PERFORMANCE SPECIFICATION Z: 

SPECIFICATIONS AND TEST PROCEDURES FOR 

HCl CONTINUOUS EMISSION MONITORING 

SYSTEMS AT STATIONARY SOURCES 

 Revision 2.0 

 October, 2006 

 
i 

EXECUTIVE SUMMARY 

This performance specification describes the criteria that a hydrochloric acid (HCl) continuous 

emission monitoring system (CEMS) must meet to be considered valid for EPA compliance and/or 

other regulatory applications. Each HCl CEMS must meet the criteria for accuracy, stability, and 

instrumental response laid out in this document. In addition, each HCl CEMS must meet the 

installation requirements in PS-Z. 

 
ii 

REVISION HISTORY 

1.1 REVISION 1.0 

This document was part of the T149 Alternative Monitoring Petition, and was approved by the Office 

of Air Quality and Standards in January of 2006 

1.2 REVISION 2.0 

This revision is an update of the original Procedure Z document, October 2006. The following are key 

updates in revision 2.0: 

1. Recommendation that all HCL QA gases be certified with a minimum tolerance of 5% 

2. Recommendation that a site specific dynamic spiking protocol be used and, the dynamic 

spiking protocol would contain the detailed test procedure(s). 

3. Discussion for the use of quantitative introduction of the HCL calibration gas and subsequent 

total flow measurement as method for determining the reference HCL concentration during 

each test run. 

4. Updated the dynamic spiking overview section for easier flow of information 

5. Updated the equations to include percent relative standard deviation and the calculation for 

the reference HCL concentration when using quantitative introduction of the HCL calibration 

gas with subsequent total flow measurement. 
iii 

TABLE OF CONTENTS 

1.1 REVISION 1.0..................................................................................................................II

1.2 REVISION 2.0..................................................................................................................II

2.0 USING PERFORMANCE SPECIFICATION Z.......................................................................4

2.1 WHAT IS THE PURPOSE AND APPLICABILITY OF PERFORMANCE 

SPECIFICATION Z?........................................................................................................4

2.2 WHAT WILL BE DISCUSSED IN PS-Z?.........................................................................4

2.3 WHAT ARE THE INSTALLATION AND PRE-PERFORMANCE 

SPECIFICATION TEST REQUIREMENTS?...................................................................5

2.4 WHAT SPECIAL DEFINITIONS APPLY TO PS-Z?........................................................6

3.0 INTERFERENCES, SAFETY, AND EQUIPMENT REQUIREMENTS ..................................9

3.1 WHAT DO I NEED TO KNOW TO ENSURE THE SAFETY OF PERSONS 

USING PS-Z? ..................................................................................................................9

3.2 WHAT EQUIPMENT AND SUPPLIES DO I NEED?.......................................................9

3.3 WHAT REGENTS AND STANDARDS DO I NEED? ....................................................10

4.0 PERFORMANCE EVALUATION PROCEDURES AND REPORTING................................11

4.1 WHAT IS THE PURPOSE OF THE PERFORMANCE SPECIFICATION 

TESTS AND WHAT IS REQUIRED TO PERFORM THE TESTS? ..............................11

4.2 HOW DO I REPORT THE RESULTS OF THE INITIAL PERFORMANCE 

SPECIFICATION TEST?...............................................................................................15

5.0 PERFORMANCE CRITERIA AND CALCULATIONS..........................................................16

5.1 WHAT ARE THE PERFORMANCE CRITERIA FOR MY HCL CEMS?........................16

5.2 WHAT CALCULATIONS, EQUATIONS, AND DATA ANALYSES ARE 

NEEDED?......................................................................................................................17

5.3 CRITERIA FOR ACCEPTANCE....................................................................................25

5.4 BIAS CORRECTION .....................................................................................................25

6.0 OTHER REQUIREMENTS AND INFORMATION................................................................27

6.1 WHAT QUALITY CONTROL MEASURES ARE REQUIRED? .....................................27

6.2 WHAT CALIBRATION AND STANDARDIZATION PROCEDURES MUST I 

PERFORM?...................................................................................................................27

6.3 WHAT POLLUTION PREVENTION PROCEDURES MUST I FOLLOW? 

[RESERVED].................................................................................................................27

7.0 RELEVANT REFERENCES.................................................................................................30

 

Table 1. Performance Specification Test Calibration Gas Ranges 

Figure 1. Dynamic Spiking Overview
4 

2.0 USING PERFORMANCE SPECIFICATION Z 

2.1 WHAT IS THE PURPOSE AND APPLICABILITY OF PERFORMANCE SPECIFICATION Z? 

The purpose of Performance Specification Z (PS-Z) is to establish the initial performance requirements for 

evaluating the acceptability of a HCl CEMS. Such applications may include, (1) instrument, method or 

procedure calibration, and (2) evaluation or certification for initial acceptance. 

2.1.1 Application 

This specification is for evaluating the acceptability of a HCl CEMS at the time of installation and during 

periodic quality assurance checks. PS-Z applies to you if you will be using a HCl CEMS to demonstrate 

compliance with a regulatory HCl or HCl/Cl2 emission standard. 

