217. In Part 60, Appendix B is amended by revising

Performance Specifications 2, 3, 4, 4A, 5, 6, 7, 8, and 9 to

read as follows:

1535

PERFORMANCE SPECIFICATION 2 - SPECIFICATIONS AND TEST

PROCEDURES FOR SO2 AND NOX CONTINUOUS EMISSION MONITORING

SYSTEMS IN STATIONARY SOURCES

1.0 Scope and Application.

1.1 Analytes.

Analyte CAS Nos.

Sulfur Dioxide

(SO2)

7449-09-5

Nitrogen Oxides

(NOx)

10102-44-0 (NO2),

10024-97-2 (NO)

1.2 Applicability.

1.2.1 This specification is for evaluating the

acceptability of SO2 and NOx continuous emission monitoring

systems (CEMS) at the time of installation or soon after and

whenever specified in the regulations. The CEMS may include,

for certain stationary sources, a diluent (O2 or CO2)

monitor.

1.2.2 This specification is not designed to evaluate

the installed CEMS performance over an extended period of

time nor does it identify specific calibration techniques

and other auxiliary procedures to assess the CEMS

performance. The source owner or operator is responsible to

calibrate, maintain, and operate the CEMS properly. The
1536

Administrator may require, under Section 114 of the Act, the

operator to conduct CEMS performance evaluations at other

times besides the initial test to evaluate the CEMS

performance. See 40 CFR Part 60, §60.13(c).

2.0 Summary of Performance Specification. 

Procedures for measuring CEMS relative accuracy and

calibration drift are outlined. CEMS installation and

measurement location specifications, equipment

specifications, performance specifications, and data

reduction procedures are included. Conformance of the CEMS

with the Performance Specification is determined.

3.0 Definitions.

3.1 Calibration Drift (CD) means the difference in

the CEMS output readings from the established reference

value after a stated period of operation during which no

unscheduled maintenance, repair, or adjustment took place.

3.2 Centroidal Area means a concentric area that is

geometrically similar to the stack or duct cross section and

is no greater than l percent of the stack or duct crosssectional area.

3.3 Continuous Emission Monitoring System means the

total equipment required for the determination of a gas

concentration or emission rate. The sample interface,
1537

pollutant analyzer, diluent analyzer, and data recorder are

the major subsystems of the CEMS.

3.4 Data Recorder means that portion of the CEMS that

provides a permanent record of the analyzer output. The

data recorder may include automatic data reduction

capabilities.

3.5 Diluent Analyzer means that portion of the CEMS

that senses the diluent gas (i.e., CO2 or O2) and generates

an output proportional to the gas concentration.

3.6 Path CEMS means a CEMS that measures the gas

concentration along a path greater than 10 percent of the

equivalent diameter of the stack or duct cross section.

3.7 Point CEMS means a CEMS that measures the gas

concentration either at a single point or along a path equal

to or less than 10 percent of the equivalent diameter of the

stack or duct cross section.

3.8 Pollutant Analyzer means that portion of the CEMS

that senses the pollutant gas and generates an output

proportional to the gas concentration.

3.9 Relative Accuracy (RA) means the absolute mean

difference between the gas concentration or emission rate

determined by the CEMS and the value determined by the

reference method (RM), plus the 2.5 percent error confidence
1538

coefficient of a series of tests, divided by the mean of the

RM tests or the applicable emission limit.

3.10 Sample Interface means that portion of the CEMS

used for one or more of the following: sample acquisition,

sample delivery, sample conditioning, or protection of the

monitor from the effects of the stack effluent.

3.11 Span Value means the concentration specified for

the affected source category in an applicable subpart of the

regulations that is used to set the calibration gas

concentration and in determining calibration drift.

4.0 Interferences. [Reserved]

5.0 Safety. 

The procedures required under this performance

specification may involve hazardous materials, operations,

and equipment. This performance specification may not

address all of the safety problems associated with these

procedures. It is the responsibility of the user to

establish appropriate safety and health practices and

determine the applicable regulatory limitations prior to

performing these procedures. The CEMS user's manual and

materials recommended by the reference method should be

consulted for specific precautions to be taken.

