Photon Factory Activity Report 2005 #23 Part B (2006)
Applied Science

9A,12C/2004G119

Speciation of sulfate in size-fractionated aerosol particles
using sulfur K-edge XANES
Yoshio TAKAHASHI1*, Yutaka KANAI2, Hikari KAMIOKA2,Atsuyuki OHTA2, and Hiroshi SHIMIZU1
1
Dept. Earth and Planetary Systems Science, Hiroshima University, Hiroshima 739-8526, Japan
2
Geological Survey of Japan, AIST, Central 7, Higashi, Tsukuba, Ibaraki 305-8567, Japan

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Users' Reportof a variety of other minerals and elements in aerosols,(iii) the mixing ratio of several sulfur species can beextracted through the simulation of the spectra, and (iv)by coupling fluorescence XANES and CEY-XANES,
sulfur species in the bulk and at the surface of theparticles can be distinguished. It is expected that thecoupling of bulk chemical analysis using ion
chromatography and sulfur speciation using XANES for
more samples will provide information on the precise
characterization of sulfate aerosols.
References[1]Y. Takahashi et al., Environ. Sci. Technol., in press.
*ytakaha@hiroshima-u.ac.jp

AbsorbanceSulfate ions are a main constituent of aerosols, which
can cause various environmental problems. In theevaluation of the influence of sulfate aerosols, it isnecessary to determine what sulfate ions are contained inthese aerosols. In this study, sulfur K-edge XANES wasused to determine sulfate species present in sizefractionated aerosol particles based on the post-edge
structure after the main absorption peak in the XANES
region.
The aerosol samples were collected various sites in
China and Japan as part of the Japan-China joint project,“Asian Dust Experiment on Climate Impact”. The aerosolsamples were collected using a low-volume Andersentype air sampler (AN-200, Shibata) to obtain sulfur
species in the aerosol particles with various diameters.
Sulfur K-edge XANES was measured at Beamline BL-9A
at Photon Factory, Japan.
A comparison of the XAES spectra of reference sulfate
materials and aerosol samples collected in Tsukuba inJapan clearly showed that (NH4)2SO4 was the main sulfur
species in particles with a smaller diameter andCaSO4⋅2H2O (gypsum) was the main sulfur species inparticles with a larger diameter. A simulation of theXANES spectra by reference materials allows us to obtain
the quantitative mixing ratios of the different sulfate
species present in the aerosol samples. The presence ofminor sulfur species other than (NH4)2SO4 and gypsum atthe surface of mineral aerosols is suggested in our
simulations and by a surface-sensitive conversion
electron/He-ion yield XANES. In the absence of acontribution from a large dust event, the moleconcentration of gypsum in the mineral aerosol fraction(particle diameter > 1 µm) determined by XANES issimilar to that of Ca which is determined independently
using ion chromatography. This shows that the Ca andsulfate in the mineral aerosols are present only as gypsum.
Considering that calcite is the main Ca minerals in theoriginal material arising from an arid and semi-arid area
in China, it is strongly suggested that gypsum is formed
in aerosol during its long-range transportation by areaction between calcite and sulfate ions.
This study has shown that sulfur K-edge XANES is a
powerful tool to identify sulfur species in aerosol samples.
The method has various merits in the chemical speciationof sulfur, or sulfate, in aerosol samples: (i) it is applicableto the small amount of size-fractionated samples collectedby an Andersen-type sampler, (ii) the spectra can bemeasured under ambient conditions, even in the presence(NH4)2SO4
Backup filter
Stage 7
Stage 6
Stage 5
Stage 4
CaSO4.2H2O
Stage 3
Stage 2
Stage 1
Stage 0

2.46

2.47

2.48
2.49
Energy (keV)

2.5

2.51

Fig. 1. Sulfur K-edge XANES for the sulfur species in aerosol
sample collected at Tsukuba in April 2002 for different particle
sizes. The particle diameters corresponding to each stages are asfollows: Stage 0 (>11 µm), Stage 1 (7–11 µm), Stage 2 (4.7–7µm), Stage 3 (3.3–4.7 µm), Stage 4 (2.1–3.3 µm), Stage 5 (1.1–2.1 µm), Stage 6 (0.65–1.1 µm), Stage 7 (0.43–0.65 µm), andthe Backup filter (< 0.43 µm). The spectra for gypsum and(NH4)2SO4 are also shown for comparison. The dotted red line
curves show the simulated spectra assuming that gypsum and(NH4)2SO4 were the main sulfur species in the samples.