No. EPA Comment Research Group Res

1 We have two key concerns that address some of the initial study objectives as 

stated in the report. Our first concern is with the following objective: "Quantify personal exposures to motor vehicle gasoline evaporative and 

combustion emissions in micro environments, (MEs) representing the upper end of the population exposure. frequency distribution (99th + percentile) of 

such exposures," (p. 1-2)It would be very helpful to evaluate whether the study accomplished this objective by comparing its findings to other exposure studies. A table comparing average and "high end" concentrations from this study to those reported in other studies would be useful in addressing whether this study captured the "99th+ percentile" exposure concentrations. Studies that might be appropriate for comparison include population-based sampling programs such as the National Human Exposure Assessment Survey (NHEXAS) Phase I studies, the Relationship of Indoor, Outdoor, and Personal Air (RIOPA) study, and others provided in the attached reference guide. Studies addressing specific microenvironments addressed in the 211 (b) report should also be noted (see 

attached reference guide).  In regards to this same concern, it would be useful to define with specificity the operational definition of "99th+ percentile" for evaluation of the study objective. For instance, what averaging time should be considered appropriate for assessing this factor? What metric (micro-environmental concentration, inhaled dose, etc.)? 

We are unable to compare “average and high end con

since no average exposures were sampled during the sand conditions were chosen to reflect high end exposuaverage values are mentioned in the report they refer tend samples. The sampling criteria used to identify hdescribed at page 1-3 and in Appendix A (pp. 3-13 to Since we sampled only high end conditions, we’re unpercentile range of high-end values from the data coll

Agency staff during protocol development lead to the ‘high end’ exposures as 

≥ 99th percentile. This rationa

compounding effect of multiple independent selection end conditions. For example, if a single sampling crite80th or 90th percentile, then samples that met several s

exceed the 99th percentile when compounded. We be

estimate since a number of individual sampling criterispeeds, down-wind locations, cold start situations, concould by themselves on occasion change near-source opposite extremes. Agency reviewers suggest that direct comparisons to averaging times would be helpful. Such preliminary cearlier to EPA in the Table 4-1 of the 3/14/2003 interireport. Model ME factor comparisons in Tables 3-2 toffer additional perspective. However, other study vachanges in fuel composition and vehicle fleet emissioinformative and not misleading. Such an approach is benzene study [http://www.tera.org/peer/VCCEP/Ben(Appendices A-2 & B)] that uses a Mobile 6 model-baHowever, such supplemental analysis is beyond the scThe operational averaging times should be taken in thcomparable to those typically spent in such high end MME sampling times were about 20 minutes to reflect tstation and in-cabin exposures on congested freeways minutes to reflect rush hour commuting trips (see EPA Handbook: http://cfpub.epa.gov/ncea/cfm/recordisplaReconstructed 1-minute data were provided in the finamodel evaluations of alternative behavioral patterns. 
2 

The 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 analyses undertaken. 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 the various types of data collected for application. The presentation of data is in descriptive and graphical form, rather than statistical. While EPA will employ these data in other contexts for specific application, some of the tables in which average values are compared for several variables (e.g., Table 4.3-1 1) would be better presented using statistical techniques such as ANOVA or mixed models. Presentations of the average values in the tables are helpful, but the reader would be better served if significance and statistical power were explicitly addressed. Furthermore, 

graphical presentation of statistical distributions of data (e.g., box plots, cumulative probability distributions) would be helpful even in interpreting summarization of data in the absence of statistical comparisons. 

As noted above, application of this high end ME expo

locations will have to address interim changes in fuel well as case-by-case similarities and differences in Mproperties, and meteorological conditions between locstudy data to other cities and other oxygenated fuels iTier 2 study report. The basic objective of the Tier 2 high end exposure stdata to EPA for their subsequent analysis. The descrisummary presentations were provided as a courtesy to supplemental statistical analysis suggested by revieweTier 2 study report. 

3 

p. ES-5, top: Background exposure measurements were made during the first 10 minutes without the test vehicle. What was the rationale for 10 minutes? What time of day were these made? How was seasonal and other variability accounted for in the decision to use a single 10-minute measurement as background? That is, it appears that the study assumes that background concentrations do not vary in time. 

