Environmental Engineering Reference
In-Depth Information
table 1.1
Direct Anthropogenic Emissions of Mercury (tons/yr)
Source
China
Asia
United States
Global
Global
Coal combustion
257
879
54 a
NR
1422
Gold mining
45
47
6 b
300
248
Nonferrous smelting
320
88
NR
NR
149
Cement production
35
90
NR
NR
140
Total all sources
696
1180
126
NR
2190
Year
2003
2000
1998/1999
NR
2000
Reference
Wu et al.,
2006
Pacyna et al.,
2006
Seigneur et al.,
2001
Lacerda, 1997
Pacyna et al.,
2006
NR
not reported.
a. Includes all fossil fuel stationary sources, but the total is dominated by facilities burning coal.
b. All mining sources.
sources Note that an estimate by Selin et al, (2008) has a
much higher emission total for anthropogenic sources
(3400 tons/yr).
Emission inventories should be considered as a “work
in progress.” By this we mean that source tests often omit
both large and small facilities, emissions are constantly
changing, factories are omitted, new information is uncov-
ered, and chemical processes and fuels change. This is
not meant as a criticism of emission inventories, only as a
realistic assessment of their limitations and uncertainties.
Emission inventories need validation against atmospheric
observations to examine consistency.
Observations downstream of a major source region can
give quantitative information on the emission. For exam-
ple Jaffe et al. (2005) used observations on the island of
Okinawa to quantify the emissions and outfl ow of mercury
from Asia. They found that a much larger source of Hg was
required to reconcile the atmospheric observations with
the existing emission inventory. Combining observations
with a transport model can improve the estimate of emis-
sions. Two studies that examined the same Okinawa data
along with data from the Mt. Bachelor Observatory in cen-
tral Oregon and using the GEOS-CHEM model (Selin et al.,
2007; Strode et al., 2008) also confi rmed a much larger
Asian source of Hg than had been previously assumed.
Strode et al. (2008) compared the Hg:CO ratio in GEOS-
Chem to observations at Okinawa and at Mt. Bachelor in
central Oregon, and found that an Asian source of 1260-
1470 tons/y r of Hg 0 was consistent with the observations.
Models can also be run in “inverse” mode, whereby the
emission inventories are derived directly from the best fi t
with observations. Using this approach with aircraft obser-
vations from the western Pacifi c, Pan et al. (2007) also
found that Hg 0 emissions were signifi cantly greater from
China than the current emission inventory, consistent
with the earlier studies mentioned above. These studies are
fairly convincing that the total outfl ow of mercury from
Asia is signifi cantly larger than that reported by the anthro-
pogenic inventory alone. This is due to a combination of
underestimates in the industrial sources, combined with
land emissions, both natural and reemissions.
In the most complete examination of anthropogenic
emissions, Selin et al. (2008) suggested that all categories
of Hg emissions were signifi cantly larger than previously
assumed, with anthropogenic emissions of 3400 tons/yr,
natural emissions of 3200 tons/yr, and reemissions of
4100 tons/yr. However, as stated previously, all of these
estimates have signifi cant uncertainty.
From Release to Global Transport
The transport and deposition of mercury from the atmo-
sphere is a crucial pathway for contamination in remote
ecosystems. Hydrologic transport also plays a role in redis-
tributing mercury, but because of the slower movement
and mixing of the oceans, this plays only a small role in the
enhancements of mercury in remote ecosystems. On con-
tinents, the transport of mercury in surface and subsurface
waters is primarily important in redistributing high mer-
cury levels near contaminated sites.
Aqueous Transport
RIVERINE
Rivers play an important role in the local transport
of mercury from contaminated sites, but have a less
signifi cant role in the global cycle. Mason et al. (2002) and
Sunderland and Mason (2007) estimate that about 1-2%
of the total sources to the ocean come from inputs from
rivers, with dissolved and particle-bound Hg being the
largest fractions. Sunderland and Mason (2007) note that
a large fraction of the particulate mercury carried by rivers
Search WWH ::




Custom Search