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