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Page **1** of **166 EO12866_CO**  **- NAAQS**  **- RIN2060**  **- AI43**  **- NFR** **- PreambleAndRegText_** **20110 8**  **1 1**  **.docx 6560**  **- 50**  **- P**  **ENVIRONMENTAL PROTECTION AGENCY**

**40 CFR Parts 50, 53 and 58 [EPA**  **- HQ**  **- OAR** **- 2008**  **- 0015; FRL**  **- 9261**  **- 4]** 

**RIN 2060**  **- AI43**  **Review of National Ambient Air Quality Standard**  **s for**  **Carbon Monoxide** 
**AGENCY:** Environmental Protection Agency (EPA). **ACTION:** Final R

ule. **SUMMARY:** This rule is being issued at this time as required b y a court order governing the schedule for completion of this review of the air quality criteria and the national ambient air quality standards (NAAQS) for carbon monoxide (CO )
. Based on its review, the EPA concludes the current primary standards are requisite to protect public health with an adequate margin of s afety , and is retaining those standards. A fter review of the air quality criteria, EPA further conclud es that no secondary standard should be set for CO at this time. EPA is also making changes to the ambient air monitoring requirements for CO , including those related to network design , and is updating, without substantive change, aspects of the federal reference method
. **DATES:** This final rule is effective on **[insert date 60 days after date of publication in**  **the FEDERAL REGISTER]**  **. ADDRESSES:**  EPA has established a docket for this action under Docket ID No. EPA
HQ
- OAR
- 2008
- 0015
. In corporated into this docket is a separate docket established for*** E.O. 12866 Review

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Page **2** of **166** the 2010 Integrated Science Assessment for Carbon Monoxide (Docket ID No. EPA
- HQ
ORD
- 2007
- 0925. All documents in the se docket s are listed on the www.regulations.gov website
. Although listed in the docket index, some information is not publicly available, e.g., confidential business information ( CBI ) or other information whose disclos ure is restricted b y statute. Certain other material, such as cop yri ghted material, is not placed on the Internet and will be publicly available for viewing at the Public Reading Room
. Abstracts of scientific studies cited in the review are also available on the Internet at EPA’s HERO Web site: http://hero.epa.gov/, b y clicking on the box on the right side of the page labeled “Search HERO.” Publicly available docket materials are available electronically

through www.re gulations.gov or may be viewed at the Public Reading Room at the Air and Radiation Docket and Information Center, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW, Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p .m., Monday through Friday , excluding legal holiday s. The telephone number for the Public Reading Room is (202) 566
- 1744 and the telephone number for the Air and Radiation Docket and Information Center is (202) 566
- 1742. **FOR FURTHER INFORMATION CONTACT:** Dr. Deirdre Murph y , Health and Environmental Impacts Division, Office of Air Quality Planning and Standards, Mail code C504
- 06 , U.S. Environmental Protection Agency , Research Triangle Park, NC 27711; telephone number : 919
- 541
- 0 7 29 ; fax number : 919
- 541
- 023 7; e - mail address : murphy .deirdre@epa.gov
. For further informati on specificall y with regard to s ection IV of this notice , contact Mr. Nealson Watkins, Air Quality Anal ys is Division, Office of Air Quality Planning and Standards, Mail code C 3 04
- 06, U.S. Environmental Protection Agency , Research Triangle Park, NC 27711; telephone number : 919
- 541
- 5522 ; fax*** E.O. 12866 Review

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Page **3** of **166** number : 919
- 541
- 1903 ; email address : watkins.nealson@epa.gov
. **SUPPLEMENTARY INFORMATION: Table of Contents**  The following topics are discussed in this preamble: **I. Background**  A. Legislative Requirements B. Related Carbon Monoxide Control Programs C. Review of the Air Quality Criteria and Standards for Ca rbon Monoxide D. Summary of Proposed Decisions on Standards for Carbon Monoxide E. Organization and Approach to Final Decisions on Standards for Carbon Monoxide **II. Rationa**  **le for Decisions on the Primary Standards** A. Introduction 1. Overview of Air Quality Information 2. Overview of Health Effects Information a . Carbox yhemoglobin as Biomarker of Exposure and Toxicity b . Nature of Effects and At
- Risk Populations c . Cardiovascular Effects 3
. Overview of Human Exposure and Dose Assessment B. Adequacy of the Current Primary Standards 1. Rationale for Proposed Decision 2
. Comments on Adequacy 3
. Conclusions Concerning Adequacy of the Primary Standards **III. Consideration of a Secondary Standard**  A. Introduction B. Rationale for Proposed Decision C. Comments on Consideration of S econdary Standard D. Conclusions Concerning a Secondary Standard **IV. Am**  **endments to Ambient Monitoring Requirements** A. Monitoring Methods 1. Proposed Changes to Part s 50 and 53 2. Public Comments 3. Decisions on Methods B. Network Design 1. Proposed Changes 2. Public Comments a. Near - road Monitoring and Co l location with Near
- road Nitrogen Dioxide Monitors b. Population Threshold s for Requiring Near
- road Carbon Monoxide Monitors c . Implementation Schedule d . Siting Criteria*** E.O. 12866 Review

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Page **4** of **166** e . Area
- Wide Monitoring f . Regional Administrator Authority 3. Conclusions on the Network Design **V. Statutory and Executive**  **Order Reviews** A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review B. Paperwork Reduction Act C. Regulatory Flexibility Act D. Unfunded Mandates Reform Act E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments G. Executive Order 13045: Protection of Children from Environmental Health and Safety Risks H. Executive Order 13211: Actions that Significantly Affect Energy Supply, Distribution or Use I. National Technology Transfer and Advancement Act J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low
-Income Populations K. Congressional Review Act References **I. Backg**  **round** A. Legislative Requirements Two sections of the Clean Air Act (CAA) govern the establishment and revision of the NAAQS. Section 108 (42 U.S.C. section 7408) directs the Administrator to identify and list certain air pollutants and then to issue air qualit y criteria for those pollutants. The Administrator is to list those air pollutants that in her “judgment, cause or contribute to air pollution which may reasonabl y be anticipated to endanger public health or welfare;” “the presence of which in the ambient air results from numerous or diverse mobile or stationary

sources;” and “for which . . . [the Administrator] plans to issue air quality criteria...” Air quality

criteria are intended to “accuratel y reflect the latest scientific knowledge useful in in dicating the kind and extent of all identifiable effects on public health or welfare which may be expected from the presence of [a] pollutant in the*** E.O. 12866 Review

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Page **5** of **166** ambient air . . .” 42 U.S.C. § 7408(b). Section 109 (42 U.S.C. 7409) directs the Administrator to propose and promulgate “primary” and “secondary” NAAQS for pollutants for which air quality criteria are issued. Section 109(b)(1) defines a primary standard as one “the attainment and maintenance of which in the judgment of the Administrator, based on such crite ria and allowing an adequate margin of safety, are requisite to protect the public health.” 1 A secondary standard, as defined in section 109(b)(2), must “specify

a level of air quality

the attainment and maintenance of which, in the judgment of the Admini strator, based on such criteria, is requisite to protect the public welfare from an y known or anticipated adverse effects associated with the presence of [the] pollutant in the ambient air.” 2 The requirement that primary standards provide an adequate margi n of safety was intended to address uncertainties associated with inconclusive scientific and technical information available at the time of standard setting. It was also intended to provide a reasonable degree of protection against hazards that research has not yet identified. See Lead Industries Association v. EPA , 647 F.2d 1130, 1154 (D.C. Cir 1980), cert. denied, 449 U.S. 1042 (1980); American Petroleum Institute v. Costle , 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert. denied, 455 U.S. 1034 (1982); Amer ican Farm Bureau Federation v. EPA, 559 F. 3d 512, 533 (D.C. Cir. 2009); Association of Battery Recyclers v. EPA , 604 F. 3d 613, 617
- 18 (D.C. Cir. 2010). Both kinds of uncertainties are components of

1 The legislative history of section 109 indicates that a primary standard is to be set at “the maximum permissible ambient air level . . . w hich will protect the health of any [sensitive] group of the population,” and that for this purpose “reference should be made to a representative sample of persons comprising the sensitive group rather than to a single person in such a group” S. Rep. No. 91
- 1196, 91st Cong., 2d Sess. 10 (1970).

2 Welfare effects as defined in section 302(h) (42 U.S.C. § 7602(h)) include, but are not limited to, “effects on soils, water, crops, vegetation, man
- made materials, animals, wil dlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as effects on economic values and on personal comfort and well
- being.”*** E.O. 12866 Review

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Page **6** of **166** the risk associated with pollution at levels below thos e at which human health effects can be said to occur with reasonable scientific certainty. Thus, in selecting primary standards that provide an adequate margin of safety , the Administrator is seeking not only to prevent pollution levels that have been dem onstrated to be harmful but also to prevent lower pollutant levels that may pose an unacceptable risk of harm, even if the risk is not precisel y identified as to nature or degree. The CAA does not require the Administrator to establish a primary

NAAQS at a zero - risk level or at background concentration levels, see Lead Industries v. EPA , 647 F.2d at 1156 n.51, but rather at a level that reduces risk sufficiently

so as to protect public health with an adequate margin of safety
. In addressing the requirement for an adequate margin of safety, the EPA considers such factors as the nature and severit y of the health effects involved, the size of sensitive population(s) at risk, and the kind and degree of the uncertainties that must be addressed. The selection of an y particular approach to providing an adequate margin of safet y is a policy choice left specifically to the Administrator’s judgment. See Lead Industries Association v. EPA , 647 F.2d at 1161
- 62; Wh itman v. American Trucking Associations , 531 U.S. 457, 495 (2001). In setting primary

and secondary standards that are “requisite” to protect public health and welfare, respectively , as provided in section 109(b), EPA’s task is to establish standards that are neither more nor less stringent than necessary for these purposes. In so doing, EPA may

not consider the costs of implementing the standards. See generall y, Whitman v. American Trucking Associations , 531 U.S. 457, 465
- 472, 475
- 76 (2001). Likewise, “[a]ttainability and technological feasibility are not relevant considerations in the promulgation of national ambient air quality standards.” American Petroleum*** E.O. 12866 Review

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Page **7** of **166** Institute v. Costle , 665 F. 2d at 1185. Section 109(d)(1) requires that “not later than December 31, 1980, and at 5
- ye ar intervals thereafter, the Administrator shall complete a thorough review of the criteria published under section 108 and the national ambient air quality standards . . . and shall make such revisions in such criteria an d standards and promulgate such new standards as may be appropriate . . . .” Section 109(d)(2) requires that an independent scientific review committee “shall complete a review of the criteria . . . and the national primary and secondary

ambient air quali ty

standards . . . and shall recommend to the Administrator any

new . . . standards and revisions of existing criteria and standards as may be appropriate . . . .” Since the earl y 1980's, this independent review function has been performed b y the Clean Ai r Scientific Advisory Committee (CASAC). 3 B. Related Carbon Monoxide Control Programs States are primarily

responsible for ensuring attainment and maintenance of ambient air quality

standards once EPA has established them. Under section 110 of the Act, and related provisions, s tates are to submit, for EPA approval, s tate implementation plans (SIPs) that provide for the attainment and maintenance of such standards through control programs directed to sources of the pollutants involved. The s tates , in conjunction with EPA, also administer the prevention of significant deterioration program . See CAA sections 160
- 169
. In addition, f ederal programs provide for nationwide reductions in emissions of these and other air pollutants through the Federal motor vehicle and motor vehicle fuel control program under title II of the Act (CAA sections 202
- 250 ) , which involves controls for emissions fro m moving sources and

3 Lists of CASAC members and of members of the CASAC CO Review P anel are available at: http://yosemite.epa.gov/sab/sabproduct.nsf/WebCASAC/CommitteesandMembership?OpenDocument
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Page **8** of **166** controls for the fuels used by these sources and new source performance standards for stationary sources und er section 111
. C. Review of the Air Quality Criteria and Standards for Carbon Monoxide EPA initially

established NAAQS for CO on April 30, 1971. The primary standards were established to protect against the occurrence of carbox yhem oglobin levels in human blood associated with health effects of concern. The standards were set at 9 parts per million (ppm), as an 8
- hour average , and 35 ppm, as a 1
- hour average, neither to be exceeded more than once per ye ar (36 FR 8186). In the 1971 decision, the Administrator judged that attainment of these standards would provide the requisite protection of public health with an adequate marg in of safet y and would also provide requisite protect ion against known and anticipated adverse effects on public welfare, and accordingl y set the secondary (welfare
- based) standards identical to the primary (health
based) standards. In 1985, EPA concluded its first periodic review of the criteria and standards for CO (50 FR 37484). In that review, EPA updated the scientific criteria upon which the initial CO standards were based through the publication of the 1979 Air Quality Criteria Document for Carbon M

onoxide (AQCD; USEPA, 1979a) and prepared a Staff Paper (USEPA, 1979b), which, along with the 1979 AQCD, served as the basis for the development of the notice of proposed rulemaking which was published on August 18, 1980 (45 FR 55066). Delay s due to uncertainties regarding the scientific basis for the final decision resulted in EPA’s announcing a second public comment period (47 FR 26407). Following substantial reexamination of the scientific data, EPA prepared an Addendum to the 1979 AQCD (USEPA, 1984a) and an updated Staff Paper (USEPA,*** E.O. 12866 Review

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Page **9** of **166** 1984b). Following review by CASAC ( Lippmann, 1984 ), EPA announced its decision not to revise the existing primary standard s and to revoke the secondary standard for CO on September 13, 1985, due to a lack of evidence of effects on public welfare at ambient concentrations (50 FR 37484). On August 1, 1994, EPA concluded its second periodic review of the criteria and standards for CO b y deciding that revisions to the CO NAAQS were not warranted at that time (59 FR 38906). This decision reflected EPA's review of relevant scientific information assembled since the last review, as contained in the 1991 AQCD (USEPA, 1991) and the 1992 Staff Paper (USEPA, 1992). Thus, the primary standards were retained at 9 ppm with an 8
- hour averaging time, and 35 ppm with a 1
- hour averaging time, neither to be exceeded more than once per year (59 FR 38906). EPA initiated the next periodic rev iew in 1997 and released the final 2000 AQCD (U.S. EPA, 2000) in August 2000. After release of the AQCD, Congress requested that the National Research Council (NRC) review the impact of meteorology and topography on ambient CO concentrations in high altit ude and extreme cold regions of the U.S. The NRC convened the Committee on Carbon Monoxide Episodes in Meteorological and Topographical Problem Areas, which focused on Fairbanks, Alaska , as a case - study
. A final report, “Managing Carbon Monoxide Polluti on in Meteorological and Topographical Problem Areas,” was published in 2003 (NRC, 2003) and offered a wide range of recommendations regarding management of CO air pollution, cold start emissions standards, ox ygen ated fuels, and CO monitoring. Following c ompletion of the NRC report, EPA did not conduct rulemaking to complete the review. On September 13, 2007, EPA issued a call for information from the public (72 FR*** E.O. 12866 Review

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Page **10** of **166** 52369) requesting the submission of recent scientific information on specified topics. O n J anuary 28

–29, 2008 , a workshop was held to discuss policy
- relevant scientific and technical information to inform EPA’s planning for the CO NAAQS review (73 FR 2490) . Following the workshop, a draft Integrated R eview P lan (IRP) (USEPA, 2008a) was made ava ilable in March 2008 for public comment and was discussed by the CASAC via a publicly

accessible teleconference consultation on April 8, 2008 (73 FR 12998; Henderson, 2008). EPA made the final IRP available in August 2008 (USEPA, 2008b). In preparing the Integrated Science Assessment for Carbon Monoxide ( ISA or Integrated Science Assessment) , EPA held an authors’ teleconference in November 2008 with invited scientific experts to discuss preliminary draft materials prepared as part of the ongoing development of the CO I SA and its supplementary annexes. The first draft ISA (USEPA, 2009a) was made available for public review on March 12, 2009 (74 FR 10734) , and reviewed b y CASAC at a meeting held on May 12
- 13, 2009 (74 FR 15265). A second draft ISA (USEPA, 20 09b) was released for CASAC and public review on September 23, 2009 (74 FR 48536), and it was reviewed b y CASAC at a meeting held on November 16
- 17, 2009 (74 FR 54042). The final ISA was released in January 2010 (USEPA, 2010a). In May 2009, OAQPS released a draft planning document, the draft Scope and Methods Plan (USEPA, 2009c), for consultation with CASAC and public review at the CASAC meeting held on May 12
- 13, 2009. Taking into consideration comments on the draft Scope and Methods Plan from CASAC (Bra in, 2009) and the public, OAQPS staff developed and released for CASAC review and public comment a first draft Risk and Exposure Assessment ( REA ) (USEPA, 2009d), which was reviewed at the CASAC*** E.O. 12866 Review

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Page **11** of **166** meeting held on November 16
- 17, 2009. Subsequent to that meet ing and taking into consideration comments from CASAC (Brain and Samet, 2010a) and public comments on the first draft REA, a second draft REA (USEPA, 2010 d) was released for CASAC review and public comment in February 2010, and reviewed at a CASAC meeting held on March 22
- 23, 2010. Drawing from information in the final CO I SA and the second draft REA, EPA released a draft Policy Assessment (PA) (USEPA, 2010 e ) in earl y March 2010 for CASAC review and public comment at the same meeting . Taking into consideration comments on the second draft REA and the draft PA from CASAC (Brain and Samet, 2010b, 2010c) and the public, staff completed the quantitative assessments which are presented in the final REA (USEPA, 2010b) . Staff additionally took into consi deration those comments and the final REA anal ys es in completing the final Policy Assessment (USEPA, 2010c) which was released in October 2010
. The proposed decision (henceforth “proposal”) on the review of the CO NAAQS was signed on January

28, 2011 , and published in the Federal Register on February 11, 2011. The EPA held a public hearing to provide direct opportunity for oral testimony

by the public on the proposal. The hearing was held on February 28, 2011 , in Arlington, Virginia. At this public heari ng, EPA heard testimony from five individuals representing themselves or specific interested organizations. Transcripts from this hearing and written testimony provided at the hearing are in the docket for this review. Additionally , written comments were received from various commenters during the public comment period on the proposal. Significant issues raised in the public comments are discussed in the preamble of this final action. A summary of all other significant comments, along with EPA’s respons es (henceforth “Response to Comments”) can be found in the docket for*** E.O. 12866 Review

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Page **12** of **166** this review. The schedule for completion of this review is governed b y a court order resolving a lawsuit filed in March 2003 by a group of plaintiffs who alleged that EPA had failed to p erform its mandatory

duty , under section 109(d)(1), to complet e a review of the CO NAAQS within the period provided b y statute. The court order that governs this review, entered b y the court on November 14, 2008 , and amended on August 30, 2010, provides that EPA will sign for publication a notice of final rulemaking concerning its review of the CO NAAQS no later than August 12, 2011. Some commenters have referred to and discussed individual scientific studies on the health effects of CO that were not in cluded in the IS A (EPA, 20 1 0a) (“'new' studies”). In considering and responding to comments for which such “new” studies were cited in support, EPA has provisionally considered the cited studies in the context of the findings of the IS A
. As in prior NAA QS reviews, EPA is basing its decision in this review on studies and related information included in the IS A , REA and Policy Assessment , which have undergone CASAC and public review. The studies assessed in the ISA and Policy Assessment , and the integrati on of the scientific evidence presented in them, have undergone extensive critical review b y EPA, CASAC, and the public. The rigor of that review makes these studies, and their integrative assessment, the most reliable source of scientific information on which to base decisions on the NAAQS, decisions that all parties recognize as of great import. NAAQS decisions can have profound impacts on public health and welfare, and NAAQS decisions should be based on studies that have been rigorousl y assessed in an integrative manner not only by EPA but also by

the*** E.O. 12866 Review

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Page **13** of **166** statutorily

mandated independent advisory committee, as well as the public review that accompanies this process. EPA’s provisional consideration of these studies did not and could not provide that kind of in
- depth critical review. This decision is consistent with EPA’s practice in prior NAAQS reviews and its interpretation of the requirements of the CAA. Since the 1970 amendments, the EPA has taken the view that NAAQS decisions are to be based on scientific studies and related info rmation that have been assessed as a part of the pertinent air quality criteria, and has consistently

followed this approach. This longstanding interpretation was strengthened by new legislative requirements enacted in 1977, which added section 109(d)(2) of the Act concerning CASAC review of air quality criteria. See 71 FR 61144, 61148 (October 17, 2006) (final decision on review of PM NAAQS) for a detailed discussion of this issue and EPA’s past practice. As discussed in EPA’s 1993 decision not to revi se the NAAQS for ozone, ‘‘new’’ studies may

sometimes be of such significance that it is appropriate to delay a decision on revision of a NAAQS and to supplement the pertinent air quality criteria so the studies can be taken into account (58 FR at 13013

– 13 014, March 9, 1993). In the present case, EPA’s provisional consideration of ‘‘new’’ studies concludes that, taken in context, the ‘‘new’’ information and findings do not materially change any of the broad scientific conclusions regarding the health effec ts and exposure pathway s of ambient CO made in the air quality

criteria. For this reason, reopening the air quality criteria review would not be warranted even if there were time to do so under the court order governing the schedule for this rulemaking. Accordingl y, EPA is basing the final decisions in this review on the studies and*** E.O. 12866 Review

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Page **14** of **166** related information included in the CO air qualit y criteria that have undergone CASAC and public review. EPA will consider the “new” studies for purposes of decision
- making i n the next periodic review of the CO NAAQS, which EPA expects to begin soon after the conclusion of this review and which will provide the opportunity to fully assess these studies through a more rigorous review process involving EPA, CASAC, and the public
. Further discussion of these ‘‘new’’ studies can be found in the Response to Comments document. D. Summary of Proposed Decisions on Standards for Carbon Monoxide For reasons discussed in the notice of proposed rulemaking, the Administrator proposed to r etain the current primary CO standards. With regard to consideration of a secondary standard, the Administrator proposed to conclude that no secondary standards should be set at this time. E. Organization and Approach to Final Decisions on Standards for C arbon Monoxide This action presents the Administrator’s final decisions in this review of the CO standards. Decisi o ns regarding the primary CO standard s are addressed below in section II. Consideration of a secondary CO standard is addressed below in section III. Ambient monitoring methods and network design related to implementation of the CO standards are addressed below in section IV. A discussion o f statutory and executive order reviews is provided in section V. Today ’s final decisions are based on a thorough review in the Integrated Science Assessment of the latest scientific information on known and potential human health and welfare effects assoc iated with exposure to CO in the environment. These final decisions*** E.O. 12866 Review

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Page **15** of **166** also take into account: (1) assessments in the P olicy Assessment of the most policy
relevant information in the Integrated Science Assessment as well as quantitative exposure , dose and risk assessments based on that information presented in the Risk and Exposure Assessment ; (2) CASAC Panel advice and recommendations, as reflected in its letters to the Administrator and its discussions of drafts of the Integrated Science Assessment, Risk and Exposure Assessment and P olicy Assessment at public meetings; (3) public comments received during the development of these documents, either in connection with CASAC Panel meetings or separately ; and (4) public comments received on the proposed rulemaki ng. **II. Rationale for Decisions on the Primary S**  **tandard s**  A. Introduction This section presents the rationale for the Administrator’s decision that the current primary standards are requisite to protect public health with an adequate margin of safety, and that they

should be retain ed
. In developing this rationale, EPA has drawn upon an integrative s ynthesis in the Integrated Science Assessment o f the entire body of evidence published through mid
- 2009 on human health effects associated with the presence of CO in the ambient air. The research studies evaluated in the I SA have undergone intensive scrutiny through multiple layers of peer review, with extended opportunities for review and comment b y the CASAC Panel and the public. As with virtually an y policy
- relevant scientific research, there is uncertainty in the characterization of health effects attributable to exposure to ambient CO. While imp ortant uncertainties remain, the review of the health effects information has been extensive and deliberate. In the judgment of the Administrator, this intensive evaluation of the scientific evidence provides an*** E.O. 12866 Review

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Page **16** of **166** adequate basis for regulatory decision maki ng at this time. This review also provides important input to EPA’s research plan for improving our future understanding of the relationships between exposures to ambient CO and health effects. The health effects information and quantitative exposure/dose assessment were summarized in sections II.B and II.C of the proposal (76 FR at 8162

– 8172) and are onl y briefl y outlined in sections II.A.2 and II.A.3 below. Responses to public comments specific to the material presented in sections II.A.1 through II.A.3 below are provided in the Response to Comments document. Subsequent sections of this preamble provide a more complete discussion of the Administrator’s rationale, in light of key issues raised in public comments, for concluding that the current standards are requisite to protect public health with an adequate margin of safet y and that it is appropriate to retain the current primary CO standards to continue to provide requisite public health protection (section II.B). 1. Overview of Air Quality Informati on This section briefl y summarizes the information on CO sources, emissions, ambient air concentrations and aspects of associated exposure presented in section II.A of the proposal, as well as in section 1.3 of the P olicy Assessment and chapter 2 of the Risk and Exposure Assessment
. Carbon monoxide in ambient air is formed b y both natural and anthropogenic processes. In areas of human activity such as urban areas, it is formed primarily b y the incomplete combustion of carbon
- containing fuels with the c ombustion conditions influencing the rate of formation. For example, as a result of the combustion conditions, CO emissions from large fossil
- fueled power plants are typicall y very low because*** E.O. 12866 Review

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Page **17** of **166** optimized fuel consumption conditions make boiler combustion h ighl y efficient. In contrast, internal combustion engines used in many mobile sources have widely varying operating conditions. As a result, higher and more varying CO formation results from the operation of mobile sources, which continue to be a signifi cant source sector for CO in ambient air (ISA, sections 3.4 and 3.5; 2000 AQCD, section 7.2; REA, section 2.2 and 3.1.3). Mobile sources are a substantial contributor to total CO emissions , particularly in urban areas (I SA, section 3.5.1.3; REA, section 3.1.3). H ighest ambient concentrations in urban areas occur on or near roadway s, particularly highly travelled roadway s, and decline somewhat steeply with distance (ISA, section 3.5.1.3; REA, section 3.1.3; Baldauf et al., 2008 a,b, Zhu et al., 2002 ). Fo r example, as described in the ISA , a study by Zhu et al (2002) documented CO concentrations at an interstate freeway to be ten times as high as an upwind monitoring site; concentrations declined rapidl y in the downwind direction to levels only approximate ly

one half roadway

concentrations within 100 to 300 meters (ISA, section 3.5.1.3, Figure 3
- 29 Zhu et al., 2002). Factors that can influenc e the steepness of the gradient include wind direction and other meteorological variables, and on
- road vehicle densi ty (I SA, section 3.5.1.3, Figures 3
- 29 and 3
- 30; Zhu et al., 2002; Baldauf et al., 2008 a,b ). T h e se traffic
- related ambient concentrations contribute to the higher short
- term ambient CO exposures experienced near busy roads and particularly

in vehicles , a s described in more detail in the REA and PA
. 2. Overview of Health Effects Information This section summarizes information presented in section II.B of the proposal pertaining to health endpoints associated with the range of exposures considered to be*** E.O. 12866 Review

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Page **1 8**  of **166** m ost relevant to current ambient CO exposure levels. Inrecognition of the use of an internal biomarker in evaluating health risk for CO , the following section summarizes key aspects of the use of carbox yhemoglobin as an internal biomarker (section II.A.2. a). This is followed first by

a summary

of the array

of CO
- induced health effects and recognition of at
- risk subpopulations (section II.A.2.b) and then b y a summary of the evidence regarding cardiovascular effects (section II.A.2.c). a. Carbox yhemoglobin as Biomarker of Exposure and Toxicity This section briefl y summarizes the current state of knowledge , as described in the Integrated Science Assessment , of the role of carbox yhemoglobin in mediating toxicity and as a biomarker of exposure . The section al so summarizes the roles of endogenousl y produced CO and exposure to ambient and nonambient CO in influencing internal CO concentrations and carbox yh emoglobin (COHb) levels
. At this time , as during past reviews , the best characterized mechanism of action of CO is tissue hy

poxia caused by

binding of CO to hemoglobin to form COHb in the blood ( e.g., USEPA, 2000; USEPA, 1991 ; I SA )
. In creasing levels of COHb in the blood stream with subsequent decrease in ox ygen av ailability for organs and tissues are of concern in people who have compromised compensatory mechanisms (e.g., lack of capacity to increase blood flow in response to hy poxia) , such as those with pre
- existing heart disease
. For example, the integrative rev iew of health effects of CO indicates that “the clearest evidence indicates that individuals with CAD [coronary artery disease] are most susceptible to an increase in CO
- induced health effects” (ISA, section 5.7.8)
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Page **19** of **166** Carbox yh emoglobin is formed in the blo od both from CO originating in the body (endogenous CO) 4 and from CO that has been inhaled into the body (exogenous CO). 5 The amount of COHb that occurs in the blood depends on factors specific to both the phy siology

of the individual (including disease state) and the exposure circumstances. These include factors associated with an individual’s rate of COHb elimination and production of endogenous CO, as well as those that influence the intake of exogenous CO into the blood, such as the differences in CO concentration (and partial pressure) in inhaled air, exhaled air , and blood ; duration of a person’s exposure to changed CO concentrations in air ; and exertion level or inhalation rate (ISA, chapter 4). Apart from the impair

ment of oxygen delivery

to tissues related to COHb formation, toxicological studies also indicate several other pathway s by which CO acts in the body , which involv e a wide range of molecular targets and internal CO concentrations (2000 AQCD, sections 5.6
- 5.9; I SA, section 5.1.3). The role of these alternative less
well
- characterized mechanisms in CO
- induced health effects at concentrations relevant to the current NAAQS, however, is not clear. New res earch based on this evidence is needed to further understand the se pathway s and their linkage to CO
- induced effects in susceptible populations. Accordingl y, COHb level in blood continues to be well recognized and most commonly used as an important internal dose metric, and is supported by

the evidence as the most usef ul indicator of CO exposure that is related to CO health effects of major concern (ISA, p. 2
- 4, sections 4.1, 4.2, 5.1.1; 1991 AQCD, 2000 AQCD, 2010 I SA).

4 Endogenous CO is produced from biochemical reactions associated with normal breakdown of heme proteins (ISA, section 4.5).

