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OAR Box 1115 

Prepped by Ryan Dugan 

Document Number: 

70) 11-A-2 

Docket Number: 

A-84-22 

Printed 4/18/2008 10:52:08 AM Sheet 70 of 94 
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United States 

Environmental Protection 

Agency 

Office of Air Quality 

Planning and Standards 

Washington DC 20460 

Stationary Source Compliance Series 

Technical 

Guideline: 

Alternative 

Procedures for 

Reduction and 

Reporting of 

Method 9 Opacity 

Readings 

-J* . 

Special Report 

October! 1983 
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This document has not been formally released by EPA and should not be construed to represent Agency 

policy. It is being circulated for comment on its technical accuracy and policy implications. I 

Special Report 

Technical Guideline: Alternative 

Procedures for Reduction and Reporting 

Of Method 9 Opacity Readings 

Final Draft Report 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

Office of Air and Radiation 

Office of Air Quality Planning and Standards 

Stationary Source Compliance Division 

Washington, D.C. 20460 

October 1983 
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TABLE OF CONTENTS 

Page 

Chapter 1.0 Introduction 1 

Chapter 2.0 Background 4 

Chapter 3.0 Preferred Methods for Time Exemption Regulations 12 

3.1 Frequency Count Method 12 

3.2 Method 9 14 

3.3 Summary of Preferred Methods for Time Exemption Regulations 16 

Chapter 4.0 Preferred Methods for Intermittent Emission Sources 18 

4.1 Three-Minute Average 18 

4.2 Frequency Count Method 19 

4.3 Summary of Preferred Methods for Intermittent Emission Sources 19 

4.4 Stopwatch Method 21 

Chapter 5.0 Evaluation of Short-Term and Nonaveraging Opacity 

Reading Methods 22 

5.1 Description of Reading Methods Used during Intermittent Plume 

Field Study 23 

5.2 Intermittent Emissions Field Study 23 

5.3 Fugitive Emissions Study 28 

5.4 Definition of Intermittent Emissions 34 

5.5 Recommended Reading Methods - Intermittent Emissions 35 

5.6 Recommended Reading Methods - Time Exemption Regulations 36 

5.7 Accuracy of the Frequency Count Method - Al l Plume Types 40 

Chapter 6.0 Relative Stringency of-Reading/Data Reduction Methods 46 

6.1 Procedure for Evaluating the Relative Stringency of Opacity 47 

Stand ard/Read ing Method Combinations 

6.2 Assumptions Used for Relative Stringency Evaluation 49 

Chapter 7.0 Summary and Major Conclusions 50 

Appendix A Federal Register, Vol. 39, No. 219, Reference Method 9 A-l 

Appendix B Alternative Methods for Visual Determination of the B-l 

Opacity of Emissions from Stationary Sources 

Appendix C Summary of Opacity Regulations (by Region) C-1 

n 
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LIST OF TABLES 

Page 

Table 1 Summary of Method 9 Requirements for Visual 6 

Determination of Opacity 

Table 2 Opacity Reading Method Specified in State Regulations, 9 

Listed by Type of Opacity Emissions Regulation 

Table 3 Intermittent Plume Field Study - Number of Six-Minute 27 

Data Sets by Plume Color and Configuration, and by 

Reading Method 

Table 4 Comparison of Errors for Different Opacity Reading 29 

Methods for Highly Intermittent Plumes -

95th Percentile 

Table 5 Between-Observer Precision for Fugitive Emissions Data 32 

(Aggregate-Time Method) 

Table 6 Between-Observer Precision for Fugitive Emissions Data 33 

(Opacity Averaging Method) 

Table 7 Error Standard Deviations by Smoke Color 37 

for Different Averaging Times 

Table 8 Difference between Observers for Fugitive Emissions 38 

Data for Different Averaging Times 

Table 9 Data Sets Used to Evaluate Frequency Count Method Accuracy 43 

Table 10 Accuracy Levels for Frequency Count Method 45 

Table 11 Relative Stringency Analysis of Intermittent Fugitive 48 

Emission Data 

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LIST OF FIGURES 

Figure 1 Example Visible Emissions Report Form 

Figure 2 Example Data Reduction Calculations for 

Frequency Count Method 

Figure 3 Example Strip Chart - Extremely Rapid Rise/Fall Plume 

Figure 4 Example Strip Chart - Rapid Rise/Fall Plume 

Figure 5 Strip Chart Run 9 - Slowly Changing Plume 

Page 

13 

15 

25 i 

26 

42 

iv 
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1.0 INTRODUCTION 

Building on prior Federal, State, and local control agency legislation 

and experience, the Clean Air Act, as amended in 1970 and 1977, authorized 

a national program of air pollution prevention and control. This program in -

 ! 

eluded national ambient air quality standards and State Implementation Plans

 ; 

(SIPs); emission standards for mobile sources; fuel additive standards; hazardous pollutant standards; and—-for the firs t time—nationwide, uniform, tech- , 

nology-based standards of performance for new and modified stationary sources.] 

The standards in thi s latte r category, which are authorized by Section 111 of , 

the Act, are commonly referred to as New Source Performance Standards (NSPS). 

To support these NSPS, reference test methods were promulgated to assure 

consistent and accurate measurements of emissions. Reference Method 9—Visual! 

i 

Determination of Emissions from Stationary Sources—provides for the determina;-

tion of the opacity of emissions by qualified observers. When Method 9 was 

revised and repromul gated in 1974, the procedure of determining average opacity 

of 24 consecutive 15-second readings (amounting to a six-minute period) was esftablished. However, the Preamble to the Method recognized that this opacityaveraging approach was not appropriate for evaluating certain sources of particulate matter with intermittent emissions or for enforcing time-exemption regulations found in many SIPs. The Preamble also indicated that alternative proce-' 

dures for evaluating emissions from intermittent sources would be investigated^ 

Field tests of the more commonly used alternative opacity reading methods 

were conducted by the Stationary Source Compliance Division of EPA starting in 

1980. This guideline document provides an evaluation of the data from these 

field tests , and the relative performance of the three major alternative 

1 
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opacity reading methods tested--the frequency count (or time distribution ) method, 

the stopwatch method, and averaging of readings for periods of three minutes 

and less. Potential measurement errors for the different methods are discussed 

along with programmatic approaches for taking these errors into consideration 

in the enforcement of opacity standards. Recommendations and detailed procedures 

are included for use of these methods, with a discussion of the circumstances 

under which each should be used. 

This technical guideline was prepared to provide support and guidance to 

air pollution control agency official s in developing methods and procedures for 

use in determining compliance of stationary sources with opacity standards and 

rules containing time exemptions and/or sources with intermittent visibl e 

emissions. 

This technical guideline is divided into the following sections: 

Chapter 1.0 -- Introduction. 

Chapter 2.0 -- Background. Includes a brief history of opacity 

regulations. Discusses differences between Federal 

and State opacity regulations and reading methods. 

Summarizes strengths of each approach. 

Chapter 3.0 -- Description of Methods for Time Exemption Regulations. 

Describes the two recommended opacity reading methods, 

frequency count and six-minute averaging. Discusses 

circumstances where each should be used. Gives example 

of use of method accuracy for frequency count methods. 

Chapter 4.0 — Description of Methods for Intermittent Emission Sources. 

Describes the two recommended opacity reading methods, 

frequency count and three-minute averaging. Discusses 

circumstances where each should be used. 

Chapter 5.0 -- Evaluation of Short-Term and Nonaveraging Opacity 

Reading Methods. Describes three field studies. 

Discussses issues surrounding choice of methods presented in Chapters 3.0 and 4.0. 
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Chapter 6.0 -- Relative Stringency of Reading/Data Reduction Methods. 

Discusses why thi s is a concern. Describes steps in 

conducting a study to compare the relative stringency 

of differen t methods. Gives results of relative 

stringency analysis of one set of typical opacity 

readings. 

Chapter 7.0 — Summary and Major Conclusions. 

Appendix A — The complete text of the Method 9 repromulgation, 

including the Preamble. 

Appendix B -- Alternative Methods for Visual Determination of the 

Opacity of Emissions from Stationary Sources. Presents detailed procedures in format of regulations. 
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...T ,....,,-.-

2.0 BACKGROUND 

Regulations limiting visible emissions were among the first legal tools 

used to reduce particulate emissions from stationary sources, and these laws 

continue to play an important role in modern air pollution control efforts. 

Opacity readings taken by trained, certified observers following prescribed 

procedures have proved accurate and effective for quickly evaluating visible 

emissions and have been so recognized by most courts. 

Opacity regulations and limitations first were adopted by local control 

agencies, primarily for boilers and incinerators. To accommodate necessary short 

periods of excessive emissions for such operations as soot blowing, many ofithese 

regulations allowed short periods above the normal emission limit. As concern 

shifted to other types of emission sources, these same time exemptions usually 

were kept to allow infrequent and minor fluctuations in process operations. A 

typical "time exemption" regulation that was adopted by Los Angeles is as follows: 

"A person shall not discharge into the atmosphere from any iw..-

source of emission whatsoever any air contaminant for a perioc1 or 

periods aggregating more than three minutes in any one hour which is: 

(a) As dark or darker in shade as that designated as No. 2 on the 

Ringelmann Chart, as published by the United States Bureau of 

Mines, or 

(b) Of such opacity as to obscure an observer's view of a degree equal 

to or greater than does smoke described in subsection (a) of this 

section." 

The Clean Air Act, Section 110 requires that States must have "a plan which 

provides for implementation, maintenance, and enforcement" of applicable ambient 

air quality standards. Stationary source emission standards are included as part 

of all State Implementation Plans (SIPs), including visible emission standards 

to limit particulate emissions.-- Most States not already having regulations 

1 

40 CFR, Part 51. 
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, 1 l-.fl-- -

adopted time exemption-type regulations similar to the Los Angeles example. EPA 

was designated responsibility for ensuring that States did in fact enforce 

their regulations and maintain clean air. 

The Clean Air Act Amendments of 1970 and 1977 also provided for EPA to set 

emission limits for certain major new sources. As New Source Performance 

Standards (NSPS) were promulgated by EPA, test methods also were promulgated to 

allow accurate and consistent measurement of different pollutant emissions!. 

Method 9 for the determination of visible emissions was first promulgated 

on December 23, 1971. This first test method required that at least 25 

readings be averaged together (each reading taken at 15- to 30-second intervals). Some brief requirements for reader positioning and certification were 

also given. 

Method 9 was substantially expanded and repromulgated on November 12, 

1974 in response to the court remand of the Portland Cement Plant NSPS 

(Portland Cement Association v. Ruckelshaus). The revised Method 9 was 

much more specific about the reader positioning, the data to be recorded 

during a reading, the data reduction method, and the conduct of the reader 

certification and testing program. Table 1 summarizes the major requirements of the revised Method 9. 

The introduction to the revised Method 9 described field trials that were 

i 

conducted by EPA to establish the accuracy and precision of Method 9. These 

tests gave measurement errors for both black and white plumes at two different 

levels, 99% and 95% of the data sets. The introduction further stated that 

the accuracy of the method had to be taken into consideration when determining 

whether or not a violation had occurred. The Preamble to the November 12,! 1974 
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TABLE 1. SUMMARY OF METHOD 9 REQUIREMENTS FOR VISUAL DETERMINATION 

OF OPACITYl 

Reader position/techniques 

Sun must be in a 140° sector behind the reader. 

Plume should be as perpendicular to reader line of sight as possible. 

Plume must be read where condensed water vapor is not present, and where 

the plume is of the greatest opacity. 

Individual opacity observations are to be taken each 15 seconds, and 

recorded to the nearest 5% opacity. 

Data reduction 

Twenty-four consecutive 15-second readings shall be averaged (six-minute 

averages). 

Certification 

. Must read 25 differen t white and 25 differen t black plumes consecutively 

within the following error margins. 

. No individual reading may be of f by more than 15% opacity. 

. The overall average error cannot exceed 7.5% opacity for either black 

or white plumes. 

. Certification i s valid for a period of six months. 

. The smoke generator must meet given specifications, which include 

calibration error, response time, zero and span drift , and other 

requirements. 

I 

As repromulgated on November 12, 1974. 
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• | T | ";>!- ' " 

amendment mentioned that Method*9 (six-minute average) was not compatible with 

time exemption-type regulations, and was not effective in dealing with intermittent emissions. 

Method 9, then, has several important advantages and disadvantages: 

I t i s detailed and formally promulgated. 

I t includes opacity observation procedures, data reduction methods, 

and certificatio n requirements. 

I t i s consistent with NSPS that limi t opacity based on a six-minute 

average. 

I t has supporting data on the accuracy of the method which should 

be considered by the Agency in determining possible violations . 

I t i s not compatible with time exemption regulations favored by many 

States. 

I t does not adequately evaluate some intermittent emissions. 

Until the late 1970s, almost al l State and local air pollution control i 

agencies used a differen t opacity reading method, called the "frequency count" 

or "aggregate-time" method. This method is used with time exemption-type 

regulations. In contrast to Method 9, where 24 readings are averaged, with the 

frequency count method each individual 15-second reading above the opacity

 ! 

limi t is counted and then multiplied by 15 seconds to obtain the aggregate 

time. I f the time above the opacity standard exceeds the time exemption period 

specified in the regulation, then the* source could be considered in noncompli'ance. 

