János Osán

Chemical speciation of individual atmospheric particles using low-Z electron probe X-ray microanalysis:: characterizing “Asian Dust” deposited with rainwater in Seoul, Korea

Chemical speciation of individual microparticles is of much interest in environmental atmospheric chemistry; e.g. the determination of the elemental concentrations in individual atmospheric aerosol particles is important to study the chemical behavior of atmospheric pollution. Recently, an EPMA technique using an X-ray detector equipped with an ultra-thin window, allowing EPMA to determine concentrations of low-Z elements, such as C, N, and O, in individual particles of micrometer size, has been developed. This technique, called low-Z electron probe X-ray microanalysis (low-Z EPMA), is applied to characterize the water-insoluble part of “Asian Dust”, deposited by washout in the form of rainwater during an Asian Dust storm event and collected in Seoul, Korea. In this study, it was demonstrated that the single particle analysis using low-Z EPMA provided detailed information on various types of chemical species in the sample. In addition to aluminosilicates, silicon oxide, iron oxide, and calcium carbonate particles, which are expected to be present, carbonaceous particles are also observed in a significant fraction. This unexpected finding that particle sample originated from an arid area contains significant amount of carbonaceous particles is supported by the investigation of a “China Loess” sample. In addition, we also performed single particle analysis for a local soil sample, in order to check the possible influence from local sources on “Asian Dust”. The characteristics of the local soil particle sample, e.g. the types of aluminosilicate particles and the abdundance of particles with deviating chemical species, are clearly different from “Asian Dust” and “China Loess” samples, whereas those two are similar, implying that the “Asian Dust” sample was not much influenced by local sources.

Thermal stability of beam sensitive atmospheric aerosol particles in electron probe microanalysis at liquid nitrogen temperature

Abstract Thin-window electron probe X-ray microanalysis offers new analytical possibilities for low-Z detection (i.e. elements with low atomic number; such as C, N and O). However, the quantitative analysis of individual particles raises some practical questions concerning the technique. From the analytical point of view, beam damage is one of the most important problems due to its big impact on the analysis of individual atmospheric particles. The dependence of the beam-damage effect on the type of collection substrate was studied using standard aerosol particles. Different metallic substrates were rigorously tested in relation to the beam damage effects to different kinds of beam sensitive particles. Ammonium sulfate, ammonium nitrate, sodium nitrate as well as sulfuric acid droplets were analyzed using a liquid nitrogen cooled sample stage on different metallic substrates such as Be, Al, Si and Ag. The obtained results confirm that the use of Be as a collection surface offers some advantages in order to minimize the damage to beam sensitive particles, as suggested in earlier research.

Quantitative trace element analysis of individual fly ash particles by means of X-ray microfluorescence

A new quantification procedure was developed for the evaluation of X-ray microfluorescence (XRF) data sets obtained from individual particles, based on iterative Monte Carlo (MC) simulation. Combined with the high sensitivity of synchrotron radiation-induced XRF spectroscopy, the method was used to obtain quantitative information down to trace-level concentrations from micrometer-sized particulate matter. The detailed XRF simulation model was validated by comparison of calculated and experimental XRF spectra obtained for glass microsphere standards, resulting in uncertainties in the range of 3-10% for the calculated elemental sensitivities. The simulation model was applied for the quantitative analysis of X-ray tube and synchrotron radiation-induced scanning micro-XRF spectra of individual coal and wood fly ash particles originating from different Hungarian power plants. By measuring the same particles by both methods the major, minor, and trace element compositions of the particles were determined. The uncertainty of the MC based quantitative analysis scheme is estimated to be in the range of 5-30%.

Study of Chemical State of Toxic Metals during the Life Cycle of Fly Ash Using X-Ray Absorption Near-Edge Structure

The non-destructive x-ray absorption near-edge structure (XANES) method was applied to the quantitative determination of chromium and arsenic species in coal fly ash. In order to study the chemical state changes caused by deposition and sedimentation of the particles, land fill and river sediment samples obtained in the neighborhood of power plants were also investigated. The measurements were carried out at the X26 beam line of the BNL National Synchrotron Light Source (USA) in fluorescent mode. For achieving quantitative results on the ratio of close-lying oxidation state forms, a non-linear fitting model was developed to process the XANES spectra obtained. The features of the spectra such as the white line, the multiple scattering resonance peak and the absorption edge were modelled with analytical functions. The results obtained show that chromium is present mostly (>95%) as Cr(III) in fly ash and the chemical state remains the same after deposition and sedimentation. Arsenic is present as As(V) in fly ash and land fill samples, while the possible As(III) content of sediment samples is around 40%.