5 Exogenous CO includes CO emitted to amb ient air, CO emitted to ambient air that has infiltrated indoors and CO that originates indoors from sources such as gas stoves, tobacco smoke and gas furnaces (ISA, section 3.6; REA, section 2.2)
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Page **20** of **166** b. Nature of Effects and At
- Risk Populations T he long
- standing body of evidence that has established many aspects of the biological effects of CO continues to contribute to our understanding of the health effects of ambient CO (PA, section 2.2.1)
. Inhaled CO elicits various health effects through binding to, and associated alteration of the function of, a number of hem e - containing molecules, mainly

hemoglobin (see e.g., ISA, section 4.1). The best characterized health effect associated with CO levels of concern is decreased ox ygen availability to critical tissues and organs, specifically the heart, indu ced by

increased COHb levels in blood (I SA, section 5.1.2). Consistent with this, medical conditions that affect the biological mechanisms which compensate for this effect (e.g., vasodilation and increased coronary blood flow with increased ox ygen delivery to the myocardium) can contribute to a reduced amount of ox ygen available to key body tissues, potentially affecting organ sy stem function and limiting exercise capacity (2000 AQCD, section 7.1). 6 This evidence newl y available in this review provides additional detail and support to our prior understanding of CO effects and population susceptibility . In this review, the clearest evidence for ambient CO
- related effects is available for cardiovascular effects. Using an established framework to characte rize the evidence as to likelihood of causal relationships between exposure to ambient CO and specific health effects (ISA, chapter 1 ) , the I SA states that "Given the consistent and coherent evidence from epidemiologic and human clinical studies, along wi th biological plausibility provided b y CO’s role in limiting ox ygen availability , it is concluded that a causal relationship is likely

to exist between relevant short
- term CO exposures and
6 For example, people with peripheral vascular diseases and heart disease patients often have markedly reduced circulatory capacity and reduced ability to compensate for increased circulatory demands during exercise and other stress (2000 AQCD, p. 7
- 7).*** E.O. 12866 Review

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Page **21** of **166** cardiovascular morbidity" (ISA, p. 2
- 6, section 2.5.1). Using the same established framework, the ISA describes the evidence as suggestive o f causal relationships between relevant ambient CO exposure and several other health effects: relevant short
- and long
term CO exposures and central nervous s ys tem ( CNS ) effects, bi rth outcomes and developmental effects following long
- term exposure, respiratory morbidity

following short
- term exposure, and mortality following short
- term exposure (ISA, section 2.5). However, there is onl y limited evidence for these relationships , and the current body of evidence continues to indicate cardiovascular effects, particularl y effects related to the role of CO in limiting oxygen availability to tissues , as those of greatest concern at low exposures with relevance to ambient concentrations (I S A, chapter 2)
. The evidence for these effects is further described in section II.A.2.c below. As described in the proposal, the terms susceptibility , vulnerability , sensitivity , and at
- risk are commonly employed in identifying population groups or life stages at relativel y higher risk for health risk from a specific pollutant . In the IS A for this review, the term susceptibility

has been used broadl y to recognize populations that have a greater likelihood of experiencing effects related to ambient CO exposure, with use of the term susceptible populations , as used in the ISA , d efined as follows (ISA, section 5.7, p. 5
- 115): Populations that have a greater likelihood of experiencing health effects related to exposure to an air pollutant (e.g., CO) due to a variety of factors including, but not limited to: genetic or developmen tal factors, race, gender, lifestage, lifestyle (e.g., smoking status and nutrition) or preexisting disease, as well as population
- level factors that can increase*** E.O. 12866 Review

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Page **22** of **166** an individual's exposure to an air pollutant (e.g., CO) such as socioeconomic status [SES ], w hich encompasses reduced access to health care, low educational attainment, residential location, and other factors. Thus, susceptible populations are at greater risk of CO effects and are also referred to as at- risk in the summary

below. As described in the proposal, the population with pre
- existing cardiovascular disease continues to be the best
- characterized population at risk of adverse CO
- induced effects, with CAD recognized as “the most important susceptibility characteristic for increase d risk due to CO exposure” (ISA, section 2.6.1). An important factor determining the increased susceptibility of this population is their inability to compensate for the reduction in tissue oxygen levels due to an already compromised cardiovascular sy stem. Individu als with a healthy cardiovascular sy stem (i.e., with healthy coronary arteries) have operative phy siologic compensatory mechanisms (e.g., increased blood flow and ox ygen extraction) for CO
- induced tissue hy poxia and are unlikely

to be at increased risk of CO
- induced effects (I SA, p. 2
- 10). 7 In addition, the high ox ygen consumption of the heart, together with the inability to compensate for tissue hy poxia, make s the cardiac muscle of a person suffering from CAD a critical target for CO
. Thus, the current evidence continues to support the identification of people with cardiovascular disease as susceptibl e to CO
- induced health effects (I SA, 2
- 12) and those having CAD as the population with the best
- characterized susceptibility (ISA, sections

7 The other we ll
- studied individuals at the time of the last review were healthy male adults that experienced decrease d exercise duration at similar COHb levels during short term maximal exercise. This population was of lesser concern since it represented a smaller sensitive group, and potentially limited to individuals that would engage in vigorous exercise such as competing athletes (1991 AQCD, section 10.3.2)
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Page **23** of **166** 5.7.1.1 and 5.7 .8). 8 An important susceptibility consideration for this population is the inability to compensate for CO
- induced h ypoxia since individuals with CAD have an already compromised cardiovascular s ys tem. This population includes those with angina pectoris (c ardiac chest pain), those who have experienced a heart attack, and those with silent ischemia or undiagnosed ischemic heart disease (AHA, 2003). People with other cardiovascular diseases, particularl y heart diseases, are also at risk of CO
- induced health effects. Cardiovascular disease comprises many t ypes of medical disorders, including heart disease, cerebrovascular disease (e.g. , stroke), hy pertension (high blood pressure), and peripheral vascular diseases. Heart disease, in turn, comprises several types of disorders, including ischemic heart disease ( coronary heart disease [CHD] or CAD, myocardial infarction, angina), conges tive heart failure, and disturbances in cardiac rhy thm (2000 AQCD, section 7.7.2.1). 9 Other t yp es of cardiovascular disease may also contribute to increased susceptibility to the adverse effects of low levels of CO (I SA, section 5.7.1.1). For example, ev idence with regard to other ty pes of cardiovascular disease such as congestive heart failure, arrh ythmia, and non
- specific cardiovascular disease, and more limited evidence for peripheral vascular and cerebrovascular disease, indicates that “the continuous nature of the progression of CAD and its close relationship

8 As recognized in the ISA, “Although the weight of evidence varies depending on the factor be ing evaluated, the clearest evidence indicates that individuals with CAD are most susceptible to an increase in CO
- induced health effects” (ISA, p. 2
- 12).

9 Coronary artery disease (CAD), often also called coronary heart disease or i schemic heart disease , is a category of cardiovascular disease associated with narrowed heart arteries. Individuals with this disease may have myocardial ischemia, which occurs when the heart muscle receives insufficient oxygen delivered by the blood. Exercise
- induced angina p ectoris (chest pain) occurs in many of them. Among all patients with diagnosed CAD, the predominant type of ischemia, as identified by electrocardiogram ST segment depression, is asymptomatic (i.e., silent). P atients who experience angina ty pically have a dditional ischemic episodes that are asymptomatic (2000 AQCD, section 7.7.2.1). In addition to such chronic conditions, C A D can lead to sudden episodes, such as myocardial infarction (ISA, p. 5 - 24).*** E.O. 12866 Review

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Page **24** of **166** with other forms of cardiovascular disease suggest that a larger population than just those individuals with a prior diagnosis of CAD may be susceptible to health effects from CO exposure” (ISA, p. 5 - 117). As described in the proposal, s everal other populations are potentially at risk of CO
- induced effects , including: those with other pre
- existing diseases that may already have limited ox ygen availability , increased COHb levels or increased endog enous CO production , such as people with obstructive lung diseases, diabetes and anemia; older adults; fetuses during critical phases of development and young infants or newborns; those who spend a substantial time on or near heavily traveled roadway s; vis itors to high
altitude locations; and people ingesting medications and other substances that enhance endogenous or metabolic CO formation (ISA, section 2.6.1)
. While the evidence suggests a potential susceptibility of the se populations, information charac terizing susceptibility

for th ese groups is limited . For example, information is lacking on specific CO exposures or COHb levels that may be associated with health effects in these other groups and the nature of those effects, as well as a way to relate the specific evidence available for the CAD population to these other populations (PA, section 2.2.1)
. c. Cardiovascular Effects Similar to the previous review, results from controlled human exposure studies of individuals with coronary artery disease (C AD) (Adams et al., 1988; Allred et al., 1989a, 1989b, 1991; Anderson et al., 1973; Kleinman et al., 1989, 1998; Sheps et al., 1987 10 ) are the “most compelling evidence of CO
- induced effects on th e cardiovascular sy stem” (I SA, s ection 5.2). Additionally , the use of an internal dose metric, COHb, adds to the

10 Statistical analyses of the data from Sheps et al., (1987) by Bissette et al
. (1986) indicate a significant decrease in time to onset of angina at 4.1% COHb if subjects that did not experience exercise
induced angina during air exposure are also included in the analyses.*** E.O. 12866 Review

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Page **25** of **166** strength of the findings in these controlled exposure studies. As a group, these studies demonstrate the role of short
- term CO exposures in increasing the susceptibility of people with CAD to incidents of exercise
- associated m yo cardial ischemia. Among the controlled human exposure studies, the I SA places principal emphasis on the study

of CAD patients by

Allred et al. (1989a, 1989b, 1991) 11 (which was also consider ed in the previous review ) for the following reasons: 1) dose
- response relationships were observed; 2) effects were observed at the lowest COHb levels tested (mean of 2
- 2.4% COHb 12 following experimental CO exposure), with no evidence of a threshold; 3) objective me asures of myocardial ischemia (ST
- segment depression) 13 were assessed, as well as the subjective measure of decreased time to induction of angina; 4) measurements were taken both by CO
- oximetry (CO
- Ox) and by gas chromatograph y (GC), which provides a more accurate measurement of COHb blood levels 14 ; 5) a large number of study subjects were used; 6) a strict protocol for selection of study subjects

11 Other controlled human exposure studies of CAD patients (listed in Table 2
- 2 of the PA, and discussed in more detail in the 1991 and 2000 AQCDs) similarly provide evidence of reduced time to exercise
- induced angina associated with elevated COHb resulting from controlled short
- duration expo sure to increased concentrations of CO.

12 These levels and other COHb levels described for this study below are based on gas chromatography analysis unless otherwise specified. M atched measurements available for CO
- oximetry (CO
- Ox) and gas chromatography (GC) in this study indicate CO
- Ox measurements of 2.65% (post
exercise mean) and 3.21% (post
- exposure mean) corresponding to the GC measurement levels o f 2.00% (post
- exercise mean) to 2.38% (post
- exposure mean) for the lower exposure level assessed in th is study (Allred et al., 1991)
.

13 The ST
- segment is a portion of the electrocardiogram, depression of which is an indication of insufficient oxygen supply to the heart muscle tissue (myocardial ischemia). M yocardial ischemia can result in chest pain (ang ina pectoris) or such characteristic changes in ECGs or both. In individuals with coronary artery disease , it t ends to occur at specific levels of exercise . The duration of exercise required to demonstrate chest pain and/or a 1
- mm change in the ST segment of the ECG were key measurements in the multicenter study by Allred et al
. (1989a, 1989b, 1991).

14 As stated in the ISA, the gas chromatographic technique fo r measuring COHb levels “ is known to be more accurate than spectrophotometric measurements, parti cularly for samples containing COHb concentrations < 5% ” (ISA, p. 5
- 41)
. CO
- oximetry is a spectrophotometric method commonly used to rapidly provide approximate concentrations of COHb during controlled exposures (ISA, p. 5
- 41). At the low concentrations of COHb (<5%) more relevant to ambient CO exposures, co
- oximeters are reported to overestimate COHb levels compared to GC measurements, while at higher concentrations, this method is reported to produce underestimates (ISA, p.4
- 18).*** E.O. 12866 Review

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Page **26** of **166** was emplo yed to include only CAD patients with reproducible exercise
- induced angina; and 7) the study was conduc ted at multiple laboratories around the U.S. This study evaluated changes in time to exercise
- induced onset of markers of m yocardial ischemia resulting from two short (approximately 1
- hour) CO exposures targeted to result in mean study subject COHb levels of 2% and 4%, respectively (I SA, section 5.2.4). In this study , subjects (n=63) on three separate occasions underwent an initial graded exercise treadmill test, followed by 50 to 70
- minute exposures under resting conditions to room air CO concentrations or CO concentrations targeted for each subject to achieve blood COHb levels of 2% and 4%. The exposures were to average CO concentrations of 0.7 ppm (room air concentration range 0
- 2 ppm), 117 ppm (range 42
- 202 ppm) and 253 ppm (range 143
- 357 ppm). After the 50
- to 70
- minute exposures, subjects underwent a second graded exercise treadmill test, and the percent change in time to onset of angina and time to ST endpoint between the first and second exercise tests was determined. For the two CO exposures, th e average post - exposure COHb concentrations were reported as 2.4% and 4.7%, and the subsequent post
- exercise average COHb concentrations were reported as 2.0% and 3.9%. 15 Across all subjects, the mean time to angina onset for control (“room” air) exposures was approximately 8.5 minutes, and the mean time to ST endpoint was approximately

9.5 minutes (Allred et al., 1989b). Relative to room
- air exposure that resulted in a mean COHb level of 0.6% (post
- exercise), exposure s to CO resulting in

15 While the COHb blood level for each subject during the exercise tests wa s intermediate between the post - exposure and subsequent post - exercise measurements (e.g., mean 2.4
- 2.0% and 4.7
- 3.9%) , the study authors noted that the measurements at the end of the exercise test represented the COHb concentrations at the approximate time of onset of myocardial ischemia as indicated by angina and ST segment changes. The corresponding ranges of CO
- Ox measurements for the two exposures were 2.7
- 3.2% and 4.7
- 5.6%. In this document, we refer to the GC
- measured mean of 2.0% or 2.0
- 2.4% for the COHb levels resulting from the lower experimental CO exposure.*** E.O. 12866 Review

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Page **27** of **166** post - exercise me an COHb concentrations of 2.0% and 3.9% were observed to decrease the exercise time required to induce ST
- segment depression by 5.1 % (p=0.01) and 12.1% (p<0.001), respectivel y. These changes were well correlated with the onset of exercise
induced angina, the time to which was shortened by 4.2% (p=0.027) and 7.1% (p=0.002), respectivel y, for the two experimental CO exposures (Allred et al., 1989a, 1989b, 1991). 16 As at the time of the last review, while ST
- segment depression is recognized as an indicator o f m yocardial ischemia, the exact physiological significance of the observed changes among those with CAD is unclear (I SA, p. 5
- 48). No controlled human exposure studies have been specificall y designed to evaluate the effect of controlled short
- term exposures to CO resulting in COHb levels lower than a study mean of 2% (I SA, section 5.2.6). However, an important finding of the multi
laboratory

study was the dose
- response relationship observed between COHb and the markers of m yo cardial ischemia, with effect s observed at the lowest increases in COHb tested, without evidence of a measurable threshold effect. As reported b y the authors, the results comparing “the effects of increasing COHb from baseline levels (0.6%) to 2 and 3.9% COHb showed that each produce d further changes in objective ECG measures of ischemia” implying that “small increments in COHb could adversel y affect myocardial function and produce ischemia” (Allred et al., 1989b, 1991). The epidemiological evidence has expanded considerabl y since the last review including numerous additional studies that are coherent with the evidence on markers of

16 Another indicator measured in the study was the combination of heart rate and systolic blood pressure which provides a clinical index of the work of the heart and myocardial oxygen consumption, since heart rate and blood pressure are major determinants of myocardial oxygen consumption (Allred et al., 1991). A decrease in oxygen to the myocardium would be expected to be paralleled by ischem ia at lower heart rate and systolic blood pressure. This heart rate
- systolic blood pressure indicator at the time to ST
- endpoint was decreased by 4.4% at the 3.9% COHb dose level and by a nonstatistically
- significant , smaller amount at the 2.0% COHb dose level
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Page **28** of **166** myocardial ischemia from controlled human exposure studies of CAD patients (I SA, section 2.7). The most recent set of epidemiological studies in the U.S. have evaluated the associations between ambient concentrations of multiple pollutants (i.e
. , fine particles or PM 2.5 , nitrogen dioxide, sulfur dioxide, ozone, and CO) at fixed
- site ambient monitors and increases in emergency department visits and hospital admissions for specific cardiovascular health outcomes including ischemic heart disease (IHD), myocardial infarction , congestive heart failure (CHF), and cardiovascular diseases (CVD) as a whole (Bell et al., 2009; Koken et al., 2003; L inn et al., 2 000; Mann et al., 2002; Metzger et al., 2004; Sy mons et al., 2006; Tolbert et al., 2007; Wellenius et al., 2005). As noted by the ISA, “[s]tudies of hospital admissions and [emergency department] visits for IHD provide the strongest [epidemiological] ev idence of ambient CO being associated with adverse CVD outcomes” (I SA, p. 5
- 40, section 5.2.3). With regard to studies for other measures of cardiovascular morbidity , the IS A notes that “[t]hough not as consistent as the IHD effects, the effects for all C VD hospital admissions (which include IHD admissions) and CHF hospital admissions also provide evidence for an association of cardiovascular outcomes and ambient CO concentrations” (ISA, section 5.2.3). While noting the difficulty in determining the extent to which CO is independently associated with CVD outcomes in this group of studies as compared to CO as a marker for the effects of another traffic
- related pollutant or mix of pollutants, the I SA concludes that the epidemiological evidence, particularly when considering the copollutant analy ses, provides support to the clinical evidence for a direct effect of short
- term ambient CO exposure on CVD morbidity (ISA, pp. 5
- 40 to 5
- 41).*** E.O. 12866 Review

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Page **29** of **166** 3. Overview of Human Exposure and Dose Assessment Our consideration of th e scientific evidence in the current review, as at the time of the last review, is informed by results from a quantitative analy sis of estimated population exposure and resultant COHb levels. This analy sis provides estimates of the percentage s of simulate d at - risk population s expected to experience dail y m aximum COHb levels at or above a range of benchmark levels under varying air quality scenarios (e.g., just meeting the current or alternative standards) , as well as characterizations of the kind and degre e of uncertainties inherent in such estimates. The benchmark COHb levels were identified based on consideration of the evidence discussed in sectio n II. A.2 above. In this section, we provide a short overview of key aspects of the assessment conducted for this review
. The assessment is summarized more full y in section II.C of the proposal, discussed in detail in the REA and summarized in the PA (section 2.2.2). The results of the anal ys es as they

relate to considerations of the adequacy of the current standards are d iscussed in section II.B. 3 below. As noted in the proposal notice, p eople can be exposed to CO in ambient air when they are outdoors and also when they are in indoor locations into which ambient (outdoor) air has infiltrated (ISA , sections 3.6.1 and 3.6.5) . Indoor locations may also contain CO from indoor sources, such as gas stoves and tobacco smoke. Where present, these indoor sources can be important contributors to total CO exposure and can contribute to much greater CO expo sures and associated COHb levels than those associated with ambient sources (I SA, section 3.6.5.2). For example, indoor source
related exposures, such as faulty furnaces or other combustion appliances, have been estimated in the past to lead to COHb level s on the order of twice as high as short
- term*** E.O. 12866 Review

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Page **30** of **166** elevations in ambient CO that were more likel y to be encountered b y the general public (2000 AQCD, p. 7
- 4). Further, some exposure/dose assessments performed for previous reviews have included modeling simulat ions both without and with indoor (nonambient) sources (gas stoves and tobacco smoke) to provide context for the assessment of ambient CO exposure and dose (e.g., US EPA, 1992; Johnson et al., 2000), and these assessments have found that nonambient sources have a substantially greater impact on the highest total exposures and COHb levels experienced b y the simulated population than do ambient sources (Johnson et al., 2000; REA, sections 1.2 and 6.3). While recognizing this potential for indoor sources, whe re present, to play a role in CO exposures and COHb levels, the exposure modeling in the current review (described below ) did not include indoor CO sources in order to focus on the impact of ambient CO on population COHb levels. The assessment estimated ambient CO exposure and associated COHb levels in simulated at - risk populations in two urban study areas in Denver and Los Angeles, in which current ambient CO concentrations are below the current standards. Estimates were developed for exposures to ambie nt CO associated with current “as is” conditions (2006 air quality) and also for higher ambient CO concentrations associated with air quality conditions simulated to just meet the current 8
- hour standard, 17 as well as for air quality conditions simulated to just meet several potential alternative standards. Although we consider it unlikely that air concentrations in many urban areas across the U.S. that are currentl y well below the current standards would i ncrease to just meet the 8
- hour standard, we recognize the potential for CO concentrations in some areas currentl y

17 As noted elsewhere, the 8
- hour standard is the controlling standard for ambient CO concentrations.*** E.O. 12866 Review

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Page **31** of **166** below the standard to increase to just meet the standard. We additionally recognize that this simulation can provide useful information in e valuating the current standard , although w e recognize the uncertainty associated with simulating this hy pothetical profile of higher CO concentrations that just meet the current 8
- hour standard. The exposure and dose modeling for the assessment , presente d in detail in the REA, relied on version 4.3 of EPA’s Air Pollutant Exposure model (APEX4.3), which estimates human exposure using a stochastic, event
- based microenvironmental approach (REA, chapter 4). T he review of the CO standards completed in 1994 re lied on population exposure and dose estimates generated from the probabilistic NAAQS exposure model (pNEM ), a model that, among other differences from the current modeling approach with APEX4.3, employed a cohort
- based approach (Johnson et al., 1992; US E PA, 1992)
. 18 , 19 Each of the model developments since the use of pNEM in that review have been designed to allow APEX to better represent human behavior, human phy siology , and microenvironmental concentrations and to more accurately estimate variability

in C O exposures and COHb levels (REA, chapter 4). 20

18 When using the cohort approach, each cohort is assumed to contain persons with identical exposures during the specified exposure period. Thus, v ariability in exposure will be attributed to differences in how the cohorts are defined, not necessarily reflecting differences in how individuals might be exposed in a population. In the assessment for the review completed in 1994, a total of 420 cohorts were used to estimate population exposure based on selected demographic information (11 groups using age, gender, work status), residential location, work location, and presence of indoor gas stoves (Johnson, et al., 1992; USEPA, 1992).

19 The use of pNEM in the prior review also 1) relied on a limited set of activity pattern data (approximately 3,600 person
- days), 2 ) used four broadly defined categories to estimate breathing rates, and 3 ) implemented a geodesic distance range methodology to approximate wo rkplace commutes (Johnson et al., 1992; US EPA, 1992). Each of these approaches used by pNEM, while appropriate given the data available at that time, would tend to limit the ability to accurately model expected variability in the population exposure and dose distributions.

20 APEX4.3 includes new algorithms to 1) simulate longitudinal activity sequences and exposure profiles for individuals, 2) estimate activity
- specific minute
- by
- minute oxygen consumption and breathing rates, 3) address spatial variability in home and work
- tract ambient concentrations for commuters, and 4) estimate event
- based microenvironmental concentrations (PA, section 2.2.2)
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Page **32** of **166** As used in the current assessment, APEX probabilistically generate s a sample of hy pothetical individuals from an actual population database and simulate s each individual’s movements through time and space (e .g., indoors at home, inside vehicles) to estimate his or her exposure to ambient CO (REA, chapter 4). Based on exposure concentrations, minute
- by
- minute activity levels, and phy siological characteristics of the simulated individuals (see REA, chapters 4 and 5), APEX estimate s the level of COHb in the blood for each individual at the end of each hour based on a nonlinear solution to the Coburn
- Forster - Kane equation (REA, section 4.4.7). As discussed in section II. A.2.b above, people with cardiovascular disease are the population of primary

focus in this review , and , more specifically , coronary artery disease, also known as coronary heart disease , is the “most important susceptibility characteristic for increased risk due to CO exposure” (I SA, p. 2
- 11). Controlled human exposure studies have provided quantitative COHb dose
- response information for this specific population with regard to effects on markers of m yocardial ischemia. Accordingl y, based on the current evidence with regard to quantitative information of COHb levels and association with specific health effects, the at
- risk populations simulated in the quantitative assessment were (1) adul ts with CHD (also known as IHD or CAD), both diagnosed and undiagnosed, and (2) adults with any heart diseases, including undiagnosed ischemia. 21 Evidence characterizing the nature of specific health effects of CO in other popul ations is limited and does not include specific COHb levels related to health effects in those groups. As a result, the quantitative assessment does not develop separate quantitative dose estimates for populations other than those with C H D

21 As described in section1.2 above, this is the same population group that was the focus of the CO NAAQS exp osure/dose assessments conducted previously (e.g., USEPA, 1992; Johnson et al., 2000)
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Page **33** of **166** or HD. APEX s imulations performed for this review focused on exposures to ambient CO occurring in eight microenvironments, 22 absent an y contribution to microenvironment concentrations from indoor (nonambient) CO sources
. Previous assessments, that have included modelin g simulations both with and without certain indoor sources, indicated that the impact of such sources can be substantial with regard to the portion of the at
- risk population experiencing higher exposures and COHb levels (Johnson et al., 2000). While we ar e limited with regard to information regarding CO emissions from indoor sources today and how they

may differ from the time of the 2000 assessment, we note that ambient contributions have notably declined, and indoor source contributions from some sources may

also have declined. Thus, as indicated in the Policy Assessment, we have no firm basis to conclude a different role for indoor sources today with regard to contribution to population CO exposure and COHb levels. In considering the REA dose estimates i n the Policy Assessment, staff considered estimates of the portion of the simulated at
- risk populations estimated to experience dail y maximum end
- of

- hour abs olute COHb levels above identified benchmark levels (at least once and on multiple occasions), as w ell as estimates of the percentage of population person - day s (the onl y metric available from the modeling for the 1994 review) , and also population estimates of daily maximum ambient contribution to end
- of
- hour COHb

22 The 8 microenvironments modeled in the REA comprised a range of indoor and outdoor locations including residences as well as motor vehicle
- related locations such as inside vehicles, and public parking and fueling facilities, where the highest exposures were estimated (REA, sections 5.9 and 6.1).*** E.O. 12866 Review

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Page **34** of **166** levels. 23 In identifying COHb benchmark levels of interest, primary attention was given to the multi
- laboratory

study in which COHb was anal yz ed b y the more accurate GC method (Allred et al., 1989a, 1989b, 1991) discussed in section II. A .2 .c above. As summarized in the proposal , the Policy Asse ssment recognized distinctions between the REA “baseline” (arising from prior ambient exposure and endogenous CO production) and the pre
- exposure COHb levels in the controlled human exposure study (arising from ambient and nonambient exposure history , as w ell as from endog enous CO production), and also noted the impact of “baseline” COHb levels on COHb levels occurring in response to short ambient CO exposure events such as those simulated in the REA. Numerous improvements have been made over the last decade that have reduced the uncertainties associated with the models used to estimate COHb levels resulting from ambient CO exposures under different air quality conditions, including those associated with just meeting the current CO NAAQS (REA, section 4.3). This progression in exposure model development has led to the model currentl y used b y the a gency (APEX4.3), which has an enhanced capacity to estimate population CO exposures and more accuratel y predicts COHb levels in persons exposed to CO. Our application of APEX4.3 in this review, using updated data and new algorithms to estimate exposures and doses experienced by individuals, better represents the variability in population exposure and COHb dose levels than the model version used in previous CO

23 As summarized in the proposal and described more fully in the REA and PA, absolute COHb refers to the REA estimates of CO Hb levels resulting from endogenously produced CO and exposure to am bient CO (in the absence of any nonambient sources). The additional REA estimates of ambient CO exposure contribution to COHb levels were calculated by subtracting COHb estimates obtained in the absence of CO exposure
- i.e., that due to endogenous CO production alone (see REA, Appendix B.6)
- from the corresponding end
- of
- hour absolute COHb estimates for each simulated individual. Thus, the REA reports estimates of the maximum end
- of
- hour am bient contributions across the simulated year, in addition to the maximum absolute end
- of hour COHb levels.*** E.O. 12866 Review

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Page **35** of **166** assessments. 24 However, while APEX 4.3 is greatly improved when compared with previously

used exposure models, its application is still limited with regard to data to inform our understanding of spati al relationships in ambient CO concentrations and within microenvironments of particular interest. Further information regarding model improvements and exposure modeling uncertainties is summarized in section 2.2.2 of the Policy Assessment and described i n detail in chapter 7 of the REA
. Taking into consideration improvements in the model algorithms and data since the last review, and having identified and characterized these uncertainties, the Policy Assessment concludes that the estimates associated with the current anal ys is, at a minimum, better reflect the full distribution of exposures and dose as compared to results from the 1992 anal ys is. As noted in the Policy Assessment , however, potentially greater uncertaint y remain s in our characterization of the upper and lower percentiles of the distribution of population exposures and COHb dose levels relative to that of other portions of the respective distribution. When considering the overall quality of the current exposure modeling approach, the algorithms, and the input data used, alongside the identified limitations and uncertainties, the REA and Policy Assessment conclude that the quantitative assessment provides reasonable estimates of CO exposure and COHb dose for the simulated population the assess ment is intended to represent (i.e., the population residing within the urban core of each study area). The Policy

Assessment a dditionally

note s the impact on the REA dose estimates for ambient CO contribution to COHb of the lack of nonambient sources in the model simulations. This aspect of the assessment design may

contribute to higher estimates of the contribution of short
-
24 APEX4.3 provides estimates for percent of population projected to experience a single or multiple occurrences of a daily maximum COHb level above the various benchmark levels, as well as percent of person
- days.*** E.O. 12866 Review

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Page **36** of **166** duration ambient CO exposures to total COHb than would result from simulations that include the range of commonly encountered CO so urces beyond just those contributing to ambient air CO concentrations. Although the specific quantitative impact of this on estimates of population percentages discussed in this document is unknown, consideration of COHb estimates from the 2000 assessment indicates a potential for the inclusion of nonambient sources to appreciabl y affect absolute COHb (REA, section 6.3) and accordingly

implies the potential, where present, for an impact on overall ambient contribution to a person’s COHb level. Key results of the exposure and dose anal ys es were presented in the Policy Assessment and summarized in the proposal (Tables 1 and 2 of the proposal). B. Adequacy of the Current Primary Standards In considering the evidence and quantitative exposure and dose estimates with regard to judgments on the adequacy afforded by

the current standards , the final decision is largely a public health policy

judgment. A final decision must draw upon scientific information and anal ys es about health effects and risks, as well as j udgments about how to consider the range and magnitude of uncertainties that are inherent in the scientific evidence and analy ses. Our approach to informing these judgments is based on the recognition that the available health effects evidence generall y r eflects a continuum, consisting of ambient levels at which scientists generall y agree that health effects are likely to occur, through lower levels at which the likelihood and magnitude of the response become increasingl y uncertain. This approach is consi stent with the requirements of the NAAQS provisions of the Act and with how EPA and the courts have historically

interpreted the Act. These provisions require the Administrator to establish*** E.O. 12866 Review

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Page **37** of **166** primary standards that, in the Administrator’s judgment, are requisite to protect public health with an adequate margin of safety . In so doing, the Administrator seeks to establish standards that are neither more nor less stringent than necessary for this purpose. The Act does not require that primary standards be set at a zero - risk level, but rather at a level that avoids unacceptable risks to public health , including the health of sensitive groups. 25 In evaluating whether it is appropriate to revise the current CO standards, the Administrator ’s considerations build on the general approach used in the last review and reflect the broader body of evidence and information now available. The approach used is based on an integration of information on health effects associated with exposure to ambient CO; expert jud gment on the adversity of such effects on individuals; and policy judgments as to when the standards are requisite to protect public health with an adequate margin of safety , which are informed by air quality

and related anal ys es, quantitative e xposure and risk assessments when possible, and qualitative assessment of impacts that could not be quantified. The Administrator has taken into account both evidence
- based and quantitative exposure
- and risk
- based considerations in developing conclusions on the adequacy

of the current primary

CO standards. The Administrator’s proposed conclusions on the adequacy of the current primary standards are summarized below (section II.B.1), followed by consideration of comments

25 The sensitive population groups identified in a NAAQS review may (or may not) be comprised of low income or minority groups. Where low income/minority groups are among the sensitive groups, the rulemaking decision will be based on providing protection for these and other sensitive population groups. To the extent that low income/minority groups are not among the sensitive groups, a decision based on providing protection of the sensiti ve groups would be expected to provide protection for the low income/minority groups (as well as any other less sensitive population groups).*** E.O. 12866 Review

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Page **38** of **166** received on the proposal (section I I. B.2) and the Administrator’s final decision with regard to the adequacy of the current primary standard s (II.B.3). 1 . Rationale for Proposed Decision At the time of the proposal, in considering the adequacy of the current standards, the Administrator carefully consider ed the available evidence and conclusions contained in the Integrated Science Assessment; the information, exposure/dose assessment, rationale and conclusions presented in the Policy Assessment; the advice and recommendations from CASAC; an d public comments as of that date. In so doing , the Administrator noted the following: (1) the long
- standing evidence base concerning effects associated with exposure to CO, including the key role played by

hy poxia (reduced ox ygen availability) induced b y increased COHb blood levels, and the use of COHb as the bioindicator and dose metric for evaluating CO exposure and the potential for health effects; (2) the strong evidence of cardiovascular effects of short
- term CO exposures including the evidence from controlled human exposure studies that demonstrate a reduction in time to onset of exercise
- induced markers of myocardial ischemia in response to increased COHb, and the health significance of responses observed at the 2% COHb level induced b y 1
- hour CO e xposure, as compared to higher COHb levels; and (3) the identification of people with cardiovascular disease as a key population at risk from short
- term ambient CO exposures. In the proposal, as at the time of the last review, the Administrator additional ly considered and took particular note of the exposure and dose modeling results, recognizing key limitations and uncertainties, and in light of judgments noted above regarding the health significance of findings from the controlled human exposure studies, placing less weight on the health significance of*** E.O. 12866 Review

