# Carbon Monoxide NAAQS **Science and Background Briefing for Final Rulemaking** 

for OMB July 28, 2011 Point of Contact: Lydia Wegman Health and Environmental Impacts Division

OAQPS

# Summary
• Key Issues in Review

– Standards: Adequacy of current CO NAAQS

– Monitoring: Need for revisions to network


## • Final Rulemaking

– Standards: Retain current CO NAAQS, without revision, as proposed

– Monitoring: Revise network to require near- road monitors, as proposed • Provide additional flexibility in monitor placement from what was proposed • Extend implementation date later than date proposed
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# Timeline of Review

**Major Milestones Completion**  **Date** Wo rkshop on Key Policy- Relevant Issues √ January 2008 Integrated Review Plan Final √ August 2008 Integrated Science Assessment Final √ January 29, 2010 Risk/Exposure Assessment Plan √ April 2009

3 Risk/Exposure Assessment Plan Final √ April 2009 √ May 28, 2010 Policy Assessment Draft Final √ March 2, 2010 √ Oct 22, 2010 **Rulemaking** Proposed Rule Signed (publication date) Jan 28, 201 1 (Feb 11 , 201 1) Public Comment Period (60 days) Feb 11 - April 12, 201 1 OMB Review -- NFR July 18 -Aug 11 Final Rule Signed Aug 12, 201 1 Underlined dates indicate court-ordered deadlines

### • Current standards - 9 ppm , 8- hour average and 35 ppm , 1 - hour average

– Not to be exceeded more than once per year 

### • Standards set in1971, reviews completed in 1985 and 1994

– No revisions made to primary standards



# Background

4 

### – No revisions made to primary standards

– Secondary standards revoked in 1985 • Scientific evidence for secondary standards still inadequate today 

### • Late 1990s – third review begun but not completed

– Air quality criteria document completed in 2000

– Review halted for Congress- requested National Research Council review of factors affecting ambient CO concentrations in high altitude/cold regions (completed 2003) 

### • 2007 – Began current review in response to deadline litigation

# Background - Health Effects Evidence

• Internal biomarker is important element in evaluating toxicity

– In the body, CO competes with oxygen in binding to hemoglobin to form **carboxyhemoglobin (**  **COHb );**  formation of COHb can reduce blood oxygen levels

– This use of a biomarker is similar to lead (focus on blood lead levels), and different from other criteria pollutants (focus on inhaled ambient concentrations) 

### • CO’s role in lowering blood oxygen levels and reducing oxygen availability to tissues (hypoxia) can affect functioning of heart, brain and other organ systems

– People with coronary heart disease identified as population with greatest susceptibility to short-term CO exposure
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# Background - Health Effects Evidence (continued) 

### • Key for assessing short-term CO effects is controlled human exposure studies (1980s) of coronary heart disease patients with exercise- induced angina

– Increases in COHb result in reduced time to exercise - induced angina (indicative of Increases result in reduced time to exercise induced (indicative of hypoxia) 

### • Interpretation of epidemiological evidence (based on ambient concentrations) is more complicated for CO compared to other criteria pollutants

– Studies for cardiovascular morbidity are logically coherent with larger, long -standing health effects evidence base and supportive of ISA conclusion of likely causality

– Limitations and uncertainties complicate interpretation, particularly with regard to estimating ambient concentrations that may be triggering health outcomes 

### • Quantitative risk and exposure assessment (REA)

– Estimates of portion of at- risk population (in two study areas) expected to experience one or more occurrences of COHb levels at or above levels associated with responses in controlled human exposure studies 6

## Controlled Human Exposure Studies: • Multiple studies of coronary artery disease patients with exercise - induced angina 

# Background - Health Ef fects Evidence (continued)

7 

### • Multiple studies of coronary artery disease patients with exercise - induced angina • These studies document physiological effects associated with changes in COHb levels induced by short-term CO exposures • Key study (multicenter): ~1 - hour exposures to CO concentrations targeted to achieve 2%a nd 4% COHb caused statistically significant reductions in time to exercise- induced indicators of myocardial ischemia

– Angina

– Specific change in electrocardiogram, well -established objective measure

– Pooled data analysis found statistically significant dose- response relationships, with no evidence of threshold

# Proposal - Standards
• Proposal

– Retain current primary standards (9 ppm , 8 - hour average and 35 ppm , 1 - hour average)

– Solicited comment on appropriateness of revision of form and level, as discussed in Policy Assessment and by CASAC

– Evidence remains insufficient to support a secondary CO standard

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### • Rationale

– Focus on levels of internal biomarker ( COHb ) associated with short-term ambient CO exposures

