Improved Methods for Signal Processing in Measurements of Elemental Mercury Vapor by Tekran<sup>®</sup> 2537A and 2537B Instruments

Abstract. Atmospheric Hg measurements are commonly carried out using Tekran® Instruments Corporation's model 2537 Hg vapor analyzers, which employ gold amalgamation pre-concentration sampling and detection by thermal desorption/atomic fluorescence spectrometry. A generally overlooked and poorly characterized source of analytical uncertainty in those measurements is the method by which the raw Hg atomic fluorescence signal is processed. Here I describe new software-based methods for processing the raw signal from the Tekran® 2537 instruments, and I evaluate the performances of those methods together with the standard Tekran® internal signal processing method. For test datasets from two Tekran® instruments (one 2537A and one 2537B), I estimate that signal processing uncertainties in Hg loadings determined with the Tekran® method are within ±[6 % + 0.94 pg]. I demonstrate that the Tekran® method produces significant low biases (≥ 5 %) not only at low Hg sample loadings (