Application of x-ray fluorescence techniques to measure elemental composition of particles in the atmosphere

The design and operation of a system for the automated X-ray fluorescence analysis of atmospheric particulates on filters will be described. Central to the system is a low-background Si(Li) semi conductor detector coupled to a low-power variable-energy X-ray tube used to generate monoenergetic photons for fluorescence excitation. Sequencing of the filter analysis, changes in X-ray excitation energy and intensity, together with data storage can be performed without operator intervention under the control of a small dedicated computer. Reduction of pulse height data and intensity calibration can be per formed in real-time in this same computer. The three analysis re quired to cover over 30 elements can be performed in a total time of one-half hour with detection limits in the worst case of 25 ng/cm 2 or less over filter areas of 7 cm 2 • A single analysis for a restricted group of 15 elements at a detection level below 10 ng/cm 2 can be per formed in ten minutes. Samples are generated using a fully automated remote sampling station designed for the unattended collecting of up to 30 filter samples using a variety of commercially available filter ing materials. The accuracy and sensitivity of the method compared to other sampling and analysis techniques will be discussed.