– Provide protection from repeated occurrences of COHb levels above 2% and from appreciably higher COHb levels associated with health effects of concern in people with cardiovascular disease • Individual or infrequent occurrences of COHb levels near 2% (lowest in human exposure studies) were judged of uncertain health significance

– Judge uncertainties and limitations of epidemiological evidence too great to provide a basis for revising the current standards • “Administrator proposes to conclude that consideration of epidemiological studies does not lead her to identify a need for any greater protection”

# Standards – CASAC Advice

• CASAC did not provide comments on proposal; had provided range of comments on draft Policy Assessment and other draft documents

– Agreed with staff’s conclusion that the body of evidence and exposure/dose assessment provide support for retaining or revising the current 8- hour standard

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### assessment provide support for retaining or revising the current 8- hour standard

– Expressed “preference” for lower standard, in light of epidemiological studies, and suggested “example options” focused on lower part of range identified by Staff in Policy Assessment

– Stated that, depending on weight given epidemiological evidence, conclusion could be drawn that health effects are occurring at levels below current NAAQS

– Recognized difficulty in interpreting epidemiological studies • Co- pollutants serving as potential confounders is particularly problematic for CO; a better understanding of the possible role of co- pollutants is relevant to regulation; CO may be a surrogate for a mix of pollutants

# Overview – Who Commented?
• Public health and environmental organizations

– American Lung Assoc., American Thoracic Soc. and Environmental Defense Fund (jointly)

– Physicians for Social Responsibility (signatories include 27 groups and ~930 individuals)

– Center for Biological Diversity and four others, including 2 of litigants (jointly)

– Safe Air for Everyone 

### • Air agencies

– 2 national/regional organizations (NACAA, NESCAUM)

10 – 7 state agencies (Indiana, New Mexico, New York, North Carolina, South Carolina, Texas, Wisconsin) 

### • Transportation agencies

– 1 national organization (AASHTO)

– 4 state agencies (New York, Texas, Virginia, Washington) 

### • Local governments (Southeast Michigan Council of Governments) • Industries/Industry organizations

– Assoc of Automobile Manufacturers, American Petroleum Institute and American Electric Power Service Corp. 

### • ~130 individuals (121 associated w. same petition)

– Notably Albert Donnay , private consultant (also significant contributor to some public health organization comments above) *Complete listing of groups commenting listed in attachment

# Standards – Public Comments

• Public health/environmental organizations conclude current standards are not requisite, recommend revision

– Cite epidemiological studies, and CASAC advice regarding weight on epidemiological studies and preference for lower standard 

### • 5 State air agencies (IN, NM, NC, TX, WI), VA DOT, Southeast Michigan

11 

### COG and all industry commenters support proposed retention

– Air agencies cite rationale in proposal and CASAC recognition of support in evidence for current standards

– Industry: agree that proposal gives appropriate weight to epidemiological studies, note little change in risk estimates since last review, claim exposure/dose assessment overstates risk

# Standards – Public Comments (continued)

• NESCAUM indicates support for NAAQS at least as protective as current

– Supports CASAC preference for lower standards but notes the epidemiological studies do not indicate a specific level 

### • Donnay : ISA and other review documents do not reflect latest

12 

### scientific knowledge useful in identifying ambient CO effects • Center for Biological Diversity (et al) states that a secondary standard should be set “at a level sufficient to attenuate the climate impacts”

NESCAUM=Northeast States for Coordinated Air Use Management

# Proposal - Monitoring
• Proposal

– Require near- road network • Co- locate with subset of NO 2 monitors ( multipollutant concept) in cities with > 1 million population (~77 monitors in 53 CBSAs) • Schedule and siting criteria synchronized with NO 2 • Solicited comment on near- road network, population threshold, and siting criteria

13 • Solicited comment on near- road network, population threshold, and siting criteria

– Regional Administrator authority • Proposed and solicited comment on RA authority to require additional monitors anywhere on case- by-case basis

– Technical updates to analytical measurement method and performance testing requirements 

### • Rationale

– Mobile sources are responsible for large majority of CO emissions

– On - road and near- road environment is where peak CO concentrations are expected to occur

– Co- locating with near- road NO 2 network provides for multipollutant monitoring and leveraging of resources

# Monitoring - Public Comments

• Near- road monitoring requirement

– Some states and health/environmental groups support near- road monitoring & multi pollutant concept • NACAA, NESCAUM, NYSDEC, ALA/ATS/EDF

