Dr. Jonathan E. Thompson
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Title: |
Associate Professor |
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Education: |
Ph.D., University of Florida, 2001 |
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Research Area: |
Analytical Chemistry |
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Office: |
Chemistry 328-A |
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Principal Research Interests
- Chemical and Optical Properties of Atmospheric Aerosols
- Molecular Spectroscopy
- High-Speed Separations Applied to Environmental Analysis
- Novel Architectures for Chemical Separations
Professor Thompson's research interests involve using modern optical and separation based techniques to study the composition and chemical transformations occurring within earth’s atmosphere. Often, these efforts are focused on understanding the chemical and optical characteristics of atmospheric particulate matter and trace gases. These analytes are known to adversely affect human health, decrease visibility, and alter earth's radiative balance.
One recent effort has been the development of a device termed the aerosol albedometer. In this work, we have designed and constructed a device to simultaneously monitor aerosol scattering (bscat) and extinction coefficient (bext) at 532 nm. The ratio of these terms is known as the aerosol single scatter albedo (SSA) and is a key variable in assessing whether ambient particulate matter leads to a net warming or cooling of climate. Measuring the scattering and extinction coefficients of the background ambient aerosol can be analytically challenging since extinction coefficients are typically < 100 Mm-1 (% Trans. > 99.99% over a 1 m path). Therefore the techniques employed must be highly sensitive.
In the future we hope to use this device in laboratory and field work to better understand how aerosol albedo varies as a function of chemical composition and mixing state. These efforts will include studies of the effect of chemical and physical transformations on the size and optical properties of various different aerosols and extraction of refractive index from measurements and application of Mie theory.
Figure 1. Aerosol extinction coefficient (bext), scattering coefficient (bscat), and albedo as measured with the aerosol albedometer at Kearney, NE over 2 two days in October 2007. Blue data points represent extinction coefficient as measured by CRDS, the red circles represent scattering coefficient as measured with the integrating sphere, the black circles represent scattering coefficient measured with the reference nephelometer, and the green trace represents measured albedo as plotted on the second y-axis. All times reflect local time at Kearney, NE. The inset shows the correlation between scattering coefficient measured by the albedometer and the M903 reference nephelometer.
In another recent project, our group has pioneered LED based cavity ring-down measurements (LED-CRDS). In this technique, light from a light emitting diode (LED) is introduced into an optical resonator formed from 2 highly reflective mirrors, the LED is then quickly turned off. Several on / off cycles are shown in figure A below.
Since the mirrors involved are highly reflective (R > 0.999), the light continues to travel between the mirrors for a few microseconds after switching off the LED. A plot of light intensity in time after switching off the LED yields an exponential decay curve as shown in the figure on the right. The time constant (tau) of this decay is the measured variable in a CRDS experiment. This time constant is a measure of the rate of optical attenuation of the sample which is placed between the mirrors. This time constant is inversely proportional to the concentration of an absorbing gas placed in the measurement cell. We have initially applied this instrument to the measurement of absorption by ozone and molecular iodine. Use of LED’s for the CRDS technique offers several advantages (inexpensive, low power, broad emission) over laser sources for CRDS, but also present certain practical challenges. In the near future we hope to explore new twists on this technique to exploit the unique characteristics of the LED source and the high sensitivity of CRDS. This project was featured in a recent issue of Laser Focus World magazine.
Representative Publications
- "Aerosol Albedometer: A Tool for Measuring Optical Scattering and Extinction of Dispersed Aerosols." Thompson, J.E., G.I.T. Laboratory Journal , 9-10, 2010.
- "Optical Properties of Aeolian Dusts Common to West Texas." Ma, L.; Hsieh, D.; Holder, D.; Zobeck, T.; C. Morgan, C.; Thompson, J.E., Aeolian Research 3, 235–242 , 2011.
- "Evaluation of a Quantitative Structure Property Relationship (QSPR) for Predicting Mid-Visible Refractive Index of Secondary Organic Aerosol (SOA)." Redmond, H. and J.E. Thompson, Phys. Chem. Chem. Phys., 2011, 13, 6872-6882, DOI: 10.1039/C0CP02270E
- "Characterization of a Novel Particle into Liquid Sampler for Analysis of Single Fluorescent Aerosol Particles Through Capillary Electrophoresis (CE)." Tang, H.; S. Hiemstra and J.E. Thompson, Analytica Chimica Acta702, (2011), 120–126.
- "Light Scattering & Absorption by Wind Blown Dust: Theory, Measurement and Recent Data." Redmond, H.; Dial, K.; Thompson, J.E.Aeolion Research, 2010, 2, 5– 26.
- "Characterization of Colored Oligomeric Products Formed During Irradiation of Aqueous Solutions Containing H2O2 and Phenolic Compounds." Chang, J.; Thompson, J.E. Atmos. Environ.2010, 44(4), 541-551.
- "Evaluation of microvolume regenerated cellulose (RC) microdialysis fibers for the sampling and detection of ammonia in air." Tang, H.; Thompson, J.E. Talanta, 2010, 81(4, 5), 1350-1356.
- "Simultaneous Measurement of Optical Scattering and Extinction on Dispersed Aerosol Samples." Dial, K.; Hiemstra, S.; Thompson, J.E. Anal. Chem. 2010, 82, 7885 – 7896.
- "Evaluation of a Quantitative Structure Property Relationship (QSPR) for Predicting Mid-Visible Refractive Index of Secondary Organic Aerosol (SOA)." Redmond, H.; Thompson, J.E. Phys. Chem. Chem. Phys., DOI:10.1039/C0CP02270E.
- "Development of a Fixed Frequency Aerosol Albedometer." Thompson, J.E.; DuVall, R.; Policarpio, D.; Barta, N.Optics Express, 2008, 16(3), 2191-2205.
- "Cavity Ring-Down Lossmeter Using a Pulsed Light Emitting Diode Source and Photon Counting" Thompson, J.E.; Myers, K. Meas. Sci.& Technol. 2007, 18(1), 147-154.
- "Tungsten Source Integrated Cavity Output Spectroscopy (W-ICOS) for the Determination of Ambient Atmospheric Extinction Coefficient" Thompson, J.E., Spangler, H. Applied Optics, 2006, 45(11), 2465-2473.
- "An Inexpensive Device for Capillary Electrophoresis (CE) with Fluorescence Detection" Thompson, J.E., Anderson, G.A., Shurrush, K. Journal of Chemical Education, 2006, 83(11), 1677 – 1680.
- "Atmospheric Aerosol Measurements by Cavity Ringdown Turbidimetry." Thompson, J.E.; Smith, B.W.; Winefordner, J.D. Aerosol Sci. and Tech., 2003, 37(3), 221-230.
- "Monitoring Atmospheric Extinction Through Cavity Ringdown Turbidity" Thompson, J.E.; Smith, B.W.; Winefordner, J.D. Anal. Chem., 2002, 74 (9), 1962 -1967.
- "Rapid Determination of Aspartate Enantiomers in Tissue Samples by Microdialysis Coupled On-Line with Capillary Electrophoresis." Thompson, J.E.; Vickroy, T.W.; Kennedy, R.T. Anal. Chem. 1999, 71, 2379-2384
- "Optically Gated Capillary Electrophoresis of o-Pthaldialdehyde/β-Mercaptoethanol Derivatives of Amino Acids for Chemical Monitoring." Tao, L.; Thompson, J.E.; Kennedy, R.T. Anal. Chem. 1998, 70, 4015-4022.