Section 211(B) Tier 2 High End Exposure Study of Conventional 

and Oxygenated Gasoline 

FINAL REPORT 

Prepared for 

AMERICAN PETROLEUM INSTITUTE 

1220 L Street 

Washington, DC 20005-4070 

Prepared by 

Barbara Zielinska, Eric M. Fujita, John C. Sagebiel, and David E. Campbell 

Division of Atmospheric Sciences 

Desert Research Institute 

Nevada System of Higher Education 

2215 Raggio Parkway 

Reno, NV 89512 

March 25, 2009 

2215 Raggio Parkway, Reno, Nevada 89512-1095 (775) 673-7300 
ACKNOWLEDGMENTS 

 We wish to acknowledge the financial support for this study by the American Petroleum 

Institute and Drs. Will Ollison and Lorraine Twerdok of the API for their administrative support 

and technical guidance. We also thank the API review committee and the staff of the U.S. 

Environmental Protection Agency for reviewing the draft exposure protocols and interim project 

results. We also acknowledge the vehicle testing performed during the control experiments in 

San Antonio by Lawrence Smith and Patrick Merritt at Southwest Research Institute and 

evaluation of potential biomarkers during the initial pilot study by Dr. Jacob McDonald of the 

Lovelace Respiratory Research Institute. We also acknowledge the assistance of Ted Johnson of 

TRJ Environmental, Inc. for his input on the candidate microenvironments and review of our 

draft exposure protocols. We also acknowledge the following DRI personnel for their assistance: 

Larry Sheetz for modifications to the sampling platforms; Aaron Centric, Diana Ceballos and 

Mark McDaniel for field sampling; Diana Ceballos for evaluation of the SPME method; and 

Katarzyna Rempala and Michael Keith for the organic speciation analysis. 

ii 
TABLE OF CONTENTS 

 Page

Acknowledgments........................................................................................................................... ii 

EXECUTIVE SUMMARY .............................................................................................................1 

1. Quantification of Personal Exposures to Motor Vehicle Emissions in High Exposure 

Microenvironments in Atlanta, Houston, and Chicago during Summer and Winter............. 1-1 

1.1 Introduction ................................................................................................................... 1-1 

1.2 Experimental.................................................................................................................. 1-2 

1.2.1 Selection of Microenvironments.......................................................................... 1-2 

1.2.2 Monitoring Methods............................................................................................ 1-4 

1.2.3 Exposure Biomarkers........................................................................................... 1-5 

1.3 Results and Discussion.................................................................................................. 1-6 

1.3.1 Variation of day-to-day exposures by ME in each city ....................................... 1-6 

1.3.2 Distribution of exposures within MEs in each city (1-minute time series) ....... 1-19 

1.3.3 Oxygenated and conventional gasoline (difference between cities).................. 1-31 

1.3.4 Effect of meteorology on exposure.................................................................... 1-35 

1.3.5 Comparison of summer and winter exposures................................................... 1-37 

1.3.6 Correlations to breath concentrations ................................................................ 1-41 

1.4 Conclusions ................................................................................................................. 1-45 

1.5 References ................................................................................................................... 1-46 

2. Relative Contributions of Vehicle Evaporative and Exhaust Emission to 

Concentrations of Volatile Air Toxics in High Exposure Microenvironments in 

Houston.................................................................................................................................. 2-1 

2.1 Introduction ................................................................................................................... 2-1 

2.2 Experimental Approach................................................................................................. 2-2 

2.3 Results ..................................................................................................................... 2-3 

2.4 Conclusions ................................................................................................................... 2-4

2.5 References ................................................................................................................... 2-10 

3. Determination of the Quantitative Relationships between Levels of Volatile Air 

Toxics and Carbon Monoxide Measured In High End Microenvironments and At 

Nearby Air Quality Monitoring Stations ............................................................................... 3-1 

3.1 Introduction ................................................................................................................... 3-1 

3.2 Experimental.................................................................................................................. 3-2 

3.3 Results and Discussion.................................................................................................. 3-3 

3.4 Conclusions ................................................................................................................... 3-4 

3.5 References ..................................................................................................................... 3-4 

4. Relationships of Attached Garage and Home Exposures to Fuel Type and Emission 

Levels of Garage Sources ...................................................................................................... 4-1 

