Dr. Jonathan E. Thompson
Title: Associate Professor
Education: Ph.D., University of Florida, 2001
Research Area: Analytical Chemistry
Office: Chemistry 328-A
Principal Research Interests
- Chemical and Optical Properties of Atmospheric Aerosols
- Molecular Spectroscopy
- High-Speed Separations Applied to Environmental Analysis
- Novel Architectures for Chemical Separations
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.
- Wei, Y., Zhang, Q. and J.E. Thompson "The Wetting Behavior of Fresh and Aged Soot Studied Through Contact Angle Measurements" Atmos. & Climate Sci. 2017, 7(1), 11-22.
- J.E. Thompson "Cavity Enhanced Spectroscopy (CES) in Condensed Phases: Recent Literature & Remaining Challenges." in press J. Spectrosc.
- J.E. Thompson "Recent Trends in National Science Foundation (NSF) Division of Chemistry Funding." The Chemical Educator, 2016, 21, 257-263.
- J.E. Thompson "Crowd-Sourced Air Quality Studies: A Review of the Literature & Portable Sensors." Trends in Environ. Anal. Chem. 2016, 11, 23-34.
- Thompson, J.E. & Brode, L. "My dear buret, your time has indeed come!" J. Chem. Educ. 2016, 93(6), pp. 988-989.
- Cao, T. and J.E. Thompson "Fully Portable Personal Monitoring of PM2.5 for Health and Exposure Studies." in press Anal. Lett, accepted June 2016 – A.S.A.P. on web version available now.
- Cao, T. and J.E. Thompson "Personal Monitoring of Ozone Exposure: A fully portable device for under $150 USD cost." Sensors & Actuators B, 2016, 224, pp. 936–943.
- T. Cao, Q. Zhang, and J.E. Thompson "An Inexpensive, Electronic Buret: A Tool for Chemical Education." J. Chem. Educ., 2015, 92 (1), pp 106–109.
- Zhang, Q. and J.E. Thompson "A Model for Absorption of Solar Radiation by Mineral Dust within Liquid Cloud Drops." J. Atmos. Solar-Terrestr. Phys. 2015, 133, pp 121-128.
- Zhang, Q. and J.E. Thompson "Effect of particle mixing morphology on aerosol scattering and absorption: A discrete dipole modelling study." GeoResJ (3–4), 9–18, 2014.
- "Light Scattering and Extinction Measurements Combined with Laser-Induced Incandescence for the Real-Time Determination of Soot Mass Absorption Cross Section." Anal. Chem., 2013, 85, 9181–9188.
- "Atmospheric Black Carbon Can Exhibit Enhanced Light Absorption at High Relative Humidity" Atmos. Chem. Phys. Discuss. 2013, 13, 29413 - 29445.
- "Technical Note: Aeolian dust proxies produce visible luminescence upon intense laser-illumination that results from incandescence of internally mixed carbon." Atmos. Meas. Tech. Disc. 2013, 6, 5173-5194.
- "Aerosol Optical Properties at Pasadena, CA During CALNEX 2010." Atmos. Environ. 2012, 55, 190–200.
- "Rayleigh Scattering Measurements of Several Fluorocarbon Gases." J. Environ. Monit., 2011, 13, 3294 – 3297.
- "Evaluation of a Quantitative Structure Property Relationship (QSPR) for Predicting Mid-Visible Refractive Index of Secondary Organic Aerosol (SOA)." Phys. Chem. Chem. Phys. 2011, 13, 6872-6882.
- "Characterization of a Novel Particle into Liquid Sampler for Analysis of Single Fluorescent Aerosol Particles Through Capillary Electrophoresis (CE)." Analytica Chimica Acta 2011, 702, 120–126.
- "Light Scattering & Absorption by Wind Blown Dust: Theory, Measurement and Recent Data." Aeolian Research, 2010, 2, 5–26.
- "Characterization of Colored Oligomeric Products Formed During Irradiation of Aqueous Solutions Containing H2O2 & Phenolic Compounds." Atmos. Environ. 2010, 44, 541-551.
- "Evaluation of microvolume regenerated cellulose (RC) microdialysis fibers for the sampling and detection of ammonia in air." Talanta 2010, 81, 1350-1356.
- "Simultaneous Measurement of Optical Scattering and Extinction on Dispersed Aerosol Samples." Anal. Chem. 2010, 82, 7885 – 7896.
- "Development of a Fixed Frequency Aerosol Albedometer." Optics Express, 2008, 16, 2191-2205.
- "Cavity Ring-Down Lossmeter Using a Pulsed Light Emitting Diode Source and Photon Counting" Meas. Sci. & Technol. 2007, 18, 147-154.
- "Tungsten Source Integrated Cavity Output Spectroscopy (W-ICOS) for the Determination of Ambient Atmospheric Extinction Coefficient" Applied Optics, 2006, 45(11), 2465-2473.