FINAL REPORT FROM THEUNIVERSITY OF WASHINGTON
TO THEPUBLIC SERVICE COMPANY OF ARIZONAUNDER CONTRACT EC80-3438-011.80("PLUME CHEMISTRY STUDY IN THE
VICINITY OF THE ARIZONAPUBLIC SERVICE CHOLLA POWER PLANT")
Peter V. Hobbs, Dean A. Heggand Mark W. Eitgroth
January, 1982
TABLE OF CONTENTS
ABSTRACT (i)
Section 1. INTRODUCTORY REMARKS
Section 2. DESIGN OF STUDY 35
2.1 Instrumentation 32.2 Sampling Procedure 122.3 Data Analysis Techniques 142.4 Visibility Model Verification and Predictions 19
Section 3. ANALYSIS OF DATA 20
3.1 Data Base and General Meteorology 203.2 Particle Dynamics in the Plume 203.3 Secondary Particle Formation 263.4 Nitrogen Dioxide Formation 453.5 Optical Depths of the Cholla Plume 52
Section 4. RESULTS FROM -THE PHOENIX MODEL 58
4. Model Validation 584.2 PHOENIX Model Predictions for Various
Scenarios at the Cholla Plant 75
Section 5. SUMMARY AND CONCLUSIONS 103
^, APPENDIX: Gross Power Generation (In MW) 108from the Cholla plant during the Universityof Washington’s plume flights.
REFERENCES 110
ACKNOWLEDGEMENTS 113
ABSTRACT
An intensive field and theoretical study has been made of particulates and
trace gases in the near field 55 km) of the Cholla coal-fired electric power
plant, located near Winslow, Arizona.
Airborne measurements showed that the total surface area and volume con-
centrations of particles in the Cholla plume peak at particle diameters of ^0.25
(the highest peak), and 0.55 and 1.11 urn. Concentrations of NO, SO^ and N0^in the plume ranged from 83-1620, 3-555 and 45-650 ppb, respectively.
Concentrations of sulfate, particulate nitrate and nitric acid ranged from
0.21-0.95, 0.22-16.6 and 0.97-5.5 pg m~3, respectively. Nitric acid accounted
for 25-8556 of the nitrate in the plume, although nitrate played a minor role in
the odd nitrogen chemistry.
Both SCL-to-SOr and NO"-to-NO~ conversion in the plume were generally tooe- X .j
low to be detected, although on one occasion an SCL-to-SO^. conversion rate of
0.6 + 0.4 %/hr was measured. The generally low gas-to-particle conversion rate
was probably due to low concentrations of ambient hydroxyl.
The concentrations of sulfate particles close to the stack did not peak
within the optically critical size range. Results from one series of measure-
ments indicate that after a travel time of ^4 hr sulfate began to accumulate in
the critical range (though not to peak there). The correlation coefficient
between the light scattering coefficient due to particles (bg^) and the total
sulfate mass concentration in the plume was only 0.51. The correlation coef-
ficient between b and the mass concentration of particles in the plume inscat
excess of ambient concentrations was 0.66. It is concluded that particle dyna-
mics (e.g. coagulation), as well as secondary sulfate production, plays a role
in visibility Impact by the Cholla plume.
(i)
ABSTRACT, Continued
In only one case did the mass concentration of nitrate in the plume peak in
the optically critical size range. Hence, nitrate particles play only
a small role in visibility degradation in the near field of the Cholla plume.
NO-to-NCL conversion rates in the plume ranged from 3.9 to 31 .0 ?/hr, the
rate being controlled by mixing of the plume with the ambient air.
Scattering by particles and absorption by NCL appear to contribute about
equally to visibility degradation by the Cholla plume. Optical depths of the
plume derived from airborne measurements were 0.054 -^ 0.036 compared to telepho-tometer measurements of 0.023 +_ 0.035.
The University of Washington’s PHOENIX plume model predicted particle size
distributions and the concentrations of SO? and 0- in the plume with goodaccuracy. However, it appears to underpredict NOp concentrations by a factor of
2 to 5. The model also overpredicted the intensity of a target and the sky
viewed through the plume compared to telephotometer measurements. However, the
model predictions of the ratio of the sky-to-target intensity (on which most
visibility parameters depend) was, on average, within 4.4^ of the telephotometer
measurements.
When the atmosphere stability is neutral, the PHOENIX model predicts that
the rate of formation of new sulfate nuclei in the plume should increase as the
ratio of NO to SO,, emissions from the stack decreases. The model also predictsJC
that the new nuclei should preferentially attach to pre-existing large particles
already present in the plume, rather than growing to new particles of measurable
size.
(ii)
ABSTRACT, Continued
The PHOENIX model was also run for seven scenario conditions at the Cholla
plant. The model predicts that when the atmospheric stability is neutral
varying the emissions of SO-, and NO over a large range would have little effect^ A
on the concentrations of particles in the plume. The concentrations of 0.55 urn
particles in the plume were predicted by the model to be 10-100 times greater in
a stable than in a neutral atmosphere; this was due to reduced diffusion under
the stable conditions. However, the concentrations of 0.024 urn particles were
predicted to be greater at some locations in the plume under the neutral con-
ditions because of enhanced gas-to-particle conversion at the edges of the
plume. For a neutral atmospheric stability, the model predicted that the peak
concentrations of 0.024 urn particles in the plume would decrease as the ratio of
NO to SOy emitted from stack increased; this is a consequence of increased^
competition for ambient -radical species. The PHOENIX model indicates that visi-
bility contrast, the blue-red ratio and discoloration, caused by the Cholla
plume, are all more sensitive to atmospheric stability than to emission rates
from the stack.
(iii)
SECTION
INTRODUCTORY REMARKS
The impact on atmospheric visibility of the emissions from coal-fired power
plants is a question that has received considerable attention in the last five
years. Due to the presumed general coincidence of visibility impact and
particulate sulfate (Bolin and Charlson, 1976; Ursenbach et al. 1977; Gillani
and Wilson, 1981) much of the research done to date has concentrated on the
formation of secondary sulfate and the effects of this sulfate on visibility.
Secondary sulfate must be considered in visibility impact because it often
forms a substantial fraction of the mass in the -0.3 1.5 urn diameter particle
size interval where scattering of visible light is most efficient. However,
Hobbs et al. (1979) showed that changes in the mass loading of particles in the
size range 0.3 1.5 urn in power plant plumes can be dominated by primary par-
ticle dynamics and that gas-to-particle (g-to-p) conversion products such as
sulfate do not always accumulate in the appropriate size interval to affect
visibility. Furthermore, a recent study of the relatively new Navajo power
plant (Richards et al. 1980) showed that absorption by nitrogen dioxide gas
was mainly responsible for the visibility impact of the plume from that plant,
at least close to the stack. These studies indicate that it is unwise to make
a priori assumptions as to the relative effects of primary particulate
emissions, secondary particles and nitrogen dioxide, for visibility impact
in a power plant plume, particularly for the plumes from modern coal plants.
-2-
INTRODUCTORY REMARKS, Continued
This report describes the results of a field and analytical study of the
plume from the Cholla coal-fired electric power plant located near Winslow,
Arizona. While the original plant was built in 1961 (unit 1) our investigation
was confined to the plumes from the two quite new units (2 and 3) The field
study and analysis concentrated on particulate dynamics and secondary particle
formation in the plume, the production of nitrogen dioxide (NO?) in the plume,
and the relative contributions of particulates and NOp to visibility reduction
by the plume. The data obtained are also used in a validation test of the
University of Washington’s PHOENIX plume model (Eitgroth and Hobbs, 1979, 1981)
This model is then employed to predict the effects of the plume on visibility
for several increasing emissions scenarios at the Cholla plant.
-3-
SECTION 2
DESIGN OF STUDY
2.1 Instrumentation
All of the aircraft data described in this report were taken aboard the
University of Washington’s B-23 research aircraft. The extensive instrumen-
tation system aboard the B-23 is shown in Figs. and 2 and in Table 1. The
aerosol equipment is capable of measuring particles with diameters between 0.01
and 60 pm. The Cascade tmpactor allows determination of the size spectra of
sulfate and nitrate particles. The trace gas equipment allows the measurement
of total sulfur gases, SO,,, 0-,, NO, NCL, NO Filters provide the con-^ 3 c. X
centrations of particulate sulfates and nitrates. The nephelometer allows the
measurement of the scattering coefficient due to particles in the plume. The
methods used for calibrating the aerosol and gas instruments have been described
by Hegg et al. (1976)
Ground based telephotometer measurements were made by Arizona Public Service
Company personnel for comparisons with our airborne measurements of particulate
scattering coefficient and light-absorbing gases in the Cholla plume. The
instrument used was a Meteorology Research Inc. (MRI) Vista Ranger, Model 3010.
Also upper-air data taken by APS Company personnel and the Winslow, Arizona
National Weather Station were analyzed.
INSTRUMENT PODMOUNTED ONFORWARD EDGEOF BELLY
Figure 1. Research instruments on the University of Washington ’’s DouglasB-23 aircraft. See pages 5-6 for key to symbols.
-5-
Figure 1. Locations of crew and research instruments on the University ofWashington ’s Douglas B-23 ai rcraft.
