Chul-Un Ro

Chemical compositions of subway particles in Seoul, Korea determined by a quantitative single particle analysis.

A novel single particle analytical technique, low-Z particle electron probe X-ray microanalysis, was applied to characterize seasonal subway samples collected at a subway station in Seoul, Korea. For all 8 samples collected twice in each season, 4 major types of subway particles, based on their chemical compositions, are significantly encountered: Fe-containing; soil-derived; carbonaceous; and secondary nitrate and/or sulfate particles. Fe-containing particles are generated indoors from wear processes at rail-wheel-brake interfaces while the others may be introduced mostly from the outdoor urban atmosphere. Fe-containing particles are the most frequently encountered with relative abundances in the range of 61-79%. In this study, it is shown that Fe-containing subway particles almost always exist either as partially or fully oxidized forms in underground subway microenvironments. Their relative abundances of Fe-containing particles increase as particle sizes decrease. Relative abundances of Fe-containing particles are higher in morning samples than in afternoon samples because of heavier train traffic in the morning. In the summertime samples, Fe-containing particles are the most abundantly encountered, whereas soil-derived and nitrate/sulfate particles are the least encountered, indicating the air-exchange between indoor and outdoor environments is limited in the summer, owing to the air-conditioning in the subway system. In our work, it was observed that the relative abundances of the particles of outdoor origin vary somewhat among seasonal samples to a lesser degree, reflecting that indoor emission sources predominate.

Investigation of the Chemical Mixing State of Individual Asian Dust Particles by the Combined Use of Electron Probe X-ray Microanalysis and Raman Microspectrometry

In this work, quantitative electron probe X-ray microanalysis (EPMA) and Raman microspectrometry (RMS) were applied in combination for the first time to characterize the complex internal structure and physicochemical properties of the same ensemble of Asian dust particles. The analytical methodology to obtain the chemical composition, mixing state, and spatial distribution of chemical species within single particles through the combined use of the two techniques is described. Asian dust aerosol particles collected in Incheon, Korea, during a moderate dust storm event were examined to assess the applicability of the methodology to resolve internal mixtures within single particles. Among 92 individual analyzed particles, EPMA and RMS identified 53% of the particles to be internally mixed with two or more chemical species. Information on the spatial distribution of chemical compounds within internally mixed individual particles can be useful for deciphering the particle aging mechanisms and sources. This study demonstrates that the characterization of individual particles, including chemical speciation and mixing state analysis, can be performed more in detail using EPMA and RMS in combination than with the two single-particle techniques alone.

Single-particle characterization of summertime arctic aerosols collected at Ny-Alesund, Svalbard.

Single-particle characterization of summertime Arctic aerosols is useful to understand the impact of air pollutants on the polar atmosphere. In the present study, a quantitative single particle analytical technique, low-Z particle electron probe X-ray microanalysis, was used to characterize 8100 individual particles overall in 16 sets of aerosol samples collected at Ny-Alesund, Svalbard, Norway on 25-31 July, 2007. Based on their X-ray spectral and secondary electron image data of individual particles, 13 particle types were identified, in which particles of marine origin were the most abundant, followed by carbonaceous and mineral dust particles. A number of aged (reacted) sea salt (and mixture) particles produced by the atmospheric reaction of genuine sea-salts, especially with NO(x) or HNO(3), were significantly encountered in almost all the aerosol samples. They greatly outnumbered genuine sea salt particles, implying that the summertime Arctic atmosphere, generally regarded as a clean background environment, is disturbed by anthropogenic air pollutants. The main sources of airborne NO(x) (or HNO(3)) are probably ship emissions around the Arctic Ocean, industry emission from northern Europe and northwestern Siberia, and renoxification of NO(3)(-) within or on the melting snow/ice surface.

Chemical speciation of size-segregated floor dusts and airborne magnetic particles collected at underground subway stations in Seoul, Korea

Previous studies have reported the major chemical species of underground subway particles to be Fe-containing species that are generated from wear and friction processes at rail-wheel-brake and catenaries-pantographs interfaces. To examine chemical composition of Fe-containing particles in more details, floor dusts were collected at five sampling locations of an underground subway station. Size-segregated floor dusts were separated into magnetic and non-magnetic fractions using a permanent magnet. Using X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDX), iron metal, which is relatively harmless, was found to be the dominating chemical species in the floor dusts of the <25 μm size fractions with minor fractions of Mg, Al, Si, Ca, S, and C. From SEM analysis, the floor dusts of the <25 μm size fractions collected on railroad ties appeared to be smaller than 10 μm, indicating that their characteristics should somewhat reflect the characteristics of airborne particles in the tunnel and the platform. As most floor dusts are magnetic, PM levels at underground subway stations can be controlled by removing magnetic indoor particles using magnets. In addition, airborne subway particles, most of which were smaller than 10 μm, were collected using permanent magnets at two underground subway stations, namely Jegi and Yangjae stations, in Seoul, Korea. XRD and SEM/EDX analyses showed that most of the magnetic aerosol particles collected at Jegi station was iron metal, whereas those at Yangjae station contained a small amount of Fe mixed with Na, Mg, Al, Si, S, Ca, and C. The difference in composition of the Fe-containing particles between the two subway stations was attributed to the different ballast tracks used.

