AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Preparation of Lead (Pb) Reference Materials by Aerosol Deposition for XRF Analysis of Ambient Particulate Matter
Hardik Amin, Sinan Yatkin, Trzepla Krystyna, ANN DILLNER, University of California, Davis
Abstract Number: 117 Working Group: Instrumentation and Methods
Abstract Lead (Pb), one of the six criteria pollutants, is a toxic element in atmospheric particulate matter (PM). X-ray Fluorescence (XRF) is commonly used to non destructively quantify elemental concentrations in PM, including Pb. However, a significant difference exists between the mass loading of Pb on commercially available reference materials (RM) used for calibrating XRF and ambient PM. Moreover, the deposition pattern and substrate of deposition for commercial standards (Nucleopore® or Mylar®) is different than the substrate used for collecting PM (Teflon®).
In this work Pb RMs were prepared by aerosolizing aqueous solution of lead acetate trihydrate. The filters were made with Pb mass loadings between 30% and 350% of NAAQS levels (Pb NAAQS = 0.15 µg/m3 or 0.3 µg/cm2). The Pb aerosol is dried using a diffusion dryer, diluted in a mixing chamber and sampled onto 47 mm Teflon filters. Two types of Teflon filters were used, MTL filters (Measurement Technologies Laboratories, 0.2 µm pore size) used by EPA for Pb sampling and Teflo filters (Pall Life Sciences, 3 µm pore size) similar to filters used by IMPROVE. The Pb aerosol is sampled using Thermo Scientific Partisol Plus 2025i Sequential Air Sampler. In initial experiments, multiple MTL filters were prepared with Pb mass loadings of 0.2 µg/cm2 and 0.6 µg/cm2. Six filters at each mass loading were analyzed using two PANalytical Epsilon 5 energy dispersive XRF instruments. Each filter was analyzed three times on each instrument and the standard deviation was <4%. These filters were also analyzed by an independent laboratory using ARL QUANT’X XRF (Thermo Scientific) instrument. Eleven of twelve filters analyzed showed less than 6% difference, with one filter at Pb mass loading of 0.2 µg/cm2 showing 8% difference, when compared to PANalytical results. XRF and ICP/MS data for additional filters with Pb mass loadings over a range will be discussed.