6.0 Equipment and Supplies.

6.1 CEMS Equipment Specifications.
1539

6.1.1 Data Recorder Scale. The CEMS data recorder

output range must include zero and a high-level value. The

high-level value is chosen by the source owner or operator

and is defined as follows:

6.1.1.1 For a CEMS intended to measure an

uncontrolled emission (e.g., SO2 measurements at the inlet

of a flue gas desulfurization unit), the high-level value

should be between 1.25 and 2 times the maximum potential

emission level over the appropriate averaging time, unless

otherwise specified in an applicable subpart of the

regulations.

6.1.1.2 For a CEMS installed to measure controlled

emissions or emissions that are in compliance with an

applicable regulation, the high-level value between 1.5

times the pollutant concentration corresponding to the

emission standard level and the span value given in the

applicable regulations is adequate.

6.1.1.3 Alternative high-level values may be used,

provided the source can measure emissions which exceed the

full-scale limit in accordance with the requirements of

applicable regulations.

6.1.1.4 If an analog data recorder is used, the data

recorder output must be established so that the high-level

value would read between 90 and 100 percent of the data
1540

recorder full scale. (This scale requirement may not be

applicable to digital data recorders.) The zero and high

level calibration gas, optical filter, or cell values should

be used to establish the data recorder scale.

6.1.2 The CEMS design should also allow the

determination of calibration drift at the zero and highlevel values. If this is not possible or practical, the

design must allow these determinations to be conducted at a

low-level value (zero to 20 percent of the high-level value)

and at a value between 50 and 100 percent of the high-level

value. In special cases, the Administrator may approve a

single-point calibration-drift determination.

6.2 Other equipment and supplies, as needed by the

applicable reference method(s) (see Section 8.4.2 of this

Performance Specification), may be required.

7.0 Reagents and Standards. 

7.1 Reference Gases, Gas Cells, or Optical Filters. 

As specified by the CEMS manufacturer for calibration of

the CEMS (these need not be certified).

 7.2 Reagents and Standards. May be required as needed

by the applicable reference method(s) (see Section 8.4.2 of

this Performance Specification).

8.0 Performance Specification Test Procedure.
1541

8.1 Installation and Measurement Location

Specifications.

8.1.1 CEMS Installation. Install the CEMS at an

accessible location where the pollutant concentration or

emission rate measurements are directly representative or

can be corrected so as to be representative of the total

emissions from the affected facility or at the measurement

location cross section. Then select representative

measurement points or paths for monitoring in locations that

the CEMS will pass the RA test (see Section 8.4). If the

cause of failure to meet the RA test is determined to be the

measurement location and a satisfactory correction technique

cannot be established, the Administrator may require the

CEMS to be relocated. Suggested measurement locations and

points or paths that are most likely to provide data that

will meet the RA requirements are listed below.

8.1.2 CEMS Measurement Location. It is suggested

that the measurement location be (1) at least two equivalent

diameters downstream from the nearest control device, the

point of pollutant generation, or other point at which a

change in the pollutant concentration or emission rate may

occur and (2) at least a half equivalent diameter upstream

from the effluent exhaust or control device.

8.1.2.1 Point CEMS. It is suggested that the

measurement point be (1) no less than 1.0 meter (3.3 ft)
1542

from the stack or duct wall or (2) within or centrally

located over the centroidal area of the stack or duct cross

section.

8.1.2.2 Path CEMS. It is suggested that the

effective measurement path (1) be totally within the inner

area bounded by a line 1.0 meter (3.3 ft) from the stack or

duct wall, or (2) have at least 70 percent of the path

within the inner 50 percent of the stack or duct crosssectional area, or (3) be centrally located over any part of

the centroidal area.

8.1.3 Reference Method Measurement Location and

Traverse Points. 

8.1.3.1 Select, as appropriate, an accessible RM

measurement point at least two equivalent diameters

downstream from the nearest control device, the point of

pollutant generation, or other point at which a change in

the pollutant concentration or emission rate may occur, and

at least a half equivalent diameter upstream from the

effluent exhaust or control device. When pollutant

concentration changes are due solely to diluent leakage

(e.g., air heater leakages) and pollutants and diluents are

simultaneously measured at the same location, a half

diameter may be used in lieu of two equivalent diameters. 

