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Document Number: 

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/YTf-??' at-*-? 

United States 

Environmental Protection 

Agency 

Environmental Sciences 

Research Laboratory 

Research Triangle Park NC 27711 

Research and Development EPA-600/S3-84-093 Nov. 1984 

&EPA Project Summary 

Evaluation of Trained Visible 

Emission Observers for Fugitive 

Emission Opacity Measurement 

Thoma s H. Rose 

The stack of a visible emission 

training school smoke generator was 

modified to emit white or black smoke 

in a horizontal direction near groundlevel to simulate fugitive emissions. 

Trained smoke observers measured the 

opacity of these simulated fugitive 

emissions against a dark terrestrial 

background and under clear sky lighting 

conditions. They measured both black 

and white emissions generated at four 

different opacities -15. 20, 30. and 40%. 

The observers also measured the same 

opacity of smoke plumes emitted from 

an unmodified training school smoke 

generator. These vertical-flow smokestack plumes were evaluated against a 

sky background to provide reference 

data on the observers ability to measure 

the opacity of conventional stack 

plumes under the same clear sky 

lighting conditions used for the fugitive 

plume tests. 

The observers measured opacities of 

whit e fugitiv e emission s wit h 

accuracies similar to the conventional 

stack emissions when opacities were in 

the range of 15 to 20%. As opacity 

increased, however, the observers 

increasingly underestimated opacity. 

At 40 % opacity, observer measurements were lower on average by about 

8% opacity. The opacities of black 

fugitive emissions were underestimated at all opacity levels. Opacity was 

lower on average by 5% opacity at the 

15% opacity level and by 11 % opacity at 

the 40 % opacity level. It was also 

observed that for both black and white 

simulated fugitive emission plumes, the 

observers sensitivity to changes in 

opacity levels declined relative to the 

conventional vertical stack plumes. 

This Project Summary was developed 

by EPA's Environmental Sciences Research Laboratory, Research Triangle 

Park, NC. to announce key findings of 

the research project that is fully 

documented in a separate report of the 

same title (see Project Report ordering 

information at back). 

Introduction 

Many types of airborne particulates 

and aerosols are not emitted from 

conventional vertical stacks. Instead, 

these emissions may come from windows, roof monitors, vents, conveyor 

belts, hoppers, storage piles, construction 

sites, roads, and a variety of other sources. 

Often these unconfined emissions originate close to the ground and move with 

the wind in a horizontal direction. Unlike 

conventional smokestack plumes that are 

viewed against the sky, these emissions 

are usually viewed against a darker 

terrestrial background. This study was 

designed to determine the biases, if any, 

introduced when certified Method 9 

smoke observers measure opacities of 

horizontal-flow, ground-level emissions. 

Experimental Design 

Smoke Generators 

Two smoke generators were used. Both 

generators were originally designed for 

training smoke observers; however, for 

the study one was modified to provide 

horizontal emissions near ground level. 

This was achieved by raising the stack 

only partially to a horizontal position and 
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placing an elbow between the lower 

vertical stack element and the upper 

horizontal stack element. The elbow was 

caulked and shimmed to prevent leaks. 

This method of generating horizontal 

emissions was selected after it was 

determined that the plume would remain 

uniform in both vertical and horizontal 

axes through the transmissometer and at 

the emission point. The determination 

consisted of viewing the white plume 

against a black velvet background at close 

range and the black plume against a 

white background. The appearances of 

both plumes were uniform along both 

axes. To further simulate the fugitive 

nature of horizontal emissions, a 12-

inch-wide board was used to block an 

observer's view of the stack end. 

The other smoke generator was set up 

in the conventional manner, with the 

stack upright to emit a vertical plume. 

Observers 

The observers selected for the study 

were six inspectors from a state agency 

and two air pollution personnel from local 

contractors. Each participant possessed a 

current Method 9 certification and a past 

record of accurate smoke reading, as 

evidenced by his ability to certify promptly 

at a smoke school. The Method 9 

certification procedure is described in the 

Federal Register. The participants ranged 

in age from 26 to 38 years old, with an 

average age of 31. Three pos_sessed 

college degrees, three had associate 

degrees, and the other two had some 

education beyond high school. Their 

experience at reading visible emissions 

ranged from one to eight years, with an 

average of 4.1 years. 

Observer Tests 

Both black and white simulated (horizontal-flow) fugitive emissions were 

measured under clear sky conditions. 

Black and white conventional (verticalflow) plumes were also measured under 

clear sky conditions to confirm the 

observers' abilities to assign unbiased 

opacity values to conventional plumes. 

The opacity levels selected for the study 

were 40, 30, 20, and 15 percent. For 

each opacity level, the observers were 

required to read for 12 minutes. Within 

that 12-minute period there was a period 

of just over six minutes of steady opacity 

smoke. The average of 24 consecutive 

readings by an observer during this sixminute period was the EPA Method 9 

evaluation of the smoke opacity. The 

observers were shown the same opacity 

levels from each generator but in random 

order. They were given no review of 

emission opacities prior to testing and 

were given no instructions except how to 

complete the test form and to read on 

signal. Smoke opacity measurements 

were recorded on computer compatible 

data forms in bound books. Th3 observers 

were instructed by a pre-recorded tape to 

read at 15-second intervals to assure 

Method 9 compatibility and standardization of the time reference. At the same 

time, the data logger made a reference 

mark on the transmissometer strip chart 

record. 

