Morphological effects on the hygroscopic properties of sodium chloride-sodium sulfate aerosols

Joshua P. Darr, Shannon Q. Davis, Yohei Kohno, Kevin McKenna, Paul Morales

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Abstract

The hygroscopic properties of sodium sulfate, Na2SO4; sodium chloride, NaCl; and their mixed aerosols are monitored using a flow-cell apparatus and Fourier-transform infrared spectroscopy. While Na2SO4 exhibits the typical water uptake for an inorganic salt, spectra of NaCl and mixed NaCl-Na2SO4 aerosols reveal water content below the deliquescence relative humidity. This is explained on the basis of two different morphologies for NaCl and Na2SO4. While Na2SO4 can be described by a simple crystalline solid, NaCl contains pockets that trap water. The NaCl-Na2SO4 mixtures contain a combination of these two structural motifs, weighted by the relative amounts of the NaCl and Na2SO4 components. This makes NaCl-Na2SO4 mixtures an interesting candidate for exploring the effects of morphology on atmospherically relevant properties in a systematic fashion. Additionally, the formation of metastable Na2SO4 (III) is confirmed using Raman spectroscopy, though its effects on the hygroscopicity of NaCl-Na2SO4 mixtures are believed to be minimal.

Original languageEnglish (US)
Pages (from-to)158-167
Number of pages10
JournalJournal of Aerosol Science
Volume77
DOIs
Publication statusPublished - Nov 1 2014

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Keywords

  • Hygroscopicity
  • Infrared spectroscopy
  • Metastable phase
  • Morphology
  • Sodium chloride aerosol
  • Sodium sulfate aerosol

ASJC Scopus subject areas

  • Environmental Engineering
  • Pollution
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes
  • Atmospheric Science

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