1-2 Pi lot and Co-pi lot 4 Instrumentation Engineer3 Meteorologica Observer 5 Fl ight Di rector
A 5 cm gyrostabi ized weather radar
B Rosemount ai rspeed, pressure altitude and tota temperature probes,MRI-turbu fence probe and electronics, J-W liquid water probe, angle ofattack sensors
C VOR-DME slaved position plotter; research power panel (3 kW 110V 60 Hz;1.6 kW 110V 400 Hz; 150 amps 28V dc) Dopp ler horizonta winds
D Electronic controls for J-W liquid water indicator, dew point thermometer,time code generator and time disp lay, WWV time standard receiver, TAS and^tot ^^"S computers, signa conditioning amplifiers, audio signa mixers,FSK time-share data mu ltiplexers (63 channels) 2-D electric field andturbu lence ana log readouts
E Minicomputer (16-bit word 16K-word capacity) computer interface toinstrumentation, remote A-D converter, keyboard and printer, floppy disk
F Hybrid analog/digita tape -recorder (7-track, 1/2") and high speed 6-channe1ana log strip chart recorder
G In let for isokinetic aerosol samp ing
H Ai rcraft oxygen, digita readout of al fl ight parameters, relative humiditysensor, time code reader and time display, heated aerosol plenum chamber,vertical velocity, Mi ipore sequentia fi lter system
I Controls for metal foi impactor, PMS-2D image processor and digitarecorder
J Aerosol analysis section, genera ly contains: integrating nephelometer,mass monitor, diffusion battery, automatic cloud condensation nucleuscounter, Whitby aerosol analyzer, Royco particle counters, automaticcondensation nucleus counter, automatic grab samplers .(28 s. and 55 i}
K PMS axial ly scattering spectrometer (sma droplet probe) vertica lymounted
(continued)
-6-
Figure 1: (Caption continued)
L Analog fl ight parameters and digital cloud physics data di splay, colorgraphics terminal and PMS 2-D image repeater
M PMS 1-D optical array precipitation and cloud partic le spectrometer
N 2-D PMS optica array precipitation and cloud particle image probes
0 Ultraviolet photometer
P Electric field mil sensor (vertical and horizontal field)
Q Automatic ice particle counter
R Metal foi hydrometeor impactor
S Ion conductivity sensor
T Gas analysis system: S02, 03, NO, NO^, hydrocarbon, NN3U Radar repeater, side-viewing automatic camera, real-time display, of 1-D
PMS data
V Radar altimeter, 2-D electric field mi electronics, 8-channel tele-metry transmitter, dew point sensor
W Instrument vacuum system (consists of four high-capacity vacuum pumps,connected individual ly to the cabin)
X Parachutes, survival gear, life raft
-7-
AUTOMATIC VALVE SEQUENTIALBAG SAMPLER (FOR OPC 8 EAA)-
-^"P~ ^^ELECTRICAL AEROSOLANALYZER (EAA) 8MASS MONITOR
.^INTEGRATING/ NEPHELOMETER
ISOKINETICPROBE
STATICPRESSURETRANSDUCER
30-t. HEATEDCHAMBER
PROBE FORMANUAL BAGSAMPLE (UPTO 3 M3CAPACITY)- FORFILTERS, CASCADEIMPACTORS, ETC.
GAS ANALYSISSYSTEM (NO.NH,N02,SOz, AND 03)
OPTICALPARTICLECOUNTERS(OPC i an)
INLET FORISOKINETICPROBE
Figure 2. More details on instrumentation aboard the University ofWashington’s B-23 aircraft.
AXIALLYSCATTERINGSPECTROMETERPROBE
openSENSOR
N-ISOKINETIC PUMP3
-8-
TABLE 1. Specifications of research instruments aboardthe University of Washington’s B-23 ai rcraft.
Parameter
Total ai rtemperature!"
Static ai rtemperature1’
Dew point1’
Pressurealtitude1’
True ai rspeed1’
Ai r turbulence^
Instrument type
P latinum w1 reresistance
Computer va lue
Dew condensation
Variablecapacitance
Variablecapacitance
Differential
Manufacturer
Rosemount Model102CY2CG + 414 LBridge
In-house
Cambridge SystemsModel TH73-244
RosemountModel 830 BA
RosemountModel 831 BA
MeteorologyResearch, Inc.Model 1120
Range (and error)*
-70 to 30C(+/- 0.1 C)
-70 to 30C(+/- 0.5C)
-40 to 50C(+/- 1C)
150 to 1060 mb(+/- 0.2%)
0 to 230 m s-1(+/- 0.2%)
0 to 10 cm2/3 s-1(+/- 10%)
Liquid watercontent^
Electric field1’
Types and sizesof hydro-meteors^ ^+
Ice particleconcentrations’
Hot wi re resistance
Rotary field mil
Metal foi impactor
Optical polarizationtechnique
Johnson-Ni liams
MeteorologyResearch, Inc.Model 611
MeteorologyResearch, Inc.
Model 1220A
In-house
0 to 2 g m-30 to 6 g m~3
0 to 110 kV(+/- 10%)
Detects particles> 250um
0 to 1000 A-1detects particles> 50um
* Al l particle sizes refer to maximum particle dimensions.f Data displayed or avai lable aboard the ai rcraft.TT Not re levant to this study.
-9-
TABLE 1 (continued)
Parameter Instrument type Manufacturer Range (and error)’
Concentration ofc loud condensa-tion nuclei ^Ice nucleusconcentrations^ ^Ice nucleusconcentrations1’ t+
Concentrations ofsodium-containingparticles"*" "*"*’Altitude aboveterrain"*"
Weather radar"*"
Aircraftposition andcourse plotter^
Time"*"
Tine ^Ground communi-cation^
Light-scatteringcoefficient^
Light-scattering
NCAR acousticalcounter
Polarizing
F lame spectrometer
Radar altimeter
5 cm gyro-stabi ized
Works off DMEand VOR
Time code generator
Radio WWV
FM transceiver
Integrating nephelo-meter
In-house
In-house
Mee Industries
In-house
AN/APN22
Radio Corp. ofAmerica, AVQ-10
In-house
Systron DonnerModel 8220
Gertsch RHF 1
Motorola
Meteorology Res.Inc. Model 1567(modified forincreased stabi ityand better responsetime)
0 to 5000 cm-3(+/- 10%)
0.01 to 500 A-l
0.1 to 10,000 A-1
0 to 10,000 A-1(+/- 1%)
0 to 6 km(+/- 5%)
100 km
180 kmkm)
h, min, s(1:105)
min
200 km
0 to 2.5 x 10-4 m-1or
0 to 10 x 10-4 m-1
* A1 partic le sizes refer to maximum particle dimensions.Data displayed or avai lable aboard the ai rcraft.
++ Not re levant to this study.
-10-
TABLE 1 (continued)
Parameter
Heading"*"
Ground speed anddri ft angle"*"
U ltravioletradiation"*"
Angle of attack"*"
Instrument type
Gyrocompass
Doppler navigator
Barrier-layerphotoelectric eel
Potentiometer
Manufacturer
Sperry Model C-2
Bendix ModelDRA-12
Eppley Laboratory,Inc. Model 14042
RosemountModel 861
Range (and
0 to 360(+/- 2%)
0 to 6 km
0.7 J m-2(+/- 5%)
+/- 23(+/- 0.5)
error)*
altitude
S-1
Photographs
Total gaseoussu lfur"
Ozone ^H3, NO. N02, N0x+
Size spectrum ofaerosol particles^"
Size spectrum ofaerosol particles^
Size spectrum ofaerosol particles’*"
Size spectrumof aerosolparticles^
Size spectrumaerosol andc loud particles’*"
35mm time-lapsecamera
FPD flamephotometric detector
Chemi luminescence(02^4)
Chemi luminescence(03)
Electrica mobi lityana lyzer
90 light-scattering
Forwardight-scattering
Diffusion battery
Forward light-scattering
AutomaxModel GS-2D-111
Meloy Mode 285
Monitor LabsModel 8410 A
Monitor LabsModel 8440
Therma Systems,Inc. Model 3030
Royco 202(in-house modified)
Royco 225(in-house modified)
Therma Systems,Inc. Model 3040with in-houseautomatic va lves &sequencing
Particle MeasuringSystems, ModelASSP100
s to 10 min
0.5 ppb ppm
0 to 5 ppm(+/- 7 ppb)
0 to 5 ppm(+/- 10 ppb)
0.0032 to 1.0 pm
0.3 to 12 urn
1.5 to 40 pm
0.01 0.2 ym
1.5 to 70 pm
* Al particle sizes refer to maximum particle dimensions.+ Data displayed or avai lable aboard the ai rcraft.t+ Not relevant to this study.
-11-
TABLE 1 (continued)
Parameter Instrument type Manufacturer Range (and error)’
Size spectrum Diodec loud particles’*"*" occu lation
Size spectrum of Diodeprecipitation occu ltationparticles^
Concentrationsof Aitken nuclei^
Concentrationsof Aitken nuc lei"*"
Sizes and typesof aerosolpartic les ’*’ "*"*"Concentrations ofice nuc lei"*"*"
Mass concentrationaerosol particles’*"
Particu late su lfur
Particu late su lfur
Light transmission
Rapid expansion
Di rect impaction
Di rect impaction
Electrostatic depo-sition onto matchedosci lators
Pa If lex fi lters(then Roberts/Husarflash volati lization)
Ion Exchange Chroma-tography on Ghiafi lters
Particle MeasuringSystems, ModelOAP-200X
Particle MeasuringSystems, ModelOAP-200Y
Genera ElectricModel CNC II
Gardner
Glass sl ides
Nuclepore/Mi iport
Therma Systems,Inc. Model 3205
In-house
Dionex Inc.
20 to 300 urn
300 to 4500 urn
102 to 106 cm-3(particles >0.001 urn)
2 x 102 to 107 cm
5 to 100 urn
0.1 to 3000 ug m-3(+/- 0.1 ug m-3)
0.1 to 50 pg m-3(for 500s. ai r samp le)
0.1 to 50 ug/m3
C loud water Centrifugesamples’*"*"
Size-segregatedconcentrationsof aerosolparticles
Cascade impactor
In-house
Sierra InstrumentsInc.
