Natural and Anthropogenic Mercury Sources
9
Table 4. Extensive measurements of the speciation of vapor-phase Hg in mid-continental ambient air
using a reftuxing mist chamber method. (Lindberg and Stratton, 1998)
TGM (ng m- 3 )
RGM (ng m 3)
Site
Location
Mean
SD
N
Mean
SD
N
Walker Branch a
Tennessee
2.19
0.64
68
0.065
0.040
75
Earlham College
Indiana
4.02
1.78
153
0.104
0.057
177
a Hgl'an concentrations at this site are generally in the range of 0.01-0.03 ng m j (Lindberg et al.
1992).
Naturally occurring species distribution of atmospheric mercury as it can be
detected at remote locations is significantly influenced by the presence of
emission sources. The emitted species are dependent on the source characteristics. Depending on the atmospheric residence time and the deposition
properties of the individual species, the relative proportions of the atmospheric
concentrations are related to the distance of the sources. For central Europe it
has become clear that several "hot spots" of anthropogenic Hg(o) emissions are
located at industrial sites in the former German Democratic Republic. Annual
atmospheric emissions from this relatively small but highly industrialized area
were estimated at 330 tons for 1988. A comparison with the emissions of entire
Europe, estimated at 726 tons for the same year, shows the significance of this
locally limited but relatively strong source of Hg(o) for central Europe (Helwig
and Neske 1990).
2.3
Speciation of Deposited Mercury
Mercury in all of its forms can be readily deposited on the Earth's surface.
However, because of its reactivity and solubility, deposition of the RGM forms of
mercury vapor are generally favored. Although Hg( 0) can be directly absorbed
by soils and plants (e.g. Lindberg et al. 1979), these processes are most important
near local sources (e.g. Hanson et al. 1995).
The major atmospheric deposition process for elemental mercury vapor in
background air is the aqueous oxidation by ozone followed by an in-droplet
adsorption primarily onto soot particles (Munthe 1992; Petersen et al. 1995). It is
important to be aware of the fact that the relation between emissions and
depositions may be nonlinear. Consequently, deposition rates cannot be derived
directly from emission rates because they are strongly influenced by secondary
pollutants such as ozone and soot (Iverfeldt 1995).
Because a small but significant fraction of the atmospheric mercury consists of
vapor-phase RGM or oxidized Hg(II), gaseous methylmercury, and particulate
phase mercury species, these forms must also be included in regional deposition
models because of their shorter atmospheric residence time relative to Hg( 0). Of
the three forms, oxidized mercury species are of great importance for the total
deposition of mercury from the atmosphere according to an Eulerian model
9
Table 4. Extensive measurements of the speciation of vapor-phase Hg in mid-continental ambient air
using a reftuxing mist chamber method. (Lindberg and Stratton, 1998)
TGM (ng m- 3 )
RGM (ng m 3)
Site
Location
Mean
SD
N
Mean
SD
N
Walker Branch a
Tennessee
2.19
0.64
68
0.065
0.040
75
Earlham College
Indiana
4.02
1.78
153
0.104
0.057
177
a Hgl'an concentrations at this site are generally in the range of 0.01-0.03 ng m j (Lindberg et al.
1992).
Naturally occurring species distribution of atmospheric mercury as it can be
detected at remote locations is significantly influenced by the presence of
emission sources. The emitted species are dependent on the source characteristics. Depending on the atmospheric residence time and the deposition
properties of the individual species, the relative proportions of the atmospheric
concentrations are related to the distance of the sources. For central Europe it
has become clear that several "hot spots" of anthropogenic Hg(o) emissions are
located at industrial sites in the former German Democratic Republic. Annual
atmospheric emissions from this relatively small but highly industrialized area
were estimated at 330 tons for 1988. A comparison with the emissions of entire
Europe, estimated at 726 tons for the same year, shows the significance of this
locally limited but relatively strong source of Hg(o) for central Europe (Helwig
and Neske 1990).
2.3
Speciation of Deposited Mercury
Mercury in all of its forms can be readily deposited on the Earth's surface.
However, because of its reactivity and solubility, deposition of the RGM forms of
mercury vapor are generally favored. Although Hg( 0) can be directly absorbed
by soils and plants (e.g. Lindberg et al. 1979), these processes are most important
near local sources (e.g. Hanson et al. 1995).
The major atmospheric deposition process for elemental mercury vapor in
background air is the aqueous oxidation by ozone followed by an in-droplet
adsorption primarily onto soot particles (Munthe 1992; Petersen et al. 1995). It is
important to be aware of the fact that the relation between emissions and
depositions may be nonlinear. Consequently, deposition rates cannot be derived
directly from emission rates because they are strongly influenced by secondary
pollutants such as ozone and soot (Iverfeldt 1995).
Because a small but significant fraction of the atmospheric mercury consists of
vapor-phase RGM or oxidized Hg(II), gaseous methylmercury, and particulate
phase mercury species, these forms must also be included in regional deposition
models because of their shorter atmospheric residence time relative to Hg( 0). Of
the three forms, oxidized mercury species are of great importance for the total
deposition of mercury from the atmosphere according to an Eulerian model