Carbon Monoxide NAA

QS 

Science and Background Briefing 

for Proposed Rulemaking for Proposed Rulemaking

for OMB

December 16, 2010

US Environmental Protec

Offi f Ai Q lit Pl i 

Point of Contact: Lydia Wegman

Health and Environmental Impacts Division

OAQPS Office o

f Air 

Quality Plannin

g 
Overview

 Timeline and Next Steps Bk d acground Health Effects Evidence  Exposure/Dose Estimates Monitoring Considerations Attachments: 

 Ambient CO: Emissions and Air Quality M f C t A bi t C t ti Maps of Current Ambient Concentrations

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Timeline and Next Steps

Major Milestones Completion DateWorkshop yy on Ke

y Polic

y-Relevant Issues

√ Januar

y 2008 

Integrated Review Plan Final

√ August 2008

Integrated Science Assessment Final

√ January 29, 2010

Risk/Exposure Assessment Plan Final

√ April 2009√ May 28, 2010 May 28, 2010

Policy Assessment Draft Final

√ March 2, 2010√ Oct 22, 2010

Rulemaking

OMB Review OMB Review -- NPR Dec 14/15 Dec 14/15 -Jan 27 ( 45 days) Jan 27 (~45 days)Proposed Rule Signed(estimated publication date)

Jan 28, 2011

(Feb 10, 2011)

Public Comment Period (60 days)

(estimated dates) Feb 10 - April 11, 2011 (estimated dates) p ,OMB Review -- NFR July 13-Aug 11 (30 days)Final Rule Signed Aug 12, 2011

Underlined dates indica

US Environmental Protection AgencyOffice of Air Quality Planning and Standards

Underlined dates indica

deadlines
Background 

 Current standards - 9 ppm, 8-hour average and 35 ppm, 1-hour av

 Not to be exceeded more than once per year Not to be exceeded more than once per year

 Standards set in1971, reviews completed in 1985 and 1994

 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 Review halted for Congress-requested National Research Council revie

requested National Research Council revie

affecting ambient CO concentrations in high altitude/cold regions (comp

 2007 – Began current review in response to deadline litigation

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Health Effects Evidence: Key Aspects of CO T

 For CO, p g

 an internal biomarker is im

portant element in evaluatin

g to

 In the body, CO competes with oxygen in binding to hemoglobin This binding forms carboxyhemoglobin (COHb) The formation of COHb can reduce blood oxygen levels

 Similar to lead, for which blood lead levels are important element i

evaluating toxicity

 Different from other criteria pollutants, which use inhaled ambient 

concent ti i l t i l ti t i it trations as primar

y element in evaluati

n

g toxicity

US Environmental Protection AgencyOffice of Air Quality Planning and Standards 
Health Effects Evidence: Key Aspects of CO T

(continued)

 Lo ered blood o gen le els (h po ia) is ell characteri ed CO mec

Lo

wered blood

o

xygen le

vels (hypo

xia) is well characteri

zed CO mec

 Can affect functioning of brain, heart and other organ systems

 Population groups with restricted blood flow (ischemia) are potentiall

 People with coronary heart disease are population with greatest suscep

People with coronary heart disease are population with greatest suscep

term CO exposure

 No evidence indicating greater susceptibility for other populations poten

 CO a d CO b occu t e body (e doge ous y) as byp oducts o a

a

n

d CO

H

b occur in th

e body (e

ndoge

nously) as byp

roducts

of na

metabolic cycles

 An individual’s COHb levels are influenced by exposures to ambient and 

(indoor) CO, as well as their endogenous CO formation

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Health Effects Evidence:

Considerations in Current Review

Controlled human exposure studies

Considerations in Current Review

 Multiple studies of coronary artery disease patients with exercise-indu These studies document physiological effects associated with change

levels induced by short-term CO exposures

 K td 1 e

y study: ~1-h t CO t ti t t d t hi 

hour exposures to CO concentrations tar

g

ete

d to achie

4% COHb caused statistically significant reductions in time to exercisindicators 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 m

 4% COHb group - on average 12% time reduction ( on average 12% time reduction ( 70 ~ seconds) seconds) 2% COHb group - on average 5% time reduction (~30 seconds) 

 Pooled data analysis found statistically significant dose-response relation

evidence of threshold

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Health Effects Evidence:

Considerations in Current Review ( ti d)