The trailing vehicle experiments are described in Sect10 min period was selected to match other 10 min segtest protocol. These measurements were used to estabconcentrations prior to each run. The ambient backgro

context. 

4 

p. ES-5, line 3: Change "include" to "included" in "Each trailing vehicle run include three scenarios. . . ." 

This typographical error has been corrected. 

5 

p. ES-5, second paragraph: We assume that the vehicles parked in a closed garage with the gasoline powered lawnmower and gasoline storage container all were filled with the same fuel, but the 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 inoted in the full description of the attached garage exp4-2 of the final report. Semi-continuous measurement by solid phase micro-eTable E-1 at page ES-3 and described in detail in App(10 minute average) is now parenthetically defined at 
6 

p. ES-5: The twelve microenvironments appear to be sufficiently diverse to characterize near-road exposures. The term "urban canyon" is used here and throughout the report, but "urban canyon" is never defined or fully characterized. Urban dispersion is highly variable from one city to the next (e.g., Houston's will be quite different from Atlanta's) and even within one city (e.g., we observed significant differences between two nearby urban canyons in NYC - Rockefeller Center and Madison Square Garden). Thus, the term should be defined generally and the specific urban canyon (i.e., ME2) in this study should be fully characterized (e.g., height 

of buildings, baffling and obstructions, distance between structures, etc.). Perhaps an appendix could be added with photographs of the urban canyon monitoring sites. 

A general expanded description of the urban canyon mselection criteria used to identify appropriate locationprovided at page 3-13 of Appendix A. Earlier city-sp

Data Report – Summer 2003 Chicago & Atlanta Field March 5, 2004 Data Report – Summer 2002 San Antoprovided to EPA identified specific street canyon loopnow footnoted specifically at pages 1-7 to 1-9 for thesAlthough the lengths of the routes for this ME were todescription of the buildings to be meaningful for polluGoogle Map link at (http://maps.google.com/maps?hl

satellite photography and street views that can be used Atlanta, Chicago, and Houston street canyon loops. 

7 

p. ES-9, ES- 14, and 4-5, Figure E- 1 : It might be helpful to make a general statement about the distribution of the four species in BTEX. For example, it appears from Figure E-4 on page ES-14 that the ratios in Houston in the summer and winter are consistent among benzene, toluene and the xylenes. However, are they evenly distributed across the twelve MEs, or does one (e.g., benzene) or two dominate in some MEs while others dominate in other MEs (e.g., xylenes)? Perhaps a discussion linking the fuel variability (Table 4.3-1 on page 4-5) would be worthwhile. Similarly, the report may provide some data to answer how much of the concentration and spread is attributable to fuel effects. 

In Figure E-4, the Houston ME/monitor BTX ratios apmeasurement error) across season for the exhaust domsuggests. However, the summer BT ratios do appear and ME7 which are dominated by refueling evaporatiwinter ratios appear less so. While the fuel specificatare typical of these cities and relevant to the garage andiscussed in Sections 4 and 5 of the report, they are noME measurements discussed in Section 3 which arise mixtures of locally available fuels. Although seasonavendors is available in annual surveys for these cities, fleet emissions is beyond the scope of the Tier 2 study 

8 

p. ES- 15, line 17: The word "below" is misspelled. This typographical error has been corrected.

9 

p. ES- 16:Can the 2.2 times higher in-cabin exposure levels for the trailing vehicle relative to 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 to show no significant difference)? We are unsure that average in-cabin levels were minimally affected by different vehicles or fuels except for an MTBE fuel effect. Comparing the values for "truck 

The 2-fold higher exposures trailing a malfunctioning attributable to cabin ventilation differences given the experiments under similar meteorological conditions 

speeds) and identical protocols regarding ventilation chigher cabin levels would be anticipated as a result of malfunctioning 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, fuel type seems to vary substantially for toluene (Chicago = 1.32, whereas Atlanta = 2.79) and ethylbenzene (Chicago = 0.120, whereas Atlanta = 0.51), and Chicago 

fuel was much lower for the xylenes. It may rest on what is meant by "minimally affected." 