Col lects clouddrop lets > 3 urn radius
0.1 3 urn(6 size fractions)
* Al particle sizes refer to maximum particle dimensions.+ Data disp layed or avai lable aboard the aircraft.++ Not re levant to this study.
-12-
2.2 Sampling Procedure
The basic flight pattern that was used to sample the Cholla plume is shown
in Fig. 3. Samples were first taken within a distance of about km from the
stack and then the aircraft was flown at different altitudes in the plume at
various distances downwind from the stack. Each horizontal traverse was
extended well out into ambient air to allow determination of the background
values for each parameter measured.
A set of plume samples normally consisted of continuous measurements across
the width of the plume of trace gases, light scattering coefficient, and
meteorological variables. When the continuous real-time measurements indicated
that the plume center had been reached, a "grab bag" sample was taken for
measurements of the particle size spectrum. While particle size spectrum
measurements require ~2 min and thus cannot be carried out in real time, the
"grab bag" technique allows characterization of the central 100 m or so of each
plume traverse (the "grab bag" filling time is -2. s at a nominal aircraft speed
of 60 m s ). The "grab bag" samples were not fed into the Royco 225 or the
ASSP-100 since these instruments measure rather large particles (>1.5 urn in
diameter) that are not sampled reliably by such a technique. When possible, the
aircraft was flown in an orbit in the plume to sample these larger particles in
situ.
When a Cascade impactor sample, or sulfate-nitrate filter sample, was
desired, the 8002. (Fig. 2) sample bag was filled as close to plume center as
possible (filling time ~4 s) and this sample was subsequently passed through
-13-
Figure 3. Aircraft fl ight pattern used for sampling the plume.
-14-
either the Cascade impactor or’ a falter. Generally, at least two bag samples
were required for a large enough sample to be collected for later chemical
analysis.
Samples were also obtained from the 800 A bag for subsequent
analysis for hdyrocarbons, CO, and CO? by gas chromatography. The sampling andanalysis procedure for such samples has been described by Rasmussen et al.
(1976).
2.3 Data Analysis Techniques
2.3. Aerosol
The plume and ambient aerosol sample data are used to create particle
number, surface area and volume concentration spectra. The number spectra are
given in terms of dN/d (log D) where dN is the number concentration of particles
between the log-size interval log D and log D + d (log D). The surface area
spectra are given in terms of dS/d (log D) where dS is the corresponding surface
area concentration of the particles. The volume spectra are given by dV/d (log
D) where dV is the volume concentration of the particles.
Particle data used in a PHOENIX model run were further analyzed by per-
forming a least square fit to the data as represented by a multi-modal, log-
normal size distribution. Thus, the number spectra are represented by:
i"2 ^2 In2^.
-15-
where k is the number of modes (i.e. the number" of log-normal distributions
required to describe the spectra) and is usually 2 or 3, Nj_ is the total number
concentration of each mode, o^ the geometric standard deviation of each mode,
and DI the geometric mean diameter of each mode. Surface and volume spectra are? ?
represented by analogous equations with S (=irD N) and V (=irD N) respectively,
replacing N in (1 ) For further details the reader is referred to Eitgroth and
Hobbs (1979).
Also required for a PHOENIX model run are the scale heights for each par-
ticle mode in the ambient air (the scale height is the altitude change required
to see a concentration difference of a factor of "e" in a particle mode).
2.3.2 Trace gases
The gases of primary interest in this study (NO, NO;?, Oo, and SO^) were
all measured continuously aboard the B-23 research aircraft. Post-flight analy-
sis consisted of determining the concentrations of NO, NO? and SO- at various
ranges from the plant (for NO-to-NO? conversion rate calculations, NO? opticaldepth determination, and plume dilution estimates, respectively) and the
SO? and NO concentrations associated with the various bag samples from whichJ\.
particulate filter samples were drawn. The determination of gas concentrations
in the bag samples was accomplished by directly measuring the SO? concentration
in each sample bag acquired for filter analysis and then scaling plume NOJ\
concentrations by the ratio of bag-to-plume SO? concentration to arrive at thebag NO concentrations. The greatest difficulty involved in assigning
A,
plume gas concentrations at each range from the stack was in the selection
of comparable points at each range. Generally, the plume center was
-16-
selected, (i.e. the point at which the measured SO? concentration reached amaximum value). We have previously found no significant difference between con-
version rates so calculated and those calculated using plume average con-
centrations (Hegg et al. 1976). The methodology employed to calculate the
NO-fco-NO? conversion rate is given by Hegg et al. (1976).
2.3.3 Teflon filters: gas-to-particle conversion
The teflon filters were analyzed for particulate sulfate and nitrate
by means of ion-exchange chromatography (Stevens et al. 1978) Volume con-
centrations of sulfate and nitrate were then calculated from the volume of air
drawn through the filters. The standad error in the concentration measurements
is considered to be +/- 20%. Concurrent measurements of SOp and NOp in each bag
allowed determination of SCL-to-SOn and NOp-to-NO" conversion rates using the
methodology described by Hobbs et al. (1979) and Hegg and Hobbs (1980) The
standard error in the derived conversion rates is ’50%.
2.3.4 Nylon filters
In order to determine gaseous nitrate (i.e. HNCL vapor) concentrations,
nylon filters were mounted behind each teflon filter to absorb any HNCL vapor
present (Spicer, 1977). While there is some question of degassing of nitrate on
the teflon pre-filter producing artifact HNCL on the nylon filter, recent tests
suggest this is not a serious interference (Spicer et al. 1981)
After collection, the nitrate was extracted from the filters following
the same procedures employed for the teflon filters and subsequently analyzed by
ion-exchange chromatography (Stevens et al. 1978). The standard errors for the
gaseous nitrate mass and volume concentration are similar to those for the
teflon filter analysis.
-IT-
2.3.5 Cascade impactor samples
The substrates of the first five stages of the Cascade tmpactor consisted
of stainless steel discs coated with grease (to prevent particle bounce) The
sixth and final stage was a teflon filter. Steel substitutes coated with grease
have been found to render particle bounce insignificant (Rao ands Whitby, 1978)
With regard to wall losses, the manufacturer (Sierra Instruments, Inc. ) specifies
wall losses as
-18-
2.3.7 Telephotometel" data
The MRI telephotometer measures the apparent brightnesses of selected
targets and the sky at four manually selected narrow band wavelengths centered at
405, 450, 550 and 630 ran. By comparison of the apparent brightness of a target
with and without the plume between the target and the observer, the optical
depth (r of the plume can be determined at the selected wavelengths by means of
the Beer-Lambert relationship:
^ - e-BOwhere B and B are the brightnesses of the target in the presence of and in the
absence of the plume. For convenience, the sky was generally selected as the
target although other targets were used on occasions.
In evaluating the PHOENIX model, direct comparison could be made between
measured brightnesses and those predicted by the model for the same view path.
2.3.8 Optical depths
Optical depths were calculated for both particle scattering and
NO., absorption in the Cholla plume. The data for these calculations are direct
measurements of the particle scattering coefficient and the concentrations of
N0^> over the dimensions of the plume, and the plume dimensions themselves. In
order to arrive at an optical depth attributable to the plume alone, the
background values of the particle scattering coefficient were subtracted from
the measured plume values before the optical depth of the plume was calculated.
(Since the background concentrations of NO? in the Cholla area were below thedetection limit of our instrument [5 Ppb], they were assumed, on the basis of
-19-
calculations and some direct measurements in the same geographical area, to
be ppb. )
2.3.9 Vertical mixing coefficient
The vertical eddy diffusion coefficient at plume elevation was determined
by calculating the Lagrangian turbulent length scale from an auto-correlation
analysis of vertical velocity (Tennekes and Lumley, 1972) and from direct
measurements of the energy dissipation rate (e) in the inertial subrange. This
coefficient was employed in the University of Washington’s PHOENIX plume model
to estimate vertical dispersion.
2.4 Visibility Model Verification and Predictions
The visibility section of the PHOENIX plume model outputs optical depths
for various wavelengths, blue-red ratios, the AE discoloration parameter, and
the apparent brightnesses of various objects at specified distances from the
observer over specified optical paths. These outputs are based upon the con-
centrations of particles of various sizes and NO? concentrations in the plume
and in the ambient air that are calculated in the PHOENIX model (Eitgroth and
Hobbs, 1981).
Verification of the visibility calculations was undertaken by comparing the
observed brightnesses of various objects over specified viewing paths with those
predicted by the PHOENIX model. Comparisons were made both for paths inter-
secting and not intersecting the plume. These results are presented in Sec. 4.1
After verification, the model was employed to predict visibility degradation
caused by the Cholia plume under a variety of conditions specified by APS. The
results of the predictions are given in Sec. 4.2.
-20-
SECTION 3
ANALYSIS OF DATA
3. Data Base and General Meteorology
The data base consists of measurements taken on eight flights during the
period from October 22 through October 27, 1980. Relevant data from each of the
flights are presented in the course of the detailed analysis given in the
following sections.
The general meteorology during the study period was rather variable. On
October 22 the situation was one of small pressure gradients with associated
light winds. On October 23 a large region of high pressure drifted towards the
study area from the northern Rocky Mountains preceded by the passage of a dry
cold front. This was accompanied by light easterly to northeasterly flow at
flight levels which persisted until October 25. On October 25 pressure gra-
dients were again flat, as a trough at the 500 mb pressure level began to deve-
lop to the southwest. By the following day (October 26) several cloud layers
had already advanced into the study area ahead of a cold front situated in
eastern Nevada and California. Brisk southwesterly winds were prevalent in the
boundary layer. On October 27 the cold core of the upper-level trough was
nearly overhead; winds at flight level were gusty in response to large surface
gradients.