Controlled human ex

posure studies ... adversity of effects

Considerations in Current Review

(continued)

p y

 No established guidelines for judging adversity of different responses 2010 Science Assessment (ISA) notes that physiological significance of sm

in time in time-to-occurrence (in key study) at lowest occurrence (in key study) at lowest COHb level studied (e g 2%

level studied (e.g., 2%

 Previous review recognized range of professional judgments, described ef

lowest studied COHb level as “potentially adverse”, and considered them adequate margin of safety (1994 final rule)

 1991 Science Assessment (AQCD): Decrements at lowest COHb levels are in r

test reproducibility, although small, the effects could limit activity and affect qua

 1994 final rule noted that majority of cardiologists regarded multiple occurrence

induced angina as a substantial risk of more severe cardiac effects

 The key study (1989, 1991) indicates a continuum of effects on indicators 

myocardial ischemia ranging from 4% COHb down to at least 2% COHb. authors considered these effects to be similar to those considered clinicallwhen evaluatin

g medications to treat an

gina from coronar

y arter

y disease

US Environmental Protection AgencyOffice of Air Quality Planning and Standards 

g g yy
Health Effects Evidence: 

Considerations in Current Review ( ti d)

Epidemiological studies

Considerations in Current Review

(continued)

 Much expanded database since 1994 Multiple studies observe positive associations between cardiovascula

and short and short-term ambient CO concentrations across a range of CO con

term ambient CO concentrations across

a range of CO con

 Studies of cardiovascular disease hospitalizations consistently report suc

 4 studies (3 with statistical significance) in U.S. locations where current stand

 Logical coherence between epidemiological study findings and larger 

Logical coherence between epidemiological study findings and larger

health effects evidence base

 Study findings are coherent with effects observed in human exposure stu

susceptible individuals and supportive to ISA conclusion of likely causalitcardiovascular morbidit

y

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Health Effects Evidence: 

C id ti i C t R i

Epidemiological studies quantitative interpretation

Considerations in 

Curren

t

Review 

(continued

)

Epidemiological studies ... quantitative interpretation Quantitative interpretation is complicated for CO compared to other c

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

 Substantially fewer CO studies in areas meeting current standards than for N CASAC:

 “the problem of co-pollutants serving as potential confounders is particularly prob “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 (man

steeper than NOx)

 Prevalence of CO / measurements near/below method detection levels

 For CO, unlike for all other criteria pollutants, the epidemiological studies use 

exposure/dose metric (air concentration) than that used in other key CO stud

 Additional information that might be used to bridge this gap is lacking

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Health Effects Evidence: 

Interpretation of Exposure/Dose Estimates

 To assess extent to which ambient CO exposures may result in at-risk p

experiencing COHb levels associated with effects in controlled human e

Interpretation of Exposure/Dose Estimates

experiencing COHb levels associated with effects in controlled human e

we use exposure/dose modeling

 In the last review, for conditions just meeting the 8-hour standard, the Adm

 “Relativel

y few” of at-risk 

pp p o

pulation estimated to ex

perience COHb >2.1% in abs

sources when current standards just met

 A daily maximum > 2.1% COHb was estimated to occur for less than 0.1% of person-d

 Standards protecting against ambient CO levels resulting in COHb >2.1% “shoul

adequate margin of safety against effects of uncertain occurrence, as well as tho

 Recognized uncertainty in significance of effects at lowest studied COHb levels, and pa

effects to other potentially susceptible populations at low exposures/COHb relevant to a

 In considering current exposure/dose modeling, we focus primarily on occur

frequency of COHb levels > 2% 

 2% is lowest level assessed in human exposure studies and in key study is asso

unclear health significance (potentially adverse)

 Exposure/dose assessment (REA) also presents estimates for higher and lower 

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Exposure/Dose: Overview of Current Assessm

 Two study areas: Denver and Los Angeles

T t i k l ti C h t di d ll

Denver



Two at-ris

k populations: 

Coronar

y

heart disease an

d all

heart disease adults

 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.