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Page **39** of **166** infrequent or rare occurrences of COHb levels at or just above 2% and more weight to the significance of repeated such occurrences, as well as occurrences of higher COHb levels. The Administrator also co nsider ed the newly available and much
- expanded epidemiological evidence, including the complexity associated with quantitative interpretation of these studies with regard to CO , particularl y the few studies available in areas where the current standards ar e met. Further, the Administrator considered the advice of CASAC, including their overall agreement with the Policy Assessment conclusion that the current evidence and quantitative exposure and dose estimates provide support for retaining the current standard s , their view that , in light of the epidemiological studies, revisions to lower the standards should be considered and their preference for a lower standard , and also their advice regarding the compl ications associated with interpreting the epidemiological studies for CO. A lthough CASAC expressed a preference for a lower standard, CASAC also indicated that the current evidence provides support for retaining the current suite of standards and CASAC’s recommen dations appear to recognize that their preference for a lower standard was contingent on a judgment as to the weight to be placed on the epidemiological evidence. For the reasons explained in the proposal , after full consideration of CASAC’s advice and th e epidemiological evidence, as well as its associated uncertainties and limitations, the Administrator proposed to judge those uncertainties and limitations to be too great for the epidemiological evidence to provide a basis for revising the current standards. Taking all these considerations together, the Administrator propos ed to conclude that the current suite of standard s provide s a very high degree of protection for the COHb levels and associated health effects of concern, as indicated b y the extremely low*** E.O. 12866 Review

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Page **40** of **166** estimates of occurrences, and provides slightl y less but a still high degree of protection for the effects associated with lower COHb levels, the phy siological significance of which is less clear. T he Administrator additionally propose d to c onclude that consideration of the epidemiological studies does not lead her to identify a need for an y greater protection. Thus, the Administrator propose d to conclude that the current suite of standards provides an adequate margin of safety against adver se effects associated with short
- term ambient CO exposures. For these and all of the reasons discussed above, and recognizing the CASAC conclusion that, overall, the current evidence and REA results provide support for retaining the current standard s , the Administrator propose d to conclude that the current suite of primary CO standards is requisite to protect public health with an adequate margin of safety from effects of ambient CO. 2 . Comments on Adequacy In considering comments on the adequacy of the current standards, the Administrator first notes the advice and recommendations from CASAC. In the context of CASAC’s review of the documents prepared during the course of the review, CASAC sent EPA five letters providing advice regarding assessment and interpretation of the available scientific evidence and the REA for the purposes of judging the adequacy of the current CO standards (Brain and Samet, 200 9 ; Brain and Samet, 2010a; Brain and Samet, 20 10b; Brain and Samet, 2010c; Brain and Samet, 2010d)
. In conveying comments on the draft Policy

Assessment, CASAC agreed with the conclusion that the current evidence provides support for retaining the current suite of standards , while they also express ed a p reference for a lower standard and stat ed that the epidemiological evidence could indicate the occurrence of adverse health effects at levels of the standards (Brain*** E.O. 12866 Review

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Page **41** of **166** and Samet, 2010 c )
. With regard to the interpretation of epidemiological studies on CO , CASAC’s collective advice included recommendations regarding the weight to be placed on the epidemiological evidence (Brain and Samet, 2010 c ) , as well as cautionary statements regarding interpretation of the epidemiological studies . Such statements included the observation that “[d] istinguishing the effects of CO per se from the consequences of CO as a marker of pollution or vehicular traffic is a challenge , which [the I SA] needs to confront as thoroughl y as possible ” (Brain and Samet, 2009 , p. 2 )
. In another letter CASAC further cautioned ( Brain and Samet, 2010 d , p. 2 ) : The problem of co
-

pollutants serving as potential confounders is particularly problematic for CO. Since exposure levels for CO are now low, consideration needs to be given to the possibility that in some situations CO may be a surrogate for exposure to a mix of pollutants generated by fossil fuel combustion. A better understanding of the possible role of co
-

pollutants is relevant to regulation and to the design, analysis, and interpre tation of epidemiologic studies on the health effects of CO. CASAC additionally noted concerns regarding the spatial coverage of the existing CO monitoring network and the sensitivity of deplo ye d monitors (Brain and Samet, 20 09 ; Brain and Samet, 2010 a ; Brain and Samet, 20 10b; Brain and Samet, 2010d). On a related note, they cautioned that “[u]nderstanding th e extent of exposure measurement error is critical for evaluating epidemiological evidence” (Brain and Samet, 2009). General comments from the publ ic based on relevant factors that either support o r oppose retention of the current primary CO standards are addressed in this section. Other specific public comments related to consideration of the adequacy of the current standards, as well as general co mments based on implementation
- related factors that are not a permissible basis for considering the need to revise th e current standards , are addressed in the Response to Comments document.*** E.O. 12866 Review

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Page **42** of **166** The public comments received on the proposal were divided with reg ard to support for the Agency ’s proposed conclusion as to the adequacy of the current standards. All of the state and local environmental agencies or governments that provided comments on the standards concurred with EPA’s proposed conclusions as did the three industry commenters. All of these commenters generally noted their agreement with the rationale provided in the proposal, with some additionally citing CASAC’s recognition of support in the evidence for the adequacy of the current standards. Some o f these commenters noted agreement with the weight given to the epidemiological studies in the proposal and also noted the little change in exposure/risk estimates since the time of the last review. One commenter additionally stated their view that the RE A overstates the exposure and risk associated with the current standards. As described in section II.B.3 below, the EPA generall y agrees with these commenters regarding the adequacy of the current CO standards and with CASAC that the evidence provides supp ort for the conclusion that the current CO standards protect public health with an adequate margin of safety. EPA additionally has given consideration to CASAC’s advice regarding interpretation of epidemiological evidence for CO, recognizing the limitatio ns associated with its use in drawing quantitative interpretations regarding levels of ambient CO related to health outcomes. Two submissions recommending revision of the standards were received from national environmental or public health organizations . Additional submissions recommending revision were received from a private consultant ; a group of scientists, phy sicians, and others ; and a group of private citizens. In support of their position, these commenters variousl y cited CASAC comments regarding emphasis to give*** E.O. 12866 Review

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Page **43** of **166** epidemiological studies and CASAC’s stated preference for a lower standard. These submissions generally disagreed with EPA’s consideration of the epidemiological evidence in the proposal and recommended that EPA give greater emphasis to epidemiological studies of a range of endpoints, including developmental and respiratory effects, based on the commenters’ view that the epidemiological studies provided evidence of harm associated with ambient CO levels belo w the current standards and inadequate protection for sensitive populations. Among these submissions, those that specified levels for revised standards recommended levels that were no higher than the lowest part of the range s for the two standards that we re identified for consideration in the Policy

Assessment and the example options that CASAC suggested for inclusion in the Policy

Assessment
. Additionally , o ne commenter described the view that the CO standards should be revised to levels at or below the range of CO concentrations in exhaled breath of health y non - smokers. EPA generall y disagrees with these commenters regarding conclusions that can be drawn from the evidence, including the epidemiological studies, pertain ing to the adequacy of the current CO standards. In considering the adequacy of the current standards, i t is important to consider both the extent to which the evidence supports a causal relationship between ambient CO exposures and adverse health effects , as well as the extent to which there is evidence pertinent to such effects under air quality conditions in which the current standards are met. With regard to the latter point, and focus ing on the epidemiological evidence , it is the studies involving air quality conditions in which the current standards were met that are most informative in evaluating the adequacy of the standards (PA, p. 2
- 30). We note that very few of the epi demiological studies*** E.O. 12866 Review

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Page **44** of **166** observing an association of cardiovascular disease
- related outcomes with short
- term CO concentrations (or those observing associations for other health effects) were conducted in areas that met the current standards throughout the peri od of study , thus limiting their usefulness with regard to judging the adequacy of the current standards (PA, p. 2
- 36)
. Further, as CASAC has cautioned, “the problem of co
- pollutants serving as potential confounders is particularl y problematic for CO” (Brain and Samet , 20 10d). While some CO epidemiological studies have applied the commonly used statistical method, two
- pollutant regression models, to inform conclusions regarding CO as the pollutant eliciting the effects in these studies, and while, in some studies, the CO associations remain robust after adjustment for another traffic combustion
- related pollutant, such as PM 2.5 or NO 2 (PA, pp. 2
- 36 to 2
- 37), the potential exists for there to be etiologicall y relevant pollutants that are correlated with CO yet absent from the anal ys is, particularl y given the many pollutants associated with fossil fuel combustion. The CASAC specifically

recognized this potential in stating that “consideration needs to be given to the possibility

that in some situations CO may be a surrogate for exposure to a mix of pollutants generated by fossil fuel combustion” and “a better understanding of the possible role of co
- pollutants is relevant to ... the interpretation of epidemiologic studies on the health effects of CO” (Brain and Samet, 2010d). In light of these issues related to potential confounding b y co - pollutants in the case of CO , uncertainty

related to exposure error for CO is of particular concern in quantitatively

interpreting the epidemiological evidence (e.g., with regard to ambient*** E.O. 12866 Review

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Page **45** of **166** concentrations contribut ing to health outcomes )
. 26 As noted above, CASAC cautioned the Agency

on the importance of understanding the extent of exposure error in evaluating the epidemiological evidence for CO (Brain and Samet, 2009). T here are two aspects to the epidemiological studies in the specific case of CO (as contrasted with other pollutant s such as PM and NO 2 ) that may contribute exposure error in the studies (PA, pp.2
- 34 to 2
- 38; 76 FR 8177
- 8178)
. The first relates to the uncertainty associated with quantitative interpretation of the epidemiological study results at low ambient concentrations in light of the sizeable portion of ambient CO measurements that are at or below monitor method detection limits (MDL s). As described in the proposal, uncertaint y related to the prevalence of ambient CO monitor concentrations at or below MDLs is a greater concern for the more recently

available epidemiological studies in which the study areas have
much reduced ambient CO concentrations compared with those in the past (PA, pp. 2
- 37 to 2
- 38). This complicates our interpretation of specific ambient CO concentrations associated with health effects (ISA, p. 3
- 91; Brain and Samet, 2010d) , providing us with reduced confidence in quantitative interpretations of epidemiological studies for CO
. Additionally , as described in the proposal, there is uncertainty and potential error associated with exposure estimates in the CO epidemiological studies that relate t o the use of area
- wide or central
- site monitor CO concentrations in light of information about the steep gradient in CO concentrations with distance from source locations such as

26 In contrasting the strength of the epidemiological evidence available for the 2000 AQCD with that in the current revie w, the ISA notes that uncertainties identified in 2000 remain, including the ability of community fixed
- site monitors to represent spatially variable ambient CO concentrations and personal exposures; the small expected increase in COHb due to ambient CO concentrations; the lack of biological plausibility for health effects to occur at such COHb levels, even in diseased individuals; and the possibility that ambient CO is serving as a surrogate for a mixture of combustion
- related pollutants. These uncertainties complicate the quantitative interpretation of the epidemiologic findings, “particularly regarding the biological plausibility of health effects occurring at COHb levels resulting from exposures to am bient CO concentrations measured at AQS monitors” (ISA, pp. 2
- 16 to 2
- 17).*** E.O. 12866 Review

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Page **46** of **166** highl y - trafficked roadway s (I SA, section 3.5.1.3). As a result of difference s in factors related to pollutant formation, this gradient is steeper for CO than for other traffic combustion
- related pollutants, such as PM 2.5 and NO 2 , contributing to a greater potential for exposure misclassification in the case of CO by the reliance o n central site monitors in the CO epidemiological studies. Thus, as noted in the proposal, we recognize that the expanded body

of epidemiological evidence available in this review includes its own set of uncertainties which complicates its interpretation, particularl y with regard to ambient concentrations that may

be eliciting health outcomes. In our integrated assessment across all t ypes of evidence in the ISA for this review, we conclude that a causal relationship is likely to exist for short
- term exposures to ambient concentrations of CO and cardiovascular morbidity . In reaching this conclusion, the I SA notes that the most compelling evidence comes from the controlled human exposure studies (ISA, p. 2
- 5), which also document a significant dose
- response relationship over a range of COHb concentrations relevant to consideration of the NAAQS (ISA, p. 2
- 13). In considering the epidemiological evidence for relevant cardiovascular outcomes, which includes multiple studies reporting associations with ambient C O concentrations under conditions when the current standards were not met (PA, p. 2
- 30), the ISA notes that these studies are coherent with the findings from the controlled human exposure studies (ISA, p. 2
- 17)
. However, as summarized here , various aspects of the evidence complicate quantitative interpretation of it with regard to ambient concentrations that might be eliciting the reported health outcomes. An additional complication to our consideration of the CO epidemiological evidence is that, i n contrast to the health effects evidence for all other criteria pollutants,*** E.O. 12866 Review

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Page **47** of **166** the epidemiological studies for CO use a different exposure/dose metric from that which i s the focus of the broader health evidence base, and additional information that might be used to bridge this gap is lacking. In the case of CO, the epidemiological studies use air concentration as the exposure/dose metric, while much of the broader health effects evidence for CO , and particularly that related to cardiovascular effects, demons trates and focuses on an internal biomarker of CO exposure (COHb) which has been considered a critical key

to CO toxicity
. 27 The strong evidence describing the role of COHb in CO toxicity is important to consider in interpreting the CO epidemiological stud ies and contributes to the biological plausibility of the ischemia
- related health outcomes that have been associated with ambient CO concentrations. Yet, we do not have information on the COHb levels of epidemiological study subjects that we can evaluate in the context of the COHb levels eliciting health effects in the controlled human exposure studies. Further, we lack additional information on the CO exposures of the epidemiological study subjects to both ambient and nonambient sources of CO that might be used to estimate their COHb levels and bridge the gap between the two study t ypes. Additionally the I SA recognizes that the changes in COHb that would likely be associated with exposure to the low ambient CO concentrations assessed in some of the epide miological studies would be smaller than changes associated with “substantially reduced [ oxygen ] delivery to tissues,” that might plausibly lead to the outcomes observed in those studies,

27 In the case of the only other criteria pollutant for which the health evidence relies on an internal dose metric

– lead
- the epidemiological studies also use that metric. For lead ( Pb ) , in contrast to CO, the epid emiological evidence is focused on associations of Pb
- related health effects with measurements of Pb in blood, providing a direct linkage between the pollutant, via the internal biomarker of dose, and the health effects. Thus, for Pb, as compared to the c ase for CO, we have less uncertainty in our interpretations of the epidemiological studies with regard to the pollutant responsible for the health effects observed. For other criteria pollutants, including PM and NO2, air concentrations are used as the exposure/dose metric in both the epidemiological studies and the other types of health evidence. Thus, there is no comparable aspect in the PM or NO 2 evidence base.*** E.O. 12866 Review

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Page **48** of **166** with additional investigation needed to determine whether there may be another mechanism of action for CO that contributes to the observed outcomes at low ambient concentrations (I SA, p. 5
- 48). Thus, there are uncertainties associated with the epidemiological evidence that “complicate the quantitative interpretation of the epidemiologic findings, particularl y regarding the biological plausibility of health effects occurring at COHb levels resulting from exposures to the ambient CO concentrations” assessed in these studies (I SA, p. 2
- 17). With regard to health effects other than cardiovascular outcomes, in addition to noting the complications cited above with regard to quantitative interpretation of the epidemiological evidence, we note that the evidence for these other categories of health effects is considered limited and only suggestive of a causal relationship with relevant exposures to CO in ambient air, or inadequate to infer such a relationship, or it supports the conclusion that such a relationship is not likely (see section II.A.2.b above). As described in the proposal sections II.B.2 and II.D.2.a, with regard to categories of health effects or outcomes for which the evidence is considered suggestive, evidence is lacking that might lend biological plausibility to epidemiological study results, and also sufficientl y rule out the role of chance, bias and confounding in the epidemiological associations observed, for outcomes such as developmental or respiratory (ISA, chapters 1 and 2). Thus, EPA disagrees with the commenters’ conclusion that the epidemiological evidence establishes that a range of health effects, including developmental or respiratory effects , are occurring as a result of exposures to CO in ambient air at or below the current standards. We additionally disagree with commenters’ statements that imply EPA has*** E.O. 12866 Review

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Page **49** of **166** inadequatel y considered the evidence with regard to protection of sensitive populations and to the protection provided by the CO standards. As noted in section II.A.2.b above, EPA’s assessment of the current evidence presented in the Integrated Science Assessment concludes that “the most important susceptibility characteristic for increased risk due to CO exposure is [CAD or CHD]” (I SA, p. 2
- 10). Accordingl y, the proposal recognized people with cardiovascular disease as a key population at risk from short
- term ambient CO exposures (proposal, section II.D.4). However, based on assessment of the evidence in the I SA, the proposal and other documents in this review also recognize the potential for susceptibility for several other populations and lifestages, including people with pre
existing diseases that may already have limited oxygen availability to tissues, increased COHb levels or increased endogenous CO production, older adults, and fetuses during critical p hases of development (as summarized in section II.A.2.b above). For these groups and lifestages, the evidence is incomplete with regard to specific CO exposures or COHb levels that may

be associated with health effects in these groups and the nature of th ose effects, as well as a way to relate the specific evidence available for the CAD population to the limited evidence for these other populations. Further, the currentl y available evidence does not indicate a greater susceptibility for an y of the other p opulations or lifestages recognized as potentiall y at risk from exposure to ambient CO. In reaching a decision on the adequacy of the current standards in protecting public health in section II.B.3 below, however, the Administrator has considered EPA’s co nclusions with regard to the effects likely to be causall y associated with exposure to ambient CO and population groups particularl y at risk, as well as those regarding the evidence with regard to the potential for other effects and sensitive groups, and the associated*** E.O. 12866 Review

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Page **50** of **166** uncertaint y. In so doing, as indicated below, the Administrator judges the current standard s to provide the requisite protect ion for public health , including the health of sensitive populations , with an adequate margin of safety . 3. Conclusions Concerning Adequacy of the Primary Standards Having carefull y considered the public comments, as discussed above, the Administrator believes that the fundamental scientific conclusions on the ef fects of CO in ambient air reached in the Integrated Science Assessment and Policy Assessment, summarized in sections II.B and II.D of the proposal remain valid. Additionally , the Administrator believes the judgments she reached in the proposal (section I I. D.4) with regard to consideration of the evidence and quantitative exposure/dose assessments and advice from CASAC remain appropriate. Thus, as described below, the Administrator concludes that the current primary standards provide the requisite protect ion of public health with an adequate margin of safety and should be retained. 28 In considering the adequacy of the current suite of primary CO standards, the Administrator has carefully considered the available evidence and conclusions contained in the Integrated Science Assessment; the information, exposure/dose assessment, rationale and conclusions presented in the Policy Assessment; the advice and recommendations from CASAC; and public c omments. The Administrator places primary consideration on the e vidence obtained from controlled human exposure studies that demonstrates a reduction in time to onset of exercise
- induced markers of myocardial ischemia in response to increased COHb resulting from short
- term CO exposures, and

28 As explained below

in section IV.A, EPA is re promulgat ing the F ederal Re ference M ethod (FRM) for CO, as set forth in Appendix C of 40 CFR part 50. Consistent with EPA’s decision to retain the standards, the recodification clarifies and updates the text of the FRM, but does not make substantive changes to it.*** E.O. 12866 Review

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Page **51** of **166** recognizes the greater signi ficance accorded both to larger reductions in time to myocardial ischemia and to more frequent occurrences of m yocardial ischemia. As at the time of the review completed in 1994, the Administrator also takes note of the results for the modeling of exposur es to ambient CO under conditions simulated to just meet the current, controlling, 8
- hour standard in two study areas, as described in the REA and Policy Assessment, and the public health significance of those results. She also considers the newl y availab le and much
- expanded epidemiological evidence, including the complexity

associated with quantitative interpretation of these studies, particularl y the few studies available in areas where the current standards are met. In so doing, she notes that i n consi dering the adequacy of the current standards, it is important to consider both the extent to which the evidence supports a causal relationship between ambient CO exposures and adverse health effects , as well as the extent to which there is evidence pertine nt to such effects under air quality conditions in which the current standards are met. Further, the Administrator considers the advice of CASAC, including both their overall agreement with the Policy Assessment conclusion that the current evidence and qu antitative exposure and dose estimates provide support for retaining the current standard s , as well as their view that in light of the epidemiological studies, revisions to lower the standards should be considered and their preference for a lower s tandard. As an initial matter, the Administrator places weight on the long
- standing evidence base that has established key aspects of CO toxicity

that are relevant to this review as they

were to the review completed in 1994. These aspects include the key role played by hy poxia (reduced oxygen availability) induced by increased COHb blood levels, the identification of people with cardiovascular disease as a key population at risk*** E.O. 12866 Review

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Page **52** of **166** from short
- term ambient CO exposures, and the use of COHb as the bioindicator and dose metric for evaluating CO exposure and the potential for health effects. The Administrator also recognizes the Integrated Science Assessment’s conclusion that a causal relationship is likely to exist between relevant short
- term exposures to CO and cardiovascular morbidity. In placing weight on the controlled human exposure studies, the Administrator also recognizes the uncertain health significance associated with the smaller responses to the lowest COHb level assessed in the study given primary consideration in this review (Allred et al., 1989a, 1989b, 1991) and with single occurrences of such responses. In the study by Allred et al. (1989a, 1989b, 1991), a 4
- 5% reduction in time (approximately 30 seconds) to the onset of exercise
- induced marker s of myocardial ischemia was associated with the 2% COHb level induced b y 1
- hour CO exposure. In considering the significance of the magnitude of the time decrement to onset of myocardial ischemia observed at the 2% COHb level induced b y short
- term CO exp osure, as well as the potential for myocardial ischemia to lead to more adverse outcomes, the EPA generall y places less weight on the health significance associated with infrequent or rare occurrences of COHb levels at or just above 2% as compared to that associated with repeated occurrences and occurrences of appreciably higher COHb levels in response to short
- term CO exposures. For example, at the 4% COHb level, the study by Allred et al., (1989a, 1989b, 1991) observed a 7
- 12% reduction in time to the on set of exercise
induced markers of m yocardial ischemia. The Administrator places more weight on this greater reduction in time to onset of exercise
- induced markers compared to the reduction in time to onset at 2% COHb. The Administrator also notes that at the time of the 1994*** E.O. 12866 Review

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Page **53** of **166** review, an intermediate level of approximately 3% COHb was identified as a level at which adverse effects had been demonstrated in persons with angina. Now, as at the time of the 1994 review, the Administrator primarily considers th e 2% COHb level, resulting from 1
- hour CO exposure , in the context of a margin of safet y against effects of concern that have been associated with higher COHb levels, such as 3
- 4% COHb. The Administrator additionally takes note of the now much
- expanded ev idence base of epidemiological studies, including the multiple studies that observe positive associations between cardiovascular outcomes and short
- term ambient CO concentrations across a range of CO concentrations, including conditions above as well as be low the current NAAQS. She notes particularl y the Integrated Science Assessment conclusion that the finding s of CO
- associated cardiovascular effects in these studies are logically coherent with the larger, long
- standing health effects evidence base for CO and the conclusions drawn from it regarding cardiovascular disease
- related susceptibility . In further considering the epidemiological evidence base with regard to the extent to which it provides support for conclusions regarding adequacy of the current s tandards, the Administrator takes note of CASAC’s conclusions that “[i]f the epidemiological evidence is given additional weight, the conclusion could be drawn that health effects are occurring at levels below the current standard, which would support the tightening of the current standard” (Brain and Samet, 2010c). Additionally, the Administrator places weight on the final Policy

Assessment consideration of aspects that complicate quantitative interpretation of the epidemiological studies with regard to ambient concentrations that might be eliciting the reported health outcomes.*** E.O. 12866 Review

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Page **54** of **166** For purposes of evaluating the adequacy of the current standards, the Administrator takes note of the multiple complicating features of the epidemiological evidence base, as desc ribed in more detail in the final Policy Assessment and in section II.D.2.a of the proposal. First, while a number of studies observed positive associations of cardiovascular disease
- related outcomes with short
- term CO concentrations, very few of these studies were conducted in areas that met the current standards throughout the period of study. Additionally , in CASAC ’s advice regarding interpretation of the currentl y available evidence , they stated that “[t]he problem of co
- pollutants serving as potentia l confounders is particularl y problematic for CO” and that given the currently low ambient CO levels, there is a possibility that CO is acting as a surrogate for a mix of pollutants generated b y fossil fuel combustion. The CASAC further stated that “[a] better understanding of the possible role of co
- pollutants is relevant to regulation” (Brain and Samet, 2010d). As described in the Policy Assessment and summarized in section II.B.2 above , there are also uncertainties related to representation of ambient CO exposures given the steep concentration gradient near roadway s, as well as the prevalence of measurements below the MDL across the database. The CASAC additionally indicated the need to consider the potential for confounding effects of indoor sources of CO (Brain and Samet, 2010c) . As discussed in section II.D.2.a of the proposal, the interpretation of epidemiological studies for CO is further complicated because, in contrast to the situation for all other criteria pollutants, the epidemiological stud ies for CO use an exposure/dose metric (air concentration) that differs from the metric commonly used in the other key CO health studies (COHb).*** E.O. 12866 Review

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Page **55** of **166** The Administrator notes that a lthough CASAC expressed a preference for a lower standard, CASAC also indicated that the current evidence provides support for retaining the current suite of standards. CASAC’s recommendations appear to recognize that their preference for a lower standard was contingent on a judgment as to the weight to be placed on the epidemiologi cal evidence. Further, as noted above and summarized in section II.C.2, CASAC has provided a range of advice regarding interpretation of the CO epidemiological studies in light of the associated uncertainties. Accordingly , in consideration of the current evidence with regard to conclusions to be drawn as to the adequacy of the current standards, the Administrator g ive s consideration to the full breadth of CASAC’s advice
. In considering the evidence and quantitative exposure and dose estimates available in this review with regard to the adequacy of public health protection provided by the current primary

standards, the Administrator recognizes that, as noted in section II.B. above, the final decision on such judgments is largel y a public health policy judgm ent, which draws upon scientific information and anal ys es about health effects and risks, as well as judgments about how to consider the range and magnitude of uncertainties that are inherent in the information and anal ys es. These judgments are informed b y the recognition that the available health effects evidence generally reflects a continuum, consisting of ambient levels at which scientists generall y agree that health effects are likely

to occur, through lower levels at which the likelihood and magnitud e of the resp o nse become increasing ly uncertain. Accordingl y, the final decision requires judgment based on an interpretation of the evidence and other information that neither overstates nor understates the strength and limitations of the evidence and information*** E.O. 12866 Review

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Page **56** of **166** nor the appropriate inferences to be drawn. As described in section I.A above, the Act does not require that primary standards be set at a zero
- risk level ; the NAAQS must be sufficient but not more stringent than necessary to protect p ublic health , including the health of sensitive groups, with an adequate margin of safety. In considering the judgments to be made regarding adequacy of the level of protection provided b y the current standards, the Administrator takes particular note of the findings of the exposure and dose assessment in light of considerations discussed above regarding the weight given to different COHb levels and their frequency of occurrence. As described in the proposal, the exposure and dose assessment results indi cate that only

a very small percentage of the at
- risk population is estimated to experience a single occurrence in a year of dail y m aximum COHb at or above 3.0% COHb under conditions just meeting the current 8
- hour standard in the two study areas evaluated , and no multiple occurrences are estimated. The Administrator also notes the results indicating that only a small percentage of the at
- risk populations are estimated to experience a single occurrence of 2% COHb in a year under conditions just meeting the standard, and still fewer are estimated to experience multiple such occurrences. Additionally , consistent with findings of the assessment performed for the review completed in 1994, less than 0.1% of person
- day s for the at
- risk populations were estimated to include occurrences of COHb at or above 2% COHb. Taken together, the Administrator judges the current standard to provide a very high degree of protection for the COHb levels and associated health effects of concern, as indicated b y the extremely low estimates of occurrences, and to provide slightly less but a still high degree of*** E.O. 12866 Review

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Page **57** of **166** protection for the effects associated with lower COHb levels, the ph ys iological significance of which is less clear. In further considering the adequacy of the margin of safet y provided b y the current standards, the Administrator has additionally considered conclusions drawn in the Integrated Science Assessment and Policy Assessment with regard to interpretation of the limited and less certain information concerning a relationship between exposure to relevant levels of ambient CO and health effects in other, potentially , susceptible groups , and with regard to the uncertainties concerning quantitative interpretation of the available epidemiological studies. In so doing, the Administrator additional ly judges the current standards to provide adequate protection against the risk of other health effects for which the evidence is less certain. Further, the Administrator concludes that consideration of the epidemiological studies does not lead her to identify a need for an y greater protection. For these and all of the reasons discussed above, and recognizing the CASAC conclusion that, overall, the current evidence and REA results provide support for retaining the current standard s , the Administrator concludes that the current suite of primary CO standards is requisite to protect public health with an adequate margin of safety from effects of ambient CO. **III. Consideration of a Secondary Standard**  As noted in section I.A. ab ove, section 109(b) of the Clean Air Act requires the Administrator to establish secondary standards that, in the judgment of the Administrator, are requisite to protect the public welfare from any known or anticipated adverse effects associated with the p resence of the pollutant in the ambient air. In so doing, the Administrator seeks to establish standards that are neither more nor less stringent than*** E.O. 12866 Review

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Page **58** of **166** necessary for this purpose. The Act does not require that secondary standards be set to eliminate all risk of adverse welfare effects, but rather at a level requisite to protect public welfare from those effects that are judged b y the Administrator to be adverse. This section presents the rationale for the Administrator’s final decision not to set a s econdary

NAAQS for CO
. Inconsidering the current air quality criteria , evidence of CO
- related welfare effects at or near ambient levels that are unrelated to climate has not been identified
. Accordingl y, in considering whether a secondary standard is requisite to protect the public welfare, the Administrator has primarily considered conclusions based on the evidence of a role for CO in effects on climate. Evaluation of this evidence in the Integrated Science Assessment and staff considerations in the Policy Assessment highlighted the limitations in th is evidence and provided information indicating that this role for atmospheric CO is predominantly indirect, through its role in chemical reacti ons in the atmosphere which result in increased concentrations of pollutants with direct contributions to the greenhouse effect or that deplete stratospheric ozone. Given the evaluation of th e evidence , as well as the views of CASAC , the Administrator con cludes that no secondary

standard should be set at this time because, as in the past reviews, having no standard is requisite to protect public welfare from any known or anticipated adverse effects from ambient CO exposures
. In this section, w e first summarize the evidence currentl y available for welfare effects to inform decisions in this review in section III. A
. Next, the rationale for the proposed conclusions is summarized in section III.B. Public comments and CASAC advice regarding consideration of a secondary standard in this review are summarized in*** E.O. 12866 Review

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Page **59** of **166** section III.C. Lastl y, the Administrator’s final conclusions with regard to a secondary standard for CO are presented in section III. D . A. Introduction In evaluating whether establishment of a secondary standard for CO is appropriate at this time , we adopted an approach in this review that builds upon the general approach used in the last review and reflects the broader body of evidence and information now available. Consideration of the evidence availab le in this review focuses on the following overarching question: Does the currently available scientific information provide support for considering the establishment of a secondary standard for CO? In considering this overarching question, the Policy A ssessment first noted that the extensive literature search performed for the current review did not identify an y evidence of public welfare effects of CO unrelated to climate at or near ambient levels (I SA, section 1.3 and p. 1
- 3). However, ambient CO has been associated with welfare effects related to climate (I SA, section 3.3). Climate
- related effects of CO were considered for the first t ime in the 2000 AQCD and are given somewhat greater focus in the current I SA relative to the 2000 AQCD in reflect ion of comments from CASAC and increased attention to the role of CO in climate forcing (Brain and Samet, 2009; I SA, section 3.3). Based on th e current evidence, the ISA concludes that “a causal relationship exists between current atmospheric concentrations of CO and effects on climate” (ISA, section 2.2). Accordingly, the discussion in the Policy Assessment (summarized in the proposal) focuses on climate
- related effects of CO in addressing the question posed above.*** E.O. 12866 Review

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Page **60** of **166** The currently

available information summarized in the I SA (ISA section, 3.3) does not alter the current well
- established understanding of the role of urban and regional CO in contine ntal and global
- scale chemistry , as outlined in the 2000 AQCD (PA, section 3.2). CO absorbs outgoing thermal infrared radiation very weakl y; thus, the direct contribution of CO itself to climate forcing (or greenhouse warming) is very small (ISA, p. 3
- 11) . Rather, the most significant effects on climate are indirect, resulting from CO’s role as the major atmospheric sink for h ydrox ylradicals. Through this role of CO in global atmospheric chemistry , CO influences the abundance of chemically reactive, maj or greenhouse gases, such as methane and ozone , that contribute directly to the greenhouse effect and of other gases that exert their effect on climate through depletion of stratospheric ozone (ISA, section 3.3 and p. 3
- 11). There is significant uncertainty concerning this effect, and it appears to be highl y variable, with the ISA recognizing that climate effects of changes to emissions of a short
- lived pollutant such as CO are very likely dependent on localized conditions (I SA section 3.3, pp. 3
- 12, 3
- 15, 3
- 16). As noted in the I SA, however, “the indirect [global warming potential] values evaluated and summarized by

