Preprints
https://doi.org/10.5194/amt-2021-108
https://doi.org/10.5194/amt-2021-108

  20 Apr 2021

20 Apr 2021

Review status: this preprint is currently under review for the journal AMT.

A Dual-Droplet Approach for Measuring the Hygroscopicity of Aqueous Aerosol

Jack M. Choczynski, Ravleen Kaur Kohli, Craig S. Sheldon, Chelsea L. Price, and James F. Davies Jack M. Choczynski et al.
  • Department of Chemistry, University of California Riverside, Riverside CA 92521 USA

Abstract. Accurate characterization of the water activity and hygroscopicity of aqueous aerosol material allows us to predict the chemical and physical state of aerosol particles exposed to humid conditions in the environment. The hygroscopicity of aerosol determines the size, phase morphology, viscosity, chemical reactivity, and optical properties of constituent particles, and directly impacts their ability to form clouds in the atmosphere. In this work, we describe measurements of hygroscopicity using a linear quadrupole electrodynamic balance (LQ-EDB). We levitate two droplets, one droplet that acts as a relative humidity (RH) probe and one sample droplet, and expose them to controlled environmental conditions. We describe the development of a RH measurement using probe droplets of aqueous NaCl or LiCl, allowing for precise in-situ measurements of RH in the LQ-EDB chamber. We demonstrate that the RH may be determined with an accuracy of 0.5 % at 50 % RH and better than 0.1 % at 90 % RH using NaCl, and show that LiCl is effective at characterizing the RH from ~10 % RH up to ~90 %. We simultaneously measure the response of sample droplets containing aqueous material (including ammonium sulfate, citric acid, 1,2,6-hexanetriol, and tetraethylene glycol) and report hygroscopic growth via their radial growth factors. We use established thermodynamic models to validate the accuracy of the RH probe and to compare with the measured hygroscopicity of the samples. This approach shows significant advantages over other methods for accurately characterizing the hygroscopicity of samples with a range of characteristics, such as high viscosity and vapor pressure.

Jack M. Choczynski et al.

Status: open (until 15 Jun 2021)

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Jack M. Choczynski et al.

Jack M. Choczynski et al.

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Short summary
Relative humidity (RH) and hygroscopicity play an important role in regulating the physical, chemical and optical properties of aerosol. In this work, we develop a new method to characterize hygroscopicity using particle levitation. We levitate two droplets with an electrodynamic balance and measure their size with light scattering methods, using one droplet as a probe of the RH. We demonstrate highly accurate and precise measurements of the RH and hygroscopic growth of a range of samples.