Carbon Monoxide NAAQSScience and Background Briefingfor Proposed RulemakingforProposedRulemakingfor OMBDecember 16, 2010US Environmental Protection AgencyOffi f Ai Q lit Pl i d St d dPoint of Contact: Lydia WegmanHealth and Environmental Impacts DivisionOffice ofAirQualityPlanningandStandardsOAQPSOverviewTimeline and Next StepsBk dacgroundHealth Effects EvidenceExposure/Dose EstimatesMonitoringConsiderationsAttachments:Ambient CO: Emissions and Air QualityM f C t A bi t C t tiMaps ofCurrentAmbientConcentrationsUS Environmental Protection AgencyOffice of Air Quality Planning and Standards2Timeline and Next StepsMajor Milestones Completion DateWorkshopon KeyPolicy-Relevant Issues√January2008yyIntegrated Review Plan Final√August 2008Integrated Science Assessment Final√January 29, 2010Risk/Exposure AssessmentPlanFinal√April 2009√May 28, 2010May28,2010Policy AssessmentDraftFinal√March 2, 2010√Oct 22, 2010RulemakingOMB ReviewNPRDec 14/15Jan 27 ( 45 days)OMBReview--Dec14/15-Jan27(~45days)Proposed Rule Signed(estimated publication date)Jan 28, 2011(Feb 10, 2011)Public Comment Period (60 days)(estimated dates)Feb 10 -April 11,2011(estimateddates)p ,OMB Review -- NFR July 13-Aug 11 (30 days)Final Rule SignedAug 12, 2011Underlineddates indicate court-orderedUS Environmental Protection AgencyOffice of Air Quality Planning and Standards3UnderlineddatesindicatecourtordereddeadlinesBackgroundCurrent standards -9 ppm, 8-hour average and 35 ppm, 1-hour averageNot to be exceeded more than once per yearNottobeexceededmorethanonceperyearStandards set in1971, reviews completed in 1985 and 1994No revisions made to primary standardsSecondary standards revoked in 1985Scientific evidence for secondarystandards 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 factorsReviewhaltedforCongressrequestedNationalResearchCouncilreviewoffactorsaffecting ambient CO concentrations in high altitude/cold regions (completed 2003)2007 – Began current review in response to deadline litigationUS Environmental Protection AgencyOffice of Air Quality Planning and Standards4Health Effects Evidence: Key Aspects of CO ToxicityFor CO,an internal biomarker is important element in evaluatingtoxicityp gyIn the body, CO competes with oxygen in binding to hemoglobinThis binding formscarboxyhemoglobin (COHb)The formation of COHb can reduce blood oxygen levelsSimilar to lead, for which blood lead levels are important element inevaluating toxicityDifferent from other criteria pollutants, which use inhaled ambientt ti i l t i l ti t i itconcentrations as primaryelementin evaluatingtoxicityUS Environmental Protection AgencyOffice of Air Quality Planning and Standards5Health Effects Evidence: Key Aspects of CO Toxicity(continued)Lo ered blood o gen le els (h po ia) is ell characteri ed CO mechanismLoweredbloodoxygenlevels(hypoxia)iswellcharacterizedCOmechanismCan affect functioning of brain, heart and other organ systemsPopulation groups with restricted blood flow (ischemia) are potentially susceptiblePeople with coronary heart disease are population with greatest susceptibility to shortPeoplewithcoronaryheartdiseasearepopulationwithgreatestsusceptibilitytoshortterm CO exposureNo evidence indicating greater susceptibility for other populations potentially at riskCOandCOHboccur inthebody(endogenously)asbyproductsof naturala d CO b occu t e body (e doge ous y) as byp oducts o atu ametabolic cyclesAn individual’s COHb levels are influenced by exposures to ambient and nonambient(indoor) CO, as well as their endogenous CO formationUS Environmental Protection AgencyOffice of Air Quality Planning and Standards6Health Effects Evidence:Considerations in Current ReviewControlled human exposure studiesConsiderationsinCurrentReviewMultiple studies of coronary artery disease patients with exercise-induced anginaThese studies document physiological effects associated with changes in COHblevels induced by short-term CO exposuresK td 1h t CO t ti t t d t hi 2% deystudy: ~1-hour exposurestoCOconcentrationstargetedto achieve2%and4% COHb caused statistically significant reductions in time to exercise-inducedindicators 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%COHbgroup-on average 12% time reduction (~seconds)onaverage12%timereduction( 70seconds)2% COHb group - on average 5% time reduction (~30 seconds)Pooled data analysis found statistically significant dose-response relationships, with noevidence of thresholdUS Environmental Protection AgencyOffice of Air Quality Planning and Standards7Health Effects Evidence:Considerations in Current Review( ti d)Controlled human exposure studies ... adversityof effectsConsiderationsinCurrentReview(continued)p yNo established guidelines for judging adversity of different responses2010 Science Assessment (ISA) notes that physiological significance of small changesin time-to-occurrence (in key study) at lowestCOHblevel studied (e g 2%) is not clearintimeoccurrence(inkeystudy)atlowestlevelstudied(e.g.,2%)isnotclearPrevious review recognized range of professional judgments, described effects atlowest studied COHb level as “potentially adverse”, and considered them in evaluatingadequate margin