Particle and Aerosol Research Vol. 3, No. 1, March 2007 |
ISSN : 1738-8716 (Print) ISSN : 2287-8130 (Online) |
Quantitative single particle analysis and its application for characterization of atmospheric aerosol particles
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Abstracts
An electron probe X-ray microanalysis (EPMA) technique using an energy-dispersive X-ray detector with an
ultra-thin window, designated low-Z particle EPMA, has been developed. The low-Z particle EPMA allows the
quantitative determination of concentrations of low-Z elements such as C, N, and O, as well as higher-Z elements
that can be analyzed by conventional energy-dispersive EPMA. The quantitative determination of low-Z elements
(using full Monte Carlo simulations, from the electron impact to the X-ray detection) in individual environmental
particles has improved the applicability of single-particle analysis, especially in atmospheric environmental aerosol
research; many environmentally important atmospheric particles, e.g. sulfates, nitrates, ammonium, and carbonaceous
particles, contain low-Z elements.
Furthermore, ¡°beam variation¡± EPMA has also been developed, which permits one to get information on the
depth heterogeneity with respect to chemical composition of single particles. Some internally mixed individual
aerosol particles are created by heterogeneous atmospheric reactions in air, for example, CaSO4 particles are produced
by the reaction between CaCO3 particles and gaseous SOx. If the reaction is not complete, then CaSO4 species
would be expected to exist more on the surface of the particles and CaCO3 more in the core. By varying the
excitation voltage, we could obtain useful information on the heterogeneity of e.g., artificially generated heterogeneous
CaSO4-CaCO3 individual particles.
This low-Z particle EPMA technique has been applied for various types of airborne particles, including urban
aerosols, marine aerosols, fly-ash particles from municipal solid waste incinerators, aerosol particles collected at a
subway station, and Asian dust particles. In this work, some new observations obtained from Asian dust particle
samples are briefly presented.
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