Source Evaluation Society 

Newsletter 

P. 0. Box 12124 

Research Triangle Park, North Carolina 27709 

Volume XXVIII, No. 4 Quarterly October-December 2004 

OFFICERS 

Pmsidsnt, Glenn England (GE EER) 

Vies Prssldsnt, Roy Owens (Owens Corning) 

Sscmtsry, Gail Westlin (Air Tech) 

Tmssursr, Peter Westlin (EPA) 

EDITOR 

Roger Shigehara (Emission Monitoring) 

SOCIETY NEWS ITEMS 

BOARD OF DIRECTORS 

Ed Nessel beck/Ron Mcleod ( 1 term) 

Jim Meador (2 terms) 

lves Tondeur/Kenneth Hinzaman (3 terms) 

Charles Duncan (GE EER), Past President. 

EDITORIAL COMMITTEE 

Lesley Sloss (lEA Coal Research) 

Larry Cottone (CCI Env. Consultants) 

1. The following items are included in this Newsletter: 

• Data Quality Committee Report 

• Announcement for Stationary Source Sampling and Analysis for Air Pollutants XXIX 

Conference 

• Call for Nomination: Matt De Vito A ward 

• George Walsh Scholarship A ward 

• Membership Update 

2. Call for Papers. WANTED!! Papers for publication in the SES Newsletter. Criteria? 

Informative, practical and useful. Please submit to the Editor for consideration. Thank you for those who 

have contributed articles. 

3. Technical Article. "Determination of Gas Stratification at Test Locations, "by Roger Shigehara 

(Emission Monitoring Inc.), Walter Smith (WalterS. Smith & Associates, Inc.), and Bill Mayhew (Source 

Testing & Consulting Services, Inc.). A-fta ctu,a 

PROPOSALS AND PROMULGATIONS OF REGULATIONS 

1. October 13, 2004 (69 FR 60837-60839). 40 CFR Part 63: CoktJ Ovsns: PushintL 

QusnchlntL snd Bsttsrv Stscks. Proposed rule; amendments. This proposed action would amend the 

parametric operating limits and associated compliance provisions for capture systems used to control 

emissions from pushing. This action also would amend the requirements for mobile scrubber cars that 

capture emissions which occur during pushing and travel. 

2. October 13, 2004 (69 FR 60813-60820). 40 CFR Part 63: CoktJ Ovsns: PushintL 

QusnchintL snd Bsttsrv Stscks. Direct final rule; amendments. This action amends the parametric 

operating limits and associated compliance provisions for capture systems used to control emissions from 
INTRODUCTION 

DETERMINATION OF GAS STRATIFICATION 

AT TEST LOCATIONS 

Roger T. Shigehara, Emission Monitoring 

WalterS. Smith, WalterS. Smith & Associates 

Bill Mayhew, Source Testing & Consulting Services 

For gaseous sampling, the U.S. Environmental Protection Agency (EPA) has used the concentrations 

at three points, i.e., 16.7%, 50.0%, and 63.3% of a measurement line, to be representative of the "true" 

concentration. A representative sample is defined as a concentration that is within ±5.0% of the "true" 

concentration. 

In the EPA procedure, a stratification test is conducted only if stratification is suspected and, 

generally, if a shorter measurement line is desired. The procedures are as follows: 

Part 60, Performance Specification 2 

If the measurement line is longer than 2.4 meters (7.8 ft) and pollutant stratification is not expected, 

the three traverse points may be located on the line at 0.4, 1.2, and 2.0 meters from the stack or duct wall. 

This option must not be used after wet scrubbers or at points where two streams with different pollutant 

concentrations are combined. If stratification is suspected, the following procedure is suggested. 

• Locate at least nine traverse points (rectangular ducts) or at least 12 total traverse points on two 

diameters (circular stacks; 6 points per diameter) according to Method 1. 

