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

Asian Chemistry Letters vol. XX, No 1 (2003) XX-XX
of atmospheric mercury, see later. Therefore, inside the atmospheric boundary layer over sea ice
during sunny conditions, it is assumed that there is an additional first order oxidation rate of ¼ hour -1
converting Hg 0 to HgO. The fast oxidation stops, when surface temperature exceeds -4 o C (the freezing
point saltwater). Removals of Hg 0 are due to the chemistry and the uptake by cloud water.
Dry deposition velocities of the reactive gaseous mercury species (in the model assumed to be HgO
and HgCl2) are based on the resistance method, where the surface resistance similar to HNO3 is used
based on the flux measurements. Dry deposition velocities for RGM have been measured and reported
from Barrow and are similar to those for HNO3 13,14 . Wet deposition of reactive and particulate
mercury is parameterized by using a simple formulation with different in-cloud and below-cloud
scavenging coefficients (see 9 ).
4. Site
The monitor was set up in a residential suburban area on the eastside of Tórshavn, the capital on Faroe
Islands, located 62 o 01’ N and 6 o 47’ W approximately 400 km north of Scotland, 600 km west of
Norway and 500 km east of Iceland. Because of this suburban location, we tested the influence of
possible local sources by examining the time series based on wind direction and concentration. No
correlation between these quantities was found, during both quiescent periods and during higher than
background level episodes, thus allowing us to conclude that any local sources were insignificant.
5. Results
Measurements from May 2000 to March 2001 of GEM are shown in Figure 1. The data vary between
a general level of about 2 ng/m 3 in the beginning of the campaign (in May) decreasing to
approximately 0.5 ng/m 3 in July and August and increasing slightly to approximately in January and
February of about 1.7 ng/m 3 . During the campaign we measured some values peaking at 3.4 ng/m 3 .
For example we observed a notable high concentration episode from June 21 to 25, which was
followed by a period where the concentration levels decreased to values between 0.8 to 1.3 ng/m 3 . The
daily mean temperature in the periods varied from 5.7 0 C in May and June to 12.1 0 C in August. The
average relative humidity was always close to 95%. During the rest of the year the concentrations
slowly increased to a level of 1.7 ng/m 3 in January and February 2001.
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