(Adopted: 07/17/12) 

AVAQMD RULE 218.1 218.1-1

Continuous Emission Monitoring Performance Specifications 

RULE 218.1 

Continuous Emission Monitoring Performance 

Specifications 

(A) General 

(1) Purpose 

(a) The purpose of this rule is to specify standards, specifications and 

requirements for new, modified and existing Continuous Emission 

Monitoring Systems (CEMS). 

(2) Applicability 

(a) The provisions of this rule shall apply to all sources that require 

CEMS pursuant to Rule 218 – Continuous Emission Monitoring. 

(B) Definitions 

(1) “Analyzer” - The part of the CEMS that analyzes the appropriate gaseous 

constituents of the conditioned gaseous sample or measures stack gas 

volumetric flow and fuel flow rates, as applicable.

(a) Contaminant Analyzer - The part of the CEMS that detects the air 

contaminant concentrations and represents those concentrations in 

a signal output. 

(b) Diluent Analyzer - The part of the CEMS that detects oxygen (O2), 

carbon dioxide (CO2) or other Diluent Gas concentrations and 

represents those concentrations in a signal output.

(c) Fuel Flowmeter - The part of the CEMS that detects the parameters 

of all essential measurement sub-systems (e.g., temperature, 

pressure, differential pressure, frequency, gas density, gas 

composition, heating value) and generates signal outputs which are 

a function of the fuel flow rate and all essential measurement 

subsystem parameters. 

(d) Stack Flowmeter - The part of the CEMS that detects the 

parameters from all essential measurement sub-systems (e.g., 

temperature, static and atmospheric pressure, gas density, gas 

composition, molecular weight, gas moisture content) and 

generates signal outputs which are a function of the stack gas 
218.1-2 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

volumetric flow rate and all essential measurement sub-system 

parameters. 

(2) “Calibration” - A procedure performed to ensure that the CEMS 

accurately measures and records the concentration of the specific air 

contaminant or Diluent Gas, flow rate and other parameters necessary to 

generate the required data, as evidenced by Calibration Checks and 

achieved by periodic manual or automatic adjustment. 

(3) “Calibration Check” - A procedure performed to determine CEMS 

response to a given gaseous compound concentration by means of 

injecting a certified calibration gas mixture into the CEMS as close to the 

probe tip as practical. 

(4) “Calibration Drift” (CD) - Change in the CEMS output or response over a 

specific period of normal continuous operation when the air contaminant 

or Diluent Gas concentration at the time of the measurements is the same 

known upscale value. CD is expressed as the sum of the absolute value of 

the mean difference and the absolute value of the Confidence Coefficient 

of a series of tests, to the Full Span Range, expressed as a percentage as 

follows: 

×100

+

=

FSR

d CC

CD

Where: 

FSR = Full Span Range 

CC = Absolute value of the 95% Confidence Coefficient 

d

= Absolute value of the mean difference. The mean 

difference, d , is calculated as: 

∑=

=

n

i

di

n

d

1

1
AVAQMD RULE 218.1 218.1-3

Continuous Emission Monitoring Performance Specifications 

Where 

∑=

n

i

di

1

= Algebraic sum of the individual differences di

n = Number of data points 

i

d = The difference between the paired response 

values of the monitoring system 

(5) “Calibration Error” (CE) 

(a) Calibration Error (as applicable to Section (D) - Standards for 

Existing CEMS) - The ratio of the difference between the air 

contaminant or Diluent Gas concentration indicated by the CEMS 

and the known concentration of the calibration gas, to the known 

concentration of the calibration gas. CE is calculated as the ratio 

of the sum of the absolute values of the mean difference and the 95 

percent Confidence Coefficient of a series of tests, to the gas 

concentration, expressed as a percentage, as follows: 

×100

+

=

C

d CC

CE

Where: 

C = Calibration gas concentration 

CC = Absolute value of the 95% Confidence Coefficient 

d = Absolute value of the mean difference. The mean 

difference is calculated as: 

∑=

=

n

i

di

n

d

1

1
218.1-4 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

Where: 

∑=

n

i

di

1

= Algebraic sum of the individual differences di

n = Number of data points 

i

d = The difference between the paired monitoring system

response value and the known gas concentration or 

the equivalent rating of the Reference Method value, 

both in units of the applicable standard 

(b) Calibration Error (as applicable to Section (C) - Standards for New 

or Modified CEMS) - The ratio of the absolute value of the 

difference between the air contaminant or Diluent Gas 

concentration indicated by the CEMS and the known concentration 

of the calibration gas, to the Full Span Range, expressed as a 

percentage, as follows: 

×100

−

=

FSR

C A

CE

Where: 

C = Calibration gas concentration 

A = Actual response or the concentration indicated by the 

monitoring system 

FSR = Full Span Range of the instrument 

(6) “CEMS Availability Percentage” - A percentage calculated as the ratio of 

the total unit operating hours for which the CEMS provided qualityassured data, to the source total unit operating hours during a specified 

period, excluding periods of Calibration, maintenance, repair, or audit, up 

to a maximum of 40 hours per month. 

(7) “Certified CEMS” - A CEMS installed, tested, operated, maintained, and 

calibrated according to the applicable requirements of Rules 218 and 

218.1; that has met the applicable performance specifications of Rule 

218.1 and, has received written approval and conditions thereto applying, 

from the APCO. 
AVAQMD RULE 218.1 218.1-5

Continuous Emission Monitoring Performance Specifications 

(8) “Certified Gas Mixture” - A gas mixture manufactured, analyzed and 

certified in accordance with the “EPA Traceability Protocol for Assay and 

Certification of Gaseous Calibration Standards” - EPA-600/R97/121, 

September 1997 Revision (EPA Traceability Protocol) or any subsequent 

version published by EPA. This definition incorporates by reference EPA 

Protocol. 

(9) “Confidence Coefficient” (CC) - The 2.5 percent error Confidence 

Coefficient for the 95 Percent Confidence Interval of a series of tests. The 

CC is calculated as follows: 

n

S

CC t

d = 975.0

Where: 

Sd = Standard deviation 

n = Number of data in a series of tests 

t0.975 = t-value (see Table of t-Values below) 

Table of t-Values* 

n t0.975 n t0.975 n t0.975

2 12.706 7 2.447 12 2.201 

3 4.303 8 2.365 13 2.179 

4 3.182 9 2.306 14 2.160 

5 2.776 10 2.262 15 2.145 

6 2.571 11 2.228 16 2.131 

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

freedom. Use n equal to the number of data points. 

(10) “Continuous Emission Monitoring System” (CEMS) – The total combined 

equipment and systems required to continuously determine air 

contaminants and Diluent Gas concentrations and/or mass emission rate of 

a source effluent (as applicable). The CEMS consists of three (3) major 

subsystems: Sampling Interface, Analyzer and Data Acquisition System. 
218.1-6 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(11) “Continuous Monitoring” - A monitoring in which a minimum of one (1) 

measurement (e.g., concentration, mass emission, flow rate) is taken and 

recorded each minute. 