• Measure the pollutant concentration and, if applicable, diluent concentration at each point. 

• Determine if the mean pollutant concentration is more than 10% different from any single point. 

If so, the cross section is considered to be stratified, and the tester may not use the alternative 

traverse point locations (i.e., 0.4, 1.2, and 2.0 meters from the stack or duct wall.) but must use 

the three traverse points at 16.7, 50.0, and 83.3 percent of the entire measurement line. 

Section 8 .1.3 .2 goes on to say that "Other traverse points may be selected, provided that they can be 

shown to the satisfaction of the Administrator to provide a representative sample over the stack or duct cross 

section." 

Part 75, Appendix A 

Part 7 5 specifies the use of three points and, alternatively, six points at any location (including 

stratified locations). Like Part 60, the stratification test is conducted only if the tester wishes to use the 

shorter traverse and if stratification is likely to occur. 

• Locate at least 12 traverse points on two diameters according to Method 1 (no distinction is 

made between rectangular ducts and circular stacks) 

• Measure the pollutant concentration and, if applicable, diluent concentration at each point. 

• If an abbreviated stratification test (i.e., at 16.7%, 50.0%, and 83.3% of the stack diameter) or 

the 12-point stratification test is conducted and the results show that each point does not differ 

by more than ±1 0.0% of the arithmetic mean of all traverse points, the traverse points may be 

located at 0.4, 1.0, and 2.0 meters from the stack wall or 4.4, 14.6, and 29.6% of the stack 

diameter. Alternative specifications are ±5 ppm or ±0.5% C02 or 0 2• 
• If a 12-point traverse is conducted and the results show that no single point exceeds ±5 .0% of 

the arithmetic average of all traverse points, or 3 ppm or ±0.3% C02 or 0 2, then a single point at 

least 1 meter from the stack wall may be used. 

(!!f..ote: The Method 20 procedure is not a stratification test, but its purpose is to locate traverse 

points with the lowest 02 concentrations.) 

The Methods Improvement Group (MIG) of the Data Quality Committee (DQC) of the Source 

Evaluation Society (SES) undertook an evaluation of the above procedures. The purposes for this document 

were to investigate the following questions: 

• Does the three-point traverse provide a representative concentration to within ±5.0% of the true 

concentration? 

• Is the six-point traverse better than the three-point traverse in providing a representative 

concentration? 

• Does the three-point traverse provide enough information to determine whether the gases are 

stratified? If not, what would be acceptable? 

• What improvements should be made in the EPA procedures? 

STRATIFICATION DATA 

Nine individuals submitted stratification test data. Altogether, there were 331 sets of data for the 

following gases: 0 2 (1 05); NOx (1 03); C02 (50); S02 (36); CO (36); and unknown (1 ). The number of data 

sets that had concentrations less than 10 ppm was 42 or 12.9%. There were only 17 dual-probe data sets. 

About a third of the data sets (1 02) were from rectangular stacks; about two-thirds (229) were from circular 

stacks. 

All conclusions in this document are based on the submitted data set. These data are not necessarily 

representative of the population of emissions testing locations. 

The number of traverse points with each data set varied. The distribution is as follows: 

Table 1 -Distribution of the number of traversepoints. 

Traverse Points Number Percent 

7 5 1.5 

8 110 33.2 

10 3 0.9 

12 123 37.2 

>12 90 27.2 

TREATMENT OF DATA AND RESULTS 

The average of all the data points in each set was considered to be the "true" average. All other 

averages were compared against this overall average. Each measurement line (port) was considered to be a 

run. Thus, a rectangular stack with four ports had four runs and a circular stack had two runs, if both 

diameters were sampled. For the evaluations, it was assumed that any stratification was due to spatial rather 

than temporal variations. The data were also assumed to be unaffected any analytical discrepancies (such as 

error, drift or noise). In addition, the alternative specifications of ±3 or ±5 ppm and ±0.3% or ±0.5% C02 or 
02 were not considered. 