– Other states and industry do not support near- road monitoring Other states and industry do not support near monitoring • IN, NM, SC, TX, Southeast Michigan Council of Gov., AAM, and AEPSC 

### • Details of near- road monitoring

– All states who support near- road monitoring want population threshold for requirement changed from 1 million to 2.5 million

– ALA/ATS/EDF want population threshold for required monitors at 500,000

– NACAA & NC want states to have freedom to have required near- road CO monitors NOT be co- located with NO 2 sites, if states choose

– Many commenters are concerned over losing area -wide monitoring sites, including transportation groups, industry, and public health/environmental groups • AASHTO, NYSDOT, TXDOT, VDOT, AAM, ALA/ATF/EDF

– States want full funding 14

# Monitoring - Public Comments (continued)

• Other monitoring network comments

– Safe Air for Everyone wants monitoring in/near agricultural burn areas Air for Everyone wants monitoring in/near agricultural

– Some states and transportation groups want required near- road monitors paired with corresponding area-wide monitoring • NESCAUM, AASHTO, NYSDOT, TXDOT, VDOT



### – Transportation groups & Texas have concern over RA Authority to require monitoring above the minimum requirements 

### • Monitoring methods comments

– API provided comments on measurement methods update 15

# Summary
• Key Issues in Review

– Standards: Adequacy of current CO NAAQS

– Monitoring: Need for revisions to network 

## • Final Rulemaking

– Standards: Retain current CO NAAQS, as proposed

– Monitoring: Revise network to require near- road monitors, as proposed • Provide additional flexibility in monitor placement from proposed

– Allow states to choose whether a required near- road CO monitor is to be co- located with a near- road NO2 monitor 

### • Extend implementation date from proposed date

– Implementation deadline of January 1, 2015 16

# Attachments

– Complete listing of public commenters

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## – Additional background • Monitoring network • CO concentrations • Health effects evidence • Risk/Exposure assessment

# Public Commenters on Proposal **National/Regional Air Organizations** 

- Northeast States for Coordinated Air Use Management (NESCAUM)

- National Association of Clean Air Agencies (NACAA) **State Environmental/Air Agencies**

– Indiana Department of E nvironmental Management (INDEM) **Medical, Public Health, and Environmental Groups** 

– American Thoracic Society (A TS), American Lung Association (ALA), Environmental Defense Fund (EDF)

– Safe Air for Everyone

– Center for Biological Diversity ( CfBD ), Communities for a Better Environment*, WildEarth Guardians, Coalition for a Safe Environment*, Alaska Center for the Environment

– Physicians for Social Responsibility (PSR)* (additional signatories included 27 organizations and ~930

18 (INDEM)

– New Mexico Air Quality Bureau (NMAQB)

– New York Department of Environmental Conservation (NYDEC)

– North Carolina Division of Air Quality (NCDAQ)

– South Carolina Department of Health and Environmental Control (SCDHEC)

– Texas Council on Environmental Quality (TXCEQ)

– Wisconsin Department of Natural Resources (WIDNR) **Transportation Associations/**  **State Agencies**

– American Association of State Highway and Transportation Officials (NAASHTO)

– Texas Dept Transportation

– Virginia Dept Transportation

– Washington Dept Transportation **Local Governments** 

– Southeast Michigan Council of Governments – Physicians for Social Responsibility (PSR)* (additional signatories included 27 organizations and ~930 individuals) **Industry Commenters** 

– Alliance of Automobile Manufacturers

– American Petroleum Institute

– American Electric Power Service Corporation **Private Citizens**, includes:

– 121 associated with email petition

– 3 with specific technical knowledge, 1 of whom was major contributor to PSR comments and email petition

– Several law class students * plaintiff in litigation

# Monitoring: Current CO Network
• 345 CO monitors operated during 2009. • Minimum monitoring requirements were removed in the 2006 monitoring rule, except for CO measurements at National Core ( NCore ) monitoring sites.

– Old requirements called for one ‘peak’ concentration site (near a high traffic road or in an urban core) and one area/community wide monitor in any urban area over 500,000 population. • We have reviewed AQS metadata to characterize monitor objectives and spatial scales.

19 • We have reviewed AQS metadata to characterize monitor objectives and spatial scales.

– Population exposure is the dominant monitoring objective.

– The neighborhood spatial scale is the most common scale of representativeness.

– Near- road and urban canyon monitors would appropriately be classified as microscale sites.