(12) “Data Acquisition System” (DAS) - The part of the CEMS that processes 

data generated by the Analyzer and records the results, thus creating a 

permanent record of the output signal in terms of concentration, flow rate, 

and any other applicable parameter necessary to generate the required data 

in units of applicable standard. The DAS consists of all equipment such as 

a computer required to convert the original recorded values to any values 

required for reporting. 

(13) “Diluent Gas” - A gas present in a calibration gas mixture or in source 

emissions that is present in quantities significantly larger than the air 

contaminant. 

(14) “Full Span Range” (FSR) - The full range of values or data display output 

that a monitor component is calibrated to measure. 

(15) “Linearity Error” (LE) - The percentage error in linearity expressed in 

terms of the ratio of the absolute value of the difference between the 

reference value and the mean CEMS response value, to the reference 

value. LE is calculated as follows: 

×100

−

=

R

R C

LE

Where: 

C = Mean of the CEMS response values 

R = Certified gas concentration as reference value 

(16) “Modification Requiring Recertification” - Any change to the basic 

equipment, control equipment, contaminant concentration, interfering 

substances, or CEMS that is deemed by the APCO to have a potential for 

adversely affecting the ability of the CEMS to provide accurate, precise 

and timely data representative of the stack emissions for which the CEMS 

(or SCEMS) is required. 

(17) “Ninety-Five Percent Confidence Interval” - The statistical estimation 

denoting a range of values which is expected to include a true value with a 

95 percent probability. 

(18) “Operating Day” - Each calendar day that emissions pass through the 

stack or duct. 
AVAQMD RULE 218.1 218.1-7

Continuous Emission Monitoring Performance Specifications 

(19) “Operational Period” - A minimum period of 168 continuous hours during 

which the CEMS shall operate, according to the manufacturer’s written 

performance and equipment specifications, without unscheduled 

maintenance, repair, or adjustment. 

(20) “Quality Assurance/Quality Control (QA/QC) Plan” – A written document 

in which the specific procedures for the operation, Calibration and 

maintenance of a Certified CEMS are described in detail, including 

additional quality assurance assessments and the corrective action system. 

The purpose of this plan is to ensure that the CEMS generates, collects and 

reports valid data that is precise, accurate, complete, and of a quality that 

meets the requirements, performance specifications, and standards of 

Rules 218 and 218.1. 

(21) “Reference Method” (RM) - The official test method employed by the 

District to determine compliance with the rules or permit conditions. A 

list of Reference Methods is identified in Table 1.

(22) “Relative Accuracy” (RA) - The absolute mean difference between the gas 

concentration or emission rate determined by the CEMS and the value 

determined by the RM plus 2.5 percent error of Confidence Coefficient of 

a series of tests, divided by the mean of the RM tests. 

(23) “Relative Accuracy Audit” (RAA) - The RA test expressed in terms of the 

ratio of the relative difference between the mean Reference Method value 

and the mean CEMS response value, to the mean value determined by the 

Reference Method or applicable standard for concentration, flow or mass 

emission rate. Unless otherwise specified, RAA shall have the same 

specifications and requirements as the Relative Accuracy Test Audit 

(RATA), except that the RAA shall require a minimum of three (3) data 

sets. When a rule requires a correction of the air contaminant 

concentration to a specific O2 or CO2 concentration, the RA requirement 

shall apply to the corrected concentration value. The RA of a RAA data 

set is calculated and expressed as a percentage as follows: 

×100 −=

RM

r RM RA

Where: 

RM = Mean of the values determined by the referenced method or 

applicable standard 

r = Mean of the CEMS response values 
218.1-8 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(24) “Relative Accuracy Test Audit” (RATA) - The RA test expressed in terms 

of the ratio of the sum of the absolute mean difference between the 

CEMS-generated data and the value determined by the applicable 

Reference Method or applicable standard and the absolute Confidence 

Coefficient, to the mean of the Reference Method or applicable standard 

value for concentration, flow or mass emission rate. When a rule requires 

a correction of the air contaminant concentration to a specific O2 or CO2

concentration, the RA requirement shall apply to the corrected 

concentration value. The RA of a RATA data set is calculated and 

expressed as a percentage as follows: 

×100

+

=

RM

d CC

RA

Where: 

d = Absolute value of the mean difference 

CC = Absolute value of the 95% Confidence Coefficient 

RM = Average RM value or applicable standard 

The arithmetic mean of the difference, d, of a set of data is calculated as 

follows: 

∑=

=

n

i

di

n

d

1

1

Where: 

∑=

n

i

di

1

= Algebraic sum of the individual differences di

i

d = The difference between the Reference Method value and 

the CEMS value, both in units of the applicable standard 

n = Number of data points 

(25) “Response Time” - The time interval from a step change in the air 

contaminant or gas diluent concentration to the time when 95 percent of 
AVAQMD RULE 218.1 218.1-9

Continuous Emission Monitoring Performance Specifications 

the corresponding final value is reached as displayed on the CEMS data 

recorder or acquisition system. The Response Time is determined by 

introducing a Certified Gas Mixture into the CEMS upstream of the 

Sampling Interface and as close to the probe inlet as practicable. 

(26) “Routine Maintenance” - Preventive evaluation and repair (if necessary) 

of CEMS performed at specified intervals to preclude System Failure. 

Routine Maintenance may be performed as recommended by the 

manufacturer or a documented standard operating procedure determined 

through operating experience and approved by the APCO. Repairs to a 

malfunctioning system are excluded from this definition. 

(27) “Sampling Interface” - That part of the CEMS that performs sample 

acquisition using one (1) or more of the following operations: extraction, 

physical/chemical separation, transportation or conditioning of a 

representative sample from a designated source. 

(28) “Semi-Continuous Emission Monitoring System” (SCEMS) - The total 

combined equipment and systems required to semi-continuously 

determine air contaminants and Diluent Gas concentrations and/or mass 

emission rate of a source effluent (as applicable). The SCEMS consists of 

three (3) major subsystems: Sampling Interface, Analyzer and Data 

Acquisition System. This class of monitoring includes but is not limited 

to gas chromatography, integrated sensitized tape analyzer, other sample 

integration based technologies, and time-shared CEMS. 

(29) “South Coast Air Quality Management District” (SCAQMD) - The air 

quality district created pursuant to Division 26, Part 3, Chapter 5.5 of the 

California Health & Safety Code (commencing with §40400). 

(30) “System Bias” - The difference between the gas concentrations exhibited 

by the CEMS when a calibration gas is introduced at a location upstream 

of the Sampling Interface, and as close to the sampling probe inlet as 

practicable, and when the same calibration gas is introduced directly to the 

Analyzer. 

(31) “System Failure” - Inability of the CEMS to meet the requirements of 

Rule 218.1. 

(32) “Time-Sharing” - A monitoring technique where an Analyzer and possibly 

the associated sample conditioning system is used on more than one (1) 

source. 

