United States
Environmental Protection
Agency
Research and Development
Atmospheric Sciences Research
Laboratory
Research Triangle Park NC 27711
EPA/600/S3-85/039 May 1985
&ERA Project Summary
i
Temporal and Spatial
Variabi ity of the Visual
Effects
of Stack Plumes
Christian Seigneur, A. Belle Hudischewskyj, and Henry Hogo
Temporal and ipatial variabilities of
stack plumes are analyzed by means of
field data analysii and computer simu-
lations. In this investigation, photo-
graphs from field p rograms of the study.
Visibility Impairment Due to Sulfur
Transport and Transformation in the
Atmosphere went analyzed via sensi-
tometry, and PLUVUE II model simula-
tions were conducted for a case study.
Analysis of the temporal variability of
plume visibility led to documentation of
the fact that the vi tual effects of plumes
vary with time because of (1) turbulent
fluctuations, (2) changes in atmospheric
stability, and (3) cr> anges in the observer-
plume-sun scattering angle. Likewise,
the analysis of thu spatial variability of
plume visibility led to the fact that the
visual effects oF plumes vary with
downwind distance from the stacks
because of (1) turbulent fluctuations,
(2) dilution of the plume and/or a
change in the obsurver-plume distance,
and (3) changes in the observer-plume-
sun scattering angle.
This Project Summary was developed
by EPA's Atmospheric Sciences Re-
search Laboratory, Research Triangle
Park. NC. to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The impact of stack plumes on atmos-
pheric visibility has been the subject of
extensive experimental and theoretical
studies over the past 5 years. Of these
studies, the Visibility Impairment Due to
Sulfur Transport and Transformation in
the Atmosphere (VISTTA) program was
comprised of four field programs con-
ducted in 1979 and 1981, as well as an
evaluation of the EPA plume visibility
models PLUVUE and PLUVUE H.
An important conclusion of these
plume-visibility studies is that there is a
major discrepancy between the nature of
the measurements of plume visibility and
computer simulations of plume visibility.
Measurements of plume visibility were
taken over a given time interval (about 15
to 30 minutes for teleradiometer meas-
urements, and instantaneous measure-
ments for the sensitometry of color slides)
and at a given location. Fluctuations of
atmospheric turbulence led to plume-
visibility effects that varied with time and
location. Simulations of plume visibility,
on the other hand, were conducted with
mathematical models that assumed
steady-state conditions, a given atmos-
pheric stability class, and time-averaged
dispersion coefficients. The discrepancy
between the time- and location-specific
nature of experimental measurements
and the time-averaged (e.g., dispersion
coefficient) and conditions-averaged (e.g.,
atmospheric stability) nature of model
simulations necessarily results in differ-
ences between experimental measure-
ments and model simulations.
In this study, we investigated the tem-
poral and spatial variability of plume vis-
ibility in a systematic fashion. We ana-
lyzed a series of color slides from the
1979 and 1981 VISTTA field programs by
means of sensitometry to determine the
temporal and spatial variability of plume
visual effects. Conclusions can thus be
drawn about the uncertainties that will
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result when using atmospheric data on
plume visibility for model evaluation or
when using a plume-visibility model in
regulatory applications.
Experimental Procedure
The data base utilized in this study con-
sisted of color slides of power plant
plumes that were selected from the
December 1979 program at the Navajo
power plant and from the February 1981
program at the Kincaid power plant.
These slides offered the best time series
of the visual effects of stack plumes col-
lected during the four VISTTA field pro-
grams. A total of 46 slides were chosen
for sensitometry (i.e., digitization). These
slides were digitized at Perkin-Elmer in
Garden Grove, California.
For the temporal variability analysis,
each slide was processed at a given loca-
tion. The section of the photograph to be
digitized corresponded to an imaginary
vertical line across the plume so that both
the background below and above the
plume andthe plume itself were digitized.
The procedure is therefore similar to the
vertical scan taken with a teleradiometer.
For the spatial variability analysis, 10 ver-
tical scans were performed on the select-
ed slides at equal horizontal intervals that
covered the entire slide range. These
scans thus corresponded to plume visibil-
ity measurements conducted at different
downwind distances from the same ob-
servation site (i.e., the site where the pho-
tograph was taken).
The slide digitization was conducted at
three wavelengths by using narrow-band
filters with peaktransmittance at 450 nm
(blue filter), 540 nm (green filter), and
above 700 nm (red filter). The sensitometry
provided pixel densities for each scan at
three wavelengths. The pixel densities
obtained from sensitometric curves were
then converted to normalized exposures
by means of characteristic curves that
were constructed from sensitometry of
reference slides. The exposure results
were then analyzed in a standard fashion
to calculate the ratio of plume radiance to
sky radiance.