4.1 Introduction ................................................................................................................... 4-1 

4.2 Experimental.................................................................................................................. 4-1 

iii
4.2.1 Vehicles and Vehicle Test Methods .................................................................... 4-1 

4.2.2 Fuel Testing ......................................................................................................... 4-2 

4.2.3 Test House ........................................................................................................... 4-2 

4.3 Results ..................................................................................................................... 4-4 

4.3.1 Fuel Analyses....................................................................................................... 4-4 

4.3.2 Vehicle Regulated and Hot Soak Emissions........................................................ 4-5 

4.3.3 Garage and Kitchen Exhaust/Evaporative Fuel Component Levels.................... 4-7 

4.3.3.1 Background and Overall Concentrations.............................................. 4-7 

4.3.3.2 Seasonal Impacts................................................................................... 4-8 

4.3.3.3 Fuel and Vehicle Effects....................................................................... 4-9 

4.3.3.4 Comparison with Emissions Data....................................................... 4-16 

4.3.3.5 Relationships of Garage and Kitchen Concentrations........................4-19 

4.4 Discussion ................................................................................................................... 4-21 

5. Effect of Ventilation, Proximity, and Emission Levels on In-Cabin Exposures of 

Trailing Vehicle. .................................................................................................................... 5-1 

5.1 Introduction ................................................................................................................... 5-1 

5.2 Experimental.................................................................................................................. 5-1 

5.2.1 Fuel Testing ......................................................................................................... 5-2 

5.2.2 Relationship between Exhaust Emission Rates and In-Cabin Exposure - 

Trailing Vehicle Test................................................................................... 5-2 

5.2.2.1 Test Protocol ......................................................................................... 5-2 

5.3 Results ..................................................................................................................... 5-6 

5.3.1 Background and Overall Concentrations............................................................. 5-6 

5.3.2 Vehicle and Fuel Effects.................................................................................... 5-12 

5.3.3 Trailing Vehicle Effects..................................................................................... 5-14 

5.3.4 Comparison with FTP Data ............................................................................... 5-16 

5.4 Discussion ................................................................................................................... 5-18 

APPENDIX A..................................................................................................................................1 

APPENDIX B ..................................................................................................................................1 

APPENDIX C ..................................................................................................................................1 

APPENDIX D..................................................................................................................................1 

APPENDIX E ..................................................................................................................................1 

APPENDIX F...................................................................................................................................1 

APPENDIX G..................................................................................................................................1 

APPENDIX H..................................................................................................................................1 

APPENDIX I ...................................................................................................................................1 

iv
LIST OF FIGURES

 Page

Figure E-1. Distribution of reconstructed 1-min BTEX exposures in high-end Atlanta 

MEs. Edges of the box = first and third quartiles; black line = median; red line = 

average. Minimum and maximum values (ppbv) are shown at the bottom and top 

of the plots. Whisker covers 99.3% of the data distribution. Filled circles > 3 

times the box interval, empty circle are within that interval. The y-axis represents 

the percentage of data distribution.................................................................................ES-9 

Figure E-2A. Comparison of average concentrations of benzene, 1,3-BD, HCHO and CO 

in three cities in Summer .............................................................................................ES-10 

Figure E-2B. Comparison of average concentrations of benzene, 1,3-BD, HCHO and CO 

in three cities in Winter................................................................................................ES-11 

Figure E-3. MTBE/benzene ratio and contribution of evaporative emissions in Houston 

MEs..............................................................................................................................ES-13 

Figure E-4. Mean ratios of ME concentrations to corresponding hourly measurements at 

the regional air monitoring station in Houston. ...........................................................ES-14 

Figure E-6. The effect of fuel and vehicle operation mode (i.e. normal or malfunction) on 

observed concentrations in the kitchen........................................................................ES-17 

Figure 1.3.1-1. Time-integrated exposure levels in different MEs in Atlanta, Summer 

2002 and 2003................................................................................................................ 1-13 

Figure 1.3.1-2. Time-integrated exposure levels in different MEs in Atlanta, Winter 2004..... 1-14 

Figure 1.3.1-3. Time-integrated exposure levels in different MEs in Chicago, Summer 

2003................................................................................................................................ 1-15 

Figure 1.3.1-4. Time-integrated exposure levels in different MEs in Chicago, Winter 