(33) “Zero Check” - A procedure performed to determine the response of the 

CEMS to a given Zero Gas standard by means of injecting the Zero Gas 

into the CEMS as close to the probe tip as practical. 
218.1-10 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(34) “Zero Drift” (ZD) - The change in the monitoring system output/response 

over a stated period of time of normal continuous operation when the air 

contaminant or Diluent Gas concentration at the time of the measurements 

is zero. The values for ZD shall be expressed as the ratio of the sum of the 

absolute value of the mean of the difference between paired instrument 

response values and the absolute value of the CC, to the Full Span Range, 

calculated as a percentage as follows: 

×100

+

=

S

d CC

ZD

Where: 

S = Full Span Range 

CC = Absolute value of the Confidence Coefficient 

d

= Absolute value of the mean difference. The mean 

difference is calculated as: 

∑=

=

n

i

di

n

d

1

1

Where: 

∑=

n

i

di

1

= Algebraic sum of the individual differences di

n = Number of data pairs 

i

d = The difference between a pair of instrument response 

values 

(35) “Zero Gas” - A gas containing less than a specified amount of the 

contaminant or Diluent Gas which, when periodically injected into the 

CEMS, is used to check CEMS’ response to the absence of the air 

contaminant or Diluent Gas. 

(C) Standards for New or Modified CEMS 

In order to be a Certified CEMS, a CEMS subject to the provisions of Rule 218, 

Sections (D)(1), (E)(1)(c), (E)(2)(c) and (E)(2)(d), as applicable, shall meet the 

operational requirements, performance specifications, and standards as follows: 
AVAQMD RULE 218.1 218.1-11

Continuous Emission Monitoring Performance Specifications 

(1) Pre-Certification Testing Requirements for New or Modified CEMS 

Before any certification or Relative Accuracy test is performed, the CEMS 

shall meet the following standards: 

(a) CEMS Location 

The CEMS shall be installed at a location that enables 

measurements of air contaminant and Diluent Gas concentration, 

and flow rates can be made which are representative of the stack 

emissions of the source. 

(b) Sampling Location 

The monitoring system sampling probe tip and the Reference 

Method sampling port locations shall be determined according to 

SCAQMD Method 1.1. The monitoring sampling probe shall be 

located where a sample may be obtained which is representative of 

the source emissions. Each probe shall not interfere with the other 

when in use. Other locations may be chosen subject to a written 

approval of the APCO. If an alternate location is chosen which 

does not conform with SCAQMD Method 1.1, the absence of flow 

disturbance shall be demonstrated using the SCAQMD method in 

the source Test Manual, Chapter X, Section 1.4 – “Alternative Site 

Selection Method,” or 40 CFR, Part 60, Appendix A, Method 1, 

Section 2.5 – “Alternative Measurement Site Selection Procedure,” 

and, the absence of stratification shall be demonstrated using the 

SCAQMD method in the source Test Manual, Chapter X, Section 

13 – “Determination of Gaseous Constituent Stratification”. 

Alternatives to sampling site selection in the presence of 

stratification are presented in Rule 218.1 Section (C)(3)(c)(ii). 

(c) Full Span Range 

(i) The FSR for mass emission rate, air contaminant, diluent 

and flow analyzers shall be set such that all data points are 

within 10 to 95 percent of the range. 

(ii) For air contaminant monitors, the FSR shall be set between 

150 and 200 percent of the concentration limit as specified 

in the applicable rule or permit condition. The FSR may be 

set at a value other than that specified, but no lower than 

120 percent, provided that the CEMS owner or operator 

demonstrates to the satisfaction of the APCO that the FSR 

will not be exceeded. Such demonstrations may include, 

but are not limited to, historical emissions data, historical 

process information, and historical operational information. 

A written approval from the APCO shall be obtained before 
218.1-12 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

the FSR may be modified outside of the 150 to 200 percent 

of the concentration limit. 

(iii) For air contaminant monitors, a multiple-span-range may 

be required to satisfy the provisions of Sections (c)(i) and 

(c)(ii) above in situations where the normal concentration 

of the air contaminant emitted is significantly less than the 

allowable concentration limit. The CEMS shall have the 

capability to automatically change from one range to the 

other as appropriate to the monitor’s measured 

concentration.

(iv) For diluent monitors, the FSR shall be set such that the full 

range of O2 and CO2 concentrations can be measured. The 

FSR shall be set at 25.0 percent O2 (maximum) and 1.0 

percent CO2 (minimum) concentrations, or at a value 

approved by the APCO. 

(v) Should any data points fall below ten (10) percent of the 

FSR, those data points shall be reported according the 

following, as applicable: 

a. For CEMS with certified multiple span ranges, the 

owner shall report data that falls below 10.0 percent 

of the higher FSR and above 95 percent of the lower

FSR, at the 10.0 percent value of the higher FSR; 

b. In the event that any of the data points gathered by 

the CEMS fall below 10.0 percent of the FSR, the 

owner or operator may elect to report the 

contaminant concentrations at the 10.0 percent FSR 

value; or 

c. In the event that any data points gathered fall below 

10.0 percent of the lowest vendor guaranteed FSR 

for that CEMS (defined as the lowest FSR that the 

vendor guarantees to be capable of meeting all 

current certification requirements of Rule 218 and 

Rule 218.1, as applicable) the owner or operator 

may elect to use the following to measure and 

report contaminant concentrations: 

1. Report data at 10.0 percent FSR value; or 

2. Report data at actual measured value, 

provided that the CEMS meets the 

Supplemental and Alternative Performance 

Requirements in Attachment A. 

(vi) Should any data points fall above 95 percent of FSR, the 

value shall be invalid for quantification and the CEMS 

shall be considered unavailable for the purposes of

determining CEMS Availability Percentage. All 

excursions above 95 percent of FSR and the duration of 
AVAQMD RULE 218.1 218.1-13

Continuous Emission Monitoring Performance Specifications 

these excursions shall be reported in the CEMS summary 

report as prescribed under Rule 218 Section (G). 

(d) Strip Chart Recorder 

(i) For CEMS where the strip chart recorder is used as the only 

means of data recording, the strip chart shall have a 

minimum width of at least 10 inches, a readability of 0.5 

percent of the span, and a minimum of 100 chart divisions. 

(ii) For CEMS where the strip chart recorder is used as a 

backup system or for recording data from only a single 

parameter, a strip chart of lesser size than specified in 

Section (d)(i) above, may be proposed in the application. 

(iii) For CEMS equipped with multiple-span ranges, the chart 

recorder shall have the capability to automatically change 

span, as appropriate. 

(e) Data Acquisition System (DAS) 

(i) The DAS shall maintain all recorded data in accordance 

with Rule 218, Section (F). 

(ii) For CEMS, DAS shall acquire data from monitored 

parameters at least once every minute. 

(iii) For SCEMS, DAS shall acquire data from monitored 

parameters at least once every 15 minutes. 