‘Table E-1’ typo is changed to Table E-2 on page ES-We agree with the reviewer’s comment and modified follows: “Average in-cabin levels were affected by bo

the vehicle and fuel composition. Use of Atlanta fuel 

concentrations in the trailing vehicle cabin, which is caromatic contents of Atlanta fuel, especially in summconcentrations were consistently higher during the sumconcert with higher aromatic contents of summer fuelAveraging over the fuels and vehicles, the high emittehigher in-cabin exposure levels for the trailing vehicle 

mode except for HCHO which was relatively unchangthe text in Section 5 (page 5-12 and 5-14) was modificonclusion. The differences between “car only” and “truck only” less pronounced than fuel effect. 

10 

p. ES-18 and 19: The conclusions appear to be scientifically sound. The statement that "although overall the average population time spent in these high end MEs is likely the 

shortest" is important and should not be left to conjecture. The actual activities associated 

with exposures to evaporative eniissions should be characterized. Activity patterns often dictate actual exposures. Concentrations alone tell only part of the exposure story. We agree that HAPEMS factors may need to be updated based on these findings, and we will provide the final version of this report to the Office of Air Quality Planning and Standards who are responsible for the HAMPEM model, which was recently upgraded to HAPEM6, http://www.epa.gov/ttn/fera/huma-nh apem.htm1. 

Other EPA documents provide adequate support for th

be repeated in the report. For example, Table 15-106 Handbook (EPA/600/P-95/002Fc) reports that 157 (18visited a gas station the day before in a survey populaminutes (median) outside the service station with an inminutes (http://www.epa.gov/ncea/efh/pdfs/efh-chapt

The HAPEM5 comment refers to ‘high end’ aspects oCARB study where the driving protocol highlighted trHDD trucks when possible, a counter-intuitive practicHAPEM factors should be lowered to simulate ‘typicacommuters are more likely to avoid such vehicles. Sifocused on ‘high end’ exposures (see response #1), co

HAPEM simulations should be restricted to ‘high end

findings should not be used to derive HAPEM factors average or typical conditions. 

11 

p. 1-20, final paragraph: Figure 1.3.2-5 is missing. There is no figure 1.3.2-5. The text on p. 1-20 was cor

12 

p. 1-21: P-values should include at least two significant figures. The p-values have expanded significant figures at pag
13 

p.2-5: Note that "OMS" has changed its title to "OTAQ (Office of Transportation and Air Quality). ‘OMS’ has been changed to ‘OTAQ’ in Table 2-1 cap

14 

p.2-9: How were the "error bars" in Figure 2-9 calculated? What components of uncertainty are accounted for here? Sampling? Instrument precision? Error propagation? 

Presumably this question concerns Figure 2-1, as thersection... A brief discussion of how uncertainties assodetermined is added to the initial paragraph at page 2-

15 

p. 3 - 1, second paragraph: The 1999 NATA does not assume constant background concentrations of all pollutants. See http://www.epa.gov/ttn/atw/natal999/background.html for additional detail. 

The report does not claim that a uniform background all pollutants. 

16 

p. 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, in comparison to other studies looking at similar microenvironments, the concentrations in this study are higher. The italicized text is likely inappropriate if this comparison does not suggest that the micro-environmental exposures presented herein are "extreme." 

We removed the italicization of the text. However, as 

the ‘high end’ study protocol was designed to sample 

more ‘extreme’ exposures that those thought ‘typical’ informative, the comparisons suggested with earlier stthemselves sampled under ‘high end’ conditions (e.g. be adjusted for interim changes in fuel composition ansuch extended analysis is beyond the scope of this rep

17 

p. 4-7 – 8, Table 4.3-6,7: The tables and text do not seem to identify whether these non-aldehyde data are from SMPE or canister samples. 

The report has been edited (p. 4.7) to identify absorptivalues. 

18 

p. 5 - 1 4, last paragraph: 

". . .after the change to low ventilation.. . little change in the in-cabin 

concentration.. ." This text appears to contradict language on p. 5-1 8, second to last paragraph, where it is noted that the range of concentrations differed under high ventilation 

situations. Please clarify the intended meaning, which appears to suggest that while average concentrations were unaffected, variability in concentration was affected by ventilation. 

The latter reading grasps the meaning intended; languclarified to state that although on average the integratesimilar for high and low ventilation, the variability (pecabin concentrations was larger during the high ventil