p.1 

OAR Box 1811 

Prepped by Keeia Richards 

Document Number: 

39) II-A-20 

Docket Number: 

A-84-22 

Printed 10/30/2008 1:19:24 PM Sheet 39 of 82 
P.2 

dBtt 

United States 

Environmental Protection 

Agency 

Environmental Sciences Research EPA 600 2-80-001 

Laboratory January 1980 

Research Triangle Park NC 27711 

Research and Development 

Comparative 

Study of Plume 

Opacity 

Measurement 

Methods 
P.3 

RESEARCH REPORTING SERIES 

Research reports of the Office of Research and Development, U.S. Environmental 

Protection Agency, have been grouped into nine series. These nine broad categories were established to facilitate further development and application of environmental technology. Elimination of traditional grouping was consciously 

planned to foster technology transfer and a maximum interface in related fields. 

The nine series are: 

1. Environmental Health Effects Research 

2. Environmental Protection Technology 

3. Ecological Research 

4. Environmental Monitoring 

5. Socioeconomic Environmental Studies 

6. Scientific and Technical Assessment Reports (STAR) 

7. Interagency Energy-Environment Research and Development 

8. "Special" Reports 

9. Miscellaneous Reports 

This report has been assigned to the ENVIRONMENTAL PROTECTION TECHNOLOGY series. This series describes research performed to develop and demonstrate instrumentation, equipment, and methodology to repair or prevent environmental degradation from point and non-point sources of pollution. This work 

provides the new or improved technology required for the control and treatment 

of pollution sources to meet environmental quality standards. 

This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161. 
P.4 

EPA-600/2-80-001 

January 1980 

COMPARATIVE STUDY OF PLUME OPACITY MEASUREMENT METHODS 

by 

William D. Conner and Norman White 

Emissions Measurement and Characterization Division 

Environmental Sciences Research Laboratory 

Research Triangle Park, North Carolina 27711 

ENVIRONMENTAL SCIENCES RESEARCH LABORATORY 

OFFICE OF RESEARCH AND DEVELOPMENT 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711 
P.5 

DISCLAIMER 

This report has been reviewed by the Environmental Sciences Research 

Laboratory, U.S. Environmental Protection Agency, and approved for publication. Mention of trade names or commercial products does not constitute 

endorsement or recommendation for use. 

n 
P.6 

ABSTRACT 

The opacities of smoke-stack emissions were measured by three methods at 

thirteen different plants and the results compared. The three opacity measurement methods were trained observer, in-stack transmissometer, and laser 

radar (lidar). The sources consisted of five coal-fired power plants, four 

oil-fired power plants, a Portland cement plant, a paper mill kraft recovery 

furnace, a phosphate fertilizer plant rock dryer, and a small oil-fired 

boiler at a chemical plant. The instrumental methods of lidar and in-stack 

transmissometer correlated better with each other than with the observer 

method and were also more precise than the observer method. The observer 

measurements were generally lower than the instrumental measurements. This 

is evidently due to a variable negative bias and/or low sensitivities associated with the observer method when evaluating plumes under viewing conditions where plume visibility is less than desired for the method. The data 

show that between 10 and 40% opacity (range of opacity emission standards), 

the observer readings averaged 6 and 11% opacity less than the instrumental 

readings of lidar and transmissometer respectively, and varied by as much as 

25% opacity below to 8% opacity above the instrumental readings. 

m 
CONTENTS 

Abstract iii 

Figures vi 

Tables vi 

Acknowledgments vii 

1. Introduction 1 

2. Opacity Measurement Methods 2 

Trained observer 2 

In-stack transmissometers 2 

Lidar 3 

3. Source and Test Descriptions 10 

Coal-fired power plants 12 

Oil-fired power plants 13 

Oil-fired boiler 0 15 

c 

Portland cement plant P 16 

Paper mill K 16 

Phosphate plant R . . . 16 

4. Results 18 

Lidar and transmissometer comparison 18 

Observer and lidar comparison 18 

Observer and transmissometer comparison 22 

5. Discussion 23 

References 26 
P.8 

FIGURES 

Number Page 

1 Mobile lidar system 5 

2 Comparison of transmissometer and lidar measured opacities 

of screen targets . . . ' 7 

3 Plume opacity measurements by lidar versus plume opacity 

measurements by in-stack transmissometers 19 

4 Plume opacity measurements by trained observers versus 

plume opacity measurements by lidar . 20 

5 Plume opacity measurements by trained observers versus 

plume opacity measurements by in-stack transmissometers 21 

6 Linear regression relationships between plume opacity 

measurements by trained observers and in-stack transmissometer at a coal-fired power plant for different 

environmental conditions 24 

TABLES 

Number Page 

1 Mobile Lidar System Characteristics 6 

2 Concurrent Opacity Measurements by Different Methods at 

Various Plants 11 

vi 
P.9 

ACKNOWLEDGMENTS 

We wish to express our appreciation to the personnel at EPA's Region IV 

and National Enforcement Investigation Center (NEIC) for assistance in the 

selection of test sites, and to the plant personnel at the various test sites 

for assistance with the tests. We also wish to express our appreciation to 

Evelyn Adams, Dr. Edward Mangold, and Pat Thompson of NEIC, to Wayne Aronson 

of Region IV, and to Bruce McElhoe of Northrop Services for their assistance 

with various parts of the study. 

v n 
P.10 

SECTION 1 

INTRODUCTION 

Particulate emissions from stationary sources must generally meet opacity 

as well as mass standards. The opacity standards are established primarily 

because they are much easier to measure than the mass standards and can be 

monitored by control agencies and plant operators to determine whether the 

emission controls required to meet the mass standard are operating properly (1) 

For this application of dual standards, the opacity standards established by 

the U. S. Environmental Protection Agency (EPA) are set less stringent than 

the mass standards so that a violation of the opacity standard will be a 

clear indication of a decline in the efficiency of the control equipment and 

a violation of the mass standards (2). 

