METHOD 203. DETERMINATION OF THE OPACITY OF EMISSIONS FROM
STATIONARY SOURCES BY CONTINUOUS OPACITY MONITORING SYSTEMS
1. APPLICABILITY AND PRINCIPLE
1.1 Applicability. This method applies to the measurement of
the opacity of emissions from stationary sources by continuous
opacity monitoring systems (COMS), in order to determine compliance
with an emissions standard. The method is not applicable where
water droplets are present in the effluent being measured.
1.2 Principle. The opacity of emissions from a stationary
source is continuously measured and recorded using a COMS that
meets all the requirements of Performance Specification 1 (PS 1) of
40 CFR Part 60, Appendix B. Minimum quality control (QC) and
quality assurance (QA) requirements are specified to assess the
quality of COMS performance. Daily zero and span checks, quarterly
performance audits, and annual zero alignment checks are required
in order to assure the proper functioning of the COMS and the
accuracy of the COMS data.
Because control and corrective action encompasses a variety of
policies, specifications, standards, and corrective measures, this
method treats QC requirements in general terms to allow the
development of a QC system that is most effective and efficient for
2.1 Continuous Opacity Monitoring System (COMS). The total
equipment required for the determination of the opacity of
emissions which meets the minimum requirements of Performance
Specification 1 of 40 CFR Part 60.
2.2 Simulated Zero Check. Method or device used to provide
a simulated zero opacity ( or low-level value between zero and 20
percent of the applicable opacity standard). Where a standard of
less than 10 percent opacity has been specified, a surrogate
opacity standard of 10 percent shall be used for determining this
2.3 Out-of-Control Periods.
2.3.1 Daily Assessments. Whenever the calibration drift (CD)
exceeds twice the specification of PS-1, the COMS is
out-of-control. The beginning of the out-of-control period is the
time corresponding to the last successful drift-check. The end of
the out-of-control period is the time corresponding to the
completion of appropriate adjustment and subsequent successful CD
2.3.2 Quarterly and Annual Assessment. Whenever a quarterly
performance audit or annual zero alignment audit indicates
unacceptable results, the COMS is "out-of-control." The beginning
of the out-of-control period is the time corresponding to the
completion of the performance audit indicating and unacceptable
performance. The end of the out-of-control period is the time
corresponding to the completion of appropriate corrective actions
and subsequent successful audit (or, if applicable, partial audit).
2.4 Upscale Opacity Condition. Method or device used to
provide a simulated upscale opacity (50 to 100 percent of the
2.5 External Zeroing Device (Zero-Jig). An external,
removable device for simulating or checking the cross-stack zero
alignment of the COMS.
3. COMS INSTALLATION, DESIGN, AND PERFORMANCE SPECIFICATIONS
In addition to the installation, design, and performance
requirements of PS 1, the following are added:
3.1 External Calibration Filter Access. The COMS must be
designed to allow for the evaluation of both the linearity and
accuracy relative to a simulated zero value and provide a check of
all system components. An adequate design would accommodate a
calibration filter assembly and permit periodic use of external
(i.e., not intrinsic to the instrument) neutral density filters.
3.2 Data Reduction/Recording. The COMS shall be designed to
allow for the data reduction, recording, and reporting in
accordance with the applicable opacity standards. Monitors that
automatically adjust the data to the corrected calibration value
must be capable of recording the amount of adjustment that is
applied to the exhaust gas stream measurement. Data recorded
during periods of COMS breakdowns, repairs, calibration checks, and
adjustments shall not be used in the data averages of Section 3.4.
3.3 Zero and Upscale Calibration Evaluations. All COMS
installed pursuant to these procedures shall include a method for
producing a simulated zero opacity condition and an upscale opacity
condition using a certified neutral density filter to produce an
known obscuration of light. Such procedures shall provide a system
check of the analyzer internal optical surfaces and all active
electronic circuitry including the lamp and photodetector assembly
used in the measurement mode.
3.4 Data Averages. All COMS installed pursuant to these
requirements shall complete a minimum of one cycle of sampling and
analyzing for each successive 10-second period and one cycle of
data recording for each specified data average, e.g., 6-minute
average. An arithmetic or integrated average of all data should be
4. OPACITY MEASUREMENT.
4.1 The opacity of emissions shall be continuously measured
and recorded in units of percent opacity, and shall be expressed in
the averaging period specified in the applicable regulation.
4.2 The COMS shall be operated, maintained and calibrated to
meet these requirements in accordance with the instructions
provided by the instrument manufacturer.
4.3 Except for COMS breakdowns, repairs, calibration checks,
zero and span checks and other quality-assurance activities, the
COMS shall be in continuous operation during all periods of source
4.4 A data average shall be considered valid if no less than
83 percent of the opacity readings upon which the data average is
based are obtained.
4.5 Any and all valid data averages may be used to determine
compliance with the applicable opacity standard. Data obtained
during "out-of-control" periods shall not be used for compliance
determination; however, the data can be used for identifying
periods of failure to meet quality assurance and control criteria.
5. QUALITY CONTROL (QC) REQUIREMENTS
5.1 Calibration Drift (CD) Assessment. The COMS shall be
checked, at least once daily and the CD quantified and recorded at
the zero (or low-level) and upscale-level opacity. The COMS shall
be adjusted whenever the CD exceeds the specification of PS-1, and
the COMS shall be declared "out-of-control" when the CD exceeds
twice the specification of PS-1. Corrective actions, followed by
a validating CD check are required when the COMS is out-of-control.
