UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION IX AIR DIVISION

Technical Support Document 

For

EPA's Direct Final Rulemaking

for the

California State Implementation Plan

South Coast Air Quality Management District, 

Rule 218.1 Continuous Emission Monitoring Performance Specifications

Prepared by: Stanley Tong

 March 18, 2010
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RULE IDENTIFICATION

Agency: South Coast Air Quality Management District (SCAQMD)

SIP Approved Rule: There is no prior version of this rule in the SIP

Subject of this TSD: Rule 218.1 - Continuous Emission Monitoring Performance 

Specifications 

Adopted May 14, 1999; 

Submitted July 23, 1999

RULE SUMMARY - Requirements from the 1981 SIP approved version of Rule 218 

were updated and divided into an administrative portion (Rule 218) and a technical 

portion (Rule 218.1). Rule 218.1 is a new rule and contains requirements for the 

certification of continuous emission monitoring systems (CEMS), the performance 

specifications of CEMS, and the operation and maintenance of CEMS.

 

The rule requirements include:

1. Standards for new or modified CEMS, and semi-continuous emission monitoring 

systems (SCEMS).

2. Standards for existing CEMS and SCEMS.

3. Requirements for time shared SCEMS

4. Requirements prior to certification or relative accuracy testing for CEMS 

sampling location, full span range, strip chart recorder, data acquisition system, 

and operational period.

5. Certification tests and specifications including calibration error, relative accuracy 

tests, response times, concentration stratification, cyclonic flow, interference 

check, and linearity error.

6. CEMS operational requirements and performance standards after certification 

including: daily calibration error, system bias test, and periodic relative accuracy 

tests.

7. Standards for calibration and zero gas.

8. Allowed reference methods.
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EPA EVALUATION - The following documents were used to evaluate the submitted 

rule. 

1. 40 CFR 60 Appendix B – Performance Specifications

2. 40 CFR 60 Appendix F – Quality Assurance Procedures

3. Enforceability - The Bluebook (Issues Relating to VOC Regulation Cutpoints, 

Deficiencies, and Deviations, EPA, May 25, 1988) and the Little Bluebook 

(Guidance Document for Correcting Common VOC & Other Rule Deficiencies,

EPA Region 9, August 21, 2001) were used to help evaluate compliance with the 

CAA §110(a)(2)(A) requirement for enforceability. 

4. SIP Relaxation - Where previous versions of rules have been SIP approved, new 

submittals must comply with CAA §110(l) and §193 regarding SIP relaxations.

The submitted rule provides performance specifications standards for new or modified 

CEMS, and standards for existing CEMS. Standards that originally appeared in Rule 

218 for existing CEMS were moved to Rule 218.1 and were generally unchanged except 

for minor technical clarifications. 

The Standards for new or modified CEMS include specifications and requirements for 

installation and sample location, certification tests, relative accuracy tests, and 

performance specifications for the operation and maintenance of the CEMS after it has 

been certified by the South Coast AQMD.

Daily calibration error tests, quarterly cylinder gas audits, and annual system bias and 

relative accuracy test audits are also required for quality assurance/quality control under 

Rule 218.1.

EPA reviewed a draft version of Rule 218.1 and provided the following general comment 

in a March 31, 1999 comment letter:

1. Absolute de-minimus value for relative accuracy (para (b)(2)(C)(i))

EPA considers that at medium to high emission limits, Rule 218.1's relative accuracy 

criteria are equivalent to, or are more stringent than the federal standards. However, at 

very low emission limits, (less than 5 ppm NOx), the rule's relative accuracy criteria using 

de-minimus values, becomes less stringent than the federal limits. 

EPA further stated in the comment letter that relative accuracy values at very low 

concentrations, such as less than 1 ppm may not be meaningful due to the limitations of 

current technology in 1999. These limitations include the availability of low 

concentration protocol calibration gases, and the degree of precision of the reference 

test method at low concentrations. 

However, technology has advanced since we made our original comment. We 

recommend the next time Rule 218.1 is amended that South Coast remove the de
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minimus limits from Rule 218.1 for NOx and CO, since 2 ppm limits are now appearing 

in permits.

The approvability comments we had on the draft rule included cases of Executive Office 

discretion for: alternative sampling locations, alternative full span ranges, alternative 

certification methods for low concentration gases, and instrument response time 

specifications exceeding standards in 40 CFR 60, Appendix A. These approvability 

issues were corrected prior to adoption of the rule by the SCAQMD.

EPA also provided a recommendation that quarterly cylinder gas audits be required. 

This recommendation was incorporated into proposed Rule 218.1 prior to adoption.

ADDITIONAL RECOMMENDATION FOR THE NEXT RULE REVISION - The following 

is recommended for the next time the rule is amended.

1. The relative accuracy performance specifications for CEMS in Rule 218.1 

(b)(2)(C)(i) allows facilities to meet the greater of either of the following conditions:

a. Less than or equal to 20 percent of the mean value of the reference method or

b. A de minimus concentration.

Rule 218.1 lists the de minimus concentration for NOx as 1.0 ppm and for CO, it is 4.0 

ppm

Equipment and technology have advanced since Rule 218.1 was originally adopted in 

1999 and equipment is now being permitted with NOx and CO limits of 2 ppm. EPA 

recommends South Coast drop the de minimus concentration option for NOx and CO 

and evaluate the applicability of the remaining de minimus concentrations (SO2, 

reduced sulfur compounds) the next time Rule 218.1 is amended.

EPA ACTION –

The submitted Rule 218.1 strengthens the SIP. There are no expected emission 

reductions from this rule as it primarily updates technical performance specifications for 

continuous emission monitoring systems. The rule largely fulfills the relevant CAA §110 

and part D requirements. EPA staff recommends approval of Rule 218.1 pursuant to 

CAA §110(k)(3) and §301(a).

ATTACHMENTS –

1. SCAQMD Rule 218.1, Continuous Emission Monitoring Performance 

Specifications, as submitted on July 23, 1999.

2. SCAQMD Rule 218, Stack Monitoring, as approved into the SIP on July 6, 1982. 
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REFERENCES -

1. "Issues Relating to VOC Regulation Cutpoints, Deficiencies, and Deviations,"

(a.k.a., Bluebook) EPA OAQPS, May 25, 1988.

2. "Guidance Document for Correcting Common VOC & Other Rule Deficiencies,"

(a.k.a., Little Bluebook), EPA Region 9, August 21, 2001 

(http://www.epa.gov/region09/air/sips/littlebluebook2001.pdf).

3. Comment letter dated March 31, 1999, Review of Proposed Amended Rule 218 

(PAR 218 – December 11, 1998) and proposed Rule 218.1 (PR 218.1 – no date)

from EPA Region IX (Andrew Steckel) to SCAQMD (Elaine Chang).