Understanding hygroscopic growth and phase transformation of aerosols using single particle Raman spectroscopy in an electrodynamic balance

Abstract

Hygroscopic growth is one of the most fundamental properties of atmospheric aerosols. By absorbing or evaporating water, an aerosol particle changes its size, morphology, phase, chemical composition and reactivity and other parameters such as its refractive index. These changes affect the fate and the environmental impacts of atmospheric aerosols, including global climate change. The ElectroDynamic Balance (EDB) has been widely accepted as a unique tool for measuring hygroscopic properties and for investigating phase transformation of aerosols via single particle levitation. Coupled with Raman spectroscopy, an EDB/Raman system is a powerful tool that can be used to investigate both physical and chemical changes associated with the hygroscopic properties of individually levitated particles under controlled environments. In this paper, we report the use of an EDB/Raman system to investigate (1) contact ion pairs formation in supersaturated magnesium sulfate solutions; (2) phase transformation in ammonium nitrate/ammonium sulfate mixed particles; (3) hygroscopicity of organically coated inorganic aerosols; and (4) heterogeneous reactions altering the hygroscopicity of organic aerosols.

An examination of boundary layer structure under the influence of the gap winds in Urumqi, China, during air pollution episode in winter

“…The relative humidity in lower layer almost remains around $80% from the early evening to early morning the next day, which play a critical role in formation of 12-day fog during the observational period. It has been demonstrated that the condition of high relative humidity could promote aerosol particle to grow hygroscopicly (Hu et al, 2010) and chemical transformation (Lee et al, 2008). Therefore, it may be taken for granted that the relative humidity in Urumqi in winter is another key factor that does make important contribution to the terrible air quality.…”

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.…”

“…To probe the temporal chemical changes in levitated droplets, a Raman spectroscopy system similar to the one used by Lee et al (2008) was employed. The system consisted of a 150-mW diode-pumped solid-state laser (Spectra-Physics Excelsior, 532-150-SLM-CDRH) and a 0.5-m monochromator (Acton SpectraPro 500) attached to a charge-coupled device (CCD) detector (Andor Technology DV420-OE), and was integrated with the EDB system.…”

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

“…Changes in the Raman shift magnitude during phase transitions of AS and AN have been reported by a few investigators (Musick et al 2000;Zhang and Chan 2002;Jordanov and Zellner 2006). The Raman peaks of solid particles are more intense and sharper relative to aqueous particles, so a sudden change in the fwhh (normalized to that at the lowest RH) of a distinct peak is also useful for phase identification (Lee et al 2008;Ling and Chan 2008). In this study, the changes in the fwhh and the positions of the ν 1 (SO for AN were also observed, consistent with literature reports.…”

“…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).…”