An Expert System for Chemical Speciation of Individual Particles Using Low-Z Particle Electron Probe X-ray Microanalysis Data

Abstract

An electron probe X-ray microanalysis (EPMA) technique, using an energy-dispersive X-ray detector with an ultrathin window, designated a 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 chemical elements that can be analyzed by conventional energy-dispersive EPMA, in individual particles. Since a data set is usually composed of data for several thousands of particles in order to make environmentally meaningful observations of real atmospheric aerosol samples, the development of a method that fully extracts chemical information contained in the low-Z particle EPMA data is important. An expert system that can rapidly and reliably perform chemical speciation from the low-Z particle EPMA data is presented. This expert system tries to mimic the logic used by experts and is implemented by applying macroprogramming available in MS Excel software. Its feasibility is confirmed by applying the expert system to data for various types of standard particles and a real atmospheric aerosol sample. By applying the expert system, the time necessary for chemical speciation becomes shortened very much and detailed information on particle data can be saved and extracted later if more information is needed for further analysis.

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

“…A Monte Carlo calculation combined with reverse successive approximations was applied to determine the particles' elemental concentrations on the basis of the X-ray intensities (Ro et al, 2003). For standard particles, the quantification procedure provided results accurate within 12% relative deviations between the calculated and nominal elemental concentrations, except for C and K where the characteristic X-rays overlap with those from the Ag substrate (Ro et al, 2001b).…”

“…For standard particles, the quantification procedure provided results accurate within 12% relative deviations between the calculated and nominal elemental concentrations, except for C and K where the characteristic X-rays overlap with those from the Ag substrate (Ro et al, 2001b). The formula concentrations and the group distributions were rapidly and reliably determined by the "expert system" program (Ro et al, 2004).…”

Investigation of aged aerosols in size-resolved Asian dust storm particles transported from Beijing, China, to Incheon, Korea, using low-<i>Z</i> particle EPMA

“…The particle equivalent diameters were estimated from their projected area, assuming the particles to be spherical. The methods for acquiring the net X-ray intensities of the elements; for simulating the measured X-ray intensities for all chemical elements, in a particle by Monte Carlo calculations; and for using the "expert system" program to perform chemical speciation and determine the particle group distributions are described elsewhere (Vekemans et al, 1994;Ro et al, 2003Ro et al, , 2004. The elemental quantification procedure provided results with an accuracy of within 12 % relative deviations between the calculated and nominal elemental concentrations for various standard particles (Ro et al, 2000(Ro et al, , 2001.…”

Microscopic characterization of carbonaceous aerosol particle aging in the outflow from Mexico City

“…Electron microscopy with energy dispersive X-ray (EDX) microanalysis or electron energy loss spectroscopy (EELS) yields spatially resolved chemical composition of individual particles Katrinak et al, 1992). One general limitation of EDX is that quantitative analysis of low-Z elements (carbon, nitrogen, and oxygen) is not always possible and requires time-intensive Monte-Carlo calculations (Ro et al, 2003(Ro et al, , 2004. TEM imaging with EELS can be used to characterize carbon content of particles, but its limited energy resolution precludes detailed analysis of carbon bonding (Katrinak et al, 1992).…”