Determination of low-Z elements in individual environmental particles using windowless EPMA

The determination of low-Z elements such as carbon, nitrogen, and oxygen in atmospheric aerosol particles is of interest in studying environmental pol lution. Conventional electron probe microanalysis technique has a limitatio n 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 char acteristic X-rays from light elements. The feasibility of low-Z element det ermination in individual particles using a windowless EDX detector is inves tigated. To develop a method capable of identifying chemical species of ind ividual particles, both the matrix and the geometric effects of particles h ave 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 observ ed radiation, especially that of light elements, experiences different exte nts of absorption, depending on the shape and size of the particles. Monte Carlo calculation is applied to explain the variation of observed X-ray int ensities according to the geometric and chemical compositional variation of individual particles, at: different primary electron beam energies. A comp arison is carried out between simulated and experimental data, collected fo r standard individual particles with chemical compositions as generally obs erved in marine and continental aerosols, Despite the many fundamental prob lematic analytical factors involved in the observation of X-rays from low-Z elements, the Monte Carlo calculation proves to be quite reliable to evalu ate those matrix and geometric effects. Practical aspects of the Monte Carl o calculation for the determination of light elements in individual particl es are also considered.