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

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F = βσv(C1-C3) (1),
where β is an empirical coefficient, the “proportionality constant”, dependent on wind speed and
turbulence, generally 0.6 for a fixed deadband and approximately 0.3 for a dynamic deadband, and
calculated via the heat flux with the Metsupport system. σv is the standard deviation of the vertical
wind velocity: both values are obtained directly as output from the REA system; C1 and C3 are the
concentrations of RGM in upward and downward air masses, respectively.
From the flux measurements the depositional velocity of RGM can be calculated if the ambient
concentration for RGM is known:
vd = F/C (2),
where C is the concentration of RGM, and F is from 1.
Due to the uncertainty of the concentration measurements in Barrow: 10 % and of the
meteorological measurements, 10 % for β, σw for the Metsupport system (Christensen et al., 2000)
the uncertainty on the flux measurements using the Landis et al. 2002, KCl coated annular denuder
sampling end, heating caps and Metsupport REA system are estimated to be within 40% on a 95%
confidence interval, though 20% would be a more conservative estimate of denuder precision, given
the fact that flow at 10 lpm is not instantaneously developed, so there is necessarily some flow and
turbulence information lost when switching at 1 Hz. This gives a conservative sampling error for
flux as 50 % for the above system in Barrow.
As a quality assurance check for the REA flux measurements, the total concentration of the
three annular denuders for each run was compared with ambient concentration from a CMDL
collocated automated RGM monitoring system described in Lindberg et al., 2002. Results were
favourable, within 25% of each other on average.
3. Results and Discussion