The CEMS and RM locations need not be the same.
1543

8.1.3.2 Select traverse points that assure

acquisition of representative samples over the stack or duct

cross section. The minimum requirements are as follows: 

Establish a "measurement line" that passes through the

centroidal area and in the direction of any expected

stratification. If this line interferes with the CEMS

measurements, displace the line up to 30 cm (12 in.) (or 5

percent of the equivalent diameter of the cross section,

whichever is less) from the centroidal area. Locate three

traverse points at 16.7, 50.0, and 83.3 percent of the

measurement line. 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. For

rectangular ducts, locate at least nine sample points in the

cross section such that sample points are the centroids of

similarly-shaped, equal area divisions of the cross section. 

Measure the pollutant concentration, and, if applicable, the

diluent concentration at each point using appropriate

reference methods or other appropriate instrument methods

that give responses relative to pollutant concentrations. 
1544

Then calculate the mean value for all sample points. For

circular ducts, conduct a 12-point traverse (i.e., six

points on each of the two perpendicular diameters) locating

the sample points as described in 40 CFR 60, Appendix A,

Method 1. Perform the measurements and calculations as

described above. 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 (...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. 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. Conduct all necessary RM tests

within 3 cm (1.2 in.) of the traverse points, but no closer

than 3 cm (1.2 in.) to the stack or duct wall.

8.2 Pretest Preparation. Install the CEMS, prepare

the RM test site according to the specifications in Section

8.1, and prepare the CEMS for operation according to the

manufacturer's written instructions.

8.3 Calibration Drift Test Procedure.

8.3.1 CD Test Period. While the affected facility is

operating at more than 50 percent of normal load, or as
1545

specified in an applicable subpart, determine the magnitude

of the CD once each day (at 24-hour intervals) for 7

consecutive days according to the procedure given in

Sections 8.3.2 through 8.3.4.

8.3.2 The purpose of the CD measurement is to verify

the ability of the CEMS to conform to the established CEMS

calibration used for determining the emission concentration

or emission rate. Therefore, if periodic automatic or

manual adjustments are made to the CEMS zero and calibration

settings, conduct the CD test immediately before these

adjustments, or conduct it in such a way that the CD can be

determined.

8.3.3 Conduct the CD test at the two points specified

in Section 6.1.2. Introduce to the CEMS the reference

gases, gas cells, or optical filters (these need not be

certified). Record the CEMS response and subtract this

value from the reference value (see example data sheet in

Figure 2-1).

8.4 Relative Accuracy Test Procedure.

8.4.1 RA Test Period. Conduct the RA test according

to the procedure given in Sections 8.4.2 through 8.4.6 while

the affected facility is operating at more than 50 percent 

of normal load, or as specified in an applicable subpart. 

The RA test may be conducted during the CD test period.
1546

8.4.2 Reference Methods. Unless otherwise specified

in an applicable subpart of the regulations, Methods 3B, 4,

6, and 7, or their approved alternatives, are the reference

methods for diluent (O2 and CO2), moisture, SO2, and NOx,

respectively.

8.4.3 Sampling Strategy for RM Tests. Conduct the RM

tests in such a way that they will yield results

representative of the emissions from the source and can be

correlated to the CEMS data. It is preferable to conduct

the diluent (if applicable), moisture (if needed), and

pollutant measurements simultaneously. However, diluent and

moisture measurements that are taken within an hour of the

pollutant measurements may be used to calculate dry

pollutant concentration and emission rates. In order to

correlate the CEMS and RM data properly, note the beginning

and end of each RM test period of each run (including the

exact time of day) on the CEMS chart recordings or other

permanent record of output. Use the following strategies

for the RM tests:

8.4.3.1 For integrated samples (e.g., Methods 6 and

Method 4), make a sample traverse of at least 21 minutes,

sampling for an equal time at each traverse point (see

Section 8.1.3.2 for discussion of traverse points.
1547

8.4.3.2 For grab samples (e.g., Method 7), take one

sample at each traverse point, scheduling the grab samples

so that they are taken simultaneously (within a 3-minute

period) or at an equal interval of time apart over the span

of time the CEM pollutant is measured. A test run for grab

samples must be made up of at least three separate

measurements.

NOTE: At times, CEMS RA tests are conducted during

new source performance standards performance tests. In

these cases, RM results obtained during CEMS RA tests may be

used to determine compliance as long as the source and test

conditions are consistent with the applicable regulations.

