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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 12 | Copyright
Atmos. Meas. Tech., 10, 5063-5073, 2017
https://doi.org/10.5194/amt-10-5063-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Dec 2017

Research article | 22 Dec 2017

Improved methods for signal processing in measurements of mercury by Tekran® 2537A and 2537B instruments

Jesse L. Ambrose Jesse L. Ambrose
  • College of Engineering and Physical Sciences, University of New Hampshire, Durham, 03824, USA

Abstract. Atmospheric Hg measurements are commonly carried out using Tekran® Instruments Corporation's model 2537 Hg vapor analyzers, which employ gold amalgamation preconcentration sampling and detection by thermal desorption (TD) and atomic fluorescence spectrometry (AFS). A generally overlooked and poorly characterized source of analytical uncertainty in those measurements is the method by which the raw Hg atomic fluorescence (AF) 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 ±[1%+ 1.2pg] and ±[6%+0.21pg], respectively. I demonstrate that the Tekran® method can produce significant low biases (≥ 5%) not only at low Hg sample loadings (< 5pg) but also at tropospheric background concentrations of gaseous elemental mercury (GEM) and total mercury (THg) (∼ 1 to 2ngm−3) under typical operating conditions (sample loadings of 5–10pg). Signal processing uncertainties associated with the Tekran® method can therefore represent a significant unaccounted for addition to the overall  ∼ 10 to 15% uncertainty previously estimated for Tekran®-based GEM and THg measurements. Signal processing bias can also add significantly to uncertainties in Tekran®-based gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) measurements, which often derive from Hg sample loadings < 5pg. In comparison, estimated signal processing uncertainties associated with the new methods described herein are low, ranging from within ±0.053pg, when the Hg thermal desorption peaks are defined manually, to within ±[2%+0.080pg] when peak definition is automated. Mercury limits of detection (LODs) decrease by 31 to 88% when the new methods are used in place of the Tekran® method. I recommend that signal processing uncertainties be quantified in future applications of the Tekran® 2537 instruments.

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Short summary
Scientific understanding of environmental Hg cycling is limited by analytical uncertainties. To better characterize analytical uncertainty associated with Hg measurements made with the Tekran® 2537 instrument, I developed new software-based methods for offline processing of the raw instrumental data. I demonstrate significant uncertainty associated with the Tekran® method. By comparison, my methods improve measurement accuracy and the Hg detection limit by as much as 95 % and 88 %, respectively.
Scientific understanding of environmental Hg cycling is limited by analytical uncertainties. To...
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