Research

Aerosol particles impact climate through their interactions with light and clouds, as well as heterogeneous chemistry.  Our goals are to understand the role of surfaces and interfaces in the chemical and physical properties of atmospheric particles.

Current Funding: NSF CAREER Award (CHE & AGS), NSF (AGS), NSF (CHE), DOE (BES), DOE (SBIR program), Penn State PSIEE Seed Grant

Current Projects:

1) Phase Separation in Organic Aerosol

Aerosol particles composed of organic compounds and inorganic salts are ubiquitous in the atmosphere.  Depending on the properties of the organic compounds, these particles can undergo phase separation to form an aqueous phase and an organic-rich phase.  We use cryo-transmission electron microscopy to examine phase separation in submicron particles.  Surprising, we observe a size dependence of the morphology for some systems in which large particles phase separate and small particles remain homogeneous.

Publications:
  1. D. P. Veghte, M. B. Altaf, M. A. Freedman, Size Dependence of the Structure of Organic Aerosol, Journal of the American Chemical Society, 2013, 135, 16046-16049. doi:10.1021/ja408903g
  2. D. P. Veghte, D. R. Bittner, M. A. Freedman, Cryo-transmission electron microscopy imaging of the morphology of submicron aerosol containing organic acids and ammonium sulfate, Analytical Chemistry, 2014, 86, 2436-2442. doi: 10.1021/ac403279f
  3. M. B. Altaf, A. Zuend, M. A. Freedman*, Role of Nucleation Mechanism on the Size Dependent Morphology of Organic Aerosol, Chemical Communications, 2016, 52, 9220-9223. doi:10.1039/C6CC03826C
  4. D. L. Losey, R. G. Parker, M. A. Freedman*, pH Dependence of Liquid-Liquid Phase Separation in Organic Aerosol, Journal of Physical Chemistry Letters, 2016, 7, 3861-3865. doi:10.1021/acs.jpclett.6b01621
  5. M. B. Altaf, M. A. Freedman*, Effect of Drying Rate on Aerosol Particle Morphology, Journal of Physical Chemistry Letters, 2017, 8, 3613-3618. doi: 10.1021/acs.jpca.7b06359
  6. M. A. Freedman*, Phase Separation in Organic Aerosol, Chemical Society Reviews, 2017, 46, 7694-7705. doi: 10.1039/c6cs00783j
  7. D. J. Losey, E.-J. E. Ott, M. A. Freedman*, Effects of High Acidity on Phase Transitions of an Organic Aerosol, Journal of Physical Chemistry A, 2018, 122, 3819-3828.
  8. M. B. Altaf, D. D Dutcher, T. M. Raymond, M. A. Freedman*, Effect of Particle Morphology on Cloud Condensation Nuclei Activity, ACS Earth and Space Chemistry, 2018, 2, 634-639. doi:10.1021/acsearthspacechem.7b00146
  9. M. A. Freedman*, E.-J. E. Ott, K. E. Marak, Role of pH in Aerosol Processes and Measurement Challenges, Journal of Physical Chemistry A, 2019, 123,1275-1284. JPCA Feature Article. ACS Editors’ Choice Article. doi:10.1021/acs.jpca.8b10676
  10. T. M. Kucinski, J. N. Dawson, M. A. Freedman, Size-Dependent Liquid-Liquid Phase Separation in Atmospherically Relevant Complex Systems, Journal of Physical Chemistry Letters, 10, 6915-6920 (2019). doi:10.1021/acs.jpclett.9b02532
  11. E.-J. E. Ott, E. M. Tackman, M. A. Freedman, Effects of Sucrose on Phase Transitions of Organic/Inorganic Aerosols, ACS Earth and Space Chemistry, accepted. doi:10.1021/acsearthspacechem.0c00006
  12. T. M. Kucinski, M. A. Freedman, Flash Freeze Flow Tube to Vitrify Aerosol Particles at Fixed Relative Humidity Values, Analytical Chemistry, accepted. doi:10.1021/acs.analchem.9b05757

2) Molecular Scale Studies of Ice Nucleation

Heterogeneous nucleation of ice is important for cloud formation, properties, and lifetime.  Some types of heterogeneous nucleation depend sensitively on the presence and activity of surface active sites.  Yet, the details of what these active sites are on the molecular scale, how they evolve in chemical and physical atmospheric processes, and how ice nucleates are unknown.  We use a variety of surface probes to investigate these questions.

