Determination of Low-Z Elements in Individual Environmental Particles Using Windowless EPMA

Abstract

The determination of low-Z elements such as carbon, nitrogen, and oxygen in atmospheric aerosol particles is of interest in studying environmental pollution. Conventional electron probe microanalysis technique has a limitation for the determination of the low-Z elements, mainly because the Be window in an energy-dispersive X-ray (EDX) detector hinders the detection of characteristic X-rays from light elements. The feasibility of low-Z element determination in individual particles using a windowless EDX detector is investigated. To develop a method capable of identifying chemical species of individual particles, both the matrix and the geometric effects of particles have to be evaluated. X-rays of low-Z elements generated by an electron beam are so soft that important matrix effects, mostly due to X-ray absorption, exist even within particles in the micrometer size range. Also, the observed radiation, especially that of light elements, experiences different extents of absorption, depending on the shape and size of the particles. Monte Carlo calculation is applied to explain the variation of observed X-ray intensities according to the geometric and chemical compositional variation of individual particles, at different primary electron beam energies. A comparison is carried out between simulated and experimental data, collected for standard individual particles with chemical compositions as generally observed in marine and continental aerosols. Despite the many fundamental problematic analytical factors involved in the observation of X-rays from low-Z elements, the Monte Carlo calculation proves to be quite reliable to evaluate those matrix and geometric effects. Practical aspects of the Monte Carlo calculation for the determination of light elements in individual particles are also considered.

Elevated nitrogen-containing particles observed in Asian dust aerosol samples collected at the marine boundary layer of the Bohai Sea and the Yellow Sea

“…The X-ray spectra were recorded under the control of EMAX Hitachi software. A 10 kV accelerating voltage, 1.0 nA of beam current, and a typical measuring time of 10 s were employed to ensure a low background level of spectra, a good sensitivity for low-Z element analysis, and statistically sufficient counts in the X-ray spectra (Ro et al, 1999 …”

Uranium aerosols at a nuclear fuel fabrication plant: Characterization using scanning electron microscopy and energy dispersive X-ray spectroscopy

“…This is probably due to a bias from oxygen in the impaction substrate (carbon was not included in the quantification) and a presence of other elements. For micron-sized particles a majority of the electron beam interaction may come from interactions in the impaction substrate, which will affect measured X-ray intensities [37]. An observation similar to Fig.…”

Comprehensive microanalytical study of welding aerosols with x‐ray and Raman based methods

“…To achieve optimal experimental conditions, such as low background levels in the spectra and high sensitivity for light element analysis, an accelerating voltage of 10 kV and a beam current of 1 nA were applied. 15 Automatic and manual measurements were carried out in the spot mode.…”

“…16 The semi-quantitative elemental composition of the particles was calculated with an iterative approximation method based on Monte Carlo simulations. 15,17,18 The obtained data set was used for the further particle classification by means of hierarchical cluster analysis performed with the Integrated Data Analysis System program. 19 The clustering was done only on the basis of the chemical composition of the aerosol particles and not on the morphological information.…”