(iv) DAS acquisition rate shall be set at a constant rate such that 

the data points are equally spaced. 

(v) All valid data points shall be used to determine compliance 

with applicable limit(s), and, for certification testing and 

RATA(s). 

(vi) DAS sample acquisition rate during certification and 

RATA(s) shall be the same as the DAS sample acquisition 

rate during normal CEMS, or SCEMS, operation. 

(f) Operational Period 

(i) The Operational Period before any certification tests shall 

be a minimum of 168 continuous hours. 

(2) Certification Requirements and Performance Specifications for New or 

Modified CEMS 

Rule 218 Section (D)(1) provides that a series of certification tests shall be 

performed to demonstrate the acceptability of CEMS performance. The 

requirements and specifications in conducting initial certification tests 

follow: 
218.1-14 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(a) Calibration Error (CE) Testing 

The 24-Hour CE Test shall be performed at the low and high ranges, 

namely 0 to 20 and 80 to 100 percent of FSR, respectively. CE 

specifications shall be less than or equal to: 

(i) 2.5 percent of the FSR for all Analyzers; and 

(ii) 3.0 percent of the FRS of the Analyzer, for flow monitors, 

when an electronic Calibration Check is applicable. 

The 24-hour CE Test shall be performed once each day as close to 

24-hour intervals as practicable, with a total of eight (8) 

consecutive tests performed. The CE specifications shall not be 

exceeded on any of the tests during the entire testing period. 

(b) Analyzer Enclosure 

(i) The Analyzer shall be contained in an environmentally 

controlled enclosure. An alarm and recording device shall 

be incorporated into the system to alert the operator to 

make corrective action should the Analyzer exceed the 

manufacturer’s recommended specifications for 

temperature drift. 

(ii) Alternatively, the owner or operator of the CEMS may 

choose to perform the 2-hour CE Tests in lieu of meeting 

the Analyzer enclosure requirement in Section (C)(2)(b)(i). 

The 2-hour CE Test shall be performed once every two (2) 

hours as close to 2-hour intervals as practicable, with total 

of thirteen consecutive tests performed. The 2-hour CE 

Test shall be performed when ambient temperature is

expected to vary diurnally at least 30°F. The test shall be 

performed at the low and high ranges of FSR, namely 0 to 

20 and 80 to 100 percent, respectively. The specifications 

in Sections (C)(2)(a)(i) and (ii) shall apply to 2-hour CE. 

(iii) The owner or operator of the CEMS may qualify for an 

exemption from Section (C)(2)(b)(i) to provide 

environmental controls for the Analyzer enclosure by 

demonstrating, to the satisfaction of the APCO, that the 

CEMS is located: 

a. In a geographic area where seasonal high and low

temperatures do not exceed the operational 

temperature specifications for the Analyzer; 

b. In a geographic area where monthly maximum 

temperature variation is less than 30°F for all 

months of the year; and 

c. The CEMS is located in a site that is protected from 

radiation and convection heating sources. 
AVAQMD RULE 218.1 218.1-15

Continuous Emission Monitoring Performance Specifications 

(c) Relative Accuracy 

RATA shall be performed for raw contaminant concentration, and 

if applicable, for corrected concentration, emission rate, O2

concentration, CO2 concentration analyzers, and stack and fuel 

flow monitors. There shall be a minimum of nine (9) sets of test 

data generated. If the number of tests exceeds nine (9) sets, data 

may be discarded if it is identified as an outlier by the technical 

guidance set forth by the APCO, or for valid reasons (e.g., process 

upsets, CEMS malfunction, etc.) which must be substantiated with 

appropriate documentation and subject to approval by the APCO. 

All data collected shall be submitted to the APCO. The CEMS 

shall meet the following RA performance specifications: 

(i) Less than or equal to 20.0 percent of the mean value of the 

Reference Method for pollutant concentrations, or the de 

minimus concentration as follows, whichever is greater: 

Pollutant De minimus Concentration 

SO2 2.0 ppm 

Reduced sulfur compounds 4.0 ppm 

(ii) Less than or equal to 10.0 percent of the mean value of the 

Reference Method for diluent concentrations, or the de 

minimus value of 1.0 percent O2, whichever is greater. 

(iii) Less than or equal to 15.0 percent of the mean value of the 

Reference Method for flow monitors, or the de minimus 

value equivalent to a calculated volumetric flow rate based 

on two (2) feet per second stack gas velocity for cases 

where the mean stack gas velocity obtained by the 

Reference Method test is less than 15 feet per second. 

(iv) Less than or equal to 20.0 percent of the mean value of the 

Reference Method for mass emission rates, or the de

minimus value equivalent to a calculated mass emission 

rate based on two (2) feet per second stack gas velocity for 

cases where the mean stack gas velocity obtained by the 

Reference Method test is less than 15 feet per second. 

The Relative Accuracy requirement may be met if the

average of the differences between the CEMS measured 

data and the Reference Method test data plus the 

Confidence Coefficient is less than or equal to the Relative 

Accuracy de minimus value. 

(3) Relative Accuracy Test Requirements for New or Modified CEMS 

Within fourteen days of, or during all Relative Accuracy tests, the CEMS 

shall meet the following requirements, except those that may be waived as 

allowed in Rule 218.1, Section (C)(4)(c): 
218.1-16 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(a) Response Time 

The Response Time for carbon monoxide (CO) CEMS shall not 

exceed 1.5 minutes except where there is a technical limitation, in 

which case the Response Time shall be five (5) minutes. The 

Response Time for all other CEMS and flow monitors, as 

applicable, shall not exceed five (5) minutes. 

(b) Calibration Error 

The CE Testing requirements are specified in Section (C)(2)(a). 

(c) Concentration Stratification 

(i) The owner or operator shall demonstrate the absence of 

stratification through testing performed according to the 

method in Chapter X, Section 13 - “Non-Standard Methods 

and Techniques”, of the SCAQMD Source Testing Manual. 

The number of tests shall be determined as follows:

a. Test(s) shall be conducted at one (1) load level if 

the owner or operator demonstrates to the 

satisfaction of the APCO that the equipment 

operates within a 20 percent load range for at least 

80 percent of the time; 

b. Test(s) shall be conducted at two (2) different load 

levels if the owner or operator demonstrates to the

satisfaction of the APCO that the equipment 

operates within a 50 percent load range for at least 

80 percent of the time; or, 

c. Test(s) shall be conducted at three (3) different load 

levels if the equipment operates outside of the 

criteria in Sections (C)(3)(c)(i)[a] and [b]. 

The absence of stratification is considered verified 

if the difference between the highest measured 

concentration (time normalized) and the lowest 

measured concentration (time normalized) divided 

by the average measured concentration (time 

normalized), when expressed as a percentage, is less 

than or equal to 10 percent. Upon verification of 

the absence of stratification, the owner or operator 

may position the CEMS sampling probe at any 

point within the stack with the exception of those 

points that are adjacent to the stack wall. The 

CEMS sampling probe should be located in the 

stack at least one-third of the stack diameter. The 

RM for RATA may be conducted at a single point 
AVAQMD RULE 218.1 218.1-17

Continuous Emission Monitoring Performance Specifications 

within the stack that is not adjacent to the stack wall 

and does not interfere with the sampling and the 

operation of the facility CEMS. 