For example, the previously cited Los Angeles regulation allows emissions of three 

minutes per hour greater than 40% opacity. I f a 60-minute reading period included 

fourteen 15-second readings above 40% opacity, then the source is in violation 

(14 readings X 15 seconds/reading = 3-1/2 minutes.) 

Administrative procedures for taking measurement error into account for 

the frequency count method vary among agencies, and appear to be set as a result 
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of experience with the method rather than from a statistical evaluation of any 

specific field study. One agency with a 20% opacity limit and three-minute time 

exemption, for example, requires four minutes of 30% opacity or more before 

enforcement action is taken. Starting in the late 1970s, many States adopted 

"Method 9" by reference into their regulations.^ However, many of these same 

States retained their time exemption-type regulations even though a six-minute 

averaging technique as in Method 9 is not compatible with a two-, three-, or 

four-minute time exemption. 

Appendix C is a summary of State opacity regulations including specified 

reading methods as of November, 1982.-^ This latest study of State opacity regulations and methods indicated increasing adoption of Method 9, but it also 

showed that, in practice, States with time exemption regulations did not use 

Method 9's specified data reduction method (six-minute averaging). The one 

exception to this is that States with a six-minute time exemption often use the 

six-minute averages. The first six-minute reading of excess emissions accounts 

for the exemption period, the second six-minute reading of excess emissions 

establishes the violation. Table 2 summarizes the reading method versus type 

of regulation used in the States. 

Several different approaches/techniques for trying to fit Method 9 to 

time exemption regulations have been used on an informal basis. These include 

the following: 

1 

Twenty-three states as of November 17, 1982. 

2 

Taken f*-om survey report prepared for EPA by Pacific Environmental Services, Inc. 

titled "Opacity Regulations: Summary of Regulations and Rulemaking Status," 

February 18, 1983. 
•'•ITH! 

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TABLE 2. OPACITY READING METHOD SPECIFIED IN STATE REGULATIONS, 

LISTED BY TYPE OF OPACITY EMISSION REGULATION1 

Opacity Reading Method 

Specified in Regulation 

Method 9 

Other Method' 

No Method Specified 

TOTAL2 

1 

1 

From Pacific Environment; 

i 1 

Number of States with Each Type of Emission Regulation 

Average 

11 

1 

8 

20 

''' "! 

Time Exemptioni 

6 minutes/hour: 51 

Other time periods: 7 

1 

4 ! 

1 6 '< 

32 

il Services, Inc. report dated February 18. 19^3. 

Includes 50 States, Puerto Rico, and the District of Columbia. 
P.16 

. Pick out the highest 15-second reading above the standard required 

for the time exemption, and then average the remaining 24 consecutive 

readings. 

. Average for a time period of six minutes + time exemption period 

(that is , for a three-minute time exemption, average nine-minute 

readings; i f any average is above standard, then i t is a violation). 

. Use Method 9 for reader positioning and certification , but use the 

standard frequency count method for data reduction (favored by most 

States). 

. Average six-minute readings, and use one excessive six-minute reading 

for time exemption (regardless of time); then second six-minute 

average above the limi t establishes the violation . 

In summary, many States are attempting to formalize their reading and 

certificatio n procedures while retaining time exemption-type regulations. 

The frequency count method of reading opacity is stil l widely used by States, 

and i t also has both advantages and disadvantages: 

. The method is compatible with time exemption regulations. 

. Although widely used, this method (at least the data reduction 

part) is rarely included in the regulations. 

. Frequency count method and time exemption regulations are effective 

tools in limitin g excessive intermittent emissions. 

. Until this current study, the method did not have an established 

measure of accuracy that could be used in determining when to take 

enforcement action. 

The EPA and State or local official s face several problems in trying 

to enforce SIP opacity regulations. Issues which may arise and require 

resolution include the following: 

. I f "Method 9" i s specified in the SIP but there are time exemption 

regulations, what data reduction method should be used? 

. I f the frequency count method of reading and data reduction i s used, 

what measurement error should be used to determine a violation? 

. For intermittent emission sources, what reading method should be used? 

This technical guideline document is intended to provide support to air 

10 
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pollution control agency official s in resolving questions about reading methods, 

measurement error, and data reduction methods. Preferred methods are presented 

in the following chapters along with recommendations as to their application to 

various types of visibl e emissions. Documentation of measurement error and 

techniques for taking into consideration measurement error are described. 

11 
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3.0 PREFERRED METHODS FOR TIME EXEMPTION REGULATIONS 

3.1 Frequency Count Method 

The opacity reading method of choice for use with time exemption regulations is basically a modification of Method 9, and it is known as the frequency 

count method. Reader positioning, plume observation procedures, data recording, 

and certification requirements are identical to Method 9. The only difference 

occurs in data reduction and the related accuracy of this modified method that 

should be considered in determing whether to proceed with enforcement actions. 

The data reduction method is to count each 15-second reading above the 

standard, and multiply by 15 seconds. If that time exceeds the time exemption 

specified in the opacity regulation, then a violation may have occurred. Figure 

1 is an example of a completed opacity reading form. 

As part of the EPA evaluation of alternative opacity methods, 1,880 sixminute data sets were evaluated using the frequency count method of data reduction. All data sets were of plumes where simultaneous tiansmissometer 

(opacity meter) values and observer readings could be compared. The differences in the transmissometer and observer readings give the accuracy of the 

frequency count method, which should be considered prior to taking enforcement 

action. 

A combination of opacity error for each individual 15-second reading plus 

a time error for each six minutes of reading was chosen.1 The actual amount of 

opacity error and time error was determined from the 1,880 data sets. Statistical 

analysis of the data sets revealed the following information: 

1 

See Section 5.5 for a further discussion of this choice of the type of 

error margin. 

12 
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FIGURE 1 

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. 99% of data sets showed no positive bias 1 when a 10% opacity 

buffer and one minute/six-minute reading buffer were used. 

. 95% of data sets showed no positive bias when a 10% opacity buffer 

and 15 seconds/six-minute reading buffer were used. 

. 85% of data sets showed no positive bias when a 5% opacity buffer 

and 15 seconds/six-minute reading buffer were used. 

Figure 2 shows an example of how to use the frequency count data reduction 

method plus error margins. This example uses the 85th percentile error margins 

described above. 

3.2 Method 9 

Method 9 should not be used with time exemption-type regulations unless 

there is a six-minute per hour time exemption and Method 9 is specified in the 

regulations as the reading method to be used. As of November, 1982, Vermont 

Virginia, Ohio, Louisiana, and North Dakota would meet these requirements. When 

using Method 9 with a six-minute per hour time exemption regulation, two sixminute averages above the standard would be required for a violation ; the firs t 

would be for the time exemption period, and the second would document the viola -

tion . The accuracy of the six-minute averaging technique should be considered 

before any enforcement action is taken. The two preferred methods for time exemption-type regulations, the frequency count method and Method 9, are summarized 

in Section 3.3. 

1 

"No positive bias" means that the time the observer read the plume at 

>20% opacity was less than the time the transmissometer read >20% opacity. 

14 
P.21 

FIGURE 2 

Example Data Reduction Calculations 

for Frequency Count Method 1 

Applicable regulation: Emissions from any wood-fired 

boiler shall not equal or exceed 40% opacity except 

for three minutes per hour. 

Data Set: 

TIME 

9:10 

11 

12 

13 

14 

9:15 

0 

35 

35 

50 

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5% opacity for each 15-second reading '. 

Extra 15 seconds of excessive emissions per six minutes of reading 

Opacity (actual value read minus 5% opacity ) # Readings Minutes Above Limi t 

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3 

4 

40% 

45% 

50% 

55% 

60% 

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2 

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minute 

From example opacity reading in Figure 1. Only the firs t six minutes of the 

readings are used in these sample calculations. In real observations, the t 

six minutes with the highest emissions would be chosen for initia l calculations, 

then the next highest six minutes (i f necessary), and so on unti l either a i 

violation is demonstrated or al l data has been evaluated and compliance shown. 

15 
P.22 

3.3 Summary of Preferred Methods for Time Exemption Regulations 

Frequency Count Method 1 

Applicability 

. All State I 

regulations ^ 

time exemption and Method 9 is specified in the regulations 

All State Implementation Plan (SIP) sources to which time exemption 

regulations apply, except where the regulations have a six-minute/hour 

Description: 

. Modification of Method 9, with only the data reduction step and associated accuracy level differing . Each 15-second reading above the applicable standards is counted and then multiplied by 15 seconds. Violation 

occurs when the time above the standard exceeds the time exemption in 

the regulation, taking into account the accuracy of the method. 

Test Data on Accuracy of Method: 

. 99% of data sets showed no positive bias with 10% opacity buffer 

and one minute/six-minute reading buffer. 

. 95% of data sets showed no positive bias with 10% opacity buffer 

and 15 seconds/six-minute reading buffer. 

. 85% of data sets showed no positive bias with 5% opacity buffer 

and 15 seconds/six-minute reading buffer. 

Reference Method 9-? 

Applicability : 

. SIP sources to which a six-minute/hour time "exemption regulation 

applies and Method 9 is specified in the SIP as the required method. 

Description: 

. Six-minute averages are calculated. Two six-minute averages above 

the standard in a 60-minute period are required for a violation . The 

accuracy of the method should be considered before taking enforcement 

action. 

1 

See Appendix B for a detailed procedure, 

2 

See Appendix A for a detailed procedure. 

16 
P.23 

-. • r-,.,- r p.,, -

Test Data on Accuracy of Method: 

. 95% of data sets had no positive bias i f 5% opacity was subtracted 

from six-minute average. 

. 99% of data sets had no positive bias i f 7.5% opacity was subtracted, 

from six-minute average. 

17 
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4.0 PREFERRED METHODS FOR INTERMITTENT EMISSION SOURCES 

Some types of industrial and commercial processes are cyclical and emit 

large amounts of visible and particulate emissions for short periods of time, 

interspersed with long periods of minimal or no emissions. Some examples of 

such operations would include soot blowing of boilers, pushing operations at 

coke ovens, and pouring operations at foundries. These sources of intermittent 

emissions can be very significant from an air pollution standpoint. It is 

clearly desirable to be able to measure these emissions visually and to limit 

them by regulation. 

The six-minute averaging time specified in Method 9 is appropriate for 

continuous or nearly continuous emission sources, but not for intermittent 

sources. If the six-minute averaging provision of Method 9 is applied to 

emission plumes that are characterized by intermittent opacity peaks, rather 

than a sustained elevated opacity level, it might be impossible to cite a 

violation because the peak opacity readings (at 15-second intervals) would be 

offset by the lower baseline opacity values over the averaging period. The 

Preamble to the repromulgation of Method 9 (November 12, 1974) indicated that 

Method 9 was not able to evaluate intermittent emissions adequately, and that 

other alternative reading methods would be investigated. These studies have 

been completed, and two alternative methods are presented here. It should be 

noted that these alternative methods may not be adequate for evaluating extremely 

short-term emissions such as those at coke ovens. Intermittent emissions are 

defined as emissions above the standard for less than six continuous minutes. 

4.1 Three-Minute Average 

This method would be used on those SIP sources with intermittent emissions 

where the emission regulations do not have time exemptions. All provisions of 

18 
p ,- -jurMethod 9 are followed except for the data reduction period and the associated! 

accuracy of the method. Twelve consecutive 15-second readings are to be 

averaged, rather than the 24 specified in Method 9. 

The accuracy of three-minute averaging was established by the studies 

referenced in Section 5.1 . Of the 1,172 six-minute data sets (each broken 

into two three-minute data sets for a total of 2,344 data sets): 

. 95% of the data sets showed no positive bias when 11.8% opacity was 

subtracted from the observer's three-minute averages.1 

. 85% of the data sets showed no positive bias when 7.5% opacity was 

subtracted from the observer's three-minute averages. 

4.2 Frequency Count Method 

The frequency count method for intermittent emissions is identical to 

that described in Section 3.1 . The frequency count method i s to be used on 

al l intermittent emission sources where the applicable emission regulations 

are of the time exemption type. The accuracy of the frequency count method 

i s the same as that described in Section 3.1 . 

The two recommended methods for intermittent sources are summarized in 

Section 4.3 and described in more detai l in Appendix B. The major issues 

considered and other alternative methods evaluated are discussed in detai l in 

Chapter 5.0. 

4.3 Summary of Preferred Methods for*Intermittent Emission Sources 

Definition of intermittent emissions: Emissions above the opacity 

standard that las t for less than six consecutive minutes. 

1 

(Observer opacity - 11.8% opacity) £ transmissometer opacity for 95% of 

three-minute averages. 

19 
P.26 

Three-Minute Averaging Method 

Applicability : 

. All State Implementation Plan (SIP) sources not subject to time exemption 

regulations. To be used when emissions from such sources are intermittent 

in nature. 

Description: 

. Identical to Method 9, except that only twelve 15-second readings 

taken over a three-minute period are averaged. 

