# Source Evaluation Society 

# Newsletter

P. 0. Box12124 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 Nesselbeck/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 andAnalysis 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 ofGas Stratification at TestLocations, "by Roger Shigehara (Emission Monitoring Inc.), Walter Smith (WalterS. Smith 

### &Associates, Inc.), and Bill Mayhew (Source Testing & Consulting Services, Inc.). 

# A-ftactu ,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 BillMayhew, 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% ofa measurement line, to be representative ofthe "true" concentration. A representative sample is defined as a concentration that is within ±5.0% ofthe "true" concentration. Inthe EPAprocedure, a stratification test is conducted only ifstratification is 

### suspectedand, generally, ifa shorter measurement line is desired. Theprocedures are as follows:


### Part60, Performance Specification 2 Ifthe measurement line is longer than 2.4 meters (7.8 ft) and pollutant stratification is not expected, the three traverse points maybe located on the line at 0.4, 1.2, and 2.0 meters from the stackorduct wall. This option must not beused after wet scrubbers or atpoints where two streams with different pollutant concentrations are combined. Ifstratification is suspected, the following procedure is suggested.
• Locate at least nine traverse points (rectangular ducts) or at least 12 total traversepoints on two diameters (circular stacks; 6 points perdiameter) according to Method 1.
• Measure the pollutant concentration and, ifapplicable, diluent concentration at each point.
• Determine ifthe mean pollutant concentration is more than 10% different from any single point. Ifso, the cross section is considered to be stratified, and the tester maynot 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 ofthe entire measurement line. Section 8.1.3.2 goes on to saythat "Othertraverse points maybe selected, provided that they can be shown to the satisfaction ofthe Administrator to provide a representative sample over the stack or duct cross section." 

### Part75, Appendix A Part 7 5 specifies the use ofthree points and, alternatively, six points at any location (including stratified locations). Like Part 60, the stratification test is conducted only ifthe tester wishes to use the shortertraverse and ifstratification is likely to occur.
• Locate at least 12 traverse points on two diameters according to Method 1 (no distinction is madebetween rectangular ducts and circular stacks)
• Measure the pollutant concentration and, ifapplicable, diluent concentration at each point.
• Ifan abbreviated stratification test (i.e., at 16.7%, 50.0%, and 83.3% ofthe stack diameter) or the 12-point stratification test is conducted and the results showthat eachpoint does not differ bymore than ±10.0% ofthe arithmetic mean ofall traverse points, the traverse points maybe located at 0.4, 1.0, and 2.0 meters from the stack wall or4.4, 14.6, and 29.6% ofthe stack diameter. Alternative specifications are ±5 ppmor ±0.5%

### C02 or

### 0 2•• Ifa 12-point traverse is conducted and theresults showthat no single point exceeds ±5.0% of the arithmetic average ofall traverse points, or 3 ppm or±0.3% C02 or0 2 , then a single point at least 1 meter from the stack wall maybeused. 

### (!!f..ote: The Method 20procedure is not a stratification test, but itspurpose is to locate traverse points with the lowest 02 concentrations.) The Methods Improvement Group (MIG) ofthe Data Quality Committee (DQC) ofthe Source Evaluation Society (SES) undertook an evaluation ofthe above procedures. Thepurposes for this document were to investigate the following questions:
• Does the three-point traverse provide a representative concentration to within ±5.0% ofthe true concentration?
• Is the six-point traverse betterthan the three-point traverse in providing a representative concentration?
• Does the three-point traverse provide enoughinformation to determine whether the gases are stratified? Ifnot, what would be acceptable?
• What improvements should bemade in the EPAprocedures?


### STRATIFICATION DATA Nine individuals submitted stratification test data. Altogether, there were 331 sets ofdata for the following gases: 0 2 (105); NOx (103); C02 (50); S02 (36); CO (36); and unknown (1). The number ofdata sets that had concentrations less than 10 ppm was 42 or 12.9%. There were only 17 dual-probe data sets. About a third ofthe 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 arenot necessarily representative ofthe population ofemissions testing locations. The number oftraverse points with each data set varied. The distribution is as follows: 

### Table 1 -Distribution of the numberof 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 OFDATA AND RESULTS The average ofall the data points in each set was considered to bethe "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, ifboth diameters were sampled. Forthe evaluations, it was assumed that any stratification was due to spatial rather than temporal variations. The data were also assumed to beunaffected any analytical discrepancies (such as error, drift ornoise). In addition, the alternative specifications of±3 or±5 ppm and ±0.3% or ±0.5% C02 or02 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 ofthe 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. Theresults were as follows: 