F l ti d d ti t

Los Angeles



Focus on population exposure an

d

dose estimates

 Percent of population at/above/below COHb levels of interest (or 

with multiple such occurrences), and percent of population persondays (metric in last review)

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Consideration of Exposure/Dose Results

 Level for 2nd Highest 1-hour Average (ppm)LA: 6.8/7.2/8.2 8.1 Denver: 4. 9.3 9.7 11.2 

979899

100

Population

 Just meeting current, 

controlling, 8-hour standard:

 Maximum COHb levels kept 

below 2% in more than 95% of both populations

94959697

mulated At-risk both populationsP

 1-hour CO concentrations 

substantially below current 1-hour standard (35 ppm)

 Higher 1-hour CO for Denver 

(vs. LA) contributes to higher

919293

Percentage Si <2.0% COHb, LA <2.0% COHb, Denver (vs. LA) contributes to higher COHb levels 

 Other Denver-specific factors 

include high altitude and lower CO spatial variability

90

2 3 4 5 6 7 

Level for 2nd Highest 8-hour Average (Current 

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Consideration of Exposure/Dose Results (contin

100

I id i l i

979899

k Population

 In considerin

g alternative 

1-hour standards

 Maximum COHb levels 

kept below 2% in more than 95% of both populations with a level

949596

mulated At-rispopulations with

a

klevel

of 13 -14 ppm



>99% of both 

populations are restricted to COHb 

levels below 2% with a

919293

Percentage Si <2.0% COHb, LA <2.0% COHb, Denver levels below 2% with

a

level of ~9 ppm

9091

4 5 6 7 8 9 10 11 

Level for 99th Percentile Daily Maximum 1-hour 

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Exposure/Dose: Key Observations

 Under conditions j g ust meetin

g current 8-hour standard, 1-hour conc

influence population estimates of maximum COHb levels > 2% COH

indicating importance of evaluating alternative 1-hour standard leve

 Key contributors to highest ambient CO exposures are in-vehicle an

vehi l i i t h l l h t th 

hi

cle microenvironments w

here exposures are lar

g

ely s

horter tha

 Study areas differ in characteristics influential to CO exposure, withi

U.S. locations

 Denver air quality data simulated for current/alternative standards have 

Denver air quality data simulated for current/alternative standards have 

variation in hourly CO than U.S. median: LA study area data have less

 Taken together the assessment results indicate occurrences of Taken together, the assessment results indicate occurrences of CO

>2% associated with 1-hour ambient concentrations that are not con

either the current 8-hour or 1-hour standard

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
CASAC Comments on Draft Policy Assessmen

 Draft document reviewed by CASAC focused on 8-hour (controllinCASAC:  Agreed with staff’s conclusion that the body of evidence and the expos

assessment provide support for retaining or revising the current 8-h

 Did not recommend any specific revision; expressed a Did not recommend any specific revision; expressed

a

“preference preference

” fo

fo

standard, in light of epidemiological studies

 Panel agrees with staff that the evidence provides support for a standard 

protective as the current standards

 Depending on the weight given to the epidemiological evidence the concl

Depending on the weight given to the epidemiological evidence, the concl

drawn that health effects are occurring at levels below the current NAAQS

 Recognized difficulty in interpreting epidemiological studies, noting that pr

pollutants serving as potential confounders is particularly problematic for C

 A b tt d t di f th ibl l f A

b

etter un

derstandi

n

g of the possible role of co-poll t t i l t t l 

llutants is relevant to re

g

ula

a surrogate for a mix of pollutants

 Suggested “example policy options” focused on lower part of range identif

 For 8-hour standard: 3 - 5 ppm (99th percentile daily maximum)

F 1 h dd5 15 (99 h il d il i )

US Environmental Protection AgencyOffice of Air Quality Planning and Standards



For 1-hour stan

dar

d: 

5 - 15 ppm (99th percentile 

d

aily maximum)
CASAC Comments on Draft Policy Assessmen

CASAC (continued):  Stated that a 1-hour standard might provide protection independen

provided by 8-hour standard; did not support revoking the 1-hour st

 Final Policy Assessment focuses more on 1-hour standard

 Concludes appropriate to consider retaining current standards or re

current 1-hour standard (15-5 ppm, 99th percentile daily maximum)

 Al i t t id t i i i i 8 Also appropriate to consider retainin

g or revisin

g

8-h t d d i j 

hour stan

dar

d in conjun

revising 1-hour standard

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Monitoring: Current CO Network

 345 CO monitors operated during 2009. Minimum monitoring requirements were removed in the 2006 monitoring rule, exce

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) a

area/community wide monitor in any urban area over 500,000 population.

 We have reviewed AQS metadata to characterize monitor objectives and spatial sc

 Po

p p gj ulation ex

posure is the dominant monitorin

g 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.