Results 

To observe the effect smoke color and 

mode of emission had upon the observers, 

opacity measurements were plotted 

against actual transmissometer values. A 

slope of 1.00 would show equal sensitivity 

between observer and transmissometer 

to opacity changes. 

Panel (averaged observer) opacity 

measurements of conventional stack 

plumes {white and black), under blue sky 

conditions and observed against a sky 

background, agreed closely with 

transmissometer opacity measurements 

over the range of opacity levels. Slopes of 

1.17 and 1.01 were calculated for the 

white and black smoke, respectively. 

Thus, the observers showed on average 

an ability to correctly measure the opacity 

of normal plumes with little bias. 

Measurements of simulated (horizontal-flow) fugitive emissions for white 

plumes on a clear day (Figure 1) revealed 

no systematic difference (bias) between 

observers and transmissometer readings 

for opacities around 15-20%. At higher 

opacities, however, an increasing 

negative observer bias was seen (Figure 

•1). At 40% opacity, this bias resulted in 

observer panel readings around 8% 

opacity lower than transmissometer 

values. Forblackemtssion lower observer 

60 

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U _. 

<*• !*-

f - ^ «*> 

40-

y 

Mean ± 95% 

Confidence Interval 

-- Regression L ine 

— I -

10 20 40 50 60 

Figure 1. 

i 

30 

Transmissometer 

% Opacity 

Observer opacity evaluations versus transmissometer measured opacities of 

simulated white fugitive plumes viewed against a terrestrial background on a clear 

day. 
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panel measurements were seen at all 

opacity levels (Figure 2). At 15% opacity, 

measurements were 5% opacity low; at 

40% opacity, they were 11 % opacity low. 

Overall, observer sensitivity to opacity 

changes, as evidenced by the slopes of 

the curves, declined for both the white 

and black (horizontal-flow) fugitive 

plumes . The change in observer 

measured per change in transmissometer measure d opacitie s decline d 

from near 1.0 for the conventional (vertical-flow) plume measurements to 0.62 

and 0.77 for the white and black simulated (horizontal-flow) fugitive plume 

measurements, respectively. 

Conclusions and 

Recommendations 

The panel of smoke observers 

measured the opacities of simulated 

.white (horizontal-flow) fugitive emissions 

with accuracies similar to (vertical-flow) 

plume opacity measurements when 

opacity levels were around 15-20%. As 

opacities increased, however, the panel 

increasingly underestimated them. They 

were lower on average by about 8% 

opacity at the 40% opacity level. 

Opacity measurements for black 

fugitive emissions were underestimated 

at all opacity levels. At 15% opacity, the 

observers measured the simulated 

fugitive emissions 5% opacity low, and at 

40% opacity they measured them 11 % 

opacity low. 

Observer panel sensitivity to opacity 

changes was less for simulated (horizontal-flow) fugitive emissions than for 

conventional smokestack plumes. The 

change in panel opacity measurement 

per change in transmissometer opacity 

measurement declined from near 1.00 

for the conventional smokestack plumes 

to 0.62 and 0.77 for the white and black 

(horizontal-flow) fugitive plumes, respectively. 

It is recommended that controlled tests 

of observer and transmissometer opacity 

measurements of simulated black and 

white fugitive emissions be conducted for 

other environmental lighting conditions, 

e.g., on an overcast day. It is also recommended that a lower opacity level around 

5 or 10% be included in the tests. 

60 

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<o a. 

*** iMean ± 95% 

Confidence Interval 

--• Regression Line 

Figure 2. 

60 

Transmissometer 

% Opacity 

Observer opacity evaluations versus transmissometer measured opacities of 

simulated black fugitive plumes viewed against a terrestrial background on a clear 

day. 
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V 

Thomas H. Rose is with Eastern Technical Associates, Raleigh, NC 27658. 

William D. Conner is the EPA Project Officer (see below). 

The complete report, entitled "Evaluation of Trained Visible Emission Observers 

for Fugitive Emission Opacity Measurement," (Order No. PB85-115 152; Cost: 

$8.50, subject to change) will be available only from: 

National Technical Information Service 

5285 Port Royal Road 

Springfield. VA 22161 

Telephone: 703-487-4650 

The EPA Project Officer can be contacted at: 

Environmental Sciences Research Laboratory 

U.S. Environmental Protection Agency 

Research Triangle Park. NC 27711 

•ir U.S. GOVERNMENT PRINTING OFFICE; 1984 — 559-016/7860 

United States 

Environmental Protection 

Agency 

Center for Environmental Research 

Information 

Cincinnati OH 45268 

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