1992;24:803-811.
Schaefer C, Horie O, Crowley JN, Moortgat GK. Geophysical Research Letters 1997;24:1611-1614.
Richard AR, Johnson D, McGill CD, Marston G. Journal of Physical Chemistry A 1999;103:7656-7664.
Siese M, Becker KH, Brockmann KJ, Geiger H, Hofzumahaus A, Holland F, Mihelcic D, Wirtz K. Environmental Science and Technology 2001;35:4660-4667.
Grosjean E, Andrade JB, Grosjean D. Environmental Science and Technology 1996;30:975-983.
Cook GA, Kiffer AD, Klumpp CV, Malik AH, Spence LA. Advances in Chemistry Series 1959;21:44-52.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 2 publications | 1 publications in selected types | All 1 journal articles |
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Type | Citation | ||
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Wedian F, Atkinson DB. Ozone modulation of volatile hydrocarbons using membrane introduction mass spectrometry. Environmental Science & Technology 2002;36(19):4152-4155. |
R828179 (2001) R828179 (Final) |
not available |
Supplemental Keywords:
atmospheric oxidation mechanisms, ion-trap mass spectrometry, ITMS, Fourier transform infrared, FTIR, fast flow tube/mass spectrometer, FF/MS, gas chromatography-flame ionization detector, GC-FID, atmospheric pressure ionization-mass spectrometer, API-MS, physics, atmosphere., RFA, Scientific Discipline, Air, Toxics, particulate matter, air toxics, Environmental Chemistry, HAPS, VOCs, Atmospheric Sciences, tropospheric ozone, Environmental Engineering, Engineering, Chemistry, & Physics, hydroxyl radical, particle size, particulates, stratospheric ozone, aerosol particles, fine particles, mass spectrometry, hydrocarbon, biogenic modeling, air modeling, ozone, atmospheric pressure ionization, ambient air, ambient emissions, chemical composition, air pollution models, treatment, biogenic hydrocarbons, hydronium, biogenic hydrocarbon mixing, hydroxyl radicals, photochemical processes, fine particulate formation, airshed models, ambient aerosol particlesProgress 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.