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

Fate of Mercury in the Arctic 46
concentration in a flux system sampling in three channels: up drafts, down drafts and all else, as
compared to levels measured in parallel annular denuders under constant sampling conditions,
could be set at 1 Hz.
In these experiments flow rates were controlled by a Tylan mass flow controller and checked
prior to and after the sampling period. The results of these experiments led to the sampling
switching rate being set in the REA system to 1 Hz with the 10 litre per minute flow rate maintained
by a mass flow controller. The air sampling-switching rate is so long compared to errors that could
be induced from physical switching and software, that these are considered negligible. Zero air was
not added to the sampling inlet system since this would mean that ambient air could not be directly
sampled into the annular denuder, but that ambient air would have to flow through an additional
inlet first. RGM is so reactive that it was thought best to directly sample it into the annular
denuders. This is possible given the 1 Hz switching rate.
Therefore, by sampling at 1 Hz, approximately 95% of the turbulence is captured and the best
compromise between the meteorological measurements and chemical sampling is obtained in order
to ensure a laminar flow in the annular denuders and thereby measure RGM flux most accurately
Measurements were made as follows: The heating mantles are turned on approximately 1 hour
prior to measurement. 4 annular denuders were prepared and blanked immediately prior to use: 3
for the system and one as the field blank. Inlets are baked prior to field deployment unless
contaminated by handling. Powder-free rubber gloves are used when handling the inlets. The
denuders are then taken outdoors and carefully placed into the heating caps. Care is taken not to
disturb the sonic alignment, or crack a denuder due to handling, nor handle the sampling inlet since
the annular denuders are relatively fragile under Arctic weather conditions, and the inlets may
easily be contaminated. Flow is checked in the sampling lines and temperature measured in the
denuders. Once the temperature of the denuders has stabilized, the REA system is started by