### Table 2- 

### Comparison of 3-Point averages_ O f:. 

### 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 byveryfew testers, the summarymaybemisleading as the data set might be somewhat biased. For example, a large number ofthe data were submitted byan engineering firm not only involved in compliance testing, but also in engineering evaluations. In addition, the request made to the SES membership was primarilyfor 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 pointdeviates bymore than ±10
.0%from the overallaverage. Forthese two categories, the questions become:
• Ifgas concentrations are non-stratified, would three points provide a representative concentration? • Ifgas 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 - 

### ompanson o - ozn averaf{es O f. 

### ams• overa 

### t "(iddt or non-s raLt 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 beconcluded that for non-stratified gas concentrations, the 3-point average will provide a representative concentration to within ±5.0%. About 93%would bewithin ±2.5%. Table 4 summarizes the data for stratified gas concentrations. 

### Table 

### 4

- Compari son of 3-Point averages a l), ainstoverall(stratifieddata ) 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 ifthe 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, sixpoints (in some cases, five) on a measurement line were selected, averaged and comparedto the overall average. Onlythose measurement lines (diameters and ports) with five ormorepoints were selected for this analysis. In some cases withrectangular stacks, the measurement line with the most number oftraverse points were selected even though ports did not exist. For example, in a rectangular stackwith 8 ports and an 8 x 4 matrix, the measurement line was taken to be in the directions ofthe 8 points which would have provided 4 measurement lines with 8 points rather than 8 measurement lines with 4 points. Theresults are shown in the table below: 

### Table 4- Compari son of 3-point averages and 6-point averages {rom overall averages. Uncorrected Uncorrected Diluent-Adjusted (Pollutant Only) Total Runs 188 133 126 No. of3-PointAverages> ±5.0% 45 35 29 No. of6-Point Averages> ±5.0% 39 30 21
Table 4 shows that the use ofsix points on a measurement line does not significantlyimprove the overall accuracy. While a 6-point line gives a better defmition ofthe measurement than a 3-point line, it does not necessarilygive a betterrepresentation ofthe overall gas concentration. This occurs because ofport-toport variations. Increasing the number oftraverse points on a measurement line 

### does notresolveport-to-port variations. Basedon the data evaluated, the EPApractice ofusing six traversepoints for stratified gas concentrations should be revised.


### Three-PointTraverse as an Indicator ofStratification To answer the question, does the three-point traverseprovide 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 ofthe three concentrations. Only stratified datawere evaluated. Theresults 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 ofTable 5, the uncorrected data are used as an example. Outof244 runs, 109 (44.7% of244) were found to be stratified at the 10% level. Ofthese 109 runs, the 3-point averages of80 runs (73.4% of 1 09) were greaterthan the overall or "true" concentrations by±5.0%. The 5.0% indicator level added 53 runs (21.7% of244). Ofthese 53, 18 (34.0% of53) had 3-point averages greater than ±5.0%. The significant statistic is that stratification was not detected in 82 out of244 (33.6%). But, only 16 out of82 had 3-point averages greaterthan±5.0%. Looking at only the 10% indicator level, 135 out of244 (55.3%) would not have been detected as being stratified, and 34 out ofthe 135 (25.2%) had 3-point averages greaterthan ±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% ofthe time.
Three/Two-Point Traverse as an Indicator ofStratification The short-fall ofa 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 ofthe stack, select one point from each ofthe outerports (16.7% from one port and 83.3% from the otherport) in rectangular stack ortwo points (16
.7% and 83.3%) from the otherdiameter
. Determine the deviation from the average ofall five points. Table 6 summarizes theresults for this scenario: 

### T bl 6 3 . t

a e - -pom vs. 3/2-pomt averages "fied d or s ratt 1 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 ornext to the centroid was used. An improvement is seen from going to a 3-point to a 3/2-point in that the percentage ofaverages greater than ±5.0% drops. However, the 3/2 point traverse does not provide representative values within ±5.0% ofthe overall average. The 3/2-point scenario was then investigated to determine whether it could beused an indicator of stratification. The results are shown in Table 7. 

