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Medientyp:
E-Artikel
Titel:
Evaluation of cation exchange membrane performance under exposure to high Hg<sup>0</sup> and HgBr<sub>2</sub> concentrations
Beteiligte:
Miller, Matthieu B.;
Dunham-Cheatham, Sarrah M.;
Gustin, Mae Sexauer;
Edwards, Grant C.
Beschreibung:
<jats:p>Abstract. Reactive mercury (RM), the sum of both gaseous oxidized Hg and particulate
bound Hg, is an important component of the global atmospheric mercury cycle,
but measurement currently depends on uncalibrated operationally defined
methods with large uncertainty and demonstrated interferences and artifacts.
Cation exchange membranes (CEMs) provide a promising alternative methodology
for quantification of RM, but method validation and improvements are ongoing.
For the CEM material to be reliable, uptake of gaseous elemental mercury
(GEM) must be negligible under all conditions and RM compounds must be
captured and retained with high efficiency. In this study, the performance of
CEM material under exposure to high concentrations of GEM (1.43×106 to 1.85×106 pg m−3) and reactive gaseous mercury
bromide (HgBr2 ∼5000 pg m−3) was explored using a
custom-built mercury vapor permeation system. Quantification of total
permeated Hg was measured via pyrolysis at 600 ∘C and detection
using a Tekran® 2537A. Permeation tests were
conducted over 24 to 72 h in clean laboratory air, with absolute humidity
levels ranging from 0.1 to 10 g m−3 water vapor. GEM uptake by the CEM
material averaged no more than 0.004 % of total exposure for all test
conditions, which equates to a non-detectable GEM artifact for typical
ambient air sample concentrations. Recovery of HgBr2 on CEM filters was
on average 127 % compared to calculated total permeated HgBr2 based on
the downstream Tekran® 2537A data. The low
HgBr2 breakthrough on the downstream CEMs (< 1 %) suggests that
the elevated recoveries are more likely related to suboptimal pyrolyzer
conditions or inefficient collection on the Tekran® 2537A gold traps.
</jats:p>