Test Data on Accuracy of Method: 

. 85% of data sets: no positive bias i f 7.5% opacity is subtracted 

from the three-minute average. 

. 95% of data sets: no positive bias i f 11.8% opacity is subtracted 

from the three-minute average. 

Frequency Count Method 

Applicability : 

. Al l SIP sources to which time exemption regulations apply. 

Description: 

. Minor modification of Method 9, with only the data reduction step and 

associated accuracy level differing . Each 15-second reading above 

the applicable standard is.counted and then multiplied by 15 seconds. 

Violation occurs when the time above the standard exceeds the time 

exemption in the regulation, taking into account the accuracy of the 

method. 

Test Data on Accuracy of Method: 

. 85% of data sets: 5% opacity subtracted from each 15-second reading 

and additional 15 seconds above standard added to each six-minute 

reading resulted in no positive bias (85% of readings with these buffers 

showed less time above standard than transmissometer). 

. 95% of data sets: 10% opacity subtracted from each. 15-second reading 

and additional 15 seconds above standard added to each six-minute 

reading resulted in no positive bias. 

. 99% of data sets: 10% opacity subtracted from each 15-second reading 

and additional one minute above standard added to each six-minute reading 

resulted in no positive bias. 

20 
,;n ..., 

4.4 Stopwatch Method 

The stopwatch method is not recommended as a general method for inter 

mittent emissions because it does not easily lend itself to factoring in ah 

i 

error buffer for opacity (see Section 5.2), although it has an error margin 

for time comparable to that of the frequency count method. However, the . 

stopwatch method has been and can be used effectively for measuring highly ! 

intermittent emissions, provided an appropriate error margin is included. 

The accuracy of the stopwatch method was determined in a field test and is 

presented in Section 5.2. 

21 
P.28 

5.0 EVALUATION OF SHORT-TERM AND NONAVERAGING OPACITY READING METHODS 

The studies described here were intended to accomplish two important objectives: 1) to evaluate different methods for reading intermittent plumes, and 

2) to determine the accuracy of the frequency count method for all plume types. 

A number of different opacity reading methods were examined for evaluating 

intermittent plumes. Two methods used for intermittent emissions by State and 

local air pollution agencies--the stopwatch method and the frequency count 

method— were evaluated, as well as short-term averaging (less than six minutes) for varying lengths of time. 

The frequency count method, which is commonly used by State and local 

agencies, has been described in previous sections. It is identical to Method 

9, except for the data reduction step and associated method accuracy. It is 

most often used with time exemption regulations. 

The stopwatch method is used by a few agencies, primarily for source 

categories where emissions are highly intermittent (such as c.-k? r. •!>*!••' , Tr 

this method, two stopwatches are normally used (or a stopwatch and a watch with 

sweep second hand). One stopwatch or watch is used to record the time of the 

entire reading. The other stopwatch is used to keep a running total of the 

time the emissions under observation exceed the opacfty standard. As the 

emission rises above the standard, the stopwatch is started. When emissions 

fall below the standard, the stopwatch is stopped. This process is repeated 

for the entire reading period as the plume opacity rises above and falls below 

the standard. The total time emissions were recorded above the standard is then 

compared to the time exemption period allowed in the applicable regulation. 

The final method evaluated was short-term averaging. One-, two-, and 

three-minute averages were examined. The same data base of 15-second readings 

22 
. ,. ,,.J -, ,.. „-, , 

was used to evaluate the frequency count and averaging data reduction method,s. 

Al l three methods use the Method 9 criteri a for reader positioning. The 

three methods are summarized in Section 5.1 . 

5.1 Description of Reading Methods Used during Intermittent Plume Field Study 

i 

Frequency Count Method 1 

. Reader positioning: same as Method 9, Section 2.1 (sun in back 140P 

sector, plume at right angles to reader, etc.). 

. Data recording: same as Method 9, Sections 2.3 and 2.5 (readings taken 

and recorded each 15 seconds to nearest 5% opacity). ' 

. Data reduction: each 15-second reading above the 20% opacity level i s 

counted in a six-minute data set, and then multiplied by 0.25 to determine 

the minutes/six-minute reading above 20% opacity. j 

Stopwatch Method 

. Reader positioning: same as Method 9, Section 2.1 . 

i 

. Data recording: stopwatch is used to accumulate time plume 

appears to be over 20% opacity during the six-minute data set. 

The stopwatch i s turned on when the plume i s greater than 20%, 

and turned of f when the plume is below 20%. 

. Data reduction: time is read of f stopwatch at the end of each 

six-minute data set. 

Short-Term Averagingl 

. Reader positioning: same as Method .9, Section 2.1 . 

. Data recording: same as Method 9, Sections 2.3 and 2.5. 

. Data reduction: 15-second readings averaged over 1 , 2, and 3 minutes. 

5.2 Intermittent Emissions Field Study 

Extensive field testing was conducted to compare these three methods 

during the week of May 19-23, 1980 at Research Triangle Park (RTP), North 

Carolina. Twelve participants observed for a total of 1,172 six-minute peribds 

I 

Same raw data sets of 15-second readings over six minutes were used 

23 
P.30 

during the five-day test . The participants, al l recently certified visibl e 

emission observers, had from less than one to 12 years of experience in reading 

opacity. During the test , they observed both black and white plumes. 

Rapidly changing plumes were examined in the RTP field test . The smoke 

generator used to generate these plumes met al l Method 9 criteria , and, in 

addition, was modified to permit more rapid change in plume opacity than is 

normally possible with the type of smoke generator used in qualifying Method 9 

observers. Examples of the two plume types used for the study are shown in 

Figures 3 and 4. The extremely rapidly rising plume shown in Figure 3 changed 

from 10% opacity to 60% opacity in only 1.5 seconds. The plume rise in Figure 

4 was somewhat slower but stil l very rapid—the opacity increased from 10% to 

50% in 24 seconds. Between one and three plume rise/fal l cycles occurred during 

each six-minute data set. 

The day before starting the field experiment, al l participants were shown practice plumes and then certified by Method 9 criteria . In addition, the readers were 

instructed in the operation of a stopwatch and how to read and record data. Al l observers were certifie d during standard Method 9 smoke reading certificatio n tests . 

Half of the readers were provided with stopwatches. Simultaneous readings 

were obtained during each run with six readers using the stopwatch and six 

readers using the frequency count method of reading.1 Each reader was required 

to read either by the stopwatch method or frequency count method during each 

run. Every 10-15 data sets, the stopwatches were given to those who had been 

reading with the frequency count method, so that each reader had about equal 

time reading with the stopwatch and frequency count methods. The number of data 

sets by color, reading method, and plume configuration are given in Table. 3. 

7. • 

The "frequency count" data was used as the raw data for short-term averaging also. 

Both the frequency count method and Method 9 use discrete observations made each 

15 seconds to the nearest 5% opacity; only the data reduction step varies . 

24 
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Figure 3 

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Extremely Rapid 

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26 
P.33 

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" " ' " "' ~ " ~ ' " " ""'•" " •• •- »r--.-|;--|T 7 

TABLE 3. INTERMITTENT PLUME FIELD STUDYl. NUMBER OF SIX-MINUTE DATA SETS 

BY PLUME COLOR AND CONFIGURATION, AND BY READING METHOD 

Plume Color 

Reading Method/PI ume Configuration 

Black White 

Frequency Count? 

Extreme rapid rise3 120 180, 

Rapid rise** 121 173 

Stopwatch Method 

Extreme rapid rise 120 179; 

Rapid rise 111 168 

TOTAL 472 700; 

t 

Conducted May 19-23, 1980 in Research Triangle Park, NC. 

Discrete 15-second readings taken. Data reduction was done in several ways 

for the same data—frequency count and averaging for differen t lengths of 1 time. 

i 

Rise/fal l of 50% opacity in 1.5 seconds. 

Rise/fal l of 40% opacity in 10-12 seconds. 

27 

••..: . 1 
P.34 

Weather and background conditions were generally very good during the field 

trial. * Green trees were used for background of white plumes, with blue sky used 

for black plumes. 

The test results for the three differen t reading and data reduction methods 

are presented in Table 4. These results are given in 95th percentiles for 

comparison purposes. 

For the stopwatch method, the error is given in minutes only. Conceivably, 

an error margin consisting of a specified opacity level plus a time could have 

been determined i f the test had been set up for it . For example, a 10% opacity 

error could have been selected before the test and then the corresponding time 

error determined by instructing the participants to include only the time when 

the plume appeared to be equal to or greater than 30% opacity (20% + 10% buffer). 

The choice was made to use only a time error for simplicity . 

The errors for short-term averages are given in percent opacity. The 

frequency count method error is given as a combination of opacity error and 

time error. (See Section 5.6 for a further discussion of the use of thi s 

combination.) 

5.3 Fugitive Emissions Study 

Visible emission observation data previously taken at several sources 

with fugitive emissionsl during studies conducted by EPA for other purposes 

were also compiled and analyzed. The.purpose of this part of the study was to 

determine i f observer error when evaluating fugitive emission sources under 

actual field conditions would be differen t from the error associated with the 

smoke generator tests . However, in the case of industrial process fugitive 

sources, no true opacity measurement is available (i.e. , no transmissometer 

T 

"Fugitive emissions" are defined as those emissions that do not come from a 

stack, and would include emissions from roof monitors, open doorways, rock 

crushers, etc. 

28 
P.35 

TABLE 4. COMPARISON OF ERRORS FOR DIFFERENT OPACITY READING METHODS 

FOR HIGHLY INTERMITTENT PLUMESl (95th PERCENTILE2) 

Frequency Count Method 

Black Smoke: 5% opacity, 0.25 minutes/six-minute reading 

White Smoke: 5% opacity, 0.50 minutes/six-minute reading 

Stopwatch Method 

Black Smoke: 1.0 minutes/six minutes 

White Smoke: 2.1 minutes/six minutes 

Short-Term Averaging Method3 

One-minute average 

Black Smoke: 7.2% opacity 

White Smoke: 15.0% opacity 

Two-minute average 

Black Smoke: 5.6% opacity 

White Smoke: 12.2% opacity 

Three-minute average 

Black Smoke: 4.8% opacity 

White Smoke: 11.8% opacity 

r Based on field study conducted May 19-23, 1980 in Research Triangle Park, NC. 

I 

95% of the data sets have less than the indicated error. Use of thi s percenti l e is for comparison purposes only, and does not constitute a recommendation 

of accuracy level for compliance purposes. ! 

3 ; 

The same raw data set of 15-second readings was used for the frequency count 

and short-term averaging data reduction method evaluations. 

29 
P.36 

or stack opacity monitor is present to provide an instrumental measurement to 

serve as the reference opacity value). Consequently, the only measure that 

could be used to assess observer error is between-observer precision. Simultaneous opacity readings by two observers were used as the basis of the betweenobserver precision calculations. 

Some of the fugitive emissions data used were obtained from basic oxygen 

furnace (BOF) roof monitors and nonmetallic mineral processing facilities and 

were gathered in support of development of NSPS. The remainder of the fugitive 

emissions data used were collected by EPA regional personnel from various iron 

and steel sources in several EPA regions as part of a VE emissions data bank 

for evaluation of reasonably available control technology (RACT). For all of 

the regional fugitive emissions data, one of the two paired observers was a 

nonagency person either associated with the source or contracted by the source. 

In total, 310 hours of observations (each observer) were evaluated. Each 

run was typically either for a 30-minute or 60-minute observation period. Once 

the initial data set was obtained and reviewed, it became apparent that at some 

of the sources a disproportionate amount of the readings were zero opacity. 

Since evaluation of observer precision based on observations at the 0-5% opacity 

level would not provide a useful indication of method accuracy, a subset of the 

total data set was established. The data subset made up approximately 80% of 

the original data set (240 hours per observer)!. 

1 

Approximately 30% of the data sets had opacities near or above the 20% 

opacity level. 

30 
P.37 

r-rr r | •-;<•• - • 

Between-observer precision for the aggregate-time method wa's calculated 

for the fugitive data set. Since no transmissometer was available to which the 

observers' data could be compared, an actual composite error estimate (observer 

bias, within-observer precision, and between-observer bias) cannot be determined. 

However, the between-observer precision term can be determined and compared tp 

the between-observer precision term calculated for the RTP data that was utilized 

in calculating a composite error estimate. As illustrated in Table 5, the mean 

between-observer precision for the fugitive emissions was 166 seconds, with a> 

range of 104-239, when determining the aggregate time over a range of 10 to 25% 

opacity. The mean between-observer error of 166 seconds with the fugitive emp'ssion data set compares to the between-observer error of 159 seconds determined 

during the RTP smoke generator study (white intermittent plumes). This is ah 

indication that the observers performed about as well in the field observing 

the fugitive emissions as they did observing the smoke generator emissions. 

Between-observer precision was also examined when opacity averaging methods 

of data analysis were employed. Table 6 shows that the standard deviation (estimate of between-observer precision) is 2.1% opacity for a six-minute averaging 

period and 2.4% for a three-minute averaging period. In both cases, the dif-! 

ference between observers is at a level that can be considered acceptable; 

furthermore, only a small increase in. between-observer precision is noted when 

a shorter averaging time is used. 

