Sources and Transport - Mercury in the Environment - page 10

out almost entirely in the industrial and power generation
sectors, whereas in developing countries, notably China, a
signifi cant fraction of coal combustion also occurs in the
residential sector (Wu et al., 2006).
Emissions from coal combustion can vary substantially
from facility to facility. The mercury emission factor from
coal combustion depends mainly on two factors:

(1997) estimate of atmospheric emissions of Hg in South
America by gold mining (179 tons/yr) is nearly twice the
total Hg emissions from all sources in South America esti-
mated by Pacyna et al. (2006). But, it should be noted that
the Pacyna et al. (2006) inventory does not quantify Hg
emissions from South American gold mining, nor does it
attempt to quantify Hg emissions from illegal gold mining
activities. In addition, the Pacyna study used an Hg emis-
sion factor of 0.5 g of Hg emitted/g of gold produced,
whereas Lacerda used a factor of 1.5. Thus, while emissions
of Hg from gold mining are clearly a substantial source for
the global atmosphere, there is signifi cant uncertainty in
the actual values.
In developed countries, emissions of mercury have
decreased in the past two decades, partly because of some
direct emission controls, but mostly as a side benefi t to
controls on other pollutants (US EPA, 1997; Pacyna et al.,
2006). Emissions in Europe have decreased nearly 50%,
partly because of controls on other pollutants, but also
because of political and economic changes that led to plant
closures and reductions in coal use.
China is the world's largest emitter of mercury, with
emissions of ~700 tons/yr (Pacyna et al., 2006; Wu et al.,
2006). This is approximately one third of the global anthro-
pogenic total. The next fi ve top-emitting countries, in order,
are South Africa, India, Japan, Australia, and the United
States. Chinese emissions are rapidly increasing because
of strong growth in the economic output and the increas-
ing utilization of coal (e.g., Kim and Kim, 2000; Tan et al.,
2000; Wu et al., 2006). It should also be noted that Chinese
Hg emissions are expected to continue to increase for some
time because of China's large coal reserves (Zhang et al.,
2002) that have moderate to high Hg content (Zheng et al.,
2007). Coal combustion and metal smelting are the two
largest sources in China, although the larger of these is still
somewhat uncertain. Metal smelting is the largest source
of mercury in China in the Wu et al. (2006) and Streets
et al. (2005) inventories, whereas coal combustion is the
largest source in the Pacyna et al. (2006) inventory. While
coal consumption is increasing rapidly in China, there
is also greater utilization of ESPs for particulate removal,
which can partially offset this increase (Wu et al., 2006).
According to Wu et al. (2006), Chinese mercury emissions
increased by 2.9% per year from 1995 to 2003.
For the United States, the anthropogenic emissions were
recently quantifi ed as part of the Clean Air Mercury Rule
(CAMR), for the years 1990, 1996, and 1999. The mercury
emissions were found to have decreased from 245 metric
tons in 1990 to 124 tons in 1999. The drop was largely due
to controls on medical and municipal incineration, as well
as controls on other pollutants, such as SO 2 and aerosols,
which had a side benefi t of also reducing mercury. As of
1999, the largest single category for mercury emissions in
the United States is coal combustion, which is responsible
for 43% of total U.S. emissions. (see http://www.epa.gov/
camr/charts.htm).

1. Concentration of mercury in the coal
2. The degree of emission controls

The concentration of mercury in coal can vary by more
than two orders of magnitude, from 0.01 to 1.5 g of Hg/ton
of coal (Pacyna et al., 2006). In addition, there are also
large variations in control technologies. For example, the
simplest particulate control technology, a cyclone, has
almost no ability to capture mercury. A more complicated
technique that is widely used, electrostatic precipitators
(ESP), can remove approximately 30% of mercury in the
stack emissions. Flue-gas desulfurization with an ESP can
remove up to 74% of the mercury (Streets et al., 2005; Wu
et al., 2006, Pacyna et al., 2006). Thus, emission factors
(e.g., kilograms of Hg emitted per ton of coal consumed)
vary greatly from plant to plant and country to country.
Coal combustion can produce Hg as GEM, RGM, or PHg.
Gold production is the second largest source of mercury
globally. These emissions are primarily the result of
large-scale mining activities of gold-rich ores (which are
almost always enriched in mercury) and small-scale,
artisanal mining, which extracts gold by amalgamating it
with mercury. Since gold and mercury are often colocated
in the same deposit, these regions generally have natu-
rally high emissions of mercury in the form of GEM (Engle
et al., 2001; Coolbaugh et al., 2002). Mining activities,
including digging, pulverizing, and roasting the ore, will
signifi cantly increase the mercury emissions. While the
use of mercury to amalgamate and concentrate gold is now
illegal in most parts of the world, this method is still used,
especially in remote, third-world locations. Emissions from
the disturbed deposits and wastes can continue for years,
and thus current emissions are a result of both current and
past practices. Some historically contaminated mining sites
can accumulate substantial water and soil mercury concen-
trations and result in signifi cant atmospheric emissions,
for example, the Carson River Superfund site in Nevada
(Gustin et al., 1996; Leonard et al., 1998). In Venezuela,
Garcia-Sanchez et al. (2006) studied several sites polluted
from past mining activities. In some gold processing shops,
they found GEM concentrations of 50 to 100 µg/m 3 ,

which is more than 20,000 times greater than background
concentrations.
Lacerda (1997) published a summary of Hg emissions from
past and current gold mining. In this estimate, 460 tons/yr
are released to the environment globally, an d65% of this is
released to the atmosphere. Of the total atmospheric emis-
sions, nearly 60% is released in South America. Lacerda's