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

3.1 RGM flux measurements
The results of the 2001 campaign in Alaska: Barrow Arctic Mercury Study (BAMS -2001) are
shown in Table 1 and Fig. 1. The largest deposition velocity in 2001 was 2.7 cm s -1 and the average
was close to 1 cm s -1 . Mean dry depositional flux was found to be - 0.4 ± 0.2 pg m -2 s -1 .
Concentrations of the three denuder tubes, up, mid and down, were added together to determine the
total concentration, and concentration was compared with the on site Tekran automatic RGM
monitor, MODEL 1130, described in Lindberg et al., 2002 (Table 1).
The machines were not running absolutely simultaneously so a linear interpretation was made
to compare concentrations. Not taking run two into account, since a valve was frozen open, it is
seen that the percent difference varies, with an average for the campaign of 24% with a standard
deviation of 42%. The percent difference between the two measurements was between 3% and
78%. This variance can be explained as a combination of the comparison method, the systems were
not started or stopped simultaneously, and the oxidation of gaseous elemental mercury to RGM is
dynamic, thus a linear extrapolation of concentration during a sampling period, is conservative. It is
seen that in all but 2 of the runs, run 2 excluded, the RGM REA total is less than the TEKRAN
1130 value, perhaps because of differences in the heating mantle system, but this observed bias
could also be because of different flow calibration systems.
The REA system when properly on the tower, after a period of time should report the same
number of counts per up and down channel, due to conservation of mass, and did so when initially
inventoried and tested during pre-deployment trials in Oak Ridge. In Barrow, there was always a
greater number, up to 30% more, of counts on the down channel, suggesting that the sonic
anemometer was not positioned properly, or a forcing of the turbulence. Therefore the channel
count data was corrected to ensure mass conservation as follows:
1) Corrected counts in Down = registered counts in Down - (registered counts in Down –
corrected Down); where corrected counts in down = counts in up channel.
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