2.1.2 Measurement Capabilities 

The HCl CEMS must be capable of measuring HCl concentrations in the units of the applicable standard 

or in units that can be converted to units of the applicable standard.

2.1.3 Other Monitoring

If your HCl CEMS is capable of reporting the HCl concentration in the units of the existing regulation, no 

additional monitoring is necessary. If your HCl CEMS does not report concentrations, in the units of the 

existing standard, then other monitoring (e.g., oxygen, temperature, and pressure) are necessary to 

convert the units reported by your CEMS to the units of the standard.

2.2 WHAT WILL BE DISCUSSED IN PS-Z? 

PS-Z covers two basic topics: (1) the instrument requirements for an HCl CEMS and (2) the requirements 

that each HCl CEMS must meet during the performance specification test. 

2.2.1 Instrument Requirements 

The HCl CEMS must be able to accurately report concentrations of HCl in stack effluent. It may do so by 

extracting a representative sample (path or point sampling may be used if the sample is representative) of 

stack effluent and analyzing the effluent to provide an output proportional to the HCl concentration. The 

CEMS operating range (zero to span) should encompass the response of the HCl CEMS for all expected 

HCl concentrations, including the applicable emission limit. The CEMS must have a system response 

time that is less than or equal to two minutes. Finally, the instrument or operator must be able to perform 

daily calibration drift tests, quarterly calibration error tests, and annual accuracy tests. 
5 

2.2.2 Performance Specification Test 

The purpose of the performance specification test is to establish the accuracy, precision, bias, and 

system response time of the HCl CEMS. Specifically, the following will be either tested or documented as 

part of the performance specification test requirements listed in Sections 3.0 and 4.0 of this document: (1) 

data recorder scale, (2) daily calibration drift, (3) installation and measurement location, (4) calibration 

drift test, (5) calibration error test, (6) system response time, (7) stratification test, (8) accuracy 

determination. 

2.3 WHAT ARE THE INSTALLATION AND PRE-PERFORMANCE SPECIFICATION TEST 

REQUIREMENTS? 

2.3.1 Installation Requirements 

The sampling location of the HCl CEMS should be downstream of all pollution control equipment at a 

position where the HCl concentration is directly representative or can be corrected so as to be 

representative of total emissions from the stationary source. It is recommended that the sampling 

location be at least two equivalent diameters downstream of the nearest control devices, point of pollution 

generation, bend, or other point at which a change in pollutant concentration or flow disturbance may 

occur. The sampling location is also recommended to be at least a half equivalent diameter upstream 

from the exhaust or control device. The equivalent diameter is calculated according 40 CFR Part 60, 

Appendix A, Method 1, Section 2.1I

. 

Either point or path sampling may be used. For point sampling the measurement point should be no less 

than 1.0 meter from the stack or duct wall or located over the centroidal area of the stack or duct cross 

section. For a path sampling CEMS the effective measurement path should be (1) totally within the inner 

area bounded by a line 1.0 meter from the stack or duct wall, or (2) have at least 70 percent of the path 

within the inner 50 percent of the stack diameter or duct cross section, or (3) be centrally located over any 

part of the centroidal area. 

The sample collection and instrumental analyzer portions of your HCl CEMS may be located any distance 

from the sampling point provided the transmission efficiency from the sampling point to the sample 

collection point can be determined and meets the criteria outlined later in this performance specification. 

It is also recommended that the sampling probe for the HCl CEMS be located at point without 

stratification (section 3.1.5).
6 

2.3.2 Reference Method Measurement Location 

You must select, as appropriate, an accessible reference method (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. If dynamic spiking is 

employed to determine the system accuracy, bias, and precision, the spiking of the calibration gas must 

encompass the sampling system of the HCL CEMS. 

2.3.2.1 Reference Method Traverse Points 

Select traverse points that assure acquisition of representative samples over the stack or duct crosssection. 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. 

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. 

2.4 WHAT SPECIAL DEFINITIONS APPLY TO PS-Z? 

Calibration Drift: The difference in the CEMS output readings from the established reference value after 

a stated period of operation during which no unscheduled maintenance or adjustment took place. 

Calibration Error: The mean difference between the concentration indicated by the CEMS and the 

known concentration generated by a calibration source at three levels when the entire CEMS, including 

the sampling interface is challenged. A CE test is performed to document the accuracy and linearity of 

the CEMS over the entire measurement range.
7 

Centroidal Area: means a concentric area that is geometrically similar to the stack or duct cross section 

and is no greater than 1 percent of the stack or duct cross-sectional area. 

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. 

Correlation Coefficient: determines the extent of a linear relationship between two fields over a given 

period of time.

Data Recorder: The portion of the CEMS that provides a record of analyzer output, flags which indicate 

normal operation, and flags indicating abnormal operation. The data recorder may record other pertinent 

data such as effluent flow rates, and various instrument temperatures. 

Diluent Analyzer: means that portion of the CEMS that senses the diluent gas (i.e. O2) and generates an 

output proportional to the gas concentration. 