Three-Point Traverse 

To answer the question, does a 3-point traverse provide average concentrations to within ±5.0% of 

the "true" concentration, the average of the 3-point traverse was compared against the overall average. For 

02 concentrations, the factor (20.9- %02) was used in the denominator when determining the percent 

deviation because this is the factor for diluent-correction. The results were as follows: 

Table 2- Comparison of 3-Point averages_ Of:. ainst overall {all data) 

Uncorrected Uncorrected (Pollutant Only) Diluent-Adjusted 

Total Runs 853 425 482 

$:1::2.5% 659 77.3% 275 64.7% 339 70.3% 

$:1::5.0% 739 86.6% 329 77.4% 390 80.9% 

> ±5.0% 114 13.4% 96 22.6% 92 19.1% 

Since Table 2 is based on data submitted by very few testers, the summary may be misleading as the 

data set might be somewhat biased. For example, a large number of the data were submitted by an 

engineering firm not only involved in compliance testing, but also in engineering evaluations. In addition, the 

request made to the SES membership was primarily for stratified data. Therefore, the data set was divided 

into two categories: (1) non-stratified and (2) stratified. Stratification is considered to exist if any traverse 

point deviates by more than ±10.0%from the overall average. For these two categories, the questions 

become: 

• If gas concentrations are non-stratified, would three points provide a representative 

concentration? 

• If gas concentrations are stratified, would three points provide a representative concentration? 

Table 3 summarizes the data for the non-stratified sources: 

T. bl 3 c {3 R . t . t a e - ompan son o - ozn averaf{es Of. ams• overa or non-s t raLt "(iddt te a a. 

Uncorrected Uncorrected (Pollutant Only) Diluent-Adjusted 

Total Runs 609 258 322 

$:1::2.5% 583 95.7% 239 92.6% 299 92.9% 

$:1::5.0% 609 100.0% 258 100.0% 321 99.7% 

> ±5.0% 0 0.0% 0 0.0% 1 0.3% 

Thus, it can be concluded that for non-stratified gas concentrations, the 3-point average will provide 

a representative concentration to within ±5.0%. About 93% would be within ±2.5%. 

Table 4 summarizes the data for stratified gas concentrations. 

Table 4 - Comparison of 3-Point averages al), ainst overall (stratified data) 

Uncorrected Uncorrected (Pollutant Only) Diluent-Adjusted 

Total Runs 244 167 160 

$:1::2.5% 76 31.1% 36 21.6% 40 25.0% 

$:1::5.0% 130 53.3% 71 42.5% 69 43.1% 

> ±5.0% 114 46.7% 96 57.5% 91 56.9% 
Table 4 shows that if the gases are stratified, there is roughly a 50% chance that the three-point 

average will not yield results to within ±5.0%. 

Six-Point Traverse 

To answer the question, is the 6-point traverse better than the 3-point traverse, six points (in some 

cases, five) on a measurement line were selected, averaged and compared to the overall average. Only those 

measurement lines (diameters and ports) with five or more points were selected for this analysis. In some 

cases with rectangular stacks, the measurement line with the most number of traverse points were selected 

even though ports did not exist. For example, in a rectangular stack with 8 ports and an 8 x 4 matrix, the 

measurement line was taken to be in the directions of the 8 points which would have provided 4 measurement 

lines with 8 points rather than 8 measurement lines with 4 points. The results are shown in the table below: 

Table 4- Comparison of 3-point averages and 6-point averages {rom overall averages. 

Uncorrected Uncorrected Diluent-Adjusted (Pollutant Only) 

Total Runs 188 133 126 

No. of3-Point Averages> ±5.0% 45 35 29 

No. of6-Point Averages> ±5.0% 39 30 21 

Table 4 shows that the use of six points on a measurement line does not significantly improve the 

overall accuracy. While a 6-point line gives a better defmition of the measurement than a 3-point line, it does 

not necessarily give a better representation of the overall gas concentration. This occurs because of port-toport variations. Increasing the number of traverse points on a measurement line does not resolve port-to-port 

variations. Based on the data evaluated, the EPA practice of using six traverse points for stratified gas 

concentrations should be revised. 

