No. EPA Comment Research Group Response1We have two key concerns that address some of the initial study objectives asstated in the report. Our first concern is with the following objective:"Quantify personal exposures to motor vehicle gasoline evaporative andcombustion emissions in micro environments, (MEs) representing the upperend of the population exposure.frequency distribution (99th+percentile) ofsuch exposures,"(p. 1-2)It would be very helpful to evaluate whether the study accomplished thisobjective by comparing its findings to other exposure studies. A table comparingaverage and "high end" concentrations from this study to those reported in otherstudies would be useful in addressing whether this study captured the "99th+percentile" exposure concentrations. Studies that might be appropriate forcomparison include population-based sampling programs such as the NationalHuman Exposure Assessment Survey (NHEXAS) Phase I studies, theRelationship of Indoor, Outdoor, and Personal Air (RIOPA) study, and othersprovided in the attached referenceguide. Studies addressing specificmicroenvironments addressed in the 211(b) report should also be noted (seeattached reference guide).In regards to this same concern, it wouldbe useful to define with specificity theoperational definition of "99th+ percentile"for evaluation of the study objective.For instance, what averaging time shouldbe considered appropriate for assessingthis factor? What metric (micro-environmental concentration, inhaled dose, etc.)?We are unable to compare “average and highend concentrationsfrom this study”since no average exposures were sampled during the study. Sampling locationsand conditions were chosen to reflect high end exposures in all cases. Whereaverage values are mentioned in the report they refer to averages of replicate highend samples. The sampling criteria used to identify high end conditions aredescribed at page 1-3 and in Appendix A (pp. 3-13 to 3-17) of the report.Since we sampled only high end conditions,we’re unable to determine the precisepercentile range of high-end values from thedata collected. Early discussions withAgency staff during protocol developmentlead to the decision to characterize‘high end’ exposures as≥99thpercentile. This rationale followed from thecompounding effect of multiple independent selection criteria used to identify highend conditions. For example, if a single sampling criterion led to exposures at the80thor 90thpercentile, then samples that met several such criteria should plausiblyexceed the 99thpercentile when compounded. We believe this to be a conservativeestimate since a number of individual sampling criteria (e.g., low to calm windspeeds, down-wind locations, cold start situations, congested rush-hour conditions)could by themselves on occasion changenear-source exposures 100-fold from theiropposite extremes.Agency reviewers suggest that direct comparisons to studies of similar MEs andaveraging times would be helpful. Suchpreliminary comparisons were providedearlier to EPA in the Table 4-1 of the 3/14/2003 interim Atlanta S211b exposurereport. Model ME factor comparisons in Tables 3-2 to 3-4 of the final report alsooffer additional perspective. However, other study values must be adjusted forchanges in fuel composition and vehicle fleet emissions for such comparisons to beinformative and not misleading. Such anapproach is described in the VCCEPbenzene study [http://www.tera.org/peer/VCCEP/Benzene/BenzeneWelcome.html(Appendices A-2 & B)] that uses a Mobile6 model-based adjustment procedure.However, such supplementalanalysis is beyond the scope of the Tier 2 study.The operational averaging times should betaken in the breathing zone for periodscomparable to those typically spent in such high end MEs. For example, refuelingME sampling times were about 20 minutes to reflect time spent at the servicestation and in-cabin exposures on congested freeways were sampled for about 40minutes to reflect rush hour commuting trips (see EPA Exposure FactorsHandbook: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=20563)Reconstructed 1-minute data were provided inthe final report to facilitate exposuremodel evaluations of alternative behavioral patterns.2The other study objective that should be further addressed is:"Extrapolate study data to other cities and other oxygenated fuels,"(p.1-2)It is unclear how such extrapolation could be performed for some of the analysesundertaken. Given the lack of a traditional "balanced" statistical design,covariance of fuel type and climate is likely to