of safety (1994 final rule)1991 Science Assessment(AQCD): Decrements at lowest COHb levels are in range of stresstest reproducibility, although small, the effects could limit activity and affect quality of life1994 final rule noted that majority of cardiologists regarded multiple occurrences of exerciseinduced angina as a substantial riskof more severe cardiac effectsThe key study (1989, 1991) indicates a continuum of effects on indicators ofmyocardial ischemia ranging from 4% COHb down to at least 2% COHb. Studyauthors considered these effects to be similarto those considered clinically significantwhen evaluatingmedications to treat angina from coronaryarterydisease.US Environmental Protection AgencyOffice of Air Quality Planning and Standards8g g yyHealth Effects Evidence:Considerations in Current Review( ti d)Epidemiological studiesConsiderationsinCurrentReview(continued)Much expanded database since 1994Multiple studies observe positive associations between cardiovascular outcomesand shortterm ambient CO concentrations across a range of CO concentrationsandshort-termambientCOconcentrationsacrossarangeofCOconcentrationsStudies of cardiovascular disease hospitalizations consistently report such associations4 studies (3 with statistical significance)in U.S. locations where current standards metLogical coherence between epidemiological study findings and larger longstandingLogicalcoherencebetweenepidemiologicalstudyfindingsandlarger,long-standinghealth effects evidence baseStudy findings are coherent with effects observed in human exposure studies ofsusceptible individuals and supportive to ISA conclusion of likely causality forcardiovascular morbidityUS Environmental Protection AgencyOffice of Air Quality Planning and Standards9Health Effects Evidence:C id ti i C t R iEpidemiological studies quantitative interpretationConsiderationsinCurrentReview(continued)Epidemiologicalstudies...quantitativeinterpretationQuantitative interpretation is complicated for CO compared to other criteriapollutants, affecting estimation of ambient concentrations that may be triggeringhealth outcomeshealthoutcomesSubstantially fewer CO studies in areasmeeting 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 concentrationsin light of near-roadway gradient (many timessteeper than NOx)f CO /Prevalence omeasurements near/below method detection levelsFor CO, unlike for all other criteria pollutants, the epidemiological studies use a differentexposure/dose metric (air concentration) thanthat used in other key CO studies (COHb)Additional information that mightbe used to bridge this gap is lackingUS Environmental Protection AgencyOffice of Air Quality Planning and Standards10Health Effects Evidence:Interpretation of Exposure/Dose EstimatesTo assess extent to which ambient CO exposures may result in at-risk populationsexperiencingCOHblevels associated with effects in controlled human exposure studiesInterpretationofExposure/DoseEstimatesexperiencingCOHblevelsassociatedwitheffectsincontrolledhumanexposurestudies,we use exposure/dose modelingIn the last review,for conditions just meeting the 8-hour standard, the Administrator noted:“Relativelyfew” of at-riskpopulation estimated to experience COHb >2.1% in absence of indoorp psources when current standards just metA daily maximum >2.1% COHb was estimated to occurfor less than 0.1% of person-daysStandards protecting against ambientCO levels resulting in COHb >2.1% “should provide anadequate margin of safety against effects of uncertain occurrence, as well as those of clear concern”Recognized uncertainty in significance of effects atlowest studied COHb levels, and paucity of evidence oneffects to other potentially susceptible populations atlow exposures/COHb relevant to ambient CO levelsIn considering current exposure/dose modeling, we focus primarily on occurrence andfrequency of COHb levels >2%2% is lowest level assessed in human exposure studiesand in key study is associated with effects ofunclear health significance (potentiallyadverse)Exposure/dose assessment (REA) also presentsestimates for higher and lower COHb levelsUS Environmental Protection AgencyOffice of Air Quality Planning and Standards11Exposure/Dose: Overview of Current AssessmentTwo study areas: Denver and Los AngelesT ti k l ti C h t di d llDenverTwo at-riskpopulations:Coronaryheartdisease andallheart disease adultsSeveral air quality scenarios: “as is” (2006), just meetingcurrent 8-hour standard and alternativesIn Denver, the 1-hour level (currentform) associated with just meetingthe current 8-hour standard was 16.2 ppm.In Los Angeles, the 1-hour level (current form) associated with justmeeting the current 8-hour standard was 11.8 ppm.F l ti d d ti tLos AngelesFocus on population exposure anddose estimatesPercent of population at/above/below COHb levels of interest (orwith multiple such occurrences), and percent of population persondays (metric in last review)US Environmental Protection AgencyOffice of Air Quality Planning and Standards12Consideration of Exposure/Dose ResultsLevel for 2ndHighest 1-hourAverage(ppm)LA:6.8/7.2/8.2 8.111.8Denver:4. 9.3 9.7 11.216.2979899100