Monitor Objectives Spatial Scales 

*one site can have multiple objectives

Population Exposure ~47%Highest Concentration ~22%

(of representativeness)Micro (~1 to 100m) Middle (100 to 500m) 

General Background ~5%Regional Transport ~2%Source Oriented ~1%

Neighborhood (500m – 4km) Urban (4km – 50km) Regional (50km

+) 

US Environmental Protection AgencyOffice of Air Quality Planning and Standards

Regional (50km ) 
Background: Ambient CO - Monitoring Station

There were 3

There were 3

operating du

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Monitoring: Issues for Consideration

 Mobile source impacts

 On-road mobile sources make up ~60% of the CO inventory. The ex

p gg p g osure/dose assessment suggests that ex

posure and risks are 

greater in vehicles.

 Stationary source impacts

 Stationary sources only make up ~5% of the inventory, however, in certain cases stationary 

steel mills, coke plants, or EGUs) may contribute to significant ground-level CO concentratio

 Urban “downtown” (including urban canyon) conditions

 Congested, stop-and-go traffic can emit more CO than ‘at speed’ vehicles, and thus CO can 

in urban cores, and can be further concentrated in urban cores that have urban canyons.



 Cold start vehicle conditions

 Vehicles emit more CO under cold start conditions than at routine operating temperatures.

 Topographic and meteorological impacts

 Certain areas are more subject to inversions due to Certain areas are more subject to inversions due to topography topography and/or meteorology which ca

and/or meteorology which ca

CO emissions; such known areas include Anchorage, AK, Calexico, CA, and Kalispell, MT, a

 Area/Community-wide concentrations

 Provide “background” (non-source-oriented) concentrations that can inform understanding of 

di t d h lth t di

US Environmental Protection AgencyOffice of Air Quality Planning and Standards

gradients an

d

health studies
Monitoring: CASAC Feedback on Network

 In the CASAC CO Committee letter on the exposure/dose assessm

noted: “More extensive [monitoring] coverage may be warranted fo

More extensive [monitoring] coverage may be warranted fo

areas...such as near roadway locations.”

 We met with the CASAC Ambient Air Monitoring Methods (AAMM) 

S b itt S t b 29th d 30thS

u

bcommittee on 

Septem

ber 29 di d 

th an

d 30th re

gardi

n

g near-roa

d mo

 We provided charge questions asking about where CO monitoring wou

appropriate.

 Key message – In their general discussions and final letter, CASA

indicated there is value in monitoring for CO at the future near-road 

sites (as well as giving some consideration to urban downtown/canareas).

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Attachments

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Background: Ambient CO - Emissions

 Nationally and in urban areas, generally, mobile sources dominate em

 ~45% reduction in national-scale anthropogenic CO emissions between 1

due primarily to reductions in on due primarily to reductions in on-road vehicle emissions road vehicle emissions

 In some individual areas, stationary source emissions important

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Background: Ambient CO - Concentration Tre

CO Air Quality, 1990 - 2009

(Based on Annual 2nd Maximum 8-hour average)

1416

)

(Based on Annual 2nd Maximum

8-hour average)

National Trend Based on 187 sites

8

1012

tration (ppm) National Standard 9 ppm 90% of sites have concentrations below this line Average among all sites

246

Concent

10% of sites have concentrations below this line

Average among all sites

0

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

10% of sites have concentrations below this line

US Environmental Protection AgencyOffice of Air Quality Planning and Standards
Background: Ambient CO - Concentration Tre

CO Air Quality, 1990 - 2009

3035

National Standard 35 ppm

(Based on Annual 2nd Maximum 1-hour average)

National Trend Based on 187 sites

202530

ation (ppm)

National Standard 35 ppm

90% of sites have concentrations below this line

5

1015

Concentr

10% f it h t ti b l thi li

Average among all sites

0

199

0

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

10% of sites 

have concentrations 

b

elow this line

US Environmental Protection AgencyOffice of Air Quality Planning and Standards

0 1 2

3

4

5

6

7

8

9

0 1 2

3

4

5

6

7

8

9
Current Ambient Concentrations (1-hour)

 Second maximum 1-hour average concentrations (current form of standard) of CO at mon

ppmcurr1hr09 0 - 4.4 4.5 - 9.4 >= 9.4 0.0-4.4 4.5-9.4 >35.4 9.4-35.4

US Environmental Protection AgencyOffice of Air Quality Planning and Standards

No. of Counties 180 17 7 0
Current Ambient Concentrations (8-hour)

 Second maximum 8-hour average concentrations (current form of standard) of CO at mon

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

US Environmental Protection AgencyOffice of Air Quality Planning and Standards

No. of Counties 176 25 3 0