Dr. Cohen’s work confirmed that the Binational Toxics
in the United States.  Specific to persistent toxic substances,
Strategy Level 1 contaminants and Critical Pollutants would
the IAQAB stated that an increase in mercury emissions as a
be subject to atmospheric transport and deposition.
result of deregulation would be contrary to the commit-
However, the incomplete knowledge of physical and
ment to virtual elimination made by the governments of the
chemical properties, the poor or unknown quality and
United States and Canada in the Great Lakes Water Quality
breadth of emissions inventories in the United States and
Agreement.  The IAQAB would further consider this source
Canada, the paucity of support for efforts to model
sector among others in its mercury transport modeling
transport and deposition, and the absence of some of the
work, described later in this report.
Critical Pollutants from ambient monitoring programs all
severely limited the number of contaminants whose
In the IJC’s Eighth Biennial Report on Great Lakes Water
transport and deposition might be modeled successfully.
Quality (June 1996), the IJC noted that, given the progress
Dr. Cohen determined that modeling could only be
made in reducing effluent inputs of persistent toxics to the
attempted for three of the Binational Toxics Strategy Level 1
Great Lakes basin, the air pathway was increasing in
contaminants — dioxin, cadmium and mercury.
significance.  The United States Toxic Release Inventory and
Canadian National Pollution Release Inventory emissions
The IAQAB subsequently engaged Dr. Cohen to further
data were cited in support of this observation.  The IJC
refine his earlier application of the NOAA-HYSPLIT model
extended the scale of its interest to “encompass most of
to the transport and deposition of dioxin into the Great
North America, and, for some purposes, the globe.”
Lakes basin.  The outcome of this work can be found in the
IJC’s 1997-1999 Priorities and Progress under the Great
Lakes Water Quality Agreement and further described as
The HYSPLIT Modeling of Dr. Mark Cohen
part of the 1999-2001 Priorities and Progress under the
Great Lakes Water Quality Agreement.  The model output
In March 1995, the Great Lakes Science Advisory Board’s
demonstrated that dioxin transported via the atmosphere
Work Group on Parties Implementation was among the first
from distant sources is a significant portion of the total
to review the Commoner/Cohen report “Quantitative
loading to the lakes, particularly Lake Superior, and
Estimation of the Entry of Dioxins, Furans and
allowed identification of the most significant known source
Hexachlorobenzene into the Great Lakes from Airborne
sectors.  Figure 1 is one of many illustrations of the
and Waterborne Sources” (Cohen et al., 1996).   Respond-
contribution of local and distant dioxin sources to deposi-
ing directly to one of the elements of Annex 15, this report
tion in Lake Superior.  Much more detail on this modeling
was a first attempt to model the atmospheric deposition of
process is available in the 1997-99 report and a recent
dioxin and related compounds to the lakes from sources
publication (Cohen et al., 2002).
and source categories throughout the United States and
In its Tenth Biennial Report on Great Lakes Water Quality
(July 2000), the IJC encouraged further identification of in-
During that year, the IJC also invited the IAQAB to become
basin and out-of-basin sources whose emissions of persis-
directly involved with the Agreement Boards (Great Lakes
tent toxic substances are deposited in the lakes via atmo-
Water Quality Board, Great Lakes Science Advisory Board
spheric transport.  It also advocated the addition of dioxin
and Council of Great Lakes Research Managers) in the
and mercury to the suite of contaminants measured by
establishment and execution of the IJC biennial Great Lakes
Integrated Atmospheric Deposition Network ambient
monitoring sites in the Great Lakes basin.
In subsequent months, as a priority activity, the IAQAB
asked Dr. Cohen to report on the adequacy of available
The IAQAB and the 1999-2001 Priorities
data, information and programs in four areas vital for
and Progress under the Great Lakes
successful modeling of atmospheric transport and deposi-
Water Quality Agreement
The IAQAB portion of the 1999-2001 Priorities and
physical and chemical properties of the Binational
Progress under the Great Lakes Water Quality Agreement
Toxics Strategy Level 1 contaminants (Critical Pollut-
contains a further refinement of the estimate of the impact
of distant sources of dioxin on the lakes.  Included was a
emission inventories for these contaminants;
delineation of the form of that impact (wet and dry
availability of models capable of estimating atmo-
deposition) as well as a comparison of the model estimates
spheric transport and deposition; and
to a limited number of available ambient dioxin measure-
adequacy of ambient monitoring information for
ments.  The IAQAB recommended further improvements in
comparison to model determinations.