3.2 Particle Dynamics in the Plume
Assuming that light absorption by particles is negligible, the proximate
cause of any visibility impact due to particles in the Cholla plume must be
particle scattering, which is a strong function of the particle size distribu-
tions in the plume. Furthermore, the rate of g-to-p conversion will be
strongly influenced by the particle size distributions, specifically their surface
area distributions. The shape and evolution of the particle size distributions
in the Cholla plume are therefore an excellent starting point for analysis of
the effects of the Cholla plume on visibility.
-21-
Representative number, surface and volume distributions of the particles
measured in the Cholla plume are shown in Fig. 4. These particular distribu-
tions were measured at a range of 3.7 km from the stack on October 23, 1980.
Distributions measured on the same day at a range of 18.5 km are shown in Fig. 5.
It is interesting to note that the number concentrations of certain sized par-
ticles in the plume nay be lower (as well as higher) than those in the ambient
air. This phenomenon has been observed in all of the power plant plumes we have
studied; we attribute it to coagulation efficiently removing particles of cer-
tain sizes (Hobbs et al. 1979). However, for the optically critical size range
from 0.3 to 1.5 urn diameter the concentratrions of particles in the Cholla plume
are generally above ambient values. Comparison of the particle number distribu-
tions at 3.7 and 18.5 km (Figs. 4 and 5) further reveals that the shape of the
distribution does not change appreciably with range from the plant, although
number concentrations are slightly reduced due to plume dilution.
The particle surface and volume distributions measured in this study
show peaks at particle diameters of 0.25, 0.55 and 1.11 pm, the major peak
being that at 0.25 urn. These peak locations are roughly the same for all of
the size distributions examined, though the peak magnitudes may change
substantially. For example, Figs. 6 and 7, which show particle size distri-
butions measured in the plume on October 22, 1980, reveal surface and volume
peaks considerably lower than those measured on October 23, 1980 but still
located at the same particle sizes. The location of the major surface area
peak at 0.25 urn is of particular importance since it is at this particular
size, just below the optically critical size range, that most condensation
of g-to-p conversion vapors should take place. Such distributions should
tend to alleviate the effects of g-to-p conversion on visibility impact.
lo7!-io6
o5
io4
10310
E 102u
Q |0’0>0
^ 10ẑ ,/.-iu
10-3
10-4
10-5 ^2 ^10 ’ 10" 10’ 10"’ 10" 10’ 10"’ 10" 10’PARTICLE DIAMETER D (/im) PARTICLE DIAMETER D (/im) PARTICLE DIAMETER D (yu.m)
( a ) ( b ) ( c)Figure 4. Number (a) surface area (b) and volume (c) distributions of particles measured in theplume (sol id ine) and in the ambient ai r (dashed line) on October 23, 1980, at 3.7 km from theChol la power plant. The plume sample was taken between 07: 12 and 08:57 and represents a plumetravel time of- 7 min. The ambient sample was taken between 07:15 and 07:45.
610
105
104
103
102
10’
IOC10"
10
Eu
Q
0
Ô"s.ZO
10’
r310
10-’
r51010-2 10 102 10-2 lO1
PARTICLE DIAMETER D (/im) PARTICLE DIAMETER D (/^m) PARTICLE DIAMETER D (/im)(a ) ( b) ( c )
Figure 5. Number (a) surface area (b) and volume (c) distributions of particles measured in the plume(solid line) and in the ambient air (dashed line) on October 23, 1980 at 18.5 km from theS^11? ^wsr ^t’- ^ P^ ^Ple was taken between 08:30 and 11 :43 and represents a plumetravel time of W min. The ambient sample was taken between 08:24 and 11 :46
105
104
103
10 o
6 102u
0
^ ^T\? 10-’10-2
10-3
50
in
E 40u
(M
=1.Q 300>
^I 2010
10
ro
S 810
0̂
T̂3
>̂-o 4
10-510-2 10o 10’ 10 -2 10 0 10’ 10
-2 100 10’
PARTICLE DIAMETER D (/im) PARTICLE DIAMETER D (/xm) PARTICLE DIAMETER D (pn)(a ) ( b) ( c )
Figure 6. Number (a) surface area (b) and volume (c) distributions of particles measured in the plume(sol id ine) and in the ambient air (dashed line) on October 22, 1980 at 3.7 km from the Chol la powerplant. The plume sample was taken between 07:54 and 09:39 and represents a plume travel time of 16 min.The ambient sample was taken between 08:07 and 08:55.
K)6
10 5
104
103
^ !>e io2u
Q 1001
^ 10’S.? 10 -’10-2
10-3
10-4
10 -5
50
’E 40\
10
’E=LQ 300>o^oŜ 20
\\
0
0-2 10 102 10-2 10 102 10-2 10 10
10
10
810E3.Q 60
^^/\ ’ 4/ \/ \/ \\
\1\1 2
li?"-S, ’^ . A^ ^ \ 2PARTICLE DIAMETER D (/im) PARTICLE
(a )DIAMETER D (/im) PARTICLE DIAMETER D (/im)
( b) ( c )
Figure 7. Number (a) surface area (b) and volume (c) distributions of particles measured in the pl ume(sol id line) and in the ambient air (dashed ine) on October 22, 1980 at 55.6 km from the stack. The plumesample was taken between 11 :56 and 11 :02 and represents a olume travel time of 234 min. The ambient sample’/"’- taken between 11: 14 and 11 :07.
-26-
Turning to a direct comparison between the particle size distributions in
the Cholla plume and the optical properties which they produce, Table 2 shows
a comparison between values of the scattering coefficient due to particles
(b ^) in the Cholla plume and the particle mass concentration between 0.3scat
and 1.5 urn (calculated from the particle volume data assuming a particle
density of 1.8 g cm ). The linear correlation coefficient between these two
variables is 0.6, significant at the 97% level. While modest for the par-
ticular data set shown, this correlation does illustrate the connection bet-
ween the particle size distributions and the optical properties of the plume.
If one considers plume minus ambient values of b and particle mass bet-
ween 0.3 and 1.5 urn, the correlation between them is the same as that given
for the gross parameters just discussed. This indicates that ambient values
for b and particle mass in the accumulation mode had little variancescat
during the study period. Values for these excess parameters are also shown
in Table 2.
3.3 Secondary particle formation
The formation of secondary particulate matter, specifically sulfate, has
been shown to be closely related to particle scattering in several power plant
plumes (Husar et al. 1978) We examine here the mechanics of sulfate formation
in the Cholla plume. We will also investigate the mechanisms of nitrate
formation in the Cholla plume since nitrate is another likely g-to-p conversion
product that may contribute to particle scattering; nitrates are also a sink for
N0,, one of the three most plausible sources of visibility impact in power
plant plumes.
The concentrations of total sulfate and nitrate in the Cholla plume are shown
in Table 3. With the exception of the particulate nitrate values for October
22, 1980, all of the particulate concentrations are similar to those we have
TABLE 2. Comparison of the mass (M ) of particles between diameters of 0.3 and 1.5 urn and b measured in theCholla plume. p sca"
Dc
October
October
October
October
October
October
October
October
October
October
October
October
October
October
ite
22,
22,
23,
23,
24,
24,
24,
24,
25,
25,
26,
26,
27,
27,
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
U.of Wash.FlightNumber
937
it
938ii
(am) 939
(pm) 940
(pm) "
(pm) "
(pm) 941
ii
942
ii
943 & 944
943 & 944
Range
(km)
3.7
55.6
3.7
18.5
24.0
3.7
9.3
18.5
3.7
14.8
3.7
1.2
1.0
27.8
scat
(in units of
10-5 m-1 )
4.5
3.3
4.0
2.4
3.5
5.0
3.0
2.5
4.0
3.5
2.5
3.0
3.0
2.2
(P,
0
0
0
0
0
0
0
0
0
0
M?g m-3)
.87
.59
.69
.59
.86
.58
.36
.95
.20
.13
.64
.72
.57
.43
M?(in
0
0
0
0
0
1
0
0
0
0
0
0.24
0
(P^0
Pg m -)
.006
16
.40
.24
.40
.33
.11
.70
.72
.69
.052
12
.08
bscat (P^(in units of
10~5 m~1)
2.3
0.8
2.0
0.4
.6
3.5
1 .5IM
1.2 ^2.2
.5
0
0
.3
0.7
* Calculated from the total particle volume assuming a density of 1.8 g cm"t P-A=plume minus ambient values.
TABLE 3. Sulfate, nitrate and precursor gas concentrations in the Cholla plume.
r
October
October
October
October
October
October
October
October
October
October
October
October
October
October
October
)ate
22,
22,
22,
23,
23,
24,
24,
24,
24,
25,
25,
25,
26,
26,
26,
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
Travel time
(hours)
0.26
2.6
ambient
0.16
0.80
0.59
1.5
3.0
ambient
0.26
1.04
ambient
0.083
0.25
ambient
S02 Pc
(ppb)
148
54
6
311
32
63
(25)
15
5
555
245
3
19.5
24.2
5
irticulate SO,.
(ug m-3)
0.69
0.48
0.21
0.37
0.39
0.77
0.22
0.83
0.49
0.95
0.76
0.35
0.57
0.50
0.57
N0
(Ppb)
322
18
307
83
105
37.5
1620
220
100
88
N0^(ppb)
270
120
187
85
100
45
650
120
100
75
Particu
(ug
16
3.
1.
0.
0.73
0.
0.