31 
P.38 

""•'*• * • .« 

TABLE 5. BETWEEN-OBSERVER PRECISION FOR FUGITIVE EMISSIONS DATA 

(AGGREGATE-TIME METHOD) 

Variable 

OT 152 

OT 20 

OT 25 

OT 30 

Mean Value 

Mean 

\ 

Aggregate 

(seconds) 

520 

296 

183 

129 

Time SD1 

(seconds) 

239 

190 

130 

104 

166 

1 

Between-observer error term. 

OT 15 = observed time >15% opacity, OT 20 = observed time >20% opacity, etc. 

32 
P.39 

r ry e -I] 

TABLE 6. BETWEEN-OBSERVER PRECISION FOR FUGITIVE EMISSIONS DATA 

(OPACITY AVERAGING METHOD) 

Variable SD1 

(% opacity) 

Observer difference _<7.5% opacity 

(percent of runs) 

Three-Minute 

Average 

2.4 92 

Six-Minute 

Average 

2.1 93 

1 

Between-observer error term. 

33 
P.40 

5.4 Definition of Intermittent Emissions 

Whenever any new regulation or measurement method is proposed, a key 

requirement is that the sources affected be clearly and unambiguously defined. 

Any definitio n of intermittent emissions wil l have to take the following into 

account: 

. Must be clear as to which emission sources the method applies. 

. Must include as many significant sources of emissions as possible which 

are not adequately covered by six-minute averages. 

. Should be easy to understand and use in the field . 

Several possible definitions were examined. They include defining by source 

type (i.e. , coke oven pushes); defining by time above the standard (less than six 

consecutive minutes above the standard); defining by time when emissions are 

greater than zero (less than six consecutive minutes of visibl e emissions); and 

defining by the statistica l variabilit y or the rate of rise and fal l of the 

plume. 

The simplest definitio n that applies to the greatest number of sources of 

significant emissions is the following: 

"Intermittent emissions are those emissions that exceed the applicable opacity standard for less than six consecutive minutes." 

Determining applicabilit y by source type could also be used in some circumstances where the source type is fairVy consistent in producing intermittent 

plumes. For example, the amended NSPS emission standard proposed for secondary 

emissions from basic oxygen furnaces, which have been designated as intermittent 

emission sources, i s determined using a three-minute average.1 

I 

Proposed January 20, 1983. 

34 
P.41 

Defining intermittent emissions as those emissions that are greater than 0% 

opacity for less than -six consecutive minutes would have the drawback of only 

i 

covering some intermittent sources; it is, therefore, not desirable as a more 

general definition. 

i 

Defining intermittent emissions by the rate of plume opacity change was 

considered. One possible definition would be to calculate the standard 'deviation 

of the opacities — if the standard deviation exceeded 12%, then the plume would 

be considered intermittent. A major drawback with this type of definition! is 

that determination of a violation would be difficult to make in the field. 

Many aaencies consider it highly desirable for the inspector to be able to: have 

, I 

I 

immediate discussions with responsible source officials when a violation occurs. 

Knowing whether or not a violation has actually occurred is an important piece 

of information for the inspector in such circumstances. Therefore, it was! 

determined that using the rate of plume opacity change to define intermittent 

emissions is not practical. 

5.5 Recommended Reading Methods - Intermittent Emissions ' 

The frequency count method should be used for intermittent emission 

sources when time exemption-type regulations apply. .The rationale for this is 

discussed in more detail in Section 5.6, but the major reasons include compatibility 

i 

of the reading method with the standard, a reasonable accuracy level, and past 

experience showing that the frequency count method is an effective tool in 

evaluating intermittent emissions sources. 

The stopwatch method can be used for intermittent sources, and, in fact, 

is often specified and effective when dealing with extremely short-torm emission 

sources such as coke ovens. Several agencies use the stopwatch method, particularly in conjunction with coke ovens. As with any method, the stopwatchimethod 

35 
P.42 

can be used i f i t i s consistent with the applicable emission standard and i f a 

suitable error margin is considered. I t i s not included as a preferred method 

for the following reasons: 

. The stopwatch method i s not in widespread use and requires some 

training in addition to Method 9 training and certification . 

. I t is desirable to have as few opacity reading methods as possible 

in a given State. The two preferred methods for intermittent emission 

sources (frequency count and three-minute average) were chosen in 

part because they were either the same or a minor modification of 

the existing method for other source types. The stopwatch method, 

however, is normally used only for highly intermittent sources, 

and i t is substantially differen t from other reading methods. 

. The stopwatch method does not easily lend itsel f to factoring in an 

error buffer for opacity. 

Three-minute averaging should be used for intermittent emission sources 

subject to average opacity-type regulations. One-and two-minute averaging could 

be used, but do have slightl y higher error margins (see Tables 7 and 8) associated 

with them than three-minute averaging. The three-minute average was chosen over 

the shorter times because i t has a greater accuracy while stil l being a short 

enough averaging time to evaluate most intermittent emission sources effectively . 

Any of these methods can be used. However, the reading/data reduction method 

must be specified and must be compatible with the applicable emission regulation, 

and the accuracy of the method should be considered before making a determination 

of compliance. 

5.6 Recommended Reading Methods - Time Exemption Regulations 

The frequency count method of reading and data reduction was recommended for use with time exemption-type regulations for the following 

reasons: 

. Frequency count is very compatible with time exemptions and is 

consistent with what i s commonly understood when one says "x minutes" 

--that is , the sum total of x minutes rather than an average of x minutes. 

36 
P.43 

TABLE- 7. ERROR STANDARD DEVIATIONS BY SMOKE COLOR 

FOR DIFFERENT AVERAGING TIMESl 

Averaging Time, 

Minutes 

Smoke 

Black 

8.30 

7.87 

7.73 

7.48 

Col or 

White 

7.83 

7.00 

6.80 

6.48 

1 

2 

3 

6 

r 

Research Triangle Institute, Research Triangle Park, NC, Letter 

Report dated September 8, 1983. 

37 
P.44 

n w w>"-y 

TABLE 8. DIFFERENCE BETWEEN OBSERVERS FOR FUGITIVE EMISSIONS DATAl 

FOR DIFFERENT AVERAGING TIMES2 

Averaging Time, 

Minutes 

1 

2 

3 

6 

Variance 

8.40 

6.71 

5.73 

4.48 

Standard 

Deviation3 

2.90 

2.59 

2.39 

2.13 

r 

There are no transmissometer readings for the fugitive emissions data; 

only differences between observers can be determined. 

Research Triangle Institute, Research Triangle Park, NC, Letter 

Report dated September 8, 1983. 

Standard Deviation = Variance. 

38 
P.45 

. Frequency count has been used with time exemption regulations for at 

least 35 years. 

. Frequency count has sufficient accuracy and has proved an effective 

tool in evaluating opacity. 

. Frequency count works well with intermittent as well as more continuous 

emissions. ' 

Six-minute averaging as specified in Method 9 can be used without modification only with six-minute time exemptions, and only where Method 9 is included 

in the regulations as the required reading method. Other time exemption periods 

could be averaged, but would require detailed and specified data reduction methods. 

The accuracy of each averaging time would have to be considered for compliance 

evaluation purposes; that is, if the reading method allowed a three-minute ^verage 

for the time exemption period and a six-minute average for comparison with the 

base opacity standard, then the accuracy of three-minute averaging would have 

t.c be considered for the three-minute average, and the accuracy of the six-minute 

nverage included for the six-minute average. 

A combination of frequency count for the time exemption period and sixminute averaging for the base standard can be used, but will be considerably 

less stringent than the straight frequency count method and is not recommended 

I 

for that reason. When using the frequency count method, only the time exemption 

period is of concern. For example, a typical time exemption regulation will 

prohibit emissions equal to or greater than 20% opacity except for three minutes 

per hour. Once the time exemption period has been exceeded (with the error 

margin figured in), then the source is in violation even if all the other 

opacity readings are "0". If six-minute averaging is attempted with a time 

exemption regulation, however, the same time exemption period (with error) 

would be required plus the remaining readings averaged together would have 

39 
P.46 

to exceed 20% plus the error margin for the six-minute average. 

Any of the reading/data reduction methods discussed in this guideline 

document can be used under appropriate circumstances subject to the following 

stipulations: 

. The data reduction method must be specific and unambiguous. 

. The data reduction method must be consistent with the opacity standard. 

. The accuracy of the reading/data reduction method must be taken into 

account before compliance with the opacity standard can be determined. 

. The relative stringency of the different reading/data reduction methods 

(including accuracy of method) should be considered before choosing a 

reading/data reduction method. 

5.7 Accuracy of the Frequency Count Method - All Plume Types 

The frequency count method of opacity reading and data reduction continues to be widely used by State and local air pollution control agencies. 

Although this method has been used for more than 30 years, no previous study 

to assess the accuracy of the method was identified prior to this report. Rather, 

agencies have estimated the accuracy of the method based on their extensive experience with it , including smoke school results. 

The intermittent emission field studyl described earlier evaluated the 

frequency count method on highly intermittent plumes. Two other brie f field 

tests were also carried out, one with slowly changing plumes and one with 

continuous plumes. 

A battery of slowly changing plumes was shown to a panel of observers in 

Jacksonville, Florida on January 17, 1981. Ten observers of varying experience 

levels read a total of 180 twelve-minute runs from a smoke generator meeting 

7. 

Conducted in Research Triangle Park, NC, May 19-23, 1980. 

40 
rj- |-,-.,-,T „ 

Method 9 specifications. Six minutes of slowly changing opacity were "hidden" 

within each 12-minute period, and only these six-minute data sets were used. 

The opacity levels were varied steadily over the six minutes in one of three 

patterns: 20% change, 40% change, and 60% change. A strip chart showing plume 

opacity for one of the runs is shown in Figure 5 as an example. Reader positioning and data recording were as per Method 9. Al l readers were certifie d 

the week before the field tria l according to Method 9 requirements. 

A similar short-term field test on continuous plumes was held in Orlando, 

Florida on October 18, 1980. Twenty observers read a total of 360 twelve-minute 

sets. Six minutes of unchanged opacity also were "hidden" within each 12-minute 

period, with the six minutes of continuous emissions constituting the data sets 

used. Again, the smoke generator met Method 9 criteria . The observers had al l 

been certified as per Method 9 specifications the week before the study. Reader 

positioning and data recording were also according to Method 9. 

In addition to these three studies, data from the EPA "Riverbend" study of 

1974 were evaluated. The Riverbend data were gathered as part of the Method 9 

repromulgation. 

These four studies of varying plume configurations were used to evaluatje 

the accuracy of the frequency count method of opacity observation and data 

reduction. Some descriptive data on-these four studies are listed in Table 9. 

Frequency Count Error Margin j 

The frequency count method error could be described three ways: 1) opatity 

error for each 15-second reading (i.e. , allow 10% opacity error for each reading); 

2) time error for each six-minute data set (i.e. , allow one minute extra of [excess 

emissions); or 3) a combination of opacity and time errors. 

41 
P.48 

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42 
P.49 

I ' 

TABLE 9. DATA SETS USED TO EVALUATE FREQUENCY COUNT METHOD ACCURACY 

1 Name/Location 

1 of Study 

Riverbend Study 

1 RTP Study 

1 (Research Triangle 

1 Florida I Study 

1 (Orlando, Florida) 

Pa 

1 Florida I I Study 

1 (Jacksonville, Florid 

He, 

a) 

NC) 

TOTAL 

Description 

Coal-fired power plant 

Highly intermittent 

emissions - smoke 

generator 

Continuous plumes -

smoke generator 

Slowly changing 

plumes - smoke 

generator 

Number of 

Data Setsl 

168 

1,172 

360 

180 

1,880 

Year of Study! 

1974 1 

1980 | 

1980 I 

i . 

1981 | 

[ 

r Six-minute data sets. 

43 
P.50 

There are two concerns with the accuracy of any opacity test method: 

1) that the opacity reading show a violation when, in fact, there is one; and 

2) that the reading not show a violation when there is no violation. In other 

words, the test method (with error margin) should show as many "true" violations 

while showing as few "false" violations as possible. 

The combination of opacity and time buffers for the frequency count method 

was chosen for two reasons: 1) its current, use by control agencies, and 2) a 

comparison of its relative stringency in the data set evaluated (see Chapter 

6.0). Two of the leading air pollution control agencies with vigorous enforcement programs use the frequency count method with the opacity/time buffer 

combination, indicating that it is, in their experience, the most practical and 

stringent error margin. Also, a comparison (see Chapter 6.0) of the number of 

violations found using the different types of error margins in a sample data 

set showed the combination of opacity and time buffers to be the most stringent. 

The actual amounts of the time and opacity errors were calculated for 

the four data sets used. Table 10 shows the accuracy levels, expressed by 

percentiles. When the given opacity and time buffers were used with the four 

data sets, the associated percentile indicates the percentage of data sets 

where there was no positive bias (the observer time with buffers above the 

standard was less than the transmissometer time above the standard). 