Three-Point Traverse as an Indicator of Stratification 

To answer the question, does the three-point traverse provide enough information to determine 

whether the gases are stratified, the 3-point traverse data were evaluated at the 10% and 5% indicator levels. 

The deviations were determined from the average of the three concentrations. Only stratified data were 

evaluated. The results are summarized in Table 5 below. 

Table 5-3-point traverse to indicate sources with stratification 

Uncorrected Uncorrected Diluent-Adjusted (Pollutant Only) 

Data Sets 73 57 55 

Total Runs 244 167 160 

Stratified at 10% level 109 44.7% 99 59.3% 88 55.0% 

3-point average >5.0% 80 73.4% 73 73.7% 67 76.1% 

Stratified at 5-10% level 53 21.7% 30 18.0% 33 20.6% 

3-point average >5.0% 18 34.0% 15 50.0% 15 45.5% 

Stratification not detected 82 33.6% 38 22.7% 39 24.4% <5.0% level 

3-point average >5.0% 16 34.0% 8 21.1% 8 20.5% 

Stratification not detected at 135 55.3% 68 40.7 62 45.0% 10% level 

3-point average >5.0% 34 25.2% 23 33.8% 23 37.1% 

In order to understand the implications of Table 5, the uncorrected data are used as an example. Out 
of244 runs, 109 (44.7% of244) were found to be stratified at the 10% level. Ofthese 109 runs, the 3-point 

averages of 80 runs (73.4% of 1 09) were greater than the overall or "true" concentrations by ±5.0%. 

The 5.0% indicator level added 53 runs (21.7% of244). Of these 53, 18 (34.0% of 53) had 3-point 

averages greater than ±5 .0%. The significant statistic is that stratification was not detected in 82 out of 244 

(33.6%). But, only 16 out of82 had 3-point averages greaterthan±5.0%. 

Looking at only the 10% indicator level, 135 out of 244 (55.3%) would not have been detected as 

being stratified, and 34 out of the 135 (25.2%) had 3-point averages greater than ±5.0%. It is obvious that 

the 3-point traverse is not effective in detecting stratification and does not provide a representative 

concentration more than 25% of the time. 

Three/Two-Point Traverse as an Indicator of Stratification 

The short-fall of a 3-point traverse is that it does not detect port-to-port stratification. A 6-point 

traverse on the same measurement line would also have the same deficiency. To account for port-to-port 

stratification, a 5-point traverse or 3/2-point traverse was formulated as follows: In addition to the 3-point 

traverse on a measurement line that passes through or near the centroid of the stack, select one point from 

each of the outer ports (16.7% from one port and 83.3% from the other port) in rectangular stack or two 

points (16.7% and 83.3%) from the other diameter. Determine the deviation from the average of all five 

points. Table 6 summarizes the results for this scenario: 

T a e bl 6 3 . - -pom t vs. 3/2 -pomt averages or s ratt "fied 1 d ata 

Uncorrected Uncorrected (Pollutant Only) Diluent-Adjusted 

3-Point 5-Point 3-Point 5-Point 3-Point 5-Point 

Total Runs 104 123 79 91 76 87 

~2.5% 31 29.8% 71 57.7% 21 26.6% 43 47.3% 22 28.9% 40 46.0% 

~5;0% 58 55.8% 88 71.5% 42 53.2% 56 61.5% 41 53.9% 51 58.6% 

>±5.0% 46 44.2% 35 28.5% 37 46.8% 35 38.5% 35 46.1% 36 41.4% 

The 3-point and the 3/2-point comparison is given since only the measurement line passing through 

or next to the centroid was used. An improvement is seen from going to a 3-point to a 3/2-point in that the 

percentage of averages greater than ±5.0% drops. However, the 3/2 point traverse does not provide 

representative values within ±5.0% of the overall average. 

