Single-particle investigation of summertime and wintertime Antarctic sea spray aerosols using low-Z particle EPMA, Raman microspectrometry, and ATR-FTIR imaging techniques

Abstract

<p><strong>Abstract.</strong> Two aerosol samples collected at King Sejong Korean scientific research station, Antarctica on Dec. 9, 2011 in the austral summer (sample S1) and July 23, 2012 in the austral winter (sample S2), when the oceanic chlorophyll-a levels were quite different, by ~19 times (2.46 vs. 0.13 μg/L, respectively), were investigated on a single particle basis using quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA), called low-Z particle EPMA, Raman microspectrometry (RMS), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) imaging techniques to obtain their characteristics based on the elemental chemical compositions, molecular species, and mixing state. X-ray analysis showed that the supermicron summertime and wintertime Antarctic aerosol samples have different elemental chemical compositions, even though all the individual particles analyzed were sea spray aerosols (SSAs); i.e., the contents of C, O, Ca, S, and Si were more elevated, whereas Cl was more depleted, for sample S1 having a much higher chlorophyll-a level than for sample S2. Based on qualitative analysis of the chemical species present in individual SSAs by the combined application of RMS and ATR-FTIR imaging, different organic species were encountered in samples S1 and S2; i.e., Mg hydrate salts of alanine were predominant in samples S1 and S2, whereas Mg salts of fatty acids internally mixed with Mg hydrate salts of alanine were significant in sample S2. Although CaSO<sub>4</sub> was encountered significantly in both samples S1 and S2, other inorganic species, such as Na<sub>2</sub>SO<sub>4</sub>, NaNO<sub>3</sub>, Mg(NO<sub>3</sub>)<sub>2</sub>, SiO<sub>2</sub>, and CH<sub>3</sub>SO<sub>3</sub>Mg, were encountered more significantly in sample S1, suggesting that those compounds may be related to the higher phytoplankton activity in summer.</p>

Computer-controlled Raman microspectroscopy (CC-Raman): A method for the rapid characterization of individual atmospheric aerosol particles

“…Specifically Raman modes provide insight into functional groups within organic molecules and other secondary components (e.g., nitrate, sulfate), or bonding environment (aqueous versus solid, binding to different cations). This has led multiple studies to use coupled electron beam and Raman microspectroscopy measurements of the same samples, but the statistics for particles analyzed by Raman has typically been limited when compared with EDX or electron probe Xray microanalysis (EPMA) (Ault et al 2013b;Eom et al 2016;Jung et al 2014;Sobanska et al 2012).…”

Single-particle Raman spectroscopy for studying physical and chemical processes of atmospheric particles

“…The Raman scattering signal-to-noise ratio can be enhanced since the incident laser energy is focused on a small volume through a high magnification (and short working distance) objective. Furthermore, 2-D Raman imaging is possible in studying particles in the order of tens of microns (Eom et al, 2016;Zhao et al, 2018). Confocal Raman microspectroscopy eliminates the Raman scattering from volumes other than the focal volume by configuring additional slits in the spectrometer.…”

Single-particle Raman spectroscopy for studying physical and chemical processes of atmospheric particles

“…Furthermore, 2D Raman imaging is possible in studying particles in the order of tens of microns. (Eom et al, 2016; in terms of mass or size ratios as a function of water activity or RH, DRH, and ERH can be easily determined by changes in mass/size and the light scattering pattern. (Mitchem et al, 2006;Chan et al, 2005) While GF, DRH, and ERH measurements are readily made for mixed particles using EDB and optical traps, the formation of mixed-phase particles before full deliquescence is more complicated.…”