### Table 

### 7- 3/2

- ]!oint traverse to indicatesources 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 I0% 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-l0% 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 ifthere weresome false negatives (indication ofno 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 withmore than 12 points. Ofthese, 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 ofthe stack. There was no obvious indicator ofwhen to increase the number oftraverse 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. Theruns 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 benoted this is a small data set and that these data all represent low emissions applications where small process variations mayinfluence 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 oftraverse 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% ofthe "true" value.
• When stratification exists, a three-point traverse will not yield representative concentrations roughly 50% ofthe time.
• Increasing the number oftraverse points on a measurement line 

### does notresolve port-to-port variations.
• Using the concentrations ofa 3-point traverse does not flag stratification roughly 40% ofthe time, and ofthese roughly 35% are greater than ±5.0% ofthe "true" average.
• The 3/2-point traverse does not flag stratification roughly 20% ofthe time, but none ofthese had average concentration greater than ±5.0% ofthe "true" average.
• The 12-point traverse does not provide averages within ±5.0% ofthe overall concentration about 8% ofthe 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 theinformation in subsequent tests areprovided in the attachment. 

### ACKNOWLEDGEMENT The authors wishto acknowledge the following for their assistance in providing data for the evaluation:
• Greg Burch, 

### Golden Specialty Consulting, Inc. • LarryCottone, 

### CCIEnvironmental Consultants • Carl Fink, 

### TRC Solutions • Brian 

### J. Kearney, 

### ReliantEnergy • Calvin W. Loomis, 

### BisonEngineering, Inc. • Bill Mayhew, 

### Source Testing & 

### Consulting Services, Inc. • Jill Merrill,

### Air Compliance Consultants, Inc. • PeterPakalnis, 

### LEHDREnvironmentalServices Limited • Roger T. Shigehara, 

### EmissionMonitoringInc.

### DETERMININATION OF GAS STRATIFICATION AT TEST LOCATIONS (SES Procedure)


### SUMMARY This document sets forth a procedure for determining the existence and degree ofgaseous stratification at continuous emission monitoring system (CEMS) relative accuracy test audit (RATA) or compliance test locations. Depending on the degree and type ofstratification, procedures for subsequent testing is suggested. This test should be conducted initially at all sources subject to compliance regulations and after any significant physical orprocess changes. It is expected the degree ofstratification (aftertime adjustment and dilution correction) will below in most cases. Therefore, subsequent test requirements would beminimal. This guideline does not address the impact ofstratification on compliance. For example, ifthe concentrations are lowrelative to the emission limit, the degree ofstratification may not affect the determination ofcompliance. Therefore, absolute values, e.g., ±0.1% 

### 02 or±0.2 ppm, are not included in any ofthe specifications. Any alternative specifications should behandled on a case-by-case basis.


### PROCEDURE 1. Apparatus 1.1 Sample Probes 1.1.1 A single-point (SP) probe ofsufficient length to traverse the stack or duct 1.1.2 A stationarypoint probe (STP). The STP probe could be that ofthe CEMS. 1.2 Sampling and Measurement Systems 1.2.1 Two (2) completelyredundant reference method systems (e.g., Method 3A, 6C, 7E), one for the SP probe and the other for the STP probe. One ofthese systems could be the CEMS. Ifa time shared system is used for the CEMS, it should be "locked in" to the stackbeing tested for the duration ofthe traverse and returned to the cycling mode after completion ofthe stratification test. 1.2.2 

### Note: The system shouldbe capable of recording readings every 10-15seconds,from which ]-minute averages oran average for the each traversepointcan be computed. 1.3 Steady-State Operations 1.3.1 Ifthe source is considered to be a steady-stateprocess, the STP probe system maybe omitted. 1.3.2 

### Note: Processes that are considered to besteadystate 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 seemingstratification; therefore it is suggested that the STPprobe notbe omitted.2. Measurement Procedure 2.I Number ofTraverse 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 ifmore than 12 points are selected, having at least 3 traversepoints on a measurement line). 2.1.2 Locate the traverse points according to Method I. Ifthe STP probe is like the SP probe, select the centroid ofthe stack orduct 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 of5 traverse points at 16.7, 50.0, and 83.3% ofone diameter and 16.7 and 83.3% ofthe 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 outsideport. 2.2 Measurements 2.2.1 With the appropriate reference methods, measure the pollutant and, ifapplicable, diluent (02 orC02) concentrations at each ofthe traverse points with the SP probe. Sample a minimum of2 minutes plus at least two times the system response time at eachpoint. 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 thatsampling time at thefirst two traversepoints be conductedata minimum of 5 minutesplus at least two times the system response time at thefirst two traverse points. 