0.
0.
0.
0.
0.81
0.
late NO"
m-3)
.6
5
8
74
2
38
46
77
46
28
63
18
22
HNO-
(pg m-3)
5.5
4.2
2.2
2.4
.3
.73
2.0
.2r\
0
1.8
1. 18
1.
0.97
.66
1. 18
1.28
-29-
pr-eviously observed in coal-fired power plant plumes (Hegg and Hobbs, 1980)
The anomalous values on October 22 are presumably due to unusual emission
conditions from the power plant itself rather than to mechanisms within the
plume, since the highest concentrations occur closest to the stack and the total
nitrate concentration decreases at the same rate as SO? (a relatively conser-vative plume tracer) On October 24, concentrations of particulate SO" and NO"
in the plume appeared to be significantly below ambient values after 1.5 h of
travel time. The same situation occurred on October 25 with respect to NO".
The October 25 anomaly is possibly attributable to NO" volatization on the pre-
fliter and subsequent capture on the backup filter, since total plume NO" is not
significantly below ambient for this case. The case of October 24, however,
most likely reflects variability in ambient levels of SO" and NO", since the
ambient value given is based on samples taken at travel times of >3 h.
The nitric acid concentrations shown are the first we have obtained in a
power plant plume and are of considerable interest. The values are systemati-
cally higher than those reported by Richards et al. (1980) for the Navajo
plume, although they are in accord with general boundary layer measurements
reported by many investigators (Spicer, 1977; Kelly et al. 1979; Hubert and
Lazrus, 1978). It should be noted that the levels of particulate nitrate we
measured are also higher than the levels reported by Richards et al. (who found
essentially no particulate NO" in the Navajo plume) However, our measurements
-30-
of particulate NO" in the Cholla plume do not differ essentially from those we
have previously found in power plant plumes (Hegg and Hobbs, 1979) Perhaps the
most interesting point revealed by the data in Table 3 is that HNCL constitutes
a substantial fraction of the nitrate in the Cholla plume, the fraction of
NO" which is HNO^ ranging from 52 to Q5%. Clearly, this species cannot be
neglected when evaluating nitrate formation in the Cholla plume. However, with
respect to the overall odd nitrogen chemistry of the plume, nitrate plays a
relatively minor role. This can be seen by evaluating the mole ratio of nitrate
to total odd nitrogen (NO~/N,n) in the Cholla plume. Such ratios are listed in
Table 4 together with similar ratios of sulfate to total sulfur (SO^/S,p)While the sulfate to total sulfur ratios are even smaller than the old nitrogen
ratios, sulfate nevertheless may be of considerable optical importance for the
reasons mentioned in the introduction to this report. It is interesting to note
that the mean ratio of plume NO’/N^, to plume SO^/S^, (B/A) shown in Table 4 is3.6 +/- 4.0. This value does not differ significantly from that found for the
same ratio by Richards et al. in the Navajo plume. It is the magnitude to be
expected if both sulfate and nitrate are being produced by oxidation of SO? and
NO.,, respectively, by OH radicals. This point leads us to direct evaluation of
SOp-to-SO^ and NOp-to-NO" conversion rates in the Cholla plume.
Considering first SOp-to-SO^ conversion, the sulfate-to-total sulfur ratiosin Table 4 were first converted to plume excess values by subtracting off
-31-
TABLE 4. Mole ratios -of the gas-to-partic le conversion products su lfate (SO,
and nitrate (NO.,") to the tota (gaseous plus particu late) mo lar
concentrations of su lfur (S-r) and odd nitrogen (N-[-) respectively,
in the Chol la plume and in the ambient ai r. The significance of the B/^
ratio is discussed in the text.
Date
October 22,
October 22,
October 22,
October 23,
October 23,
October 24,
October 24,
October 24,
October 24,
October 25,
October 25,
October 25,
October 26,
October 26,
October 26,
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
Travel time(hours)
0.26
2.6
ambient
0.16
0.8
0.6
1.5
3.0
ambient
0.26
1.04
ambient
0.083
0.25
ambient
Bag SC(PPb)
50
23
6
253
22
38
25
11
5
435
355
3
17
16
5
I? S04~/ST(-A)
3.2 x 10"34.9 x 10"38.2 x 10"33.4 x 10"44.6 x 10"34.8 x 10"33.1 x 10"31.8 x 10"22.5 x 10"25.1 x 10"45.1 x 10"42.7 x 10"27.8 x 10"37.8 x 10"32.7 x 10"2
N03"/Ny(=B)
3.99 x 10"22.75 x 10"29.6 x 10"12.82 x 10"37.85 x 10"3.7.22 x 10"32.0 x 10"29.8 x 10"36.2 x 10"13.3 x 10"45.36 x 10"43.85 x 10"15.89 x 10"36.65 x 10"33.61 x 10"1
B/A
12.5
5.6
117.0
8.29
1.7
1.5
6.5
0.54
24.8
0.65
1.05
14.3
0.76
0.85
13.4
-32-
ambient sulfate and SO? concentrations from those in the plume. This was doneto avoid spurious calculations of sulfate production caused by the relatively
high sulfate-to-tofcal sulfur ratios in ambient air (Hegg and Hobbs, 1980)
After this correction has been made, non-zero SCL-to-SOi. conversion rates are
found in only two of the cases shown in Table 4: the case of October 22 where
the rate was found to be 0.06 +/- 0.06^/hr, and that of October 24, between 3.7 and
18 km range, where the rate was found to be 0.6 +/- 0.4^/hr. Clearly only the
second rate is significant. Hence, SOp-to-SOn conversion was measurable in the
Cholla plume on only one out of the five flights for which data suitable for
conversion calculations were available. This general lack of significant
sulfate production in the Cholla plume is in contrast to the situation in most
of the other power plant plumes that we have studied (Hegg and Hobbs, 1980)
The data on odd nitrogen show even less evidence of nitrate production.
Indeed, after following the same ambient correction procedure used for the
sulfur data, none of the five data sets showed significant NO -to-NO"x ->production in the Cholla plume.
The general lack of measurable sulfate and nitrate production in the Cholla
plume during the study period is of considerable interest. No doubt both
nitrate and sulfate production are taking place at levels below our minimum
detection limits, but this in itself is in contrast to previous studies we have
conducted. While such diverse factors as plant operating conditions, meteoro-
logy, and ambient oxidant concentrations could plausibly be the source of this
contrast, the fact that both SOn and NO" production rates are low, and that
the fraction of the odd nitrogen partition ratio to the sulfur partition ratio
is consistent with oxidation by OH radicals, suggests that the oxidant producing
-33-
both sulfate and nitrate is the OH radical and that its concentration in the
Cholla plume was substantially below that which was present during our studies
of other power plants.
To explore this possibility, the concentrations of OH radicals present in
the ambient air for the cases shown in Table 4 were calculated using the
procedure outlined in Sec. 2.3.6. These concentrations are shown in Table 5.
The mean concentration of 1.3 x 10 molecules cm"-, while in accord with both
tropospheric modeling results (Altshuller, 1979) and direct measurements in
background air (Campbell et al. 1979) is considerably lower than we have
considered to be the case- in our previous studies. For example, during our
study of the Four Corners power plant, in which relatively high SOp-to-SOn
conversion rates were observed, we estimate, based on the measurements of Davis
(1977) at the same locale and time of year, that the OH concentrations were
7 -?^10 molecules cm It is therefore possible that the low sulfate and nitrate
production rates that were present in the Cholla plume during our field study
period were due to the relatively low concentrations of OH radical in the
ambient air.
The other aspect of sulfate production that must be examined before a
realistic evaluation of the effect of sulfate on visibility can be arrived at is
the question of the mass distribution of sulfate over the particle size
spectrum. The measured distributions, derived from the Cascade impactor samples
exposed in the Cholla plume are shown in Figs. 8-11. It is immediately apparent
that the peak in the sulfate size distribution does not commonly occur in the
-34-
TABLE 5. Concentrations of OH radica ls in ambient ai r near the Chol lapower plant. Va lues are estimates based on ca lcu lationsdescribed in Sec. 2.3.6.
Date
October 22, 1980
October 23, 1980
October 24, 1980*October 25, 1980
October 26, 1980
[OH] (molecu les cm"3)
1.0 x 1051.0 x 1053.7 x 1043.4 x 1043.8 x 105
Mean 1.3 x 105
* No CO measurement was avai lable on this date. Therefore, the va lue shownhere is based on the average value of CO measured on the other days. Therange of OH concentrations based on the range of CO values would be1.8 x 104 1.3 x 105 molecu les cm-3.
-35-
E 0.4
1II0W
-36-
? 0.26
L’3- o.i11
-37-
PART1CLE SIZE INTERVAL (yLLm)
Fiqure 10. Size distribution of sulfate particles measured in the Chol la
pl ume on October 24, 1980 at a range of 24.0 km (1.63 hr travel time)
PARTICLE SIZE NTERVAL (/im)(a )
ro
CP
^’o-en
-39-
optically critical size range. Indeed, only one of the seven distributions
measured (that on October 27 at a range of km from the stack) shows such a
peak. However, a comparison of the distributions measured at plume travel times
of 0.26 hr and 4.0 hr on October 22 (Fig. 8) suggests that secondary sulfate may
begin to accumulate in the optically critical size range after the plume has aged
sufficiently. The four hour incubation period for this process, suggested by
the October 22 data, is similar to the period commonly suggested as that
necessary before appreciable sulfate formation can take place within power plant
plumes (Husar et al. 1978; Whitby et al. 1978)
In order to examine nore critically the influence of secondary sulfate on
the particle size distribution in the near field of the Cholla plume, we
consider next the net change in the sulfate distribution as a function of time
and compare -it to the net change in the total particle volume distribution.