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### Monitor Objectiv**es** ***one site can have multiple objectives**  Population Exposure ~47% Highest Concentration ~22% General Background ~5% Regional Transport ~2% Source Oriented ~1% 

### Spatial **Scales (of representativ** **eness)** Micro (~1 to 100m) ~16% Middle (100 to 500m) ~10% Neighborhood (500m – 4km) ~43% Urban (4km – 50km) ~5% Regional (50km +) ~2%

# Background: Ambient CO - Monitoring Stations (2009)

There were 345 CO monitors operating during the year 2009.

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# Monitoring: CASAC Feedback on Network  In the CASAC CO Committee letter on the exposure/dose assessment, they noted: “More extensive [monitoring] coverage may be warranted for areas...such as near roadway locations.”

21 

###  We met with the CASAC Ambient Air Monitoring Methods (AAMM) Subcommittee on September 29 th 

### and 30 th 

### regarding near- road monitoring.  We provided charge questions asking about where CO monitoring would be appropriate. 

###  **Key message** – In their general discussions and final letter, CASAC indicated there is value in monitoring for CO at the future near- road NO 2 

### sites (as well as giving some consideration to urban downtown/canyon areas).

# Background: Ambient CO - Emissions • Nationally and in urban areas, generally, mobile sources dominate emissions

– ~45%reduction in national -scale anthropogenic CO emissions between 1990 and 2005, due primarily to reductions in on - road vehicle emissions

– In some individual areas, stationary source emissions important

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# Background: Ambient CO - Concentration Trend (8 - hour)

**16** 

### CO Air Quality **, 1990 -**  **2009**

(Based on Annual 2nd Maximum 8- hour average) National Trend Based on 187 sites

23 **0 2**  **4 6**  **8 10**  **12 14** 

**1 9**  **9 0**  **1 9**  **9 1**  **1 9**  **9 2**  **1 9**  **9 3**  **1 9**  **9 4**  **1 9**  **9 5**  **1 9**  **9 6**  **1 9**  **9 7**  **1 9**  **9 8**  **1 9**  **9 9**  **2 0**  **0 0**  **2 0**  **0 1**  **2 0**  **0 2**  **2 0**  **0 3**  **2 0**  **0 4**  **2 0**  **0 5**  **2 0**  **0 6**  **2 0**  **0 7**  **2 0**  **0 8**  **2 0**  **0 9** Concentration(ppm) National Standard 9 ppm 90% of sites have concentrations below this line
10% of sites have concentrations belowthis line Average among all sites

# Background: Ambient CO - Concentration Trend (1 - hour)

**35** 

### CO Air Quality **, 1990 -**  **2009**

(Based on Annual 2nd Maximum 1 - hour average) National Trend Based on 187 sites

24 **0 5**  **10 15**  **20 25**  **30**

**1 9**  **9 0**  **1 9**  **9 1**  **1 9**  **9 2**  **1 9**  **9 3**  **1 9**  **9 4**  **1 9**  **9 5**  **1 9**  **9 6**  **1 9**  **9 7**  **1 9**  **9 8**  **1 9**  **9 9**  **2 0**  **0 0**  **2 0**  **0 1**  **2 0**  **0 2**  **2 0**  **0 3**  **2 0**  **0 4**  **2 0**  **0 5**  **2 0**  **0 6**  **2 0**  **0 7**  **2 0**  **0 8**  **2 0**  **0 9** Concentration(ppm) National Standard 35 ppm 90% of sites have concentrations belowthis line
10% of sites have concentrations belowthis line Average among all sites

# Current Ambient Concentrations (1 - hour)
• Second maximum 1 - hour average concentrations (current form of standard) of CO at monitors nationally, 2009

25 0.0 -4.4 9.4 - 35.4

4.5 - 9.4 >35.4 ppm No. of Counties 180 17 7 0 curr1hr09 0 - 4.4 4.5 - 9.4 >= 9.4

# Current Ambient Concentrations (8 - hour)
• Second maximum 8 - hour average concentrations (current form of standard) of CO at monitors nationally, 2009

26 curr8h09 0 - 2.4 2.5 - 6.4 >= 6.4 0.0 -2.4 6.4 - 9.4

2.5 - 6.4 >9.4 ppm No. of Counties 176 25 3 0

### Controlled **human exposure**  **studies** • Multiple studies of coronary artery disease patients with exercise - induced angina • These studies document physiological effects associated with changes in COHb levels induced by short-term CO exposures 

# Health Ef fects Evidence: Considerations in Current Review

27 

### levels induced by short-term CO exposures • Key study: ~1 - hour exposures to CO concentrations targeted to achieve 2%a nd 4% COHb caused statistically significant reductions in time to exercise- induced indicators of myocardial ischemia