44 
P.51 

' •• r ' 'vi''-

TABLE 10. ACCURACY LEVELS FOR FREQUENCY COUNT METHOD1 

99% of data sets: 

Black Smoke: 0.4 minute/6 minutes, 10% opacity each 15-second reading 

White Smoke: 1.0 minute/6 minutes, 10% opacity each 15-second reading 

95% of data sets: 

Black Smoke: 

White Smoke: 

85% of data sets: 

Black Smoke: 

White Smoke: 

0.1 minute/6 minutes, 10% opacity each 15-second reading 

0.2 minute/6 minutes, 10% opacity each 15-second reading 

0.04 minute/6 minutes, 5% opacity each 15-second reading 

0.2 minute/6 minutes, 5% opacity each 15-second reading 

1,880 six-minute sets of data from these studies: 

Park, Florida I, and Florida II. 

Riverbend, Research Trilangle 

45 
P.52 

6.0 RELATIVE STRINGENCY OF READING/DATA REDUCTION METHODS 

Each opacity reading and data reduction method wil l have some level 

of accuracy associated with i t that should be considered before deciding that a 

violatio n has occurred. Agencies that change their standards or reading methods, 

or establish new standards or reading methods in regulations, permits, or 

consent decrees, are concerned about the relative stringency of their choices. 

For a given source category, for example, wil l there be more violations found i f 

a three-minute time exemption standard plus stopwatch reading method is used, 

or i f no time exemption and a three-minute average i s used? 

A method for comparing different opacity stand ard/read ing method combinations was developed and used in evaluating intermittent fugitive emissions from iron 

and steel and from nonmetallic mineral processing facilities. ! Section 6.1 list s 

the steps in performing a relative stringency analysis. Basically, the analysis 

involves evaluating different actual opacity readings and determining how many 

violations occur with the different method/standard combinations; the combination 

with the most violations is the most stringent. 

For thi s analysis, we compared the following three method/standard combinations: 

Cannot exceed 20% opacity, six-minute average. 

. Cannot exceed 20% opacity, three-minute average. 

. Cannot equal or exceed 20% opacity except for three minutes/hour, 

frequency count method. 

The specific assumptions and error margins for these combinations appear in 

Section 6.2. 

I

 : 

This data was the same as that used for the between-observer precision 

evaluation discussed in Section 5.3, and i t is more full y described there. 

46 
During the analysis, the opacity readings were "tested" first by assuming no 

margin of error for the reading method, and then by assuming the appropriate 

margin of error. The results show that the time exemption-type regulation' with 

the frequency count method was more stringent with no error margin than the threeminute average, but almost identical in stringency when the error margin Was 

figured in. As expected, the six-minute average was not as stringent on these 

intermittent emissions. A summary of the analysis appears in Table 11. 

The raw data used for this analysis are considered typical for intermittent 

emission sources. The nearly identical stringency of the two recommended methods, 

i 

the frequency count and three-minute average, indicates that either can be' used 

on intermittent emission sources, provided the reading method is consistent with 

the opacity standard. Different emission sources with plumes of different variability may show one method to be significantly more stringent than the other. 

Stringency analyses can be performed following the guidelines in Section 6.2 for 

specific source categories to determine more precisely the most stringent opacity 

standard/reading method combination. 

6.1 Procedure for Evaluating the Relative Stringency of Opacity Standard/Reading 

Method Combinations J 

. Obtain a statistically sufficient body of opacity readings at or above 

the opacity standard from different facilities. 

. Break the opacity data into 60-minute data sets. 

Assume a level of accuracy'to be used in comparing the methods (say, 

85% accuracy level). 

. Determine one combination of opacity standard/reading method (say, 

no more than 20% opacity except 3 minutes/hour, using the frequency 

count method) to be tested. 

. Test the opacity standard/reading method, taking into account the |1 eve! 

of accuracy of the method. Determine the number of 60-minute datia sets. 

in violation of the standard. 

47 
TABLE 11 

Relative Stringency Analysis of Intermittent Fugitive Emission Data! 

j Opacity Reading 

I Method 

I Frequency Count Method 

1 Violation with no 

1 error margin 

j Violation with 

I error margin 

I Three-Minute Average 

1 Violation with no 

I error margin 

I Violation with 

1 error margin 

1 Six-Minute Average 

1 Violation with no 

j error margin 

I Violation with 

1 7.5% opacity error 

Nonmetallic 

Sources (21 

# Sets 

21 

3 

6 

2 

5 

2 

Mineral 

Sets) 

% Sets 

100 

14 

29 

10 

24 

10 

Iron & Steel Sources 

(137 Sets) 

# Sets % Sets 

133 

69 

113 

69 

84 

55 

97 

50 

82 

50 

61 

40 

Al l Sources --

Reading <30 

Minutes T89 Sets) 

# Sets % Sets 

86 

31 

56 

26 

36 

15 

97 

35 

63 

29 

40 

17 

Al l Sources 

60-Minute 

Readings(69 Sets) 

# Sets % Sets 

68 

41 

63 

45 

53 

42 

99 

59 

91 

65 

77 

61 

TOTAL Al l 

Al l Read in 

(158 Sets) 

# Sets % 

154 

72 

119 

71 

89 

57 

Sources| 

gs 1 

Sets j 

97 | 

46 | 

75 | 

45 | 

56 | 

36 | 

1 

516 data sets total , with two readings (two observers) for each of the 516 data sets. The firs t reading of each pair was 

chosen for evaluation. Only those readings showing a violation by any of the three method/standard combinations were 

included in the 158 sets. 

48 
. Repeat the two previous steps with other combinations of opacity 

stand ard /read ing methods under consideration. 

. The opacity stand ard/read ing method showing the most violations is. 

the most stringent. 

6.2 Assumptions Used for Relative Stringency Evaluation 

Regulations/reading method compared: 

. Shall not equal or exceed 20% opacity except for three minutes/hour 

( frequency count method). 

Shall not exceed 20% opacity (3-minute and 6-minute averaging methods). 

Confidence interval chosen for error margins: 

a 95%. 

Error margins used: 

. 10% opacity + 15 seconds/6 minutes: frequency count method. 

. 11.8% opacity: 3-minute average. 

7.5% opacity: 6-minute average. 

Frequency count data reduction: 

. For 1-hour readings: 14 readings at >30% opacity (1 extra reading for 

each additional 6-minute period where 15-second readings are used for 

time exemption). 

. For 30-minute readings: 8 readings at ^30% opacity (1 extra reading 

for each additional 6-minute period where 15-second readings are used, 

for time exemption)!. i 

. For no error margin: 13 readings >20% opacity for 1-hour reading; 7 

readings >20% opacity for 30-minute readings. 

Only firs t reading of each pair was evaluated. 

Only readings where one or more methods showed violations were included in 

the data set (158 readings out of 516 reviewed). 

1 

For 30-minute readings, a 1-1/2-minute time exemption period was assumed 

rather than the 3 minutes per hour. 

49 
P.56 

7.0 SUMMARY AND MAJOR CONCLUSIONS 

Opacity observations taken by certifie d readers following proper reading 

procedures continue to be the most effective method of evaluating visibl e emissions. 

Based on the evaluation of three principal opacity reading methods and data from 

four field studies, the major conclusions are as follows: 

. For intermittent emission sources, the recommended reading methods are: 

1) frequency count for use with time exemption-type regulations, and 2) 

three-minute averaging for use with averaging opacity-type regulations. 

. The stopwatch method is in current use, particularl y with highly intermittent 

plumes. I t can be used effectively , provided an appropriate error margin 

is included. 

. A usable definitio n of intermittent emissions is "emissions in excess of the 

opacity standard for less than six consecutive minutes". 

. The frequency count method should be used with most time exemption-type 

regulations. Six-minute averaging should only be used when the time exemption period i s six minutes and six-minute averaging is specified in the 

promulgated reading method. Other averaging methods are not recommended 

for use with time exemption-type regulations, but could be used i f specified in the promulgated reading method. 

. The level of accuracy is established and included in this document for the 

frequency count method (al l plume types); one-, two- and three-minute averaging (intermittent plumes); and the stopwatch method (intermittent plumes). 

. The relative stringency-of differen t opacity standard/reading method combinations is an important consideration when new regulations are adopted, 

old regulations are changed, or permits or consent decrees are negotiated. 

A procedure for comparing the relative stringencies for specific source 

categories or individual facilitie s is presented in this document. 

. The three-minute average and frequency count methods were found to be almost 

identical in stringency when a typical data set of intermittent emissions 

was analyzed. 

50 
P.57 

APPENDIX A 

Federal Register, Vol. 39, No. 219, Reference Method 9 
P.58 

Title 40 — Protection of the Environment 

CHAPTER 1—ENVIRONMENTAL PROTECTION AGENCY 

Subchapter C--Air Programs 

(FRL 391-6) 

PART 60—STANDARDS OF PERFORMANCE FOR NEW STATIONARY SOURCES 

Opacity Provisions 

"On June 29, 1973, the United States Court of Appeals for the District of 

Columbia in 'Portland Cement Association v. Ruckelshaus,' 486 F.2d 375 (1973) 

remanded to EPA the standard of performance for Portland cement plants (40 CFR 

60.60 et seq.) promulgated by EPA under section 111 of the Clean Air Act. In 

the remand, the Court directed EPA to reconsider among other things the use of 

the opacity standards. EPA has prepared a response to the remand. Copies of 

this response are available from the Emission Standards and Engineering Division, 

Environmental Protection Agency, Research Triangle Park, N. C. 27711, Attn: Mr. 

Don R. Goodwin. In developing the response, EPA collected and evaluated a substantial amount of information which is summarized and referenced in the response. 

Copies of this information are available for inspection during normal office hours 

at EPA's Office of Public Affairs, 401 M Street SW., Washington, D. C. EPA determined that the Portland cement plant standards generally did not require revision but did (not, sic) find that certain revisions are appropriate to the opacity provisions of tho standards. The provisions promulgated herein include .*i 

revision of §60.11, Compliance with Standards and Maine--" "'; -,

 :. • ••>..-.t'-s , .-• 

revision to the opacity standard for Portland cement plants, and revisions to 

Reference Method 9. The bases for the revisions are discussed in detail in the 

Agency's response to the remand. They are summarized below. 

The revisions to §60.11 include the modification of paragraph (b) and the 

addition of paragraph (e). Paragraph (b) has been revised to indicate that while 

Reference Method 9 remains the primary and accepted means for determining compliance 

with opacity standards in this part, EPA will accept'as probative evidence in 

certain situations and under certain conditions the results of continuous monitoring 

by transmissometer to determine whether a violation has in fact occurred. The 

revision makes clear that even in such situations the results of opacity readings 

by Method 9 remain presumptively valid and correct. 

The provisions in paragraph (e) provide a mechanism for an owner or operator 

to petition the Administrator to establish an opacity standard for an affected 

facility where such facility meets all applicable standards for which a performance 

test is conducted under §60.8 but fails to meet an applicable opacity standard. 

This provision is intended primarily to apply to cases where a source installs a verv 

large diameter stack which causes the opacity of the emissions to be greater than 

if a stack of the diameter ordinarily used in the industry were installed. 

Although this situation is considered to be very unlikely to occur, this provision 

will accommodate such a situation. The provision could also apply to other 

situations where for any reason an affected facility could fail to meet opacity 

A-l 
P.59 

standards while meeting mass emission standards, although no such situations are 

expected to occur. 

A revision to the opacity standard for Portland cement plants is promulgated 

herein. The revision changes the opacity limit for kilns from 10 percent to 20 

percent. This revision is based on EPA's policy on opacity standards and the new 

emission data from Portland cement plants evaluated by EPA during its reconsideration. The preamble to the standards of performance which were promulgated on 

March 8, 1974 (39 FR 9308) sets forth EPA's policy on opacity standards: (1) 

Opacity limits are independent enforceable standards; (2) where opacity and 

mass/concentration standards are applicable to the same source, the mass/concentration standards are established at a level which will result in the design, installation, and operation of the best adequately demonstrated system of emission 

reduction (taking costs into account); and (3) the opacity standards are established at a level which will require proper operation and maintenance of such 

control systems. The new data indicate that increasing the opacity limits! for 

kilns from 10 percent to 20 percent is justified, because such a standard will 

still require the design, installation, and operation of the best adequately 

demonstrated system of emission reduction (taking costs into account) while 

eliminating or minimizing the situations where it will be necessary to promulgate 

a new opacity standard under §60.11(e). 

In evaluating the accuracy of results from qualified observers following the 

procedures of Reference Method 9, EPA determined that (some revisions to Reference 

Method 9 are consistently able to evaluation showed that, sic) observers trained 

and certified in accordance with the procedures prescribed under Reference Method 

9 are consistently able to read opacity with errors not exceeding + 7.5 percentbased upon single sets of the average of 24 readings. V--- r: ••;-io*-" I"'-' Rs>f> •"••"-nee 

Method 9 include the following: 

1. An introductory section is added. This includes a discussion of the 

concept of visible emission reading and describes the effect of variable viewing 

conditions. Information is also presented concerning the accuracy ofth e method 

noting that the accuracy of the method must be taken into account when determining 

possible violations of applicable opacity standards. 