The sulfate and total particle volume distributions were first corrected for
the effects of entrainment of ambient air by the plume. The three cases for
which sufficient data were available for such a comparison to be made are shown
in Figs. 12-14. It can be seen that while the change in total particle volume
shows a definite peak at around 0.2 urn diameter in all three cases, the net
change in the mass of the sulfate particles shows a definite peak only for the
case of October 22 and then at particle diameters below 0.17 pm. The peak at
0.2 urn diameter in the total volume change is to be expected since it reflects
the existence of the accumulation mode in the particle size distribution. While
this mode is centered slightly below the optically critical size range, the mode
does overlap the optically critical size range and it seems plausible that with
increased plume age this mode might nore closely coincide with the optical
range, as has commonly been assumed to be the case. The lack of a peak in
sulfate mss in the optically critical size range, on the other hand, shows that
10
010
^
2.0
.6
.2
Q
]? 0.8-0^s.
^ 0.4<0
-/ ’,/ -///
//
^.-r--r’^r77r, ^. T^Y /
A/ \/ \
/ \/ -’
-\\\\\\\\ ^"- /// -^ /
0.4
0.3
0.2
O.I
0
-O.I
-2 010 10’ 10 10’PARTICLE DIAMETER D (/im)
Figure 12. Comparison of changes in the sulfatetotal particle volume distribution (dashed ine)plume from the Cholla power plant on October 22,
mass distribution (solid ine) with changes in thebetween 3. 7 and 55.6 km from the stack in the1980. Data are adjusted for di lution by diffusion.
I
2.0r
,6
2
j? 0.8-o
^
^ 0.4<0
////
//
--------------/-
rt
"Eu10
Q̂
Oi
û
^-0<
2.0r
.6
.2
0.8
0.4
0
i
-A 1/ \\
,’ \----^ \ -i/’
/ i :/ \
^---/ \^"’--^/0.
0.
0.
0
u-0
-2 010 10-’ 10’10
ro
en0.4 3-
(^0.3 (/3<
LJ
&=)0)
LU0Z.<I0
PARTI CLE DIAMETER D (/^m)
Figure 14. Comparison of changes in the sulfate mass distribution (sol id line) with changes inthe total particle volume distribution (dashed line) between 1 and 27.8 km from the stack in theplume from the Cholla power plant .on October 27, 1980. Data are adjusted for dilution by diffusion.
-43-
a considerable fraction of the secondary sulfate is not accumulating in the
primary light-scattering range, at least in the near field. Thus, even though
most of the particulate mass in the optically critical size range is commonly
sulfate, we would not expect to see the high correlation between plume excess
sulfate and plume excess light-scattering coefficient that has been observed in
plumes in the Eastern United States (e.g. Husar et al. 1978) The data
available for such a correlation analysis in the Cholla plume are shown in Table
6. The correlation coefficient between b (due to particles) and sulfate is a
modest 0.51 significant at the 83% level. This is in contrast to the correla-
tion coefficient of 0.87 for these parameters found in the Labadie plume (Husar
et al. 1978). The correlation coefficient between b and total particle
mass (between 0.3 and 1.5 urn) in the plume in excess of ambient concentrations
(for the same cases analyzed for sulfate) is an appreciably higher 0.66, signi-
ficant at the 95% level. Since most of the mass in the size range 0.3 to 1.5 pm
is attributable to SOi", a similar correlation between excess SOj" in this size
range and excess b is expected. However, such a correlation is of little3C3.L’
practical importance since it is nuch easier to measure total excess mass in
this range than to measure SOJ’. In any case, it is the total mass in this size
range that is important for light scattering-not SO,, alone. These comparisons
strongly suggest that secondary sulfate, while playing a role in visibility
impact by particles in the near field of the Cholla plume, is not the sole
source of such visibility impact and that particle dynamics must be considered
at least as important.
The rate of secondary particulate nitrate in visibility impact in power
plant plumes has always been assumed to be slight due to the relatively low
levels of such nitrate and the presumption that it does not accumulate in the
optically critical size range. We have already noted that particulate nitrate
TABLE 6. Comparison of plume excess bg^ with plume excess su lfate mass concentrations and plumeexcess partic le mass between 0.3 urn and 1.5 \in diameter.
Date
October 22,
October 22,
October 24,
October 24,
October 24,
October 25,
October 25,
October 26,
October 26,
1980
1980
1980
1980
1980
1980
1980
1980
1980
Travel time
(hr)
0.26
2.6
0.6
1.5
3.0
0.26
1.04
0.083
0.25
Excess 504(ug m-3)
0.48
0.27
0.28
-0.27
0.34
0.60
0.41
0.0
-0.07
Excess b^cat(in units of 10-5 m"1)
2.3
0.8
3.5
1.5
1.2
2.2
1.5
0
0
Excess partic le mass from
0.3 1.5 urn (ug m-3)
0.006
0.16
1.33
1.11
0.702
0.715
0.648
0.052
0.122
0
* Ca lcu lated from partic le volume measurements assuming a density of 1.8 g cm"
-45-
concentrations are generally low in the Cholla plume; we now turn to the nitrate
mass distributions.
The data available on nitrate mass distributions are shown in Figs. 15-18.
As with sulfate, there is only one case (that of October 22, 1980 at a travel
time of 4 hr) in which a peak in nitrate mass occurs in the optically critical
size range. This suggests that particulate nitrate also plays a small role in
visibility impact in the near field of the Cholla plume.
3.4 Nitrogen Dioxide Formation
The third plume constituent that might effect visibility impact by the
Cholla plume is nitrogen dioxide. Indeed, the analysis from the previous sec-
tion suggests that, at least in the near field, the effect of NO plume chem-
istry on visibility impact will be restricted to absorption of visible light by
NO?. This has some interesting consequences. Since, in the near field at
least, the major sink for NO? is not conversion to nitrate, it must be either
diffusion to background levels (under which phenomenon we include dry deposi-
tional loss) or photolysis of NO?, or both. Because the net loss of NO? viaphotolysis will be directly related to the amount of ozone available to re-
oxidize the product NO back to NO?, the net photolytic loss rate should be
dependent on the entrainment rate of ambient ozone into the ozone-depleted plume
(at least in the near field). Thus, both of these sinks for NO? are plausiblyrelated to the rate of plume mixing.
The source of NO? in power plant plumes is the reaction of primary NO with
0, entrained from the ambient air. In previous work (Hegg et al. 1977) we
10
o*
=t
0̂
0.2
O.I
-47-
? 0.2ECT
^- O.10
0~7 ^^-\ \ i r^^i
-49-
t0
-50-
have found this reaction to be commonly diffusion controlled and to take place
on the time-scale of plume mixing. Thus, the main source and sinks of NO.,
occur on comparable time scales. It is therefore conceivable that the con-
centrations of NO? that occur in a plume may diffuse down to background levels
before sufficient NOp has been produced to affect visibility. Certainly the
travel time (or range) at which visibility impairment will occur will be depen-
dent on the NO-to-NCL conversion rate and the related mixing rate. We may also
postulate that it is the vertical mixing rate that is most important for the
visual impact of the plume because the mixing coefficients in the vertical are
much smaller than those in the horizontal and consequently optical depths along
horizontal views through the plume will be much greater than those along ver-
tical views. A more detailed discussion of this relationship is reserved for
Sec. 3.5.
The conversion rates of NO-to-NO? for the cases where sufficient data were
available for reliable estimates are given in Table 7. The individual, rates
shown in Table 7 are in accord with previous measurements (Davis et al. W^;
Hegg et al. 1977). A regression of the rates shown in Table 7 onto the average
travel time yields a power law dependence of --0.736 (with a correlation coef-
ficient of 0.62) on the average travel time. If the conversion rates were
strictly related to reaction kinetics, then the rate should decrease at the same
rate at which the concentration of NO decreases in the plume. Analysis of the
data in Table 3 shows an average dependence of NO on travel time of -0.552. The
observed higher dependence of the conversion rate suggests diffusion control.
TABLE 7. NO-to-NO^ conversion rates measured in the Chol la plume.
Date______ Travel time interval (hr) Conversion rate (%/hr) Average travel time (min)
October 22, 1980 0.26-2.6 3.9 86
October 23, 1980 0.16-0.8 31.0 29
October 24, 1980 0.6-3.0 4.6 108
October 25, 1980 0.26-1.04 12.8 39
October 26, 1980 0.08-0.25 17.6 10
*The mid-point of each travel time interval for which the conversion rates were ca lcu lated.
-52-
3.5 Optical Depths of the Cholla Plume
Having dealt with factors contributing to visibility impact by the
Cholla plume, it remains to evaluate the effects of the plume on visibility from
the direct airborne measurement of its optical properties. These measurements
consisted of the optical depth of the plume for both particle scattering and
NO,, absorption. The procedure for calculating these properties has been given
in Sec. 2.3.8 and the results of the calculations for the Cholla data are given
in Table 8. It should be noted that while the optical depths for scattering
(T ) and absorption by NO,, (r ) are listed as measured at 550 nm, the nephelo-s ^ ameter we employ actually measured scattering in a band centered at 525 nm with
half-power points of 505 and 550 nm. However, assuming an Angstrom coefficient
of 2, the listed values should be. only about 9% higher than those derivable from
direct measurements at 550 nm. The view path is horizontally through the plume,
perpendicular to the plume axis or the mean wind direction.
