Toward establishing the stability of multi-year monitoring of elements in airborne particles.

Crocker Nuclear Laboratory uses a custom built energy-dispersive X-ray fluorescence system with a molybdenum anode to provide routine analysis of elements from nickel to zirconium and lead in Interagency Monitoring of Protected Visual Environments (IMPROVE) samples. Standard methods are used to ensure accuracy and statistical control of the data, including repeated analysis of single-element standards, standard reference materials, and selected actual samples from the IMPROVE network. This paper compares the short-term (week) precision and long-term (2-yr) reproducibility revealed by the actual sample reanalyses. Currently reported analytical uncertainties are shown to predict actual 2-yr reproducibility within a factor of 2.