Partial crystallization and deliquescence of particles containing ammonium sulfate and dicarboxylic acids

Abstract

[1] The partial crystallization and deliquescence of ammonium sulfate (AS) particles internally mixed with malonic acid (MA), glutaric acid (GA), and succinic acid (SA) were studied. Hygroscopic properties, elastic light scattering, and Raman spectra were measured during water uptake and evaporation of single particles suspended in an electrodynamic balance. AS/MA particles remained partially crystallized at RHs as low as 16%, while AS/GA and AS/SA particles became completely dry at about 30-36% RH and below. Partial deliquescence was observed at intermediate RHs of <10% to 79%, 70% to 80%, and 80% to >90% for the AS/MA, AS/GA, and AS/SA particles, respectively. Solid inclusions in various amounts were in equilibrium with the aqueous solutions. The Raman spectra show solid inclusions of both AS and MA in AS/MA particles, suggesting the heterogeneous crystallization of MA on solid AS. AS was found to deliquesce first at 76% RH in the AS/GA system, followed by GA at 78% RH. In the SA/AS system, AS was observed to dissolve at 80% RH, while SA remained as solid for RH as high as 90%. Comparisons to the thermodynamic model E-AIM demonstrated the necessity to correctly predict the solid phase during partial deliquescence for accurate water content estimation. The Raman spectra also revealed the formation of metastable forms of organic acids upon crystallization from supersaturated droplets of AS/GA and AS/SA. Transformation of metastable solids to stable forms was observed before water uptake in the AS/GA particles, while the SA in AS/SA particles transformed in the presence of water.Citation: Ling, T. Y., and C. K. Chan (2008), Partial crystallization and deliquescence of particles containing ammonium sulfate and dicarboxylic acids,

Water Content and Phase Transitions in Particles of Inorganic and Organic Species and their Mixtures Using Micro-Raman Spectroscopy

“…The AS-MA particles in this study are of the same composition (1:1 mole ratio) with those studied in the literature. The spectral results were consistent with the hygroscopic properties described by Ling and Chan (2008). However, a difference between these measurements and those of Choi and Chan (2002) was seen in the evaporation measurements.…”

“…Variation in the water content of the AS-MA particles in the course of a humidity cycle is shown in Figure 3 along with data from previous measurements using the EDB techniques (Choi and Chan 2002;Ling and Chan 2008). The AS-MA particles in this study are of the same composition (1:1 mole ratio) with those studied in the literature.…”

“…Hygroscopicity (WSR, mass of water/mass of solute) of AS-GA mixed particles (in 1:1 mole ratio) undergoing (a) evaporation and (b) growth processes obtained by micro-Raman spectroscopy. Data from Choi and Chan (2002) and Ling and Chan (2008) and predictions from the ZSR and E-AIM models are also included.…”

“…An aerosol flow tube coupled with a Fourier transform infrared (FTIR) spectrometer has been used to study phase transitions of suspended particles (Cziczo et al 1997;Onasch et al 1999). In addition, a combined EDB/Raman spectrometer (Fung and Tang 1988) has been demonstrated to provide solid spectral evidence of the phase 270 M. C. YEUNG AND C. K. CHAN state of a particle simultaneously with hygroscopicity measurements (Zhang and Chan 2002;Jordanov and Zellner 2006;Lee et al 2008;Ling and Chan 2008). More recently, micro-Raman spectroscopic systems have been employed to investigate the molecular interactions in supersaturated droplets of different inorganic species (Wang et al 2005;Li et al 2006;Dong et al 2007) and the polymorphic transformation of NH 4 NO 3 particles deposited on a hydrophobic substrate (Wu and Chan 2008).…”

Roles of the Phase State and Water Content in Ozonolysis of Internal Mixtures of Maleic Acid and Ammonium Sulfate Particles

“…Raman spectra of pure AS, pure MA, and their internal mixture with 30 wt% MA have been reported using our EDB/Raman system (Lee et al 2008;Ling and Chan 2008). As shown in Figure 6a and b, the spectra of both crystalline (<5% RH) and aqueous (80% RH) 30 wt% MA particles are the approximate superpositions of the corresponding pure AS and MA spectra approximately.…”