8.4.4 Number of RM Tests. Conduct a minimum of nine

sets of all necessary RM test runs.

NOTE: More than nine sets of RM tests may be

performed. If this option is chosen, a maximum of three sets

of the test results may be rejected so long as the total

number of test results used to determine the RA is greater

than or equal to nine. However, all data must be reported,

including the rejected data.

8.4.5 Correlation of RM and CEMS Data. Correlate the

CEMS and the RM test data as to the time and duration by

first determining from the CEMS final output (the one used

for reporting) the integrated average pollutant
1548

concentration or emission rate for each pollutant RM test

period. Consider system response time, if important, and

confirm that the pair of results are on a consistent

moisture, temperature, and diluent concentration basis. 

Then, compare each integrated CEMS value against the

corresponding average RM value. Use the following

guidelines to make these comparisons.

8.4.5.1 If the RM has an integrated sampling

technique, make a direct comparison of the RM results and

CEMS integrated average value.

8.4.5.2 If the RM has a grab sampling technique,

first average the results from all grab samples taken during

the test run, and then compare this average value against

the integrated value obtained from the CEMS chart recording

or output during the run. If the pollutant concentration is

varying with time over the run, the arithmetic average of

the CEMS value recorded at the time of each grab sample may

be used.

8.4.6 Calculate the mean difference between the RM

and CEMS values in the units of the emission standard, the

standard deviation, the confidence coefficient, and the

relative accuracy according to the procedures in Section

12.0.

8.5 Reporting. At a minimum (check with the

appropriate regional office, State, or Local agency for
1549

additional requirements, if any), summarize in tabular form

the results of the CD tests and the RA tests or alternative

RA procedure, as appropriate. Include all data sheets,

calculations, charts (records of CEMS responses), cylinder

gas concentration certifications, and calibration cell

response certifications (if applicable) necessary to confirm

that the performance of the CEMS met the performance

specifications.

9.0 Quality Control. [Reserved]

10.0 Calibration and Standardization. [Reserved]

11.0 Analytical Procedure. 

Sample collection and analysis are concurrent for this

Performance Specification (see Section 8.0). Refer to the

RM for specific analytical procedures.

12.0 Calculations and Data Analysis.

Summarize the results on a data sheet similar to that

shown in Figure 2-2 (in Section 18.0).

12.1 All data from the RM and CEMS must be on a

consistent dry basis and, as applicable, on a consistent

diluent basis and in the units of the emission standard. 

Correct the RM and CEMS data for moisture and diluent as

follows:

12.1.1 Moisture Correction (as applicable). Correct

each wet RM run for moisture with the corresponding Method 4
1550

Concentration(dry)'

Concentration(wet)

(1&Bws)

Eq. 2-1

ppm(corr)' ppm(uncorr)[

20.9&7.0

20.9&%O2(dry)

] Eq. 2-2

d '

1

n j

n

i'1

diEq. 2-3

j

n

i'1

di' Algebraic summation of the individual differences di.

data; correct each wet CEMS run using the corresponding CEMS

moisture monitor date using Equation 2-1.

12.1.2 Correction to Units of Standard (as

applicable). Correct each dry RM run to the units of the

emission standard with the corresponding Method 3B data;

correct each dry CEMS run using the corresponding CEMS

diluent monitor data as follows:

12.1.2.1 Correct to Diluent Basis. The following is

an example of concentration (ppm) correction to 7% oxygen.

The following is an example of mass/gross calorific

value (lbs/million Btu) correction.

lbs/MMBtu = Conc(dry) (F-factor) (20.9/20.9- %02)

12.2 Arithmetic Mean. Calculate the arithmetic mean

of the difference, d, of a data set as follows:

where: 

n = Number of data points.
1551

Sd'

j

n

i'1

d

2

i

&

j

n

i'1

di

2

n

n&1

1

2

Eq. 2-4

CC ' t0.975

Sd

n

Eq. 2-5

RA '

d % CC

RM

x 100 Eq. 2-6

12.3 Standard Deviation. Calculate the standard

deviation, Sd, as follows:

12.4 Confidence Coefficient. Calculate the 2.5

percent error confidence coefficient (one-tailed), CC, as

follows:

where: t0.975 = t-value (see Table 2-1).

