AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Mass Spectrometric Analysis of Aerosol Particles Levitated in an Electrodynamic Balance: a Platform for Atmospheric Chemistry Research
ADAM BIRDSALL, Ulrich Krieger, Frank Keutsch, Harvard University
Abstract Number: 552 Working Group: Instrumentation and Methods
Abstract A droplet levitation device that suspends single aerosol droplets, such as an electrodynamic balance (EDB), provides an attractive system for atmospheric chemistry research. Laboratory control of aerosol composition allows isolation and careful study of particular physical or chemical processes of interest, on the timescale of an aerosol particle’s multiday atmospheric lifetime. A suspended aerosol particle can depict more realistically the coupling of chemical and physical processes that can influence multiphase reactions, phase partitioning, or surface-mediated reactions, for instance, compared to bulk condensed-phase laboratory experiments. Considerable research with levitated droplets has been conducted using optical detection techniques; however, chemically complex systems can be better-suited to an analytical technique with more molecular specificity, such as mass spectrometry.
Here, an EDB has been coupled with a custom-built ionization source and commercial time-of-flight mass spectrometer as a platform for atmospheric chemistry research. A charged droplet (typical size 5-10 µm) is injected into the EDB and levitated for an arbitrarily long amount of time in an electric field within the trap, surrounded by a gas phase whose composition, including relative humidity, can be controlled. To analyze the droplet, the gas flow and electric field is manipulated to transfer the droplet to a vaporization–corona discharge ionization region before mass spectral analysis. The temporal evolution of an aerosol particle’s composition is mapped out by analysing a series of identical particles that reside in the trap for increasing amounts of time. The apparatus is more than sufficiently sensitive for mass spectral analysis of a single particle in this size range. The utility of this system has been demonstrated with an experiment measuring differential gas-phase loss timescales for a family of model compounds mixed in a single droplet.