Margaret E. Greenslade
- B.A., 1998, Bryn Mawr College
- Ph.D., 2005, University of Pennsylvania
- Research Scientist, 2005 - 2007, Cooperative Institute for Research in Environmental Science (CIRES) at University of Colorado, Boulder and an affiliate of the National Oceanic and Atmospheric Administration (NOAA)
- CHEM 404: General Chemistry II, Spring 2012, 2014
- CHEM 685: Physical Chemistry Laboratory I, Fall 2007, 2008, 2009, 2013
- CHEM 686: Physical Chemistry Laboratory II, Spring 2008, 2009, 2010
- CHEM 699: Thesis, AY 2007-2008, 2008-2009, Sp 2011- Fall 2012, 2013-2014
- CHEM 776/876: Physical Chemistry III with Lab, Fall 2010, 2011
- CHEM 927: Molecular Reaction Dynamics (10%), Spring 2008
- CHEM 995D: Colloquium/Physical Chemistry, Spectroscopy, Fall 2009
- CHEM 998A: Graduate Seminar, Spring 2011
- Scheduled to Teach CHEM 685: Physical Chemistry Laboratory I, Fall 2014 and CHEM 684: Physical Chemistry II, Spring 2015
Physical and Atmospheric Chemistry. Aerosol optical properties are of specific interest.
Current Research Interests
Aerosols are ubiquitous in the atmosphere and play intriguing roles in physical and chemical processes impacting fields such as atmospheric sciences, climate change, combustion, medicine, and health. Aerosols are fine, solid or liquid particles suspended in a gaseous medium. They are composed of many molecules since the bulk of aerosols are 10s to 100s of nanometers in diameter and 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. CRD is commonly used to measure absorption of gas phase species. Since 2001, it has been used to measure aerosol extinction in situ. We built a custom, mobile CRD instrument at UNH. The instrument operates at 532 nm using the frequency doubled Nd:YAG output, but we have capability to set up cavities in the future at 1064 and 355 nm. 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. So far we have focused on increased relative humidity as the environmental change of interest.
To date we have studied a number of aerosols with the CRD including three types of clay that are found in ambient mineral dust (montmorillonite, kaolinite, illite) and montmorillonite mixed with sodium chloride, ammonium sulfate, and three dicarboxylic acids (malonic, succinic and glutaric acids). The clays we have studied are layered aluminum-silicate clays with rough edges and are thus difficult to accurately model via spherical Mie theory. Please see our publications for detailed results.
Figure 1: Schematic of a typical cavity ring-down experimental set-up.
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. To date, the AE-DOAS has been used to characterize polystyrene spheres (an aerosol standard), nigrosine dye and ambient air influenced by the 2010 Canadian wildfires.
Figure 2: The AE-DOS shematic on left with photographs of various views of the instrument on right. The beam
path illumination was created using a green laser at the light inlet of the gas cell. The mirrors can be adjusted to
determine the number of passes and thus the path length.
We also extensively use computer programs coded to perform Mie Theory calculations.
Additional laboratory equipment includes: Two custom built, constant output atomizers with molecular sieve driers; a scanning particle mobility sizer (SMPS, TSI, Inc., Model 3936L75 including DMA and CPC) with Dell Latitude laptop; two GPFLO1 Flowmeters (TSI, Inc., Model 4140); a balance (Shimadzu Model AUX120); mass flow controllers (Sierra Instruments, Model 810); ultrasonic bath; stir/heating plates; custom made, temperature controlled humidifier; RH/T probes; and various supplies, tools and safety equipment.
Current Group Members (2014-2015)
Tyler R. Galpin (3rd year Ph.D. Student)
Chris E. Redus (Undergraduate Researcher)
We are often looking for undergraduate and graduate students to join our research efforts. If you are interested, please contact Meg.
Former Group Members
Alexis R. Attwood (Ph.D. awarded 2012, now at U Colorado Boulder/NOAA)
Ryan T. Chartier (M.S. awarded 2010, now at RTI International)
Adam Knedeisen (B.S. awarded 2014, thesis)
Carleen Dingman (B.S. awarded 2013, thesis)
Jennifer Pollack (B.S. awarded 2009, thesis)
Justin Pleva (B.S. awarded 2008, thesis)
Elizabeth Mentis (Research Scientist, now at Auburn Environmental Consulting & Testing)
Douglas Collins (Ph.D. student, now at U California San Diego)
James Hendrickx (M.S. student)
Undergraduate research students: Meaghan Elrick, Zachary Rice, Nicholas Levergood, Jasmine Humphries, Olivia Segit-Rix
- A. R. Attwood**, M. E. Greenslade, “Deliquescence Behavior of Internally Mixed Clay and Salt Aerosols by Optical Extinction Measurements,” J. Phys. Chem. A.116, 4518 (2012). Published on-line April 18, 2012: http://pubs.acs.org/doi/abs/10.1021/jp2124026
- R. T. Chartier**, M. E. Greenslade, “Initial investigation of the wavelength dependence of optical properties measured with a new multi-pass aerosol extinction differential optical absorption spectrometer (AE-DOAS),” Atmos. Meas. Tech. 5, 709 (2012). Reviews available: http://www.atmos-meas-tech-discuss.net/4/6315/2011/amtd-4-6315-2011.html
- A. R. Attwood**, M. E. Greenslade, “Optical Properties and Associated Hygroscopicity of Clay Aerosols”, Aerosol Sci. Technol., 45, 1350 (2011).