12.5 Relative Accuracy. Calculate the RA of a set of

data as follows:

where:

|db| = Absolute value of the mean differences (from

Equation 2-3).

|CC|= Absolute value of the confidence coefficient

(from Equation 2-3).
1552

R ̄M ̄ = Average RM value. In cases where the

average emissions for the test are less than

50 percent of the applicable standard,

substitute the emission standard value in

the denominator of Eq. 2-6 in place of R ̄M ̄. 

In all other cases, use R ̄M ̄.

13.0 Method Performance.

13.1 Calibration Drift Performance Specification. 

The CEMS calibration must not drift or deviate from the

reference value of the gas cylinder, gas cell, or optical

filter by more than 2.5 percent of the span value. If the

CEMS includes pollutant and diluent monitors, the CD must be

determined separately for each in terms of concentrations

(See Performance Specification 3 for the diluent

specifications), and none of the CDs may exceed the

specification. 

13.2 Relative Accuracy Performance Specification. 

The RA of the CEMS must be no greater than 20 percent when

R ̄M ̄ is used in the denominator of Eq. 2-6 (average emissions

during test are greater than 50 percent of the emission

standard) or 10 percent when the applicable emission

standard is used in the denominator of Eq. 2-6 (average

emissions during test are less than 50 percent of the

emission standard).
1553

13.3 For instruments that use common components to

measure more than one effluent gas constituent, all channels

must simultaneously pass the RA requirement, unless it can

be demonstrated that any adjustments made to one channel did

not affect the others.

14.0 Pollution Prevention. [Reserved]

15.0 Waste Management. [Reserved]

16.0 Alternative Procedures. 

Paragraphs 60.13(j)(1) and (2) of 40 CFR part 60

contain criteria for which the reference method procedure

for determining relative accuracy (see Section 8.4 of this

Performance Specification) may be waived and the following

procedure substituted.

16.1 Conduct a complete CEMS status check following

the manufacturer's written instructions. The check should

include operation of the light source, signal receiver,

timing mechanism functions, data acquisition and data

reduction functions, data recorders, mechanically operated

functions (mirror movements, zero pipe operation,

calibration gas valve operations, etc.), sample filters,

sample line heaters, moisture traps, and other related

functions of the CEMS, as applicable. All parts of the CEMS

shall be functioning properly before proceeding to the

alternative RA procedure.
1554

16.2 Alternative RA Procedure.

16.2.1 Challenge each monitor (both pollutant and

diluent, if applicable) with cylinder gases of known

concentrations or calibration cells that produce known

responses at two measurement points within the ranges

shown in Table 2-2 (Section 18).

16.2.2 Use a separate cylinder gas (for point CEMS

only) or calibration cell (for path CEMS or where compressed

gas cylinders can not be used) for measurement points 1 and

2. Challenge the CEMS and record the responses three times

at each measurement point. The Administrator may allow

dilution of cylinder gas using the performance criteria in

Test Method 205, 40 CFR Part 51, Appendix M. Use the

average of the three responses in determining relative

accuracy.

16.2.3 Operate each monitor in its normal sampling

mode as nearly as possible. When using cylinder gases, pass

the cylinder gas through all filters, scrubbers,

conditioners, and other monitor components used during

normal sampling and as much of the sampling probe as

practical. When using calibration cells, the CEMS

components used in the normal sampling mode should not be

by-passed during the RA determination. These include light

sources, lenses, detectors, and reference cells. The CEMS

should be challenged at each measurement point for a
1555

sufficient period of time to assure adsorption-desorption

reactions on the CEMS surfaces have stabilized.

16.2.4 Use cylinder gases that have been certified by

comparison to National Institute of Standards and Technology

(NIST) gaseous standard reference material (SRM) or NIST/EPA

approved gas manufacturer's certified reference material

(CRM) (See Reference 2 in Section 17.0) following EPA

Traceability Protocol Number 1 (See Reference 3 in Section

17.0). As an alternative to Protocol Number 1 gases, CRM's

may be used directly as alternative RA cylinder gases. A

list of gas manufacturers that have prepared approved CRM's

is available from EPA at the address shown in Reference 2. 

