Measurement of Haze and Visual Effects

Project Description
Project MOHAVE was an extensive monitoring, modeling, and data
assessment project designed to estimate the contributions of the
Mohave Power Plant (MPP) to haze at the Grand Canyon National Park
(GCNP). The field study component of the project was conducted in 1992
and contained two intensive monitoring periods (~30 days in the winter
and ~50 days in the summer). Unique, non-depositing, non-reactive
perfluorocarbon tracer (PFT) materials were continuously released from
the MPP stack during the two intensive periods to enable the tracking
of emissions specifically from MPP. Tracer, ambient particulate
composition, and SO2 concentrations were measured at about 30
locations in a four-state region. Two of these monitoring sites, Hopi
Point (HOPO) near the main visitor center at the south rim of the
canyon and Meadview (MEAD) near the far western end of the national
park were used as key receptor sites representative of GCNP.

Project MOHAVE operated under the joint technical and program
management of the Environmental Protection Agency (EPA) and Southern
California Edison (SCE) in close partnership with the National Park
Service (NPS). Numerous other organizations contributed to the
operations and assessment work of the project. Since the end of the
field study component of the project, data assessment and modeling
efforts were undertaken by the many participants and have led to
numerous papers and reports. By design these efforts have been the
products of their respective authors and have not been endorsed as
findings of Project MOHAVE.

The primary goal of Project MOHAVE was to determine the contribution
of the MPP emissions to haze at GCNP and other nearby mandatory Class
I areas where visibility is an important air quality related
value. Secondary goals included an increased knowledge of the
contributions of other sources to haze in GCNP and the southwestern
United States in general. The specific objectives to accomplish these
goals were:

1.Evaluate the measurements for applicability to modeling and
data analysis activities.

2.Describe the visibility, air quality and meteorology during
the field study period and to determine the degree to which
these measurements represent typical visibility events at the
Grand Canyon.

3.Further develop conceptual models of physical and chemical
processes which affect visibility impairment at the Grand

4.Estimate the contributions from different emissions sources to
visibility impairment at the Grand Canyon, and quantitatively
evaluate the uncertainties of those estimates.

5.Reconcile different scientific interpretations of the same
data and present this reconciliation to policy-makers

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