Publications:

  1. S. K. Sihvonen, G. P. Schill, N. A. Lyktey, D. P. Veghte, M. A. Tolbert, M. A. Freedman*, Chemical and Physical Transformations of Aluminosilicate Clay Minerals due to Acid Treatment and Consequences for Heterogeneous Ice Nucleation, Journal of Physical Chemistry A, 2014, 118, 8787-8796. doi:10.1021/jp504846g
  2. M. A. Freedman, Sites for Ice Nucleation on Aluminosilicate Clay Minerals and Related Materials, Journal of Physical Chemistry Letters, 2015, 6, 3850-3858. doi:10.1021/acs.jpclett.5b01326
  3. V. J. Alstadt, J. D. Kubicki, M. A. Freedman*, Competitive Adsorption of Acetic Acid and Water on Kaolinite, Journal of Physical Chemistry A, 2016, 120, 8339-8346. doi: 10.1021/acs.jpca.6b06968
  4. V. J. Alstadt, J. N. Dawson, D. J. Losey, S. K. Sihvonen, M. A. Freedman*, Heterogeneous Freezing of Carbon Nanotubes: A Model System for Pore Condensation and Freezing in the Atmosphere, Journal of Physical Chemistry A, 2017, 121, 8166-8175. doi: 10.1021/acs.jpclett.7b01327
  5. S. K. Sihvonen, K. A. Murphy, N. M. Washton, M. B. Altaf, V. J. Alstadt, K. T. Mueller, M. A. Freedman*, Effect of Acid on Surface Hydroxyl Groups on Kaolinite and Montmorillonite, Zeitschrift fur Physikalische Chemie, accepted.
  6. D. J. Losey, S. K. Sihvonen, D. P. Veghte, E. Chong, M. A. Freedman*, Acidic Processing of Fly Ash: Chemical Characterization, Morphology, and Immersion Freezing, Environmental Science: Processes & Impacts, 2018, 20, 1581-1592. doi:10.1039/C8EM00319J
  7. E. Chong, M. King#, K. E. Marak, M. A. Freedman*, The Effect of Crystallinity and Crystal Structure on the Immersion Freezing of Alumina Aerosol, Journal of Physical Chemistry A, 2019, 123, 2447-2456. Special Virtual Issue: Young Scientists. doi:10.1021/acs.jpca.8b12258

3) Optical Properties of Mineral Dust Aerosol

Cavity ring-down spectroscopy is the most sensitive technique that has been developed for the study of aerosol optical properties.  In particular, this sensitivity allows us to study size-selected aerosol particles. We are currently developing methods to study non-spherical mineral dust particles.  Specifically, the size selection technique is designed for spherical particles, and we have found that incorporation of microscopy characterization of non-spherical particles is needed to model their optical properties accurately.

Publications:

  1. D. P. Veghte, M. A. Freedman, The Necessity of Microscopy to Characterize the Optical Properties of Size-Selected, Nonspherical Aerosol Particles, Analytical Chemistry, 2012, 84, 9101-9108. doi:10.1021/ac3017373
  2. D. P. Veghte, M. A. Freedman, Facile method for determining the aspect ratios of mineral dust aerosol by electron microscopy, Aerosol Science and Technology, 2014, 48, 715-724. doi:10.1080/02786826.2014.920484
  3. D. P. Veghte, J. E. Moore, L. Jensen, M. A. Freedman*, Influence of shape on the optical properties of hematite aerosol, Journal of Geophysical Research – Atmospheres, 2015, 120, 7025-7039.doi:10.1002/2015JD023160
  4. D. P. Veghte, M. B. Altaf, M. A. Freedman*, Optical Properties of Non-Absorbing Mineral Dust Components and Mixtures, Aerosol Science and Technology, 2016, accepted. doi:10.1080/02786826.2016.1225153

4) Hygroscopicity of Aerosol Particles

Using two-cell tandem cavity ring-down spectroscopy, the optical hygroscopicity of particles can be determined and converted to a growth factor and kappa parameter.  Our interest is in the hygroscopicity of particles with different phase states, morphologies, and mixing states.

5) Field Studies of Aerosol Particle Morphology

While the primary emphasis of the Freedman group is on laboratory studies of model systems, we also perform occasional field studies to determine ambient particle morphology and composition.

Publications:

  1. C. A. Hasenkopf*, D. P. Veghte, G. P. Schill, S. Lodoysamba, M. A. Freedman*, M. A. Tolbert*, Ice nucleation, shape, and composition of aerosol particles in one of the most polluted cities in the world: Ulaanbaatar, Mongolia, Atmospheric Environment, 2016, 139, 222-229. doi:10.1016/j.atmosenv.2016.05.037
  2. V. J. Alstadt, K. T. Jansen, E.-J. E. Ott, M. B. Altaf, M. A. Freedman*, Local Aerosol Composition Before and During the Transition from Coal-fired Power to Natural Gas, Atmospheric Environment, 2018, 190, 169-176. doi:10.1016/j.atmosenv.2018.07.013