The opacity of an emission is defined in the Federal Register as a 

measure of the degree to which the emission reduces the transmission of light 

and obscures the view of an object in the background (3). Consequently, the 

percent opacity of a plume is determined directly by measuring its percent 

transmittance and subtracting from 100%. This paper describes a comparative 

study of three methods of measuring the opacity of smoke-stack plumes: 

trained observer, in-stack transmissometer, and laser radar (lidar). The 

comparisons are of concurrently obtained measurements that were made under 

field conditions at a variety of emission sources. 
P.11 

SECTION 2 

OPACITY MEASUREMENT METHODS 

TRAINED OBSERVER 

The trained observer is the method generally used by control agencies 

for evaluating the opacity of source emissions, and it is the opacity compliance test method used by EPA (2). The observers are trained at smoke inspector training schools to evaluate opacities of training plumes with prescribed 

accuracies relative to transmissometer measurement of their opacities. Upon 

passing the course, they become certified by the school as capable of evaluating the opacities of smoke plumes by visual inspection. When inspecting a 

plume the method requires that the observer stand (a) at a distance from the 

plume sufficient to provide a clear view of the emissions, (b) with his line 

of vision approximately perpendicular to the plume direction, and (c) with 

the sun oriented in the quadrant to his back. The method also requires that 

readings be made by observing the plume momentarily at 15 sec intervals over 

a 6 min period and at the point of greatest opacity. The average of these 24 

readings is the observer opacity evaluation of the plume. All of the viewing 

constraints were used for this study except that the readings were always 

made on the plume approximately 0.5 stack diameter above the stack exit; 

also, observer evaluations are not averages of 24 readings. They are usually 

averages of more than 24 readings taken over periods longer than 6 min which 

coincided with or overlapped the lidar measurement periods. Four different 

observers were used during the study. 

IN-STACK TRANSMISSOMETERS 

In-stack transmissometers are often used to monitor the opacity of stack 

effluents; their installation is required on some sources by local control 

agencies and EPA. Design and performance specifications for such 
P.12 

transmissometers have been promulgated by EPA (4). The in-stack opacity data 

for sampling ports when plant transmissometers were not available. The plant 

transmissometers were all Lear Siegler* model RM4 instruments. The portable 

transmissometer was a Lear Siegler model RM41P. All transmissometer opacity 

data are transmissometer was a Lear Siegler model RM41P. All transmissometer 

opacity data are for pathlengths equal to the stack exit diameter of the 

source being measured. When the transmissometer pathlength was different 

than the stack exit diameter, their opacity measurement was adjusted to 

represent the opacity of the effluent for a pathlength equal the stack exit 

diameter as required for monitoring opacity by transmissometer (4). 

The RM4 transmissometer was designed and developed in Germany by the 

Irwin Sick Company to meet the requirements of the German pollution regulatory agency for in-stack particulate monitoring. With modification of the 

spectral response to meet EPA specifications, the instrument was marketed in 

the United States by Lear Siegler, Inc. for in-stack opacity monitoring. A 

detailed description of the RM4 has been published by Beutner (5). The RM4 

has subsequently been replaced by a new model RM41 transmissometer. 

The RM41P portable transmissometer is basically the RM41 equipped with a 

probe that is inserted into a standard 10.16 cm (4 inch) stack sampling port 

for the opacity measurement. The probe is a stainless steel tube with a 

diameter of 7.6 cm and an overall length of 1.5 m through which light is 

projected to a small (1.3 cm) retroreflector at the end where it is reflected 

back to the RM41 transceiver. A slot (1 m by 5.1 cm) in the tube allows the 

effluent to flow through the beam when inserted into the stack. The reflector 

and transceiver are protected from the effluent by a clean air purge. For 

detailed descriptions of the RM41 and RM41P transmissometers, the manufacturer's literature is recommended (6). 

LIDAR 

|he lidar evaluation of plume opacity is made by beaming a short pulse 

of laser light through the plume and measuring the amount of light back-

* 

Mention of trade names or commercial products does not constitute endorsement 

or recommendation for use by the U.S. Environmental Protection Agency. 
P.13 

scattered from the pulse by the atmosphere in back of the plume relative to 

the amount scattered by the atmosphere in front of the plume. This ratio is 

a measure of the two way transmittance (T ) of the laser light through the 

plume. The opacity of the plume is (1 - T) . The method was first proposed 

and demonstrated by the Stanford Research Institute (7). The van mounted 

lidar used for this study was designed and developed for EPA by the General 

Electric Company specifically for plume opacity measurements. The lidar is 

shown in Figure 1. Its design and operational characteristics are shown in 

Table 1. For a complete description of the lidar system and its operation, 

the reports on its development are recommended (8,9). 