[the Intergovernmental Panel on Climate Change] are global and cannot reflect effects of localized emissions or emissions changes” (ISA at p. 3
- 16). Accordingl y, the Policy

Assessment stated that , a s a result of the spatial an d temporal variation in emissions and concentrations of CO and the localized chemical interdependencies that cause the indirect climate effects of CO , it is highl y proble matic to evaluate the indirect effects of CO on climate ( PA , p. 3
- 3 )
. Based upon the information and considerations summarized above, the Policy Assessment conclu ded a s an initial matter that, with respect to non
- climate welfare*** E.O. 12866 Review

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Page **61** of **166** effects, including ecologic al effects and impacts to vegetation, there is no currentl y available scientific information that supports a CO secondary standard (PA, section 3.4). Secondly , with respect to climate
- related effects, the Policy Assessment recognized the evidence of climate forcing effects associated with CO , most predominantly through its participation in chemical reactions in the atmospher e which contribute to increased concentrations of other more direct acting climate
- forcing pollutants (I SA, sections 2.2 and 3.3)
. The PA also not ed, however, that the available information provides no basis for estimating how localized changes in the temporal and spatial patterns of ambient CO likely to occur across the U.S. with (or without) a secondary standard would affect local, regional, or nationwide changes in climate. Moreover, more than half of the indirect forcing effect of CO is attributable to O 3 formation, and welfare
- related effects of O 3 are more appropriatel y considered in the context of the review of the O 3 NAAQS, rather than in this CO NAAQS review (PA, section 3.4). For these reasons, the Policy Assessment concluded that there is insufficient information at this time to support the consideration of a secondary

standard based on CO effects on climate processes (PA, section 3.4). B. Rationale for Proposed Decision In considering a secondary standard for CO, the proposed conclusions presented in the proposal were based on the assessment and integrative s ynthesis of the scientific evidence presented in the I SA, buildi ng on the evidence described in the 2000 AQCD, as well as staff consideration of this evidence in the Policy Assessment and CASAC advice. As an initial matter, the proposal conclude d that the currently available scientific information with respect to non
- climate welfare effects, including ecological effects and impacts to vegetation, does not support a CO secondary standard. Secondly , with respect*** E.O. 12866 Review

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Page **62** of **166** to climate
- related effects, the proposal took note of staff considerations in the Policy Assessment and concur

red with staff conclusions that information is insufficient at this time to provide support for a CO secondary standard. Thus, based on consider ation of the evidence, staff considerations in the Policy Assessment, as well as the views of CASAC, the Admin istrator propose d to conclude that no secondary standards should be set at this time because, as in the past reviews, having no standard is requisite to protect public welfare from an y known or anticipated adverse effects from ambient CO exposures. C. Comm ents on Consideration of Secondary Standard In considering the need for a secondary standard, the Administrator first notes the advice and recommendations from CASAC based on their review of two drafts of the Integrated Science Assessment and of the draft Policy Assessment. With regard to consideration of a secondary standard for CO, CASAC noted without objection or disagreement the staff’s conclusions that there is insufficient information to support consideration of a secondary standard at this time (Brain and Samet, 2010c). One public comment generally concerning EPA’s proposed decision on a secondary standard is addressed below. Other more specific public comments related to consideration of a secondary standard are addressed in the Response to Comments document. One comment (joint submission from Center for Biological Diversity and others) stated that due to the global influence of CO on climate, EPA must establish a secondary NAAQS
. The comment provided no information as to what form, level, or other elements of a secondary

standard would be appropriate in light of the substantial uncertainties and regional variation in the indirect effects of CO. Rather, the comment*** E.O. 12866 Review

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Page **63** of **166** asserted that there is “a substantial body of knowledge, a s reviewed in the ISA, regarding CO and climate” and that “uncertainty does not absolve the EPA of the obligation to protect public welfare” (Center for Biological Diversity comments at p . 9 ). As noted by

the commenter, the ISA reviewed the body of knowled ge regarding CO and climate. As discussed above, the IS A concluded that CO has climate
- related effects, that the direct effects of CO are weak , that there are significant uncertainties concerning the indirect climate effects of CO, and that these effects appear to be highl y variable and dependent on localized conditions
. Further, as noted in the Policy Assessment , the spatial an d temporal variation in emissions and concentrations of CO and the localized chemical interdependencies that cause the indirect c limate effects of CO make it highl y problematic to evaluate the indirect effects of CO on climate. In light of the fact that the climate effects of CO are not onl y uncertain but highly variable and dependent on local conditions (e. g. , concentrations of other pollutants), EPA believes that there is not adequate information available to conclude that a secondary standard in the United States is requisite to protect public welfare. The comment points to the estimated global effects of CO on climate, but nowh ere does the comment provide evidence that EPA’s conclusion regarding adequacy of the available information is in error. EPA fully appreciates that the NAAQS are often established on the frontiers of scientific knowledge, and EPA continually assesses sci entific uncertainties in judging what NAAQS are requisite to protect public health and welfare. EPA is not asserting that the fact that there are some uncertainties prevents EPA from setting a standard. Rather, EPA has judged that, in light of both the s ignificant uncertainties and the evidence of the direct effects being weak and the indirect effects being highl y variable and dependent on*** E.O. 12866 Review

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Page **64** of **166** local conditions, particularly in light of CO’s short lifetime , it is not possible to anticipate how any secondary

standard that would limit ambient CO concentrations in the United States would in turn affect climate and thus an y associated welfare effects
. As additionally

discussed in section III.D below, EPA has reviewed the available information and judged the absence of a standard as being requisite to protect public welfare
. D. Conclusions Concerning a Secondary Standard The conclusions presented here are based on the assessment and integrative sy nthesis of the scientific evidence presented in the I SA, building on the evi dence described in the 2000 AQCD, as well as staff consideration of this evidence in the Policy Assessment and CASAC advice , and with consideration of the views of public commenters on the need for a secondary standard
. In considering whether the current ly available scientific information supports setting a secondary

standard for CO, EPA takes note of the ISA and Policy Assessment consideration of the body of available evidence (briefly summarized above in section III. A ). First, EPA concludes that the currently available scientific information with respect to non - climate welfare effects, including ecological effects and impacts to vegetation, does not support the need for a CO secondary standard. Secondly , with respect to climate
- related effects, the EPA takes note of the ISA’s conclusions that there are significant uncertainties concerning the indirect climate effects of CO, and that these effects appear to be highly variable and dependent on localized conditions as well as staff considerations in the Po licy Assessment and concurs with staff conclusions that information is insufficient at this time to support the need for a CO secondary standard.*** E.O. 12866 Review

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Page **65** of **166** More specificall y, as more fully discussed in consideration of public comments in section III.C above, EPA ha s judged that, in light of both the significant uncertainties and the evidence of the direct effects of CO on climate being weak and the indirect effects being highl y variable and dependent on local conditions, particularl y in light of CO’s short lifetime, it is not possible to anticipate how any secondary standard that would limit ambient CO concentrations in the United States would affect climate. Consequently, information that might indicate the need for additional protection from CO environmental effec ts and on which basis EPA might identify a secondary

standard for the purposes of protecting against CO effects on climate processes is not available. Thus, in considering the evidence, staff considerations in the Policy Assessment summarized here, as we ll as the views of CASAC and the public , summarized above, the Administrator conclude s that no secondary standards should be set at this time because, as in the past reviews, having no standard is requisite to protect public welfare from any known or anticipated adverse effects from ambient CO exposures. **IV. Am**  **endments to Ambient Monitoring Requirements**  The EPA is finalizing changes to ambient air CO monitoring methods and the ambient monitoring network design requirements to support the NAAQS for CO discussed above in Section II. Because ambient CO monitoring data are essential to the impl ementation of the NAAQS for CO, EPA is finalizing minimum monitoring requirements for the ambient CO monitoring network. S tate, local, and tribal monitoring agencies (“monitoring agencies”) collect ambient CO monitoring data in accordance with the m onitoring requirements contained in 40 CFR parts 50, 53, and 58
. A. Monitoring Methods*** E.O. 12866 Review

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Page **66** of **166** This section provides background and rationale for the amendments that EPA proposed to the Federal Reference Method (FRM) for CO and to the associated performance specifications for automated CO analy zers. It also discusses the public comments on those proposed amendments and the few minor changes made to them as they are being promulgated today
. The use of FRMs for the collection of air monitoring data provides un iform, reproducible measurements of pollutant concentrations in ambient air. Federal equivalent methods (FEMs) allow for the introduction of new or alternative technologies for the same purpose, provided these methods produce measurements directl y compara ble to the reference methods. EPA has established procedures for determining and designating FRMs and FEMs at 40 CFR part 53. For ambient air monitoring data for CO to be used for determining compliance with the CO NAAQS, such data must be obtained using either an FRM or an FEM, as defined in 40 CFR parts 50 and 53. All CO monitoring methods in use currently by s tate and local monitoring agencies are EPA
- designated FRM anal yz ers. No FEM anal yz er, i.e. one using an alternative measurement principle, has yet been designated by EPA for CO. These continuous FRM analyzers have been used in monitoring networks for many ye ars and provide CO monitoring data adequate for determining CO NAAQS compliance. The current list of all approved FRMs capable of provi ding ambient CO data for this purpose may be found on the EPA website, http://www.epa.gov/ttn/amtic/files/ambient/criteria/reference
- equivalent
- methods
- list.pdf. Although both the existing CO FRM in 40 CFR part 50 and the FRM and FEM designation requireme nts in p art 53 remain adequate to support the CO NAAQS, EPA*** E.O. 12866 Review

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Page **67** of **166** nevertheless proposed editorial revisions to the CO FRM and both technical and editorial revisions to p art 53, as discussed below. 1. Proposed Changes to Parts 50 and 53 Reference methods for crit eria pollutants are described in several appendices to 40 CFR part 50; the CO FRM is set forth in appendix C. A non
- dispersive infrared photometry

(NDIR) measurement principle is formally prescribed as the basis for the CO FRM. Appendix C describes the t echnical nature of the NDIR measurement principle stipulated for CO FRM analyzers as well as two acceptable calibration procedures for CO FRM anal yz ers. It further requires that an FRM analyzer must meet specific performance, performance testing, and other requirements set forth in 40 CFR part 53. The CO FRM was first promulgated on April 30, 1971 (36 FR 8186), in conjunction with EPA’s establishment (originally as 42 CFR part 410) of the first NAAQS for six pollutants (including CO) as now set forth in 40 CFR part 50. The method was amended in 1982 and 1983 (47 FR 54922; 48 FR 17355) to incorporate minor updates, but no substantive changes in the fundamental NDIR measurement technique have been made since its original promulgation. In connection with th e current review of the NAAQS for CO, EPA reviewed the existing CO FRM to determine if it was still adequate or if improved or more suitable measurement technology has become available to better meet current FRM needs as well as potential future FRM requir ements. EPA determined that no new ambient CO measurement technique has become available that is superior to the NDIR technique specified for the current FRM, and that the existing FRM continues to be well suited for both FRM purposes and for use in routi ne CO monitoring. No substantive changes were*** E.O. 12866 Review

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Page **68** of **166** needed to the basic NDIR FRM measurement principle. Several high quality FRM anal yz er models have been available for many years and continue to be offered and supported by

multiple analyzer manufacturers. How ever, EPA found that the existing CO FRM should be improved and updated to clarify the language of some provisions, to make the format match more closely the format of more recently

promulgated automated FRMs, and to better reflect the design and improved performance of current, commercially available CO FRM analyzers. Accordingl y, EPA proposed appropriate, albeit minor, changes to the FRM. Because these mostly

editorial changes were quite numerous, the entire text of the CO FRM was revised and re
- propose d. In close association with the proposed editorial revision to the CO FRM described above, EPA also proposed to update the performance requirements for CO FRM anal yz ers that are contained in 40 CFR part 53. These requirements were established in the 1970 ’s, based primarily on the NDIR CO measurement technology available at that time. While the fundamental NDIR measurement principle, as implemented in commercial FRM anal yz ers, has changed little over several decades, FRM anal yz er performance has improved markedl y. Contemporary advances in digital electronics, sensor technology , and manufacturing capabilities have permitted today ’s NDIR anal yz ers to exhibit substantially improved measurement performance, reliability , and operational convenience at modest c ost. This improved instrument performance was not reflected in the previous performance requirements for CO FRM anal yz ers specified in 40 CFR part 53, indicating a need for an update to reflect that improved performance.*** E.O. 12866 Review

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Page **69** of **166** The updated performance requireme nts that EPA proposed for CO anal yz ers make them more consistent with the ty pical performance capability available in contemporary

FRM analyzers and will ensure that newly designated FRM anal yz ers will have this improved measurement performance. A review of anal yz er manufacturers’ specifications has determined that all existing CO anal yz er models currently in use in the monitoring network already meet the proposed new requirements (for the standard measurement range). Also in conjunction with this moderni zation of the analyzer performance requirements, EPA proposed new, more stringent performance requirements applicable, on an optional basis, to analyzers that feature one or more lower, more sensitive measurement ranges. Such lower ranges will support imp roved monitoring data quality in areas of low CO concentrations. These updated and new performance requirements are being promulgated as amendments to subpart B of 40 CFR part 53, which prescribes the explicit procedures to be used for testing specified performance aspects of candidate FRM and FEM anal yz ers, along with the minimum performance requirements that such anal yz ers must meet to qualify for FRM or FEM designation. In particular, the new performance requirements appear in table B
- 1 of subpart B of 40 CFR part 53. Although table B
- 1 covers candidate methods for sulfur dioxide (SO 2 ), O 3 , CO, and nitrogen dioxide (NO 2 ), the updates to table B
- 1 that EPA is promulgating today affect only

candidate methods for CO. The updated performance requirements appl y to candidate CO anal yz ers that operate on the specified “standard” measurement range (0 to 50 ppm). This measurement range remains unchanged from the existing requirements as it appropriatel y addresses the monitoring data needed for assessing attai nment. The measurement noise limit is*** E.O. 12866 Review

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Page **70** of **166** reduced from 0.5 to 0.2 ppm, and the lower detectable limit is reduced from 1 to 0.4 ppm. Limits for zero drift and span drift are lowered, respectively, from 1.0 to 0.5 ppm, and from 2.5% to 2.0%. The previously ex isting mid
- span drift limit requirement, tested at 20% of the upper range limit (URL), is withdrawn, as EPA has found that the mid
- span drift requirement was unnecessary for CO instruments because the upper level span drift (tested at 80% of the URL) compl etel y and more accuratel y measures analyzer span drift performance. The lag time limit is reduced from 10 to 2 minutes, and the rise and fall time limits are lowered from 5 to 2 minutes. For precision, EPA is changing the form of the precision limit speci fications from an absolute measure (ppm) to percent (of the URL) for CO analyzers and setting the precision limit at 1 percent tested at both 20% and 80% of the URL . One percent is equivalent to the previous limit value of 0.5 ppm for precision for the st andard (0 to 50 ppm) measurement range. This change in units from ppm to percent makes the requirement responsive to higher and lower measurement ranges (i.e., more demanding for lower ranges). The interference equivalent limit of 1 ppm for each interfere nt is not changed, but EPA is withdrawing the previously existing limit requirement for the total of all interferents. EPA has found that the total interferent limit is unnecessary because modern CO analyzers are subject to only a few interferences, and they tend to be well controlled. The new performance requirements appl y only to newly designated CO FRM or FEM anal yz ers; however, essentially all existing FRM anal yz ers in use today , as noted previously , already m eet these requirements, so existing FRM anal yz ers are not required*** E.O. 12866 Review

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Page **71** of **166** to be re
- tested and re
- designated under the new requirements. All currently designated FRM anal yz ers retain their original FRM designations. EPA also recognized that some CO monitoring objectives (e.g., area
- wide monitoring away from major roads and rural area surveillance) require analyzers with lower, more sensitive measurement ranges than the standard range used for ty pical ambient monitoring. To improve data quality for such lower
- range measurements, EPA is adding a separate set of performance requirements that apply specifically

to lower ranges (i.e., those having a URLof less than 50 ppm) for CO anal yz ers. These additional, lower
- range requirements are listed in the revised table B
- 1. A candidate anal yz er that meets the t able B
- 1 requirements for the standard measurement range (0 to 50 ppm) can optionally

have one or more lower ranges included in its FRM or FEM designation b y further testing to show that it also meets these supplemental, lower
- range requirements. Although no substantive changes were determined to be needed to the test procedures and associated provisions of subpart B for CO, the detailed language in many of the subpart B sections was in need of significant updates, clarifications, refinement, and (in a fe w cases) correction of minor ty pographical errors. These changes to the subpart B text (apart from the changes proposed for table B
- 1 discussed above) are very minor and almost entirely editorial in nature, but quite numerous. Therefore, EPA has revised and is re
- promulgating the entire text of subpart B text. As discussed previousl y, table B
- 1, which sets forth the pollutant
- specific performance limits, is being amended onl y as applicable to CO anal yz ers. EPA amended*** E.O. 12866 Review

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Page **72** of **166** table B
- 1 as applicable to SO 2 metho ds on June 22, 2010 and intends to amend table B
- 1 for O 3 and NO 2 later, if appropriate, when the associated NAAQS are reviewed. 2. Public Comments EPA notes first that CASAC stated that “ more sensitive and precise monitors need to be deployed to measure levels that are less than or equal to 1 ppm .” (Brain and Samet 2010b). Comments from the public on the proposed revisions to CO monitoring methods are addressed in this section or in the Response to Comments document. Comments on the proposed changes to the CO monitoring methodology were received from only one member of the public, the American Petroleum Institute. The commenter was generall y supportive of EPA’s efforts to clarify and update the regulations for the CO FRM and the CO analyzer performance requirements. In regard to the CO FRM (40 CFR part 50, appendix C), the commenter questioned EPA’s proposed relaxation in a flow rate control requirement in the dilution
- method calibration procedure, from 1% to 2%. However, EPA believes that the origina l 1% requirement is unnecessarily stringent, and that this change is appropriate and commensurate with the existing 2% flow rate measurement accuracy and with the overall calibration accuracy needed to obtain adequate data quality with the method. To furth er improve clarity of the FRM calibration section, the commenter also suggested a minor change to Equation 1 and the addition of language indicating that the measurement display

or read
- out device connected to the anal yz er to monitor its reading during cal ibration should be the actual, or at least closely representative of the actual, data recording s ys tem used during field operation of the anal yz er. EPA has accepted*** E.O. 12866 Review

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Page **73** of **166** both of these suggestions, and appropriate changes have been incorporated into the changes being made to the CO FRM in this action. Another comment questioned the proposed withdrawal of the previous total interference limit requirement. In response to this comment, EPA re
- evaluated the efficacy of this limit for CO analyzers and again determin ed that the limit was not necessary , because the number of individual interferences to which FRM (and most potential FEM) CO analyzers are subject is small (only 2 for FRMs), as listed in table B
3 of 40 CFR part 53. Also, response to these interferents i s t ypicall y well controlled in modern CO anal yz ers. In addition, the new, individual interference limit for the lower measurement ranges is one half the limit for the standard range, which further mitigates any need for a separate, total interference limi t. The commenter questioned EPA’s proposed withdrawal of the previousl y existing limit requirement for span drift measured at 20% of the upper range limit (URL), contending that this limit was important because it is closer in concentration to the existing NAAQS than the span drift measured at 80% of the URL. However, the purpose of the span drift limit is not to directly assess measurement error at a particular, mid
- scale concentration level. That purpose is served b y the 1
- point quality control check fo r CO monitors described in section 3.2.1 of appendix A of 40 CFR part 58. Rather, for the purpose of anal yz er performance testing, the linear input/output functional characteristic of the anal yz er is best described b y its zero point and its slope, because these parameters are generally

subject to change (drift) independently . Thus, zero drift (change in the zero point) and span drift (change in the slope) are tested separately . Zero drift is, of course, measured at zero concentration, and span drift is m ost accurately measured at a*** E.O. 12866 Review

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Page **74** of **166** concentration near the URL . The span drift test at 80% URL(when the zero drift is within the specified requirement) more accuratel y determines an y change in the slope parameter then a test at 20% URL . The previously specifie d test at 20% URLthus serves little, if any , purpose in regard to determining change in the slope. Therefore, EPA has concluded that this requirement can be withdrawn. Finally , the commenter was concerned that existing FRM anal yz ers approved under the pr eviously

existing performance requirements may provide data quality

inferior to that of anal yz ers approved under the proposed new requirements and that older anal yz ers may

be unacceptable for some applications that demanded higher performance or higher dat a quality . A “tiered” approach was suggested to handle this situation. In proposing more stringent performance requirements for approval of new FRM and FEM anal yz ers, EPA noted that the performance of anal yz ers approved under the existing performance requ irements was full y adequate for most routine compliance monitoring applications, and that the proposed new requirements were largely to bring the base FRM and FEM performance requirements up to date and more commensurate with the performance of modern comm ercially available CO anal yz ers. EPA further noted that all currently

designated FRM analyzers already meet the proposed new requirements. This means that the quality of routine CO monitoring data currentl y being obtained is already of the higher level p ortended by the proposed new performance requirements. In the proposal, however, EPA did recognize that some special CO monitoring applications do require a higher level of performance than that required for routine applications. Therefore, EPA is promulgating optional, more stringent performance*** E.O. 12866 Review

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Page **75** of **166** requirements for anal yz ers having a more sensitive, “lower range” available for such applications. This is, in fact, a “tiered” approach. Applicants would be able to elect to have such lower ranges approved as part of their FRM or FEM designation. These new, specia l performance requirements will alert monitoring agencies that they should consider low
- range performance of an anal yz er for those applications that may require better low
- level performance, and they can select an anal yz er that has such a lower range appro ved under its FRM (or FEM) designation. 3. Decisions on Methods As discussed above, a few relativel y minor changes have been incorporated into the proposed revised CO FRM in appendix C of part 50, in response to public comments received b y EPA. With th ese changes, the revised appendix C is being promulgated as otherwise proposed. Only one change has been made to the revision proposed for subpart B of part 53, to fix a ty

pographical error that appeared in proposed table B
- 1 concerning reversed entries f

or the span drift limits for the 20% and 80% URL for the CO “lower range” column. Aside from this correction, the revised s ubpart B is being promulgated exactly as proposed. B. Network Design This section on CO network design provides information on the proposed network design, the public comments received on the proposed network design, and the EPA’s conclusions, including rationale and details, on the final changes to the CO network design requirements. 1. Proposed Changes*** E.O. 12866 Review

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Page **76** of **166** The objective of an ambient monitoring network is to 1) provide air pollution data to the general public in a timely manner, 2) support compliance with ambient air quality standards and emissions strategy development, and 3) provide support for air pollution research (40 CFR part 58 , appendix D). The proposed CO network design was intended to directly

support the NAAQS by

requiring monitoring that provides data for use in the designation process and ongoing assessment of air quality . In particular, the proposed network design was i ntended to require a sufficient number of monitors to collect data for compliance purposes in the near
- road environment, where, as noted in section II.A.1 above, the highest ambient CO concentrations generall y occur, particularl y in urban areas (I SA, secti on 3.5.1.3; REA, section 3.1.3). The EPA proposed CO monitoring to be required within a subset of near
- road NO 2 monitoring stations, which are required in 40 CFR part 58, appendix D, section 4.3. Per the preamble to the final rule for the NO 2 NAAQS promulgated on February 9 th , 2010 (75 FR 6474), near
- road NO 2 monitoring stations are intended to be placed in the near
road environment at locations of expected maximum 1
- hour NO 2 concentrations and are triggered for metropolitan areas based on Core Based Statistical Area (CBSA) population thresholds and a traffic
- related threshold based on annual average daily traffic (AADT) 30

. The EPA proposed that CO monitors be required to operate in an y C BSA having a population of 1 million or more persons, collocated wi th required near
- road NO 2 monitoring stations. Based upon 2009 Census Bureau estimates and 2008 traffic statistics maintained by

the US Department of Transportation (US DOT) Federal

30 One near
- road NO 2 mo nitor is required in any CBSA having a population of 500,000 or more persons. Two near - road NO 2 mo nitors are required in any CBSA having a population of 2.5 million or mo re persons, or in any CBSA that has one or more road segments with an AADT count of 250,000 or mo re (40 CFR Part 58, Appendix D, Section 4.3).*** E.O. 12866 Review

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Page **77** of **166** Highway s Administration (FHWA), the CO monitoring proposal was estimated to require approximately

77 CO monitors to be collocated with near
- road NO 2 monitors within 53 CBSAs 31

. The EPA proposed that any required near
- road CO monitors shall be reflected in State annual monitoring network plans due in July 2012. Furth er, the Agency proposed that required near
- road CO monitors be operational by January 1, 2013. Due to the proposed collocation of required CO monitors with required near
- road NO 2 monitors, these implementation dates were proposed in order to match those o f the forthcoming near - road NO 2 monitoring network. In light of the proposal to require near
- road CO monitors be collocated with required near
- road NO 2 monitors, the EPA proposed that siting criteria for microscale CO monitors be revised to match those o f microscale near
- road NO 2 monitors (and also microscale PM 2.5 monitors). In particular, the EPA proposed that microscale CO siting criteria for probe height and horizontal spacing be changed to match those of near
- road NO 2 monitors as prescribed in 40 CF R part 58 appendix E, sections 2, 4(d), 6.4(a), and table E
- 4. Specifically , EPA proposed the following: 1) to allow microscale CO monitor inlet probes to be between 2 and 7 meters above the ground; 2) that microscale near
- road CO monitor inlet probes be placed so they have an unobstructed air flow, where no obstacles exist at or above the height of the monitor probe, between the monitor probe and the outside nearest edge of the traffic lanes of the target road segment; and 3) that required near
- road CO mo nitor inlet probes shall be as near as practicable to the outside nearest edge of the traffic lanes of the target road segment, but shall not be located at a

31 Since the proposal, EPA has estimat ed that using 2010 Census Bureau counts the proposed rule wo uld have resulted in approximately 75 monitors in 52 CBSAs being required.*** E.O. 12866 Review

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Page **78** of **166** distance greater than 50 meters in the horizontal from the outside nearest edge of the traffic lan es of the target road segment. Finally , the EPA recognized that a single monitoring network design may not alway s be sufficient for fulfilling specific or otherwise unique data needs or monitoring objectives for every

area across the nation. As such, the EPA proposed to provide the Regional Administrators with the discretion to require monitoring above the minimum requirements as necessary to address situations where minimum monitoring requirements are not sufficient to meet monitoring objectives. 2. Publi c Comments EPA first notes that CASAC expressed concern over the current monitoring network, stating “[m]ore extensive coverage may be warranted for areas where concentrations may

be more elevated, such as near roadway locations. The Panel found that in s ome instances current networks underestimated carbon monoxide levels near roadway s.” (Brain and Samet 2010b). General comments from the public based on relevant factors that either support or oppose the proposed changes to the CO network design are addre ssed in this section. Specific public comments related to the network design, but with regard to material which was not specificall y proposed b y the EPA or posed for solicitation of comment, are addressed in the Response to Comments document. a. Near - roa d Monitoring and Collocation with Near
- road Nitrogen Dioxide Monitors The EPA received multiple public comments on the overall merit of monitoring for CO in the near
- road environment, the proposal that required CO monitors be*** E.O. 12866 Review

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Page **79** of **166** collocated with required near
- road NO 2 monitors, and the number of required CO monitors that might be appropriate. In general, public health and environmental groups (e.g., American Lung Association [ALA], American Thoracic Society [ATS], Environmental Defense Fund [EDF]), some states or state environmental agencies or organizations (e.g. National Association of Clean Air Agencies [NACAA], Northeast States for Coordinated Air Use Management [NESCAUM], New York State Department of Environment Conservation [NYSDEC], and State of Wisconsi n Department of Natural Resources [WIDNR]), and some private citizen commenters provided support for a requirement for CO monitors in the near
- road environment. For example, ALA, ATS, and EDF state that they

“...are pleased to s ee EPA take seriousl y the public health threats that are posed to millions of residents and other sensitive receptors who live near or work on or near highway s as well as other high exposure areas.” They go on to note that “[near
- road ambient monitoring] data have been sorely lacking from the national monitoring network and are long overdue.” Further, many of the commenters who were supportive of near
- road monitoring were supportive of collocating CO monitors with near - road NO 2 monitors as it establishes multipollutant monitoring within the ambient air monitoring network. For example, NACAA stated the following in their comments: “...NACAA supports EPA’s proposal to collocate CO near roadway monitors at a subset of NO 2 near - roadway

sites. This is consistent with the recommendations of EPA’s Clean Air Scientific Advisory

Committee (CASAC), which urged the agency to develop the near roadway

monitoring network with a multipollutant focus and included CO in its list of pollutants that should be measured.”*** E.O. 12866 Review

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Page **80** of **166** So me industry

commenters (e.g., Association of Automobile Manufacturers [AAM] and American Electric Power Service Corporation [AEPSC]) and a number of other states or state groups (e.g., Indiana Department of Environmental Management [IDEM], North Carolina Department of Air Quality [NCDAQ], New Mexico Air Quality Bureau [NMAQB], South Carolina Department of Health and Environmental Control [SCDHEC], Southeast Michigan Council of Governments [SEMCOG], and Texas Commission on Environmental Quality [TCEQ]) gen erall y did not support the proposed near - road CO monitoring requirements. For example, IDEM stated that “CO measured by roadside monitors is not representative of ambient air quality every where in a city or county containing the roadway” and that “... roads ide monitoring measurements represent source - specific data. Therefore, Indiana does not believe that roadside monitoring should apply

to an ambient air qualit y standard.” SCDHEC stated it “... does not believe that the use of a near
- road monitoring network in a state
- wide ambient air monitoring network is the appropriate choice to protect our community ’s public health” and that “this monitoring method biases the monitoring effort into areas of little or no population while monitoring for the community popul ation exposure is neglected.” Similarly , industry

commenter AAM stated that “the current proposal does not include a requirement that the near
- roadway monitors be sited in locations where there is actual human exposure to the ambient air for time periods corresponding to the 1
- hour or 8
- hour CO NAAQS.” The EPA stated in the CO proposal (76 FR 8158) that the proposed near
- road CO monitoring requirements were intended to ensure a network of adequate size and focus to provide data for comparison to the NAA QS, support health studies and model*** E.O. 12866 Review

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Page **81** of **166** verification, and to fulfill Agency multipollutant monitoring objectives. In response to the comment that near
- road monitoring data would be “source
- specific” and may not be appropriatel y applicable to an ambient air s tandard, the Agency notes that monitoring for CO in the near
- road environment (as a mobile source oriented measurement) is a longstanding agency

practice, as evidenced by the first monitoring rule promulgated in 1979 (44 FR 27558, May 10, 1979). That 1979 monitoring rule included the requirement to monitor for “peak” CO concentrations in urban areas having populations of 500,000 people or more in locations “...around major traffic arteries and near heavily traveled streets in downtown areas.” The Agency bel ieves that the use of near
- road CO monitors as proposed is not a departure from the Agency ’s longstanding intent to measure peak concentrations of CO in the near
- road environment. Rather, the proposal was consistent with the Agency ’s approach to require m onitors for CO, and other criteria pollutants, in locations that likely

experience peak ambient concentrations. The Agency also notes that source - oriented monitoring is and has long been a common practice in ambient monitoring networks, although more ofte n associated with stationary sources, where the ambient data collected are used for comparison to the NAAQS. Data on ambient air concentrations, including near
- road data, which may be most appropriately

classified as on - road mobile source oriented, are a ppropriate to compare to the NAAQS. With regard to the comments asserting that near
- road monitoring would result in monitoring areas of “little or no population” and thus population exposure is not represented, the EPA notes that on
- road mobile sources are ubiquitous in urban areas and are a dominant component of the national CO emissions inventory , at nearly 60% of the total inventory , based on the 2008 NEI. As such, microenvironments influenced by on -*** E.O. 12866 Review