After the digitized data were processed,
the digitization scans were reviewed to
select the scans that could be analyzed,
i.e., those for which a plume was discern-
ible above the noise of the measure-
ments. The list of slides selected for tem-
poral variability analysis was reduced to
32. These 32 slides included sights of the
Navajo power plant plume on December 7
and 15, 1979, and of the Kincaid power
plant plume on February 20 and 24,
1981.
Temporal Variability of Plume
Visibility
The ratios of plume radiance to sky
radiance were calculated by the sensito-
metric technique and plotted for each
case study as a function of time. The case
studies considered included the Navajo
power plant plume observed from two dif-
ferent sites on December 7, 1979, and
from one site on December 15,1979, and
the Kincaid power plant plume observed
on February 20, 1981, and on February
24, 1981. The later Kincaid power plant
plume was dark on the left side and bright
on the right side of the slide; the analysis
was therefore conducted at two locations
on the slide.
The study of the temporal variability of
plume visibility has shown that notable
variations in the plume visual effects
occur as a function of time. These varia-
tions, which exceed the uncertainties of
the sensitometric measurements, may
represent:
1. An evolution of atmospheric stabil-
ity toward more unstable conditions
that lead to a more dispersed and
less discernible plume; this effect
was observed for the Navajo power
plant plume on December 15,1979,
and the Kincaid power plant plume
on February 20, 1981.
2. A variation in plume visual effects
that results from a change in the
scattering angle andthe associated
varying effects of particulate scat-
tering; this phenomenon was ob-
served in measurements and model
simulations of the Kincaid power
plant plume on February 24, 1984.
3. Turbulent fluctuations that occur in
a random manner and are reflected
in nonstationary characteristics of
the plume; this phenomenon was
observed for the Navajo power plant
plume on December 7, 1979.
Spatial Variability of Plume
Visibility
The ratios of plume radiance to sky
radiance were calculated by the sensito-
metric technique and plotted for each of
the four analyzed case studies as a func-
tion of theobserved azimuth angle, i.e., as
a function of the horizontal distance along
the color slide. The four case studies con-
sidered were the Navajo power plant
plume on December 7 and 15,1979, and
the Kincaid power plant plume on Febru-
ary 20 and 24, 1981.
The study of the spatial variability of
plume visibility showed that variations in
the plume visual effects occur as the
muth of the observer's line of s
changes. These variations exceed
uncertainties of the sensitometric mi
urements and may occur in a monoti
form, representing any of the follov
conditions:
1. A decrease in plume visual eff
due to dilution of the plume anc
an increase in the observer-pli
distance; this phenomenon '
observed for the Navajo power p
plume on December 7 and 15,1 £
2. A variation in plume visual off
(e.g., from bright to dark plume)
results from a change in the seal
ing angle and the associated v
ing effects of particulate scatter
this effect was observed and,
certain extent, simulated for
Kincaid power plant plume on F
ruary 24, 1981.
3. Turbulent fluctuations that lea-
nonhomogeneous characteris
of the plume; this phenomenon \
more evident in observations of
Kincaid power plant plume on F
ruary 20, 1981.
Conclusions
This investigation demonstrates I
the visual effects of plumes vary v
time because of several factors.
1. Turbulent fluctuations lead to r
dom temporal and spatial variati
in plume visibility.
2. Evolution of atmospheric stab
toward more unstable conditi
leads to a temporal variation
plume visibility dueto a moredil
plume.
3. Dilution of the plume and/or
crease in the observer-plume i
tance lead to a spatial variatior
plume visibility.
4. A change in the observer-plur
sun scattering angle may leac
temporal and spatial variations
plume visual effects (e.g., fr
bright to dark); these temporal <
spatial variabilities in plume visi
ity were documented in our am
sis of power plant plumes. Preli
nary simulations of the power pi
plume visual effects with
PLUVUE II model tend to supp
our experimental results.
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Christian Seigneur. A. B. Hudischewskyj, and H. Hogo are with Systems
Applications, Inc.. San Rafael, CA 94903.
William Conner is the EPA Project Officer (see below).
The complete report, entitled "Temporal and Spatial Variability of the Visual
Effects of Stack Plumes," (Order No. PB 85-200 020/AS; Cost: $8.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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United States
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