The accuracy of the lidar has been evaluated at various times by making 

remote measurements on a series of neutral density screen targets of known 

opacities(9). The screen targets are 1 m in diameter, and their opacities 

are known from laboratory calibration measurements with conventional transmissometers. The laboratory transmissometers met the EPA design requirements 

for monitoring opacity (4) and were checked for accuracy with neutral density 

optical filters. For the remote measurements the targets are usually located 

approximately 200 m from the lidar. Figure 2 shows a series of measurements 

made on targets of 24-, 32-, 43-, and 52-% opacity just prior to the study. 

These measurements and the earlier tests indicate that the accuracy of the 

lidar is within 3% opacity for opacities under 50%. 

Since the lidar uses a ruby (red light) laser and the opacity standards 

are for green light obscuration, it is necessary to correct the red light 

lidar measurements to values that would be obtained for green light when the 

measurements are made on emissions with predominantly submicrometer particle 

sizes. The correction is not needed if the emissions are composed of particles with mean sizes several micrometers or greater in size; however, for 

very small submicrometer size particulate emissions, the red light opacity 

measurement may be as much as 50% lower. No wavelength correction was o, 

required for the other methods since the training of the visible emission 

observer and the spectral response requirements for the in-stack transmissometers are for photopic or green light. 
cn 

Figure 1. Mobile lida r system 
TABLE 1. MOBILE 

Component 

Transmitter 

Laser 

Wavelength 

Pulse Width (FWHH) 

Maximum Output 

Repetition Rate 

Cooling 

Objective lens 

Beam Divergence 

Receiver 

Objective Lens 

Field-of-view 

Bandpass (FWHH) . 

Photomultiplier 

Off-gating 

Response 

LIDAR SYSTEM CHARACTERISTICS 

Characteristic 

Rotating prism, Q-switched ruby 

694.3 nm 

<30 ns 

1.0 j 

3 pulses per minute 

Deionized wager 

12.7 cm, f/5 

^0.5 mrad full angle 

15.25 cm, f/b 

4 mrad full angle 

1.2 nm 

IT&T F4084 (modified S-20) 

>60 dB 

^100 ns 

P.15 
P.16 

60 

( ) NUMBER OF MEASUREMENTS 

MEAN VALUE OF MEASUREMENTS 

AND 95% CONFIDENCE INTERVAL 

n. 

< 

a. 

a 

a 

V) 

< 

S 

oc 

< 

a 

10 20 30 40 50 

TRANSMISSOMETER MEASURED OPACITY, percent 

60 

Figure 2. Comparison of transmissometer and 

lidar measured opacities of screen targets. 
P.17 

The opacity-wavelength characteristics of the submicrometer emissions 

were measured with dual-wavelength sun photometers. The sun photometer 

method of determining plume opacity requires measurement of the relative 

intensity of the sun when viewed beside and through the plume with the 

photometer. Clearly, this procedure requires that the sun not be obstructed 

by clouds and that the shadow of the plume be in an accessible location. For 

accurate opacity measurements, it also requires that the sun be viewed through 

a defined cross section of the plume. However, for this study where only 

relative measurements were required, two sun photometers operating at different 

wavelengths were coupled and operated together as a unit to obtain concurrent 

opacity-wavelength measurements; consequently, a well-defined plume cross 

section was not necessary. 

To correct the lidar measurements, it is first necessary to calculate 

the extinction coefficient ratio Q(green)/Q(red) from green and red light sun 

photometer opacity measurements. It follows from Bouguer's law (10), that 

the Q(green)/Q(red) ratio is equal to the ratio of log (1-green light opacity) 

to log (1-red light opacity). The corrected lidar opacity (0G) is then 

calculated from the measured lidar opacity (0R) and the Q(green)/Q(red) ratio 

with the equation: 

0G=1 - (1 . o R )

Q ( 9reen)/Q(red) . 

Additional information on dual wavelength sun photometer instrumentation, and 

its application to extinction-wavelength ratio measurements of plumes can be 

found in reference (10). 

In this study, only the lidar measurements on the oil-fired power plants 

and boiler emissions required wavelength corrections. Sun photometer measurements were made at all of the oil-fired power plants. The Q(green)/Q(red) 

ratio of the emissions varied from 1.5 at two of the plants to 2.0 at the 

other two plants. At the oil-fired boiler, sun photometer measurements were 

not obtained due to overcast sky conditions and a Q(green)/Q(red) average 

value estimate of 1.75 from the oil-fired power plant measurements was used 

to correct the lidar measurements. Sun photometer measurements at the other 
P.18_ 

sources or particle size data on similar sources showed that the particle 

sizes were large and wavelength correction of the lidar measurements was not 

necessary. 
P.19 

SECTION 3 

SOURCE AND TEST DESCRIPTIONS 

Plume opacity measurements were made at thirteen different plants: five 

coal-fired power plants, four oil-fired power plants, a portland cement 

plant, a kraft recovery furnace at a paper mill, a rock dryer at a phosphate 

fertilizer plant, and a small oil-fired boiler at a chemical plant. The 

plants were generally located in the Southeastern United States. Plant 

selection was based primarily on the availability of in-stack monitoring data 

from plant-owned transmissometers or on the availability of sampling ports 

for installation of the portable transmissometer to obtain the in-stack 

opacity data. At seven of the plants, concurrent opacity measurements were 

obtained with all three methods. Opacity measurements were obtained with the 

observer method at all plants. However, no opacity measurements were obtained 

with the in-stack transmissometer method at four of the plants; no opacity 

measurements were obtained with the lidar method at one of the plants; 