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Page **82** of **166** road mobile sources are important contributors to ambient CO exposures, particularl y in urban areas (REA, section 2.7). Further, the ambient CO exposures of most concern are short
- term. Accordingly , near - road monitoring is focused on characterizing peak or elevated ambient concentrations. The relevance o f this focus for the purposes of both ensuring compliance with the NAAQS and gathering data to inform our consideration of ambient CO exposures is demonstrated b y the ubiquity of on
- road mobile sources throughout urban areas, the time spent by people on or near roadway s and the large number of American citizens living in urban areas and near roadway s. As was noted in the I SA, the 2007 American Housing Survey (http://www.census.gov/hh es/www/housing/ahs/ahs07/ahs07.html ) estimates that 17.9 million housing units are within 300 feet (~91 meters) of a 4
- lane highway , airport, or railroad. Using the same survey , and considering that the average number of residential occupants in a housing unit is approximately 2.25, an estimate can be made that at least 40 million American citizens live near 4
- lane highway s, airports, or railroads. Among these three transportation facilities, roads are the most pervasive of the three, suggesting that a si gnificant number of people may live near major roads. Furthermore, the 2008 American Time Use Survey (http://www.bls.gov/tus/) reported that the average U.S. civilian spent over 70 minutes traveling per day . Based on these considerations, the Agency has concluded that monitoring in the near
- road environment would characterize the ambient concentrations that contribute to ambient CO exposure for a significant portion of the population that would otherwise not be captured. The AAM also commented that the EPA “...proposal to locate more near roadway monitors appears to be an attempt to find problems where none are likely to*** E.O. 12866 Review

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Page **83** of **166** exist.” The Agency

proposal for near
- road monitors is in line with longstanding monitoring objectives to monitor for peak or elevated ambient pollutant concentrations where they

may occur. The Agency

agrees that CO is no longer as pervasive a problem as it was in the past; however, there is still a responsibility to appropriatel y characterize and assess ambient concentrations to ensure th at they do not exceed the NAAQS. In comments on the first draft of the ISA, CASAC advised that “...rel yi ng only on EPA’s [current] fixed monitoring network, CO measurements may underestimate CO exposures for specific vulnerable populations such as individua ls residing near heavily trafficked roads and who commute to work on a dail y basis.” In comments on the second draft of the I SA, CASAC commented that “the panel expresses concern about the existing CO monitoring network, both for its [ spatial ] coverage an d for its utility in estimating human exposure” and that “CO exposures may not be adequatel y characterized for populations that may be exposed to higher CO levels because of where they live and work,” such as the near
- road environment. Finally , in comment s on the second draft of the REA, CASAC stated that “the approach for siting monitors needs greater consideration. More extensive coverage may

be warranted for areas where concentrations may be more elevated, such as near
- roadway locations.” In light of these comments and upon a review of the existing CO network, the Administrator concluded that the current CO monitoring network (circa 2010) lacked a necessary focus. While some currently existing sites that were established in the 1970s and 1980s continu e to monitor near
- road locations in downtown areas or within urban street can yons, and a minimum number of area
- wide monitors are currentl y required at National Core (NCore) multipollutant stations, few monitors exist that characterize the more heavily tra fficked roads that are prevalent in the*** E.O. 12866 Review

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Page **84** of **166** modern roadway

network, particularl y in our larger urban areas. The Agency ’s proposal was intended to require a modest but appropriate number of CO monitors to characterize the near
- road environment where peak or el evated ambient CO concentrations are expected to occur near heavily trafficked roads, as compared with neighborhood or urban background concentrations. If CO levels turn out to be low in these near
- road locations, so much the better for public health, and monitoring networks can be adjusted in the future, as they

have over time in response to an increased understanding of where levels of concern to public health are likel y to occur. Although the EPA received a number of comments that were largel y supportiv e for the proposed requirement of collocating CO monitors within the forthcoming near
road NO 2 monitoring stations, several commenters encouraged the Agency to provide flexibility to allow for the separation of the newl y required CO monitors from the near
road NO 2 sites, if necessary , to better monitor peak near
- road CO concentrations. In their comments supporting the collocation concept, NACAA also stated that their organization “...also encourages EPA to allow flexibility for state and local agencies to us e alternative siting of near
- roadway

CO monitors on a case
- by
- case basis, where there is a scientific justification for siting the CO monitor in a different location from the NO 2 monitor, to ensure the best possible measurement of near roadway CO concentrations.” Similarly , NCDAQ recognized that “...light duty vehicles tend to have more impact on CO concentrations than do heav y [duty] vehicles” and went on to surmise that “...not all near - road NO 2 monitoring stations will be well situated to measure maximum CO concentrations.”*** E.O. 12866 Review

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Page **85** of **166** The Agency

has expressed its intent to pursue the integration of monitoring networks and programs through the encouragement of multipollutant monitoring wherever possible, as evidenced b y actions taken in the 2006 monitoring rule that created the NCore network, the expression of the multipollutant paradigm in the 2008 Ambient Air Monitoring Strategy

for State, Local, and Tribal Air Agencies, and within this rulemaking process as part of the rationale in proposing the collocation of requir ed near
road CO monitors with near
- road NO 2 monitors. Multipollutant monitoring is viewed as a means to broaden the understanding of air quality conditions and pollutant interactions, furthering the capability

to evaluate air quality

models, develop emiss ion control strategies, and support research, including health studies. However, the Agency also recognizes that the measurement objectives of individual pollutants may not always correspond in a way

that would support multipollutant monitoring as the mos t appropriate option in a network design. On the issue raised b y NACAA and NCDAQ on the potential difference in locations of peak CO and NO 2 concentrations in the near
- road environment, the EPA recognizes the primary influence to be the different emission characteristics between light duty (LD) and heav y duty (HD) vehicles and vehicle operating conditions, which were discussed in section III.B.2 of the CO proposal. The public comments suggesting the need for flexibility in siting near
- road CO monitors derives from the fact that near
- road NO 2 sites will be sited at locations where peak NO 2 are expected to occur. Since NO 2 is more heavily influenced by

HD vehicles and CO is more heavil y influenced by LD vehicles on a per vehicle basis, respectively, there may be cases where the peak CO and NO 2 concentrations could occur along different road segments within the same CBSA. A s a general observation, the EPA believes that this*** E.O. 12866 Review

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Page **86** of **166** situation may

have more likelihood of occurring in the relativel y larger (b y population) CBSAs where a higher number of heavily trafficked roads with a wider variety of fleet mix (e.g. HD to LD vehicle ratios) tend to exist versus relativel y smaller CBSAs. In recognition of these considerations, the final regulation allows for flexibility in CO monitor placement in the near
- road environment when justified, as discussed below in section IV.B.3. b. Population Thresholds for Requiring Near
- road Carbon Monoxide Monitors The EPA proposed that required CO monitors be collocated with every required near - road NO 2 monitor in a CBSA with a population of 1 million or more persons. Due to the req uirement to locate one CO monitor at each required near
- road NO 2 site, the proposal would have required two monitors in CBSAs having 2.5 million or more persons or having one or more road segments with Annual Average Daily Traffic (AADT) counts of 250,000 or more. The proposal would have also required one monitor within those CBSAs having 1 million or more persons (but fewer than 2.5 million persons). 32 Based upon 2009 Census Bureau estimates and US DOT maintained traffic summary data, the propo sal was estimated to require 77 monitors within 53 CBSAs. Using recent 2010 Census data, and US DOT maintained traffic summary data, the proposal would have required approximately 75 monitors within 52 CBSAs. The EPA received a number of comments sup porting different population thresholds by

which to require near
- road CO monitors. Those states or state agencies or state agency

groups who generall y supported required CO monitoring in the near
- road

32 One near
- road NO 2 mo nitor is required in any CBSA having a population of 500,000 or more persons. Two near - road NO 2 mo n itors are required in CBSAs with population of greater than 2.5 million, or in any CBSA with a population of 500,000 or more persons that has one or more roadway segments with annual average daily traffic ( AADT ) counts of 250,000 or more. (40 CFR Part 58, Appendix D, Section 4.3).*** E.O. 12866 Review

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Page **87** of **166** environment (e.g., NACAA, NESCAUM, NYSDEC, and WIDNR) suggested a population threshold of 2.5 million by which near
- road CO monitors should be required. In addition, NCDAQ, who did not support near
- road CO monitoring, suggested that if it is required, it be required only within CBSAs of 2.5 million or more. The use of a population threshold of 2.5 million persons, versus 1 million as proposed, would require approximately 42 near - road CO monitors within 21 CBSAs , based on 2010 Census data
. Industry commenter American Petroleum Institute (API) stated that the proposed population threshold of 1 million persons “...appears appropriate, but EPA should not require that both [near
- road NO 2 ] sites in the largest CBSAs host CO monitors.” API’s suggestion would require approximately 52 near - road CO monitors withi n 52 CBSAs. Finally , the public health and environmental groups ALA, ATS, and EDF suggested the EPA promulgate minimum monitoring requirements “...to encompass cities in smaller metro areas, including cities with populations of 500,000 or more, similar to the requirements for NO 2 roadside monitoring.” ALA, ATS, and EDF’s suggestion would result in the requirement of approximately 126 monitors within 103 CBSAs. As was noted in the proposal, the Agency believes that with the continuing decline of ambient CO levels, as summarized in the EPA’s most recent trends report Our Nation’s Air: Status and Trends Through 2008 (http://www.epa.gov/airtrends/2010/), the Agency believes that there is less likelihood for high CO concentrations in relativel y smaller CBSAs (b y population). Accordingl y, the Agency proposed the requirement for what it believes would be a sufficient number of CO monitors, which would be collocated with required near
- road NO 2 monitors, in CBSAs having populations of 1 million or more persons. The Administrator considered alternative population thresholds,*** E.O. 12866 Review

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Page **88** of **166** including the 2.5 million and 500,000 person thre sholds, but concluded that those thresholds would require too few or too man y monitors, respectivel y, in light of existing information on CO emissions data, ambient data, and the lack of data for locations near highl y trafficked roads. The rationale for this proposed 1 million person threshold was to require a modest but sufficiently sized network that would effectivel y assess near - road CO concentrations for comparison to the NAAQS and could also provide data from within a multipollutant framework to suppo rt research (which includes health studies), facilitate model verification, and assess and evaluate emissions control strategies. However, after considering public comments, the EPA has concluded that one monitor in each CBSA of 1 million or more persons will provide for monitoring of a wide range of diverse situations with regard to traffic volume, traffic patterns, roadway designs, terrain/topograph y, meteorology , climate, as well as surrounding land use and population characteristics. Accordingl y, in th e final rule EPA has modified the proposed requirements for CO monitors so that only one CO monitor is required in CBSAs of 1 million or more persons, as discussed in Section IV.B.3 below. c. Implementation Schedule The EPA received a number of comments on the timeline for implementation of any required CO monitoring promulgated as part of this rulemaking. ALA, ATS, and EDF stated that they

“...support EPA’s requirement that CO monitors be installed in near - highway

locations by

July 1, 2013.” In light of the support these commenters expressed for rapid deploy ment of near road CO monitors, these commenters may have intended to support the proposed implementation date of January 1, 2013 instead of July 1, 2013 as quoted. The Agency received a number of c omments from state agencies,*** E.O. 12866 Review

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Page **89** of **166** state agency

organizations, and industry encouraging the Agency to extend the time by which an y required monitoring must be implemented. For example, APIsuggested that the proposed date b y which required near
- road CO monitors be established be extended to July 1, 2013, while NACAA and WIDNR suggested January 1, 2014. Several commenters suggested that required near
- road monitors should be phased in over a period of time. For example, NACAA, stated “[i]t may be necessary

to de velop a program for phasing in new monitoring sites and reevaluate network implementation.” NACAA also pointed to comments from CASAC that it would be advisable to phase in near
- road monitoring for NO 2 , because “[t]he first round of sites could be used to gather information on appropriate siting in the near roadway environment, near roadway gradient, and spatial relationships.” The EPA recognizes that states are already implementing newly required monitoring related to lead and NO 2 , and that the current financial and logistical burdens may make the implementation of new monitoring requirements difficult. A number of state and industry

commenters noted the need for funding to accommodate a new monitoring requirement, and some also noted the financial and logistical hardships that many states are currently experiencing (e.g., IDEM, NACAA, NCDAQ, SCDHEC, and WIDNR). The EPA recognizes the significance of the financial and logistical burden that new monitoring requirements pose and the impact of multiple new monitoring requirements stemming from other recent rulemakings. As such, the Agency has taken these comments into consideration in the final rule with regard to when required CO monitors are to be operational, as discussed in Section IV.B.3 below.*** E.O. 12866 Review

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Page **90** of **166** d. Si ting Criteria The EPA received comments regarding the proposed revisions to microscale CO siting criteria. Those who commented (AAM, API, and NCDAQ) all supported having two sets of siting criteria that would apply to near - road CO monitors such as those that might be collocated with near
- road NO 2 monitors and to those CO monitors operating in downtown areas and urban street can yon locations, respectivel y. AAM stated that “...there should be two separate criteria for siting microscale CO monitors. The earli er height and distance guidelines are still appropriate for downtown areas and arterial highway s with sidewalks, but a separate set of guidelines should be established for limited access, heavily
- travelled expressway s.” APIcommented that “...the proposed C O [near
- road] criteria are acceptable. EPA should create two
- tiered siting criteria for microscale CO monitoring...” and that “there will be an ongoing need for CO monitoring in downtown, urban and/or street can yon[s] for health
- related concerns as well as SIP related issues.” Finall y, NCDAQ stated that “...the US EPA should maintain separate siting criteria for the two ty pes of micro
- scale CO monitoring sites...” noting that the current siting criteria intended for downtown areas and urban street canyon sites “...are still valid for that purpose and CO monitoring stations being placed for this purpose should still be required to meet these siting criteria.” The EPA agrees with the commenters that the existing siting criteria are still appropriate for an y existing or future downtown area or urban street canyon CO monitoring site, and that new siting criteria are appropriate for CO monitors being collocated with near road NO 2 monitors. As such, the Agency is finalizing siting criteria for microscale CO sites that i nclude criteria for both downtown area/urban street canyon*** E.O. 12866 Review

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Page **91** of **166** microscale sites and other near
- road microscale CO sites, as presented below in Section IV .B.3. e. Area
- wide Monitoring The EPA received a number of comments from transportation groups, public hea lth and environmental groups, and an industry commenter (e.g., AAM, ALA/ATS/EDF, American Association of State Highway and Transportation Officials [AASHTO], New York State Department of Transportation [NYSDOT], Texas Department of Transp ortation [TXDOT], and Virginia Department of Transportation [VDOT]) regarding the fate of man y of the CO monitors in the current network that characterize concentrations representative of neighborhood or larger spatial scales 35 , known as ar ea - wide monitors. For example, AASHTO commented that “EPA appears to be proposing that CO monitoring sites to characterize area
- wide CO concentration levels at the neighborhood and larger spatial scales is no longer required. AASHTO is concerned that thi s proposal will de
- emphasize the need for neighborhood scale CO monitors.” AASHTO and some state DOTs expressed that the data for neighborhood scale monitors are used for other purposes, such as National Environmental Policy Act

35 Spatial scales are defined in 40 CFR Part 58 Appendix D, Section 1.2, where the scales of representativeness of most interest for the monitoring site types include: 1. Microscale

– Defines the concentration in air volumes associated with area dimensions ranging from several meters up to about 100 meters. 2. Middle scale

– Defines the concentration typical of areas up to several city blocks in size, with dimensions ranging from about 100 meters to 0.5 kilometers. 3. Neighborhood scale

– Defines concentrations within some extended area of the city that has relatively uniform land use with dimensions in the 0.5 to 4.0 kilometers range. 4. Urban scale

– Defines concentrations within an area of city
- like dimensions, on the order of 4 to 50 kilometers. Within a city, the geographic placement of sources may result in there being no single site that can be said to represent air quality on an urban scale. The neighborhood and urban scales have the potential to overlap in applications that concern secondarily formed or homogeneously distributed air pollutants. 5. Regional scale

– Defines usually a rural area of reasonably homogeneous geography without large sources, and extends from tens to hundreds of kilometers.*** E.O. 12866 Review

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Page **92** of **166** (NEPA) and transportation c onformity , and that they are concerned about the potential loss of these ty

pes of data in the future. In another example, ALA/ATS/EDF stated that they call upon EPA to “establish a comprehensive roadside air pollution network, while retaining the current area - wide CO network.” The EPA notes that prior to this final rulemaking, the only required CO monitoring within 40 CFR part 58, appendix D was for the operation of a CO monitor within all NCore multipollutant monitoring stations. There are approximatel y 80 NCore stations nationwide, and by design, they

are area - wide monitoring sites. In the proposal, the Agency

estimated that 345 CO monitors were operational at some point during 2009. A more recent examination of AQS data (utilizing EPA’s Air Explorer web tools located at www.epa.gov/airexplorer) indicate that approximately 328 CO monitors were operational as of May

20, 2011. These 328 active CO monitors include the 80 NCore monitors now in operation nationwide. This means that a significant portion of the current network is composed of monitors that are additional to those required by EPA as part of a national network design. It is critical to note that in this rulemaking the EPA is actuall y increasing th e total number of required sites in the national CO monitoring network design and is not removing an y area - wide monitoring requirements as AASHTO and other commenters suggested. Some of the potential for misperception on this issue may have arisen from th e Agency ’s stated expectation that state and local air monitoring agencies will likel y move existing CO monitors into near
- road locations to satisfy the minimum monitoring requirements promulgated in this rulemaking. Based on this final rule , state and local agencies would only move, at most, approximately 52 monitors out of the 328 in operation (circa May 2011). Therefore a majorit y of CO monitors would*** E.O. 12866 Review

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Page **93** of **166** likely continue operating in their existing locations. However, it should be noted that with ambient CO concentrations well below the NAAQS, particularl y at area - wide sites, states may

identify some area - wide CO monitors to be no longer necessary . As such, the retirement of these sites may be justified, and their removal would save state and local resources. The EPA does recognize the value of maintaining some level of area
- wide CO monitoring to meet the overarching monitoring objectives, which includes tracking long
te rm trends and to supporting research. In the proposal, the Agency did not propose establishing requirements for additional area
- wide monitoring sites because: 1) there is the existing NCore requirement, and 2) there is an expectation based on experience that some number of non
- required area
- wide sites will continue to operate in the future without minimum monitoring requirements. Regarding the removal or shutdown of any individual ambient air pollutant monitor, the Agency notes that there is a publicly tr ansparent process b y which an y existing CO monitor would be shut
- down. The shut
down of an y State and Local Air Monitoring Station (SLAMS) monitor is allowable under certain conditions specified in 40 CFR 58.14 System Modification . These conditions provi de state and local air agencies multiple options by which they

may propose, with justification, for a monitor to be shut down. Whatever the justification may be, each monitor proposed to be shut
- down must go through an established process to receive EPA R egional Administrator approval for shut
- down. As part of that process, the EPA Regional Administrator provides opportunity for public comment before making a decision to approve or disapprove the request. In conclusion, the EPA believes that even without requirements for area
- wide CO monitors additional to the NCore sites, some number of area
- wide monitors will continue to operate into the future. EPA anticipates*** E.O. 12866 Review

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Page **94** of **166** that monitors that states find useful for other regulatory purposes, such as NEPA, would be among the monitors that may continue to operate. The NCore sites, along with monitors currentl y operating in the absence of other area
- wide monitoring requirements, will likely

provide a sufficient set of area
- wide monitors to meet monitoring objectives. The EPA also received a number of comments from transportation groups, state and local groups, and an industry commenter (e.g., AAM, AASHTO, NESCAUM, NYSDEC, NYSDOT, TXDOT, and VDOT) suggesting that required near
- road CO monitors should be paired with an area - wide CO monitor within the same CBSA. For example, AASHTO recommended that “...EPA ensure that adequate coverage continues from neighborhood
- scale monitors to estimate background concentration levels, and that there is at least one neighborhood scale m onitor in every urbanized area that is required to have a near
- road monitor.” NESCAUM recommended “...that EPA locate near
- road CO monitors near urban NCore CO sites” (as noted above, NCore sites are area
- wide sites by design). The EPA recognizes that a pai ring of near
- road CO monitors with area
- wide CO monitors will provide information by which an estimate of the difference between near
road concentrations to relative background concentrations might be determined. As noted earlier, the Agency believes that the combination of required NCore sites and those area - wide monitors currently operating in the absence of minimum monitoring requirements (of which many will likel y continue operating in the future) will largel y fulfill the area
- wide component of an y near - road site/area
- wide site pairing in an urban area. An anal ys is of NCore site locations (site data available from /www.epa.gov/ttn/amtic/ncore/index.html ), along with all those area
- wide CO moni tors*** E.O. 12866 Review

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Page **95** of **166** believed to be operating as of May 20, 2011 (utilizing EPA’s Air Explorer web tools located at www.epa.gov/airexplorer) indicated that of the 52 CBSAs with a population of 1 million persons or more, based on 2010 Census data, , only 4 are believed to be without an area - wide CO monitor 37 . The EPA believes that, based on the considerations discussed above, the existing network will likely provide sufficient area
- wide CO concentration information on which a near - road to area
- wide data comparison could be based. f. Regional Administrator Authority The EPA received a number of comments from states and transportation groups (e.g., AASHTO, NYSDOT, TCEQ, TXDOT, and VDOT) on the proposal for Regional Administrato rs to have the discretion to require monitoring above the minimum requirements as necessary to address situations where minimum monitoring requirements are not sufficient to meet monitoring objectives. For example, AASHTO commented that “the proposed rule includes some examples of where additional monitors may be necessary . AASHTO is concerned that these brief examples may not be sufficient to ensure uniform application of this additional authority among the EPA Regions,” and that EPA should provide guidance on this so that there is “reasonable uniformity between EPA Regions in the implementation of these provisions.” TCEQ commented that it “does not agree that this discretion is appropriate, particularl y where EPA has not proposed a process b y which Regi onal Administrators must consult with states and the public regarding these decisions.” Further TCEQ stated that “...the potential requirement for additional monitors when ‘minimum monitoring requirements are not sufficient to

37 The EPA notes that of the 53 CBSAs that have 1 million or more persons, 39 CBSAs contain an NCore monitoring station, which includes a CO monitor.*** E.O. 12866 Review

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Page **96** of **166** meet monitoring objectives’ is overl y broad and should be refined to include objective criteria that will consistently applied across all EPA Regions.” The EPA notes that the authority of Regional Administrators to require additional monitoring above the minimum required is not unique to the CO NAAQS. For example, Regional Administrators have the authority to use their discretion to require additional NO 2 , lead, and sulfur dioxide monitors ( 40 CFR part 58 appendix D sections 4.3.4, 4.4.3, and 4.5, respectivel y) and to work with state and local air agencies in designing and/or maintaining an appropriate ozone monitoring network ( 40 CFR part 58 appendix D section 4.1) . The EPA believes that a nationall y applicable network design may not alway s account for all locations in every area whe re monitors may be warranted. Example situations where the Regional Administrator authority could be utilized, which were provided in the proposal, could be for unmonitored locations where data or other information suggest that CO concentrations may be ap proaching or exceeding the NAAQS due to stationary CO sources, in downtown areas or urban street canyons, or in areas that are subject to high ground
- level CO concentrations particularl y due to or enhanced b y topographical and meteorological impacts. The Agency cannot anticipate every example that may

exist where the Regional Administrator authority might be used for inclusion in this preamble text. However, the Agency believes it is important for Regional Administrators to have the authority to address p ossible gaps in the minimally required monitoring network in situations such as those examples provided here. In response to public comments, the EPA notes that Regional Administrators would use their authority

in collaboration with state agencies, workin g with stakeholders to design and/or maintain the most appropriate CO monitoring network to meet the needs of a*** E.O. 12866 Review

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Page **97** of **166** given area. Finall y, the Agency notes that an y m onitor required b y the Regional Administrator (or an y new monitor proposed b y the state itself) is not done so with unfettered discretion. Any such action would be included in the Annual Monitoring Network Plan per 40 CFR §58.10, and this plan must be made available for public inspection and comment before an y decisions are made b y the EPA Regional Administrator. 3. Conclusions on the Network Design This section provides the rationale and details for the final decision on changes to the CO monitoring network design and siting criteria. As discussed above in section IV .B.2.a, motor vehicle emissions are important contributors to ambient CO concentrations (REA , section 2.2), contributing nearly 60% of the total CO emitted nationally (per the 2008 NEI). As a result, microenvironments influenced by on - road mobile sources are important contrib utors to ambient CO exposures, particularly in urban areas (REA, section 2.7). Therefore, the Administrator has concluded that monitoring in the near
- road environment to characterize and assess ambient CO concentrations continues to be an appropriate obje ctive for the CO monitoring network. The EPA believes that the promulgation of minimum requirements for CO monitors in the near
road environment is necessary to ensure a network of adequate size and focus to provide data for comparison to the NAAQS, suppo rt research which includes health studies, allow for model verification, and fulfill multipollutant monitoring objectives. Further, considering the lack of CO monitors assessing higher trafficked roads in urban areas and CASAC’s advice that the Agency dev elop greater monitoring capacity for CO in near
road environments (Brain and Samet, 2010b), the Agency believes that a number of CO*** E.O. 12866 Review

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Page **98** of **166** monitors should be focused in such locations. Highly trafficked roads are expected to show elevated CO concentrations relative to area
- wide concentrations and to represent the locations where ambient CO concentrations may be highest in an area. Regarding the locations where required near
- road CO monitors might be placed, the EPA proposed that they be collocated with a subset of near
- road NO 2 monitors. The EPA expects required near - road NO 2 monitors (as prescribed in 40 CFR part 58, appendix D, Section 4.3) to be adjacent to highl y trafficked roads within the CBSAs where they are required. Recognizing this and also recognizi ng the benefits associated with collocating monitors at the same site, the Agency is finalizing requirements for near
- road CO monitors that will leverage required near
- road NO 2 monitoring sites to house collocated near
- road CO monitors to create data for c omparison to the NAAQS, support research which includes health studies, provide data for model evaluation, and foster the fulfillment of multipollutant objectives. As noted above, after considering public comments, EPA has modified the requirements for CO monitors from that which was proposed so that onl y one CO monitor is required in each CBSA in which near
- road CO monitoring is required. 38 This approach reduces the total number of monitors that would have been required under the proposal from 75 monitors within 52 CBSAs to 52 monitors within 52 CBSAs (based o n 2010 Census data). The EPA believes this network design addresses public comments while maintaining monitoring in a sufficientl y diverse set of locations throughout 52 different urban areas around the country . By having monitors within 52 different CBS As, this network design is expected to provide for monitoring in a wide range of

38 This approach only requires one CO monitor to be installed in those CBSAs that have two required near
- roa d NO 2 mo nitors.*** E.O. 12866 Review

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Page **99** of **166** diverse situations with regard to traffic volumes, traffic patterns, roadway designs, terrain/topograph y, meteorology , climate, as well as surrounding land use and population characteristics. The EPA is generall y requiring CO monitors to be collocated with near
road NO 2 monitors. However, upon consideration of public comments, the Agency is allowing flexibility

for states to use an alternate near
- road location, which include s downtown areas, urban street can yons, and other near
- road locations, for a required CO monitor on a case
- by
- case basis, with EPA Regional Administrator approval, when the state can provide quantitative justification showing the expectation of peak CO con centrations for that alternate location compared to a near
- road NO 2 location. Such requests could be based upon appropriate modeling, exploratory monitoring, or other methods, comparing the alternative CO location and the near
- road NO 2 location. In summary , based upon 2010 Census Bureau data this final rule for CO
m onitoring will require approximately 52 CO monitors to be collocated with near
- road NO 2 monitors (or otherwise operated at an alternate, EPA Regional Administrator approved, near
- road location where peak CO concentrations are expected) within 52 CBSAs that have populations of 1 million or more persons. Regarding the deplo ym ent and operation of required CO monitors, the Agency recognizes that man y state and local air agencies are under financial and related resource duress. EPA has concluded that allowing additional time for installing CO monitors will provide an opportunit y for state and local agencies to work with EPA Regions to identify which existing CO monitors may be appropriate to relocate to the near
- road locations. In many cases, EPA and the state may believe it is appropriate to relocate monitors , including some of those that are currently operated pursuant to existing maintenance*** E.O. 12866 Review

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Page **100** of **166** plans. In these cases, additional time may be necessary

to allow states to revisit and p ossibly revise, in consultation with (and subject to the approval of) the EPA Regions, existing maintenance plans in a way that may allow certain CO monitors to be free for relocation, if appropriate. Further, if a state chooses to investigate whether it will request that a required near
- road CO monitor be sited in a near
- road location other than a required near
- road NO 2 site, the time allotted will provide states with some time to perform necessary

analy ses for submission to the Regional Administrator for approval. Furthermore, EPA has concluded that public comments suggesting a phased
- in implementation, allowing for later stages to benefit from experience in an initial round of monitor installations, have merit. As a result , the EPA has chosen not t o require the implementation of required CO sites by January 1, 2013 as was proposed. Instead, the Agency is finalizing a two - phased implementation requirement . Those CO monitors required within CBSAs having 2.5 million or more persons are to be operational by January 1, 2015 , although the Agency strongl y encourages the implementation of these required monitors as soon as practicable. Those CO monitors required in CBSAs having 1 million or more persons (and fewer than 2.5 million persons) are to be operational b y J anuary 1, 2017. EPA intends to review the experience of states with the first round of near
- road CO monitors and the data produced by such monitors and consider whether adjustments to the network requirements are warrant ed. These required CO monitors shall be reflected in a state’s annual monitoring network plans due six months prior to installation, i.e., on July 1, 2014 or July

1, 2016, respectivel y .*** E.O. 12866 Review

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Page **101** of **166** Regarding siting criteria, the EPA received public support to ad just microscale CO siting criteria to match those of near
- road NO 2 monitors (and microscale PM 2.5 monitors). The Agency

also was urged to retain the existing microscale siting criteria, for explicit use with microscale CO sites in downtown areas or urban street canyon settings. As a result, the EPA is retaining the existing siting criteria for microscale CO monitors in downtown areas and urban street can yons and is finalizing the additional siting criteria for those near
- road microscale CO monitors outsid e of downtown areas and urban street can yons to have probe height and horizontal spacing to match those of near
- road NO 2 monitors as prescribed in 40 CFR part 58 appendix E, sections 2, 4(d), 6.4(a), and table E - 4. Specificall y, the Agency is finalizing the following: 1) a microscale near
- road CO monitor inlet probe shall be between 2 and 7 meters above the ground; 2) a microscale CO monitor inlet probes in the near
- road environment shall be placed so it has an unobs tructed air flow, where no obstacles exist at or above the height of the monitor probe, between the monitor probe and the outside nearest edge of the traffic lanes of the target road segment; and 3) that CO monitors in the near
- road environment shall have inlet probes as near as practicable to the outside nearest edge of the traffic lanes of the target road segment, but shall not be located at a distance greater than 50 meters in the horizontal from the outside nearest edge of the traffic lanes of the targe t road segment. Further, as suggested through public comments, the EPA is retaining existing regulatory

siting criteria language for microscale CO monitors in downtown areas or urban street can yon locations, where: 1) the inlet probe for a near
- road micro scale CO monitor in a downtown area or urban street canyo n shall be between 2.5 meters and 3.5*** E.O. 12866 Review

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Page **102** of **166** meters above ground level; 2) the inlet probe for a near
- road microscale CO monitor in a downtown area or urban street can yon shall be within 10 meters from the edge of the nearest traffic lane; and 3) near
- road microscale CO monitors in street can yons are required to be at least 10 meters from an intersection. Finally , the EPA recognizes that a monitoring network design may not alway s require monitoring on a nati onal scale that is sufficient in fulfilling specific or otherwise unique data needs or monitoring objectives for every area across the nation. Thus, the EPA is finalizing the provision that EPA Regional Administrators have the authority to require monitoring above the minimum requirements, as necessary , in an y area, to address situations where the minimally required monitoring network is not sufficient to meet monitoring objectives. Example situations where the Regional Administrator Authority could be ut ilized include, but are not limited to, those unmonitored locations where data or other information suggest that CO concentrations may be approaching or exceeding the NAAQS due to stationary CO sources, in downtown areas or urban street can yons, or in area s that are subject to high ground
- level CO concentrations particularl y due to or enhanced b y topographical and meteorological impacts. In all cases in which a Regional Administrator may consider the need for additional monitoring, it is expected that the Regional Administrators will work with the state or local air agencies to evaluate evidence or needs to determine whether a particular area may warrant additional monitoring. **V. Statutory and Executive Order Reviews**  A. Executive Order 12866: Regulatory Pla nning and Review and Executive Order 13563: Improving Regulation and Regulatory Review*** E.O. 12866 Review