The most important point illustrated by the data in Table 8 is that both
particle scattering and NO? absorption contribute importantly to visibility
impact by the Cholla plume. Indeed, if the values of Malm et al. (1980)
for minimum perceptable contrast at 550 nm for both NOp absorption and particle
scattering are translated into optical depths, the resultant value is found to
be 0.025 in both cases. This indicates that both particle scattering and NOp
absorption can affect the perceptibility of the Cholla plume. Furthermore, the
data in Table 8 indicate that these two processes commonly contribute about
equally to visibility impact.
-53-
TABLE 8. Horizonta optica depths across the width of the Chol la plumeat a wavelength of 550 nm for both particle scattering (rand N(L absorption (i-,).c. a
Date Travel Tinie (hr) ^ ^ T^ T^/T^0.035 0.038 0.073 0.48
0.014 0.017 0.031 0.45
0.026 0.025 0.051 0.51
0.016 0.027 0.043 0.37
0.046 0.018 0.064 0.72
0.042 0.019 0.061 0.69
0.072 0.021 0.093 0.77
0.020 0.037 0.057 0.35
0.025 0.029 0.054 0.46
0 0.004 0.004 0
0 0.022 0.022 0
October
October
October
October
October
October
October
October
October
October
October
22,
22,
23,
23,
24,
24,
24,
25,
25,
26,
26,
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
1980
0.
2.
0.
0.
0.6
1.
3.
0.
1.
0.08
0.25
26
6
16
8
5
0
26
04
0.035
0.014
0.026
0.016
0.046
0.042
0.072
0.020
0.025
0
0
-54-
The data in Table 8 show a tendency for the optical depth due to particle
scattering to decrease with travel time compared to the optical depth due to
NCL absorption. Indeed, the only significant increase with travel time of the
optical depth due to particle scattering occurred after considerable travel time
on October 24, 1980 the only date upon which really significant gas-to-
particle conversion of sulfur was measured. This result is in accord with the
findings of Richards et al. (1980) for the Navajo plume. Our data base,
however, is not large enough to allow any firm conclusions to be drawn on this
point.
During the course of the study, a preliminary attempt was made to compare
values of optical depth derived from ’in situ plume measurements with those
derived from telephotometer measurements taken along the flight track of
aircraft through the plume.
Such joint measurements were obtained on October 25, 1980. Optical depths
derived from airborne and telephotometer measurements on this day for five dif-
ferent view paths through the plume are listed in Table 9, and the view paths
are shown in Fig. 19. It can be seen that the total optical depths (T + Td S
derived from the in situ airborne measurements are generally higher than those
derived from the telephotometer data’ ("r ) An explanation for this is found in
the measurement technique of the telephotometer. The telephotometer measures
the difference in light intensity between two lines of sight with a 0.34 dif-
ference in elevation angle. The one line of sight is presumed to be within and
the other outside of the plume. The different intensities then yield the opti-
cal depth attributable to the plume.
-55-
TABLE 9. Optica depths (-r) at a wavelength of 550 nm through theChol la plume on October 25, 1980 deri ved from in situmeasurements of particles (re) and N0^ (i-g) ancTfromtelephotometer measurements (T along the fl ightpath of the ai rcraft.
View Path 1-3 Tg Tg + -r^ ^1 0.016 0 0.0 16
2 0.010 0.028 0.038
3 0.025 0.031 0.056
4 0.066 0.037 0.103
5 0.026 0.027 0.053
Mean of data 0.029+/-0.022 0.025+/-0.014 0.054+/-0.036
0.01
0.085
0.013
0
0.005
0.023+/-0.035
SANFRANCISCOPEAKS(VIEWS6 ond 9)
CHOLLA POWERPLANT
OBSERVER
Figure 19. View paths for the telephotometer measurements made on October 25 1980.
-57-
However, given the range of the telephotometer from the plume centerline
(10.4 6.9 km, depending upon the aircraft flight path) the 0.34 elevation
difference yields view paths separated in the plume by only 41 to 62 meters.
Our measurements in the plume suggest plume fluctuations over this scale were
taking place. Therefore, both the telephotometer viewing paths could have been
through the plume, albeit through different parts of it. The optical depths
derived from the telephotometer are therefore only partial plume optical depths
and should therefore be lower than those derived from the in situ measurements.
A definitive comparison between telephotometer and in situ measurements of opti-
cal depths must therefore await further study.
-58-
SECTION 4
RESULTS FROM THE PHOENIX MODEL
4.1 Model Validation
The first step in the validation of the PHOENIX plume model is to check if
the model predictions of particle and gas concentrations in the Cholla plume are
in reasonable agreement with the measurements. The case study of October 24,
1980 provides data to do this.
Figure 20 shows a cross-section of the plume along the centerline and
parallel to the plume axis. Shown are the concentrations of 0.025 urn (Fig. 20a)
and 0.55 urn (Fig. 20b) diameter particles in the plume in excess of those in the
ambient air. Figure 21 shows the corresponding concentrations predicted by the
PHOENIX plume model. The model results are in good agreement with the
measurements, generally showing the same surplus (positive values) and deficits
(negative values) compared to ambient values as indicated by the measurements.
For example, a region of below-ambient concentrations of 0.024 pm particles
is both predicted by the model and observed in the data, although the model
predicts the deficit to occur somewhat closer to the stack than was observed.
The deficit is due to insufficient formation of particles below 0.025 urn to
offset loss of this size particle via coagulation with larger particles.
The concentrations of SOp and 0-, predicted by the PHOENIX model were also
found to be in good agreement with the data. However, because the measured
levels of NO were rather low on October 24, a definitive comparison between
the data and model predictions of NO was not possible. However, on the
basis of measurements made on the following day, October 25, 1980, and
PHOENIX predictions for this day, we judge that the PHOENIX model could be_
-59-
2200h
2000
\QOO\-JO
5 10 15 20DISTANCE FROM STACK (KM)
( a )
2200
2000
800
5 10 15 20
DISTANCE FROM STACK (KM )( b )
Figure 20. Measured excess concentrations (dN/dlog) above ambient val ues of
particles in the plume from the Cholla power plant on October 24, 1980. (a)0 -3
Particles 0.024 pir. in equivalent diameter (in units of 10 cm (b) Particles
0.55 pm in equivalent diameter (in units of 10 cm )
"liToo"
a0.0
a-4.9
a-4.8
a-5.7
ID-8.2
n-11.2
n0.0
00.0
a-4.4
a-4.6
a-5.5
a-7.7
a-10.2
a0.0
a0.0
-2
a-4.0
a-4.1
a-5.1
a-7.0
0-8.5
a0.0
-2
5. 00 20. 00 25. 00 30. 00 35. 0010. 00 40. 00D I STRNCE FROM STRCK (KM)
( a )Figure 21. Excess concentrations (dN/dlogD) above ambient values of particles in the plume fromChol la power plant on October 24, 1980 as provided by the PHOENIX model (aj Particles 0,024 pm inequivalent diameter (in units of 102 cm-3) (b). Particles 0.55 pm in equivalent diameter (in units of
Am*10 cm’ )--see next page,
no.o
no.o
ID0.0
ID0.0
n0.0
ao.o
ao.u
a0.5
a0.4
ID0.4
a0.7
n0.8
D0.8
a0.7
a0.0
ID0.6
a0.7
a0.7
ID0.6
a0.0
ID0.0
ego.o
5. 00 10. 00 liToO 20. 00 25. 00 30. 00D I STRNCE FROM STRCK (KM)
( b )
Figure 21. (Continued)
-62-
underpredicting NO? concentrations by a factor ranging from 2 to 5. This should
be kept in mind when assessing PHOENIX model predictions of the relative contributions
of NO? and particles to visibility impact by the Cholla plume.
Turning to validation of the visibility section of the PHOENIX model, we
first consider results for the case of October 24, 1980 for which particle and
gas measurements and model predictions have just been compared.
Nine telephotometer measurements were made along the line of sight of the
flight tracks on October 24. The viewing paths are shown in Fig. 22 and they
are listed in Table 10. These viewing paths were fixed, and monitored by
Arizona Public Service Co. personnel, regardless of the plume trajectory, in
order to provide time-series data on visibility near the Cholla plant.
Unfortunately, both the wind data and aircraft measurements of particles and
gases indicate that the plume did not intersect any of the viewing paths on
October 24 while we were sampling the plume (though it may have intersected
them at other times). Model-data comparisons for this date are therefore
restricted to ambient air situations. A comparison between the observed and
predicted target and sky intensities, as viewed along the paths listed in Table
10, is given in Table 11 It can be seen that both the target and sky inten-
sities are overestimated by the model, the latter by an average factor of 3.7.
The precise difference between calculated and measured target intensities is
difficult to estimate because of the uncertainty in the reflectivity of the
targets viewed. Because of this uncertainty, calculated intensities are listed
in Table 11 for two assumed target reflectivities, R=0 and 0.5. The percentage
difference in the calculated intensities for the two reflectivities seems to
vary more at the longer wavelengths possibly indicating that the reflectivity of
the target was strongly wavelength dependent. With respect to visibility, it is
the target-to-sky intensity ratio that is of prime importance. We now turn to
an examination of this ratio.
MONTEZUMA’S CHAIR(VIEWS 1,4,5,8)
CHOLLA POWER PLANT
^OBSERVER
0 20 KMCENTER LINEOF PLUME FROMTHE CHOLLA ^PLANT
Figure 22. Plan view of geometry for the line-of-sight telephotometer measurement takenon October 24, 1980.
-64-
TABLE 10. View paths for telephotometer readings on October 24, 1980.None of the view paths measured intersected the plumeaccording to aircraft measurements. The observation pointwas 6.4 km due south of the Cholla plant.
