the emission inventories for this contaminant, particularly
within the Great Lakes Air Toxics Emission Inventory, and
The plume associated with large urban centers was
inclusion of estimates of emissions arising from backyard
refuse burning.
shown to contain significant concentrations of some
persistent  toxic  substances,  such  as  PCBs.    For
The IAQAB sponsored two cooperative workshops that
example, the plume from Chicago, particularly in
examined various models and methodologies for the
determination of atmospheric transport and loading of
the summer months, includes substantial amounts
selected persistent toxic substances to various important
of this contaminant; these amounts are greatly in
watersheds.  As one outcome, the IAQAB concluded that, if
good quality data on the physical and chemical properties
excess  of  the  total  from  known  point  sources  in
of the contaminant and emissions are available, along with
the region.
ambient data for verification, current models can estimate
the input of several persistent toxic substances to the Great
Lakes basin.  Adequate emissions inventories are crucial to
Recommended actions included further effort to character-
any modeling effort, and the quality of these should be
ize areal sources such as landfills, wastewater sludge drying
determined as a first step in considering any modeling
operations and transformer storage yards in urban settings
around the basin and their subsequent incorporation as
sources into models.
Further, model outputs can be indicative of the approxi-
mate significance of various source sectors, and large
The IAQAB expressed concern that the Integrated Atmo-
individual sources.  An examination of current and historic
spheric Deposition Network master station at Sleeping Bear
land use records and the use of pesticide volatilization
Dunes, Michigan due to its relatively remote location on
models to better qualify deposition of banned pesticides
the eastern shore of Lake Michigan, appears to underesti-
were also noted as approaches worthy of further consider-
mate the concentrations of PCBs and other contaminants
prevailing over the lake.  The extent of this underestimation
should be determined by over-lake sampling and the
The plume associated with large urban centers was shown
application of models.  The completion of the Lake
to contain significant concentrations of some persistent
Michigan Mass Balance Study for all pathways for PCBs,
toxic substances, such as PCBs.  For example, the plume
mercury, trans-nonachlor and atrazine and the extension of
from Chicago, particularly in the summer months, includes
this approach to other persistent toxic contaminants also
substantial amounts of this contaminant; these amounts are
were encouraged.
greatly in excess of the total from known point sources in
the region.  Recent estimates suggest that the amount in
The IJC, in its Eleventh Biennial Report on Great Lakes
question is in hundreds of kilograms per year as compared
Water Quality, amplified the recommended needed
to a sum total of approximately 30 kg/yr estimated as
improvements in emissions inventories and the extension
emitted from the point sources.
of monitoring activities to better estimate urban plumes
and other inputs.