Dynamic Spiking: a procedure used to document the accuracy, precision, and bias of the monitoring 

system by quantitatively spiking a certified gas into the pollutant gas stream. 

High-level drift: means the absolute difference between a high-level calibration gas and the monitor 

response, in units of the applicable standard. 

Instrument Measurement Range: The range of HCl concentrations the instrument can reliably measure 

from the lowest concentration to the highest. 

Intercept: value of the Y variable when the X variable is equal to zero. 

Linear Regression: a methodology used to find a formula that can be used to relate two variables that 

are linearly related. 

Path Sampling CEMS: A CEMS that samples the source effluent along a path greater than 10 percent of 

the equivalent diameter of the stack or duct cross section. 

Point Sampling CEMS: A CEMS that samples the source effluent at a single point. 
8 

Pollutant Analyzer: means that portion of the CEMS that senses the pollutant gas and generates an 

output proportional to the gas concentration. 

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. 

Response Time: The time interval between the start of a step change in the system input and when the 

pollutant analyzer output reached 95% of the final value. 

Sample Interface: The portion of the CEMS used for one or more of the following: sample acquisition, 

sample transport, sample conditioning, or protection of the monitor from the effects of stack gas. 

Slope: The rate of change of Y relative to the change in X. 

Stratification: means the change in effluent concentration in a duct, over time when comparing a 

reference measurement (centroid of duct) to traversed sampling concentrations. 

Zero drift: means the absolute difference between a high-level calibration gas and the monitor response, 

in units of the applicable standard. 
9 

3.0 INTERFERENCES, SAFETY, AND EQUIPMENT REQUIREMENTS 

3.1 WHAT DO I NEED TO KNOW TO ENSURE THE SAFETY OF PERSONS USING PS-Z? 

People using PS-Z may be exposed to hazardous material, operational hazards, and hazardous site 

conditions. PS-Z does not address all the safety issues associated with its use. It is your responsibility to 

ensure the safety of persons using PS-Z. Some helpful references may include the CEMS manual, the 

CEMS manufacturer, other reference methods, and on-site safety regulations. 

3.2 WHAT EQUIPMENT AND SUPPLIES DO I NEED? 

3.2.1 Equipment for the CEMS 

1. Sample Extraction System: This portion of the CEMS must present a sample of source 

effluent to the sampling module that is directly representative or can be corrected so as to be 

representative of source. The sample extraction system typically consists of a sample probe 

and a heated umbilical line. 

2. Pressure Regulation Module: The pressure regulation module is designed to remove both 

free particulates and water-soluble aerosols from the gas stream prior to analysis by the 

sampling module. This module also provides a sample gas to the analyzer at a constant 

pressure (optional). 

3. Analysis module: The portion of the CEMS that quantitates stack gas concentrations of HCl. 

4. Diluent Module: This portion of the CEMS quantifies stack gas concentrations of oxygen or 

CO2. For systems with a multi-component analyzer, the same analyzer quantifies the 

concentration of all measured analytes.

5. System Controller: This portion of the CEMS provides control of the analyzer, sample 

probe, pressure regulation module and the sample interface. 

6. Data recorder: Your HCl CEMS must be able to record HCl concentrations and instrument 

status signals (flags). 

3.2.2 Equipment Specifications 

The CEMS data recorder output range must include zero and a high-level value. The range of the data 

recorder and the measurement range of the HCl CEMS will be documented. The high-level value is 

chosen by the source owner or operator and is defined as follows: 
10 

For an HCl CEMS installed to measure controlled emissions or emissions that are in compliance with an 

applicable regulation, the high-level value should be at least 1.5 times the emission standard level and 

encompass the HCl concentration levels expected by the process. 

 The CEMS design should also allow the determination of calibration drift at the zero and high-level 

values. In special cases, the Administrator may approve a single-point calibration-drift determination. 

3.3 WHAT REGENTS AND STANDARDS DO I NEED? 

3.3.1 Reference Gases, Gas Cells, or Optical Filters 

See Table 1 for reference gas concentration ranges. 

 
11 

4.0 PERFORMANCE EVALUATION PROCEDURES AND REPORTING 

4.1 WHAT IS THE PURPOSE OF THE PERFORMANCE SPECIFICATION TESTS AND WHAT IS 

REQUIRED TO PERFORM THE TESTS? 

The purpose of the performance specification tests is to determine the accuracy, precision, bias, and 

system response time of the HCl CEMS. 

4.1.1 Pretest Preparation 

Prior to the start of your initial performance specification tests, you must be sure that the HCl CEMS is 

installed according to the specifications laid out in this document. After installing the HCl CEMS, it is 

recommended you use the CEMS for a period of time to familiarize yourself with its operation. It is also 

recommend that you conduct daily checks of the zero and high-level drift, conduct a calibration error test, 

and conduct a calibration drift check to verify that the instrument is functioning properly. When you are 

confident that the instrument is performing satisfactorily it is time to prepare for the performance 

specification tests. 

