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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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