FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

For all flux measurements, heating was kept constant, since the heat will affect the laminar flow
within the denuder, the gas diffusion coefficient and the relative adherence of the gas to the KCl
surface. The temperature was checked prior to and after measurement. The heating mantles
employed are high temperature polyvinylchlorid, PVC, pipes, which allow a 2 cm airspace around
the outside of the annular denuder, and enclose the denuder from the tip of the inlet to the top of a
filter pack at the outlet. The outer portion of the pipe is wrapped with a silver tape to ensure heat
transfer from self-regulating heat tape. The length of the heating tape is manufacturer and electrical
voltage dependent, but is cut long enough to heat the air inside the tube to 50 o C and keep it at that
temperature. From campaign experience, we found it necessary to improve the heating mantles to
achieve 50 0 C. The original heating mantle assembly was placed inside a larger PVC pipe, allowing
5 cm spacing between sidewalls, giving an overall diameter of approximately 9.6 cm. The space
between the two shells was then filled with self-expanding polyurethane foam thermal insulation.
After sampling, the denuders were taken into the laboratory for thermal desorption in
accordance with Landis et al. 2002, using a TEKRAN 2537A mercury analyser, to quantify the
RGM as Hg 0 .
For all measurements a field blank was obtained by handling a denuder in the field. Hg mass
from this field blank was subtracted from the measured Hg masses on the exposed denuders. If
there was any indication of Hg(0) adsorption, then the denuder was cleaned and re-coated, since as
pointed out by Sheu and Mason, 2001, just 1% of Hg(0) adsorption on a denuder is enough to
compromise RGM measurements. All accuracies with the denuders were found to be in good
agreement with those reported by Landis et al., 2002. In the Barrow 2001 campaign, the manual
denuders exhibited a precision of 10%, based on co-located parallel measurements, and were on
average within 25% of the automated RGM sampling system running separately and independently,
on the roof of Barrow CMDL.
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