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

Fate of Mercury in the Arctic 91
amount to more than the 10 to 15 % error from analysing the annular denuders, or the error in their
reproducibility, and may therefore be used for RGM REA measurements.
While at Station Nord, it was pointed out that the denuder sampling technique is very
sensitive to the vapour pressure of the compound, especially compounds distributed between gas
and particulate phase as demonstrated in studies of polycyclic aromatic hydrocarbons (PAH) (e.g.
Feilberg et al. 2000) experiments were therefore made to test the effect of measurements with and
without heating in the Arctic, Figure 9., page 67.
It seen that for higher RGM concentrations, there is an apparent difference, with heated
denuders reporting more RGM. However the reason for this observation is not clear. The central
question is if TPM is converted to RGM in the denuder or if the denuder is not functioning well at
low temperatures, as described by Landis et al. (2002). At lower concentrations, 5 pg m -3 , heated
and non heated denuders report approximately the same. This level may therefore be an expression
of the detection limit of the KCl coated annular denuder, rather than true ambient values.
This work confirms that the Landis et al., 2002 method not only is sensitive to differences in
field application, but also is sensitive to differences in analytical application. For example, Landis et
al., 2002 prescribes the use of co-axial fans in the analytical desorption train. Figure 10., page 68,
shows that this is a consideration that will affect results, with higher values coming from systems
that do not employ coaxial fans. How much cooling effect is needed from the fan? This is probably
dependent on the type of sampling line used. Subjectively, the sampling lines in this experiment
were warm to the touch, when co-axial fans were not used.
The results from the tests confirm the recommendation made in Schroeder et al., 2003, for the
need of a robust calibration system. The denuders were designed based on data from only HgCl2
(Landis et al., 2002) and to date, there are no published methods for calibrating the annular
denuders, though 2 research groups, Eric Prestbo and Julia Lu, report on calibrating the annular