P opulationJust meeting current,controlling, 8-hourstandard:Maximum COHb levels keptbelow 2% in more than 95% ofboth populations94959697

mulated At-risk Pbothpopulations1-hour CO concentrationssubstantially below current1-hour standard (35 ppm)Higher 1-hour CO for Denver(vs. LA) contributes to higher919293

Percentage Si<2.0% COHb, LA<2.0% COHb, Denver(vs.LA)contributestohigherCOHb levelsOther Denver-specific factorsinclude high altitude and lowerCO spatial variability902 3 4 5 6 7 8 9 10Level for 2nd Highest 8-hourAverage (Current Form), ppmCurrent 8-hrStandardUS Environmental Protection AgencyOffice of Air Quality Planning and Standards13Consideration of Exposure/Dose Results(continued)100I id i l i979899

k PopulationIn consideringalternative1-hourstandardsMaximum COHb levelskept below 2% in morethan 95% of bothpopulations with a level949596

mulated At-ris kpopulationswithalevelof 13 -14 ppm>99% of bothpopulations arerestricted to COHblevels below 2% with a919293

Percentage Si<2.0% COHb, LA<2.0% COHb, Denverlevelsbelow2%withalevel of ~9 ppm90914 5 6 7 8 9 10 11 12 13 14Level for 99th Percentile Daily Maximum 1-hourAverage, ppmUS Environmental Protection AgencyOffice of Air Quality Planning and Standards14Exposure/Dose: Key ObservationsUnder conditionsjust meetingcurrent 8-hour standard, 1-hour concentrationsginfluence population estimates of maximum COHb levels >2% COHb,indicating importance of evaluating alternative 1-hour standard levelsKey contributors to highest ambient CO exposures are in-vehicle and nearhi l i i t h l l h t th 8 hvehicle microenvironments where exposures arelargelyshorterthan8hoursStudy areas differ in characteristics influential to CO exposure, within range ofU.S. locationsDenver air quality data simulated for current/alternative standards have greaterDenverairqualitydatasimulatedforcurrent/alternativestandardshavegreatervariation in hourly CO than U.S. median: LA study area data have lessTaken together the assessment results indicate occurrences ofCOHblevelsTakentogether,theassessmentresultsindicateoccurrencesof>2% associated with 1-hour ambient concentrations that are not controlled byeither the current 8-hour or 1-hour standardUS Environmental Protection AgencyOffice of Air Quality Planning and Standards15CASAC Comments on Draft Policy AssessmentDraft document reviewed by CASAC focused on 8-hour (controlling) standardCASAC:Agreed with staff’s conclusion that the body of evidence and the exposure/doseassessment providesupport for retaining or revisingthe current 8-hour standardDid not recommend any specific revision; expressed a“preference”for lowerDidnotrecommendanyspecificrevision;expressedapreferenceforlowerstandard, in light of epidemiological studiesPanel agrees with staff that the evidenceprovides support for a standard at least asprotective as the current standardsDepending on the weight given to the epidemiological evidence the conclusion could beDependingontheweightgiventotheepidemiologicalevidence,theconclusioncouldbedrawn that health effects are occurring at levels below the current NAAQSRecognized difficulty in interpreting epidemiological studies, noting that problem of copollutants serving as potential confounders is particularly problematic for COA b tt d t di f th ibl l fll t t i l t t l ti CO bAbetter understandingofthe possible role ofco-pollutantsis relevantto regulation;COmaybea surrogate for a mix of pollutantsSuggested “example policy options” focused on lower part of range identified by StaffFor 8-hour standard: 3 - 5 ppm (99thpercentile daily maximum)F 1h dd515(99 h il d il i )US Environmental Protection AgencyOffice of Air Quality Planning and Standards16For1-hour standard:5-15ppm(99thpercentiledailymaximum)CASAC Comments on Draft Policy Assessment(continued)CASAC (continued):Stated that a 1-hour standard might provide protection independent of thatprovided by 8-hour standard; did not support revoking the 1-hour standardFinal Policy Assessment focuses more on 1-hour standardConcludes appropriate to considerretaining current standardsorrevisingcurrent 