Procedures for preparation of CRM's are described in

Reference 2.

16.2.5 Use calibration cells certified by the

manufacturer to produce a known response in the CEMS. The

cell certification procedure shall include determination of

CEMS response produced by the calibration cell in direct

comparison with measurement of gases of known concentration. 

This can be accomplished using SRM or CRM gases in a

laboratory source simulator or through extended tests using

reference methods at the CEMS location in the exhaust stack. 

These procedures are discussed in Reference 4 in Section

17.0. The calibration cell certification procedure is

subject to approval of the Administrator.
1556

RA ' /

0

0

0

/

0

0

0

d

AC

100 # 15 percent Eq. 2-7

16.3 The differences between the known concentrations

of the cylinder gases and the concentrations indicated by

the CEMS are used to assess the accuracy of the CEMS. The

calculations and limits of acceptable relative accuracy are

as follows:

16.3.1 For pollutant CEMS:

where:

db = Average difference between responses and the

concentration/responses (see Section

16.2.2).

AC = The known concentration/response of the

cylinder gas or calibration cell.

16.3.2 For diluent CEMS:

RA = |db| < O.7 percent O2 or CO2, as applicable.

NOTE: Waiver of the relative accuracy test in favor

of the alternative RA procedure does not preclude the

requirements to complete the CD tests nor any other

requirements specified in an applicable subpart for

reporting CEMS data and performing CEMS drift checks or

audits.

17.0 References.
1557

1. Department of Commerce. Experimental Statistics. 

Handbook 91. Washington, D.C. p. 3-31, paragraphs 

3-3.1.4.

2. "A Procedure for Establishing Traceability of Gas

Mixtures to Certain National Bureau of Standards Standard

Reference Materials." Joint publication by NBS and EPA. 

EPA 600/7-81-010. Available from U.S. Environmental

Protection Agency, Quality Assurance Division (MD-77),

Research Triangle Park, North Carolina 27711.

3. "Traceability Protocol for Establishing True

Concentrations of Gases Used for Calibration and Audits of

Continuous Source Emission Monitors. (Protocol Number 1)." 

June 1978. Protocol Number 1 is included in the Quality

Assurance Handbook for Air Pollution Measurement Systems,

Volume III, Stationary Source Specific Methods. EPA-600/4-

77-027b. August 1977. 

4. "Gaseous Continuous Emission Monitoring Systems -

Performance Specification Guidelines for SO2, NOx, CO2, O2,

and TRS." EPA-450/3-82-026. Available from the U.S. EPA,

Emission Measurement Center, Emission Monitoring and Data

Analysis Division (MD-19), Research Triangle Park, North

Carolina 27711. 

18.0 Tables, Diagrams, Flowcharts, and Validation Data.
1558

TABLE 2-1. t-VALUES.

n

a t0.975 na t0.975 na t0.975

2 12.706 7 2.447 12 2.201

3 4.303 8 2.365 13 2.179

4 3.182 9 2.306 14 2.160

5 2.776 10 2.262 15 2.145

6 2.571 11 2.228 16 2.131

a The values in this table are already corrected for n-1 degrees of

freedom. Use n equal to the number of individual values.
1559

Table 2-2. Measurement Range.

Measurement

Point

Pollutant

Monitor

Diluent Monitor for

CO2 O2

1 20-30% of

span value

5-8% by

volume

4-6% by 

volume

2 50-60% of 

span value

10-14% by 

volume

8-12% by

volume

Lowlevel

Day

Date

and

Time

Calibration

Value

(C)

Monitor

Value

(M)

Difference

(C-M)

Percent of

span value

(C-M)/Span

Value x

100

Highlevel

Figure 2-1. Calibration Drift Determination.
1560

Run

No.

Date

and

Time

SO2

 b

NOx

 a

CO2 or O2

 a

SO2

 a

NOx

RM CEMS Diff RM CEMS Diff RM CEMS RM CEM

S

Diff RM CEMS Diff

ppmc ppmc %

c %c mass/GCV mass/GCV

1

2

3

4

5

6

7

8

9

10

11

12

Average

Confidence Interval

Accuracy

a For steam generators

b Average of three samples

c Make sure that RM and CEMS data are on a consistent basis, either wet or dry.

Figure 2-2. Relative Accuracy Determination.