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

the circumstances.



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

opacity standard).

2.5 External Zeroing Device (Zero-Jig). An external,

removable device for simulating or checking the cross-stack zero

alignment of the COMS.


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



4.1 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.


5.1 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

considered invalid.

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. 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. 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. 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

opacity standard. 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.


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

performance audit.

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