1-hour standard(15-5 ppm, 99thpercentile daily maximum)Al i t t id t i i i i 8h t d d i j ti ithAlso appropriateto consider retainingor revising8-hour standardin conjunction withrevising 1-hour standardUS Environmental Protection AgencyOffice of Air Quality Planning and Standards17Monitoring: Current CO Network345 CO monitors operated during 2009.Minimum monitoring requirements were removedin the 2006 monitoring rule, except for COmeasurements 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 onearea/community wide monitor in anyurban area over 500,000 population.We have reviewed AQS metadata to characterize monitor objectives and spatial scales.Population exposure is the dominant monitoringobjective.p gjThe neighborhood spatial scale is the most common scale of representativeness.Near-road and urban canyonmonitors would appropriately beclassified as microscale sites.Monitor ObjectivesSpatial Scales*one site can have multiple objectivesPopulation Exposure ~47%Highest Concentration ~22%(of representativeness)Micro (~1 to 100m) ~16%Middle (100 to 500m) ~10%General Background ~5%Regional Transport ~2%Source Oriented ~1%Neighborhood (500m – 4km) ~43%Urban (4km – 50km) ~5%Regional(50km+)~2%US Environmental Protection AgencyOffice of Air Quality Planning and Standards18Regional(50km)2%Background: Ambient CO - Monitoring Stations (2009)There were 345 CO monitorsTherewere345COmonitorsoperating during the year 2009.US Environmental Protection AgencyOffice of Air Quality Planning and Standards19Monitoring: Issues for ConsiderationMobile source impactsOn-road mobile sources make up~60% of the CO inventory.The exposure/dose assessment suggests that exposure and risks aregreater in vehicles.gg p gStationary source impactsStationary sources only make up ~5% of the inventory,however, in certain cases stationary sources (such assteel mills, coke plants, or EGUs) may contribute to significant ground-level CO concentrationUrban “downtown” (including urban canyon) conditionsCongested, stop-and-go traffic can emitmore CO than ‘at speed’ vehicles, and thus CO can be concentratedin 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 routineoperating temperatures.Topographic and meteorological impactsCertain areas are more subject to inversions due totopography and/or meteorology which can concentrateCertainareasaremoresubjecttoinversionsduetotopographyand/ormeteorologywhichcanconcentrateCO emissions; such known areasinclude Anchorage, AK, Calexico,CA, and Kalispell, MT, among others.Area/Community-wide concentrationsProvide “background” (non-source-oriented) concentrations that can inform understanding of urban COdi t d h lth t diUS Environmental Protection AgencyOffice of Air Quality Planning and Standards20gradients andhealthstudiesMonitoring: CASAC Feedback on NetworkIn the CASAC CO Committee letter on the exposure/dose assessment, theynoted:“More extensive [monitoring] coverage may be warranted forMoreextensive[monitoring]coveragemaybewarrantedforareas...such as near roadway locations.”We met with the CASAC Ambient Air Monitoring Methods (AAMM)S b itt S t b 29thd 30thdid it iSubcommittee onSeptember29thand30thregardingnear-roadmonitoring.We provided charge questions asking about where CO monitoring would beappropriate.Key message– In their general discussions and final letter, CASACindicated there is value in monitoring for CO at the future near-road NO2sites (as well as giving some consideration to urban downtown/canyonareas).US Environmental Protection AgencyOffice of Air Quality Planning and Standards21AttachmentsUS Environmental Protection AgencyOffice of Air Quality Planning and Standards22Background: 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 onroad vehicle emissionsdueprimarilytoreductionsinon-roadvehicleemissionsIn some individual areas, stationary source emissions importantUS Environmental Protection AgencyOffice of Air Quality Planning and Standards23Background: Ambient CO - Concentration Trend (8-hour)CO Air Quality, 1990 - 2009(Based on Annual 2nd Maximum 8-hour average)1416