The 3/2-point scenario was then investigated to determine whether it could be used an indicator of 

stratification. The results are shown in Table 7. 

Table 7- 3/2-]!oint traverse to indicate sources with stratification 

Uncorrected Uncorrected (Pollutant Only) Diluent-Adjusted 

3-Point 3/2-Point 3-Point 3/2-Point 3-Point 3/2-Point 

Total Runs 104 123 79 91 76 87 

Stratified at I 0% level 47 45.2% 91 74.0% 42 53.2% 72 79.1% 43 56.6% 70 80.5% 

Averages >5.0% 31 66.0% 35 38.5% 27 64.3% 35 48.6% 28 65.1% 34 58.6% 

Stratified at 5-l 0% level 25 24.0% 11 8.9% 18 22.8% 7 7.7% 16 21.0% 6 6.9% 

Averages >5.0% 8 32.0% 0 0.0% 7 38.9% 0 0.0% 5 31.3 0 0.0% 

Stratification not detected 32 30.8% 21 17.1% 19 24.1% 12 13.2% 17 22.4 11 12.6% <5.0% level 

Averages >5.0% 6 18.8% 0 0.0 2 10.5% 0 0.0% 5 11.8 0 0.0% 

Stratification not detected 57 54.8% 32 26.0% 37 46.8% 19 20.9% 33 43.4% 17 19.5% 

at 10% level 

Averages >5.0% 14 24.6% 0 0.0% 9 24.3% 0 0.0% 10 30.3% 0 0.0% 

Table 7 shows that the 3/2-point traverse is effective in indicating stratification. Even if there were 
some false negatives (indication of no stratification when it is in fact stratified), there were no 3/2 averages 

greater than ±5.0% from the overall averages in these false negative cases. 

Twelve-Point Traverse 

The EPA procedure requires a 12-point traverse to determine whether stratification exists. The 

question is whether 12 points are sufficient to provide a representative sample. The database had 39 sets of 

data with more than 12 points. Of these, 3 gave 12-point averages that were greater than ±5.0% from the 

overall average. Two had very similar profiles, with high concentrations in the mid port. The other also had 

high concentrations toward the center of the stack. There was no obvious indicator of when to increase the 

number of traverse points. Using either the maximum deviation from the average of 12 points or the relative 

standard deviation did not provide a definitive answer. In one case, increasing the number to 16 did not 

provide a representative concentration; in fact, it gave a worse result. 

The runs with greater than ±5.0% were as follows: 

Table 8- Runs with excessive deviations. 

No. Traverse Pts Overall Average 12-Point Average %Deviation 

28 9.7 10.2 5.7 

28 6.1 6.6 8.0 

48 1.5 1.4 -6.0 

It should be noted this is a small data set and that these data all represent low emissions 

applications where small process variations may influence emissions levels more significantly as a percent of 

the total concentration. It is possible that accounting for temporal changes would reduce the degree of 

stratification, but this is speculation. Similarly, at these levels, minor analytical errors and instrument drift 

can have a greater impact on a percentage basis. Since increasing the number of traverse points beyond 12 

would penalize the other 36 sources, and the deviations are less than ±8.0%, it is recommended that the 12-

point traverse be kept. 

CONCLUSIONS 

• When no stratification exists, a three-point traverse would provide a representative concentration 

within ±5.0% of the "true" value. 

• When stratification exists, a three-point traverse will not yield representative concentrations 

roughly 50% of the time. 

• Increasing the number of traverse points on a measurement line does not resolve port-to-port 

variations. 

• Using the concentrations of a 3-point traverse does not flag stratification roughly 40% of the 

time, and of these roughly 35% are greater than ±5.0% of the "true" average. 

