Miriam Freedman

Professional Appointments and Affiliations

Professor of Chemistry

Office

205 Benkovic Building
University Park, PA 16802

Education

B. A., Swarthmore College, 2000

M. S., University of Minnesota, 2002 (Mathematics)

M. S., University of Chicago, 2003

Ph. D., University of Chicago, 2008

Honors and Awards

Fellow, Penn State Institutes for Energy and the Environment 2024-2027

ACS Physical Chemistry Division Early-Career Award for Experimental Physical Chemistry 2021

Penn State Eberly College of Science Dean’s Climate and Diversity Award 2019

NSF Career Award 2014-2020

NOAA Climate and Global Change Postdoctoral Fellowship 2008-2010

NSF Graduate Fellowship 2003-2006

Research

Aerosol particles impact climate through their interactions with light, clouds, as well as heterogeneous chemistry.  The physical and chemical properties of aerosol particles that determine the nature of these interactions depend on particle size, shape, composition, and morphology.  Our goals are two-fold: 1) characterize aerosol structure (shape and morphology) and determine the effects of structure on aerosol physical and chemical properties and 2) develop methods for the study of submicron aerosol particles.

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.

Phase Separation in Organic/Inorganic 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.

Acidity of Organic/Inorganic Aerosol

The heterogeneous chemistry in which aerosol particles is sensitive to the acidity of the aerosol particles.  Historically, composition combined with thermodynamic models have been used to determine the acidity of aerosol particles.  Recently, several direct experimental measures of acidity have been developed.  In this vein, we develop probes for the measurement of aerosol acidity and apply them to understand the acidity of model systems.

Field Studies of Aerosol Particles

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.

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.

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.  Our interest is in the hygroscopicity of particles with different phase states, morphologies, and mixing states.

Selected Publications

• Q. Huang, K. R. Pitta, A. Zuend, M. A. Freedman, Predicting Liquid-Liquid Phase Separation of Submicron Proxies for Atmospheric Secondary Aerosol, Environmental Science and Technology: Air, 2025, 2, 530-539.
• N. Ferdousi-Rokib, K. A. Malek, K. Gohil, K. R. Pitta, D. D. Dutcher, T. M. Raymond, M. A. Freedman, A. A. Asa-Awuku, Salting Out and Nitrogen Effects on Cloud-Nucleating Ability of Amino Acid Aerosol Mixtures, Environmental Science: Atmospheres, 2025, 5, 485-501.
• H. L. Busse, D. Ariyasena, J. Orris, M. A. Freedman, Pristine and Aged Microplastics Can Nucleate Ice Through Immersion Freezing, Environmental Science and Technology: Air, 2024, 1, 1579-1588.
• M. A. Freedman, Q. Huang, K. R. Pitta, Phase Transitions in Organic and Organic/Inorganic Aerosol Particles, Annual Review of Physical Chemistry, 2024, 75, 257-281.
• E. C. Tackman, K. Jaswal, M. A. Freedman, Size Dependence of Organic/Inorganic Aerosol Morphology and the Role of Oxidation and Aromaticity of the Organic Component, Environmental Science and Technology: Air, 2024, 1, 405-413.
• Q. Huang, K. R. Pitta, K. Constantini#, E.-J. E. Ott, A. Zuend, M. A. Freedman, Experimental Phase Diagram and Its Temporal Evolution for Submicron 2-Methylglutaric Acid and Ammonium Sulfate Aerosol Particles, Physical Chemistry Chemical Physics, 2024, 26, 2887-2894.
• E. C. Tackman, D. N. Higgins, M. V. Johnston, M. A. Freedman, Morphology of Organic/Inorganic Aerosol with Varying Seed Particle Water Content, ACS Earth and Space Chemistry, 2023, 7, 2105-2118.