and no concurrent opacity measurements with the observer and lidar methods 

were obtained at one of the plants. At four of the coal-fired power plants 

and at the phosphate plant rock dryer, measurements were made at two different 

opacity levels. The higher opacity levels were obtained by turning off 

sections of the electrostatic particulate emission control equipment. Two 

sets of measurements were made on consecutive days at one of the oil-fired 

power plants. Table 2 is a list of each concurrent opacity measurement set, 

the type of plant studied, and the types of opacity measurements made for 

each measurement set. 

10 
TABLE 2. CONCURRENT OPACITY MEASUREMENTS BY DIFFERENT METHODS AT VARIOUS PLANTS 

Plant 

Symbol Type Time 

Lidar 

„b 

Transmissometer 

N Opacity , % Type Opacity Ob. Time 

Observer 

m N Opacity , % 

Coal-fired power plant No. 1 

Coal-fired power plant No. 1 

Coal-fired power plant No. 2 

Coal-fired power plant No. 3 

Coal-fired power plant No. 3 

Coal-fired power plant No. 4 

Coal-fired power plant No. 4 

Coal-fired power plant No. 5 

Coal-fired power plant No. 5 

Oil-fired power plant No. 1 

Oil-fired power plant No. 1 

Oil-fired power plant No. 2 

Oil-fired power plant No. 3 

Oil-fired power plant No. 4 

Oil-fired boiler (chemical plant) 

Portland cement plant 

Paper mill (kraft recovery furnace) 

Phosphate plant (rock dryer) 

Phosphate plant (rock dryer) 

Phosphate plant (rock dryer) 

16 

12 

18 

11 

17 

30 

20 

--

— 

9 

13 

23 

17 

13 

17 

10 

18 

5 

— 

--

10 

14 

15 

15 

25 

19 

22 

--

--

11 

10 

29 

16 

16 

9 

13 

11 

6 

~ 

— 

9±4 

11±5 

53±2 

9±2 

22+1 

28±3 

58±3 

— 

— 

23±4 

31±4 

10±4 

8±3 

10±2 

11±4 

10±4 

5±2 

46±2 

— 

--

— 

— 

'--

S 

S 

S 

s 

s 

s 

p 

p 

--

p 

p 

--

s 

p 

p 

p 

p 

— 

~ 

— 

5±1 

18+3 

36±2 

58±7 

13±1 

25±2 

199±2 

209+2 

— 

7±2 

3+1 

--

14+3 

4±0 

34+5 

28±4 

57±5 

A/B 

A/B 

A/B 

A/B 

A/B 

C 

C 

D 

D 

D * 

D 

C 

C 

D 

A 

C/D 

C 

--

C/D 

C/D 

16/16 

12/12 

18/18 

11/11 

17/17 

15 

20 

30 

30/30 

34 

22 

28 

23 

21 

17 ' 

31/10 

22 

— 

17/17 

18/16 

14/14 

14/14 

14/14 

15/15 

25/25 

60 

84 

121 

121/121 

136 

88 

110 

90 

85 

10 

124/38 

88 

--

68/68 

72/64 

0/0 

0/0 

35+4/33±2 

0/0 

0/0 

30+2 

82±3 

6±0 

25+l/33±l 

27±T 

30±1 

17+1 

7±1 

6±1 

0 

7+l/5+lh 

4±1 

--

10±l/9±lh 

32+1/33+2 

Test period 

Number of opacity measurements during test period 

"Mean + 95% confidence interval of opacity measurements 

n 

S = Lear Siegler RM4 across-stack transmissometer 

P = Lear Siegler RM41P portable transmissometer 

eMean opacity ± opacity range (estimated by visual inspection of chart) 

Specific observers are designated A, B, C, and D 

9Transmissometer data not used (see text) 

H Average of the two evaluations used for data analyses 
P.21 

COAL-FIRED POWER PLANTS 

The generating capacities of units tested at the five coal-fired power 

plants ranged from 150 to 680 megawatts. They all burned pulverized coal 

from southern Appalachia, northwestern Kentucky, or Ohio, and they all had 

electrostatic particulate emission control equipment. 

Coal-fired Power Plant C, 

At this power plant, emissions were measured from two 150-MW units. The 

emissions from each unit were emitted through separate 61 m high by 3.7 m 

exit diameter stacks. No in-stack transmissometer data were obtained at the 

plant. Lidar and observer plume opacity measurements of the emissions were 

made from a common location 300 and 360 m from the respective plumes. Atmospheric conditions for the lidar measurements were fair. Conditions for the 

observer measurements were poor. The sky was overcast and the plumes were 

not visible. 

Coal-fired Power Plant Co 

At this power plant, emissions were measured from a 680-MW unit. The 

emissions were emitted through an 85 m high by 4.6 m exit diameter stack. No 

in-stack tramsmissometer data were obtained at the plant. Lidar and observer 

plume opacity measurements were made from a common location 350 m northeast 

of the plume. Atmospheric conditions for the lidar measurements were good. 