- M. E. Greenslade, M. I. Lester, D. Č. Radenović, A. J. A. van Roij, D. H. Parker, “(2+1) Resonance Enhanced Ionization Spectroscopy of a State Selected Beam of OH Radicals,” J. Chem. Phys. 123, 074309 (2005).
- E. L. Derro, I. B. Pollack, L. P. Dempsey, M. E. Greenslade, Y. Lei, D. Č. Radenović, M. I. Lester, “Fluorescence-Dip Infrared Spectroscopy and Predissociation Dynamics of OH A 2Σ+ (v=4) Radicals,” J. Chem. Phys. 122, 24431 (2005).
- M. D. Marshall, J. B. Davey, M. E. Greenslade, M. I. Lester, “Evidence for partial quenching of orbital angular momentum upon complex formation in the infrared spectrum of OH-acetylene,” J. Chem. Phys. 121, 5845 (2004).
- J. B. Davey, M. E. Greenslade, M. D. Marshall, M. I. Lester, M. D. Wheeler, “Infrared spectrum and stability of a π-type hydrogen-bonded complex between the OH and C2H2 reactants,” J. Chem. Phys. 121, 3009 (2004).
- D. Č. Radenović, A. J. A. Van Roij, D. A. Chestakov, A. T. J. B. Eppink, J. J. ter Meulen, D. H. Parker, M. P. J. Van der Loo, G. C. Groenenboom, M. E. Greenslade, M. I. Lester, “Photodissociation of the OD radical at 226 and 243 nm,” J. Chem. Phys. 119, 9341 (2003).
- M. E. Greenslade, M. Tsiouris, R. T. Bonn, M. I. Lester, “Electronic Spectroscopy of the OH-CO Reactant Complex,” Chem. Phys. Lett. 354, 203 (2002).
- Massachusetts Institute of Technology, Program in Atmospheres, Oceans and Climate, MIT Atmospheric Science Seminar, Cambridge, MA, June 2014
Invited Presentation: “Optical Properties of Clay Aerosols and Their Mixtures”
- Hendrix College, Conway, AR and Trinity College, Hartford, CT, November 2013 & January 2014
Invited Presentation: “Cavity Ring Down Spectroscopy of Clay Aerosols”
- University of Vermont, Burlington, VT, October 2013
Invited Presentation: “Relative Humidity Dependent Optical Properties of Clay Aerosols and their Mixtures”
***I also taught a class session for graduate level course on Analytical Spectroscopy.
- Gordon Research Conference on Atmospheric Chemistry, Mt. Snow, VT, July 2013
Poster Presentation: M. E. Greenslade, A. R. Attwood**, “Extinction Enhancements Upon Mixing Clay Aerosols with Dicarboxylic Acids”
- American Geophysical Union Fall Meeting 2012, San Francisco, CA, December 2012
Presentation: M. E. Greenslade, A. R. Attwood**, “Relative Humidity Dependent Optical Properties of Clay Aerosols and their Mixtures”
- Georgia Southern University, Statesboro, GA, March 2012
Invited Presentation: “Cavity Ring Down Spectroscopy and Aerosols”
- American Geophysical Union Fall Meeting 2011, San Francisco, CA, December 2011
Poster Presentation: A. R. Attwood**, M. E. Greenslade, “Deliquescence Behavior of Internally Mixed Clay and Salt Aerosols by Optical Extinction Measurements”
***2011 Outstanding Student Paper Award***
- Gordon Research Conference on Atmospheric Chemistry, Mt. Snow, VT, July 2011
Poster Presentation: M. E. Greenslade, “Wavelength Dependent Aerosol fRH”
- Merrimack College, North Andover, MA and University of Maine, Orono, ME, January 2011 & October 2010
Invited Presentation: “Wavelength and Humidity Dependent Aerosol Extinction”
- 240th ACS National Meeting, Boston, MA, August 2010
Presentation: A. R. Attwood**, R. T. Chartier**, M. E. Greenslade, “Wavelength and Humidity Dependent Aerosol Extinction”
- ACS Northeast Regional Meeting (NERM), Hartford, CT, October 2009
Poster Presentation: Ryan T. Chartier** and Margaret E. Greenslade, “A UV-Vis Instrument to Measure Aerosol Extinction”
- Atmospheric Science Collaborations and Enriching NeTworks (ASCENT) workshop,
Steamboat Springs, CO, June 2009
Poster Presentation: M. E. Greenslade, D. A. Lack, T. Baynard, A. R. Ravishankara, E. R. Lovejoy,
“A New Look at Optical Properties of Absorbing Aerosols as a Function of Relative Humidity”
Video available: http://www.youtube.com/watch?v=YM32nnFSfD0
- University of New England, Chemistry Department Seminar, Biddeford, ME, November 2008
Invited Presentation: “Optical Properties of Aerosols”
Presenter is underlined; * undergraduate student,** graduate student
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