– Angina • 4% COHb group - on average 7% time reduction (~40 seconds) • 2% COHb group - on average 4% time reduction (~20 seconds)



### – Change in electrocardiogram [ECG], which is well -established objective measure • 4% COHb group - on average 12% time reduction (~70 seconds) • 2% COHb group - on average 5% time reduction (~30 seconds)



### – Pooled data analysis found statistically significant dose- response relationships, with no evidence of threshold

### Controlled **human exposure**  **studies ... adversity of effects**  • No established guidelines for judging adversity of different responses 

# Health Ef fects Evidence: Considerations in Current Review (continued)

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### • 2010 Science Assessment (ISA) notes that physiological significance of small changes in time-to-occurrence (in key study) at lowest COHb level studied (e.g., 2%) is not clear • Previous review recognized range of professional judgments, described effects at lowest studied COHb level as “potentially adverse”, and considered them in evaluating adequate margin of safety (1994 final rule) • The key study (1989, 1991) indicates a continuum of effects on indicators of myocardial ischemia ranging from 4% COHb down to at least 2% COHb .

– Study authors considered these effects to be similar to those considered clinically significant when evaluating medications to treat angina from coronary artery disease.

### Epidemiological **studies** • Much expanded database since 1994 

# Health Ef fects Evidence: Considerations in Current Review (continued)

29 

### • Much expanded database since 1994 • Multiple studies observe positive associations between cardiovascular outcomes and short-term ambient CO concentrations across a range of CO concentrations

– Studies of cardiovascular disease hospitalizations consistently report such associations • Although only 4 studies (3 with statistical significance) in U.S. locations where current standards met 

### • Logical coherence between epidemiological study findings and larger, long -standing health effects evidence base

– Study findings are coherent with effects observed in human exposure studies of susceptible individuals and supportive to ISA conclusion of likely causality for cardiovascular morbidity

### Epidemiological **studies ... quantitative**  **interpretation** • Quantitative interpretation is complicated for CO compared to other criteria pollutants, affecting estimation of ambient concentrations that may be triggering 

# Health Effects Evidence: Considerations in Current Review (continued)

30 

### pollutants, affecting estimation of ambient concentrations that may be triggering health outcomes

– Substantially fewer CO studies in areas meeting current standards than for NOx and PM

– CASAC: • “the problem of co- pollutants serving as potential confounders is particularly problematic for CO” • “CO may be a surrogate for mix of pollutants related to fossil fuel combustion”

– Reduced confidence in representation of ambient CO exposures • Use of central -site ambient concentrations in light of near- roadway gradient (many times steeper than NOx) • Prevalence of CO measurements near/below method detection levels

– For CO, unlike for all other criteria pollutants, the epidemiological studies use a different exposure/dose metric (air concentration) than that used in other key CO studies ( COHb ) • Additional information that might be used to bridge this gap is lacking

### • To assess extent to which ambient CO exposures may result in at- risk populations experiencing COHb levels associated with effects in controlled human exposure studies, we use exposure/dose modeling

– **In the last review,** for conditions just meeting the 8- hour standard, the Administrator noted: 

# Health Ef fects Evidence: Interpretation of Exposure/Dose Estimates

31 

### – **In the last review,** for conditions just meeting the 8- hour standard, the Administrator noted: • “Relatively few” of at- risk population estimated to experience COHb > 2.1% in absence of indoor sources when current standards just met

– A daily maximum > 2.1% COHb was estimated to occur for less than 0.1% of person -days • Standards protecting against ambient CO levels resulting in COHb > 2.1% “should provide an adequate margin of safety against effects of uncertain occurrence, as well as those of clear concern”



### – In considering current exposure/dose modeling, we focus primarily on occurrence and frequency of COHb levels > 2% • 2% is lowest level assessed in human exposure studies • Exposure/dose assessment (REA) also presents estimates for higher and lower COHb levels

# Exposure/Dose: Overview of Current Assessment

• Two study areas: Denver and Los Angeles • Two at- risk populations: Coronary heart disease and all heart disease adults • Several air quality scenarios: “as is” (2006), just meeting **Denver**

32 

### • Several air quality scenarios: “as is” (2006), just meeting current 8- hour standard and alternatives

– In Denver, the 1 - hour level (current form) associated with just meeting the current 8- hour standard was 16.2 ppm .
– In Los Angeles, the 1 - hour level (current form) associated with just meeting the current 8- hour standard was 11.8 ppm . 

### • Focus on population exposure and dose estimates

– Percent of population at/above/below COHb levels of interest (or with multiple such occurrences), and percent of population person -days (metric in last review) **Los An**  **geles**