Size-Resolved Nanoparticle Composition Project (in collaboration with UCR’s Prof. Kelley Barsanti and Prof. Bryan Wong)

The goal of this project is to test how well bulk-phase pKa and pKb represent chemical processes of acids and bases in and on atmospheric nanoparticles. In our case, we refer to nanoparticles as particles of the size range less than or equal to 50 nm. We are collaborating with our very own Nanna Myllys (Smith/Gerber group), UC Riverside’s Prof. Kelley Barsanti (mechanistic modeling), Prof. Bryan Wong (molecular modeling with DFT) in order to bridge the gap between experimental results and theoretical modeling to gain a better idea of what is happening in these tiny particles, both within our measurement range above a 5 nm particle diameter and below.  For our part of this project, we are producing atmospheric nanoparticles by reacting various organic and inorganic acids and bases under different environmental variables (temperature, relative humidity) and seeing how these variables affect particle growth and composition. This project utilizes our Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS), as well as a myriad of other analytical techniques, to probe nanoparticle composition.  From these techniques, we are able to get size-resolved measurements of nanoparticle composition and compare our results with computational methods so that we can better understand the acid-base chemistry occurring within ambient nanoparticles.

Variable Residence Hygroscopicity Tandem Differential Mobility Analyzer (VRHTDMA)

For many years particles were assumed to exist in a liquid state, but recent work has shown that ambient atmospheric particles can exist in more viscous states. We have developed an instrument to probe the phase state of atmospheric particles by measuring the timescale of water uptake and loss by the particles, called the Variable Residence Hygroscopicity Tandem Differential Mobility Analyzer (VRHTDMA). Our goal is to use this instrument to measure water uptake and loss in both ambient and lab-generated particles. The VRHTDMA was built by Dr. Smith in 2008, and is currently being characterized and modified to make these kinds of measurements for ultrafine particles.

Nitrate Radical Oxidation of Monoterpenes:

The goal of this project is to probe the chemical mechanism of nitrate oxidation of monoterpenes and specifically how that mechanism leads to secondary organic aerosol formation. We have a large suite of instrumentation to look at precursors and gas and particle phase products. For gas phase products, we use a HR-TOF-CIMS with various reagent ions enabling us to see a range of oxidation states. For particle phase, we use the TDCIMS for size resolved composition of ultrafine particles. Offline techniques are also used to assess gas and particle composition.

This project is in collaboration with Prof Julie Fry at Reed College and Prof Alex Guenther at UCI.

Computational Studies 

• Quantum chemical studies of clustering and reaction mechanisms.
• Dynamics simulations for particle formation and properties.
• Theory development for cluster-phase properties.