)(BasedonAnnual2ndMaximum8-houraverage)National Trend Based on 187 sites81012

t ration (ppm )National Standard 9 ppm90% of sites have concentrations below this lineAverage among all sites246

Concen t10% of sites have concentrations below this lineAverageamongallsites01990199119921993199419951996199719981999200020012002200320042005200620072008200910%ofsiteshaveconcentrationsbelowthislineUS Environmental Protection AgencyOffice of Air Quality Planning and Standards24Background: Ambient CO - Concentration Trend (1-hour)CO Air Quality, 1990 - 20093035National Standard 35ppm(Based on Annual 2nd Maximum 1-hour average)National Trend Based on 187 sites202530

ation (ppm)NationalStandard35ppm90% of sites have concentrations below this line51015

Concentr10% f it h t ti b l thi liAverage among all sites01990199119921993199419951996199719981999200020012002200320042005200620072008200910%ofsiteshave concentrationsbelowthislineUS Environmental Protection AgencyOffice of Air Quality Planning and Standards2501234567890123456789Current Ambient Concentrations (1-hour)Second maximum 1-hour average concentrations (current form of standard)of CO at monitors nationally, 20090.0-4.49.4-35.44.5-9.4 >35.4ppmcurr1hr09 0 - 4.4 4.5 - 9.4 >= 9.4US Environmental Protection AgencyOffice of Air Quality Planning and Standards26No. of Counties180 17 7 0Current Ambient Concentrations (8-hour)Second maximum 8-hour average concentrations (current form of standard)of CO at monitors nationally, 2009curr8h09 0 - 2.4 2.5 - 6.4 >= 6.40.0-2.4 6.4-9.42.5-6.4>9.4ppmUS Environmental Protection AgencyOffice of Air Quality Planning and Standards27No. of Counties176 25 3 0