Single‐particle characterization of four aerosol samples collected in ChunCheon, Korea, during Asian dust storm events in 2002

[1]xa0A single-particle analytical technique, named low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA), employing an ultrathin window X-ray detector and enabling the quantitative determination of even low-Z elements such as C, N, and O, was applied to characterize “Asian dust” samples, collected in ChunCheon, Korea, during four Asian dust storm events on 21 March, 9 April, 17 April, and 11 November in 2002. In this study, it is demonstrated that single-particle analysis using the low-Z particle EPMA provides detailed information on various types of chemical species in the samples. The most abundantly encountered particles, both in coarse and fine fractions, are soil-derived particles such as aluminosilicates and silicon dioxide, except for the sample collected on 11 November 2002, where reacted CaCO3 particles are the most abundantly encountered. All four samples are found to have experienced chemical modifications during long-range transport because the samples contain a significant number of particles composed of chemical species, such as nitrate and sulfate, which resulted from atmospheric reactions of CaCO3 and sea-salt particles. This finding implies that CaCO3 and sea-salt particles reacted with sulfur and nitrogen oxide species during long-range transport. The sample collected on 11 November 2002 experienced the most extensive chemical modification during its transport. For this sample, the overall relative abundances of reacted CaCO3 and reacted sea-salt particles are 29.9% and 23.2%, respectively. In addition to the observation of the reacted CaCO3 and sea-salt particles, reacted K-containing particles are also encountered in this sample. In this work, it is observed that chemical modification of sea-salt particles was more extensive than that of CaCO3 particles. By considering the relative abundances of nitrate- and sulfate-containing particles, nitrate formation from CaCO3 and sea-salt particles in the air is found to be more favorable than sulfate formation.

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

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.

Characterization of individual submicrometer aerosol particles collected in Incheon, Korea, by quantitative transmission electron microscopy energy‐dispersive X‐ray spectrometry

[1]xa0For the last decade the Monte Carlo calculation method has been proven to be an excellent tool for accurately simulating electron-solid interactions in atmospheric individual particles of micrometer size. Although it was designed for application to scanning electron microscopy, in the present study it is demonstrated that the Monte Carlo calculation can also be applied in a quantitative single particle analysis using transmission electron microscopy (TEM) with an ultrathin window energy-dispersive X-ray (EDX) spectrometer with a high accelerating voltage (200 kV). By utilizing an iterative reverse Monte Carlo simulation combined with successive approximation, atomic elemental concentrations (including low-Z elements) of submicrometer standard particles were determined with high accuracy for electron beam refractory particles such as NaCl, KCl, SiO2, Fe2O3, Na2SO4, K2SO4, CaCO3, and CaSO4. On the basis of quantitative X-ray analysis together with morphological information from TEM images, overall 1638 submicrometer individual particles from 10 sets of aerosol samples collected in Incheon, Korea, were identified. The most frequently encountered particle types are carbonaceous and (NH4)2SO4/NH4HSO4-containing particles, followed by mineral (e.g., aluminosilicate, SiO2, CaCO3), sea salt, K-rich (e.g., K2SO4 and KCl), Fe-rich, fly ash, and transition or heavy-metal-containing (e.g., ZnSO4, ZnCl2, PbSO4) particles. The relative abundances of the submicrometer particle types vary among samples collected in different seasons and also depend on different air mass transport routes. This study demonstrates that the quantitative TEM-EDX individual particle analysis is a useful and reliable technique in characterizing urban submicrometer aerosol particles.

Annual resolution analysis of a SW-France stalagmite by X-ray synchrotron microprobe analysis

Abstract A sample of stalagmite from Grotte de Villars, Dordogne, France was analyzed by the use of X-ray synchrotron microprobe in LURE, Orsay, France. Together with the signal of Ca, the main element, much weaker but clear signals of Sr, Fe, Zn and Pb were registered. The X-ray scattered radiation was applied for recognition of the annual zones in the stalagmite structure in parallel with the gray scale morphology from the optical microscope. The elemental scans were superimposed on the optical image of the sample. It was established that places corresponding to dark locations on the annual rings were narrower, composed of less porous matter and had much greater contents of iron and zinc and elevated ratio of Sr/Ca. In the supplementary electron microprobe measurements, the elevated amounts of lighter elements, Si and Mg were found in the same locations. These results will allow a very accurate study of stalagmite elemental composition which is of first importance for paleoclimatic studies from speleothems.

Simulation study on regeneration of depth profiles from angle-resolved XPS data

This simulation study investigates the influences of sampling schemes, errors in the data and depth profiling functions on the extraction of the depth profiles from angle-resolved XPS data. An equiangular sampling scheme is more susceptible to the ill-posedness in the inverse operation of the Laplace transform than equidistance or gravimetric samplings. The influence of errors in the data can be considerable, depending on the types of depth profiles. Smooth depth profiling functions are well recovered, even for data with 10% errors. For discontinuous depth profiles, regenerated depth profiles do not represent the sharp change of original depth profiles at the interface.

Iron Speciation of Airborne Subway Particles by the Combined Use of Energy Dispersive Electron Probe X-ray Microanalysis and Raman Microspectrometry

Quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA), known as low-Z particle EPMA, and Raman microspectrometry (RMS) were applied in combination for an analysis of the iron species in airborne PM10 particles collected in underground subway tunnels. Iron species have been reported to be a major chemical species in underground subway particles generated mainly from mechanical wear and friction processes. In particular, iron-containing particles in subway tunnels are expected to be generated with minimal outdoor influence on the particle composition. Because iron-containing particles have different toxicity and magnetic properties depending on their oxidation states, it is important to determine the iron species of underground subway particles in the context of both indoor public health and control measures. A recently developed analytical methodology, i.e., the combined use of low-Z particle EPMA and RMS, was used to identify the chemical species of the same individual subway particles on a single particle basis, and the bulk iron compositions of airborne subway particles were also analyzed by X-ray diffraction. The majority of airborne subway particles collected in the underground tunnels were found to be magnetite, hematite, and iron metal. All the particles collected in the tunnels of underground subway stations were attracted to permanent magnets due mainly to the almost ubiquitous ferrimagnetic magnetite, indicating that airborne subway particles can be removed using magnets as a control measure.