Environmental Engineering Reference
In-Depth Information
CHAPTER 5
Atmospheric Chemistry, Modeling, and
Biogeochemistry of Mercury
NOELLE ECKLEY SELIN
and their distribution in the atmosphere. This includes
the oxidation and reduction reactions that alter the form
and properties of atmospheric mercury, and the wet and
dry deposition processes that control its deposition to eco-
systems. This is followed by a brief survey of atmospheric
models that have been used in combination with measure-
ments to further scientifi c understanding of atmospheric
mercury. The chapter concludes by summarizing future
challenges for atmospheric mercury research.
GLOBAL BUDGET OF MERCURY
FORMS AND DISTRIBUTION OF MERCURY IN THE ATMOSPHERE
OXIDATION AND REDUCTION PROCESSES
DEPOSITION PROCESSES
ATMOSPHERIC MODELS AND APPLICATIONS
FUTURE CHALLENGES
Mercury in the environment is of increasing concern glob-
ally because it can travel long distances through the atmo-
sphere. For example, atmospheric transport and deposition
of mercury from lower latitudes to the Arctic environment
poses environmental and human health risks, despite few
sources within the Arctic. On a more local scale, atmo-
spheric chemical reactions and meteorologic processes can
determine whether mercury deposits near sources or circu-
lates globally. Understanding the chemistry and transport
of atmospheric mercury is thus vitally important for man-
aging mercury pollution.
There remain several critical uncertainties surrounding
the behavior of mercury in the atmosphere. The global
biogeochemical budget of mercury is not well constrained,
particularly the magnitude of fl uxes from land and ocean
surfaces. The chemical reactions that control the transfor-
mation of mercury between its forms in the atmosphere are
uncertain. However, some improvements in measurement
techniques and the development of models at scales from
local to global have provided important new insights into
atmospheric mercury.
This chapter addresses the atmospheric chemistry and
transport of mercury. It begins with an overview of the
global biogeochemical budget of mercury, with particu-
lar attention to fl uxes into and out of the atmosphere. It
then surveys the different forms of atmospheric mercury
Global Budget of Mercury
Prior to the onset of human industrial activities, the
amount of natural mercury cycling through the land-
ocean-atmosphere system was roughly one third of pres-
ent levels. This represents the natural background level of
mercury in the environment, which human activities have
augmented. The origin of this natural background is geo-
logic activity, including erupting volcanoes and emissions
from the so-called global mercuriferous belts, where land
is enriched with mercury (Fitzgerald and Lamborg, 2005).
The natural cycle accounts for about a third of present-
day mercury entering the atmosphere; however, direct
anthropogenic emissions are roughly comparable in mag-
nitude. Anthropogenic activities that release mercury to
the atmosphere include coal burning, industrial processes,
waste incineration, and mining and metallurgical activi-
ties (Pacyna et al., 2006). The total amount of anthropo-
genic emissions to the atmosphere has remained relatively
stable over the past decade; however, decreases in North
America and Europe have been offset by increasing emis-
sions in rapidly developing regions such as Asia (Pacyna
et al., 2006).
The remaining third of emissions to the atmosphere is
a result of the legacy of anthropogenic activity that has
released mercury since industrialization. Human activities
