People

Professor, Department of Chemistry

Professor, Department of Mechanical Engineering

Courtesy Appointment, Civil and Environmental Engineering

Associate Director, Institute for Green Science

Ryan started his research group in environmental chemistry at Carnegie Mellon University in 2012, as part of the Center for Atmospheric Particle Studies. He conducted his postdoctoral research with Sonia Kreidenweis and Paul DeMott in the Department of Atmospheric Science at Colorado State University, after completing his Ph.D. in atmospheric chemistry with Kimberly Prather in the Department of Chemistry & Biochemistry at the University of California, San Diego. Ryan engaged in undergraduate research with Kimberly Strong, Scott Mabury, and Jonathan Abbatt while completing his Hon.B.Sc. in environmental chemistry at the University of Toronto. Ryan has a joint faculty appointment in the Department of Chemistry and the Department of Mechanical Engineering at CMU, and is the Associate Director of the Institute for Green Science.

Ryan leads a group of chemists and engineers that work together to investigate the chemistry that tiny aerosol particles experience in the atmosphere. We seek to understand the role that chemistry catalyzed by aerosols plays in changing air pollution and impairing air quality. We study how these reactions change critical properties of the particles that alter how they create and change clouds, and the role of aerosol chemistry in changing the planet’s climate and energy budget. Our aerosol experiments are facilitated by the new methods and instruments we engineer that can probe individual particles one-at-a-time, using aerosol optical tweezers, laser ablation mass spectrometry, and microfluidics. The multiphase chemical evolution of biomass-burning aerosol produced from trees and tall grasses is a major current focus, along with investigating how this chemistry alters the ice nucleating particles emitted by biomass combustion. Our optical tweezers experiments allow us to uniquely determine how a particle’s chemistry and properties such as pH and phase separations evolve over hours of reactions with trace gases, and how this in turn alters the particle’s ability to further accelerate chemical reactions. As part of the Institute for Green Science, we are developing advanced water purification technologies for the removal of persistent micropollutants.

Graduate Student (PhD, Chemistry)

Riley is a PhD student in the Chemistry department who joined the Sullivan group in Fall 2019. She graduated from Kent State University in 2019 with BS degrees in Chemistry and Environmental & Conservation Biology. She uses various mass spectrometric techniques to characterize (1) the destruction of per- and polyfluorinated alkyl substances (PFAS) in aqueous media using microdroplet-accelerated photo-oxidation, as well as (2) combustion aerosol from the burning of flame-retardant laden consumer furniture. The overarching goal of her work is to improve our understanding of the fate and transformations of toxics (PFAS, flame retardants) in the environment as well as develop remediation strategies for reducing human and environmental exposure to synthetic toxic chemicals.

Graduate Student (PhD, Mechanical Engineering)

Wendy is a Mechanical Engineering PhD student who joined the Sullivan group in Fall 2020. She completed a B.S. in Mechanical Engineering at Universidad del Turabo- Gurabo, Puerto Rico and an M.S. in Mechanical Engineering at University of New Mexico (UNM)- Albuquerque. Wendy’s previous research combined thermographic phosphors with laser diagnostics techniques to obtain surface temperatures and expansion/displacement (strain) measurements. Her current research focuses on better understanding the physicochemical properties of aerosol single—particles by improving the performance of the LAAPTOF (laser ablation aerosol particle time-of-flight) mass spectrometer’s ablation laser for single-particle analysis and of a microfluidics single-particle-droplet capture technique, while also working to combine it with SERS (Surface Enhanced Raman Spectrometry) for chemical analysis. Additionally, she looks at the ice nucleating properties of aerosols using microfluidic devices to better inform climate model predictions.

Graduate Student (PhD, Chemistry)

Danny is a PhD student in Chemistry who joined the Sullivan group in Fall 2022. He graduated from Xavier University, receiving a B.S. in Chemistry. At Xavier University, he researched synthesis methods for natural products. During internships at Ames National Laboratory and Argonne National Laboratory, he developed algorithms to assess energy-efficient olefin-paraffin separation membranes and the degradation rate of plastics in the environment. His current research focuses on the production of reactive oxygen species by biomass-burning aerosol, assessing how the structural and optical properties of aqueous aerosol extracts affect their quantum yield for singlet oxygen using molecular probes to assess production of the intermediate and size exclusion chromatography, mass spectroscopy, and NMR to determine the aerosol structure.

Graduate Student (PhD, Chemistry)

Kiara is a Chemistry PhD student who joined the Sullivan group in Spring 2024. They graduated from Taylor University with a BS in Biochemistry as part of the Ockenga Honors Guild. While at Taylor, they explored a variety of directed research projects in genomics, biochemistry, and computational biology. They also spent several summers working on a forestry crew, solidifying their passion for environmental science. Their current research focuses on investigating the degradation of novel controllably-degradable polymers using simulated environmental aging conditions and nontarget HR-LCMS. Outside of the lab, Kiara enjoys playing club spikeball, hosting game nights, and visiting PA’s many lovely state forests.

Graduate Student (PhD, Chemistry)

Dennis is a PhD student in Chemistry who joined the Sullivan group in the Fall of 2024. They completed a BA and BS in Studio Art and Chemistry from the University of Pittsburgh in 2019. During summer internships at the Naval Research Laboratories they studied synthesis and optical properties of plasmonic nanoparticles. They completed their MFA in Sculpture and Post Studio Practice from the University of Colorado at Boulder where they studied multisensory installation and artistic research perspectives of atmospheric chemistry. They are currently interested in studying the chemistry of and reactive uptake onto aerosol droplets. When not in the lab, Dennis is usually found running through the city or reading books on their couch.

Group Photos

Sullivan Group in September 2021
Ryan Sullivan, Guy Symonds, Victoria Patella, Luke Monroe, Graham Thornhill, Wendy Flores-Brito, Riley Weatherholt, Bailey Bowers