Conditions for the observer measurements were poor. The plume background was 

a bright hazy sky which reduced plume visibility and made the observer 

measurements difficult. 

Coal-fired Power Plant C3 

At this power plant, emissions were measured from a 150-MW unit. The 

emissions were emitted through a 25 m high by 2.7 m diameter stack on the 

roof of the plant. A velocity cone at the top of the stack abruptly reduced 

the stack to an exit diameter of 1.9 m. The top of the stack was 66 m above 

ground. An LSI RM4 transmissometer was located in the stack approximately 2 

m above the plant roof for monitoring opacity. Lidar and observer plume 

12 
opacity measurements of emissions were made from a common location 340 m west 

of the plume. Measurements were made at two emission levels. Atmospheric 

conditions for the lidar measurements were very good. Conditions for the 

observer measurements were poor. The plume background was a bright hazy sky 

which made the plumes not visible to the observer. 

Coal-fired Power Plant C^ 

At this power plant, emissions were measured from a 154-MW unit. The 

emissions were emitted through a 91 m high by 4.4 m exit diameter stack. An 

LSI RM4 was located in the stack at approximately the 46 m level. Lidar and 

observer plume opacity measurements were made from different positions 300 m 

north and 200 m southwest of the plume, respectively. Measurements were made 

at two emission levels. Atmospheric conditions for the lidar measurements 

were good. Conditions for the observer measurements were fair. The observer 

was viewing the plume against a partly cloudy background. 

Coal-fired Power Plant C,-

At this power plant, emissions were measured from a 300-MW unit. The 

emissions were emitted through a 178 m high by 4.7 m exit diameter stack. An 

LSI RM4 transmissometer was located in the stack at the 54 m level. No lidar 

data were obtained at this plant because the lidar equipment was not available at the time. Observer plume opacity measurements were made from a 

location 340 m east of the plume. Measurement conditions for the observer 

were fair. The background varied from partly cloudy blue sky at the low 

emission level to high scattered clouds and light haze at the high emission 

level. 

OIL-FIRED POWER PLANTS 

The generating capacities of the units tested at the four oil-fired 

power plants ranged from 70 to 520 MW. They all burned residual fuel oil 

with an additive to inhibit corrosion. None had emission control equipment. 

13 
P.23 

Oil-fired Power Plant 0, 

At this power plant, emissions were measured from a large 520-MW capacity boiler burning high sulfur {^ 2.5% by' weight) residual fuel oil. The 

emissions were emitted through a 153 m high by 5.2 m exit diameter stack 

that was breeched with a long horizontal duct (4.3 m wide by 8.4 m high by 51 

m long). The LSI RM41P portable transmissometer was installed near the 

middle of the duct 160 m from the stack exit. Lidar and observer plume 

opacity measurements were made from a common location 375 m south of the 

plume. Measurements were made on two consecutive days near noon with the 

plant operating at normal full load conditions. Atmospheric conditions for 

the lidar measurements were good both days. Conditions for the observer 

measurements were fair to good. The sky background varied from hazy with 

broken clouds the first day to blue with broken clouds the second day. 

The in-stack opacity data obtained at this plant clearly did not correlate with the plume opacity measurements and were not used. The measurements showed that the opacity of the plume was much higher than in-stack, 

indicating that the plume opacity is largely due to an interaction between 

the effluent and the atmosphere and cannot be monitored by a transmissometer 

in the stack. This condition was apparently due to the high sulfur content 

of the fuel oil burned at the plant, which resulted in the condensation and 

hydration of sulfuric acid. More extensive measurements at this plant made 

over a range of plant operating conditions support this observation and also 

show an increase in opacity of the plume with distance from the stack exit 

(11). The condition was not observed at any of the other plants. The lidar 

and observer plume opacity measurement data are used for this correlation 

study since they were made on the plume at the same point. 

Oil-fired Power Plant OQ 

At this power plant, emissions were measured from a 380-MW unit that was 

burning a mixture of 20% gas and 80% medium sulfur [% 1.5% by weight) residual fuel oil. The emissions were emitted through a 106 m high by 4.6 m exit 

diameter stack. No in-stack transmissometer opacity data were obtained at 

this plant. Lidar and observer plume opacity measurements were made from a 

14 
common location 315 m southwest of the plume. Atmospheric conditions for the 

lidar measurements were good. Conditions for the observer measurements were 

good. The. plume was viewed against a clear blue sky. 

Oil-fired Power Plant Oo 

At this power plant, emissions were measured from a small 70-MW unit 

that was burning a medium sulfur (^ 1.5% by weight) residual fuel oil. The 

emissions were emitted to the atmosphere through a 45.6 m high by 3.3 m exit 

diameter stack. The in-stack opacity was measured with the LSI RM41P portable transmissometer that was installed in the stack 3 m from the stack exit. 

Lidar plume opacity measurements were made from a location 320 m east of the 

plume and observer plume opacity measurements were made from a location 152 m 

southwest of the plume. Atmospheric conditions for the lidar measurements 

were fair. Conditions for the observer measurements were good. The observer 

evaluation of the plume was made against a blue sky background. 

Oil-fired Power Plant 0. 