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Page **103** of **166** Under Executive Order 12866 (58 FR 51735, October 4, 1993), this action is a "significant regulatory

action” because it was deemed to “raise novel legal or policy issu es.” Accordingl y, EPA submitted this action to the Office of Management and Budget (OMB) for review under Executive Order s 12866 and 13563 (76 FR 3821, January 21, 2011) and any

changes made in response to OMB recommendations have been documented in the d ocket for this action. B. Paperwork Reduction Act The information collection requirements in this final rule have been submitted for approval to the Office of Management and Budget (OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The information collection requirements are not enforceable until OMB approves them. The Information Collection Request (I CR) document prepared b y EPA for these revisions to part 58 has been assigned EPA I CR number 0940.2 4
. The information collected under 40 CFR part 53 (e.g., test results, monitoring records, instruction manual, and other associated information) is needed to determine whether a candidate method intended for use in determining attainment of the NAAQS in 40 CFR part 50 will meet comparability requirements for designation as a FRM or FEM . We do not expect the number of FRM or FEM determinations to increase over the number that is currently

used to estimate burden associated with CO FRM/FEM determinations provided in the current ICR for 40 CFR part 53 (EPA ICR numbers 0940.2 4 ). As such, n o change in the burden estimate for 40 CFR part 53 has been made as part of this rulemaking.*** E.O. 12866 Review

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Page **104** of **166** The information collected and reported under 40 CFR part 58 is needed to determine compliance with the NAAQS, to characterize air quality and associated health i mpacts, to develop emissions control strategies, and to measure progress for the air pollution program. The amendments would revise the technical requirements for CO monitoring sites, require the relocation or siting of ambient CO air monitors, and the rep orting of the collected ambient CO monitoring data to EPA’s Air Quality Sy stem (AQS). The annual average reporting burden for the collection under 40 CFR part 58 (averaged over the first 3 years of this ICR) for a network of 311 CO monitors is $7,235,483. Burden is defined at 5 CFR 1320.3(b). State, local, and Tribal entities are eligible for State assistance grants provided b y the Federal government under the CAA which can be used for monitors and related activities. An agency

may not conduct or sponsor , and a person is not required to respond to, a collection of information unless it display s a currently valid OMB control number. The OMB control numbers for EPA’s regulations in 40 CFR are listed in 40 CFR part 9. When this I CR is approved by OMB, the A genc y will publish a technical amendment to 40 CFR part 9 in the Federal Register to display the OMB control number for the approved information collection requirements contained in this final rule. C. Regulatory Flexibility Act The Regulatory

Flexibility Act (RFA) generall y requires an agency to prepare a regulatory

flexibility

analy sis of any

rule subject to notice and comment rulemaking requirements under the Administrative Procedure Act or any other statute unless the agency certifies that the rule will not have a significant economic impact on a substantial*** E.O. 12866 Review

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Page **105** of **166** number of small entities. Small entities include small businesses, small organizations, and small governmental jurisdictions. For purposes of assessing the impacts of today ’s rule on small entities, small entity is defined as: (1) a small business that is a small industrial entity as defined by

the Small Business Administration’s (SBA) regulations at 13 CFR 121.201; (2) a small governmental jurisdiction that is a government of a city , county , town, school district or special district with a population of less than 50,000; and (3) a small organization that is any not - for
- profit enterprise which is independently owned and operated and is not dominant in its field. After considering the econom ic impacts of this final rule on small entities, I certify that this action will not have a significant economic impact on a substantial number of small entities. This final rule will not impose an y requirements on small entities. Rather, this rule retai n s existing national standards for allowable concentrations of CO in ambient air as required b y section 109 of the CAA. See also American Trucking Associations v. EPA . 175 F. 3d at 1044
- 45 (NAAQS do not have significant impacts upon small entities because NAAQS themselves impose no regulations upon small entities). Similarly , the amendments to 40 CFR part 58 address the requirements for States to collect information and report compliance with the NAAQS and will not impose any

requirements on small entitie s. D. Unfunded Mandates Reform Act T his rule does not contain a Federal mandate that may result in expenditures of $100 million or more for State, local, and Tribal governments, in the aggregate, or the private sector in an y one year. This rule retains the existing national ambient air quality*** E.O. 12866 Review

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Page **106** of **166** standards for carbon monoxide. The expected costs associated with the monitoring requirements are described in EPA’s I CR document, but those costs are expected to be well less than $100 million (adjusted for inflation) in the aggregate for any year. Furthermore, as indicated previously , in setting a NAAQS, EPA cannot consider the economic or technological feasibility of attaining ambient air quality standards. T hus, this rule is not subject to the requirements of sections 202 or 205 of the UMRA. T his rule is also not subject to the requirements of section 203 of the UMRA because it imposes no enforceable duty on an y small governments. E. Executive Order 13132: Federalism This action does not have federalism implic ations. It will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government, as specified in Executive O rder 13132. The rule does not alter the relationship between the Federal government and the States regarding the establishment and implementation of air quality improvement programs as codified in the CAA. Under section 109 of the CAA, EPA is mandated to establish and review NAAQS; however, CAA section 116 preserves the rights of States to establish more stringent requirements if deemed necessary

by a St ate. Furthermore, this rule does not impact CAA section 107 which establishes that the States have primary responsibility

for implementation of the NAAQS. Finall y, as noted in section D (above) on UMRA, this rule does not impose significant costs on State, local or Tribal gov ernments or the private sector. Thus, Executive Order 13132 does not apply to this rule.*** E.O. 12866 Review

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Page **107** of **166** F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments This action does not have tribal implications, as specified in Executive Order 13175 (65FR 67249, November 9, 2000). Itdoes not have a substantial direct effect on one or more Indian Tribes, since Tribes are not obligated to adopt or implement any NAAQS. Thus, Executive Order 13175 does not apply to this action
. G. Executive Ord

er 13045: Protection of Children from Environmental Health and Safety Risks This action is not subject to EO 13045 (62 FR 19885, April 23, 1997) because it is not economicall y significant as defined in EO 12866, and because the Agency does not believe the environmental health or safety risks addressed b y this action present a disproportionate risk to children. This action’s health and risk assessments are described in section II. A
. H. Executive Order 13211: Actions that Significantly Affect Energy Supply, Distribution or Use This action is not a “significant energy action” as defined in Executive Order 13211, (66 FR 28355 (May 22, 2001)) because it is not likely to have a significant adverse effect on the supply , distribution, or use of energ y. The rule concerns the review of the NAAQS for CO. The rule does not prescribe specific pollution control strategies by which these ambient standards will be met. Such strategies are developed by States on a case - by
- case basis, and EPA cannot predict whether the control options selected by States will include regulations on energy suppliers, distributors, or users. I. National Technology Transfer and Advancement Act*** E.O. 12866 Review

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Page **108** of **166** Section 12(d) of the National Technology Transfer and Advancement Act of 1995 (NTTAA), Public Law 104

– 113, section 12(d) (15 U.S.C. 272 note) directs EPA to use voluntary consensus standards in its regulatory activities unless to do so would be inconsistent with applicable law or otherwise impractical. Voluntary consensus standards are tec hnical standards (e.g., materials specifications, test methods, sampling procedures, and business practices) that are developed or adopted by voluntary

consensus standards bodies. The NTTAA directs EPA to provide Congress, through OMB, explanations when th e Agency

decides not to use available and applicable voluntary consensus standards. This rulemaking involves technical standards with regard to ambient monitoring of CO. We have not identified any potentially

applicable voluntary

consensus standards that would adequatel y characterize ambient CO concentrations for the purposes of determining compliance with the CO NAAQS and none have been brought to our attention in comments
. Therefore, EPA has decided to use the method “Measurement Principle and Calibrati on Procedure for the Measurement of Carbon Monoxide in the Atmosphere (Non
- Dispersive Infrared Photometry)” (40 CFR Part 50, appendix C), as revised b y this action, for the purposes of ambient monitoring of CO concentrations. J. Executive Order 12898: Fede ral Actions to Address Environmental Justice in Minority Populations and Low
-Income Populations Executive Order 12898 (59 FR 7629 (Feb. 16, 1994)) establishes federal executive policy

on environmental justice. Its main provision directs federal agencies, to the greatest extent practicable and permitted b y law, to make environmental justice part of their mission by

identifying and addressing, as appropriate, disproportionately high*** E.O. 12866 Review

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Page **109** of **166** and adverse human health or environmental effects of their programs, policie s, and activities on minority

populations and low
- income populations in the United States. EPA has determined that this final rule will not have disproportionatel y high and adverse human health or environmental effects on minority or low
- income populati ons because it does not affect the level of protection provided to human health or the environment. The action in this notice is to retain without revision the existing NAAQS for CO. Therefore this action will not cause increases in source emissions or a ir concentrations. K. Congressional Review Act The Congressional Review Act, 5 U.S.C. 801 et seq., as added b y the Small Business Regulatory

Enforcement Fairness Act of 1996, generall y provides that before a rule may take effect, the agency

promulgating the rule must submit a rule report, which includes a cop y of the rule, to each House of the Congress and to the Comptroller General of the United States. EPA will submit a report containing this rule and other required information to the U.S. Senate, the U.S. House of Representatives, and the Comptroller General of the United States prior to publication of the rule in the Federal Register . A major rule cannot take effect until 60 day s after it is published in the Federal Register . This action is not a “major rule” as defined by 5 U.S.C. 804(2). This rule will be effective **[insert date 60 days after publication in the Federal Register]**
.*** E.O. 12866 Review

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Page **110** of **166 References**  Adams K.F.; Koch G.; Chatterjee B.; Goldstein G.M.; O'Neil J.J.; Bromberg P.A.; Sheps D.S.; McAllister S.; Price C.J.; Bissette J. (1988) Acute elevation of blood carbox yhemoglobin to 6% impairs exercise performance and aggravates symptoms in patients with ischemic heart disease. J. Am. Coll. Cardiol. 12:900
- 909. Allred E.N.; Bleecker E.R.; Chaitman B.R.; Dahms T.E.; Gottlieb S.O.; Hackney J.D.; Pagano M.; Selvester R.H.; Walden S.M.; Warren J. (1989a) Short
- term effects of carbon monoxide exposure on the exercise perform ance of subjects with coronary artery disease. N. Engl. J. Med. 321:1426
- 1432. Allred E.N.; Bleecker,E.R.; Chaitman B.R.; Dahms T.E.; Gottlieb S.O.; Hackney J.D.; Hayes D.; Pagano M.; Selvester R.H.; Walden S.M.; Warren J. (1989b) Acute effects of carbon m onoxide exposure on individuals with coronary artery disease. Cambridge, MA: Health Effects Institute; research report no. 25. Allred E. N.; Bleecker E. R.; Chaitman B. R.; Dahms T. E.; Gottlieb S. O.; Hackney J. D.; Pagano M.; Selvester R. H.; Walden S. M .; Warren J. (1991) Effects of carbon monoxide on myocardial ischemia. Environ. Health Perspect. 91:89
- 132. AHA. (2003) Heart and Stroke Facts. American Heart Association, Dallas, TX. Available at: http://www.americanheart.org/downloadable/heart/10567199 19740HSFacts2003text.pdf Anderson E.W.; Andelman R.J.; Strauch J.M.; Fortuin N.J. and Knelson, J.H. (1973) Effect of low level carbon monoxide exposure on onset and duration of angina pectoris. Annals of Internal Medicine 79:46
- 50. Baldauf R.; Thoma E.; Hays M.; Shores R.; Kinsey J.; Gullett B.; Kimbrough S.; Is akov V.; Long T.; Snow R.; Khly stov A.; Weinstein J.; Chen F.L .; Seila R.; Olson D.; Gilmour I .; Cho S.H.; Watkins N.; Rowley P.; Bang J. (2008a). Traffic and meteorological impacts on near
- road air quality : Summary of methods and trends from the Raleigh near
- road study . J Air Waste Manag Assoc, 58: 865
- 878. 190239 Baldauf R.; Thoma E.; Khly stov A.; Isakov V.; Bowker G.; Long T.; Snow R. (2008b). Impacts of noise barriers on near
- road air quality . Atm os Environ, 42: 7502
- 7507. Bell M.L.; Peng R.D.; Dominici F.; Samet J.M. (2009) Emergency admissions for cardiovascular disease and ambient levels of carbon monoxide: Results for 126 U.S. urban counties, 1999
- 2005. Circulation, 120:949
- 955. Bissette J.; Carr G. ; Koch G.G. ; Adams K.F. ; Sheps D.S. (1986) Anal ys is of (events/time at risk) ratios from two period crossover studies. In: American Statistical Association 1986 proceedings of the Biopharmaceutical Section; August; Chicago, IL., Washington, DC: American Statistical Asssociation ; pp. 104
- 108. Brain, J.D. (2009) Letter from Dr. J.D. Brain to Administrator L isa Jackson. Re: Consultation on EPA’s Carbon Monoxide National Ambient Air Quality Standards: Scope and Methods Plan for Health Risk and Expos ure Assessment. CASAC
- 09
- 012. July 14, 2009.*** E.O. 12866 Review

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Page **111** of **166** Brain J. and Samet J. (2009) Letter from Drs. J.D. Brain and J.M. Samet to Administrator L isa Jackson. Re: Review of EPA's Integrated Science Assessment for Carbon Monoxide (First External Review Draft) EPA
- CASAC
- 09
- 011.June 24, 2009. Brain, J.D. and Samet, J.M. (2010a) Letter from Drs. J.D. Brain and J.M. Samet to Administrator L isa Jackson. Re: Review of the Risk and Exposure Assessment to Support the Review of the Carbon Monoxide (CO) Primary National Ambient Air Quality Standards: First External Review Draft. EPA
- CASAC
- 10
- 006. February 12, 2010. Brain J.D. and Samet J.M. (2010b) Letter from Drs. J.D. Brain and J.M. Samet to Administrator L isa Jackson. Re: Review of the Risk and Exposure Assessment to Support the Review of the Carbon Monoxide (CO) Primary National Ambient Air Quality Standards: Second External Review Draft. EPA
- CASAC
- 10
- 012. May 19, 2010. Brain J.D. and Samet J.M. (2010c) Letter from Drs. J.D. Brain and J.M. Samet to Administrator L isa Jackson. Re: Review of the Policy Assessment for the Review of the Carbon Monoxide National Ambient Air Quality Standards (NAAQS): External Review Draft. EPA
- CASAC
- 10
- 013. June 8, 2010. Brain J.D. and Samet J.M. (2010d) Letter from Drs. J.D. Brain an d J.M. Samet to Administrator L isa Jackson. Re: Review of Integrated Science Assessment for Carbon Monoxide (Second External Review Draft). EPA
- CASAC
- 10
- 005. January 20, 2010. Henderson R. (2008) Letter from Dr. Rogene Henderson, Chairman, Clean Air Scientific Advisory

Committee, to Administrator Stephen Johnson. Re: Consultation on EPA’s Draft Plan for Review of the Primary NAAQS for Carbon Monoxide CASAC
- 08
- 013. June 12, 2008. Johnson T.; Capel J.; Paul R.; Wijnberg L. (1992) Estimation of Carbon Monoxi de Exposure and associated Carbox yh emoglobin levels in Denver Residents Using a Probabalistic verion of NEM, prepared b y International Technology for U.S. EPA, Office of Air Quality Planning and Standards, Durham, NC, Contract No. 68
- D0
- 0062. Johnson T.; M ihlan G.; LaPointe J.; Fletcher K.; Capel J. (2000) Estimation of Carbon Monoxide Exposures and Associated Carboxy hemoglobin Levels for Residents of Denver and Los Angeles Using pNEM/CO (Version 2.1). Report prepared by I CF Consulting and TRJ Environmental, Inc., under EPA Contract No. 68
- D6
- 0064. U.S. Environmental Protection Agency , Research Triangle Park, North Carolina. Available at: http://www.epa.gov/ttn/fera/human_related.html. June 2000. Kleinman M.T.; Davidson D.M.; Vandagriff R.B.; Caiozzo V.J .; Whittenberger J.L . (1989) Effects of short
- term exposure to carbon monoxide in subjects with coronary artery disease. Arch. Environ. Health 44:361
- 369. Kleinman M.T.; Leaf D.A.; Kelly E.; Caiozzo V.; Osann K.; O'Niell T. (1998) Urban angina in the mount ains: effects of carbon monoxide and mild hy poxemia on subjects with chronic stable angina. Arch. Environ.Health 53:388
- 397. Koken P.J.M.; Piver W.T.; Ye F.; Elixhauser A.; Olsen L .M.; Portier C.J. (2003) Temperature, air pollution, and hospitalization for cardiovascular diseases among elderl y*** E.O. 12866 Review

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Page **112** of **166** people in Denver. Environ Health Perspect, 111:1312
- 1317. Lippmann, M. (1984) CASAC Findings and Recommendations on the Scientific Basis for a Revised NAAQS for Carbon Monoxide. [L etter to W.D. Ruckelshous, EPA Admini strator]. May

17. Linn W.S.; Szlachcic Y.; Gong H. Jr; Kinney P.L.; Berhane K.T. (2000) Air pollution and daily

hospital admissions in metropolitan L os Angeles. Environ Health Perspect, 108:427
- 434. Mann J.K.; Tager I.B.; Lurmann F.; Segal M.; Quesenberry C.P. Jr; Lugg M.M.; Shan J.; Van den Eeden S.K. (2002) Air pollution and hospital admissions for ischemic heart disease in persons with congestive heart failure or arrhythmia. Environ Health Perspect, 110:1247
- 1252. Metzger K.B.; Tolbert P.E.; Klein M.; Peel J.L .; Flanders W.D.; Todd K.H.; Mulholland J.A.; Ryan P.B.; Frumkin H. (2004) Ambient air pollution and cardiovascular emergency

department visits. Epidemiology , 15:46
- 56. National Research Council. (2003) Managing Carbon Monoxide Pollution in Meteoro logical and Topographical Problem Areas. The National Academies Press, Washington, D.C. Sheps D.S.; Adams K.F. Jr.; Bromberg P.A.; Goldstein G.M.; O'Neil J.J.; Horstman D.; Koch G. (1987) Lack of effect of low levels of carbox yhemoglobin on cardiovascular function in patients with ischemic heart disease. Arch. Environ. Health 42:108
- 116. Sy mons J.M.; Wang L.; Guallar E.; Howell E.; Dominici F.; Schwab M.; Ange B.A.; Samet J.; Ondov J.; Harrison D.; Gey h A. (2006) A case
- crossover study of fine particulate matter air pollution and onset of congestive heart failure s ymptom exacerbation leading to hospitalization. Am J Epidemiol, 164:421
- 433. Tolbert P.E.; Klein M.; Peel J.L .; Sarnat S.E.; Sarnat J.A. (2007) Multipollutant modeling issues in a study of ambient air qualit y and emergency department visits in Atlanta. J Expo Sci Environ Epidemiol, 17:S29
- S35. U.S. Environmental Protection Agency . (1979a) Air Quality Criteria for Carbon Monoxide. Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office, Research Triangle Park, NC. EPA
- 600/8
- 79
- 022. U.S. Environmental Protection Agency . (1979b) Assessment of Adverse Health Effects from Carbon Monoxide and Implications for Possible Modifications of the Standard. Office of Air Quality Planning and Standards, Research Triangle Park, NC. U.S. Environmental Protection Agency . (1984a) Revised Evaluation of Health Effects Associated with Carbon Monoxide Exposure: An Addendum to the 1979 EPA Air Quality Criteria Document for Carbon Monoxide. Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office, Research Triangle Park, NC. EPA
- 600/8
- 83
- 033F
. U.S. Environmental Protection Agency . (1984b) Review of the NAAQS for Carbon Monoxide: Reassessment of Scientific a nd Technical Information. Office of Air*** E.O. 12866 Review

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Page **113** of **166** Quality Planning and Standards, Research Triangle Park. NC. EPA
- 450/584
- 904
. U.S. Environmental Protection Agency . (1991) Air Quality Criteria for Carbon Monoxide. Office of Health and Environmental Assessment, Envi ronmental Criteria and Assessment Office, Research Triangle Park, NC. EPA/600/8
- 90/045F. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_pr.html
. U.S. Environmental Protection Agency . (1992) Review of the National Ambient Air Quality

Standard s for Carbon Monoxide: Assessment of Scientific and Technical In formation, OAQPS Staff Paper. Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA/452/R
- 92
- 004. U.S. Environmental Protection Agency . (2000) Air Quality Criteria for Carbon Monoxide. National Center for Environmental Assessment, Office of Research and Development, Research Triangle Park, NC. EPA/600/P
- 99/001F. Available at: http://cfpub.epa.gov/ncea/cfm/recordisplay .cfm?deid=18163

. U.S. Environmental Protection Agency . (2008a) Draft Plan for Review of the National Ambient Air Quality Standards for Carbon Monoxide. Also known as Draft Integrated Review Plan. National Center for Environmental Assessment and Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA
- 452/D
- 08
- 001. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pd.html. U.S. Environmenta l Protection Agency . (2008b) Plan for Review of the National Ambient Air Quality

Standards for Carbon Monoxide. Also known as Integrated Review Plan. National Center for Environmental Assessment and Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA
- 452/R
- 08
- 005. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pd.html. U.S. Environmental Protection Agency . (2009a) Integrated Science Assessment for Carbon Monoxide, First External Review Draft. National Center for Environmental Assessment, Research Triangle Park, NC. EPA/600/R
- 00/019. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_isa.html
. U.S. Environmental Protection Agency . (2009b) Integrated Science Assessment for Carbon Monoxide, Second Exter nal Review Draft. National Center for Environmental Assessment, Research Triangle Park, NC. EPA/600/R
- 09/019B. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_isa.html
. U.S. Environmental Protection Agency . (2009c) Carbon Monoxide Nation al Ambient Air Quality

Standards: Scope and Methods Plan for Health Risk and Exposure Assessment. Draft. Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA
- 452/R
- 09
- 004. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pd.html
. U.S. Environmental Protection Agency . (2009d) Risk and Exposure Assessment to Support the Review of the Carbon Monoxide Primary National Ambient Air Quality Standards, First External Review Draft. Office of Air Quality Planning and Standard s, Research Triangle Park, NC. EPA
- 452/P
- 09
- 008. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_rea.html

. U.S. Environmental Protection Agency . (2010a) Integrated Science Assessment*** E.O. 12866 Review

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Page **114** of **166** for Carbon Monoxide. National Center for Environmental Assessment, Research Triangle Park, NC. EPA/600/R
- 09/019F. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_isa.html
. U.S. Environmental Protection Agency . (2010b) Quantitative Risk and Exposure Assessment for Carbon Monoxide
- Amended. Office of Air Qualit y Planning and Standards, Research Triangle Park, NC. EPA
- 452/R
- 10
- 009. Available at: http://www.ep a.gov/ttn/naaqs/standards/co/s_co_cr_rea.html
. U.S. Environmental Protection Agency . (2010c) Policy Assessment for the Review of the Carbon Monoxide National Ambient Air Quality Standards. Office of Air Quality Planning and Standards, Research Triangle Par k, NC. EPA 452/R
- 10
- 007. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pa.html
. U.S. Environmental Protection Agency . (2010d) Risk and Exposure Assessment to Support the Review of the Carbon Monoxide Primary National Ambient Air Quality Standards, Second External Review Draft, U.S Environmental Protection Agency , Research Triangle Park, N C, report no. EPA
- 452/P
- 10
- 004. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_rea.html
. U.S. Environmental Protection Agency . (2010e) Policy Assessment for the Review of the Carbon Monoxide National Ambient Air Quality Standards, Exter

nal Review Draft. Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA
- 452/P
- 10
- 005. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pa.html
. Watkins N. and Thompson R. (2010) CO Monitoring Network Background and Review. Memorandum to the Carbon Monoxide NAAQS Review Docket. EPA
- HQ
OAR
- 2008
- 0015. Wellenius G.A.; Bateson T.F.; Mittleman M.A.; Schwartz J. (2005) Particulate air pollution and the rate of hospitalization for congestive heart failure among medicare beneficiaries in Pittsburgh, Pennsylvania. Am J Epidemiol 161:1030
- 1036. Zhu Y.; Hinds W.C.; Kim S.; Shen S.; Sioutas C. (2002) Study of ultrafine particles near a major highway with heav y - duty

diesel traffic. Atmos Environ, 36: 4323
- 4335.*** E.O. 12866 Review

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Page **115** of **166 List of Subjects**  **40 CFR Part 50** Environmental protection, Air pollution control, Carbon monoxide, Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides. **40 CFR Part 53** Environmental protection, Administrative practice and procedure, Air pollution control, Intergovernmental relations, Reporting and recordkeeping requirements. **40 CFR Part 58** Environmental protection, Admini strative practice and procedure, Air pollution control, Intergovernmental relations, Reporting and recordkeeping requirements Dated: August 1 2, 2011
Lisa P. Jackson, Administrator.*** E.O. 12866 Review

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Page **116** of **166** For the reasons stated in the preamble, title 40, chapter I of the Code of Federal Regulations is amended as follows: **PART 50**
**– NATIONAL PRIMARY AND SECONDARYAMBIENT AIR**  **QUALITY STANDARDS** 1. The authority citation for part 50 continues to read as follows: Authority : 42 U.S.C. 7401, et seq. 2. Appendix C to p art 50 is revised to read as follows: **Appendix C to Part 50**
**— Measurement Principle and Calibration Procedure for the**  **Measurement of Carbon Monoxide in the Atmosphere (Non -**  **Dispersive Infrared Photometry)**  1.0 Applicability 1.1 This non
- dispersive infrared photometry (NDIR) Federal Reference Method (FRM) provid es measurements of the concentration of carbon monoxide (CO) in ambient air for determining compliance with the primary and secondary

National Ambient Air Quality Standards (NAAQS) for CO as specified in § 50.8 of this chapter. The method is applicable to continuous sampling and measurement of ambient CO concentrations suitable for determining 1
- hour or longer average measurements. The method may also provide measurements of shorter averaging times, subject to specific anal yz er performance limitations. Ad ditional CO monitoring quality assurance procedures and guidance are provided in part 58, appendix A, of this chapter and in reference 1 of this appendix C. 2.0 Measurement Principle*** E.O. 12866 Review

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Page **1 17**  of **166** 2.1 Measurements of CO in ambient air are based on automated measure ment of the absorption of infrared radiation by CO in an ambient air sample drawn into an anal yz er employing non
- wavelength
- dispersive, infrared photometry (NDIR method). Infrared energy from a source in the photometer is passed through a cell containing the air sample to be anal yz ed, and the quantitative absorption of energy by CO in the sample cell is measured b y a suitable detector. The photometer is sensitized specifically to CO by employing CO gas in a filter cell in the optical path, which, when comp ared to a differential optical path without a CO filter cell, limits the measured absorption to one or more of the characteristic wavelengths at which CO strongl y absorbs. However, to meet measurement performance requirements, various optical filters, ref erence cells, rotating gas filter cells, dual
- beam configurations, moisture traps, or other means may also be used to further enhance sensitivity and stability

of the photometer and to minimize potential measurement interference from water vapor, carbon di oxide (CO 2 ), or other species. Also, various schemes may be used to provide a suitable zero reference for the photometer, and optional automatic compensation may be provided for the actual pressure and temperature of the air sample in the measurement cell. The measured infrared absorption, converted to a digital reading or an electrical output signal, indicates the measured CO concentration.
2.2 The measurement s ys tem is calibrated b y referencing the analyzer’s CO measurements to CO concentration stand ards traceable to a National Institute of Standards and Technology (NI ST) primary standard for CO, as described in the associated calibration procedure specified in section 4 of this reference method.*** E.O. 12866 Review

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Page **118** of **166** 2.3 An anal yz er implementing this measurement principle will be considered a reference method onl y if it has been designated as a reference method in accordance with part 53 of this chapter. 2.4 Sampling considerations. The use of a particle filter in the sample inlet line of a CO FRM anal yz er is optional and left to the discretion of the user unless such a filter is specified or recommended by the anal yz er manufacturer in the anal yz er’s associated operation or instruct ion manual.
3.0 Interferences 3.1 The NDIR measurement principle is potentially susceptible to interference from water vapor and CO 2 , which have some infrared absorption at wavelengths in common with CO and normally

exist in the atmosphere. Various ins trumental techniques can be used to effectivel y minimize these interferences.
4.0 Calibration Procedures 4.1 Principle . Either of two methods may be selected for dy

namic multipoint calibration of FRM CO analyzers, using test gases of accuratel y known CO concentrations obtained from one or more compressed gas cylinders certified as CO transfer standards:
4.1.1 Dilution method: A single certified standard cylinder of CO is quantitatively diluted as necessary

with zero air to obtain the various calibr ation concentration standards needed.*** E.O. 12866 Review

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Page **119** of **166** 4.1.2 Multiple
- cylinder method: Multiple, individually certified standard cylinders of CO are used for each of the various calibration concentration standards needed.
4.1.3 Additional information on calibration m ay be found in Section 12 of reference 1. 4.2 Apparatus
. The major components and typical configurations of the calibration sy stems for the two calibration methods are shown in Figures 1 and 2. Either s ys tem may be made up using common laboratory compo nents, or it may

be a commercially manufactured s ys tem. In either case, the principal components are as follows:
4.2.1 CO standard gas flow control and measurement devices (or a combined device) capable of regulating and maintaining the standard gas fl ow rate constant to within ±2 percent and measuring the gas flow rate accurate to within ±2 percent, properly calibrated to a NI ST
- traceable standard. 4.2.2 For the dilution method (Figure 1), dilution air flow control and measurement devices (or a comb ined device) capable of regulating and maintaining the air flow rate constant to within ±2 percent and measuring the air flow rate accurate to within ±2 percent, properl y calibrated to a NIST
- traceable standard. 4.2.3 Standard gas pressure regulator(s) for the standard CO cylinder(s), suitable for use with a high
- pressure CO gas cylinder and having a non
- reactive diaphragm and internal parts and a suitable delivery pressure. 4.2.4 Mixing chamber for the dilution method, of an inert material and of pro per*** E.O. 12866 Review

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Page **120** of **166** design to provide thorough mixing of CO standard gas and diluent air streams. 4.2.5 Output sampling manifold, constructed of an inert material and of sufficient diameter to ensure an insignificant pressure drop at the anal yz er connection. The sy ste m must have a vent designed to ensure nearl y atmospheric pressure at the analy zer connection port and to prevent ambient air from entering the manifold. 4.3 Reagents
. 4.3.1 CO gas concentration transfer standard(s) of CO in air, containing an appropriate concentration of CO suitable for the selected operating range of the anal yz er under calibration and traceable to a NIST standard reference material (SRM). If the CO anal yz er has significant sensitivity to CO 2 , the CO standard(s) should also co ntain 350 to 400 ppm CO 2 to replicate the typical CO 2 concentration in ambient air. However, if the zero air dilution ratio used for the dilution method is not less than 100:1 and the zero air contains ambient levels of CO 2 , then the CO standard may be contained in nitrogen and need not contain CO 2 . 4.3.2 For the dilution method, clean zero air, free of contaminants that could cause a detectable response on or a change in sensitivity of the CO anal yz er. The zero air should contain <0.1 ppm CO.
4.4 Procedure Using the Dilution Method. 4.4.1 Assemble or obtain a suitable dy namic dilution calibration s ys tem such as the one shown schematically in Figure 1. Generally , all calibration gases including zero air must be introduced into the sample inlet of the analyzer. However, if the analyzer has*** E.O. 12866 Review

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Page **121** of **166** special, approved zero and span inlets and automatic valves to specifically allow introduction of calibration standards at near atmospheric pressure, such inlets may be used for calibration in lieu of the sample in let. For specific operating instructions, refer to the manufacturer’s manual. 4.4.2 Ensure that there are no leaks in the calibration sy stem and that all flowmeters are properl y and accurately calibrated, under the conditions of use, if appropriate, against a reliable volume or flow rate standard such as a soap
- bubble meter or wet
- test meter traceable to a NI ST standard. All volumetric flow rates should be corrected to the same temperature and pressure such as 298.15 K (25 °C) and 760 mm Hg (101 kPa), u sing a correction formula such as the following:
(1) where: F c = corrected flow rate (L/min at 25 oC and 760 mm Hg), F m = measured flow rate (at temperature T m and pressure Pm ), Pm = measured pressure in mm Hg (absolute), and T m = measured temperature in degrees Celsius. 4.4.3 Select the operating range of the CO anal yz er to be calibrated. Connect the measurement signal output of the anal yz er to an appropriate readout instrument to allow the anal yz er’s measurement output to be continuously monitored during the calibration. Where possible, this readout instrument should be the same one used to record routine monitoring data, or, at least, an instrument that is as closel y representative of that system as feasible. ) 15
. 273 ( 760 15
. 298    m m m c T P F F*** E.O. 12866 Review

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Page **122** of **166** 4.4.4 Connect the inlet of the CO ana ly zer to the output
- sampling manifold of the calibration s ys tem. 4.4.5 Adjust the calibration sy stem to deliver zero air to the output manifold. The total air flow must exceed the total demand of the anal yz er(s) connected to the output manifold to ensur e that no ambient air is pulled into the manifold vent. Allow the anal yz er to sample zero air until a stable response is obtained. After the response has stabilized, adjust the analyzer zero reading. 4.4.6 Adjust the zero air flow rate and the CO gas f low rate from the standard CO cylinder to provide a diluted CO concentration of approximately 80 percent of the measurement upper range limit (URL) of the operating range of the anal yz er. The total air flow rate must exceed the total demand of the analyzer (s) connected to the output manifold to ensure that no ambient air is pulled into the manifold vent. The exact CO concentration is calculated from:
(2) where: [ CO ] OUT = diluted CO concentration at the output manifold (ppm), [ CO ] STD = concentration of the undiluted CO standard (ppm), F CO = flow rate of the CO standard (L/min), and F D = flow rate of the dilution air (L/min). Sample this CO concentration until a stable response is obtained. Adjust the anal yz er span control to obtain the desired analyzer response reading equivalent to the calculated standard concentration. If substantial adjustment of the anal yz er span control is required, it may be necessary

to recheck the zero and span adjustments by repeating steps 4.4.5 and 4.4.6. Record the CO concentration and the anal yzer’s final response. CO D CO STD OUT 

### F F F CO CO    ] [ ] [*** E.O. 12866 Review

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Page **123** of **166** 4.4.7 Generate several additional concentrations (at least three evenl y spaced points across the remaining scale are suggested to verify linearity) by

decreasing F

CO or increasing F

D . Be sure the total flow exce eds the anal yz er’s total flow demand. For each concentration generated, calculate the exact CO concentration using equation (2). Record the concentration and the anal yz er’s stable response for each concentration. Plot the anal yz er responses (vertical or y - axis) versus the corresponding CO concentrations (horizontal or x
- axis). Calculate the linear regression slope and intercept of the calibration curve and verify that no point deviates from this line by more than 2 percent of the highest concentration te sted.
4.5 Procedure Using the Multiple
- Cylinder Method. Use the procedure for the dilution method with the following changes: 4.5.1 Use a multi
- cylinder, dy namic calibration system such as the ty pical one shown in Figure 2. 4.5.2 The flowmeter need no t be accuratel y calibrated, provided the flow in the output manifold can be verified to exceed the anal yz er’s flow demand. 4.5.3 The various CO calibration concentrations required in Steps 4.4.5, 4.4.6, and 4.4.7 are obtained without dilution by selecting zero air or the appropriate certified standard cylinder. 4.6 Frequency of Calibration. The frequency of calibration, as well as the number of points necessary

to establish the calibration curve and the frequency of other performance checking, will vary by

analyzer. However, the minimum frequency , acceptance criteria, and subsequent actions are specified in reference 1, appendix D, “Measurement Quality Objectives and Validation Template for CO” (page 5 of 30). The user’s quality control program should p rovide guidelines for initial establishment of these variables and for*** E.O. 12866 Review

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Page **124** of **166** subsequent alteration as operational experience is accumulated. Manufacturers of CO anal yz ers should include in their instruction/operation manuals information and guidance as to these variables and on other matters of operation, calibration, routine maintenance, and quality

control. 5.0 Reference 1. QA Handbook for Air Pollution Measurement Systems

— Volume II. Ambient Air Quality Monitoring Program. U.S. EPA. EPA

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125 Figure 1. Dilution method for calibrat ion of CO analyzers. Flow co ntroller Flow me ter

Flow co ntr oller Flow me ter Mi xi ng ch am ber Zero air

Ex tra outlets c apped Vent

To inlet of a naly zer CO std. Ou tput ma nif old **F C**  **F D** *** E.O. 12866 Review

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126 Figure 2
. Multiple cylinder method for calibrat ion of CO analyzers. Flow co ntroller Flow me ter

Ex tra outlets ca pped wh en not in use Ve nt

To inlet ofa naly zer under c alibration CO std.

