RESEARCH OVERVIEW: In the Greenslade group, we have been focused on studying atmospheric aerosols and the chemicals that compose these. Aerosols are ubiquitous in the atmosphere and play intriguing roles in physical and chemical processes impacting fields such as atmospheric sciences, climate, combustion, medicine, and health. Aerosols are fine, solid or liquid particles suspended in a gaseous medium. The bulk of aerosols are 10s to 100s of nanometers in diameter and are composed of many molecules thus can have complicated chemical compositions. We investigate aerosol properties using physical chemistry, specifically spectroscopic methods and relate the results to broader questions, especially regarding climate change.
Complex aerosols are of special interest. Whether uniquely shaped or of mixed composition, we are interested in understanding their optical and morphological properties and how these change as a function of environmental influence.
One of the main techniques we use is cavity ring-down (CRD) spectroscopy at 532 nm using the frequency doubled Nd:YAG output. This green wavelength is near the center of the solar spectrum. Because the technique relies on the time decay of the light in the cavity instead of intensity changes, random fluctuations have limited impact and the instrument is especially sensitive to small optical changes, even extinction from just one aerosol particle! One other advantage of our instrument is that it also allows for the interrogation of aerosols before and after an environmental change.
Our other main spectroscopic tool is the AE-DOAS instrument. This is another custom instrument which was built for us by Cerex Monitoring Solutions. It is based on a standard UV/Vis spectrometer but it uses a multipass gas cell with an adjustable path length of up to nearly 20 m for in situ determination of aerosol extinction. Having the best detection limit from 235-700 nm with a resolution of 0.5 nm, it has unique broad band capabilities to capture the wavelength dependence of aerosol optical properties.
CURRENT GROUP MEMBERS:
Jillian Morang, Vahid Hosseinpour Hashemi, Jackson Kaspari;
Elizabeth Frinak Mentis;
Alexis Attwood,,Ryan Chartier, Douglas Collins, James Hendrickx, Tyler Galpin, Sean Dinneen (co-advised with Prof. Deravi);
Justin Pleva, Jennifer Pollock, Olivia Segit-Rix, Jasmine Humphries, Carleen Dingman, Nicholas Levergood, Zachary Rice, Adam Knedeisen, Meaghan Elrick, Matthew Reuter, Christopher Redus, Anthony Jennings, Cynthia Gerber, Brent Lawson, Jackson Kaspari, Alexandra Singh
Ph.D., Physical Chemistry, University of Pennsylvania
B.A., Chemistry, Bryn Mawr College
Marine Atmospheric Chemistry
CHEM 684: Physical Chemistry II
CHEM 685: Physical Chemistry Laboratory
CHEM 696: Independent Study
CHEM 699: Thesis
CHEM 798: Senior Seminar
CHEM 927: Kinetics and Dynamics
CHEM 995: Colloquium
INCO 590: Rsrch Exp/Chemistry
INCO 790: Adv Rsrch Exp/Chemistry
TECH 500: Integrated CEPS Seminar I
TECH 501: Integrated CEPS Seminar II
Morang, J. L., Galpin, T., & Greenslade, M. E. (2018). Effective Refractive Index Values and Single Scattering Albedo Implications for Dry-Generated Clays As Retrieved from Cavity Ring-Down Spectroscopy. Analytical Chemistry, 90(19), 11248-11255. doi:10.1021/acs.analchem.8b01319
Dinneen, S. R., Deravi, L. F., & Greenslade, M. E. (2018). An iterative correction approach used to retrieve the refractive index of squid pigment aerosols. Journal of Optics, 20(3), 034003. doi:10.1088/2040-8986/aaa6ff
Galpin, T., Chartier, R. T., Levergood, N., & Greenslade, M. E. (2017). Refractive index retrievals for polystyrene latex spheres in the spectral range 220–420 nm. Aerosol Science and Technology, 51(10), 1158-1167. doi:10.1080/02786826.2017.1339014
Dinneen, S. R., Greenslade, M. E., & Deravi, L. F. (2017). Optical extinction of size-controlled aerosols generated from squid chromatophore pigments. APL Materials, 5(10), 104802. doi:10.1063/1.5002153
Dinneen, S. R., Osgood, R. M., Greenslade, M. E., & Deravi, L. F. (2017). Color Richness in Cephalopod Chromatophores Originating from High Refractive Index Biomolecules. The Journal of Physical Chemistry Letters, 8(1), 313-317. doi:10.1021/acs.jpclett.6b02398
Greenslade, M. E., Lester, M. I., Radenović, D. Č., van Roij, A. J. A., & Parker, D. H. (2005). (2+1) Resonance-enhanced ionization spectroscopy of a state-selected beam of OH radicals. The Journal of Chemical Physics, 123(7), 074309. doi:10.1063/1.1997132
Marshall, M. D., Davey, J. B., Greenslade, M. E., & Lester, M. I. (2004). Evidence for partial quenching of orbital angular momentum upon complex formation in the infrared spectrum of OH-acetylene. The Journal of Chemical Physics, 121(12), 5845-5851. doi:10.1063/1.1784444
Davey, J. B., Greenslade, M. E., Marshall, M. D., Lester, M. I., & Wheeler, M. D. (2004). Infrared spectrum and stability of a π-type hydrogen-bonded complex between the OH and C2H2 reactants. The Journal of Chemical Physics, 121(7), 3009-3018. doi:10.1063/1.1768933
Radenović, D. Č., van Roij, A. J. A., Chestakov, D. A., Eppink, A. T. J. B., ter Meulen, J. J., Parker, D. H., . . . Lester, M. I. (2003). Photodissociation of the OD radical at 226 and 243 nm. The Journal of Chemical Physics, 119(18), 9341-9343. doi:10.1063/1.1623175
Chartier, R. T., & Greenslade, M. E. (n.d.). Initial investigation of the wavelength dependence of optical properties measured with a new multi-pass Aerosol Extinction Differential Optical Absorption Spectrometer (AE-DOAS). Atmospheric Measurement Techniques, 5(4), 709-721. doi:10.5194/amt-5-709-2012