At this power plant, emissions were measured from a 190-MW unit burning 

a medium sulfur (^ 1.1% by weight) residual fuel oil. The emissions were 

emitted through a 60 m high by 3 m exit diameter stack. The in-stack opacity 

was measured with the LSI RM41P portable transmissometer, that was installed 

in the stack approximately 30 m from the stack exit. Lidar and observer 

plume opacity measurements were made from a common location 260 m southwest 

of the plume. Atmospheric conditions for the lidar measurements were poor. 

Conditions for the observer measurements were good. Observer evaluations 

were made against a blue sky background. 

OIL-FIRED BOILER 0C 

This source was a small oil-fired industrial boiler at a chemical plant. 

The emissions were emitted through a 53 m high by 3.7 m exit diameter stack. 

No in-stack transmissometer data were obtained at the plant. Lidar and 

observer measurements were made from a common location 280 m from the plume. 

15 
P.25 

Atmospheric conditions for the lidar measurements were fair. Conditions for 

the observer measurements were poor. The plume was viewed against an overcast sky, and was not visible except for occasional puffs that were not 

measured. 

PORTLAND CEMENT PLANT P 

At this source, emissions were measured from a wet process rotary cement 

kiln. The emissions were emitted through a 76 m high by 4.6 m exit diameter 

stack. Particulate emissions were controlled with electrostatic precipitators, 

The LSI RM41P portable transmissometer was installed in the stack breeching 

15 m from the bottom of the stack for in-stack opacity measurement. Lidar 

and observer plume opacity measurements were made from different positions 

240 m southeast of the plume and 150 m west of the plume, respectively. 

Atmospheric conditions for the lidar measurements were good. Conditions for 

the observer measurements were good. Conditions for the observer measurements were fair. The observer evaluations were made while viewing the plume 

against a clear blue sky; however, the data were taken late in the day near 

sunset, which may have made the plume difficult to read. 

PAPER MILL K 

At this source, emissions were measured from the kraft recovery furnace 

at a paper mill. The emissions were emitted through a 93 m high by 2.8 m 

exit diameter stack. Particulate emissions were controlled with electrostatic precipitators. An LSI RM4 transmissometer was located in the stack 

approximately 5 m from the stack exit. Lidar and observer plume opacity 

measurements were made from a common location 700 m southeast of the plume. 

Conditions for the lidar and observer measurements were good. Observer 

evaluation of ^he plume was made against a clear blue sky background. 

PHOSPHATE PLANT R 

At this source, emissions were measured from a phosphate fertilizer 

plant (rock dryer). The emissions were emitted through a 25 m high by 2 m 

exit diameter stack. Particulate emissions were controlled with 

16 
P.26 

electrostatic precipitators. The LSI RM41P portable transmissometer was 

installed in the stack approximately 2 m from the stack exit for in-stack 

opacity measurements. Lidar and observer plume opacity measurements were 

made from different positions 246 m southeast and 120 m west of the plume, 

respectively. Atmospheric conditions for the lidar measurements went from 

fair to impossible. After obtaining one series of lidar measurements, a 

conveyor upwind of the stack was put into operation and interference from 

particulate emissions from the conveyor contaminated the atmosphere around 

the stack and made its scatter too irregular and variable to obtain additional lidar measurements. The observer plume opacity measurements were not 

made concurrent with the lidar measurements but were made at two emission 

levels. Conditions for the observer measurements were good. The plume was 

evaluated against a clear blue sky. 

. 17 
P.27 

SECTION 4 

RESULTS 

The comparisons between the three opacity measurement methods are shown 

in Figures 3, 4, and 5. The correlation coefficients, linear regression lines 

and their 95% confidence intervals are calculated and shown in the figures. 

The comparisons are of concurrently obtained measurements on relatively 

steady state emissions. Whenever the opacity of a plume was evaluated by 

more than one observer during a test, the evaluations were averaged to give a 

single data point. To prevent measurements from one plant overly affecting a 

comparison, no more than two emission levels were studied or two data points 

generated from any one plant. In analyzing the data, the results for opacities between 10 and 40% are considered most important because they form the 

range of the opacity emission standards. 

LIDAR AND TRANSMISSOMETER COMPARISON 

The best correlation observed was between the lidar and in-stack transmissometer opacity measurement methods (Figure 3). The coefficient of correlation between the methods was 0.95, and the linear regression line was 

within 3% opacity of the ideal one-to-one relationship over the entire range 

of opacities studied. Over the 10 to 40% opacity range, the measurement 

differences between the methods (lidar-transmissometer) ranged from -8 to 

+12% opacity, and the lidar measurements averaged 2.2% opacity higher than 

the in-stack transmissometer measurements. 

OBSERVER AND LIDAR COMPARISON 

The next best correlation was observed between the observer and lidar 

opacity measurement methods (Figure 4). The coefficient of correlation 

between the methods was 0.88. The linear regression line was within ±5% 

opacity of the ideal one-to-one relationship over the entire range of 

18 
P.28 

80 

70 

60 

S 50 

- COAL-FIRED POWER PLANTS 3,4 

- OIL-FIRED POWER PLANTS 3,4 

- PHOSPHATE PLANT, ROCK DRYER* 

- PAPER MILL, KRAFT RECOVERY FURNACE 

-PORTLAND CEMENT PLANT 

IN-STACK TRANSMISSOMETER 

• LSI RM4 

O LSI RM41P 

CORRELATION 

COEFFICIENT=0.95 

C3.C4 

O3.O4 

R 

K 

P 

< 

a 

u 

< 

a. 