(ii) Should testing demonstrate the presence of stratification, 

the owner or operator may elect one (1) of the following 

alternatives: 

a. If the stratification is greater than 10 percent but the 

difference between the highest measured 

concentration (time normalized) and the lowest 

measured concentration (time normalized) is less 

than or equal to 1.0 ppmv: 

1. Then the CEMS sampling probe may be 

located at any point within the stack except 

any points that is adjacent to the stack or 

adjacent to the highest measured 

concentration (time normalized) and the 

lowest measured concentration (time 

normalized); or 

2. If it is not possible to avoid using a point 

adjacent to either the highest measured 

concentration (time normalized) or the 

lowest measured concentration (time 

normalized), then locate the CEMS 

sampling probe such that the placement 

minimizes the difference between the 

concentration at the proposed probe location 

and the concentration at the point of highest 

measured concentration (time normalized) 

or the lowest measured concentration (time 

normalized). 

b. Determine a representative CEMS probe location 

such that the following criteria are met: 

1. All traverse point concentrations are within 

10.0 percent of the average of all traverse 

point concentrations (time normalized), or, 

the difference is less than or equal to 1.0 

ppm, whichever is greater; 

2. There exists at least one (1) traverse point 

concentration (Xr), not located next to the 

stack or duct wall, that is less than or equal 

to 10.0 percent each adjacent traverse point 

concentration of Xr, or the difference is less 

than or equal to 1.0 ppm, whichever is 

greater; and 

3. The CEMS probe is located at (or as near as 

practical) Xr with minimum adjacent 
218.1-18 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

traverse point concentration fluctuations as 

determined in Section (C)(3)(c)(ii)[b][2], 

above. 

c. Determine a representative multiple point sampling 

configuration as approved by the APCO, following 

the guidance document by Emission Measurement 

Technical Information Center, “Evaluation 

Procedure for Multi-Hole Sample Probes” (EMTIC 

GD-031). 

d. Modify the stack and/or CEMS sampling probe 

location and retest for the absence of stratification. 

(d) Cyclonic Flow 

The owner or operator shall perform tests to verify the absence of 

cyclonic flow for the CEMS and Reference Method sampling 

probes. The cyclonic flow test shall be required when measuring 

mass emission rates and shall be performed according to the 

SCAQMD method in the Source Test Manual, Chapter X: NonStandard Methods and Techniques following the testing conditions 

of Section (C)(3)(c)(i)[a], [b] or [c], as applicable. 

(e) Interference 

The owner or operator shall perform tests to verify the absence of 

sampling, analytical and flow interference, as applicable. 

(f) Linearity Error 

LE tests shall be performed at the low, middle and high ranges of 

concentration, namely 20 to 30, 50 to 60, and 80 to 100 percent. 

Each calibration gas shall be introduced into the CEMS three (3) 

times. The same gas shall not be used twice in succession. LE 

shall be less than or equal to 5.0 percent of the calibration gas 

concentration. 

(g) Multiple-Span-Range 

For CEMS that have multiple-span-range, all certification tests 

shall be performed at the lowest range. Except for RA and 

interference tests, all other certification tests shall be performed on 

other ranges. 

(4) Operational Requirements and Performance Specifications for New or 

Modified CEMS 

After final approval, the CEMS shall be subsequently operated and 

maintained according to the following requirements and specifications: 
AVAQMD RULE 218.1 218.1-19

Continuous Emission Monitoring Performance Specifications 

(a) 24-Hour CE 

CE Tests shall be performed once each Operating Day as close to 

24 hour intervals as practicable at the low (0 to 20 percent) and 

high (80 to 100 percent) ranges of concentration. CE Test results 

which are greater than the limits specified in Sections (C)(2)(a)(i) 

and (ii), but less than or equal to 5.0 percent of the FSR shall be 

addressed by QA/QC Plan remediation. The CEMS shall be 

deemed out-of-control during such period when any CE Test result 

is greater than the specified limits and greater than 5.0 percent of 

the Full Span Range, until the CE Test meets the specifications. 

All data generated by the CEMS during an out-of-control period 

shall be deemed invalid but shall not be deleted or excluded from 

the records or database. 

(b) System Bias Test 

A System Bias shall be conducted every 12 months in conjunction 

with RAA required under Rule 218.1 Section (C)(4)(c). The 

CEMS System Bias shall not exceed ±5.0 percent of the FSR for 

contaminant Analyzers. In addition, the owner or operator shall 

include in the facility QA/QC Plan, criteria for excessive drift (e.g. 

control limits on cumulative drift) and appropriate diagnostic 

techniques to identify sources of Analyzer drift and System Bias 

when control limits are exceeded. 

(c) Relative Accuracy Testing 

RATA and RAA, as applicable, shall be performed at least once 

every 12 months. The test shall be completed annually no later 

than the end of the calendar quarter in which the date of the 

original certification test was performed. During any RA tests 

after CEMS certification, the owner or operator may request a 

waiver from stratification, cyclonic flow, and/or interference 

requirements in Sections (C)(3)(c), (d) and (e), respectively, by 

submitting to the APCO, for approval, any applicable 

documentation or previous test or historical data that meets the 

stratification, cyclonic flow, and/or interference requirements. 

(d) Cylinder Gas Audit (CGA) 

A CGA shall be performed every calendar quarter but in no more 

than three (3) quarters in succession. The CGA shall be conducted 

according to the provisions of 40 CFR 60, Appendix F. The audit 

gases shall be according to the certification requirements of Rule 

218.1. 
218.1-20 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(e) The APCO may require recertification of the CEMS if the annual 

availability percentage is below 95 percent. Annual CEMS 

Availability Percentage calculations will be based on the year 

ending on the last day of the calendar quarter in which the CEMS 

was originally certified. 

(f) The owner or operator of a CEMS that requires moisture correction 

in reporting flow and concentration shall measure and monitor 

moisture in the stack gas used for emission data calculations in 

accordance with the written technical guidance document set forth 

by the APCO. Alternatively, with APCO approval, for equipment 

whose moisture source is only from fuel combustion, the operator 

may calculate the moisture content using fuel properties and 

ambient air humidity data or, for processes that saturate the 

exhaust gas with moisture, such as a wet scrubber system, the 

operator may use the saturation temperature for moisture content 

data. 

