Fróðskaparrit - 01.07.2004, Blaðsíða 91

KYKSILVUR í FØROYUM - EIN GJØGNUMGONGD AV TØKUM DÁTUM
89
Also, and very interestingly, a significant
increase in the deposition of gaseous mer-
cury in the samplers with increasing station
elevation above sea level was observed, an
observation which would also be predicted
from the cold condensation mechanism
which have been suggested as important
pathways for the transport of POPs and
mercury to the Arctic (Mackay et al., 1995;
Wania and Mackay, 1995).
Recently, Christensen (2003) simulated
the air transport of mercury, sulphur and
lead to the Faroe Islands. The simulations
were based on the Danish Hemispheric
Eulerian Model system developed at NERI
(Christensen 1997; 1999). There were 13
mercury species in the DEHM, of which 3
in gas phase (Hg°, HgO and HgCl2), 9
species in the aqueous phase, and one
species of particulate mercury. As input
data to the model were used the 1995 glob-
al inventory on mercury (Pacyna and Pacy-
na, 2002) which includes Hg°, reactive
gaseous mercury (RGM) and particulate
mercury and a background concentration of
1,5 ng/m3 of Hg° were used as initial con-
centration and boundary conditions. The
model is capable of incorporating the polar-
sunrise driven mercury depletion into the
composite transport and deposition predic-
tion. The model which was run for the peri-
od October 1998 to December 2000, pre-
dicted that the polar sunrise event will re-
sult in a modest 8% increase in the mercury
deposition on the Faroe Islands where the
increase in the total area north of the polar
circle amounts to more that 100 %. The
model also predicted that mercury emitted
as particles will be a minor part (2%) of the
mercury deposited in the Faroes whereas
the atmospheric reservoir of elemental
mercury, Hg°, is the main contribution
(more than 93%) to the total deposition, a
reservoir which is global and which com-
bines both natural and anthropogenic mer-
cury. It was also calculated that the total de-
position would amount to approx. half the
deposition of mercury in Denmark.
The model have been compared with
measurements many places in Europe and
generally there have been very good agree-
ment between the calculated results and the
measured ones. For the Faroes however,
there was a poor agreement between the
calculated values and the observed concen-
tration of gaseous mercury Hg° (Chris-
tensen, 2003; Skov et al., 2003), and the
model results for lead and SOx were not
compared to measured ones. The reason for
the lack of agreement between the model
values of mercury deposition to those actu-
ally measured were later accounted to mal-
functioning of the mercury analyser in the
high humidity environment of the Faroe Is-
lands (Skov, personal comm.).
Precipitation
As mentioned in the last section, an EMEP
station run by NERI was operative at
Akraberg in the period 1979 to 1991. At
this station acid rain components and para-
meters were analysed in deposition, and for
the last four years also the major cations
sodium, potassium, magnesium and calci-
um was included in the analyses scheme
(Kemp 1984; 1993; 1994). This scheme did
not encompass mercury, neither do the
analyses performed by the Heilsufrøðiliga