Is
mercury a significant contaminant in the Arctic?
Is the Arctic a missing sink for
mercury?:
New measurements of mercury speciation and depletion events at Point
Barrow
Steve Lindberg
Oak Ridge National Laboratory
and
Steve Brooks
NOAA / Air Resources Laboratory
In the past decade many
new sources of diffuse mercury emissions have been measured. These
sources significantly increase the estimates of global mercury emissions,
and suggest there may be missing mercury sinks in global models.
Mercury levels in Arctic wildlife are elevated above normal levels,
but there are few known Arctic mercury sources, and long range transport
of mercury must be considered. The discovery of mercury depletion
events (MDE, similar to ozone depletion) at Alert, NWT suggests
a mechanism for mercury accumulation from the global pool. One hypothesis
is that mercury is transformed into a reactive gaseous mercury (RGM)
species which deposits locally. This species has never been measured
in the Arctic, and MDE's must be confirmed at other Arctic sites.
|
|
|
As
part of the Barrow Arctic Mercury Study (BAMS), we have measured
gaseous elemental mercury (GEM) at Barrow, AK since September, 1998
with an automated Tekran analyzer [1].
The initial data provide the first confirmation of MDE's at this
more southerly, Arctic site. MDE events begin soon after Polar sunrise,
and persist until snowmelt. During MDE mercury exhibits a strong
correlation with ozone, suggesting a link with the reactions that
destroy tropospheric ozone. We have developed a simple model using
local meteorological data which closely simulates the patterns of
depletion events, and suggests that turbulence and temperature are
important factors. There are a number of potential reaction pathways
with mercury and bromine to explain the depletion events, which
suggest that during these events mercury is oxidized to RGM. The
model predicts a mercury deposition rate much higher than measured
in the eastern US. To test our hypotheses, we are currently measuring
RGM prior to and following polar sunrise during winter-spring 2000,
and plan to measure mercury speciation and evasion in snowmelt during
polar summer. The winter-spring 2000 RGM data are just now becoming
available and represent the first confirmation of important rates
of conversion of GEM to RGM in the Arctic. At Barrow we have recently
measured some of the highest concetrations of RGM ever reported,
including downwind of major point sources. To follow up on this
important discovery, we are planning a major sampling campaign for
next year: BAMS-2001 will include studies of reactive halogens and
particulate mercury by Bob Stevens and Matt Landis of EPA-NERL,
evasion from snowpack by Hong Zhang and George Sourhworth of ORNL,
mercury dynamics in snow including studies of organic and bioavailable
mercury by Karen Scott, John Rudd, and Carol Kelly of the University
of Manitoba, and modeling of atmospheric reactions of mercury by
Jerry Lin of Lamar University.
References:
CMDL Point
Barrow Observatory
News
article on mercury in the Arctic
Long
range transport and transformation of mercury to the Arctic
|