• The 3/2-point traverse does not flag stratification roughly 20% of the time, but none of these had 

average concentration greater than ±5.0% of the "true" average. 

• The 12-point traverse does not provide averages within ±5.0% of the overall concentration about 

8% of the time for the data set evaluated. However, the deviations observed were less than about 

8%, which isn't appreciable when the low concentration levels are considered. 

Based on the above, a test method for determining initial stratification and procedure for utilizing the 
information in subsequent tests are provided in the attachment. 

ACKNOWLEDGEMENT 

The authors wish to acknowledge the following for their assistance in providing data for the 

evaluation: 

• Greg Burch, Golden Specialty Consulting, Inc. 

• Larry Cottone, CCI Environmental Consultants 

• Carl Fink, TRC Solutions 

• Brian J. Kearney, Reliant Energy 

• Calvin W. Loomis, Bison Engineering, Inc. 

• Bill Mayhew, Source Testing & Consulting Services, Inc. 

• Jill Merrill, Air Compliance Consultants, Inc. 

• Peter Pakalnis, LEHDR Environmental Services Limited 

• Roger T. Shigehara, Emission Monitoring Inc. 
DETERMININATION OF GAS STRATIFICATION 

AT TEST LOCATIONS 

(SES Procedure) 

SUMMARY 

This document sets forth a procedure for determining the existence and degree of gaseous 

stratification at continuous emission monitoring system (CEMS) relative accuracy test audit (RAT A) or 

compliance test locations. Depending on the degree and type of stratification, procedures for subsequent 

testing is suggested. 

This test should be conducted initially at all sources subject to compliance regulations and after any 

significant physical or process changes. It is expected the degree of stratification (after time adjustment and 

dilution correction) will be low in most cases. Therefore, subsequent test requirements would be minimal. 

This guideline does not address the impact of stratification on compliance. For example, if the 

concentrations are low relative to the emission limit, the degree of stratification may not affect the 

determination of compliance. Therefore, absolute values, e.g., ±0.1% 02 or ±0.2 ppm, are not included in any 

of the specifications. Any alternative specifications should be handled on a case-by-case basis. 

PROCEDURE 

1. Apparatus 

1.1 Sample Probes 

1.1.1 A single-point (SP) probe of sufficient length to traverse the stack or duct 

1.1.2 A stationary point probe (STP). The STP probe could be that of the CEMS. 

1.2 Sampling and Measurement Systems 

1.2.1 Two (2) completely redundant reference method systems (e.g., Method 3A, 6C, 7E), one for the SP 

probe and the other for the STP probe. One of these systems could be the CEMS. If a time shared 

system is used for the CEMS, it should be "locked in" to the stack being tested for the duration of the 

traverse and returned to the cycling mode after completion of the stratification test. 

1.2.2 Note: The system should be capable of recording readings every 10-15 seconds,from which 

]-minute averages or an average for the each traverse point can be computed. 

1.3 Steady-State Operations 

1.3 .1 If the source is considered to be a steady-state process, the STP probe system may be omitted. 

1.3.2 Note: Processes that are considered to be steady state may have temporal variations as a result 

of, e.g., burner operations, variable dilution, or variable feed. Temporal variations tend to show 

up as a seeming stratification; therefore it is suggested that the STP probe not be omitted. 
2. Measurement Procedure 

2.I Number of Traverse Points and Locations 

2.1.1 Select a minimum of I2 traverse points for circular stacks (six points each on two diameters 90° 

apart) and rectangular ducts (balanced matrix, e.g., 4x3, and if more than 12 points are selected, 

having at least 3 traverse points on a measurement line). 

2.1.2 Locate the traverse points according to Method I. If the STP probe is like the SP probe, select the 

centroid of the stack or duct or a point at least I meter from the stack wall. 