2. Provisions are added which specify that the determination of opacity requires averaging 24 readings taken at 15-second intervals. The purpose for taking 

24 readings is both to extend the averaging time over which the observations are 

made, and to take sufficient readings to insure acceptable accuracy. 

3. More specific criteria concerning observer position with respect to the 

sun are added. Specifically, the sun must be within a 140° sector to the observer's 

back. 

4. Criteria concerning an observer's position with respect to the plume are 

added. Specific guidance is also provided for reading emissions from rectangular 

emission points with large length to width ratios, and for reading emissions from 

multiple stacks. In each of these cases, emissions are to be read across the 

shortest path length. 

A-2 
P.60 

5. Provisions are added to make clear the opacity of contaminated water or 

steam plumes is to be read at a point where water does not exist in condensed 

form. Two specific instructions are provided: One for the case where opacity 

can be observed prior to the formation of the condensed water plume, and one for 

the case where opacity is to be observed after the condensed water plume has 

dissipated. 

6. Specifications are added for the smoke generator used for qualification 

of observers so that State or local air pollution control agencies may provide 

observer qualification training consistent with EPA training. 

In developing this regulation we have taken into account the comments received 

in response to the September 11, 1974 (39 FR 35852) notice of proposed rulemaking 

which proposed among other things certain minor changes to Reference Method 9. This 

regulation represents the rulemaking with respect to the revisions to Method 9. 

The determination of compliance with applicable opacity standards will be 

based on an average of 24 consecutive opacity readings taken at 15 second intervals. 

This approach is a satisfactory means of enforcing opacity standards in cases where 

the violation is a continuing one and time exceptions are not part of the applicable 

opacity standard. However, the opacity standards for steam electric generators 

in 40 CFR 60.42 and fluid catalytic cracking unit catalyst regenerators in 40 CFR 

60.102 and numerous opacity standards in State Implementation Plans specify various 

time exceptions. Many State and local air pollution control agencies use a different 

approach in enforcing opacity standards than the six-minute average period specified 

in this revision to Method 9. EPA recognizes that certain types of opacity violations that are intermittent in nature require a different approach in applying the 

opacity standards than this revision to Method 9. It . •• :y?': \ = <.-• nt ;..• pr-r-pr-ie an 

additional revision tc Method 9 specifying an alternative method to enforce opacity 

standards. It is our intent that this method specify a minimum number of readings 

that must be taken, such as a minimum of ten readings above the standard in ?.ny one 

hour period prior to citing a violation. EPA is in the process of analyzing svailable data and determining the error involved in reading opacity in this manner and 

will propose this revision to Method 9 as soon as this analysisis completed. The 

Agency solicits comments and recommendations on the need for this additional revision 

to Method 9 and would welcome any suggestions particularly from air pollution control 

agencies on how we might make Method 9 more responsive to the needs of these agencies. 

These actions are effective on November 12, 1974. The Agency finds good cause 

exists for not publishing these actions as a notice of proposed rulemaking and for 

making them effective immediately upon publication for the following reasons: 

(1) Only minor amendments are being made to the opacity standards which 

were remanded. 

(2) The U. S. Court of Appeals for the District of Columbia instructed EPA 

to complete the remand proceeding with respect to the Portland cement plant 

standards by November 5, 1974. 

(3) Because opacity standards are the subject of other litigation, it is 

necessary to reach a final determination with respect to the basic issues involving 

A-3 
P.61 

opacity at this time in order to properly respond to this issue with respect to 

such other litigation. 

These regulations are issued udner the authority of sections 111 and 114 of 

the Clean Air Act, as amended (42 U.S.C. 1857c-6 and 9). 

Dated: November 1, 1974. 

John Quarles 

Acting Administrator." 

A-4 
P.62 

METHOD 9 — VISUAL DETERMINATION OF THE OPACITY OF 

EMISSIONS FROM STATIONARY SOURCES 

The current Method 9, published in the Federal Register, Volume 39, No. 219 

on November 12, 1974, i s reproduced below: 

"Many stationary sources discharge visibl e emissions into the atmosphere; 

these emissions are usually in the shape of a plume. This method involves the 

determination of plume opacity by qualified observers. The method includes procedures for the training and certificatio n of observers, and procedures to be 

used in the field for determination of plume opacity. The appearance of a plume 

as viewed by an observer depends upon a number of variables, some of which may 

be controllable and some of which may not be controllable in the field . Variables which can be controlled to an extent to which they no longer exert a significant influence upon plume appearance include: Angle of the observer with 

respect to the plume; angle of the observer with respect to the sun; point of 

observation of attached and detached steam plume; and angle of the observer with 

respect to a plume emitted from a rectangular stack with a large length to width 

ratio . The method includes specific criteri a applicable to these variables. 

Other variables which may not be controllable in the field are luminescence 

and color contrast between the plume and the background against which the plume 

is viewed. These variables exert an influence upon the appearance of a plume as 

viewed by an observer, and can affect the abilit y of the observer to accurately 

assign opacity values to the observed plume. Studies of the theory of plume 

opacity and field studies have demonstrated that a plume is most visibl e and 

presents the greatest apparent opacity when viewed against a contrasting background. I t follows from this , and is confirmed by field trials , that the opacity 

of a plume, viewed under conditions where a contrasting background i s present can 

be assigned with the greatest degree of accuracy. However, the potential for a 

positive error is also the greatest when a plume is viewed under such contrasting 

conditions. Under conditions presenting a less contrasting background, the apparent 

opacity of a plume i s less and. approaches zero as the color and luminescence contrast 

decrease toward zero. As a result, significant negative bias and negative errors 

can be made when a plume is viewed under less contrasting conditions. A negative 

bias decreases rather than increases the possibilit y that a plant operator wil l 

be cited for a violation of opacity standards due to observer error. 

Studies have been undertaken to determine the magnitude of positive errors 

which can be made by qualified observers while reading plumes under contrasting 

conditions and using the procedures set forth in this method. The results of 

these studies (fiel d trails ) which involve a total of 769 sets of 25 readings 

each are as follows: 

1) For black plumes (133 sets at a smoke generator), 100 percent of the sets 

were read with a positive error! of less than 7.5 percent opacity; 99 

percent were read with a positive error of less than 5 percent opacity. 

I 

Fcr a set, positive error = average opacity determined by observer's 25 observations - average opacity determined from transmissometer's 25 recordings. 

A-5 
P.63 

2) For white plumes (170 sets at a smoke generator, 168 sets at a coalfired power plant, 298 sets at a sulfuric acid plant), 99 percent of 

the sets were read with a positive error of less than 7.5 percent 

opacity; 95 percent were read with a positive error of less than 5 

percent opacity. 

The positive observational error associated with an average of twenty-five 

readings is therefore established. The accuracy of the method must be taken intoaccount when determining possible violations of applicable opacity standards. 

1. PRINCIPLE AND APPLICABILITY 

1.1 PRINCIPLE 

The opacity of emissions from stationary sources is determined visually by 

a qualified observer. 

1.2 APPLICABILITY 

This method is applicable for the determination of the opacity of emissions 

from stationary sources pursuant to §60.11 (b) and for qualifying observers for 

visually determining opacity of emissions. 

2. PROCEDURES 

The observer qualified in accordance with paragraph 3 of this method shall 

use the following procedures for visually determining the opacity of emissions. 

2.1 POSITION 

The qualified observer shall stand at a distance sufficient to orovide a 

clear view of the emissions with the sun oriented in the 140° sector u- his back. 

Consistent with maintaining the above requirement, the observer shall, as murh as 

possible, make his observations from a position such that his line of vision is 

approximately perpendicular to the plume direction, and when observing opacity of 

emissions from rectangular outlets (e.g. roof monitors, open baghouses, noncircular 

stacks), approximately perpendicular to the longer axis of the outlet. The 

observer's line of sight should not include more than one plume at a time when 

multiple stacks are involved, and in any case the observer should make his 

observations with his line of sight perpendicular to the longer axis of such a 

set of multiple stacks (e.g. stub stacks on baghouses). 

2.2 FIELD RECORDS 

The observer shall record the name of the plant, emission location, type 

facility, observer's name and affiliation, and the date on a field data sheet 

(Figure 9-1). The time, estimated distance to the emission location, approximate 

wind direction, estimated wind speed, description of the sky condition (presence 

and color of clouds), and plume background are recorded on a field data sheet at 

the time opacity readings are initiated and completed. 

A-6 
P.64 

2.3 OBSERVATIONS 

Opacity observations shall be made at the point of greatest opacity in 

that portion of the plume where condensed water vapor is not present. The observer 

shall not look continuously at the plume, but instead shall observe the plume 

momentarily at 15-second intervals . 

2.3.1 ATTACHED STEAM PLUMES 

When condensed water vapor is present within the plume as i t emerges from 

the emission outlet , opacity observations shall be made beyond the point in the 

plume at which condensed water vapor is no longer visible . The observer shall 

record the approximate distance from the emission outlet to the point in the 

plume at which the observations are made. 

2.3.2 DETACHED STEAM PLUME 

When water vapor in the plume condenses and becomes visibl e at a distinc t 

distance from the emission outlet , the opacity of emissions should be evaluated 

at the emission outlet prior to the condensation of water vapor and the formation 

of the steam plume. 

2.4 RECORDING OBSERVATIONS 

Opacity observations shall be recorded to the nearest 5 percent at 15-

second intervals on an observational record sheet. (See Figure 9-2 for an 

example.) A minimum of 24 observations shall be recorded. Each momentary 

observation recorded shall be deemed to represent the average opacity of 

emissions for a 15-second period. 

2.5 DATA REDUCTION 

Opacity shall be determined as an average of 24 consecutive observations 

recorded at 15-second intervals . Divide the observations recorded on the record 

sheet into sets of 24 consecutive observations. A set is composed of any 24 

consecutive observations. Sets need not be consecutive in time and in no case 

shall two sets overlap. For each set of 24 observations, calculate the average 

by summing the opacity of the 24 observations and dividing thi s sum by 24. I f an 

applicable standard specifies an averaging time requiring more than 24 observations, 

calculate the average for al l observations made during the specified time period. 

Record the average opacity on a record sheet. (See Figure 9-1 for an example.) 

3. QUALIFICATIONS AND TESTING 

3.1 CERTIFICATION REQUIREMENTS 

To receive certificatio n as a qualified observer, a candidate must be tested 

and demonstrate the abilit y to assign opacity readings in 5 percent increments to 

25 different black plumes and 25 differen t white plumes, with an error not to 

exceed 15 percent opacity on any one reading and an average error not to exceed 

7.5 percent opacity in each category. Candidates shall be tested according to the 

A-7 
P.65 

i l"i 

procedures described in paragraph 3.2. Smokt ^>.^. u..«i .. U a ^ KU1J 1 

graph 3.2 shall be equipped with a smoke meter which meets the req 

paragraph 3.3. 

Smoke generators used pursuant to parai meter which meets the requirements' of 

The certification shall be valid for a period of 6 months, at which time the 

qualification procedure must be repeated by any observer in order to retairi 

certification. i 

3.2. CERTIFICATION PROCEDURE 

The certification test consists of showing the candidate a complete run 

of 50 plumes - 25 black plumes and 25 white plumes - generated by a smoke generator. 

Plumes within each set of 25 black and 25 white runs shall be presented in random 

order. The candidate assigns an opacity value to each plume and records his 

observation on a suitable form. At the completion of each run of 50 readings, 

the score of the candidate is determined. If a candidate fails to qualify,' the 

complete run of 50 readings must be repeated in any retest. The smoke test' may 

be administered as part of a smoke school or training program, and may be preceded 

by training or familiarization runs of the smoke generator during which candidates 

are shown black and white plumes of known opacity. ' 

3.3 SMOKE GENERATOR SPECIFICATIONS 

Any smoke generator used for the purpose of paragraph 3.2 shall be equipped 

with a smoke meter installed to measure opacity across the diameter of thejsmoke 

generator stack.. The smoke meter output shall display in-stack opacity based 

upon a path length equal to the stack exit diameter, on a full 0 to 100 percent 

chart recorder scale. The smoke meter optical design and performance shall| meet 

the specifications shown in Table 9-1. The smoke mete -?:.-•''! '-;- calibrated ?. 

prescribed -n paragraph 3.3.1 prior to the conduct of each smoke reading test. 

At the completion of each test, the zero and span drift shall be checked and if 

the drift exceeds ±1 percent opacity, the condition shall be corrected prior to 

conducting any subsequent test runs. The smoke meter shall be demonstrated at 

the time of installation, to meet the specifications listed in Table 9-1. |This 

demonstration shall be repeated following any subsequent repair or replacement of 

the photocell or associated electronic circuitry including the chart recorder or 

output meter, or every 6 months, whichever occurs first. 

TABLE 9-1 — SMOKE METER DESIGN AND PERFORMANCE SPECIFICATIONS 

Parameter 

a. Light sourceb. Spectral response of 

photocell 

c. Angle of view 

d. Angle of projection 

Specification 

Incandescent lamp operated at nominal 

rated voltage. 