Comparison of nuclear and X-ray techniques for actinide analysis of environmental hot particles

Actinide-containing radioactive hot particles have been dispersed into the environment during atmospheric nuclear tests, accidents of the nuclear fuel cycle and authorized discharges from nuclear reprocessing plants. Several other activities like illicit trafficking of radioactive material or the use of depleted uranium in shielding, weapons can also be considered as possible sources of contamination by actinides. The paper compares detection limits for actinide analysis by nuclear spectroscopy as well as various X-ray micro-fluorescence and absorption techniques using laboratory and synchrotron sources. The detection limits for X-ray techniques were calculated using Monte Carlo simulations. Detection limits obtained for X-ray microanalysis using synchrotron sources were close to that of nuclear analysis. For long half-life nuclides (more than 105 years), X-ray spectrometry was more sensitive, while being non-destructive and offering additional information on oxidation states using X-ray absorption. For U, α spectrometry resulted only in 10−7 g (238U) contrasting 10−13 g obtained for monochromatic beam µ-XRF (micro X-ray fluorescence) at HASYLAB Beamline L. Using the combination of autoradiography and µ-XRF, identification and quantitative analysis of individual radioactive particles of 20 µm diameter were possible. Despite the strong spectral overlap with the Rb-Kα characteristic line, in fluorescence mode µ-XANES (micro X-ray absorption near-edge structure) it was possible to determine the oxidation state of 15 µg g−1 U in a single hot particle.

Reference-free quantification of particle-like surface contaminations by grazing incidence X-ray fluorescence analysis

The analysis of the elemental composition of aerosol particles by non-destructive grazing incidence X-ray fluorescence analysis (GIXRF) is possible if the particles are deposited on a flat substrate. If those particles exhibit surface areas parallel to the substrate surface, under certain experimental conditions, total reflection of incident X-rays might arise also at those sites thereby preventing X-rays from penetrating the particles. For a reliable quantitative analysis, this effect and the interaction with the X-ray standing wave field (XSW) has to be further investigated in detail. To study the effects occurring when nanoscaled objects are probed with GIXRF, artificial nanostructures of known size, shape and composition have been manufactured on flat silicon wafer surfaces, with the intention to simulate deposited nanoscaled aerosol particles. A reference-free quantification of the deposited mass was performed employing a simple model for the propagation of the XSW through the sample material. Depending on the quality of the manufactured structures, good agreement between nominal masses and measured values could be stated. Only moderate agreement was found for samples that were more difficult to manufacture. GIXRF measurements yield information on the physical dimensions of the structures which are well in line with results obtained by a combination of scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM/EDX). The presented quantification model, which is based on existing software for XSW calculations, can be transferred to environmental nanoparticles sampled directly from the aerosol phase. All measurements were performed in the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at BESSY II using well-characterized monochromatic synchrotron radiation and calibrated instrumentation.

Micro-distribution of heavy elements in highly inhomogeneous particles generated from μ-beam XRF/XRD analysis

Abstract By simultaneously recording X-ray fluorescence intensities and X-ray diffraction pattern at a microscopic level highly heterogeneous samples of fly-ash particles have been analyzed. From the data achieved by this combined experiment, the main minerals in the particles have been identified and the size distributions of these minerals have also been determined. The distribution of heavy elements, recorded from their fluorescent intensity, is presented and the impact of sample surface topology and anomalous attenuation is discussed. Estimates of the concentration of the these heavy elements are given and correlation analysis has been performed indicating that most of these elements seem to appear at the surface of the fly-ash particles.