(D) Standards for Existing CEMS 

In order to be a Certified CEMS, a CEMS subject to the provisions of Rule 218 

Sections (E)(1) and (E)(2), shall meet the following operational requirements and 

performance specifications, and the standards of Rule 218.1 Section (E): 

(1) Performance Specifications for Existing Gaseous Air Contaminant CEMS 

 Parameter Specifications 

(a) Operational Period Greater than or equal to 168 hours 

(b) Calibration Error Less than or equal to 5 percent of the 

calibration gas value 

(c) Response Time Less than or equal to 10 minutes 

(d) Zero Drift (2-hour) Less than or equal to 2 percent of FSR 

(e) Zero Drift (24-hour) Less than or equal to 2 percent of FSR 

(f) Calibration Drift (2-hour) Less than or equal to 2 percent of FSR 

(g) Calibration Drift (24-hour) Less than or equal to 2.5 percent of FSR 

(h) Relative Accuracy Less than or equal to 20 percent of the 

mean value of the RM test data, or, less 

than or equal to 10 percent of the allowed 

concentration, whichever is greater 
AVAQMD RULE 218.1 218.1-21

Continuous Emission Monitoring Performance Specifications 

(2) Performance Specifications for Existing Diluent Gas CEMS 

 Parameter Specifications 

(a) Operational Period Greater than or equal to 168 hours 

(b) Calibration Error Less than or equal to 5 percent of 

the calibration gas value 

(c) Response Time Less than or equal to 10 minutes 

(d) Zero Drift (2-hour) Less than or equal to 0.4 percent 

CO2 or O2

(e) Zero Drift (24-hour) Less than or equal to 0.5 percent 

CO2 or O2

(f) Calibration Drift (2-hour) Less than or equal to 0.4 percent 

CO2 or O2

(g) Calibration Drift (24-hour) Less than or equal to 0.5 percent 

CO2 or O2

(3) Full Span Range for Existing CEMS 

The instrument FSR shall be equivalent to approximately 200 percent of 

the concentration limit as specified in the applicable rule, or at a value 

approved by the APCO. O2 and CO2 instrument full span readings shall 

be such that the full range of concentrations encountered can be measured. 

(4) Cycle of Operation for Existing CEMS 

The CEMS shall complete a minimum of one (1) cycle of operation 

(sampling, analyzing and data recording), for each successive 15 minute 

period. 

(E) Standards, Specifications and Requirements for New, Modified and 

Existing CEMS: 

(1) Calibration Gas 

(a) Calibration gas mixtures, as defined in Rule Section 218.1 (B)(8), 

shall be manufactured, analyzed and certified in accordance with 

the “EPA Traceability Protocol for Assay and Certification of 

Gaseous Calibration Standards” - EPA-600/R97/121, September 

1997 Revision (EPA Protocol). The certification period and 
218.1-22 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

recertification requirements, as applicable, shall be according to 

the EPA Protocol. 

(b) For gas calibration standards not explicitly covered by the EPA 

Protocol, the CEMS owner or operator shall submit the gas 

manufacturer’s alternative certification protocol for the specific 

compound or compounds. 

(i) The procedures of the EPA Protocol shall be used for gas 

calibration standards not explicitly covered therein, except 

that the gas manufacturer must identify a recertification 

period and submit data documenting the applicability of 

this period. The gas manufacturer may submit alternative 

performance standards for certification and recertification, 

based on supporting technical data also provided by the 

manufacturer. This alternative shall be subject to the 

approval of APCO. 

(ii) If there is no existing National Institute of Standards and 

Technology (NIST) standard for the measured parameter, 

the gas manufacturer may submit an alternative reference 

standard and the supporting technical data that define the 

stability, accuracy, and precision of the alternative 

reference standard. This alternative shall be subject to the 

approval of APCO. 

(iii) The CEMS owner or operator may submit an alternative 

protocol to the EPA Protocol, provided that the CEMS 

owner or operator demonstrates through supporting 

technical data that the procedures therein are not applicable 

to the constituent in the calibration gas standard being 

certified. This alternative shall be subject to the approval 

of APCO. 

(c) Compressed and/or filtered air, such as instrument air, may also be 

used in lieu of oxygen span gas provided that the CEMS owner or 

operator demonstrates, to the satisfaction of the APCO, that it is of 

equivalent quality to the calibration gas standards above. As part 

of such documentation, the owner or operator shall include in their 

QA/QC Plan the process or operation in producing such 

compressed and/or filtered air and periodically checking that 

compressed air and/or filtered air continues to meet the calibration 

gas standards. 

(2) Zero Gas 

Zero Gases used shall meet the following criteria: 
AVAQMD RULE 218.1 218.1-23

Continuous Emission Monitoring Performance Specifications 

(a) For gaseous air contaminant monitors, the Zero Gas shall be 

certified by the manufacturer to contain no more than 0.1 ppm of 

the air contaminant analyzed by the subject monitor or 1.0 percent 

of the applicable standard, whichever is less. 

(b) For CO monitors, the Zero Gas shall be certified by the 

manufacturer to contain less than 0.5 ppm carbon CO or 1.0 

percent of the applicable standard, whichever is less. 

(c) For CO2 and O2 monitors, the Zero Gas shall be certified by the 

manufacturer to contain less than 1.0 ppm CO2 or O2. 

(d) Compressed and/or filtered air, such as instrument air, may also be 

used in lieu of Zero Gas provided that the CEMS owner or 

operator demonstrates, to the satisfaction of the APCO, that it is of 

equivalent quality to the above Zero Gas standards. As part of 

such documentation, the owner or operator shall include in their 

QA/QC plan the process or operation in producing such 

compressed and/or filtered air and periodically checking that 

compressed air and/or filtered air continues to meet the Zero Gas 

standards. 

(3) Automatic Calibration Data 

If automatic adjustments to the monitor settings are made, conduct the 

calibration tests in a way that the magnitude of the adjustments can be 

determined and recorded. 

(4) F-Factors 

The owner or operator shall use in the CEMS calculations the Fd factors 

listed in 40 CFR Part 60, Appendix A, Method 19, Table 19-1, as 

applicable. When alternative fuels are fired, the owner or operator shall 

submit data to develop Fd factors and obtain APCO approval. 

(5) NO2 to NO Conversion Efficiency 

The conversion efficiency tests shall be conducted according to the 

requirements of SCAQMD Method 100.1. The value for the NO2 gas 

shall be greater than or equal to the maximum expected or recorded NO2

and greater than or equal to 20 percent of the FSR.

(F) Time-Sharing Requirements 

A time-shared CEMS for which an application is submitted after July 17, 2012 

shall meet all of the performance specifications as well as the following 

requirements: 
218.1-24 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(1) All sources shall have mutually compatible range(s) of air contaminant 

gases at all times. 

(2) Each source shall have a data-reading period, at a minimum, equal to three 

(3) times the longest Response Time of the system. For shared systems 

the Response Time is measured at the input or probe at each source. A 

demonstration of Response Time for each source shall be made during 

certification testing. Data are not to be collected following a switch of 

sample sources until a period of time equal to one (1) Response Time has 

passed. 