4.1.2 Data Recorder Scale Check 

The range of the data recorder and the measurement range of the HCl CEMS will be documented. The 

CEMS operating range (zero to span) and the range of the data recorder should encompass both the 

response of the HCl CEMS for all expected HCl concentrations and the applicable emission limit. 

4.1.3 Calibration Drift Check 

The HCL CEMS must perform a calibration check at least once per day. Certified gases must be used to 

perform the zero and high-level drift checks. All data will be recorded. 

4.1.4 Installation and Measurement Location Check 

The installation location of the HCL CEMS must adhere to section 1.3.1 of this document. In addition, the 

location of any reference method testing must adhere to section 1.3.2 of this document. 

4.1.5 Stratification Test 

 The stratification test must be conducted when the facility is operating during normal operation. The 

purpose of this test is to verify that excess stratification of the target pollutant does not exist at the 

sampling point of the monitoring system. 

 To determine whether effluent stratification exists, a dual probe system should be used to determine the 

average effluent concentration while measurements at each traverse point are being made. One probe, 
12 

located at the stack or duct centroid, is used as a stationary reference point to indicate change in the 

effluent concentration over time. The second probe is used for sampling at the traverse points specified 

in Method 1. The traverse points are sampled for five minutes at each point. You may test for 

stratification at the HCl CEMS sampling point by using either velocity tests as described in Method 2II, HCl 

concentrations using Methods 26 or 26A, or an acceptable alternative (i.e. CO or Nox) A minimum of 12 

sampling points will be used, with 6 sampling points along each of the two traverses. 

4.1.6 Seven-day Calibration Drift Test 

The seven-day calibration drift test must be conducted when the facility is operating during normal 

operation. The purpose of this test is to verify that the instrument operation is stable. During the 

calibration drift test period you must determine the magnitude of the zero calibration drift and the highlevel calibration drift at least once each day. During the stability tests no adjustments or calibrations may 

be made to the CEMS. If periodic automatic or manual adjustments are made to the CEMS zero and 

high-level calibration settings, conduct the CD test immediately before these adjustments, or conduct it in 

such a way that the CD may also be determined. 

The calibration drift will be determined at the zero and high-level value of the HCl CEMS. Introduce to the 

CEMS the reference gases, gas cells, or optical filters (these need not be certified) for the zero and high 

level values. Record the CEMS response and subtract this value from the reference value. The 

calibration gas concentrations are provided in Table 1. 

4.1.7 Calibration Error 

 The HCL CEMS will be challenged three non-consecutive times with zero, mid-level, and high-level 

certified HCL gases (Table 1). The cylinder gases need not be EPA Protocol 1 gases. The calibration 

gases will be injected into the sample system as close to the sampling probe outlet as practical and will 

pass through all CEMS components used during normal monitoring. The difference between the 

instrument response and the reference value (certified gas) will be calculated after each injection and the 

resulting three differences will be averaged to determine the CE at each measurement point. 

4.1.8 System Response Time 

Introduce zero gas into the analyzer. When the system output has stabilized (no change greater than 1 

percent of full scale for 30 sec), introduce an upscale calibration gas and wait for a stable value. Record 

the time (upscale response time) required to reach 95 percent of the final stable value. Next, reintroduce 

the zero gas and wait for a stable reading before recording the response time (downscale response time). 

Repeat the entire procedure three times and determine the mean upscale and downscale response 

times. The slower or longer of the two means is the system response time. 
13 

Calibration gas ranges for the response time test are provided in Table 1. If using a multi-component 

analyzer, the response time can be based on any analyte measured by the CEMS. 

4.1.9 CEMS Accuracy 

The accuracy of the HCl CEMS shall be determined by performing either a relative accuracy 

determination or by dynamic spiking. 

4.1.9.1 Relative Accuracy (RA) 

Conduct the RA test while the affected facility is operating during normal operation, or as specified in an 

applicable subpart. The RA test may be conducted during the CD test period. 

Reference Methods (RM). Unless otherwise specified in an applicable subpart of the regulations, 

Methods 26 or 26A, or their approved alternatives, are the reference methods for HCl. Other reference 

methods for moisture, oxygen, etc. may be necessary. 

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. 

For integrated samples make a sample traverse of at least 21 minutes, sampling for an equal time at 

each traverse point. 

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. 

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. If the RM has an integrated sampling technique, make a direct comparison of the RM 

results and CEMS integrated average value. 
14 

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 4.0. 

4.1.9.2 Dynamic Spiking 

Dynamic spiking can be used in lieu of the Relative Accuracy Determination as an alternative method for 

documenting the accuracy, precision, and bias of the HCl CEMS. This section provides an overview of a 

typical dynamic spiking procedure. A site specific dynamic spiking protocol, which provides detailed 

steps of the actual procedure, is required. Figure 1 provides an overview of a typical dynamic spiking 

arrangement. 

While the HCl CEMS is sampling flue gas, HCl reference gas is introduced into the CEMS sample 

interface by using a mass flow controller (or equivalent). The target ratio of actual flue gas to the HCl 

reference gas is 9:1, but must be kept at a minimum ratio of 1:1. The HCl concentration is quantitated by 

the HCl CEMS. 

