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

Fate of Mercury in the Arctic 72
and the additive product of the denuders, up, mid, down were within 25% of the constantly sampled
denuder. There was a good mass balance between the up and down channel.
The results of the 2001 campaign in Alaska (Barrow Arctic Mercury Study (BAMS)) are
shown in Table 1. page 73 and Figure 14 page 77. The largest deposition velocity in 2001 was
approximately 2.8 cm s -1 and the average was close to 1 cm 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, Appendix C. Since the machines were not running absolutely
simultaneously, a linear interpretation was made to compare concentrations for the same time
frame. The heating system for the annular denuder heating system for the 1130 kept the denuders
warmer than the heating mantles on the REA system. 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. Percent difference between the two
measurements was as small as 3% and as large as 78%. It is seen that in all but 2 of the runs, run 2
excluded, the RGM REA total is less than the 1130 value, perhaps because of differences in the
heating mantle system or in differences of flow calibration between the two 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 prior to
deployment in Barrow at Walker Branch. 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. 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 – counts in up).
Control: total counts for all channels registered = total counts with down corrected.
2) Corrected Counts for Mid = registered Counts for Mid - (Registered Counts for Down - corrected
counts for Down); The lost mass must be placed in mid channel for later concentration calculation.
Control: Corrected counts Mid > registered counts mid, but total counts all channels still the same.
3) Corrected Counts Up = Old Counts up Up, since down was preferred during sampling.