(3) The CEMS shall be capable of performing and recording zero and span 

calibrations at each source, including the calibration factors and correction 

values before and after every automatic Calibration. 
AVAQMD RULE 218.1 218.1-25

Continuous Emission Monitoring Performance Specifications 

Table 1 

REFERENCE METHODS 

RULE 218.1 

SCAQMD Method 1.1 Sample and Velocity Traverses for Stationary Sources 

SCAQMD Method 1.2 Sample and Velocity Traverses for Stationary Sources with 

Small Stack or Ducts 

SCAQMD Method 2.1 Determination of Stack Gas Velocity and Volumetric Flow 

Rate (S-type Pitot tube) 

SCAQMD Method 2.2 Direct Measurement of Gas Volume through Pipes and 

Small Ducts 

SCAQMD Method 2.3 Determination of Gas Velocity and Volumetric Flow Rate 

from Small Stacks or Ducts 

SCAQMD Method 3.1 Gas Analysis for Dry Molecular Weight and Excess Air 

SCAQMD Method 4.1 Determination of Moisture Content in Stack Gases 

SCAQMD Method 6.1 Determination of Sulfuric Acid and Sulfur Oxides from 

Stationary Sources 

SCAQMD Method 7.1 Determination of Nitrogen Oxide Emissions for Stationary 

Sources 

SCAQMD Method 100.1 Instrumental Analyzer Procedures for Continuous Gaseous 

Emission Sampling 

SCAQMD Method 307.91 Determination of Sulfur in a Gaseous Matrix 

EPA Method 6 Determination of Sulfur Dioxide Emissions from 

Stationary Sources 

EPA Method 19 Determination of Sulfur Dioxide Removal Efficiency and 

Particulate, Sulfur Dioxide and Nitrogen Oxides Emission 

Rates from Electric Utility Steam Generator (40 CFR Part 

60, Appendix A) 

ASTM Method D 4294-03 Standard Test Method for Sulfur in Petroleum and 

Petroleum Products by Energy Dispersive X-Ray 

Fluorescence Spectrometry 

ASTM Method D2622 -05 Standard Test Method for Sulfur in Petroleum Products by 

Wavelength Dispersive X-ray Fluorescence Spectrometry 
218.1-26 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

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AVAQMD RULE 218.1 218.1-27

Continuous Emission Monitoring Performance Specifications 

ATTACHMENT A 

SUPPLEMENTAL AND ALTERNATIVE 

CEMS PERFORMANCE REQUIREMENTS 

(A) Applicability of Supplemental and Alternative Performance 

Requirements 

The CEMS operator who elects (or who may be required) to measure 

concentrations that fall below 10 percent of the lowest vendor guaranteed full 

scale span range, shall satisfy the performance requirements as specified in Table 

A-1 listed below. 

TABLE A-1 

Alternative Performance Requirement(s) 

CEMS Certified per 

Rule 218.1 

Yes or No

Performance Requirement(s) 

LLSR/BFD HLSR/BFD LLR/BFD LLCE 

Yes X + X 

No X X + X 

(1) + (plus) denotes an additional performance requirement that shall be 

conducted if the mandatory performance requirement(s) cannot be met. 

(2) If the concentration of the CEMS is such that the specifications for the low 

level spike recovery/bias factor determination cannot be met, the facility 

permit holder shall conduct a low level RATA/bias factor determination. 

(3) Abbreviations used in this attachment are: 

Low Level Spike Recovery/Bias Factor Determination (LLSR/BFD) 

High Level Spike Recovery/Bias Factor Determination (HLSR/BFD) 

Low Level RATA/Bias Factor Determination (LLR/BFD) 

Low Level Calibration Error (LLCE) 

Relative Accuracy Test Audit (RATA) 

Relative Accuracy (RA) 

National Institute of Standards Traceability (NIST)

(B) Test Definitions, Performance Specifications and Test Procedures 

This section explains in detail how each performance requirement is to be 

conducted. 

(1) Low Level Calibration Error 
218.1-28 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

The low level CE test is defined as challenging the CEMS (from probe to 

monitor) with certified calibration gases (e.g., NO in N2) at three (3) levels 

in the 0-20 percent Full Span Range. Since Certified Gas Mixtures or 

standards may not be available at the concentrations required for this test, 

gas dilution systems may be used, with District approval, if they are used 

according to either District or EPA protocols as specified in Rule 218.1, 

for the verification of gas dilution systems in the field. The CEMS highlevel calibration gas may be diluted for the purpose of conducting the low 

level CE test. 

(a) Performance Specifications 

Introduce pollutant concentrations at approximately the 20 percent, 

10 percent, and 5 percent of full span levels through the normal 

CEMS Calibration system. No low level CE shall exceed 2.5 

percent of full scale span. 

(b) Testing Procedures 

(i) Perform a standard zero/span check; if zero or span check 

exceeds 2.5 percent full span, adjust monitor and redo 

zero/span check. 

(ii) After zero/span check allow the CEMS to sample stack gas 

for at least 15 minutes. 

(iii) Introduce any of the low level CE or standards through the 

CEMS Calibration system. 

(iv) Read the CEMS response to the calibration gas starting no 

later than three (3) system Response Times after 

introducing the calibration gas; the CEMS response shall be 

averaged for at least three (3) Response Times and for no 

longer than six (6) Response Times. 

(v) After the low level CE check allow the CEMS to sample 

stack gas for at least 15 minutes. 

(vi) Repeat steps (iii) through (v) until all three (3) low level 

CE checks are complete. 

(vii) Conduct post test calibration and Zero Checks. 

(2) Spike Recovery and Bias Factor Determinations 

Spiking is defined as introducing known concentrations of the pollutant of 

interest (e.g., gas standard to contain a mixture of NO and NO2 is 

representative of the ratio of NO and NO2 in stack gas) and an appropriate 

non-reactive, noncondensable and non-soluble tracer gas from a single 

cylinder (EPA Protocol as specified in Rule 218.1 or NIST traceable to 

two (2) percent analytical accuracy if no EPA Protocol is available) near 

the probe and upstream of any sample conditioning systems, at a flow rate 

not to exceed 10 percent of the total sample gas flow rate. The purpose of 
AVAQMD RULE 218.1 218.1-29

Continuous Emission Monitoring Performance Specifications 

the 10 percent limitation is to ensure that the gas matrix (water, CO2, 

particulates, interferences) is essentially the same as the stack gas alone. 

The tracer gas is monitored in real time and the ratio of the monitored 

concentration to the certified concentration in the cylinder is the dilution 

factor. The expected pollutant concentration (dilution factor times the 

certified pollutant concentration in the cylinder) is compared to the 

monitored pollutant concentration. 

(3) High Level Spike Recovery/Bias Factor Determination 

The high level spike recovery/bias factor determination is used when it is 

technologically not possible to certify the CEMS per the standard Rule 

218.1 requirements. The spiking facility/interface shall be a permanently 

installed part of the CEMS sample acquisition system and accessible to the 

APCO as well as the CEMS operator. 

(a) Performance Specifications 

The CEMS shall demonstrate a RA ≤20 percent, where the spike value is 

used in place of the Reference Method in the normal RA calculation, as 

described below. 

