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Mercury
Seeking a Better Understanding of Atmospheric
Mercury
The Air Resources Laboratory measures and models atmospheric
mercury to provide essential information to policy-makers and
planners
 It
may be the name of a car, a planet, and a Roman god, but (as
best we know) none of those are toxic to humans or the environment.
Mercury, a natural element of the Earth, is now better known
as a potentially deadly metal. It is a potent neurotoxin,
particularly damaging to the development of fetuses, infants
and young children. Our exposure to methylated mercury, the
most toxic form, is largely through eating contaminated fish.
Today,
nearly every U.S. state warns residents to restrict their
consumption of certain fish due to mercury contamination.
The U.S. Food and Drug Administration and U.S. Environmental
Protection Agency also have fish consumption advisories for
mercury. In addition, new research indicates that mercury
also is accumulating at potentially dangerous levels in terrestrial
wildlife, some of which are not fish-eating animals.
But
mercury doesn't start out in living organisms, it gets there.
Through mostly human activities (and some natural sources
too), mercury is released from ores, minerals and fossil fuels
into the biosphere where it can circulate throughout the globe
and accumulate in living organisms.
Although
many uses of mercury have been curtailed, mercury compounds
continue to be released into the atmosphere. The largest sources
of mercury emissions in the U.S. and worldwide are coal-fired
power plants, waste incinerators, metallurgy/mining operations
(especially gold mining), and chlor-alkali plants that employ
mercury-cell technology. A potentially growing source of mercury
is disposable products, such as compact fluorescent bulbs
and personal electronics (cell phones, LCD TVs, digital cameras),
which contain mercury. The mercury eventually leaks into the
atmosphere when broken or crushed in a landfill.
What
is tricky about mercury is that it exists in a variety of
chemical and physical forms and can change from one form to
another. Some forms are more toxic than others. Depending
on its form, mercury released into the air can travel short
or long distances even all the way around the world - and
cycle between the earth's surface and the atmosphere. Unless
it is contained, mercury can be re-emitted into the air.
 Concentrations
of mercury in the air are usually low and are generally not
an air quality concern. It is when mercury deposits to land
and water surfaces that it becomes an issue. While measuring
mercury in precipitation is relatively easy, measuring ambient
air concentrations and understanding how and where it deposits
in dry form is quite another story. These challenges make
it difficult to understand the relative contribution of mercury
to ecosystems from various geographic regions and types of
sources. Such understanding is essential for developing effective
regulations and policies.
Scientists
at NOAA's Air Resources Laboratory (ARL) have taken on this
challenge. Teaming up with U.S. EPA and other scientists,
ARL researchers are using their measurement capabilities at
three core mercury monitoring sites: Beltsville, Maryland;
Grand Bay Mississippi; and Canaan Valley, West Virginia. These
sites are part of a new multi-agency national monitoring network
designed to address total mercury deposition across the country.
Each
site monitors important mercury species (elemental, reactive
gaseous, and particulate) in the air using sophisticated mercury
analyzers. Some sites also measure mercury in precipitation
and snow pack. These data are then correlated with other air
quality data and meteorological measurements to provide an
overall sense of how the airborne mercury is transported and
deposited.
 Yet,
monitoring and measurement studies alone do not conclusively
reveal the origin of the mercury or how it is transformed
as it mixes with other pollutants in the air. To address these
and other issues, ARL researchers turn to their mercury modeling
capabilities. Using state-of-the-art atmospheric fate and
transport models (CMAQ and HYSPLIT), scientists are attempting
to track mercury in the atmosphere from emissions sources
to eventual deposition. These models make use of detailed
NOAA weather data and emissions inventories from U.S. EPA
and other agencies. The mercury models are then interpreted
and evaluated using measurements of ambient air concentrations
and deposition, including measurements collected at NOAA's
core sites.
Through
the integration of monitoring and modeling tools, ARL scientists
are able to provide the Nation with the capability to identify
important sources contributing mercury to ecosystems and to
estimate the consequences of potential alternative policies
for reducing mercury emissions. Air quality policymakers and
planners require that information to both effectively protect
public health and maintain a vibrant economy.
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