Abstract View
A Dual-Droplet Approach to Characterizing Hygroscopic Growth using a Linear Quadrupole Electrodynamic Balance
JACK CHOCZYNSKI, James F. Davies, University of California, Riverside
Abstract Number: 302
Working Group: Instrumentation and Methods
Abstract
Aerosols in the atmosphere scatter and absorb atmospheric radiation, serve as cloud condensation nuclei (CCN), act as substrates for chemical processes, and impact air quality and human health. The physiochemical properties of atmospheric aerosols must be well characterized to understand their impact and predict their behavior in the atmosphere. Their optical and hygroscopic properties are of particular interest because they impact the radiative balance of the earth through direct and indirect aerosol effects.
In this work we use a linear quadrupole electrodynamic balance (LQ-EDB) for the contactless analysis of single aerosol droplets by levitation with electric fields. Droplets are exposed to controlled relative humidity (RH) and Mie resonance spectroscopy is used to determine their size and refractive index in response to changes in RH. Measurements of RH-dependent processes such as hygroscopic growth, deliquescence, efflorescence, and phase separations, require accurate in-situ RH determination, which is achieved through the use of a probe droplet. We simultaneously trap two droplets of different composition (a probe NaCl or LiCl droplet, and a sample droplet) and use the size and/or refractive index response of the probe to determine the RH.
The hygroscopic growth properties of model chemical systems using atmospherically relevant compounds will be explored. We are particularly interested in the hygroscopic response of systems containing mixtures of inorganic salts (e.g. NaCl, (NH4)2SO4, and CaCl2) and oxygenated organic compounds, such as carboxylic acids and sugar-alcohols. The chemical systems and methods discussed here will form the basis for the interpretation of more complex mixtures that better represent real aerosol.