Anal. Chem. 2010, 82, 6193–6202
Speciation of Individual Mineral Particles of Micrometer Size by the Combined Use of Attenuated Total Reflectance-Fourier Transform-Infrared Imaging and Quantitative Energy-Dispersive Electron Probe X-ray Microanalysis Techniques Hae-Jin Jung, Md Abdul Malek, JiYeon Ryu, BoWha Kim, Young-Chul Song, HyeKyeong Kim, and Chul-Un Ro* Department of Chemistry, Inha University, 253, Yonghyun-dong, Nam-gu, Incheon 402-751, Korea Our previous work demonstrated for the first time the potential of the combined use of two techniques, attenuated total reflectance FT-IR (ATR-FT-IR) imaging and a quantitative energy-dispersive electron probe X-ray microanalysis, low-Z particle EPMA, for the characterization of individual aerosol particles. In this work, the speciation of mineral particles was performed on a single particle level for 24 mineral samples, including kaolinite, montmorillonite, vermiculite, talc, quartz, feldspar, calcite, gypsum, and apatite, by the combined use of ATR-FT-IR imaging and low-Z particle EPMA techniques. These two single particle analytical techniques provide complementary information, the ATR-FT-IR imaging on mineral types and low-Z particle EPMA on the morphology and elemental concentrations, on the same individual particles. This work demonstrates that the combined use of the two single particle analytical techniques can powerfully characterize externally heterogeneous mineral particle samples in detail and has great potential for the characterization of airborne mineral dust particles. Airborne mineral dust particles, naturally borne from soils, are the most abundant particulate matter in coarse atmospheric aerosols, and the recent recognition of multiple roles of mineral dust particles in atmospheric processes has made research on mineral dust a central topic in environmental studies.1,2 Mineral dust can influence global climate directly by scattering and absorbing solar radiation and indirectly by serving as cloud condensation nuclei (CCN).3 On a global scale, arid and semiarid areas, such as the Saharan desert and central China, are major sources of airborne mineral dust. Nearly every spring, usually from March to May, “Asian Dust,” mostly originating in Central China’s arid areas, is transported into Eastern China, the industrialized * Corresponding author. Phone: +82 32 860 7676. Fax: +82 32 867 5604. E-mail:
[email protected]. (1) Dentener, F. J.; Carmichael, G. R.; Zhang, Y.; Lelieveld, J.; Crutzen, P. J. J. Geophys. Res. 1996, 101 (D17), 22869–22889. (2) Usher, C. R.; Michel, A. E.; Grassian, V. H. Chem. Rev. 2003, 103, 4883– 4939. (3) Satheesh, S. K.; Moorthy, K. K. Atmos. Environ. 2005, 39, 2089–2110. 10.1021/ac101006h 2010 American Chemical Society Published on Web 06/22/2010
regions of China, and over the Yellow Sea to Korea, Japan, and even the Pacific Ocean, such that the vast amount of soil particles lifted from the arid source regions can be transported eastward and can adversely influence human health. Airborne mineral dust can also alter the chemical balance of the atmosphere by modifying its composition due to heterogeneous chemical reactions. The reactivity of mineral dust is closely related to its mineralogy. For example, calcite (CaCO3) and dolomite (CaMg(CO3)2) particles can react with NOx and/or HNO3 to form nitrate species, whereas gypsum (CaSO4 · 2H2O) does not.4,5 Recently, it was pointed out that airborne silicate mineral particles can react with nitrogen and sulfur oxide species to form nitrate and/or sulfate.6,7 It was also observed that in the same aerosol sample, some silicate particles contained nitrate and/ or sulfate but some did not,8 indicating that the different reactivity of silicate particles should be related to their different mineralogy. Soil particles are mainly composed of rock-forming minerals. It is known that, although specific areas differ in the detailed mineralogy of their soils, the chemical compositions of soil minerals around the world do not vary much in their contents of ∼60% SiO2 and ∼10-15% Al2O3.2 Minerals are classified into different types according to their chemical composition, such as silicate, carbonate, oxide, sulfate, phosphate, etc.9 Silicate minerals, which include quartz, feldspar, pyroxene, olivine, mica, and clay minerals, are the most abundant minerals, constituting ∼90% of the crust of the Earth. Thus, chemical elements of silicate minerals, such as Si, Al, Na, K, Mg, Ca, and Fe, are major constituents of soil-derived airborne mineral dust particles. Particles with