Certified HCL calibration gas is spiked at a minimum of three levels (low, mid, high) through the HCL 

CEMS measurement range. For each test level, a minimum of 30, one minute averaged HCL values are 

collected. The percent relative standard deviation, for each data set, should not exceed 20%. Table 1 

provides guidance on the HCL concentrations for the low, mid, and high test runs. 

Several methods exist to calculate the dynamically spiked HCL concentration (represents the reference 

HCL concentration). Two common methods are: (1) Use of an element of opportunity and (2) 

Quantitative introduction of the HCL calibration gas with total flow measurement. Other methods may be 

used; however, a site specific protocol should document the procedure(s) used. 

An element of opportunity can be used to calculate the dynamically spiked HCl concentration (represents 

the reference HCl concentration). The element of opportunity can either be be an analyte, which would 

normally be present in the flue gas at steady concentrations, or total flow through the system. Examples 

of prospective analytes which could be used as elements of opportunity are O2, NOx, SO2, CO2, or 

moisture. The analyte(s) is measured using a certified reference CEMS, separate from the HCL CEMS. 

Total flow through the system may also be used as an element of opportunity to calculate the dynamically 

spiked HCL concentration. Examples the total flow measurement are the use of a calibrated laminar flow 

element, or use of a tracer gas with subsequent downstream measurement (for example: hydrocarbon 

tracer gas with subsequent calibrated GC measurement downstream). 

Regardless of the element of opportunity, It is recommended that the element of opportunity data set, for 

each test level (low, mid, high) have a relative percent standard deviation less than or equal to 20%. 
15 

Quantitatively introducing the HCL calibration gas, and, measuring the total flow is another method for 

documenting the dilution, and subsequent theoretical value of the HCL concentration spiked for each test 

run. Use of this method requires documenting the quantitative introduction of HCL gas into the system; 

such as a method 205 procedure or similar protocol. 

It is important to compensate the HCl reference concentration(s) for any background HCL present in the 

flue gas. The HCl concentration of the flue gas (baseline HCL) shall be determined prior to each spiking 

trial. The baseline HCl concentration is based upon a series of at least 10, one-minute averaged data 

points. Baseline data must be collected immediately prior to each test run. The data points must include 

the HCl concentration, element of opportunity concentration(s) and/or the total flow. A site-specific 

standard operating procedure for the HCL dynamic spiking is required. 

Linear regression is used to establish the accuracy, precision, and bias of the HCl CEMS. The criteria for 

the HCl dynamic spiking are: 

1. The correlation coefficient (r) must be greater than or equal to 0.90 

2. The slope must be 1.0, +/- 0.15 

3. The Intercept must be equal to or less than 15% of the instrument span 

4.2 HOW DO I REPORT THE RESULTS OF THE INITIAL PERFORMANCE SPECIFICATION TEST? 

Summarize the results of the calibration drift, calibration error, response time, stratification, and accuracy 

tests in tabular form. Include all data sheets, calculations, and records of CEMS measurements 

necessary to substantiate the performance of the CEMS and any other devices or methods (e.g., method 

26A). The CEMS measurements shall be reported to the agency in units of ppmv, on a dry basis. 
16 

5.0 PERFORMANCE CRITERIA AND CALCULATIONS 

5.1 WHAT ARE THE PERFORMANCE CRITERIA FOR MY HCL CEMS? 

You must demonstrate that your HCl CEMS has adequate precision, accuracy, system response time and 

data reporting capabilities to determine if your facility is in compliance with HCl emission standards or 

operating permit limits as specified in applicable regulations or permits. You will demonstrate this 

capacity by showing that your HCl CEMS meets the following performance criteria. 

5.1.1 Data Recorder Scale 

The measurement range of the HCL CEMS, and the data recorder scale, must encompass the expected 

HCL concentrations as well as the applicable emission limit. 

5.1.2 Calibration Drift 

The daily zero and high-level calibration drift is 5% of the instrument span. Zero and high-level calibration 

drifts shall be adjusted, at a minimum, whenever the 24-hour zero drift exceeds the limits of the 

calibration drift specification. The amount of excess zero and high-level drift measured at the 24-hour 

interval checks will be recorded. Section 4.2 provides the equations for calculating the zero and highlevel calibration drifts. 

5.1.3 Installation and Measurement Location 

The installation requirements and measurement location of the HCL CEMS will meet the specifications 

outlined in section 3.1.1 and 3.1.2 of this document. 

5.1.4 Stratification Test 

The stratification in the stack or duct, at the measurement location, must be less than or equal to a 10 

percent between the average concentration in the duct or stack and the concentration at any point more 

than 1.0 meter form the duct or stack wall. Section 4.2.2 provides the equation for calculating the 

stratification of the stack or duct. 

5.1.5 Seven-day Calibration Drift Test Criteria 

The daily zero and high-level drift each must be less than 5% of the instrument span for seven 

consecutive days. See Section 4.2.2 for the equations used to determine the zero and high-level drift.
17 

5.1.6 Calibration Error Test 

The mean difference between the CEMS and the reference values, at all three test levels, must be no 

greater than 5% of span. See Section 4.2.3 for the equation used to determine the calibration error. 

