Influence of Collecting Substrates on the Characterization of Hygroscopic Properties of Inorganic Aerosol Particles

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• 作者：Hyo-Jin Eom ; Dhrubajyoti Gupta ; Xue Li ; Hae-Jin Jung ; HyeKyeong Kim ; Chul-Un Ro
• 刊名：Analytical Chemistry
• 出版年：2014
• 出版时间：March 4, 2014
• 年：2014
• 卷：86
• 期：5
• 页码：2648-2656
• 全文大小：504K
• 年卷期：v.86,no.5(March 4, 2014)
• ISSN：1520-6882

文摘

The influence of six collecting substrates with different physical properties on the hygroscopicity measurement of inorganic aerosol particle surrogates and the potential applications of these substrates were examined experimentally. Laboratory-generated single salt particles, such as NaCl, KCl, and (NH₄)₂SO₄, 1鈥? 渭m in size, were deposited on transmission electron microscopy grids (TEM grids), parafilm-M, Al foil, Ag foil, silicon wafer, and cover glass. The particle hygroscopic properties were examined by optical microscopy. Contact angle measurements showed that parafilm-M is hydrophobic, and cover glass, silicon wafer, Al foil, and Ag foil substrates are hydrophilic. The observed deliquescence relative humidity (DRH) values for NaCl, KCl, and (NH₄)₂SO₄ on the TEM grids and parafilm-M substrates agreed well with the literature values, whereas the DRHs obtained on the hydrophilic substrates were consistently 1鈥?% lower, compared to those on the hydrophobic substrates. The water layer adsorbed on the salt crystals prior to deliquescence increases the Gibb鈥檚 free energy of the salt crystal鈥搒ubstrate system compared to the free energy of the salt droplet鈥搒ubstrate system, which in turn reduces the DRHs. The hydrophilic nature of the substrate does not affect the measured efflorescence RH (ERH) values. However, the Cl^{鈥?/sup> or SO₄2鈥?/sup> ions in aqueous salt droplets seem to have reacted with Ag foil to form AgCl or Ag₂SO₄, respectively, which in turn acts as seeds for the heterogeneous nucleation of the original salts, leading to higher ERHs. The TEM grids were found to be most suitable for the hygroscopic measurements of individual inorganic aerosol particles by optical microscopy and when multiple analytical techniques, such as scanning electron microscopy-energy dispersive X-ray spectroscopy, TEM-EDX, and/or Raman microspectrometry, are applied to the same individual particles.}