Abstract
Abstract. Two aerosol samples collected at King Sejong Korean scientific research station, Antarctica, on 9 December 2011 in the austral summer (sample S1) and 23 July 2012 in the austral winter (sample S2), when the oceanic chlorophyll a levels on the collection days of the samples were quite different, by ∼ 19 times (2.46 vs. 0.13 µg L−1, 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 reflection 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 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 observed 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 CaSO4 was observed significantly in both samples S1 and S2, other inorganic species, such as Na2SO4, NaNO3, Mg(NO3)2, SiO2, and CH3SO3Mg, were observed more significantly in sample S1, suggesting that those compounds may be related to the higher phytoplankton activity in summer.
Highlights
As more than 70 % of the Earth’s surface is covered by ocean, sea spray aerosols (SSAs) make a dominant contribution to the total aerosol load in the air (Quinn et al, 2015)
As ambient relative humidity (RH) at the sampling times was higher than 87.6 % and the efflorescence RHs (ERHs) of the inorganic sea salt components (e.g., ERHs of NaCl and CaSO4 are ∼ 45–47 and ∼ 80–90 %, respectively; Gupta et al, 2015; Schindelholz et al, 2014; Xiao et al, 2008), the SSAs would be collected as aqueous droplets at the time of collection
X-ray analysis of a single-particle analysis showed that the supermicron summertime and wintertime Antarctic samples have different elemental chemical compositions, even though all the individual particles analyzed were SSAs; i.e., contents of C, O, Ca, S, and Si are more elevated, whereas Cl is more depleted for the summertime sample S1 than for the wintertime sample S2
Summary
As more than 70 % of the Earth’s surface is covered by ocean, sea spray aerosols (SSAs) make a dominant contribution to the total aerosol load in the air (Quinn et al, 2015). It was claimed that the chlorophyll a level showed a complicated correlation with the organic matters in nascent SSAs, and the bacterial enzyme activities should be considered to better understand the overall generation and temporal variations of organic matter (Wang et al, 2015), strongly suggesting the necessity for further studies. Low-Z particle EPMA was applied to investigate the elemental compositional contrast between the summertime and wintertime samples, and two vibrational spectroscopic techniques, such as RMS and ATR-FTIR imaging, were employed on a single-particle basis to identify the organic and inorganic molecular species present in Antarctic aerosol samples, clearly revealing the different chemical features between two samples
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