O 

ui 

40 

= 30 

20 

10 

10 20 30 40 50 60 

PLUME OPACITY (IN-STACK TRANSMISSOMETER), percent 

Figure 3. Plume opacity measurements by lidar 

versus plume opacity measurements by in-stack 

transmissometers. 

. 19 
P.29 

90 

Cl, C2. C3, C4 - COAL-FIRED POWER PLANTS 

1,2,3,4 

— 01 , O2, O3, O4 - OIL-FIRED POWER PLANTS 

1.2,3,4 

Oc - OIL-FIRED BOILER, 

CHEMICAL PLANT 

K - PAPER MILL, KRAFT 

RECOVERY FURNACE 

P - PORTLAND CEMENT 

PLANT 

CORRELATION 

~COEFFICIENT=0.88 

cc 

UJ 

> • tr 

U l 

CO 

GO 

o 

>-

o 

< 

3 

_ l 

a. 

20 30 40 

PLUME OPACITY (LIDAR), percent 

Figure 4. Plume opacity measurements by 

trained observers versus plume opacity 

measurements by lidar. 

20 
P.30 

> 

OC 

UJ 

tn 

ea 

o 

> 

H 

u 

< 

10 20 30 40 50 

PLUME OPACITY (IN-STACK TRANSMISSOMETER), percent 

Figure 5. Plume opacity measurements by 

trained observers versus plume opacity 

measurements by in-stack transmissometers. 

21 
~ P.31 

opacities studied. Over the 10 to 40% opacity range, the measurement differences between the methods (observer-lidar) ranged from -22 to 7% opacity, and 

the observer measurements averaged 5.9% opacity lower than the lidar 

measurements. 

OBSERVER AND TRANSMISSOMETER COMPARISON 

The correlation observed between the observer and in-stack transmissometer (Figure 5) was similar but slightly below the correlation observed 

above between the observer and lidar. The coefficient of correlation between 

the methods was 0.84. The linear regression line was offset 4 to 6% opacity 

from the ideal one-to-one relationship over the entire range of opacities 

studied. Over the 10 to 40% opacity range, the measurement differences 

between the methods (observer-transmissometer) ranged from -24 to +4% opacity, 

and the observer measurements averaged 11% opacity lower than the in-stack 

transmissometer measurements. 

22 
SECTION 5 

DISCUSSION 

The results of the study show that of the three opacity measurement 

methods studied (lidar, observer, and in-stack transmissometer), the instrumental methods of lidar and in-stack transmissometer correlated best (correlation coefficient 0.95). The observer and lidar correlation was second 

(correlation coefficient 0.88), and the observer and in-stack transmissometer 

correlation was worst (correlation coefficient 0.84). The data also show that 

the observer opacity measurements were generally lower than either the lidar 

or the in-stack transmissometer opacity measurements. 

The lower opacity measurements by the observer method and its relatively 

poor correlation with instrumental methods is to be expected whenever the comparison is of data obtained under a variety of environmental lighting and 

plume background viewing conditions. It is primarily due to the low measurements associated with the observer method when evaluating plumes under less 

than desirable viewing conditions. Low observer opacity measurements relative 

to transmissometer opacity measurements has also been observed by Hamil (12) 

during a series of comparative tests between observers and in-stack transmissometers that were conducted at a coal-fired power plant under different environmental conditions. Their data (Figure 6) show that the low observer measurements were related to the environmental lighting and background viewing 

conditions of the plumes which caused a reduction in sensitivity and/or 

negative bias of the observer method. In Figure 6, a reduction in sensitivity and/or negative bias of the observer method relative to the transmissometer are represented by low slopes (less than 1) and/or negative translations 

of the curves, respectively. Low observer opacity measurements were also 

reported by Hood (13) for a comparative study between the observer and instack transmissometer opacity measurement methods at a kraft recovery furnace. 

23 
P.33 

40 

> 

cc 

UJ 

3 

o 

< 

a. 

o 

UJ 

S 

ENVIRONMENTAL CONDITIONS: 

TEST1. CLOUDY, LOW HAZE 

TEST 2. SOLID OVERCAST 

TEST 3. CLOUDLESS SKY, BRIGHT SUNSHINE 

i 71 

10 20 30 

PLUME OPACITY (IN-STACK TRANSMISSOMETER). percent 

40 

Figure 6. Linear regression relationships between plume opacity measurements by 

trained observers and in-stack transmissometer 

at a .coal-fired power plant for different environmental conditions(12). 

24 
P.34 

A variable negative bias of the observer opacity measurement method is recognized by EPA, and its significance with respect to the enforcement of opacity 

standards by the trained observer (Compliance Test Method 9) is discussed in 

the introduction to the method (2). From the enforcement point of view, it 

is important to note that over the important 10 to 40% opacity range of the 

opacity emission standards, the data show that no observer measurements were 

greater than in-stack transmissometer or lidar measurements by more than 8% 

opacity. 

Although the data reported here have been analyzed statistically to show 

the degree of correlation and linear regression line relationships observed 

between the three measurement methods, the results are based on too little 

data to show much more than trends. More data are needed to completely 

evaluate the methods. It is likely that with more data on the general application of the methods, (a) the degree of correlation and relative accuracy 

indicated for the instrumental methods of lidar and in-stack transmissometer 

will not change significantly, (b) the correlations between the observer and 

the instrumental methods will become similar but remain below the correlation 

observed between the instrumental methods, and (c) the observer measurements 

will continue to be generally lower than the instrumental measurements. 