5.1.7 Response Time Test 

The CEMS response time shall not exceed 2.0 min to achieve 95 percent of the final stable value. If 

using a multi-component analyzer, the response time can be based on any analyte measured by the 

CEMS. 

5.1.8 Relative Accuracy 

The RA of the CEMS must not be greater than 20% of the mean value of the reference method (RM) test 

data, or not greater than 10% in terms of the emission standard (ppmv, dry), or have an absolute 

difference of less than 5 ppmv between the mean reference value and the mean CEMS value. See 

Section 4.2.5 for the equations used to determine the relative accuracy of your CEMS. 

5.1.9 Dynamic Spiking 

Dynamically spiking may be used in lieu of a relative accuracy test as a means to document the accuracy, 

precision, and bias of the HCl CEMS. 

The criteria for the HCl dynamic spiking is: 

• The correlation coefficient, r, must be greater than or equal to 0.90 

• The slope must be 1.0, +/- 0.15 

• The Intercept must be equal to or less than 15% of the instrument span. 

See Section 4.2.8 for equations to determine the linear correlation coefficient, the slope and the intercept. 

At a minimum, the data set must meet the correlation coefficient. If this is not met, the dynamic spiking 

procedure must be repeated until the correlation coefficient criteria is met. If the HCl CEMS has met the 

correlation coefficient requirement, but does not meet either the slope, or intercept criteria, a bias exists 

and a correction factor must be applied to the HCl CEMS for data collection. The equations to determine 

the corrected value are provided in Section 4.2.8.1. The correction factor must be applied to the HCl 

CEMS one-minute average data until a new dynamic spiking procedure indicates the specific bias no 

longer exists, or, a different correction factor (bias) is indicated. 

5.2 WHAT CALCULATIONS, EQUATIONS, AND DATA ANALYSES ARE NEEDED? 
18 

5.2.1 Daily Upscale and Zero Drift 

 CD =(⎪R - A⎪/ S ) * 100 (Equation 1) 

where: 

 CD = Percent calibration drift (%), 

 R = Reference value of zero or high level calibration gas introduced into the 

monitoring system (ppmv), 

 A = Actual monitor response to calibration gas (ppmv), 

 S = Span of the instrument (ppmv). 

5.2.2 Calibration Error 

 CE = ⎪davg / S⎪ * 100 (Equation 2) 

where: 

 CE = Percent calibration error (%), 

 davg = Mean difference between CEMS response and the known reference gas (ppmv), 

 S = Span of the monitor (ppmv). 

5.2.3 Mean Difference 

Calculate the arithmetic mean difference as follows: 

= ∑ i avg d

n

d 1 (Equation 3) 

where : 

davg = Arithmetic mean of differences 

n = Number of data sets 

di = difference of each data set 
19 

And 

di = xi − yi (Equation 4)

where: 

xi = Value at data set x 

yi = Value at data set y

5.2.4 Relative Accuracy 

The RA for the monitors will be calculated using the least restrictive of equation 6 or equation 7: 

RA = (⎪davg⎪ + ⎪CC⎪) (Equation 5)

 or 

RA = ((⎪davg⎪ + ⎪CC⎪) / TMavg ) * 100 (Equation 6)

where: 

RA = Relative accuracy, either percent or ppmv or % absolute, 

 davg = Arithmetic mean of differences between value measured by the installed CEMS and the 

reference method, 

 CC = Confidence coefficient, 

 TMavg = Average value measured by the reference test method monitors. 

5.2.5 Confidence Coefficient 

The confidence coefficient will be calculated using equation 8: 

 CC = t0.975 * (Sd / (n1⁄2)) (Equation 7)

where: 

 CC = Confidence coefficient, 

 t0.975 = t-value obtained from Table 2.1 in Performance Specification 2, 40 CFR Part 60 

Appendix B 
20 

5.2.6 Standard Deviation (of Differences) 

Sd = Standard deviation of differences measured between the installed CEMS and the 

reference methods calculated using equation 8: 

1 / 2 2

1

1

2

1

⎥

⎥

⎥

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎢

⎢

⎢

⎣

⎡

−

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

=

∑ ∑ =

=

n

n

d

S

n

i i n

i i

d

d (Equation 8)

where: n = Number of values in this data set. 

5.2.7 Stratification 

The value, at each traverse point, is compared to the average value for all sampling points to determine 

the percent stratification using the following equation: 

S = Ci −Cave *100% (Equation 9)

where: 

 S = percent stratification 

 Ci

 = concentration or velocity at sampling point i 

 Cave = average concentration or velocity at all sampling points 

5.2.8 Baseline data 

5.2.8.1 HCL CEMS data 

The baseline HCL concentration is measured prior to each dynamic spiking run. For each baseline HCL 

data set, calculate the average, in ppm, using equation 10. 

