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

2.3 The RGM REA system and flux measurement
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Relaxed eddy accumulation, REA, is a micrometeorological method for trace gas flux
determination. REA “relaxes” the requirement for instantaneous gas analysis by preferentially
collecting air over time into some type of accumulator for up and down drafts, and all other air, the
mid-channel. The trace gas in the collected sample is analysed after the sampling period.
RGM flux measurements were performed from 29 March, 2001 through April 12, 2001, with
the system set up at approximately 3 m above the snow pack surface on a guy-wire support of the
NOAA, Barrow, CMDL tower, oriented into the prevailing winds, arriving from the Beaufort Sea.
The measurements were made using a micrometeorological flux measurement system built by
METSUPPORT aps, Denmark in January 2001 for this campaign. This system was coupled with
the Landis et al., 2002 annular denuder method for measuring RGM, and the previously described
heating caps, as the sampling front end. A similar METSUPPORT system and components have
been previously deployed by NERI for measuring volatile organic compounds (VOCs) and is
described in detail in Christensen et al. 2000.
The REA flux measurement system was set up on a steel rod affixed to the CMDL tower guy-
line support pole with the head of the sonic anemometer facing into the predominant wind direction,
and oriented towards North. The support beam was hung such that the heating caps and therefore
inlets of the sampling system were perpendicular to, and 1 meter behind the centrum of the sonic
head. The inlets were 1-2 mm longer than flush protruding from the bottom of the heating caps. The
denuders for the up and down draft were co-located nearest the centre of the mast, while the parallel
measurements or denuders sampling the air that is not coming either as down or up, were located
near the edges of the mast. A quartz filter was kept in each of the filter packs, to ensure a constant
pressure drop. Temperature in the heating caps was measured prior to and after sampling. From the
quick connect at the top of the filter pack were connected 3.2 m long neoprene hoses into 3 fast