2004................................................................................................................................ 1-16 

Figure 1.3.1-5. Time-integrated exposure levels in different MEs in Houston, Summer 

2004................................................................................................................................ 1-17 

Figure 1.3.1-6. Time-integrated exposure levels in different MEs in Houston, Winter 

2005................................................................................................................................ 1-18 

Figure 1.3.2-1. 1-Minute time series for in-cabin exposures: ME1 (congested freeway), 

ME2 (urban canyon); ME4 (underground garage) and ME5 (toll plaza)...................... 1-27 

Figure 1.3.2-2. 1-Minute time series for in-cabin exposures: ME6 (tunnel); ME13 

(following high-emitting vehicle); ME3 (in-cabin refueling) and out-of-cabin 

refueling, ME7 ............................................................................................................... 1-28 

Figure 1.3.2-3. 1-Minute time series for out-of cabin outdoor exposures:ME8 (sidewalk); 

ME10 (surface parking); ME11 (underground garage) and ME12 (toll plaza)............. 1-29 

Figure 1.3.2-4. Correlations between 5-minute canister samples and surrogate 1-minute 

values, averaged over corresponding 5 minutes. ........................................................... 1-30 

v
Figure 1.3.3-1. MTBE and EtOH concentrations in Houston and Chicago, 

respectively..Note different y-axis scales for Chicago Sumer and Winter.................... 1-32 

Figure 1.3.3-2. Comparison of benzene, 1,3-BD, HCHO, and CO average concentrations 

in three cities in Summer ............................................................................................... 1-33 

Figure 1.3.3-3. Comparison of benzene, 1,3-BD, HCHO, and CO average concentrations 

in three cities in Winter.................................................................................................. 1-34 

Figure 1.3.5-1. Time integrated average exposure levels in different MEs in Atlanta in 

Summer and Winter season. .......................................................................................... 1-38 

Figure 1.3.5-2. Time integrated average exposure levels in different MEs in Chicago in 

Summer and Winter season ........................................................................................... 1-39 

Figure 1.3.5-3. Time integrated average exposure levels in different MEs in Houston in 

Summer and Winter season ........................................................................................... 1-40 

Figure 1.3.6-1. Average breath BTEX, 1,3-BD, MTBE, EtOH, and CO2 concentrations in 

three cities in Summer ................................................................................................... 1-42 

Figure 1.3.6-2. Average breath BTEX, 1,3-BD, MTBE, EtOH, and CO2 concentrations in 

three cities in Winter...................................................................................................... 1-43 

Figure 1.3.6-3. Correlations between 1-minute surrogate benzene and 1,3-BD max values 

and post-exposure breath concentrations (upper panel) and comparison of these 

concentrations in different ME and cities (lower panel)................................................ 1-44 

Figure 2-1.Fractional contributions of evaporative emissions to total motor vehicles 

emissions in Houston by ME. .......................................................................................... 2-9 

Figure 3.1a. Location of ME sampling and fixed monitoring stations in Chicago Metro 

Area.................................................................................................................................. 3-9 

Figure 3.1b. Location of ME sampling and fixed monitoring stations in Houston Metro 

Area................................................................................................................................ 3-10 

Figure 3-2a. Comparison of average versus the maximum 1-minute benzene levels by 

city, season and microenvironment................................................................................ 3-12 

Figure 3-2b. Comparison of average versus the maximum 1-minute 1,3-butadiene levels 

by city, season and microenvironment........................................................................... 3-13 

Figure 3-2c. Comparison of average versus the maximum 1-minute formaldehyde levels 

by city, season and microenvironment........................................................................... 3-14 

Figure 4.3-1. Effect of fuel and mode on observed concentrations in the garage. The 

legend “N” is normal and “F” is malfunction. The 1,3-BD value for Houston-F is 

suspect............................................................................................................................ 4-10 

Figure 4.3-2. Effect of fuel and mode on observed concentrations in the kitchen. The 

legend “N” is normal and “F” is malfunction. The 1,3-BD value for Houston-F is 

suspect............................................................................................................................ 4-11 

vi
Figure 4.3-3. Effect of fuel and mode on observed sedan garage levels. The legend “N” is 

normal and “F” is malfunction. The 1,3-BD level for Houston-F is suspect, see 

text.................................................................................................................................. 4-12 

Figure 4.3-4. Effect of fuel and mode on observed truck garage levels. The legend “N” is 

normal and “F” is malfunction. The 1,3-BD level for Houston-F is suspect, see 

text.................................................................................................................................. 4-12 

Figure 4.3-5. Concentrations of 1,3-butadiene, MTBE and BTEX and CO as measured 

from canisters in the garage and the adjacent kitchen in Summer 2002........................ 4-14 

Figure 4.3-6. Concentrations of 1,3-butadiene, MTBE and BTEX (A) and CO (B) as 

measured from canisters in the garage and the adjacent kitchen in Winter 2005. 