Determination of trace elements in lithium niobate crystals by solid sampling and solution-based spectrometry methods

Solid sampling (SS) graphite furnace atomic absorption spectrometry (GFAAS) and solution-based (SB) methods of GFAAS, flame atomic absorption spectrometry (FAAS), inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) were elaborated and/or optimized for the determination of Cr, Fe and Mn trace elements used as dopants in lithium niobate optical crystals. The calibration of the SS-GFAAS analysis was possible with the application of the three-point-estimation standard addition method, while the SB methods were mostly calibrated against matrix-matched and/or acidic standards. Spectral and non-spectral interferences were studied in SB-GFAAS after digestion of the samples. The SS-GFAAS method required the use of less sensitive spectral lines of the analytes and a higher internal furnace gas (Ar) flow rate to decrease the sensitivity for crystal samples of higher (doped) analyte content. The chemical forms of the matrix produced at various stages of the graphite furnace heating cycle, dispensed either as a solid sample or a solution (after digestion), were studied by means of the X-ray near-edge absorption structure (XANES). These results revealed that the solid matrix vaporized/deposited in the graphite furnace is mostly present in the metallic form, while the dry residue from the solution form mostly vaporized/deposited as the oxide of niobium.

A measurement based analysis of the spatial distribution, temporal variation and chemical composition of particulate matter in Munich and Augsburg

The objective of the studies presented in this paper is to present an analysis of spatial distribution and temporal variation of particulate matter in Munich and Augsburg, Germany, and to identify and discuss the factors determining the aerosol pollution in both areas. Surface-based in-situ and remote sensing measurements of particle mass and particle size distribution have been performed in, around, and above the two cities. Two measurement campaigns were conducted in Munich, one in late spring and one in winter 2003. Another campaign has been on-going in Augsburg since 2004. Spatial and temporal variations are analyzed from this data (PM 10 , PM 2.5 and PM 1 ). There are higher particle mass concentrations at the urban site than at the surrounding rural sites, especially in winter. No significant difference in the major ionic composition of the particles between the urban and the rural site was detected. This is considered to be related to the spatial distribution of secondary inorganic aerosol that is more homogeneous than aerosol resulting from other sources like traffic or urban releases in general. During the measurement campaigns mixing layer heights were determined continuously by remote sensing (SODAR, ceilometer, RASS). Significant dependence of particle size distribution and particle mass concentration on mixing layer height was found. This finding paves the way to new applications of satellite remote sensing products.

Investigation of chemical composition of belemnite rostra by synchrotron-based X-ray microfluorescence and diffraction and electron microprobe

Abstract Rostra (bullet-shaped internal shells) of two species of belemnites: Belemnopsis sp. (from Bathonian Stage sediments ∼161–166 Ma ago) and Hibolites sp. (from Middle Oxfordian sediments ∼154–157 Ma) were investigated by the use of 1B2 microfluorescence beamline in Pohang Light Source in Korea. The cross-sections of the rostra showed an ordered structure of concentric growth laminae cut across by radial calcite crystals. The inner and outer parts of the cross-section differ in the size of calcite crystals, building the block. Very fine crystals existing in the inner parts of rostra are replaced by monocrystals in their external parts. Some compounds of metallic elements such as iron and zinc are present in the calcite matrices of belemnites. Their presence is especially pronounced in the zones separating particular growth rings. The concentrations of elements in calcite matrix were calibrated by atomic absorption method and the results for alkaline elements are: for Sr ∼1000 ppm for Oxfordian specimen and ∼3000 ppm for Bathonian; for Na, ∼2000 and ∼1400 ppm; for K, ∼160 and ∼100 ppm, respectively. The synchrotron-based investigations were complemented with the electron microprobe search for low-Z elements; using this method sodium, potassium, aluminum, silicon, chlorine and sulfur were detected in the matrix. The variability of molar Mg/Ca ratio follows the optical variability of the annual growth zones of the samples, suggesting that this ratio could be used as a palaeothermometer. Possibilities of both application of the elemental data for the estimation of palaeotemperatures, and cross-checking with the isotopic data are discussed. The substantial amounts of the excess carbon were detected in the samples. They are concluded to be potentially useful for the analysis of remnants of original biological matter.