Quantitative characterization of individual aerosol particles by thin-window electron probe microanalysis combined with iterative simulation

A new data evaluation method and integrated software have been developed fo r the quantification of individual aerosol particles based on an iterative reverse Monte Carlo simulation combined with successive approximation for t he elemental composition. The computer code supports the automatic spectrum processing and the statistical analysis by clustering of the measured and calculated data of the particles: X-ray characteristic intensities, calcula ted elemental concentrations and the particle sizes. The analytical procedu re was tested rigorously by measurement of standard single particles such a s (NH4)(2)SO4, NH4NO3, CaCO3, CaSO4, SiO2, Fe2O3, BaSO4, KNO3, NaCl and a g ood agreement between the nominal and calculated quantitative composition w as found within 5-15 relative %. The correction of the second order process es caused by the characteristic fluorescence line of the substrate material (Al-K alpha) on the calculated concentration was estimated theoretically b y a single mathematical model for particles with a spherical shape. The k r atio for the fluorescence correction was found to be less than 0.1-0.7% for low-Z analysis. The present semi-automated method was applied to analyse m arine aerosol samples collected over the North Sea. Results of approximatel y 500 small individual particles show the capability of the method to quant ify the elemental composition of sub-micrometre particles down to 0.2 mu m. (C) 2000 Elsevier Science B.V. All rights reserved.