2.1.3 Stacks <24" in Diameter or <24" x 24": For circular stacks, select a minimum of 5 traverse points 

at 16.7, 50.0, and 83.3% of one diameter and 16.7 and 83.3% of the other diameter (3/2 traverse). In 

rectangular ducts, use 16.7, 50.0, and 83.3% in the port closest to the centroid and 16.7% on one 

outside port and 83.3% on the other outside port. 

2.2 Measurements 

2.2.1 With the appropriate reference methods, measure the pollutant and, if applicable, diluent (02 or C02) 

concentrations at each of the traverse points with the SP probe. Sample a minimum of 2 minutes 

plus at least two times the system response time at each point. 

2.2.2 While the SP probe is traversing each point and taking measurements, record readings continuously 

from the STP probe. 

2.2.3 Note: It is suggested that sampling time at the first two traverse points be conducted at a 

minimum of 5 minutes plus at least two times the system response time at the first two traverse 

points. If temporal variations are not noted, the sampling time at the remaining traverse points 

may be reduced to 2 minutes plus at least two times the system response time. The degree of 

temporal variation is a matter of judgment; generally, when temporal variations are present, it is 

better to sample longer at a traverse point. 

2.2.4 Note: The stratification test may (option) be conducted during the first RATA or compliance test 

run, if such a test is being conducted simultaneously. 

3. Calculations 

3.1 Point-Average 

3 .I.I If sampling time at a traverse point is more than 2 minutes, average the appropriate number of 

readings to obtain one "matching" pair (SP and STP) for each traverse point. Be sure to consider 

differences in the response time between the SP and STP systems. 

3.I.2 Note: It is helpful to plot the readings from both the SP and STP probes on a line graph; this 

graph may be used to consider the differences in response times and to match the readings from 

the STP probe with the corresponding readings from the SP probe. The plot of the concentrations 

from the STP probe is also helpful in determining (or confirming) whether temporal variations 

are occurring and whether the averaging time is adequate. 

3.2 Overall Average and Deviation 

3 .2.1 Calculate the overall average from the STP probe, and calculate the average of all traverse points and 

percent deviation of each concentration from the SP average using the "as measured" (i.e., no 

corrections or adjustments), except as specified in the options below: 
3.2.2 Option 1 

3.2.2.1 If temporal changes are occurring, adjust the SP probe concentrations for time variation as follows: 

where: 

Ctak = time-adjusted concentration, where k = traverse points 1 ... n 

Cm1 = STP concentration when SP is at traverse point "1" (any other reference point 

may be used including the average) 

Cmk = STP concentration when SP is at traverse point "k" 

Csk = SP concentration at traverse point "k" 

n = numberoftraversepoints(e.g., 12) 

3.2.2.2 Note: It is highly recommended that this option be taken since the time-adjusted concentrations 

tend to eliminate the seeming stratification from temporal variations. ff stratification increases 

as a result of time adjustments, the cause should be investigated.) 

3.2.3 Option 2 

3.2.3.1 If 0 2 is used to adjust the pollutant concentration for dilution, use the quantity (20.9-%02avJ in the 

denominator when calculating the percent deviation for 0 2. For example, if the deviation of a 

traverse point from the overall average is 0.2% 02, then divide this quantity by (20.9-%02avJ times 

100 to obtain the percent deviation. 

3.2.3.2 Note: The quantity (20.9-%02) shall not be applied if02 is used for other than dilution 

correction, e.g., in wet/dry 02 measurements for moisture determination systems. The use of this 

quantity aids in assessing the impact of02 imprecision at high levels of02 often encountered in 

gas turbines; the imprecision shows up as variation. 

3.2.4 Option 3 

3.2.4.1 If the CEMS is being evaluated in terms of dilution-corrected concentrations, adjust the pollutants for 

dilution (e.g., 15% or 7%02, 12% C02, or lb/mmBtu) for both the STP and SP concentrations. 