limit the range of extrapolation.The report should include the investigators' assessment of the suitability of thevarious types of data collected for application.The presentation of data is in descriptive and graphical form, rather thanstatistical. While EPA will employ these data in other contexts for specificapplication, some of the tables in which average values are compared for severalvariables (e.g., Table 4.3-1 1) wouldbe better presented using statisticaltechniques such as ANOVA or mixed models. Presentations of the averagevalues in the tables are helpful, but the reader would be better served ifsignificance and statisticalpower were explicitlyaddressed. Furthermore,graphical presentation of statistical distributions ofdata (e.g., box plots,cumulative probability distributions) would be helpful even in interpretingsummarization of data in the absence of statistical comparisons.As noted above, application of this highend ME exposure datato other times andlocations will have to address interim changes in fuel and fleet characteristics aswell as case-by-case similarities anddifferences in MEs, fuel componentproperties, and meteorologicalconditions between locations. Extrapolation of thestudy data to other cities and other oxygenated fuels is beyond the scope of thisTier 2 study report.The basic objective of the Tier 2 high end exposure study is to provide exposuredata to EPA for their subsequent analysis. The descriptive statistics and datasummary presentations were provided as a courtesy to the Agency. Thesupplemental statisticalanalysis suggested by reviewers is beyond the scope of theTier 2 study report.3p. ES-5, top:Background exposure measurements weremade during the first 10 minuteswithout the test vehicle. What was therationale for 10 minutes? What time of daywere these made? How wasseasonal and other variability accounted for in thedecision to use a single 10-minute measurement as background? That is, itappears that the study assumes that background concentrations do not vary intime.The trailing vehicle experiments are described in Section 5 of the final report. The10 min period was selected to match other 10 min segments of the trailing vehicletest protocol. These measurements wereused to establish the initial in-cabinconcentrations prior to eachrun. The ambient backgroundis not relevant in thiscontext.4p. ES-5, line 3:Change "include" to "included" in "Each trailing vehicle run include threescenarios. . . ."This typographical error has been corrected.5p. ES-5, second paragraph:We assume that the vehicles parked in a closed garage with the gasoline poweredlawnmower and gasoline storage container all were filled with the same fuel, butthe report should explicitly state whether or not this is the case.Also, please further explain the meaning of semi-continuous measurement.The assumption is correct. A statement to this effect is added at page ES-5 and isnoted in the full descriptionof the attached garage experiments in Section 4 at page4-2 of the final report.Semi-continuous measurement by solid phase micro-extraction (SPME) is listed inTable E-1 at page ES-3 and describedin detail in Appendix C. Semi-continuous(10 minute average) is now parenthetically defined at ES-5.6p. ES-5:The twelve microenvironments appear to be sufficiently diverse to characterizenear-road exposures.The term "urban canyon" is used hereand throughout the report, but "urbancanyon" is never defined or fully characterized. Urban dispersion is highlyvariable from one city to the next (e.g., Houston's will be quite different fromAtlanta's) and even within one city (e.g., we observed significant differencesbetween two nearby urban canyons inNYC - Rockefeller Center and MadisonSquare Garden). Thus, the term shouldbe defined generally and the specificurban canyon (i.e., ME2) in this study should be fully characterized (e.g., heightof buildings, baffling and obstructions, distance between structures, etc.). Perhapsan appendix could be added with photographs of the urban canyon monitoringsites.A general expanded description of theurban canyon microenvironment and theselection criteria used to identify appropriate locations in the cities tested areprovided at page 3-13 of Appendix A.Earlier city-specificreports [May 5, 2004Data Report – Summer 2003 Chicago & Atlanta Field Studies – Appendix A;March 5, 2004 Data Report – Summer 2002 San Antonio & Houston Field Studies]provided to EPA identified specific streetcanyon loops selected for testing that arenow footnoted specifically atpages 1-7 to 1-9 for these cities