Photopic (daylight spectral response 

of the human eye - reference 4.3). 

15° maximum total angle. 

15° maximum total angle. 

A-8 
e. Calibration errorf. Zero and span drift 

g. Response time 

3.3.1. CALIBRATION 

+_ 3% opacity, maximum. 

+_ 1% opacity, 30 minutes, 

< 5 seconds. 

The smoke meter is calibrated after allowing a minimum of 30 minutes warmup 

by alternately producing simulated opacity of 0 percent and 100 percent. When 

stable response at 0 percent or 100 percent is noted, the smoke meter is adjusted 

to produce an output of 0 percent or 100 percent as appropriate. This calibration 

shall be repeated until stable 0 percent and 100 percent readings are produced 

without adjustment. Simulated 0 percent and 100 percent opacity values may be 

produced by alternately switching the power to the light source on and off while 

the smoke generator is not producing smoke. 

3.3.2 SMOKE METER EVALUATION 

The smoke meter design and performance are to be evaluated as follows: 

3.3.2.1 LIGHT SOURCE 

Verify from manufacturer's data and from voltage measurements made at the 

lamp, as installed, that the lamp is operated within +5 percent of the nominal 

rated voltage. 

3.3.2.2 SPECTRAL RESPONSE OF PHOTOCELL 

Verify from manufacturer's data that the photocell has a photopic response; 

i.e. , the spectral sensitivit y of the cell shall closely approximate the standard 

spectral-luminosity curve for photopic vision which is referenced in (b) of Table 

9-1 . 

3.3.2.3 ANGLE OF VIEW 

Check construction geometry to ensure that the total angle of view of the 

smoke plume, as seen by the photocell, does not exceed 15°. The total angle of 

view may be calculated from: 9= 2 tan-1 d/2L, where e = total angle of view; 

d = the sum of the photocell diameter + the diameter of the limiting aperture; 

and L = the distance from the photocell to the limiting aperture. The limiting 

aperture is the point in the path between the photocell and the smoke plume where 

the angle of view is most restricted. In smoke genertor smoke meters this is 

normally an orifice plate. 

3.3.2.4 ANGLE OF PROJECTION 

Check construction geometry to ensure that the total angle of projection of 

the lamp on the smoke plume does not exceed 15°. The total angle of projection 

may be calculated from: 9= 2 tan"1 d/2L, where 9 = total angle of projection; 

d = the sum of the length of the lamp filament + the diameter of the limiting 

aperture; and L = distance from the lamp to the limiting aperture. 

A-9 
• p--|---:t|-rT -

3.3.2.5 CALIBRATION ERROR j 

Using neutral-density filters of known opacity, check the error between the 

actual response and the theoretical linear response of the smoke meter. This 

check is accomplished by first calibrating the smoke meter according to 3.3.1 and 

then inserting a series of three neutral-density filters of nominal opacity of 

20, 50, and 75 percent in the smoke meter pathlength. Filters calibrated [within, 

+2 percent shall be used. Care should be taken when inserting the filters to 

prevent stray light from affecting the meter. Make a total of five nonconjsecutive 

readings for each filter. The maximum error on any one reading shall be 3 percent 

opacity. ' ! 

3.3.2.6 ZERO AND SPAN DRIFT 

Determine the zero and span drift by calibrating and operating the smoke 

generator in a normal manner over a 1-hour period. The drift is measured jby 

checking the zero and span at the end of this period. < 

3.3.2.7 RESPONSE TIME 

Determine the response time by producing the series of five simulated 0 

percent and 100 percent opacity values and observing the time required to jreach 

stable response. Opacity values of 0 percent and 100 percent may be simulated by 

alternately switching the power to the light source off and on while the smoke 

generator is not operating. ' 

4. REFERENCES 

| 

4.1 Air Pollution Control District Rules and Regulations, Los Angeles County 

Air Pollution Control District, Regulation IV, Prohibitions, Rule 50. 

4.2 Weisburd, Melvin I., Field Operations and Enforcement Manual for Air,] U.S, 

Environmental Protect' 

1972. pp. 4.1 - 4.36. 

-

Environmental Protection Agency, Research Triangle Park, N. C , APTD-1100,! August 

4.3 Condon, E.U., and Odishaw, H., Handbook of Physics, McGraw-Hill Co., N,.Y., 

N.Y. 1958, Table 3.1, p. 6-52." 

A-10 
P.68 

APPENDIX B 

Alternative Methods for Visual Determination 

of the Opacity of Emissions from Stationary Sources 

Appendix B contains introductory comments and detailed procedures for the 

two preferred methods. The methods are drafted in a regulatory format similar to 

that of Method 9. 
P.69 

ALTERNATIVE METHODS FOR VISUAL DETERMINATION 

OF THE OPACITY OF EMISSIONS FROM STATIONARY SOURCES 

On November 12, 1974, the Environmental Protection Agency (EPA) revised and 

repromulgated Reference Method 9 (40 CFR 60, Appendix A) for determination by 

qualified observers of the opacity of visible emissions from stationary sources. 

The Reference Method is applicable to sources subject to standards of performance 

promulgated under Sections 111 and 112 of the Clean Air Act. Reference Method 9 

includes procedures for the training and certification of observers, as well as 

field procedures for the determination of plume opacity. 

Reference Method 9 specifies the determination of-an average opacity from 

24 consecutive opacity observations taken at 15-second intervals. The Preamble 

to Reference Method 9 recognizes that certain types of opacity violations that are 

intermittent in nature or that are subject to time exemption-type regulations 

require an approach in applying the opacity standard; tii.r.: •...:'.\:'-s •..•;•:

 ; !•; >. oi 

the six-minute average of Revised Method 9. The Preamble further states EPA's 

intention to conduct more study and ultimately to propose alternative methods to 

Method 9 that better assess the compliance status of such sources of particulate 

emissions. 

Two acceptable procedures for determining the opacity of intermittent 

emissions in excess of an applicable standard are (1) by use of Method 9, except 

using a three-minute average; and (2) by aggregation of discrete measurements 

made at 15-second intervals to determine the accumulated time the opacity exceeds 

the standard (frequency count method). 

B-l 
•: • ..• p |T,„ , . , m, . 

To evaluate these procedures, a series of field experiments was conducted 

under controlled field conditions, using ligh t and dark visibl e plumes generated 

using a smoke generator, and with a transmissometer meeting the specifications of 

Method 9. During these evaluation tests , panels of qualified observers (certifie d 

by Method 9 procedures) read the generated plumes in 5% opacity increments and at 

15-second intervals. The data were reduced using the frequency count method and by 

averaging for varying lengths of time. Data from the earlier field trial s also 

were evaluated. Observer measurements were then compared to the reference values 

measured by the smoke generator transmissometer. Overall, 1,880 six-minute data 

sets were evaluated. 

The accuracy of the three-minute averaging methods for these data sets is as 

follows: 

. 85% of the data sets had an error of less than +7.5% opacity. 

. 95% of the data sets had an error of less than +11.8% opacity. 

Evaluating the accuracy of the frequency count method is somewhat more 

complicated. A combination of opacity error and time error was determined to 

be the most practical measure of method accuracy, in keeping with common practice 

by those State and local air control agencies using this method. The opaciity 

error factor (either 5% or 10% opacity) i s applied by subtracting i t from each 15-

second reading and then counting the number of 15-second readings above the| 

applicable standard. The time error factor (15 seconds/six-minute reading) i s 

applied by requiring the emissions in excess of the standard to be recorded for 

i 

i 

the time exemption period specified in the regulation plus the added time error 

period. For the 1,880 data sets evaluated: 

.85% of the data sets had no positive bias when a 5% opacity error factor 

and 15 seconds/six-minute reading time error factor were used. 

.95% of the data sets had no positive bias when a 10% opacity error factor 

and 15 seconds/six-minute reading time error factor were used. 

B-2 
P.71 

In the above statements, "no positive bias" means that the observed time 

above the standard (after error factors were added in) was always less than the 

transmissometer time above the standard. 

The accuracy of each method must be taken into account when determining 

possible violations of opacity standards. 

The three-minute average is applicable to those intermittent emission sources 

subject to an averaged opacity standard, or when the three-minute averaging method 

is specifically referred to in the regulation. The frequency count method is 

applicable to all time exemption-type regulations, both for intermittent and more 

continuous plume types. The one exception is for six minutes per hour time 

exemption regulations; in this case, a six-minute averaged reading should be used 

rather than the frequency count method if Method 9 is specified by regulation as 

the method to be used. 

1.0 PRINCIPLE AND APPLICABILITY 

1.1 PRINCIPLE 

The opacity of emissions from stationary sources is determined visually by a 

qualified observer. 

1.2 APPLICABILITY 

This method is applicable for the determination of the opacity of emissions 

from stationary sources with intermittent plumes and for all plume types where 

time exemption regulations apply. 'Intermittent plumes are defined in Section 

2.6.1 of this method. 

2.0 PROCEDURES 

An observer qualified in accordance with Section 3 of Reference Method 9 (40 

CFR 60, Appendix A) shall use the following procedures for visually determining 

the opacity of emissions from stationary sources with intermittent plumes. 

B-3 
2.1 POSITION 

The qualified observer shall stand at a distance sufficient to provide a 

clear view of the emissions with the sun oriented in the 140° sector to his or 

i 

her back. Consistent with maintaining the above requirement, the observer? shall, 

as much as possible, make his or her observations from a position such that 

his or her line of vision is approximately perpendicular to the plume direction, 

and, when observing opacity of emissions from rectangular outlets (e.g., roof 

monitors, open baghouses, noncircular stacks), approximately perpendicular to the 

longer axis of the outlet. The observer's line of sight should not include more 

than one plume at a time when multiple stacks are involved, and, in any case, the 

observer should make his or her observations with his or her line of sight 

perpendicular to the longer axis of such a set of multiple stacks (e.g., stub 

stacks on baghouses). 

2.2 FIELD RECORDS 

The observer shall record the name of the plant, emi i,sion locoucn, type of 

facility, observer's name and affiliation, and the date on a field data sheet. 

The time, estimated distance to the emission location, approximate wind direction, 

estimated wind speed, description of the sky condition (presence and color of 

clouds), and plume background are recorded on a field data sheet at the time 

opacity readings are initiated and completed. 

2.3 POINT OF OBSERVATION 

Opacity observations shall be made at the point of greatest opacity in that 

portion of the plume where condensed water vapor is not present. 

2.3.1 ATTACHED STEAM PLUMES 

When condensed water vapor is present within the plume as it emerges' from 

the emission outlet, opacity observations shall be made beyond the point in the 

B-4 
P.73 

plume at which condensed water vapor is no longer visible. The observer shall 

record the approximate distance from the emission outlet to the point in the 

plume at which the observations are made. 

2.3.2 DETACHED STEAM PLUMES 

When water vapor in the plume condenses and becomes visible at a distinct 

distance from the emission outlet, the opacity of emissions shall be evaluated at 

the emission outlet prior to the condensation of water vapor and the formation 

of the steam plume. 

2.4 OBSERVATION PROCEDURES 

2.4.1 FREQUENCY COUNT METHOD 

This method applies to al l sources subject to time exemption regulations, 

except where the time exemption period is for six minutes/hour and Reference 

Method 9 is specified as the required reading method. The observer shall not 

look continuously at the plume, but instead shall observe the plume momentarily 

at 15-second intervals . 

2.4.2 THREE-MINUTE AVERAGING METHOD 

This method applies to intermittent emission plumes from sources subject to 

averaged opacity regulations. Intermittent emissions are defined in Section 

2.6.1 . 

The observer shall not look continuously at the plume, but instead shall 

observe the plume momentarily at 15-second intervals. 

2.5 RECORDING OBSERVATIONS 

2.5.1 FREQUENCY COUNT METHOD 

Opacity observations shall be recorded to the nearest 5 percent at 15-second 

intervals on an observational record sheet. (See Figure B-l for an example.) 

B-5 
FIGURE B-l 

Data Reduction and Computation Form 

for 

Frequency Count Procedure 

r , r . . . „,,,,-

vl&itJLe civi.ibiO.Ni ut36tKVM I IUM r-L'rti.i 

SOURCE I-.AMC OBSERVATION OATC STA RT TIME STO P TIM E 

AOORESS SCC 

MIN 1 3 30 

\se c 

M1N \ 

SOURCE IO NUMBED 

POOCCSS EQUIPMENT 

CONTROL EQUIPMENT 

OPERATING MODE 

OPERATING MODE 

DESCRIBE EMISSION POINT 

START 

1 EIGHT ABOVE GROUND LEVEL 

DISTANCE FROM OBSERVER 

HEIGHT RELATIVE TO OBSERVER 

DIRECTION FROM OBSERVER 

DESCRIBE EMISSIONS 

START 

EMISSION COLOR 

START ST 

PLUME TYPE: CONTINUOUS 0 

FUGITIVE O INTERMITTENT Q 

WATER OROPLETS PRESENTNO a YES a IF WATER DROPLET PLUME: 

ATTACHED O DETACHED Q 

POINT IN THE PLUME AT WHICH OPACITY WAS DETERMINED 

START STOP 

DESCRIBE BACKGROUND 

DACKAnoUNO COLOR 

START STOP 

SKY CONDITIONS 

START STOP 

WIND SPEED 

START STOP 

WINO DIRECTION 

START STOP 

AMBIENT TEMP. 