Calculate the arithmetic mean of a data set as follows: 

= ∑xi

n

x

1

(Equation 10) 

where : 
21 

x = Arithmetic mean 

n = Number of data points 

xi = Value of each data point 

5.2.8.2 Element of Opportunity Data 

The element of opportunity data set is acquired prior to each dynamic spiking test run, simultaneous to 

the baseline HCL concentration data set. For each element of opportunity, calculate the average value 

using equation 10. 

5.2.8.3 Flow via dilution 

When using dilution of a measured analyte (such as a hydrocarbon with subsequent GC measurement) 

as an indicator of total flow, calculate the total flow, in liters per minute using equation 11. 

Calculate the total flow as follows: 

 Tflow = 

( )

( ) *

Analyte measured

Analtye spike Tflow

−

− (Equation 11)

 Tflow = Total flow through the system in lpm 

 Analyte-Spike = Concentration of Spiked Analyte (ppm) 

 Analyte-measured = Measurement, downstream, of spiked Analyte (ppm) 

Calculate the average flow value, for the data set, using equation 10. 

5.2.9 Dynamic Spiking Test run data 

5.2.9.1 HCL CEMS data 

For each dynamic spiking test run, calculate the average and percent relative standard deviation of the 

data set using equations 10 and 12, respectively. 
22 

Calculate the percent standard deviation as follows: 

1 / 2 2

1

1

2

1

⎥

⎥

⎥

⎥

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎢

⎢

⎢

⎢

⎣

⎡

−

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

=

∑ ∑ =

=

n

n

d

PRS

n

i i n

i i

d

d (Equation 12)

 x

Where: 

PRSd = Percent Relative Standard Deviation of the data set 

 x = Arithmetic mean 

5.2.9.2 Element of Opportunity data 

For each dynamic spiking test run, calculate the average and percent relative standard deviation of the 

data set using equations 10 and 12, respectively. If using total flow as a means to determine the 

reference HCL calibration gas concentration, use equation 11 to calculate the total flow prior to 

determining the average and percent relative standard deviation of the data set. 

5.2.10 Reference HCL concentration calculations 

5.2.10.1 Element of opportunity to calculate reference HCL concentration 

Equation 13 is used to calculate the reference HCL concentration for a given dynamic spiking test run. 
23 

HCl ref = CalGas BaselineHCl

Opp pre

Opp post

avg

avg + −

− 1− * (Equation 13)

where: 

 

 Opp-post avg = average reference element of opportunity value during dynamic spiking test run 

 Opp-pre avg = average reference element of opportunity value during baseline test run 

 CalGas = HCl calibration gas concentration 

 Baseline HCl = CEMS HCl average baseline value 

5.2.10.2 Quantitative HCL calibration gas introduction and total flow to calculate reference HCL 

concentration 

When using the quantitative introduction of calibration gas and total system flow to calculation the 

reference HCL concentration for a given dynamic spiking test run, use equation 14. Equation 11 is used 

to calculate the total system flow. 

HCl ref = CalGas BaselineHCl

Tflow

Cflow

avg

avg * + (Equation 14)

Where: 

HCl ref = Reference HCl value for run “X” 

 Cflow = Average calibration HCL gas flow rate into system (lpm) 

 Tflow = Average Total System Flow during run (lpm) 

 CalGas = HCl calibration gas concentration 

 Baseline HCl = CEMS HCl average baseline value 
24 

5.2.11 Linear Regression 

Linear regression is used to calculate the accuracy, precision, and bias of the HCL CEMS. For each 

dynamic spiking test run, plot the HCL CEMS reference value, Xaxis, versus the HCL measured value, Y 

axis. Determine the correlation coefficient (r ), the slope, and the intercept using equations 15-18. 

y b b x o 1 ˆ = + (Equation 15)

where: 

bo = The y intercept 

b1 = The slope 

The intercept is calculated according to the following equation: 

b y b x o = − 1 (Equation 16)

where: 

∑=

=

n

i

i x

n

x

1

1 

∑=

=

n

i

i y

n

y

1

1 

The slope of the line is calculated according to equation below: 

∑

∑

=

=

−

− −

= n

i 1

2

i

n

i 1

i i

1

( x x )

( x x )( y y )

b (Equation 17) 

The linear correlation coefficient is calculated according to the following equation. 
25 

∑ ∑

∑

= =

=

− −

⎟

⎠

⎞ ⎜

⎝

⎛ − −

= n

i

i

n

i

i

n

i

i i

x x y y

x x y y

r

1

2

1

2

2

2 1

( ) ( )

( )( )

 (Equation 18) 

5.3 CRITERIA FOR ACCEPTANCE 

The criteria for the HCl dynamic spiking is: 

• The correlation coefficient, r, must be greater than or equal to 0.90 

• The slope must be 1.0, +/- 0.15 

• The Intercept must be equal to or less than 15% of the instrument span. 

At a minimum, the data set must meet the correlation coefficient. If this is not met, the dynamic spiking 

procedure must be repeated until the correlation coefficient criteria are met. If the HCl CEMS has met the 

correlation coefficient requirement, but does not meet either the slope, or intercept criteria, a bias exists 

and a correction factor must be applied to the HCl CEMS for data collection. The equations to determine 

the corrected value are provided in Section 5.4. The correction factor must be applied to the HCl CEMS 

one-minute average data until a new dynamic spiking procedure indicates the specific bias no longer 

exists, or, a different correction factor (bias) is indicated. 