in the final report.Although the lengths of the routes for this ME were too long for any detaileddescription of the buildingsto be meaningful for pollutant dispersion purposes, aGoogle Map link at (http://maps.google.com/maps?hl=en&tab=wl) providessatellite photography and street views that can be used to characterize theseAtlanta, Chicago, and Houston street canyon loops.7p. ES-9, ES- 14, and 4-5, Figure E- 1 :It might be helpful to make a general statement about the distribution of the fourspecies in BTEX. For example, it appears from Figure E-4 on page ES-14 that theratios in Houston in the summer and winter are consistent among benzene,toluene and the xylenes. However, are they evenly distributed across the twelveMEs, or does one (e.g., benzene) ortwo dominate in some MEs while othersdominate in other MEs (e.g., xylenes)?Perhaps a discussion linking the fuelvariability (Table 4.3-1 on page 4-5) would be worthwhile. Similarly, the reportmay provide some data to answer how much of the concentration and spread isattributable to fuel effects.In Figure E-4, the Houston ME/monitorBTX ratios appear similar (withinmeasurement error) across season for the exhaust dominated MEs as the reviewersuggests. However, the summer BT ratios do appear larger than X ratios for ME3and ME7 which are dominated by refueling evaporative emissions, although thewinter ratios appear less so. While the fuel specifications provided in Table 4.3-1are typical of these cities and relevant to the garage and trailing vehicle testsdiscussed in Sections 4 and 5 of the report,they are not directly applicable to theME measurements discussed in Section 3 which arise from actual but unknownmixtures of locally available fuels.Although seasonal fuel sampling of localvendors is available in annual surveys for these cities, modeling of fuel effects infleet emissions is beyond the scope of the Tier 2 study report.8p. ES- 15, line 17:The word "below" is misspelled.This typographical error has been corrected.9p. ES- 16:Can the 2.2 times higher in-cabin exposurelevels for the trailing vehicle relativeto the normal emitter mode be attributed to the differences in ventilation? Or,does vehicle type come into play here(even though the test vehicles seem toshow no significant difference)?We are unsure that average in-cabin levels were minimally affected by differentvehicles or fuels except for an MTBE fuel effect. Comparing the values for "truckThe 2-fold higher exposures trailing a malfunctioning lead vehicle are likely notattributable to cabin ventilation differences given the efforts made to conduct theexperiments under similarmeteorological conditions (e.g., calm or low windspeeds) and identical protocols regarding ventilation conditions. The relativelyhigher cabin levels would be anticipated as a result of higher emissions from amalfunctioning lead vehicle.only" and "car only" in Table E-2 on page ES-17, it appears that 1,3-butadiene,orthoxylene, carbon monoxide and formaldehyde differ substantially. Also, fueltype seems to vary substantially for toluene (Chicago=1.32, whereas Atlanta=2.79) and ethylbenzene (Chicago=0.120, whereas Atlanta=0.51), and Chicagofuel was much lower for the xylenes. It may rest on what is meant by "minimallyaffected."‘Table E-1’ typo is changed to Table E-2 on page ES-16.We agreewith the reviewer’s comment and modified the statement on page E16 asfollows: “Average in-cabin levels were affected by both state of maintenance ofthe vehicle and fuel composition. Use ofAtlanta fuel resulted in higher BTEXconcentrations in the trailing vehicle cabin, which is consistent with higheraromatic contents of Atlanta fuel, especially in summer. Similarly BTEXconcentrations were consistently higher during the summer, which is also inconcert with higher aromatic contents of summer fuels, especially for Atlanta.Averaging over the fuels and vehicles, the high emitter mode resulted in 2.2 timeshigher in-cabin exposure levels for the trailing vehicle thanthe normal emittermode except for HCHO which was relatively unchanged from background.” Also,the text in Section 5 (page5-12 and 5-14) was modifiedaccordingly to reflect thisconclusion.The differences between “car only” and “truck only” seem to be less consistent andless pronounced than fuel effect.10p. ES-18 and 19:The conclusions appear to be scientifically sound. The statement that "althoughoverall the average population time spentin these high endMEs is likely theshortest"is important and should not be left to conjecture. The actual activities associatedwithexposures to