## If temporal variations are notnoted, the sampling time at the remaining traversepoints may be reduced to 2 minutesplus at least two times the system response time. The degree of temporal variation is a matter of judgment; generally, when temporal variations arepresent, it is better to sample longer ata traversepoint. 2.2.4 

### Note: The stratification test may (option) be conductedduring thefirstRATA or compliance test run, 

### if such a test is beingconductedsimultaneously.
3. Calculations 3.1 Point-Average 3.I.I Ifsampling 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 toplot the readings from both the SPandSTP 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 readingsfrom the SP probe. Theplotof the concentrations from the STP probe is also helpful in determining (or confirming) whether temporal variations are occurring andwhether 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 ofall traverse points and percent deviation ofeach 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 Iftemporal changes are occurring, adjust the SP probe concentrations for time variation as follows:

where: Ctak 

### = time-adjusted concentration, where 

### k 

### = traverse points 1
... n Cm 1 

### = STP concentration when SP is at traverse point "1" (any other reference point maybeused 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 seemingstratification 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 If0 2is 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, ifthe deviation ofa traverse point from the overall average is 0.2% 02, then divide this quantityby (20.9-%02avJ times 100 to obtain the percent deviation. 3.2.3.2 

### Note: The quantity (20.9-%02 ) 

### shall not be applied if02is 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 athigh levels of02 often encountered in gas turbines; the imprecision shows up as variation. 3.2.4 Option 3 3.2.4.1 Ifthe CEMS is being evaluated in terms ofdilution-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 oremission limit is on the basis of a mass emission rate (e.g., lb/hr), DONOTuse this option unless the flow rate is also determined on the same basis (e.g., 15% 02, 7% 

### 02, or 12% C02). ffthe mass emission rate is determined by multiplying lb/mmBtu by the heat input rate, then it is acceptable to use Option 3. ffthis option is used, apply dilution correction to both the STPandM-3probes.
4. Evaluation 4.1 Condition 1. Ifthe concentration at any ofthe individual traverse points deviates from the overall average byno more than ±5.0%, then: 4.1.1 Anyofthe traverse points having concentrations within±1.0% ofthe overall average maybeused for RATAs or compliance tests. Itis preferablenot to select traverse points closest to the port holes orwalls. Ifno 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% ofthe 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% ofthe overall average based on the initial12-point stratification test. 4.1.2.1 Ifthe maximum absolute percent deviation from the average ofthe three points is

**~.0%,** a single point closest to the average maybeused after the initial RATA or compliance test run. 4.1.2.2 Ifthe maximum absolute percent deviation is greater than 5.0%, but :Sl.O.O%, then the 3-point traverse must beused for all subsequent runs. 4.2 Condition 2. Ifthe concentration at any ofthe individual traverse points deviates from the overall average byno more than ±10.0%, then: 4.2.1 Select anythree points on a measurement line whose average falls within ±1.0% ofthe overall average. It is preferable that the measurement line passes through ornear the centroid ofthe stackor duct. Use these three points as traverse points for RATA orcompliance 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% ofthemeasurement line is used in its place. The traverse points selected under Step 4.2.1 maybe used as an alternative. 4.2.2.1 Ifthe maximum absolute percent deviation from the average ofthe three points is :Sl.O.O%, you may continue to use the 3-point traverse for all RATA or compliance test runs. 4.2.2.2 Ifthe 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. Ifthe concentration at any ofthe individual traverse points deviates from the overall average bymore 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 traversepoints. Use the velocity-weighted concentrations to determine whetherstratification 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 ofat least two additional ful112-point stratification tests (three in all). The selection ofthe 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% ofone diameter and two points at 16.7 and 83.3% ofthe 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 threepoints on a measurement line thatpasses through ornear the centroidof the stackorduct and havingat least two otherpoints. For circularstacks, the twopoints should be on the other diameter;for rectangularstacks, onepointshould be from each of the two outerports. 4.3.5 

### Note: Data usedto demonstrate "consistency" (see Section 4.3.3) requires a definition, which has notyetbeen developed. Based on the 3/2-point traverse data, it is believed that ±1.0to ±2.5% is be a "reasonable" range for consistency.