AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Design and Application of Aerosol Optical Tweezers to Investigate Organic Aerosol Morphology
KYLE GORKOWSKI, Mark Aboff, Hassan Beydoun, Michael Polen, Jim Walker, Neil Donahue, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 407 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosols containing multiple organic and/or inorganic components can phase separate into distinct liquid phases, resulting in either a core-shell or a partial-shell particle structure. Understanding and predicting when each of these structures forms is critical to understanding the gas/particle partitioning of organic compounds, water uptake and cloud droplet activation, and chemical reactions involving atmospheric aerosols. Liquid-liquid phase mixing and the resulting morphology of organic aerosols is also important when interpreting smog chamber experiments where SOA coatings onto existing particles are usually assumed to form a core-shell structure.
We have constructed a new aerosol optical tweezers (AOT) system to investigate the thermodynamic properties of organic aerosols in Carnegie Mellon University’s Center for Atmospheric Particles Studies. The AOT system is a highly accurate real-time probe for studying individual particles larger than 4 microns. The retrieved Cavity Enhanced Raman Spectrum allows us to measure the trapped particle’s size and composition (via the refractive index) with high accuracy and sensitivity. We constructed a unique AOT chamber that enhances the probability of tweezed droplet-particle coagulation and trapping stability. The chamber was also designed to deliver a highly uniform conditioned air flow to the tweezed particle, making it ideal for probing particle-gas interactions.
We have investigated the phase mixing of multicomponent organic and aqueous inorganic particles. Experiments were conducted by first trapping the core particle and then the second organic component was added through coagulation of smaller particles or condensation of vapor. The morphology and any phase separations of the resulting multicomponent particle were then determined from the presence or absence of the Cavity Enhanced Raman Spectrum. Using this technique has enabled us to uniquely distinguish between core-shell, partial-shell, and internally mixed morphologies for a series of multicomponent (inorganic/organic/aqueous) particle systems, and how this morphology changes with changes in particle composition and relative humidity.