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

Abstract

Hygroscopicity and phase transitions were measured with deposited particles of ammonium sulfate (AS), ammonium nitrate (AN), malonic acid (MA), glutaric acid (GA), glyoxylic acid (GlyA), as well as two mixed particle systems AS-MA and AS-GA using micro-Raman spectroscopy. Hygroscopicity was presented in terms of water-to-solute mass ratios, which were obtained from the integrated area ratios of the Raman water band to a distinct solute peak. Deliquescence and crystallization were confirmed by abrupt changes in the Raman peak positions and the full-widthhalf-heights of distinct solute peaks. The results for AS, AN, MA, and GA agreed well with literature reports and model predictions. For GlyA, we detected the Raman water band at near 0% RH, indicating that the spectral technique is sensitive for hygroscopic measurements at very low RH. Additional spectral feature at ∼0% RH was also observed. In the case of more complicated ASdicarboxylic acid mixed systems, the partial phase transitions of the organic components were identified using the intensity ratios of aqueous to solid C=O peaks. AS-MA particles did not completely crystallize and gradual water uptake with increasing RH from 3% was observed. Moreover, it was found that AS-GA particles showed step-wise crystallization in which the AS fraction crystallized prior to the GA fraction. The measured water content and complete DRH of both mixed systems were consistent with the published values. The results show the utility of micro-Raman spectroscopic analysis in studying hygroscopicity and phase characterizations of the chemical species in mixed particles.

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

“…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. The envelop of overlapping peaks at ∼3240 and 3430 cm −1 originating from particle-phase water (Yeung and Chan 2010) is absent in the spectra of crystalline particles and the Raman peaks of crystalline particles are sharper than those of their aqueous counterparts.…”

“…The spectrum of the flow cell particle contained some minimized substrate (Teflon) signals at 289,384,730,1089,1297, and 1379 cm −1 , as indicated by solid lines (Yeung et al 2009;Yeung and Chan 2010). The reacted particles from both the EDB and the flow cell experiments lost most of the MA peaks, while the AS peaks at about 452, 613, and 974 cm −1 remained dominant.…”

“…The resolution of the spectrum obtained was about 6 cm −1 . For reaction flow cell studies, Raman spectra of deposited droplets were acquired using a Renishaw RM series micro-Raman spectrometer (Yeung and Chan 2010). A 20-mW Argon ion laser (514.5 nm) was applied for sample excitation.…”

Electrospray surface-enhanced Raman spectroscopy (ES-SERS) for probing surface chemical compositions of atmospherically relevant particles

“…Nonetheless, the current results clearly demonstrate that the addition of SA into AS has a substantial influence on the availability of aqueous sulfate anions on the analyte particle surface. Overall, SERS experiments reveal the availability of surface aqueous sulfate in the three particle sys- Particle phase can be inferred from the position and shape of the Raman peaks (Yeung and Chan, 2010). Table 2 shows the peak position and FWHM of the v(SO 2− 4 ) mode obtained using Gaussian fittings.…”

Hygroscopic behavior of atmospherically relevant water-soluble carboxylic salts and their influence on the water uptake of ammonium sulfate

“…Zardini et al, 2008;Hameri et al, 2002;Marcolli and Krieger, 2006b). Ling and Chan (2008) and Yeung and Chan (2010) investigated partial deliquescence of AS and dicarboxylic acids mixtures using an EDB and a Raman spectrometer. They observed that malonic acid with lower DRH contributed to the taking up of water at low RH; deliquescence of ammonium sulfate gradually took place starting from 69 % RH, then the mixture completely deliquescent at 75 %.…”