However, comparisons of the methods at specific sources at specific times may 

show better or worse correlations and accuracies. These differences will be 

related to the specific atmospheric conditions and/or real in-stack and plume 

opacity differences. 

25 
P.35 

REFERENCES 

1. Federal Register Vol. 39, No. 47:9808-98089, March 8, 1974. 

2. Federal Register Vol. 39, No. 219:39872-39875, November 12, 1974. 

3. Federal Register Vol. 36, No. 247:24877, December 23, 1971. 

4. Federal Register Vol. 4D, No. 194:46259-46263, October 6, 1975. 

5. Beutner, H. P. Measurement of Opacity and Particulate Emissions with an 

On-Stack Transmissometer. J. Air Poll. Control Assoc., 24(9):865-871, 

1974. 

6. Lear Siegler, Inc., Englewood, Colorado. 

7. Evans, W. E. Development of Lidar Stack Effluent Opacity Measuring 

System, NTIS PB 233-135/AS, Springfield, Virginia, 1967. 96 pp. 

8. Cook, C. S., G. W. Bethke, and W. D. Conner. Remote Measurement of 

Smoke Plume Transmittance Using Lidar. Appl. Opt., 11(8):1742-1748, 

1972. 

9. Bethke, G. W. Development of Range Squared and Off-Gating Modifications 

for a Lidar System, NTIS PB 228-715, Springfield, Virginia, 1973. 47 pp. 

10. Conner, W. D. and J. R. Hodkinson. Optical Properties and Visual Effects 

of Smoke-Stack Plumes, U.S. Public Health Service Report No. 999-AP-30. 

NTIS PB 174-705, Springfield, Virginia, 1967. 89 pp. 

11. Conner, W. D. A Comparison between In-Stack and Plume Opacity Measurements at Oil-Fired Power Plants, In: Proceedings of the Fourth National 

Conference on Energy and the Environment, Dayton Sect. Am. Inst, of 

Chem. Eng., Dayton, Ohio, 1976. pp. 478-83. 

12. Hamil, H. F., R. E. Thomas, and N. F. Swynnerton. Evaluation and 

Collaborative Study of Method for Visual Determination of Opacity of 

Emissions from Stationary Sources, NTIS PB 257 948/OBA, Springfield, 

Virginia, 1975. 70 pp. 

13. Hood, K. T., and A. L. Caron. The Relationship between Particulate Mass 

Emission Rate and Observed Plume Appearance from Kraft Recovery Furnaces, 

Paper 74-AP-08, presented at PNNIS-APCA Meeting, Boise, Idaho, November 

1974. 

26 
P.36 

TECHNICAL REPORT DATA 

(Please read Instructions on the reverse before completing) 

1. REPORT NO. 

EPA-600/2-80-001 

4. TITLE AND SUBTITLE 

COMPARATIVE STUDY OF PLUME OPACITY MEASUREMENT METHODS 

3. RECIPIENT'S ACCESSION NO. 

5. REPORT DATE 

January 1980 

6. PERFORMING ORGANIZATION CODE 

7. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO. 

W. D. Conner and'N. White 

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO. 

(Same as Block 12) 

1AD712B BA-010 (FY-79) 

11. CONTRACT/GRANT NO. 

12. SPONSORING AGENCY NAME AND ADDRESS 

Environmental Sciences Research Laboratory 

Office of Research and Development 

U.S. Environmental Protection Agency 

Research Triangle Park, N. C. 27711 

13. TYPE OF REPORT AND PERIOD COVERED 

RTP, NC In-house 

14. SPONSORING AGENCY CODE 

EPA/600/09 

15. SUPPLEMENTARY NOTES 

16. ABSTRACT 

The opacity of smoke-stack emissions was measured by three methods at thirteen 

different plants and the results compared. The three opacity measurement methods are 

trained observer, in-stack transmissometer, and laser radar (lidar). The instrumental 

methods, lidar and in-stack transmissometer, correlated better with each other than 

with the observer method and were also more precise than the observer method. 

Observer measurements were generally lower than instrumental measurements. Data show 

that for the range of opacity emission standards (between 10 and 40% opacity), the 

observer readings averaged 6 and 11% opacity less than the instrumental readings of 

lidar and transmissometer, respectively, and varied by as much as 25% opacity below 

to 8% opacity above the instrumental readings. 

17. KEY WORDS AND DOCUMENT ANALYSIS 

DESCRIPTORS b.lDENTIFIERS/OPEN ENDED TERMS c. COS AT I Field/Group 

* Air pollution 

Chimneys 

* Plumes 

Opacity 

Measurement 

Comparison 

Observation 

Optical radar 

Transmissometers 

13B 

13M 

21B 

17H 

14B 

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RELEASE TO PUBLIC 

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UNCLASSIFIED 

2 1 . NO. OF PAGES 

35 

20. SECURITY CLASS (This page) 

UNCLASSIFIED 

22. PRICE 

EPA Form 2220-1 (Rev. 4-77) PREVIOU S EDITIO N IS OBSOLET E 

27 
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