PERFORMANCE
SPECIFICATION 2 - SPECIFICATIONS AND TEST PROCEDURES FOR SO2 AND NOX CONTINUOUS
EMISSION MONITORING SYSTEMS IN STATIONARY SOURCES
2.0 Summary of
Performance Specification.
3.3 Continuous Emission
Monitoring System
6.1 CEMS Equipment
Specifications.
6.2 Other equipment and
supplies
8.0 Performance
Specification Test Procedure.
8.1 Installation and
Measurement Location Specifications.
8.1.2 CEMS Measurement
Location.
8.1.3 Reference Method
Measurement Location and Traverse Points.
8.3 Calibration Drift
Test Procedure.
8.4 Relative Accuracy
Test Procedure.
9.0 Quality Control.
[Reserved]
10.0 Calibration and
Standardization. [Reserved]
12.0 Calculations and
Data Analysis.
14.0 Pollution
Prevention. [Reserved]
15.0 Waste Management.
[Reserved]
18.0 Tables, Diagrams,
Flowcharts, and Validation Data.
1.0 Scope and Application.
1.1 Analytes.
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 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 cross-sectional 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, 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 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.
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 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
high-level 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.
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 cross-sectional 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.
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.
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 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.
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.
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 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 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 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.
12.2 Arithmetic Mean.
Calculate the arithmetic mean of the difference, d, of a data set as follows:
where:
n = Number of
data points.
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:
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 RøMø 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).
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.
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 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.
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:
16.3.2 For diluent
CEMS:
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.
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.
Figure 2-1.
Calibration Drift Determination.
Figure 2-2. Relative
Accuracy Determination.
