Chemical Transformations in Aerosol

Student(s): Ravleen Kaur Kohli

To explore the connection between physical properties and chemical composition, we couple our linear quadrupole EDB (LQ-EDB) with mass spectrometry (MS) and generate ions using paper spray (PS). Our goal is to explore how aerosol become transformed through heterogenous reactions and photochemistry in single levitated aerosol particles. Initial development of our single particle PS-MS method is described in our recent publication.

Spectroscopic Characterization of Levitated Droplets

Student(s): Chelsea Price, Jack Choczynski

A broadband light source is used to illuminate a droplet in our LQ-EDB. Morphology dependent resonances (MDRs) in the Mie resonance spectrum are used to determine the size and optical properties (refractive index, dispersion and absorption). Using these data, a variety of droplet properties including vapor pressures, phase transitions, hygroscopic growth, water transport, and light absorption can be explored.

Light Absorption in Brown Carbon Aerosol

Student(s): Chelsea Price

Using Mie resonance spectroscopy, we measure the light-absorbing characteristics of brown carbon and humic-like substances. Absorption leads to a broadening of resonance peaks in the spectrum characteristic of the imaginary part of the refractive index. Our work explores the optical properties of particles that consist of nitroaromatic compounds, such as 4-nitrocatechol and 4-nitrophenol, which are known to absorb light in the UV/vis spectral range and whose physical properties (hygroscopicity, vapor pressure etc.) are not well-characterized. Light-absorbing chromophores in aerosol direct impacts on incoming solar radiation and indirectly influence cloud formation.

Hygroscopicity and Phase Transitions in Aerosol

Student(s): Jack Choczynski

Atmospheric aerosol particles are complex mixtures of many components with a range of physicochemical properties. The environmental relative humidity (RH) and temperature determines the amount of water partitioned into the condensed phase. Using the LQ-EDB, we measure the hygroscopic properties of particles containing both organic and inorganic compounds. We are developing methods to precisely determine the experimental RH and identify key phase transformations (e.g. efflorescence/deliquescence, LLPS etc.) in sample systems. By comparing our results to aerosol thermodynamic models, such as E-AIM and AIOMFAC, we aim to better understand how molecular interactions in complex systems give rise to observed behaviors.

Water Transport and Chemistry in Amorphous Aerosol

Student(s): Craig Sheldon, Ravleen Kaur Kohli

Under low RH conditions, organic aerosol particles are known to form highly viscous liquid phases that inhibit molecular transport due to slow diffusion. Recently, the formation of two-phase gel states have been shown to produce similar effects, albeit by different mechanisms. We aim to identify and characterize water transport limitations in aerosol particles containing atmospherically relevant mixtures of organic and inorganic material using spectroscopic methods in our LQ-EDB. In addition to water transport effects, chemical reactions may be slowed as reactants become limited to regions of the particle accessible by diffusion. Using PS-MS coupled with our LQ-EDB, we will explore changes in reaction mechanisms and kinetics due to the formation of amorphous states.