3.2.4.2 Note: ffthe RATA comparison or emission limit is on the basis of a mass emission rate (e.g., 

lb/hr), DO NOT use this option unless the flow rate is also determined on the same basis 

(e.g., 15% 02, 7% 02, or 12% C02). ff the mass emission rate is determined by multiplying 

lb/mmBtu by the heat input rate, then it is acceptable to use Option 3. ff this option is used, apply 

dilution correction to both the STP and M-3 probes. 

4. Evaluation 

4.1 Condition 1. If the concentration at any of the individual traverse points deviates from the overall 

average by no more than ±5 .0%, then: 

4.1.1 Any of the traverse points having concentrations within± 1.0% of the overall average may be used 

for RAT As or compliance tests. It is preferable not to select traverse points closest to the port holes 

or walls. If no points are within ±1.0%, select at least two points whose average is within ±1.0% of 

the overall average. 
4.1.2 In subsequent stratification tests, this source and location are exempted from the full12-point 

traverse provided that a 3-point traverse at 16.7, 50.0, and 83.3% of the measurement line is used in 

its place. As an alternative, you may substitute three other points on a measurement line, provided 

that its average is within ±1.0% of the overall average based on the initial12-point stratification test. 

4.1.2.1 If the maximum absolute percent deviation from the average of the three points is ~.0%, a single 

point closest to the average may be used after the initial RAT A or compliance test run. 

4.1.2.2 If the maximum absolute percent deviation is greater than 5.0%, but :Sl.O.O%, then the 3-point 

traverse must be used for all subsequent runs. 

4.2 Condition 2. If the concentration at any of the individual traverse points deviates from the overall 

average by no more than ±10.0%, then: 

4.2.1 Select any three points on a measurement line whose average falls within ±1.0% of the overall 

average. It is preferable that the measurement line passes through or near the centroid of the stack or 

duct. Use these three points as traverse points for RATA or compliance tests. 

4.2.2 In subsequent tests, this source and location are exempted from the full12-point traverse provided 

that a 3-point traverse at 16.7, 50.0, and 83.3% ofthe measurement line is used in its place. The 

traverse points selected under Step 4.2.1 may be used as an alternative. 

4.2.2.1 If the maximum absolute percent deviation from the average of the three points is :Sl.O.O%, you may 

continue to use the 3-point traverse for all RAT A or compliance test runs. 

4.2.2.2 If the maximum absolute percent deviation is greater than 10.0%, then you must use the full12 

traverse points for all subsequent runs. 

4.3 Condition 3. If the concentration at any of the individual traverse points deviates from the overall 

average by more than ±10.0%, then: 

4.3.1 Use al112 traverse points for RATA or compliance tests. 

4.3.2 Note: If Condition 3 is the case, measure velocity simultaneously at each of the traverse points. 

Use the velocity-weighted concentrations to determine whether stratification exists. 

4.3.3 All subsequent tests must use the full12-point traverse, unless data are provided to demonstrate that 

fewer points consistently yield an appropriate average. This demonstration shall consist of at least 

two additional ful112-point stratification tests (three in all). The selection of the traverse points 

must be consistent from test to test for any given source/location. For example, in a circular stack, 

the traverse points might be at 16.7, 50.0, and 83.3% of one diameter and two points at 16.7 and 

83.3% of the other diameter (referred to as 3/2-traverse). 

4.3.4 Note: Historical stratification data have shown that when stratification exists it is best to select 

three points on a measurement line that passes through or near the centroid of the stack or duct 

and having at least two other points. For circular stacks, the two points should be on the other 

diameter; for rectangular stacks, one point should be from each of the two outer ports. 

4.3.5 Note: Data used to demonstrate "consistency" (see Section 4.3.3) requires a definition, which 

has not yet been developed. Based on the 3/2-point traverse data, it is believed that ±1.0 to ±2.5% 

is be a "reasonable" range for consistency.