View Time of ObjectObservation Viewed(local)
ScatteringAngle (deg)
1332
1335
3
4
5
6
7
8
1431
1437
1530
1535
1656
1700
Montezuma’s 101Chair (MC)
San Francisco 79Peaks (SF)
SF 66
MC 94
MC 89
SF 53
SF 33
MC 77
This parameter, which is essentially the angle between the path of the light
impinging on the plume from the sun and the path along which this light is
scattered, is necessary to obtain light intensities from the PHOENIX model at
the selected observation points. It was obtained from the calculated zenith
angle, the position of the plume, and the relative position of the observation
point.
-65-0
TABLE 11. Comparisons for October 24, 1980 of intensities (in units of pM cm per100A) of targets (San Francisco Peaks or Montezuma ’s Chair) and the skyfor the view paths (1 through 8) shown in Fi g. 22. The ca lcu latedva lues are those from the PHOENIX plume model and the measured valuesare from the telephotometer. Ca lcu lated va lues are given for two assumedreflectivities (R) of the targets. The surface of the earth is assumedto have an albedo of 0.3.
View
10.450.55
2
0.550.65
3
40.450.550.65
50.45
0.65
60.450.550.65
70.450.550.65
80.45
Wavelengths(um)
0.40
0.65
0.400.45
0.400.450.550.65
0.40
0.40
0.55
0.40
0.40
0.40
0.550.65
Ca lciR=0
162.1151.459.329.2
410.4463.5225.9123.0
394.5453.0225.7124.7
144.2135.453.525.3
124.7118.647.023.4
372.0441.4230.4130.9
315.3411.8243.2149.4
87.888.336.518.9
TARGET INTElatedR=0.5
311.3365.6221.7175.4
428.6499.9250.0143.4
411.5486.9248.6144.1
251.2278.3144.9104.7
198.1204.883.148.0
387.2472.1251.5148.9
327.7437.4261.4165.0
154.7159.067.140.1
NSITYMeasured Ca lcu lated
122.0160.6124.075.9
103.9138.6127.078.8
111.9153.6146.283.9
100.2126.3105.657.5
85.9110.490.646.8
106.5155.0155.397.0
43.686.0124.087.6
23.536.738.521.8
SKY IN
488.9662.5458.5346.3
491. 7667.3453.4341.5
482.3665.3461.0349.6
446.5609.8422.4317.5
398.3550.9383.4288.6
465.9663.5479.0371.4
404.2633.2515.0437.9
293.1430.2311.9242.8
TENSITYMeasured
135.4183.5171.2100.4
106.5144.5140.585.30
112.7158.5155.091.0
112.3156.5151.789.0
97.2140.1136.378.4
109.8162.6168.599.7
44.891.0
134.889.8
28.049.063.540.0
-66-
Table 12 lists the calculated and measured sky-to-target ratios for the view
paths already discussed. The targets are assumed to have uniform reflectivities
of 0.5. It can be seen that the largest percentage difference between the
calculated and measured ratios is 259^, the model overpredicting the observed
intensity ratio. Once again the discrepancy is largest for the longer
wavelengths.
The calculated and observed ratios could be brought into fairly good
agreeement by an appropriate choice of a wavelength dependent target
reflectivity. While there are certainly grounds for complicated reflectivity
functions (Bergstrom et al. 1980) for natural objects, we prefer not to add
what is essentially a "correction factor" to the PHOENIX model. Another
possible explanation for the discrepancies between the calculated and measured
S/T ratios lies in the assumption of horizontal homogeneity incorporated into
the PHOENIX model. This assumption is almost certainly unwarranted when view
paths cross complex terrain with high relief, as was the case on October 24.
More detailed measurements (both horizontally and vertically) than were acquired
during this study would be necessary for a truly definitive validation of such a
case.
A second suitable case for detailed comparisons of PHOENIX visibility pre-
dictions and telephotometer measurements is the flight of October 25 during
which in situ plume (and ambient) measurements were made along lines of sight
of the telephotometer. In addition to these direct comparisons between telepho-
tometer data and visibility calculations based on airborne measurements, two views
each of regularly monitored targets were made with the telephotometer during
October 25. Measurements in the ambient air and in the plume were available at
-67-
TABLE 12. Comparisons of PHOENIX model prediction (-’) and telephotoneterS ca
measurements r-i of sky-to-target intensity ratios on October 24,
1980 for the views listed in Table 10.
View
1
2
3
4
5
6
7
8
Wavelength
0.400.450.550.65
0.400.450.550.65
0.400.450.550.65
0.400.450.550.65
0.400.450.550.65
0.400.450.550.60
0.400.450.550.65
0.400.450.550.65
(pm)
1̂.571.812.071.97
1.151.331.812.38
1.171.371.852.42
1.782.192.913.03
2.012.694.616.00
1.201.401.902.49
1.231.451.972.65
2.012.714.656.06
^mea
1.111.221.381.32
1.021.041.111.08
1.011.031.061.08
1.121.241.441.55
1.131.271.521.67
1.031.051.081.03
1.031.061.091.02
1.201.341.651.84
(f)
41.4
50.049.2
12.827.963.1
33.074.5
124.1
76.6102.195.5
77.9111.8203.3259.3
16.533.375.9
142.7
80.7
67.5102.2181.8
ca
(f)
48.4
120.4
15.8
58.9
19.436.8
159.8
229.3
T "ly-loo
nea
-68-
a number of points along the viewing paths to produce futher comparisons between
the PHOENIX model predictions (based on aircraft data) and the telephofcometer
measurements. The geometries for the five telephotometer measurements that were
made (views 1-5) along lines of sight of aircraft tracks and the views (6-9) of the
two ground targets are given in Table 13. (See Fig. 18 for the view paths
between the telephotometer and the two targets observed on October 25.)
We compare first the PHOENIX model predictions and the telephotometer
measurements along the line of sight of the aircraft flight tracks. The pre-
dicted and directly measured light intensities at four wavelengths are shown in
Table 14. All five views were of the clear sky viewed through the width of the
plume. It should be noted that the intensities labeled target are for points
0.34 lower in elevation than those labeled "sky" but that our aircraft measure-
ments indicate that both of the view paths so defined intersected the plume,
though at different points. Thus the "sky"-target ratios, which in principle
should ’determine the optical depth of the plume, actually give only a partial
optical depth of the plume. It can be seen that the intensities for both target
and "sky" calculated from the PHOENIX model are consistently higher than the
measurements. This systematic error most likely arises from the assumption of
horizontal homogeneity in the background air. The ratio of sky-to-target inten-
sities should therefore be relatively free of this error. These ratios are
shown in Table 15 where it can be seen that the percentage difference between
the model-predicted and measured ratios do indeed show little evidence of the
large systematic error shown by the intensities. The largest error shown is
14.7^ and the mean error is 4.4^. Since most of the parameters of interest in
visibility calculation (e.g. optical depth, contrast, discoloraton, etc. ) are
-69-
TABLE 13. Geometry of views along which telephotometer measurementswere made on October 25, 1980. The telephotometer waslocated 6.4 km di rect ly south of the Chol la plant.
View
1
2
3
4
5
6
7
8
9
Time ofobservationloca
0738
0750
0800
0822
0845
0900
0905
1000
1005
Distancescenter lineplume (km)
10.4
9.0
6.9
8.9
10.4
6.9
6.9
San FransicsoPeaks
toof Object
viewed
Sky
Sky
Sky
Sky
Sky
San FranciPeaks
Montezuma’Chai r
Montezuma1Chai r
SCO
s
s
Scatteangle
113
111
92
109
115
132
98
111
122
’ring(deg)
-70-
0
TABLE 14. Comparisons for October 25, 1980 of intensities (in units of uW cm"per 100A) of the targets (San Francisco Peaks or Montezuna’s Chai r)and the "sky" for the line-of-sight view paths (1-5) along aircraft fl ighttracks. The ca lcu lated values are from the PHOENIX plume model and themeasured va lues from the telephotometer. See text for interpretation ofresu lts. The surface of the earth is assumed to have an albedo of 0.3.
View
1
2
3
4
5
Wave-lengths(urn)
0.400.450.550.63
0.400.450.550.63
0.400.450.550.63
0.400.450.550.63
0.400.450.550.63
TAR
Ca lcu lated
146.8216.4191.8171.9
159.5232.2203.2180.6
165.2240.7217.8196.7
192.4271.9231.3201.9
217.1300.9250.3215.6
GET INTENS]
Measured
59.997.2
112.172.1
87.2134.8142.686.3
98.1147.1135.474.3
104.4154.7157.191.37
113.2169.1172.1101.7
[TY
Ratio ofCa lcu latedto Measured
2.452.231.712.38
1.831.721.422.09
1.681.641.612.65
1.841.761.472.21
1.921.771.452.17
S
Calculated
142.7210.6188.8170.3
154.8255.6200.1179.1
163.1237.6215.0195.4
185.7262.7227.4200.1
211.5293.1246.3212.7
KY INTENSIT’
Measured
68.3106.6113.471.7
88.4123.9130.983.2
99.3146.8137.275.2
109.0160.3157.191.7
122.4173.5171.2100.8
/
Ratio ofCa lcu latedto Measured
2.091.981.662.38
1.751.821.532.15
1.641.621.572.60
1.701.641.452.18
1.731.691.442.11
-71-
cTABLE 15. Comparison of PHOENIX model predictions f-~\ and te lephotometer
T ca
Smeasurements r-j of sky-to-target intensity ratios onmea
October 25, 1980 for the views listed in Table 14.
Viewc c
Wavelength (urn) (-’) r-iT cal mea ^c. l- ^e.-100
^,
0.400.450.550.65
0.400.450.550.65
0.400.450.550.65
0.400.450.550.65
0.400.450.550.65