Ou tput ma nif old CO st d. CO st d. Zero air CO st d.*** E.O. 12866 Review

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Page **127** of **166 PART 53** 
**– AMBIENT AIR**  **QUALITY REFERENCE AND EQUIVALENT METHODS** 3. The authority citation for part 53 continues to read as follows: Authority : 42 U.S.C. 7401, et seq. 4. Subpart B of p art 53 is revised to read as follows: **Subpart B**
**– Procedures for Testing Performance**  **Characteristics of Automated Methods for SO**  **2 , CO, O**  **3 , and NO**  **2** Sec. 53.20 General Provisions 53.21 Test Conditions 53.22 Generation of Test Atmospheres 53. 2 3 Test Procedure Appendix A to Subpart B

– Optional Forms For Reporting Test Results **Subpart B**
**– Procedures for Testing Performance Characteristics of Automated Methods for**  **SO 2**  **, CO, O 3**  **, and NO 2**  **§ 53.20 General provisions.** (a) The test procedures given in this subpart shall be used to test the performance of candidate automated methods against the p erformance requirement specifications given in table B
- 1. A test anal yz er representative of the candidate automated method must exhibit performance better than, or not outside, the specified limit or limits for each such performance parameter specified (ex cept range) to satisfy the requirements of this subpart. Except as provided in paragraph (b) of this section, the measurement range of the candidate method must be the standard range specified in table B
- 1 to satisfy the requirements of this subpart. (b) Measurement ranges. For a candidate method having more than one selectable measurement range, one range must be the standard range specified in table B
- 1, and a test analyzer representative of the method must pass the tests required b y this subpart while operated in that range. (i) Higher ranges. The tests may be repeated for one or more higher (broader) ranges ( i.e. , ranges extending to higher concentrations) than the standard range specified in table B
- 1, provided that the range does not extend to conce ntrations more than four times the upper range limit of the standard*** E.O. 12866 Review

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Page **128** of **166** range specified in table B
- 1. For such higher ranges, only the tests for range (calibration), noise at 80% of the upper range limit, and lag, rise and fall time are required to be repeat ed. For the purpose of testing a higher range, the test procedure of §53.23(e) may be abridged to include only those components needed to test lag, rise and fall time. (ii) Lower ranges. The tests may be repeated for one or more lower (narrower) ranges ( i.e. , ones extending to lower concentrations) than the standard range specified in table B
- 1. For methods for some pollutants, table B
- 1 specifies special performance limit requirements for lower ranges. If special low
- range performance limit requirement s are not specified in table B
- 1, then the performance limit requirements for the standard range apply . For lower ranges for any method, only

the tests for range (calibration), noise at 0 % of the measurement range, lower detectable limit, (and nitric oxid e interference for SO 2 UVF methods) are required to be repeated, provided the tests for the standard range shows the applicable limit specifications are met for the other test parameters. (iii) If the tests are conducted and passed only for the specified standard range, any FRM or FEM determination with respect to the method will be limited to that range. If the tests are passed for both the specified range and one or more higher or lower ranges, an y such determination will include the additional higher o r lower range(s) as well as the specified standard range. Appropriate test data shall be submitted for each range sought to be included in a FRM or FEM method determination under this paragraph (b). (c) For each performance parameter (except range), the test procedure shall be initially repeated seven (7) times to yi eld 7 test results. Each result shall be compared with the corresponding performance limit specification in table B
- 1; a value higher than or outside the specified limit or limits constitutes a failure. These 7 results for each parameter shall be interpreted as follows: (1) Zero (0) failures: The candidate method passes the test for the performance parameter. (2) Three (3) or more failures: The candidate method fails the test for the performa nce parameter.*** E.O. 12866 Review

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Page **129** of **166** (3) One (1) or two (2) failures: Repeat the test procedures for the performance parameter eight (8) additional times yielding a total of fifteen (15) test results. The combined total of 15 test results shall then be interpreted as follows: (i) One (1) or two (2) failures: The candidate method passes the test for the performance parameter. (ii) Three (3) or more failures: The candidate method fails the test for the performance parameter. (d) The tests for zero drift, span drift, lag time, rise time, fall time, and precision shall be carried out in a single integrated procedure conducted at various line voltages and ambient temperatures specified in § 53.23(e). A temperature
- controlled environmental test chamber large enough to contain the t est anal yz er is recommended for this test. The tests for noise, lower detectable limit, and interference equivalent shall be conducted at any ambient temperature between 20 °C and 30 °C, at any normal line voltage between 105 and 125 volts, and shall be co nducted such that not more than three (3) test results for each parameter are obtained in an y 24
- hour period. (e) If necessary , all measurement response readings to be recorded shall be converted to concentration units or adjusted according to the calibration curve constructed in accordance with §53.21(b). (f) All recorder chart tracings (or equivalent data plots), records, test data and other documentation obtained from or pertinent to these tests shall be identified, dated, signed by the anal ys t performing the test, and submitted. N OT E TO § 53.20 : Suggested formats for reporting the test results and calculations are provided in Figures B
- 2, B
- 3, B
- 4, B
- 5, and B
- 6 in appendix A to this subpart. Sy mbols and abbreviations used in this subpart are l isted in table B

– 5 of appendix A to this subpart.*** E.O. 12866 Review

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Page **130** of **166** T ABLE B - 1
— P ERFORMANCE L IMIT S PECIFICATIONS FOR A UTOMATED M ETHODS Performance parameter Units 1 SO 2 O 3 (Std. range) CO NO 2 (Std. range) Definitions and test

procedures Std. range 3 Lower

range 2,3 Std.

range 3 Lower

range 2,3 1. Range ppm 0 - 0.5 <0.5 0 - 0.5 0 - 50 <50 0 - 0.5 Sec. 53.23(a). 2. Noise ppm 0.001 0.0005 0.005 0.2 0.1 0.005 Sec. 53.23(b). 3. Lower detectable limit ppm 0.002 0.001 0.010 0.4 0.2 0.010 Sec. 53.23(c). 4. Interference equivalent Each interferent Total, all interferents ppm ppm ±0.005

--- 4 ±0.005

--- ±0.02

0.06 ±1.0

--- ±0.5 ±0.02

0.04 Sec. 53.23(d). Sec. 53.23(d). 5. Zero drift, 12 and 24 hour ppm ±0.004 ±0.002 ±0.02 ±0.5 ±0.3 ±0.02 Sec. 53.23(e). 6. Span drift, 24 hour 20% of upper range limit 80% of upper range limit Percent Percent ---

± 3.0 ---

± 3.0 ±20.0

±5.0 --- ±2.0 ---

±2.0 ±20.0

±5.0 Sec. 53.23(e) Sec. 53.23(e). 7. Lag time Minutes 2 2 20 2.0 2.0 20 Sec. 53.23(e). 8. Rise time Minutes 2 2 15 2.0 2.0 15 Sec. 53.23(e). 9. Fall time Minutes 2 2 15 2.0 2.0 15 Sec. 53.23(e). 10. Precision 20 % of upper range limit 80 % of upper range limit ppm Percent ppm Percent ---

2

--- 2 ---

2

--- 2 0.010

--- 0.010

--- ---

1.0

--- 1.0 ---

1.0

--- 1.0 0.020

--- 0.030

--- Sec. 53.23(e).

Sec. 53.23(e). Sec. 53.23(e). Sec. 53.23(e). 1. To convert from parts per million (ppm) to μg/m 3 at 25 °C and 760 mm Hg, multiply by M/0.02447, where M is the molecular weight of the gas. Percent means percent of the upper measurement range limit. 2. Tests for interference equivalent and lag time do not need to be repeated for any lower range provided the test for the standard range shows that the lower ran ge specification (if applicable) is met for each of these test parameters. 3. For candidate analyzers having automatic or adaptive time constants or smoothing filters, describe their functional nature, and describe and conduct suitable tests to demonstrate their function aspects and verify that performances for calibration, noise, lag, rise, fall times, and precisi on are within speci fications under all applicable conditions. For candidate analyzers with operator- selectable time constants or smoothing filters, conduct calibration, noise, lag, rise, fall times, and precision tests at the highest and lowest settings that are to be inclu ded in the FRM or FEM designation. 4. For nitric oxide interference for the SO 2 UVF method, interference equivalent is ±0.0003 ppm for the lower range.*** E.O. 12866 Review

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Page **131** of **166 §**  **53.21 Test conditions.** (a) Set
- up and start
- up of the test anal yz er shall be in strict accordance with the operating instructions specified in the manual referred to in § 53.4(b)(3). Allow adequate warm
- up or stabilization time as indicated in the operating instructions before beginning the tests. The test procedures assume that the test anal yz er has a conventional analog measurement signal output that is connected to a suitable strip chart recorder of the servo, null
- balance t ype. This recorder shall have a chart width of a least 25 centimeters, ch art speeds up to 10 cm per hour, a response time of 1 second or less, a deadband of not more than 0.25 percent of full scale, and capability either of reading measurements at least 5 percent below zero or of offsetting the zero b y at least 5 percent. If the test anal yz er does not have an analog signal output, or if a digital or other type of measurement data output is used for the tests, an alternative measurement data recording device (or devices) may be used for recording the test data, provided that the device is reasonabl y suited to the nature and purposes of the tests, and an analog representation of the anal yz er measurements for each test can be plotted or otherwise generated that is reasonabl y similar to the analog measurement recordings that would b e produced b y a conventional chart recorder connected to a conventional analog signal output. (b) Calibration of the test analyzer shall be carried out prior to conducting the tests described in this subpart. The calibration shall be as indicated in the manual referred to in § 53.4(b)(3) and as follows: I f the chart recorder or alternative data recorder does not have below zero capability, adjust either the controls of the test analyzer or the chart or data recorder to obtain a +5% offset zero reading on the recorder chart to facilitate observing negative response or drift. If the candidate method is not capable of negative response, the test anal yz er (not the data recorder) shall be operated with a similar offset zero. Construct and submit a calibration curve showing a plot of recorder scale readings or other measurement output readings (vertical or y - axis) against pollutant concentrations presented to the anal yz er for measurement (horizontal or x
- axis). I f applicable, a plot of base analog output units (v olts,*** E.O. 12866 Review

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Page **132** of **166** millivolts, milliamps, etc.) against pollutant concentrations shall also be obtained and submitted. All such calibration plots shall consist of at least seven (7) approximately equally spaced, identifiable points, including 0 and 90±5 percent of the upper range limit (URL). (c) Once the test anal yz er has been set up and calibrated and the tests started, manual adjustment or normal periodic maintenance is permitted only every 3 day s. Automatic adjustments which the test anal yz er performs by

itself are permitted at any time. The submitted records shall show clearl y when any manual adjustment or periodic maintenance was made during the tests and describe the specific operations performed. (d) If the test anal yz er should malfunction during any of the per formance tests, the tests for that parameter shall be repeated. A detailed explanation of the malfunction, remedial action taken, and whether recalibration was necessary (along with all pertinent records and charts) shall be submitted. If more than one mal function occurs, all performance test procedures for all parameters shall be repeated. (e) Tests for all performance parameters shall be completed on the same test analyzer; however, use of multiple test analyzers to accelerate testing is permissible for testing additional ranges of a multi
- range candidate method. **§ 53.22 Generation of test atmospheres.**  (a) Table B
- 2 specifies preferred methods for generating test atmospheres and suggested methods of verifying their concentrations. Only one means of estab lishing the concentration of a test atmosphere is normall y required, provided that that means is adequatel y accurate and credible. If the method of generation can produce accurate, reproducible concentrations, verification is optional. If the method of gen eration is not reproducible or reasonably quantifiable, then establishment of the concentration by

some credible verification method is required.*** E.O. 12866 Review

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Page **133** of **166** (b) The test atmosphere delivery s ys tem shall be designed and constructed so as not to significantl y alter the test atmosphere composition or concentration during the period of the test. The sy stem shall be vented to insure that test atmospheres are presented to the test anal yz er at very nearly atmospheric pressure. The delivery

s ystem shall be fabricated from b orosilicate glass, FEP Teflon, or other material that is inert with regard to the gas or gases to be used. (c) The output of the test atmosphere generation s ystem shall be sufficientl y stable to obtain stable response readings from the test anal yz er during the required tests. If a permeation device is used for generation of a test atmosphere, the device, as well as the air passing over it, shall be controlled to 0.1 oC. (d) All diluent air shall be zero air free of contaminants likely to react with the test atmospheres or cause a detectable response on the test anal yz er. (e) The concentration of each test atmosphere used shall be quantitatively established and/or verified before or during each series of tests. Samples for verifying test concentrations s hall be collected from the test atmosphere delivery s ys tem as close as feasible to the sample intake port of the test analyzer. (f) The accuracy

of all flow measurements used to calculate test atmosphere concentrations shall be documented and referenced t o a primary flow rate or volume standard (such as a spirometer, bubble meter, etc.). An y corrections shall be clearl y shown. All flow measurements given in volume units shall be standardized to 25 oC. and 760 mm Hg. (g) Schematic drawings, photos, descrip tions, and other information showing complete procedural details of the test atmosphere generation, verification, and delivery s ys tem shall be provided. All pertinent calculations shall be clearl y indicated.*** E.O. 12866 Review

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Page **134** of **166** T ABLE B - 2
—T EST ATMOSPHERES **Test gas Generation**  **Verification** Ammonia Permeation device. Similar to system described

in references 1 and 2 Indophenol method, reference 3. Carbon dioxide Cylinder of zero air or nitrogen containing CO 2 as

required to obtain the concentration specified in table B - 3. Use NIST - certified standards whenever possible. If NIST standards are not available, obtain 2 standards from independent sources which agree within 2 percent, or obtain one standard and subm it it to an independent laboratory for analysis, which must agree within 2 percent of the supplier’s nominal analysis. Carbon monoxide Cylinder of zero air or nitrogen containing CO as

required to obtain the concentration specified in table B - 3. Use an FR M CO analyzer as described in reference 8. Ethane Cylinder of zero air or nitrogen containing ethane

as required to obtain the concentration specified in table B - 3. Gas chromatography, ASTM D2820, reference 10. Use NIST - traceable gaseous methane or prop ane standards for calibration. Ethylene Cylinder of pre - purified nitrogen containing

ethylene as required to obtain the concentration specified in table B - 3. Do. Hydrogen chloride Cylinder 1 of pre - purified nitrogen containing

approximately 100 ppm of gaseous HCl. Dilute with zero air to concentration specified in table B - 3 Collect samples in bubbler containing distilled water and analyze by the mercuric thiocyanate method, ASTM (D612), p. 29 , reference 4. Hydrogen sulfide Permeation device system described in references

1 and 2. Tentative method of analysis for H 2 S content of the atmosphere, p. 426, reference 5. Methane Cylinder of zero air containing methane as required

to obtain the concentration specified in table B - 3. Gas chromatography ASTM D2820, reference 10. Use NIST - traceable methane standards for calibration.
Nitric oxide Cylinder 1 of pre - purified nitrogen containing

approximately 100 ppm NO. Dilute with zero air to required concentration. Gas phase titration as described in reference 6, section 7.1 Nitrogen dioxide 1. Gas phase titration as described in reference 6.

2. Permeation device, similar to system described in reference 6. 1. Use an FRM NO 2 analyzer calibrated with a gravimetrically calibrated permeation device. 2. Use an FRM NO 2 analyzer calibrated by gas phase titration as described in reference 6. Ozone Calibrated ozone generator as described in

reference 9. Use an FEM ozone analyzer ca librated as described in reference 9. Sulfur dioxide 1. Permeation device as described in references 1

and 2. 2. Dynamic dilution of a cylinder containing approximately 100 ppm SO 2 as described in Reference 7. Use an SO 2 FRM or FEM analyzer as described in reference 7.*** E.O. 12866 Review

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Page **135** of **166** T ABLE B - 2
—T EST ATMOSPHERES (C ONTINUED )

1 Use stainless steel pressure regulator dedicated to the pollutant measured. Reference 1. O'Keefe, A. E., and Ortaman, G. C. "Primary Standards for Trace Gas Analysis," Anal. Chem . 38, 760 (1966). Reference 2. Scaringelli, F. P., A. E. . Rosenberg, E*, and Bell, J. P., " Primary Standards for Trace Gas Analysis." Anal. Chem . 42, 871 (1970). Reference 3. "Tentative Method of Analysis for Ammonia in the Atmosphere (Indophenol Method)", Health Lab Sciences , vol. 10, No. 2, 115 - 118, April 1973. Reference 4. 1973 Annual Book of ASTM Standards, American Society for Testing and Materials, 1916 Race St., Philadelphia, PA. Reference 5. Methods for Air Sampling and Analysis , Intersociety Committee, 1972, American Public Health Association, 1015. Reference 6. 40 CFR 50 Appendix F, "Me asurement Principle and Calibration Principle for the Measurement of Nitrogen Dioxide in the Atmosphere (Gas Phase Chemiluminescence)." Reference 7. 40 CFR 50 Appendix A - 1, "Measurement Principle and Calibration Procedure for the Measurement of Sulfur Diox ide in the Atmosphere (Ultraviolet FIuorscence)." Reference 8. 40 CFR 50 Appendix C, "Measurement Principle and Calibration Procedure for the Measurement of Carbon Monoxide in the Atmosphere" (Non - Dispersive Infrared Photometry)". Reference 9. 40 CFR 50 Ap pendix D, "Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere". Reference 10. "Standard Test Method for C, through C5 Hydrocarbons in the Atmosphere by Gas Chromatography", D 2820, 1987 Annual Book of Aston Stand ards, vol 11.03, American Society for Testing and Materials, 1916 Race St., Philadelphia, PA 19103. **§ 53.23 Test procedures.**  (a) Range

— (1) Technical definition. The nominal minimum and maximum concentrations that a method is capable of measuring. N OT E TO § 53.2 3(a)(1) : The nominal range is given as the lower and upper range limits in concentration units, for example, 0
- 0.5 parts per million (ppm). **Test gas Generation**  **Verification** Wa ter Pass zero air through distilled water at a fixed known

temperature between 20° and 30° C such that the air stream becomes saturated. Dilute with zero air to concentration specified in table B - 3. Measure relative humidity by means of a dew point indicator, calibrated electrolytic or piezo electric hygrometer, or wet/dry bulb thermometer. Xylene Cylinder of pre - purified nitro gen containing 100 ppm

xylene. Dilute with zero air to concentration specified in table B - 3. Use NIST - certified standards whenever possible. If NIST standards are not available, obtain 2 standards from independent sources which agree within 2 percent, or obtain one standard and submit it to an independent laboratory for analysis, which must agree within 2 percent of the supplier’s nominal analysis. Zero air 1. Ambient air purified by appropriate scrubbers or

other devices such that it is free of contamin ants likely to cause a detectable response on the analyzer. 2. Cylinder of compressed zero air certified by the supplier or an independent laboratory to be free of contaminants likely to cause a detectable response on the analyzer.*** E.O. 12866 Review

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Page **136** of **166** (2) Test procedure. Determine and submit a suitable calibration curve, as specified in § 53.21(b), showing the test anal yz er's measurement response over at least 95 percent of the required or indicated measurement range. N OT E T O § 53.2 3(a)(2) : A single calibration curve for each measurement range for which an FRM or FEM designation is sought will norma lly suffice. (b) Noise

— (1) Technical definition. Spontaneous, short duration deviations in measurements or measurement signal output, about the mean output, that are not caused b y i nput concentration changes. Measurement noise is determined as the standard deviation of a series of measurements of a constant concentration about the mean and is expressed in concentration units. (2) Test procedure. (i) Allow sufficient time for the test anal yz er to warm up and stabilize. Determine measurement noise at each o f two fixed concentrations, first using zero air and then a pollutant test gas concentration as indicated below. The noise limit specification in table B
- 1 shall apply to both of these tests. (ii) For an anal yz er with an analog signal output, connect an i ntegrating
- ty pe digital meter (DM) suitable for the test analyzer's output and accurate to three significant digits, to determine the analyzer's measurement output signal. N OT E T O § 53.2 3(b)(2) : Use of a chart recorder in addition to the DM is optional. (iii) Measure zero air with the test anal yz er for 60 minutes. During this 60
- minute interval, record twenty - five (25) test analyzer concentration measurements or DM readings at 2
- minute intervals. (See Figure B
- 2 in appendix A of this subpart.) (iv) If ap plicable, convert each DM test reading to concentration units (ppm) or adjust the test readings (if necessary) by reference to the test analyzer's calibration curve as determined in § 53.21(b). Label and record the test measurements or converted DM reading s as r 1 , r 2 , r3 ... ri ... r

25 .*** E.O. 12866 Review

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Page **137** of **166** (v) Calculate measurement noise as the standard deviation, S, as follows:

where i indicates the i - th test measurement or DM reading in ppm. (vi) Let S at 0 ppm be identified as S 0 ; compare S

0 to the noise limit specification given in table B
1. (vii) Repeat steps in Paragraphs (b)(2)(iii) through (v) of this section using a pollutant test atmosphere concentration of 80±5 percent of the URLinstead of zero air, and let S at 80 percent of the U RLbe identified as S 80 . Compare S

80 to the noise limit specification given in table B
- 1 of this subpart. (viii) Both S

0 and S

80 must be less than or equal to the table B
- 1 noise limit specification to pass the test for the noise parameter. (c) Lower detectable limit

— (1) Technical definition. The minimum pollutant concentration that produces a measurement or measurement output signal of at least twice the noise level. (2) Test procedure. (i) Allow sufficient time for the test anal yz er to warm up and stab ilize. Measure zero air and record the stable measurement reading in ppm as B Z . (See Figure B
- 3 in appendix A of this subpart.) (ii) Generate and measure a pollutant test concentration equal to the value for the lower detectable limit specified in table B
- 1. N OT E T O § 53.2 3(c)(2) : If necessary , the test concentration may be generated or verified at a higher concentration, then quantitatively and accuratel y diluted with zero air to the final required test concentration. (iii) Record the test analyzer's stable measurement reading, in ppm, as B L .         

    

  

##  

  2

25 1 25 1 2 25 1 24 1 i i i i r r S*** E.O. 12866 Review

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Page **138** of **166** (iv) Determine the lower detectable limit ( LDL ) test result as LDL = B L − B Z . Compare this LDL value with the noise level, S 0 , determined in § 53.23(b), for the 0 concentration te st atmosphere. LDL must be equal to or higher than 2 × S 0 to pass this test. (d) Interference equivalent

— (1) Technical definition. Positive or negative measurement response caused b y a substance other than the one being measured. (2) Test procedure. The test anal yz er shall be tested for all substances likel y to cause a detectable response. The test anal yz er shall be challenged, in turn, with each potential interfering agent (interferent) specified in table B
- 3. In the event that there are substances likel y to cause a significant interference which have not been specified in table B
- 3, these substances shall also be tested, in a manner similar to that for the specified interferents, at a concentration substantially higher than that likely to be found in the ambient air. The interference may be either positive or negative, depending on whether the test anal yz er's measurement response is increased or decreased by the presence of the interferent. Interference equivalents shall be determined by mixing each inter ferent, one at a time, with the pollutant at an interferent test concentration not lower than the test concentration specified in table B - 3 (or as otherwise required for unlisted interferents), and comparing the test anal yz er's measurement response to the response caused by the pollutant alone. Known gas
- phase reactions that might occur between a listed interferent and the pollutant are designated b y footnote 3 in table B
- 3. In these cases, the interference equivalent shall be determined without mixing with the pollutant. (i) Allow sufficient time for warm
- up and stabilization of the test anal yz er. (ii) For a candidate method using a prefilter or scrubber device based upon a chemical reaction to derive part of its specificity and which device requires peri odic service or maintenance, the test anal yz er shall be “conditioned” prior to conducting each interference test series. This requirement includes conditioning for the NO 2 converter in chemiluminescence NO/NO 2 /NO x analyzers and for the ozone scrubber in UV
- absorption ozone analyzers. Conditioning is as follows:*** E.O. 12866 Review

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Page **139** of **166** (A) Service or perform the indicated maintenance on the scrubber or prefilter device, as if it were due for such maintenance, as directed in the manual referred to in § 53.4(b)(3). (B) Before testi ng for each potential interferent, allow the test anal yz er to sample through the prefilter or scrubber device a test atmosphere containing the interferent at a concentration not lower than the value specified in table B
- 3 (or, for unlisted potential interf erents, at a concentration substantially

higher than likely

to be found in ambient air). Sampling shall be at the normal flow rate and shall be continued for 6 continuous hours prior to the interference test series. Conditioning for all applicable interfe rents prior to any of the interference tests is permissible. Also permissible is simultaneous conditioning with multiple interferents, provided no interferent reactions are likel y to occur in the conditioning sy stem. (iii) Generate three test atmosphere streams as follows: (A) Test atmosphere P : Pollutant test concentration. (B) Test atmosphere I: Interferent test concentration. (C) Test atmosphere Z : Zero air. (iv) Adjust the individual flow rates and the pollutant or interferent generators for the three test atmospheres as follows: (A) The flow rates of test atmospheres I and Z shall be equal. (B) The concentration of the pollutant in test atmosphere P shall be adjusted such that when P is mixed (diluted) with either test atmosphere I or Z, the resulting concentration of pollutant shall be as specified in table B
- 3. (C) The concentration of the interferent in test atmosphere I shall be adjusted such that when I is mixed (diluted) with test atmosphere P , the resulting concentration of interferent shall be not less than the value specified in table B
- 3 (or as otherwise required for unlisted potential interferents).*** E.O. 12866 Review

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Page **140** of **166** (D) To minimize concentration errors due to flow rate differences between I and Z, it is recommended that, when possible, the flow rat e of P be from 10 to 20 times larger than the flow rates of I and Z. (v) Mix test atmospheres P and Z by passing the total flow of both atmospheres through a (passive) mixing component to insure complete mixing of the gases. (vi) Sample and measure the m ixture of test atmospheres P and Z with the test anal yz er. Allow for a stable measurement reading, and record the reading, in concentration units, as R (see Figure B
- 3). (vii) Mix test atmospheres P and I by passing the total flow of both atmospheres thro ugh a (passive) mixing component to insure complete mixing of the gases. (viii) Sample and measure this mixture of P and I with the test analyzer. Record the stable measurement reading, in concentration units, as RI. (ix) Calculate the interference equiv alent ( IE) test result as: IE = RI − R. IE must be within the limits (inclusive) specified in table B
- 1 for each interferent tested to pass the interference equivalent test. (x) Follow steps (iii) through (ix) of this section, in turn, to determine the interference equivalent for each listed interferent as well as for an y other potential interferents identified. (xi) For those potential interferents which cannot be mixed with the pollutant, as indicated by footnote (3) in table B
- 3, adjust the concentration of test atmosphere I to the specified value without being mixed or diluted by the pollutant test atmosphere. Determine IE as follows: (A) Sample and measure test atmosphere Z (zero air). Allow for a stable measurement reading and record the reading, in concentration units, as R . (B) Sample and measure the interferent test atmosphere I . I f the test anal yz er is not capable of negative readings, adjust the anal yz er (not the recorder) to give an offset zero. Record the stable*** E.O. 12866 Review

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Page **141** of **166** reading in concentration uni ts as RI , extrapolating the calibration curve, if necessary , to represent negative readings. (C) Calculate IE = RI − R . IE must be within the limits (inclusive) specified in table B
- 1 for each interferent tested to pass the interference equivalent test. (xii) Sum the absolute value of all the individual interference equivalent test results. This sum must be equal to or less than the total interferent limit given in table B
- 1 to pass the test.*** E.O. 12866 Review

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Page **142** of **166** T ABLE B - 3
— I NTERFERENT T EST C ONCENTRATION , 1 P ARTS P ER M ILLION Pollu tant Analyzer Type Hydro chloric acid Ammo nia Hydro gen sulfide Sulfur dioxide Nitrogen

dioxide Nitric

oxide Carbon dioxide Ethy lene Ozone M xylene Wa ter

vapor Carbon

mon oxide Meth ane Ethane Naphth alene SO 2 Ultraviolet fluorescence 0.1 5 0.14 4 0.5 0.5 0.5 0.2 20,000 0.05 6 SO 2 Flame photometric 0.01 0.14 4 750 20,000 3 50 SO 2 Gas chromatography 0.1 0.14 4 750 20,000 3 50 SO 2 Spectrophotometric wet chemical (pararosanaline) 0.2 0.1 0.1 0.14 4 0.5 750 0.5 SO 2 Electrochemical 0.2 0.1 0.1 0.14 4 0.5 0.5 0.2 0.5 20,000 3 SO 2 Conductivity 0.2 0.1 0.14 4 0.5 750 SO 2 Spectrophotometric gas phase, including DOAS 0.14 4 0.5 0.5 0.2 O 3 Chemiluminescent 0.1 3 750 0.08 4 20,000 3 O 3 Electrochemical 0.1 3 0.5 0.5 0.08 4 O 3 Spectrophotometric wet chemical (potassium iodide) 0.1 3 0.5 0.5 0.5 3 0.08 4
O 3 Spectrophotometric gas phase, including ultraviolet absorption and DOAS) 0.5 0.5 0.5 0.08 4 0.02 20,000 CO Non - dispersive Infrared 750 20,000 10 4 CO Gas chromatography with flame ionization detector 20,000 10 4 0.5 CO Electrochemical 0.5 0.2 20,000 10 4 CO Catalytic combustion thermal detection 0.1 750 0.2 20,000 10 4 5.0 0.5 CO IR fluorescence 750 20,000 10 4 0.5 CO Mercury replacement - UV photometric 0.2 10 4 0.5*** E.O. 12866 Review