5.2 Fault indicators Assessment. At least daily, the fault
lamp indicators, data acquisition system error messages, and other
system self diagnostic indicators shall be checked. The
appropriate corrective actions should be taken when the COMS is
operating outside preset limits. All COMS data recorded during
periods in which fault indicators are illuminated shall be
5.3 Performance audits. Checks of the individual COMS
components and factors affecting the accuracy of the monitoring
data, as described below, shall be conducted on a quarterly basis.
Examples of detailed audit procedures may be found in Reference 1,
"Performance Audit Procedures for Opacity Monitors", and Reference
2, "CEMS Pilot Project: Evaluation of CEMS Reliability and QA
Procedures Volume 1". The following identify the absolute minimum
checks that shall be included in the performance audit:
5.3.1 Optical Alignment Assessment. The status of the
optical alignment of the monitor components shall be checked and
recorded according to the procedures specified by the monitor
manufacturer. Realign as necessary.
5.3.2 Optical Surface Dust Accumulation Assessment. The
apparent effluent opacity shall be compared and recorded before and
after cleaning of each of the exposed optical surfaces. The total
optical surface dust accumulation shall be determined by summing
the apparent reductions in opacity for all of the optical surfaces
that are cleaned. Caution should be employed in performing this
check since fluctuations in effluent opacity occurring during the
cleaning cycle may adversely affect the results.
5.3.3 Zero and Upscale Response Assessment. The zero and
upscale response errors shall be determined and recorded according
to the CD procedures. The error is defined as the difference (in
% opacity) between the correct value and the observed value for the
zero and high-level calibration checks.
5.3.4 Zero Compensation Assessment. The value of the zero
compensation applied at the time of the audit shall be calculated
as equivalent opacity, corrected to stack exit conditions as
necessary, according to the procedures specified by the
manufacturer. Record the compensation applied to the effluent
recorded by the monitor system.
5.3.5 Stack Exit Correlation Error Assessment. The optical
pathlength correction ratio (OPLR) shall be computed form the
monitor pathlength and stack exit diameter and shall be compared,
and the difference recorded, to the monitor setup value. The stack
exit correlation error shall be determined as the absolute value of
the difference between the measured value and the correct value,
expressed as a percentage of the correct value.
5.3.6 Calibration Error Assessment. A three-point
calibration error test of the COMS shall be conducted. For either
calibration error test methods below, three neutral density filters
meeting the requirements of PS-1, shall be placed in the COMS light
beam path five consecutive times and the monitor responses shall be
independently recorded from the permanent COMS data recorder.
Additional guidance for conducting this test is included in Section
7.0 of PS-1. The low-, mid-, and high-range calibration error
results shall be computed as the mean difference and 95 percent
confidence interval for the difference between the expected and
actual responses of the monitor as corrected to stack exit
conditions. These values shall be calculated using the procedures
of Section 8.0 of PS-1.
220.127.116.11 Primary Calibration Error Method. The calibration
error test requires the installation of an external calibration
audit device (zero-jig). The zero-jig shall be adjusted to provide
the same zero response as the monitor's simulated zero.
18.104.22.168 Alternative Calibration Error Method. Conduct an
incremental calibration test by superimposing the neutral density
filters over the effluent opacity and comparing the COMS responses
to the expected value calculated from the filter and opacity values
immediately preceding the superimposing. Record both the stack
effluent opacity and the calibration filter value prior to each
test. This method is sensitive to fluctuations in the effluent
opacity during the test.
22.214.171.124 Attenuators. Use calibration attenuators (i.e.
neutral density filters) with values that have been determined
according to Section 7.1.3 "Attenuator Calibration" of PS 1,
Appendix B, 40 CFR Part 60, and produce simulated opacities
(corrected to stack exit conditions as necsesary) in the ranges
listed in Table 1 below. For emission standards of 10 percent (or
less) opacity, attenuator selection may be based on a 10 percent
126.96.36.199. Attenuator Stability. The stability of the
attenuator values should be checked at least once per year
according to the procedures specified in PS-1. The attenuators
shall be recalibrated if the stability checks indicate a change of
two percent opacity or greater.
TABLE 1 - FILTER RANGES FOR COMS PERFORMANCE AUDITS
Audit Point -- Audit Filter Range (% Op)
1 20 - 60 Percent of the Emission Limit (low)
2 80 - 120 Percent of the Emission Limit (mid)
3 150 - 200 Percent of the Emission Limit (high)
5.4 Zero alignment Assessment. Compare the COMSs simulated
zero to the actual clear path zero of the installation annually.
The audit may be conducted in conjunction with, but prior to, a
5.4.1 Primary Zero Alignment Method. The primary zero
alignment shall be performed under clear path conditions. This may
be accomplished if the process is not operating and the monitor
pathlength is free of particulate matter or the monitor may be
removed from its installation and set up under clear path
conditions. The absence of particulate matter shall be
demonstrated prior to conducting the test at the installed site.
No adjustment to the monitor is allowed other than the
establishment of the proper monitor pathlength and correct optical
alignment of the monitor components. Record the monitor response
to a clear path condition and to the monitor's simulated zero
condition as percent opacity corrected to stack exit conditions as
necessary. For monitors with automatic zero compensation,
disconnect or disable the zero compensation mechanism or record the
amount of correction applied to the monitor's simulated zero
condition. The response difference in percent opacity to the clear
path and simulated zero conditions shall be recorded as the zero
alignment error. Adjust the monitor's simulated zero device to
provide the same response as the clear path condition. Restore the
COMS to its operating mode.
5.4.2 Alternate Zero Alignment Method. Monitors capable of
allowing the installation of an external, removable zero-jig, may
use the equipment for an alternative zero alignment provided that
the zero-jig setting is established for the monitor pathlength and
recorded for the specific COMS by comparison of the COMS responses
to the installed zero-jig and to the clear path condition; the
zero-jig is demonstrated to be capable of producing a consistent