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

Fate of Mercury in the Arctic 35
The denuders were then cleaned, coated, dried, and prepared according to the protocol for
manual denuder measurements provided by Dr. Landis. As published in Landis et al., 2002.
Each denuder was then tested for eventual variation of the blanks of the denuders. Denuders
were also concurrently sampled in pairs to ensure that collocated precision was < 15%, in
agreement with the findings reported for the method in Landis et. al., 2002.
Denuders were exposed to laboratory air with relatively high RGM concentrations,
approximately twice that expected in ambient air, due to the past and present use of HgCl2 in the
building at Oak Ridge National Lab; and ambient air at Walker Branch Watershed Research Area,
Oak Ridge, Tennessee with and without end caps to test if there was any appreciable passive
diffusion. This is important since only one of three denuders is actively sampled in the flux system
at any given time. Over the sampling period it is expected that the denuder will be idle, subject only
to passive uptake two thirds of the total sampling time.
The heating mantels are different than those used by Landis, et al., 2000, since theirs were
judged to be too bulky for use in the flux system where at least two would be required. The heating
mantels used in this work are originally developed while at NOAA, under guidance of chief
engineer, Mark Hall. The original mantles are seen hanging from the tower in Figure 3., page 39.
The heating mantles are described as follows: high temperature polyvinylchlorid, PVC, pipes,
which allow for a 2 cm airspace around the outside of the annular denuder, and encloses 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 heat tape is
uniformly wrapped around the pipe and grounded on the metal tape. This is then covered with
insulating 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.