(b) Testing Procedures 

(i) Spike the sample to the CEMS with a calibration standard 

containing the pollutant of interest and CO or other nonsoluble, non-reacting alternative tracer gas (alternative 

tracer gas) at a flow rate not to exceed 10 percent of the 

CEMS sampling flow rate and of such concentrations as to 

produce an expected 40-80 percent of full scale span for the 

pollutant of interest and a quantifiable concentration of CO 

(or alternative tracer gas) that is at least a factor of 10 

higher than expected in the unspiked stack gas. The 

calibration standards for both pollutants of interest and CO 

(or alternative tracer gas) must meet Rule 218.1 

requirements. 

(ii) Monitor the CO (or alternative tracer gas) using an 

appropriate continuous (or semi-continuous if necessary) 

monitor meeting the requirements of SCAQMD Method 

100.1 and all data falling within the 10-95 percent full scale 

span, and preferably within 30-70 percent full scale span. 

(iii) Alternate spiked sample gas and unspiked sample gas for a 

total of nine (9) runs of spiked sample gas and ten runs of 

unspiked sample gas. Sampling times should be 

sufficiently long to mitigate Response Time and averaging 

effects. 
218.1-30 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(iv) For each run, the average CEMS reading must be between 

40 percent full scale span and 80 percent full scale span. If 

not, adjust spiking as necessary and continue runs, but 

expected spike must represent at least 50 percent of the 

total pollutant value read by the CEMS. 

(v) Calculate the spike recovery for both the pollutant and the 

CO (or alternative tracer gas) for each run by first 

averaging the pre- and post-spike values for each run and 

subtracting that value from the spiked value to yield nine 

(9) values for recovered spikes. 

(vi) Using the CO (or alternative tracer gas) spike recovery 

values for each run and the certified CO (or alternative 

tracer gas) concentration, calculate the dilution ratio for 

each run. Multiply the certified pollutant concentration by 

the dilution factor for each run to determine the expected 

diluted pollutant concentrations. Using the expected 

diluted concentrations as the “Reference Method” value, 

calculate the Relative Accuracy. The RA shall be ≤20 

percent. 

(4) Low Level Spike Recovery/Bias Factor Determination 

The low-level spike recovery/bias factor determination is used to 

determine if a significant bias exists at concentrations near the 10 percent 

full scale span level. The spiking facility/interface shall be a permanently 

installed part of the CEMS sample acquisition system and accessible to the 

APCO staff as well as the CEMS operator. 

(a) Performance Specifications 

There are no pass/fail criteria with respect to the magnitude of the 

percent RA. There are performance criteria for the range of 

concentration on the CEMS the extent to which the spike must be 

greater than the background pollutant level. 

(b) Testing Procedures 

(i) Spike the sample to the CEMS with a calibration standard 

containing the pollutant of interest and CO or other nonsoluble, non-reacting alternative tracer gas (alternative 

tracer gas) at a flow rate not to exceed 10 percent of the 

CEMS sampling flow rate and of such concentrations as to 

produce an expected 10-25 percent of full scale span for the 

pollutant of interest and a quantifiable concentration of CO 

(or alternative tracer gas) that is at least a factor of 10 

higher than expected in the unspiked stack gas. The 

calibration standards for both pollutants of interest and CO 
AVAQMD RULE 218.1 218.1-31

Continuous Emission Monitoring Performance Specifications 

(or alternative tracer gas) must meet Rule 218.1 

requirements. 

(ii) Monitor the CO (or alternative tracer gas) using an 

appropriate continuous (or semi-continuous if necessary) 

monitor meeting the requirements of SCAQMD Method 

100.1 and all data falling within the 10-95 percent full scale 

span, and preferably within 30-70 percent full scale span. 

(iii) Alternate spiked sample gas and unspiked sample gas for a 

total of nine (9) runs of spiked sample gas and ten runs of 

unspiked sample gas. Sampling times should be 

sufficiently long to mitigate Response Time and averaging 

effects. 

(iv) For each run, the average CEMS reading must be below 25 

percent full scale span and >10 percent full scale span. If 

not, adjust spiking as necessary and continue runs; but 

expected spike must represent at least 50 percent of the 

total pollutant value read by the CEMS. 

(v) Calculate the spike recovery for both the pollutant and the 

CO (or alternative tracer gas) for each run by first 

averaging the pre- and post-spike values for each run and 

subtracting that value from the spiked value to yield nine 

(9) values for recovered spikes. 

(vi) Using the CO (or alternative tracer gas) spike recovery 

values for each run and the certified CO (or alternative 

tracer gas) concentration, calculate the dilution ratio for 

each run. Multiply the certified pollutant concentration by 

the dilution factor for each run to determine the expected 

diluted pollutant concentrations. Using the expected 

diluted concentrations as the “Reference Method” value, 

calculate the RA as specified in Rule 218.1. If the average 

difference is less than the CC then no low level bias factor 

is applied. If the average difference is greater than the CC 

and the average expected spike is less than the average 

CEMS measured spike, then no low level bias factor is 

applied. If the average difference is greater than the CC 

and the average expected spike is greater than the average 

CEMS measured spike, then a low level bias factor equal to 

the absolute value of the average difference is added to data 

reported at or below the 10 percent of full scale span. 

(5) Low Level RATA/Bias Factor Determination using Enhanced Reference 

Method 6.1 

A low level RATA/bias factor determination is designed to determine if 

there exists a statistically significant bias at low level concentrations. It 

consists of nine (9) test runs that measure the stack concentration and the 

CEMS concentration concurrently. 
218.1-32 AVAQMD RULE 218.1 

Continuous Emission Monitoring Performance Specifications 

(a) Performance Specifications 

There are no pass/fail criteria with respect to the magnitude of the 

percent Relative Accuracy. There are performance criteria for the 

special RATA with respect to the Reference Method and range of 

concentration on the CEMS. 

(b) Testing Procedures 

The Reference Method for the low level RATA/bias factor 

determination is SCAQMD Method 100.1 

(i) Perform a minimum of nine (9) runs of low level RATA for 

CEMS versus the Reference Method at actual levels 

(unspiked). 

(ii) The full scale span range for the Reference Method shall be 

such that all data falls with 20 - 95 percent of full scale 

span range. 

(iii) The Reference Method shall meet all SCAQMD Method 

100.1 performance criteria. 

(iv) Calculate the average difference (d = CEMS - Reference 

Method, ppm) and CC (cc = statistical calculated, ppm). 

(v) If d > 0 then the bias = 0 ppm; if d < 0 and |d| > cc then bias 

= d; if d <0 and |d| < cc then bias = 0 ppm. 

(C) Testing Frequency 

For each CEMS, perform the aforementioned performance requirements once a 

year thereafter. These annual assessments shall be completed within six (6) 

months of the end of the calendar quarter in which the CEMS was originally 

certified. 

See SIP Table at http://www.avaqmd.ca.gov/Modules/ShowDocument.aspx?documentid=921