evaporative eniissions should be characterized. Activity patternsoftendictate actual exposures. Concentrations alone tell only part of the exposure story.We agree that HAPEMS factors may needto be updated based on these findings,andwe will provide the final version of this report to the Office of Air QualityPlanningand Standards who are responsible forthe HAMPEM model, which was recentlyupgraded to HAPEM6,http://www.epa.gov/ttn/fera/huma-nh apem.htm1.Other EPA documents provide adequate support for this statement which need notbe repeated in the report. For example, Table 15-106 of the EPA Exposure FactorsHandbook (EPA/600/P-95/002Fc) reports that157 (18-64 y) subjects, who hadvisited a gas station the day before in a survey population of 9386, averaged 10minutes (median) outside the service station with an inter-quartile range of 5-15minutes (http://www.epa.gov/ncea/efh/pdfs/efh-chapter15.pdf).The HAPEM5 comment refers to ‘high end’aspects of the 1998 Rodes et al. (p. xi)CARB study where the driving protocol highlighted trailing diesel city buses andHDD trucks when possible, a counter-intuitive practice for most drivers. CurrentHAPEM factors should be lowered tosimulate ‘typical’ behaviors wherecommuters are more likely to avoid such vehicles. Since the current report is alsofocused on ‘high end’ exposures (see response #1), comparisons with correctedHAPEM simulations should berestricted to ‘high end’model projections. Reportfindings should not be used to deriveHAPEM factors thoughtto characterizeaverage or typical conditions.11p. 1-20, final paragraph:Figure 1.3.2-5 is missing.There is no figure 1.3.2-5. The texton p. 1-20 was corrected accordingly.12p. 1-21:P-values should include at least two significant figures.The p-values have expanded significant figures at page 1-21 and 1-22.13p.2-5:Note that "OMS" has changed its title to "OTAQ (Office of Transportation andAir Quality).‘OMS’ has been changed to ‘OTAQ’in Table 2-1 caption at page 2-5.14p.2-9:How were the "error bars" in Figure2-9 calculated? What components ofuncertainty are accounted for here? Sampling? Instrument precision? Errorpropagation?Presumably this question concerns Figure 2-1, as there is only one figure in thissection... A brief discussion of how uncertainties associated with Figure 2-1 weredetermined is added to the initial paragraph at page 2-4.15p. 3 - 1, second paragraph:The 1999 NATA does not assume constantbackground concentrations of allpollutants. See http://www.epa.gov/ttn/atw/natal999/background.html foradditional detail.The report does not claim that a uniformbackground concentration is assumed forallpollutants.16p. 3-3, first paragraph, last sentence:The italicized text should be evaluated in light of the "general comment" above.Notably, this text is appropriate if, incomparison to other studies looking atsimilar microenvironments, the concentrations in this study are higher. Theitalicized text is likely inappropriate if this comparison does not suggest that themicro-environmental exposures presented herein are "extreme."We removed the italicization of the text.However, as notedin responses #1 & 10,the ‘high end’ study protocol was designed to sample under conditions leading tomore ‘extreme’ exposures that those thought ‘typical’ or average. To beinformative, the comparisons suggestedwith earlier studies, some of whichthemselves sampled under ‘high end’ conditions (e.g. Rodes et al., 1998), shouldbe adjusted for interim changes in fuelcomposition and fleet emissions: however,such extended analysis is beyond the scope of this report.17p. 4-7 – 8, Table 4.3-6,7:The tables and text do notseem to identify whether these non-aldehyde data arefrom SMPE or canister samples.The report has been edited (p. 4.7) to identify absorption tube, canister, and SPMEvalues.18p. 5-1 4, last paragraph:". ..after the change to low ventilation...little change in the in-cabinconcentration..."This text appears to contradict languageon p. 5-1 8, second to last paragraph,where it is noted that the range of concentrations differed under high ventilationsituations.Please clarify the intended meaning, whichappears to suggest that while averageconcentrations were unaffected, variability in concentration was affected byventilation.The latter reading grasps the meaning intended; language at p. 5-14 has beenclarified to state that although on average the integrated in-cabin levels weresimilar for high and low ventilation, the variability (peaks and valleys) of the incabin concentrations was larger during the high ventilation condition.