START 

WET BULB TEMP . RH , percent 

SOURCE LAYOUT SKETCH DRAW NORTH ARROW 

o 

X EMISSION POINT 

SUN <> WIND 

PLUME AN O STACK 

COMMENTS 

OBSERVERS POSITION 

AVERAGE OPACITY FOR 

HIGHEST PERIOD X 0.25 = 

MINUTF.S EXCESS 

-.4 0 

SUN LOCATION LINE 

RANGE OF OPACIT Y READINGS 

MINIMU M >1 A X IMUM 

OBSERVER'S NAME (PRINT) 

OBSERVER'S SIGNATURE 

ORG ANIZ A T ION 

I HAVE RECEIVED A COPT OT THESE 0*-*CIT T OBSERVATIONS 

SIGNATURE 

CERTIFIED BY 

;£»lHE O BY 

B-6 
Each momentary observation recorded shall be deemed to represent the average 

opacity of emissions for a 15-second period. • 

2.5.2 THREE-MINUTE AVERAGING METHOD 

Opacity observations shall be recorded to the nearest 5 percent at 15-second 

intervals on an observational record sheet. (See Figure B-2 for an example.) 

Each momentary observation recorded shall be deemed to represent the average 

opacity of emissions for a 15-second period. 

2.6 DATA ANALYSIS 

2.6.1 DETERMINATION OF PLUME TYPE 

Determine the longest continuous time that the opacity observation as 

recorded exceeded the applicable opacity standards. If this time was less 

than six minutes, the emissions shall be considered intermittent. 

2.6.2 DATA ANALYSIS (FREQUENCY COUNT METHOD) 

Count the number of readings with opacity above the applicable standard, 

and multiply that number by 0.25 to determine the minut-v. j •.-. ,;: ^ •, :r>-.^. 

the standard. 

2.6.3 DATA ANALYSIS (THREE-MINUTE AVERAGING METHOD) 

Opacity shall be determined as an average of 12 consecutive observations 

recorded at 15-second intervals. Divide the observations recorded on the record 

sheet into sets of 12 consecutive observations. A set is composed of sny 12 consecutive observations. Sets need not be consecutive in time and in no case shall 

two sets overlap. For each set of 12 observations, calculate the average by summing the opacity of the 12 observations and dividing this sum by 12. Record the 

average opacity on a record sheet. 

2.7 OBSERVER CERTIFICATION REQUIREMENTS 

All observers shall be certified according to the procedures of Sections 

3.1-3.3, Reference Method 9. 

B-7 • 
FIGURE B-2 

Data Reduction and Computation Form 

for 

Three-Minute Averaging Procedure 

P.76 

• T i I""' 

VISIbL e ei.ll!>S>ilvi\i UdbcriVA l IUM H-t-rti.i 

SOURC E NAM E 

AOORES S 

CIT Y JSTA7 C 

1 

PHON E 

-* IP 

SOURC E I D NUMBE D 

PROCES S EQUIPMEN T 

CONTRO L EQUIPMEN T 

OPERATIN G MOD E 

OPERATIN G MOO C 

DESCRIB E EMISSIO N POIN T 

STAR T STO P 

HEIGH T ABOV E GROUN D LEVE L 

STAR T STO P 

DISTANC E FRO M OBSERVE R 

STAR T STO P 

HEIGH T RELATIV E T O OBSERVE R 

STAR T STO P 

DIRECTIO N FRO M OBSERVE R 

STAR T STO P 

DESCRIB E EMISSION S 

STAR T STO P 

EMISSIO N COLO R 

STAR T STO P 

WATE R DROPLET S PRESENT -

N O 0 YE S a 

PLUM E TYPE l CONTINUOU S 0 

FUGITIV E O INTERMITTEN T 0 

I F WATE R DROPLE T PLUME : 

ATTACHE D O DETACHE D O 

POIN T I N TH E PLUM E A T WHIC H OPACIT Y WA S DETERMINE D 

STAR T STO P 

DESCRIB E BACKGROUN D 

STAR T STO P 

BACKGROUN D COLO R 

STAR T STO P 

WIN D SPEE. ? 

STAR T STO P 

AMBIEN T TEMP . 

STAR T STO P 

S K Y CONDITION S 

STAR T STO P 

WIN D OlRfc.CT.O N 

STAR T STO P 

W C T BUL B TEMP . RH. percent 

SOURC E LAYOU T SKETC H DRA W NORT H ARRO W 

• o 

S U N <> AIN O ^ 

PLUME ANO STACK <XZ , ^OBSERVER S POSITIO N 

^^^0**'^ ^140-* ^ ^^^-..w ^ 

S U N LOCATIO N LIN E 

COMMENT S 

1 HAV E RECEIVE D A COH f O F T t-t E S E OPACIT Y OBSC->V»TiOh S 

SIGNATUR E 

T ITL E lOAT l 

OBSERVATIO N DAT E 

MIN \ 

• 

2 

J 

4 

s 

c 

7 

8 

•. 

t o 

1 1 

I z 

1 3 

* 4 

1 S 

1 * 

1 7 

t S 

i n 

2 0 

2 1 

2 2 

2 3 

2 4 

2 S 

2 « 

2 7 

2 8 

2 9 

3 0 

0 15 j 3 0 

STAR T TIM E 

* 5 

AVERAG E OPACIT Y FO R 

HIGHES T PERIO D 

Mltt V 0 

3 , j 

» 1 

3 3 

3 4 

3 3 

3 C 

3 7 

1 1 

3 9 

4 0 

4 1 

4 2 

4 3 

4 4 

« S 

4 4 

4 7 

4 8 

STO P TIM E 

I s 3 0 

_••. ; i . i _ 

. • 

t>2 

S 3 

5 4 

» S 

5 K 

5 7 

S S 

4 » 

C O 

NUMBE R O F READING S A B 

•». wr.R E 

RANG E O F OPACl T Y REAOlNG S 

MINIMU M MAXIMU M 

I S 

1 

j 

1 

i 

1 

J 

• 

' 

! 

! 

; 

1 

1 

1 

1 

r ue 

| 

OBSERVER' S NAM E IPRlNT I > 

OBSERVER' S SIGNATUR E DAT E 

ORCANt Z ATIO N 

CERTIFIE D B Y 

VCRI f IC O B Y 

-

DATE . 

O A T 

B-8 
P.77 

APPENDIX C 

Summary of General Opacity Regulations 

(by Region) 
Summary of r.--<-••-•" op ;•,.-: 

J-J i.cjglon; 

j lations 

STATE 

New Jersey 

New York 

Puerto Rico 

Delaware 

District of 

Columbia 

Maryland 

Pennsylvania 

Allegheny Cty 

Virginia 

West Virginia 

OPACITY 

LIMIT2 

TIME 

EXEMPTION REGION READING METHOD SPECIFIED IN REGULATIONS 

I 

Connecticut 

Ma i ne 

1 stack with 

2 or more 

sources or 

Massachusetts 

New Hampshire 

Rhode Island 

Vermont 

After 4/30/70 

20%/40% 

20% 

40% 

80% 

20%/40% 

20% 

20% 

40%/60% 

20%/60% 

5 min./hr 

5 min./hr 

20 min./hr 

10 min./hr 

6 min./hr 

3 min./hr 

3 min./hr 

6 min./hr 

Method 9 

Method 9 

Method 9 

Method 9 

II 

20% 3 min./30 min. 

20% 

20%/60% 4 min.'/30 min. 

Method 9, minimum 30-minute reading 

III 

20% 

0%/40% 

0%/20% 

Metro/Rural 

20%/60% 

20%/60% 

20%/60% 

20%/40% 

3 min./hr OR 

15 min./24 hr 

2 min./hr OR 

12 min./24 hr 

3 min./hr 

3 min./hr 

6 min./hr 

5 min./hr 

Method 9, except data reduction section 

1 

From "Opacity Regulations: Summary of Rev 

Environmental Services, Inc. for Stationa,. 

Method 9, except some sources instantaneous readings 

Method 9 

^on s and Rulemaking Status", prepared by Pacific 

Source Compliance Division, EPA, February 18, 1983. 

Where two opacity limits are given, the SP. >nd is a "cap" or maximum opacity never to be 

exceeded; "Connecticut", forexampleT-aMows- 5-minutes/hour-of— emissions -great er--than-20%-butless than 40%; no reading above 40% is allowed. 

C-1 
STATE 

Alabama 

Jefferson Cty 

Florida 

Georgia 

Kentucky 

existing 

new 

Mississippi 

North CaroMna 

before 7/01/71 

after 7/01/71 

South Carolina (No 

Boilers 

(before 2/71) 

(after 2/71) 

Tennessee 

attainment 

nonattainment 

Illinoi s 

Indiana 

attainment 

nonattainment 

Lake Cty (prop) 

Michigan 

proposed 

Minnesota 

existing 

new 

Ohio 

OPACITY 

LIMIT2 

2U%/40% 

20%/40% 

20% 

40% 

40% 

20% 

40% 

40% 

20% 

process rule) 

40% 

20% 

20% 

10% 

30%/60% 

30%/60% 

40%/60% 

30% 

20%/40% 

20%/27% 

20%/40% 

20% 

20%/60% 

TIME 

EXEMPTION 

6 min./hr 

6 min./hr 

5 min./hr 

20 min./24 

5 min./hr 

20 min./25 

5 min./hr 

OR 

hr 

OR 

hr 

OR 

20 min./24 hr 

5 min./hr 

20 min./24 

. 

8 min./hr 

15 min./hr 

15 min./hr 

3 min./hr 

6 min./hr 

4 min./hr 

5 min./hr 

OR 

hr 

CREGION 

IV 

V 

2 

READING METHOD SPECIFIED IN REGULATION 

Method 9, reading time specified 

Method 9 

Method 9, with exceptions for specified 

sources 

Method 9 

6-minute average, except for intermittent 

emissions (frequency count) 

Method 9, except for iron and steel 

Method 9 

Method 9 
STATE 

Wisconsin 

before 4/01/72 

after 4/01/72 

OPACITY 

LIMIT2 

40% 

20% 

TIME 

EXEMPTION REGION 

V 

VI 

READING METHOD SPECIFIED IN REGULATION 

Method 9 

Arkansas 

before 1/30/72 40% 

after 1/30/72 20% 

Louisiana 20% 

New Mexico 20% 

Oklahoma 20% 

Texas 

before 1/31/72 30% 

after 1/31/72 20% 

flow >100,000 acfm 15% 

5 min./hr OR 

15 min./24 hr 

6 min./hr Method 9 

Method 9, except 10-minute average 

Method 9, except 5-minute average 

TTT 

Iowa 

Kansas 

existing 

new 

Missouri 

Kansas City 

Out-of-State 

existing 

new 

SpringfieldGreen Cty 

existing 

new 

St. Louis 

Nebraska 

Ttethod 9 

Method 9 

Ringelmann Chart to be used, minimum 

of one-hour reading 

40% 

40% 

20% 

20%/60% 

40%/60% 

20%/60% 

40%/60% 

20%/60% 

20%/40% 

20% 

6 min./hr 

6 min./hr 

6 min./hr 

6 min./hr 

6 min./hr 

6 min./hr 

Ringelmann Chart to be used, minimum 

of one-hour reading 

Method 9 

C-3 

oo 

o 
OPACITY 

LIMIT2 

TIME 

STATE EXEMPTION REGION READING METHOD SPECIFIED IN REGULATION 

T U T 

Colorado 20% 

Montana 

before 11/23/68 40% 

after 11/23/68 20% 

North Dakota 

existing 40%/60% 

new 20%/40% 

South Dakota 20%/60% 

Utah 20% 

Wyomi ng 

existing 40% 

new single source 20% 

6 min./hr 

6 min./hr 

3 min./hr 

Method 9, except when intermittent emissions, 

exclude periods of no emissions 

Method 9 

TX 

Ari zona 

existing 40% 

new/nonpoint 

sources 20% 

California 40% 

Bay Area 20% 

San Bernardino 20% 

San Diego 20% 

South Coast 20% 

Hawai i 

existing 40% 

new 20% 

Nevada 20% 

3 min./hr 

3 min./hr 

3 min./hr 

3 min./hr 

3 mjn./hr 

3 min./hr 

Method 9 

Alaska 20% 3 min./hr 

Idaho 20% 3 min.hr 

Oregon 

before 6/01/70 40% 3 min./hr 

after 6/01/70 20% 3 min./hr 

Washington 20% 3 min./hr 

Revised Method 9 

C-4 

-o 

co 
United Slates 

Environmental Protection 

Agency 

Office ol Air Ouality Planning and Standards 

Stationary Source Compliance Division 

Washington D.C. 20460 

Official Business 

Penalty for Private Use 

S300 

Publication No Special Report Postage and 

Fees Paid 

Environmental 

Protection 

Agency 

EPA 335 

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