| Our research specializes in the development and implementation of powerful new measurement methodologies to chemical problems of environmental importance. An example is the recently developed cavity ring-down (CRD) absorption spectroscopic technique, a very sensitive variant of normal absorption spectroscopy which uses light from pulsed or continuous laser sources. Implementation projects include the measurement of chemical reaction rates of free radicals extant in the terrestrial atmosphere and the ultra-sensitive quantitative determination of atmospheric trace gas concentrations using CRD. On the development side, a project is under way to extend the powerfulCRD method into the condensed phase, opening up the potential for a number of pollution monitoring and/or kinetic applications.
The main thrust of the research focuses on the reactivity of (free) radicals in the terrestrial and other planetary and cometary atmospheres. Because of their high concentrations and rapid reaction rates, radicals control the concentrations and fates of nearly all pollutants. Sophisticated computer models are able to use the rate coefficients for elementary reaction steps along with other data to predict the effect of anthropogenic (man-made) emissions. By conducting both laboratory based and field measurements, these models can be verified and refined.
One method for refining the atmospheric chemical models is to augment the base information or inputs which are used to generate the model. Included in this data set are the photolysis rates and product branching ratios for the radical and closed-shell components, particularly those known to be important in subsequent chemistry, and the chemical reaction kinetic data that describes the reactivity of the radicals involved. These parameters are most readily measured in a well-controlled laboratory environment under known conditions of temperature and pressure using considerably simpler model reaction sequences than those encountered in nature. The power that CRD brings to the measurements in these situations is ready quantitation, sensitivity and selectivity, determination of absolute densities of radicals and other species, and detection of small amounts of species in the presence of large amounts and varieties of contaminants.
Verification of the atmospheric models is achieved by accurately measuring the concentration of a few "trace" species along with various meteorological factors, including the solar flux, and comparing these with the model predictions. Dr. O~RBrien and his group have developed a suite of methods for the determination of extremely short-lived species, as well as some of the more stable ones. Interestingly, CRD is complementary to the main analytical method that is used, Laser Excited Fluorescence, in that a variety of compounds which are "invisible" to LEF are readily accessible to it. Thus the doorway to a number of &quo
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F. Wedian and D. B. Atkinson, “Ozone Modulation of Volatile Hydrocarbons Using Membrane Introduction Mass Spectrometry”, Environmental Science & Tech., 36, 4152, (2002).
D. B. Atkinson and J. L. Spillman, “Alkyl Peroxy Radical Kinetics Measured Using CW-Cavity Ring-down Spectroscopy”, J. Phys. Chem. A, 106, 8891, (2002).
M. A. Ostrovsky, Y. V. Sergeev, D. B. Atkinson, L. V. Soustov, J. F. Hejtmancik, “Comparison of Ultraviolet Induced Photo-kinetics for Lens-derived and Recombinant beta-crystallins”, Molecular Vision, 8, 72, (2002).
J. D. Smith and D. B. Atkinson, "A Portable Pulsed Cavity Ring-Down Transmissometer for Measurement of the Optical Extinction of the Atmospheric Aerosol", Analyst, 126, 1216, (2001).
D. B. Atkinson and J. W. Hudgens, "Chlorination Chemistry. 2. Rate Coefficients, Reaction Mechanism, and Spectrum of the Chlorine Adduct of Allene", J. Phys. Chem. A., 104, 811, (2000).
D. B. Atkinson and J. W. Hudgens, "Chlorination Chemistry. 1. Rate Coefficients, Reaction Mechanisms, and Spectra of the Chlorine and Bromine Adducts of Propargyl Halides", J. Phys. Chem. A., 103, 7978, (1999).
D. B. Atkinson, J. W. Hudgens, and A. J. Orr-Ewing, "Kinetic Studies of the Reactions of IO Radicals Determined by Cavity Ring-Down Spectroscopy", J. Phys. Chem. A., 103, 6173 (1999).
D. B. Atkinson and J. W. Hudgens, "Rate Coefficients for the Propargyl Radical Self-Reaction and Oxygen Addition Reaction Measured Using Ultraviolet Cavity Ring-down Spectroscopy.", J. Phys. Chem. A., 103, 4242 (1999).
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