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Page **143** of **166** T ABLE B - 3
— I NTERFERANT T EST C ONCENTRATION , 1 P ARTS P ER M ILLION (C ONTINUED ) Pollu tant Analyzer Type Hydro chloric acid Ammo nia Hydro gen sulfide Sulfur dioxide Nitrogen

dioxide Nitric

oxide Carbon dioxide Ethy lene Ozone M xylene Wa ter

vapor Carbon

mon oxide Meth ane Ethane Naphth alene NO 2 Chemiluminescent 0.1 3 0.5 0.1 4 0.5 20,000 NO 2 Spectrophotometric wet chemical (azo dye reaction) 0.5 0.1 4 0.5 750 0.5 NO 2 Electrochemical 0.2 0.1 3 0.5 0.1 4 0.5 750 0.5 20,000 50 NO 2 Spectrophotometric gas phase 0.1 3 0.5 0.1 4 0.5 0.5 20,000 50 1. Concentrations of interferent listed must be prepared and controlled to ±10 percent of the stated value. 2. Analyzer types not listed will be considered by the Administrator as special cases. 3. Do not mix with the pollutant. 4. Concentration of pollutant used for test. These pollutant concentrations must be prepared to ±10 percent of the stated value. 5. If candidate method utilizes an elevated - temperature scrubber for removal of aromatic hydrocarbons, perform this interference test. 6. If naphthalene test concentrat ion cannot be accurately quantified, remove the scrubber, use a test concentration that causes a full scale response, reattac h the scrubber, and evaluate response for interference.*** E.O. 12866 Review

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Page **144** of **166** (e) Zero drift, span drift, lag time, rise tim e, fall time, and precision

— (1) Technical definitions

— (i) Zero drift: The change in measurement response to zero pollutant concentration over 12
- and 24
- hour periods of continuous unadjusted operation. (ii) Span drift: The percent change in measurement response to an up
- scale pollutant concentration over a 24
- hour period of continuous unadjusted operation. (iii) Lag time: The time interval between a step change in input concentration and the first observable correspond ing change in measurement response. (iv) Rise time: The time interval between initial measurement response and 95 percent of final response after a step increase in input concentration. (v) Fall time: The time interval between initial measurement respons e and 95 percent of final response after a step decrease in input concentration. (vi) Precision: Variation about the mean of repeated measurements of the same pollutant concentration, expressed as one standard deviation. (2) Tests for these performanc e parameters shall be accomplished over a period of seven (7) or fifteen (15) test day s. During this time, the line voltage supplied to the test anal yz er and the ambient temperature surrounding the anal yz er shall be changed from day to day , as required in paragraph(e)(4) of this section. One test result for each performance parameter shall be obtained each test day , for seven (7) or fifteen (15) test day s, as determined from the test results of the first seven day s. The tests for each test day are performed in a single integrated procedure. (3) The 24
- hour test day

may begin at any

clock hour. The first approximately 12 hours of each test day

are required for testing 12
- hour zero drift. Tests for the other parameters shall be conducted an y time during the r emaining 12 hours.*** E.O. 12866 Review

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Page **145** of **166** (4) Table B
- 4 of this section specifies the line voltage and room temperature to be used for each test day . The applicant may elect to specify

a wider temperature range (minimum and maximum temperatures) than the range specified in tabl e B - 4 and to conduct these tests over that wider temperature range in lieu of the specified temperature range. If the test results show that all test parameters of this section §53.23(e) are passed over this wider temperature range, a subsequent FRM or FEM designation for the candidate method based in part on this test shall indicate approval for operation of the method over such wider temperature range. The line voltage and temperature shall be changed to the specified values (or to the alternative, wider temperature values, if applicable) at the start of each test day ( i.e. , at the start of the 12
- hour zero test). Initial adjustments (day

zero) shall be made at a line voltage of 115 volts (rms) and a room temperature of 25 oC. (5) The tests shall be condu cted in blocks consisting of 3 test day s each until 7 (or 15, if necessary) test results have been obtained. (The final block may contain fewer than three test day s.) Test days need not be contiguous day s, but during any idle time between tests or test days , the test anal yz er must operate continuously and measurements must be recorded continuously

at a low chart speed (or equivalent data recording) and included with the test data. If a test is interrupted by an occurrence other than a malfunction of the t est analyzer, only

the block during which the interruption occurred shall be repeated. (6) During each test block, manual adjustments to the electronics, gas, or reagent flows or periodic maintenance shall not be permitted. Automatic adjustments that the test anal yz er performs by

itself are permitted at any time.*** E.O. 12866 Review

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Page **146** of **166** (7) At least 4 hours prior to the start of the first test day of each test block, the test anal yz er may

be adjusted and/or serviced according to the periodic maintenance procedures specified in the manual referred to in § 53.4(b)(3). If a new block is to immediately

follow a previous block, such adjustments or servicing may be done immediately

after completion of the day's tests for the last day of the previous block and at the voltage and temperature specified for that day , but onl y on test days 3, 6, 9, and 12. N OT E T O § 53.2 3(e)(7) : If necessary , the beginning of the test day s succeeding such maintenance or adjustment may be delayed as required to complete the service or adjustment operation. (8) All measurement response readings to be recorded shall be converted to concentration units or adjusted (if necessary) according to the calibration curve. Whenever a test atmosphere is to be measured but a stable reading is not required, the test atmosp here shall be sampled and measured long enough to cause a change in measurement response of at least 10% of full scale. I dentify all readings and other pertinent data on the strip chart (or equivalent test data record). (See Figure B
- 1 illustrating the pattern of the required readings.)
Table B - 4
— Line Voltage and Room Temperature Test Conditions Test day Line volt age, 1 rms Room tem perature, 2 oC Comments 0 115 25 Initial set - up and adjustments. 1 125 20 2 105 20 3 125 30 Adjustments and/or periodic maintenance permitted at end of tests. 4 105 30 5 125 20 6 105 20 Adjustments and/or periodic maintenance permitted at end of tests.*** E.O. 12866 Review

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Page **147** of **166** 7 125 30 Examine test results to ascertain if further testing is required. 8 105 30 9 125 20 Adjustments and/or periodic maintenance permitted at end of tests. 10 105 20 11 125 30 12 105 30 Adjustments and/or periodic maintenance permitted at end of tests. 13 125 20 14 105 20 15 125 30 1 Voltage specified shall be controlled to ±1 volt. 2 Te mp eratures shall be controlled to ±1 oC.*** E.O. 12866 Review

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Page **148** of **166** Figure B - 1. Example showing the nature of the tracing obtained

during the test sequence for 24 - hour drift, lag time, rise time, fall time, and precision. The time scale has been greatly compressed. (9) Test procedure. (i) Arrange to generate pollutant test atmospheres as follows. Test atmospheres A 0 , A 20 , and A 80 shall be maintained consistent during the tests and reproducible from test day to test day
. Test atmosphere Pollutant concentration (percent) A 0 ......................... Zero air. A 20 ....................... 20±5 of the upper range limit. A 30 ....................... 30±5 of the upper range limit. A 80 ....................... 80±5 of the upper range limit. A 90 ....................... 90±5 of the upper range limit. (ii) For steps within paragraphs (e)(9) (xxv) through (e)(9)(xxxi) of this section, a chart speed of at least 10 centimeters per hour (or equivalent resolution for a digital representation) shall be used to clearl y show changes in measurement responses. The actual chart speed, chart speed changes, and time checks shall be clearly marked on the chart. (iii) Test day 0 . Allow sufficient time for the test anal yz er to warm up and stabilize at a line voltage of 115 volts and a room temperature o f 25 oC. Adjust the zero baseline to 5 percent of chart (see § 53.21(b)) and recalibrate, if necessary . No further adjustments shall be made to the analyzer until the end of the tests on the third, sixth, ninth, or twelfth test day
. (iv) Measure test atmosphere A 0 until a stable measurement reading is obtained and record this reading (in ppm) as Z’n , where n = 0 (see Figure B
- 4 in appendix A of this subpart). (v) [Reserved.]*** E.O. 12866 Review

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Page **149** of **166** (vi) Measure test atmosphere A 80 . Allow for a stable measurement reading and record it as S’n , where n = 0. (vii) The above readings for Z’0 and S’0 should be taken at least four (4) hours prior to the beginning of test day

1. (viii) At the beginning of each test day , adjust the line v oltage and room temperature to the values given in table B
- 4 of this subpart (or to the corresponding alternative temperature if a wider temperature range is being tested). (ix) Measure test atmosphere A 0 continuously for at least twelve (12) continuous h ours during each test day
. (x) After the 12
- hour zero drift test (step ix) is complete, sample test atmosphere A 0 . A stable reading is not required. (xi) Measure test atmosphere A 20 and record the stable reading (in ppm) as P 1 . (See Figure B
- 4 in appendi x A.) (xii) Sample test atmosphere A 30 ; a stable reading is not required. (xiii) Measure test atmosphere A 20 and record the stable reading as P2 . (xiv) Sample test atmosphere A 0 ; a stable reading is not required. (xv) Measure test atmosphere A 20 and re cord the stable reading as P3 . (xvi) Sample test atmosphere A 30 ; a stable reading is not required. (xvii) Measure test atmosphere A 20 and record the stable reading as P 4 . (xviii) Sample test atmosphere A 0 ; a stable reading is not required. (xix) Measur e test atmosphere A 20 and record the stable reading as P 5 . (xx) Sample test atmosphere A 30 ; a stable reading is not required. (xxi) Measure test atmosphere A 20 and record the stable reading as P 6 .*** E.O. 12866 Review

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Page **150** of **166** (xxii) Measure test atmosphere A 80 and record the stable reading as P7 . (xxiii) Sample test atmosphere A 90 ; a stable reading is not required. (xxiv) Measure test atmosphere A 80 and record the stable reading as P 8 . Increase the chart speed to at least 10 centimeters per hour. (xxv) Measure test atmosphere A 0 . Record the stable reading as L 1 . (xxvi) Quickly

switch the test anal yz er to measure test atmosphere A 80 and mark the recorder chart to show, or otherwise record, the exact time when the switch occurred. (xxvii) Measure test atmosph ere A 80 and record the stable reading as P9 . (xxviii) Sample test atmosphere A 90 ; a stable reading is not required. (xxix) Measure test atmosphere A 80 and record the stable reading as P 10 . (xxx) Measure test atmosphere A 0 and record the stable reading a s L 2 . (xxxi) Measure test atmosphere A 80 and record the stable reading as P 11 . (xxxii) Sample test atmosphere A 90 ; a stable reading is not required. (xxxiii) Measure test atmosphere A 80 and record the stable reading as P 12 . (xxxiv) Repeat steps within paragraphs (e)(9)(viii) through (e)(9)(xxxiii) of this section, each test day
. (xxxv) I f zero and span adjustments are made after the readings are taken on test day s 3, 6, 9, or 12, complete all adjustments; then measure test atmospheres A 0 and A 80 . Allow for a stable reading on each, and record the readings as Z’n and S’n , respectively , where n = the test day

number (3, 6, 9, or 12). These readings must be made at least 4 hours prior to the start of the next test day
. (10) Determine the results of each day 's tests as follows. Mark the recorder chart to show readings and determinations.*** E.O. 12866 Review

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Page **151** of **166** (i) Zero drift. (A) Determine the 12
- hour zero drift by examining the strip chart pertaining to the 12
- hour continuous zero air test. Determine the minimum ( C min. ) and maximum ( C

max. ) measurement readings (in ppm) during this period of 12 consecutive hours, extrapolating the calibration curve to negative concentration units if necessary
. Calculate the 12
- hour zero drift (12 ZD ) as 12 ZD = C max. – C

min. (See Figure B
- 5 in appendix A.) (B) Calculate the 24
- hour zero drift (24 ZD ) for the n - th test day as 24 ZD n = Z

n − Z n - 1 , or 24 ZD n = Z

n − Z’n - 1 if zero adjustment was made on the previous test day, where Z n = 1⁄2( L 1 + L 2 ) for L 1 and L 2 taken on the n - th test day
. (C) Compar e 12 ZD and 24 ZD to the zero drift limit specifications in table B
- 1. Both 12 ZD and 24 ZD must be within the specified limits (inclusive) to pass the test for zero drift. (ii) Span drift. (A) Calculate the span drift (SD ) as:

or if a span adjustment was made on the previous test day ,

where

,
n indicates the n - th test day , and i indicates the i - th measurement reading on the n - th test day
. % 100 1 1   

 

n n n n S S S SD

%

100 1 1   

 

 

n n n n S S S SD


## 

  12

7 6 1 i i n P S*** E.O. 12866 Review

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Page **152** of **166** (B) SD must be within the span drift limits (inclusive) specified in table B
- 1 to pass the test for span drift. (iii) Lag time. Determine, from the strip chart (or alternative test data record), the elapsed time in minutes between the change in test concentration (or mark) made in step (xxvi) and the first observable (two times the noise level) measurement re sponse. This time must be equal to or less than the lag time limit specified in table B
- 1 to pass the test for lag time. (iv) Rise time. Calculate 95 percent of measurement reading P9 and determine, from the recorder chart (or alternative test data record), the elapsed time between the first observable (two times noise level) measurement response and a response equal to 95 percent of the P9 reading. This time must be equal to or less than the rise time limit specified in table B
- 1 to pass the test for rise time. (v) Fall time. Calculate five percent of ( P 10 − L 2 ) and determine, from the strip chart (or alternative test record), the elapsed time in minutes between the first observable d ecrease in measurement response following reading P 10 and a response equal to L2 + five percent of (

P 10 − L 2 ). This time must be equal to or less than the fall time limit specification in table B
- 1 to pass the test for fall time. (vi) Precision. Calculate precision (both P20 and P 80 ) for each test day as follows: (A)

(B) % 100 6 1 5 1 1 2 6 1 6 1 2 20          

    

  

#  

  i i i i P P URL P*** E.O. 12866 Review

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Page **153** of **166** (C) Both P20 and P 80 must be equal to or less than the precision limits specified in table B
- 1 to pass the test for precision.

Table B - 5
— Symbols and Abbreviations BL ........... Analyzer reading at the specified LDL test concentration for the LDL test. Bz ............ Analyzer reading at 0 concentration for the LDL test. DM ......... Digital meter. C max. ........ Maximum analyzer reading during the 12 ZD test period. C min. ......... Minimum analyzer reading during the 12 ZD test period. i ............... Subscript indicating the i - th quantity in a series. IE ............ Interference equivalent. L 1 ............ First analyzer zero reading for the 24 ZD test. L 2 ......... ... Second analyzer zero reading for the 24 ZD test. n .............. Subscript indicating the test day number. P .............. Analyzer reading for the span drift and precision tests. P i ............. The i - th analyzer reading for the span drift and prec ision tests. P20 .......... Precision at 20 percent of URL. P 80 .......... Precision at 80 percent of URL. ppb ......... Parts per billion of pollutant gas (usually in air), by volume. ppm ........ Parts per million of pollutant gas (usually in air), by volume. R ............. Analyzer reading of pollutant alone for the IE test. RI ............ Analyzer reading with interferent added for the IE test. ri .............. The i - th analyzer or DM reading for the noise test. S
.............. Standard deviation of the noise test readings. S 0 ............ Noise value ( S

) measured at 0 concentration. S80 ........... Noise value ( S ) measured at 80 percent of the URL. S n ............ Average of P 7 . . . P 12 for the n
- th test day of the SD test. S’n ........... Ad

justed span reading on the n - th test day. SD ........ Span drift URL ........ Upper range limit of the analyzer’s measurement range. Z ............. Average of L 1 and L 2 readings for the 24ZD test. Z n ............ Average of L 1 and L 2 readings on the n - th test day for the 24ZD test. Z’n ........... Adjusted analyzer zero reading on the n - th test day for the 24ZD test. ZD .......... Zero drift. 12 ZD ....... 12
- hour zero drift. 24 ZD ....... 24
- hour zero drift. A PPENDIX A TO S UBPART B OF P ART 53

– O PTIONAL F ORMS FOR REPORTING T EST RESULTS % 100 6 1 5 1 1 2 12 7 12 7 2 80          

    

  

#  

  i i i i P P URL P*** E.O. 12866 Review

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Page **154** of **166 NOISE TEST DA** 

**TA** Applicant ______________________________________ Date ____________________ Analyzer ______________________________________ Pollutant _________________ Range _____________________ Test No.

_________________ READING NUMBER (i) TIME 0% of URL 80% of URL DM READING r i , ppm DM

READING r i , ppm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 STD. DEVIATION S 0 = S 80 =

Figure B - 2. Form for noise test data (see §53.23(b)).*** E.O. 12866 Review

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Page **155** of **166 LDL and INTERFERENCE TEST DA**  **TA** Applicant ____________________________________________ Date

____________________ Analyzer _____________________________________________ Pollutant _________________ TEST PARAMETER READING or

CALCULATION TEST NUMBER

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 LO WE R DETECTABLE LIMIT B Z B L LDL = B L BZ

INTER FERENCE EQUIV ALENT 1 R 1 R I1 IE = R I1 – R 1 2 R 2

R I2 IE = R I2 – R 2 3* R 3

R I3 IE = R I3 – R 3 4* R 4

R I4 IE = R I4 – R 4 5* R 5

R I5 IE = R I5 – R 5 TOTAL* *If required. Figure B - 3. Form for test data and calculations for lower detectable limit (LDL) and interference equivalent (IE) (see § 53.23(c) and (d)). **DRIFT A ND PRECISION TEST DA**  **TA** 

## 

 n i i IE 1*** E.O. 12866 Review

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Page **156** of **166** Applicant ____________________________________________ Date ____________________ Analyzer

_____________________________________________ Pollutant _________________ ANALYZER READING, ppm TEST DAY 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 DATE P 1 P2 P3 P 4 P5 P 6 P 7 P8 P9 P 10 P 11 P 12
L 1 L 2 Z’ n S’ n Cmax Cmin Figure B - 4. Form for drift and precision test data (see § 53.23(e)). 

## 

  12 7 6 1 i i n P S*** E.O. 12866 Review

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Page **157** of **166 CA**  **LCULA**

**TION OF ZERO DRIFT, SPA N DRIFT, A**  **ND PRECISION** Applicant ____________________________________________ Date

____________________ Analyzer _____________________________________________ Pollutant _________________ TEST PARAMETER CALCULATION TEST DAY (n) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
ZERO DRIFT 12 HOUR 12ZD = C max – C min

24 HOUR Z = (L 1 + L 2 )/2 24ZD = Z

n – Z n - 1 24ZD = Z’

n – Z’ n - 1

SPAN DRIFT 24

HOUR

PREC ISION 20%

URL ( P20 ) P20 = STANDARD

DEVIATION of ( P 1 ...P 6 ) 80% URL ( P80 ) P80 = STANDARD

DEVIATION of ( P 7 ...P 12 )

Figure B - 5. Form for calculating zero drift, span drift, and precision (§ 53.23(e)). 

## 

  12

7 6 1 i i n P S %

100 1 1   

 

n n n n S S S SD %

100 ' ' 1 1   

 

n n n n S S S SD*** E.O. 12866 Review

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Page **158** of **16 6**  **TEST DATA SUMMARY** Applicant ___________________________________________ Analyst

_____________________________________________ Analyzer ____________________________________________ Pollutant

____________________________________________ Range _______________________ Other information _____________________________________ Test dates _____

____________ **Performance Parameter**  **Table**

**B -**  **1 Spec.**  **Test Number (first set) Test Number (second set)**  **Number of**  **Failures Pass** 

**or Fail**  **1 2**  **3 4**  **5 6**  **7 8**  **9 10**  **11 12**  **13 14**  **15 Noise**  , ppm 0%

URL 80% URL **LDL** (> 2 x 0% noise)
**Inter**   ** ference** **Equiv**   ** lent,** ppm IE1

IE2 I E3 I E4 I E5 I E6 Total **Zero Drift,**  ppm 12 hr

24 hr. **Span Drift**  , % 80%

URL **Lag Time** , min **Rise Time** , min **Fall Time** , min **Precision,** percent 20%

URL 80% URL Figure B - 6. Form for reporting a summary of the test results (see § 53.23).*** E.O. 12866 Review

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Page **159** of **166 PART 58**  **-- AMBIENT AIR QUALITY SURVEILLANCE**  5. The authorit y citation for part 58 continues to read as follows: **Authority:** 42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619. **Subpart B [Amended]** 6. Section 58.10, is amended by adding paragraph (a)(7) to read as follows: 

### §58.10 **Annual monitoring network plan and periodic network assessment.** (a) * * * ( 7 ) A plan for establishing CO monitoring sites in accordance with the requirements of appendix D to this part shall be submitted to the EPA Regional Administrator . Plans for required CO monit ors shall be submitted at least six months prior to the date such monitors must be established as required by section 58.13. * * * * * 7. Section 58.13 is amended by adding paragraph (e) to read as follows: 

### §58.13 **Monitoring network completion**
. * * * * * ( e ) The CO monitors required under Appendix D, section 4.2 of this part must be phy sicall y established and operating under all of the requirement s of this part, including the requirements of appendices A, C, D, and E to this part no later than: 1) January

1, 2015 for CO monitors in CBSAs having 2.5 million persons or more; or*** E.O. 12866 Review

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Page **160** of **166** 2) January

1, 2017 for other CO monitors. 8. Appendix D to Part 58 is amended b y revising section 4.2 to read as follows: **Appendix D to Part 58**
**— Network Design Criteria for Ambient Air Quality Monitoring**  * * * * * 4. 2 Carbon Monoxide (CO) Design Criteria. 4.2.1 General Requirements. (a) Except as provided in subsection (b), one CO monitor is required to operate collocated with one required near
- road NO 2 monitor, as required in Section 4.3.2 of this part, in CBSAs having a population of 1,000,000 or more persons. If a CBSA has more than one required near
- road NO 2 monitor, only one CO monitor is required to be collocated with a near
- road NO 2 monitor within that CBSA. (b) If a state provides quantitative evidence demonstrating that peak ambient CO concentrations would occur in a near
- road location which meets microscale siting criteria in Appendix E of this part but is not a near
- road NO 2 monitoring site , then the EPA Regional Administrator may approve a request by

a state to use such an alternate near
- road location fo r a CO monitor in place of collocating a monitor at near
- road NO 2 monitoring site. 4.2.2 Regional Administrator Required Monitoring. (a) The Regional Administrators, in collaboration with states, may require additional CO monitors above the minimum numb er of monitors required in 4.2.1 of this part, where the minimum monitoring requirements are not sufficient to meet monitoring objectives. The Regional Administrator may require, at his/her discretion, additional monitors in situations where data or other information suggest that CO concentrations may

be approaching or exceeding the NAAQS. Such situations include, but are*** E.O. 12866 Review

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Page **161** of **166** not limited to, 1) characterizing impacts on ground
- level concentrations due to stationary CO sources, 2) characterizing CO concentratio ns in downtown areas or urban street can yons, and 3) characterizing CO concentrations in areas that are subject to high ground level CO concentrations particularly due or enhanced b y topographical and meteorological impacts. The Regional Administrator and the responsible State or local air monitoring agency shall work together to design and maintain the most appropriate CO network to address the data needs for an area, and include all monitors under this provision in the annual monitoring network plan **.** 4.2.3 CO Monitoring Spatial Scales. (a) Microscale and middle scale measurements are the most useful site classifications for CO monitoring sites since most people have the potential for exposure on these scales. Carbon monoxide maxima occur primaril y in areas near major roadway s and intersections with high traffic density and often in areas with poor atmospheric ventilation. (1) Microscale

—Microscale measurements typically represent areas in close proximity to major roadway s, within street canyons, over s idewalks, and in some cases, point and area sources. Emissions on roadway s result in high ground level CO concentrations at the microscale , where concentration gradients generall y exhibit a marked decrease with increasing downwind distance from major roads , or within downtown areas including urban street can yons. Emissions from stationary

point and area sources, and non
- road sources may , under certain plume conditions, result in high ground level concentrations at the microscale. (2) Middle scale

—Middle scale measurements are intended to represent areas with dimensions from 100 meters to 0.5 kilometer. In certain cases, middle scale measurements may apply to areas that have a total length of several kilometers, such as “line” emission source areas.*** E.O. 12866 Review

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Page **162** of **166** This type of emission sources areas would include air quality along a commerciall y developed street or shopping plaza, freeway corridors, parking lots and feeder streets. (3) Neighborhood scale

– Neighborhood scale measurements are intended to represent areas wi th dimensions from 0.5 kilometers to 4 kilometers. Measurements of CO in this category would represent conditions throughout some reasonably urban sub
- regions. In some cases, neighborhood scale data may represent not only

the immediate neighborhood spati al area, but also other similar such areas across the larger urban area. Neighborhood scale measurements provide relative area
- wide concentration data which are useful for providing relative urban background concentrations, supporting health and scientifi c research, and for use in modeling. * * * * * 9. Appendix E to Part 58 is amended b y revising sections 2 and 6.2(a), 6.2(b), 6.2(c), and Table E - 4 to read as follows: **Appendix E to Part 58**
**— Probe and Monitoring Path Siting Criteria for Ambient Air**  **Qualit y Monitoring**  * * * * * 2. Horizontal and Vertical Placement The probe or at least 80 percent of the monitoring path must be located between 2 and 15 meters above ground level for all O 3 and SO 2 monitoring sites, and for neighborhood or larger spatial scale Pb, PM 10 , PM 10

–2.5 , PM 2.5 , NO 2 , and CO sites. Middle scale PM 10

–2.5 sites are required to have sampler inlets between 2 and 7 meters above ground level. Microscale Pb, PM 10 , PM 10

–2.5 , and PM 2.5 sites are required to have sampler inlets between 2 and 7 meters above ground level.*** E.O. 12866 Review

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Page **163** of **166** Microscale near
- road NO 2 monitoring sites are required to have sampler inlets between 2 and 7 meters above ground level. The inlet probes for microscale carbon monoxide monitors that are being used to measure concentrations near roadway s must be between 2 and 7 meters above ground level. Those inlet probes for microscale carbon monoxide monitors measuring concentrations near roadway s in downtown areas or urban street can yons must be between 2.5 and 3.5 meters above ground level. The probe or at least 90 percent of the monitoring path must be at least 1 meter vertically or horizontally

away from any

supporting structure, walls, parapets, penthouses, etc., and away from dusty

or dirty areas. If the probe or a significant portion of the monitoring path is located near the side of a building or wall, then it should be located on the windward side of the building relative to the prevailing wind direction during the season of highest concentration potential for the pollutant being measured. * * * * * 6. * * * 6.2 Spacing for Carbon Monoxide Probes and Monitoring Paths. (a) Near
- road microscale CO monitoring sites, including those located in downtown areas, urban street can yons, and other near
- road locations such as those adjacent to highl y trafficked roads, are intended to provide a measurement of the influence of the immediate source on the pollution exposure on the adjacent area. (b) Microscale CO monitor inlets probes in downtown areas or urban street can yon locations shall be located a minimum distance of 2 meters and a maximum distance of 10 meters from the edge of the nearest traffic lane. (c) Microscale CO monitor inlet probes in downtown areas or urban street canyon locations shall be located at least 10 meters from an intersection and preferabl y at a mi dblock location.*** E.O. 12866 Review

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Page **164** of **166** Midblock locations are preferable to intersection locations because intersections represent a much smaller portion of downtown space than do the streets between them. Pedestrian exposure is probably

also greater in street canyon/corridors than at intersections. (d) Microscale CO monitor inlet probes in the near
- road environment, outside of downtown areas or urban street can yons, shall be as near as practicable to the outside nearest edge of the traffic lanes of the target road segment; b ut shall not be located at a distance greater than 50 meters, in the horizontal, from the outside nearest edge of the traffic lanes of the target road segment
. (e) In determining the minimum separation between a neighborhood scale monitoring site and a spe cific roadway , the presumption is made that measurements should not be substantially influenced b y an y one roadway . Computations were made to determine the separation distance, and Table E

–2 of this appendix provides the required minimum separation distanc e between roadway s and a probe or 90 percent of a monitoring path. Probes or monitoring paths that are located closer to roads than this criterion allows should not be classified as neighborhood scale, since the measurements from such a site would closely represent the middle scale. Therefore, sites not meeting this criterion should be classified as middle scale. * * * * **** E.O. 12866 Review

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Page **165** of **166** Table E
- 4 of Appendix E to Part 58. Summary of Probe and Monitoring Path Siting Criteria Pollutant Scale (maximum

monitoring path length, meters) 1 Height from

ground to probe, inlet or 80% of monitoring path 1 Horizontal and

vertical distance from supporting structures 2 to probe, inlet or 90% of monitoring path 1 (meters) Distance from

trees to probe, inlet or 90% of mo nitoring path 1 (meters) Distance from

roadways to probe, inlet or monitoring path 1 (meters)

SO 2 3,4,5,6 Middle

(300 m) Neighborhood Urban, and Regional (1 km) 2
- 15 > 1 > 10 N/A

CO 4,5,7 Micro [downtown

or street canyon sites], micro [near
road sites] , middle (300 m) and Neighborhood (1 km) 2.5
- 3.5; 2
- 7; 2
-

15 > 1 > 10 2
- 10 for downtown areas or street canyon microscale; < 50 for near
- road microscale ; see Table E
- 2 of this appendix for middle and neighborhood scales. O 3 3,4,5 Middle (300 m)

Neighborhood, Urban, and Regional (1 km) 2
- 15 > 1 > 10 See Table E
- 1 of this appendix for all scales. NO 2 3,4,5 Micro (Near
- road

[50
- 300 ] ) Middle(300m) Neighborhood, Urban, and Regional (1 km) 2
- 7 (micro);

2
- 15(all other scales) > 1 > 10 < 50 meters for near - road microscale; See Table E
- 1 of this appendix for all other scales Ozone precursors (for PAMS) 3,4,5 Neighborhood and

Urban (1 km) 2
- 15 > 1 > 10 See Table E
- 4 of this appendix for all scales. PM,Pb 3,4,5,6,8 Micro: Middle,

Neighborhood, Urban and Regional 2
- 7 (micro);

2
- 7 (middle PM 10
- 2.5 ); 2
- 15 (all other scales) > 2 (all scales,

horizontal distance only) > 10 (all scales) 2
- 10 (micro); see Figure E
- 1 of this appendix for all other scales. N/A
--Not applicable. 1 Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring, middle, neighborhood, urban, and regional scale NO 2 mo nitoring, and all applicable scales for monitoring SO 2 ,O 3 , and O 3 precursors. 2 When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses located on roof. 3 Should be >20 meters from the drip
- line of tree(s) and must be 10 meters from the drip
- line when the tree(s) act as an obstruction. 4 Distance from sampler, probe, or 90% of monitoring path to obstacle, such as a building, must be at least twice the*** E.O. 12866 Review

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Page **166** of **166** height the obstacle protrudes above the sampler, probe, or monitoring path. Sites not meeting this criterio n may be classified as middle scale (see text). 5 Must have unrestricted airflow 270 degrees around the probe or sampler; 180 degrees if the probe is on the side of a building or a wall. 6 The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration flues. The separation distance is dependent on the height of the minor source's emission point (such as a flue), the type of fuel or waste burned, and the quality of the fuel (sulfur, ash, or lead content). This criterion is designed to avoid undue influences from minor sources. 7 For microscale CO monitoring sites in downtown areas or street canyons (not at near
- road NO 2 mo nitoring sites) , the probe must be >10 meters from a street intersection and preferably at a midblock location. 8 Collocated monitors must be within 4 meters of each other and at least 2 meters apart for flow rates greater than 200 liters/min or at least 1 meter apart for samplers having flow rates less than 200 liters/min to preclude airflow interference.
* * * * *