5.4 BIAS CORRECTION 

If the HCl CEMS fails to meet both the slope and intercept criteria, the following correction factor must be 

applied to the one-minute average HCl data: 

1

0

b

y b CC i − = (Equation 19) 

Where:

C C = corrected CEMS HCL concentration 
26 

yi

 = CEMS reported HCL concentration 

b0 = the intercept of the least squares linear regression line 

b1 = the slope of the least squares linear regression line 

b). If the HCl CEMS fails to meet the slope criteria, but meets the intercept criteria, the following 

correction factor must be applied to the one-minute average HCl data: 

1 b

y CC i = (Equation 20)

c). If the HCl CEMS fails to meet the intercept criteria, but meets the slope criteria, the following correction 

factor must be applied to the one-minute average HCl data: 

0 C y b i

C = − (Equation 21)
27 

6.0 OTHER REQUIREMENTS AND INFORMATION 

6.1 WHAT QUALITY CONTROL MEASURES ARE REQUIRED? 

Ongoing quality control will include daily calibration drift tests, quarterly calibration error audits (absolute 

calibration audit), and annual accuracy test audits. Specific procedures and performance criteria are 

included in Procedure DD: Quality Control and Quality Assurance Requirements for Hydrochloric Acid 

Continuous Emission Monitoring Systems at Stationary Sources. 

6.2 WHAT CALIBRATION AND STANDARDIZATION PROCEDURES MUST I PERFORM? 

Refer to your CEMS owner’s manual and manufacturer to determine what calibration and standardization 

procedures are required for your HCl CEMS. 

6.3 WHAT POLLUTION PREVENTION PROCEDURES MUST I FOLLOW? [RESERVED] 
28 

Table 1. Performance Specification Test Calibration Gas Ranges 

 HCl Calibration Gas Concentrations a

Test Units Zero Mid-Level High-Level 

Calibration Drift and 

Response Time Test b

% of Span 0-30 NA 50-100 

Calibration Error Test % of Span 0-30 30-50 50-100 

Dynamic Spiking % of Span 0-50 25-75 50-100 

a

A copy of the supplier’s certificate of analysis must be provided for each gas cylinder. Calibration gases 

do not need to be Protocol 1 gases. It is recommended that the calibration gases, for all QA, have a 

minimum tolerance of 5%. 

b

If conducting the response time using a multi-component analyzer, the response time test can be based 

on any measured analyte. 
29 

Figure 1. Typical Dynamic Spiking Apparatus 

Typical Dynamic Spiking Apparatus

HCL 

CEMS

900-1000 ppm HCL in N2

Calibration Manifold

(Mass flow meters)

Sample Probe

•Heated Filter 

• Pressure Control

•Laminar Flow 

Element

Heated sample line

Flue Gas

Gas

Conditioner

Reference

Measurement(s)

Heated line inside 

sample umbillical
30 

7.0 RELEVANT REFERENCES 

I. United States. Environmental Protection Agency [EPA]. Technology Transfer Network. Emission 

Measurement Center. Promulgated Methods. Method 1: Sample and Velocity Traverses for 

Stationary Sources. Washington, DC: EPA; 2004. Available: 

http://www.epa.gov/ttn/emc/promgate/m-01.pdf via the Internet. 

II. United States. Environmental Protection Agency [EPA}. Technology Transfer Network. 

Emission Measurement Center. Promulgated Methods. Method 2: Determination of Stack Gas 

Velocity and Volumetric Flow Rate. Washington, D.C: EPA; 2004. Available: 

http://www.epa.gov/ttn/emc/promgate/m-02.pdf via the Internet. 

III. United States. Environmental Protection Agency (EPA). Technology Transfer Network. Emission 

Measurement Center. Performance Specifications. Performance Specification 2- Specifications 

and Test Procedures for SO2 and NOx Continuous Emission Monitoring Systems in Stationary 

Sources, 40 CFR 60 Appendix B, February 2000. Available: 

http://www.epa.gov/ttn/emc/perfspec.html via the Internet. 

IV. United States. Environmental Protection Agency (EPA). Technology Transfer Network. Emission 

Measurement Center. Performance Specifications. Performance Specification 4A - 

Specifications and Test Procedures for Carbon Monoxide Continuous Emission Monitoring 

Systems in Stationary Sources, 40 CFR 60 Appendix B, February 2000. Available: 

http://www.epa.gov/ttn/emc/perfspec.html via the Internet. 

V. United States. Environmental Protection Agency (EPA). Technology Transfer Network. Emission 

Measurement Center. Performance Specifications. Performance Specification 4B - 

Specifications and Test Procedures for Carbon Monoxide and Oxygen Continuous Emission 

Monitoring Systems in Stationary Sources, 40 CFR 60 Appendix B, September 30, 1999. 

Available: http://www.epa.gov/ttn/emc/perfspec.html via the Internet.