M=sample missing or invalid. ....................................................................................... 4-15 

Figure 4.3-7. Comparison of SHED results with the observed canister concentration in 

the garage for benzene. .................................................................................................. 4-16 

Figure 4.3-8. Comparison of the SHED results with the observed SPME hot soak 

concentration in the garage for benzene A: all data, B: two outliers removed.............. 4-16 

Figure 4.3-9. Comparison of FTP Bag 1 emissions and observed garage levels of 1,3-BD. .... 4-17 

Figure 4.3-10. Comparison of FTP Bag 1 benzene emissions and observed garage levels. ..... 4-18 

Figure 4.3-11. Comparison of hot soak FTP Bag 1 benzene emissions and observed 

SPME garage values. ..................................................................................................... 4-18 

Figure 4.3-12. Comparison of garage and kitchen concentrations for 1,3-BD. A – all data, 

B- with two outliers removed (see text)......................................................................... 4-19 

Figure 4.3-13. Comparison of garage and kitchen concentrations of carbon monoxide. .......... 4-20 

Figure 4.3-14. Comparison of garage and kitchen concentrations of benzene.......................... 4-20 

Figure 5.2-1. Map of Driving Test Location near San Antonio. The blue markers indicate 

the location of the driving tests........................................................................................ 5-4 

Figure 5.2-2. Map of Driving Test Location near Moore, TX.................................................... 5-5 

Figure 5.2-3. Elevation Profile of the Driving Route near Moore, TX. ..................................... 5-5 

Figure 5.3-1. Comparison of Summer and Winter Background Concentrations with 

Standard Deviations. HCHO is divided by 10 for scale. ................................................. 5-7 

Figure 5-3-2. Concentrations of 1,3-BD, MTBE and BTEX (A) and CO (B) as measured 

in the cabin of the trailing vehicle, Summer 2002........................................................... 5-8 

Figure 5-3-3. Concentrations of 1,3-BD, MTBE and BTEX and CO as measured in the 

cabin of the trailing vehicle, Winter 2005 ....................................................................... 5-9 

Figure 5.3-4. Comparison of Summer and Winter Concentrations for the Trailing tests.......... 5-10 

Figure 5.3-5. Comparison of Summer Background and Test Values........................................ 5-11 

Figure 5.3-6. Comparison of Winter Background and Test Values. ......................................... 5-11 

vii
Figure 5.3-7. Scatter plot of Normal Emitter and High Emitter Mean In-cabin Values for 

all species except HCHO and EtOH. ............................................................................. 5-13 

Figure 5.3-8. Time Series of In-Cabin (PID1) and Outside (PID2) PID Values....................... 5-15 

Figure 5.3-9. Comparison of FTP Bag 2 Benzene Emissions to In-cabin Concentration in 

the Trailing Vehicle. ...................................................................................................... 5-16 

Figure 5.3-10. Comparison of FTP Bag 2 MTBE emissions to in-cabin concentrations in 

the trailing vehicle.......................................................................................................... 5-17 

Figure 5.3-11. Comparison of FTP Bag 2 1,3-BD Emissions to In-cabin Concentrations 

in the Trailing Vehicle. .................................................................................................. 5-17 

viii
LIST OF TABLES 

 Page

Table E-1. Measurement methods used in the Section 211(B) Tier 2 High-End Exposure 

Screening Study. Data applications for specific methods are classified as 

reference, confirmatory, and surrogate. ...............................................................................3 

Table E-2. The effects of changing vehicle, fuel and operational mode (i.e. normal or 

malfunction) on observed concentrations in the trailing vehicle cabin. ............................17 

Table 1.2.1-1. Microenvironmental Sampling............................................................................. 1-3 

Table 1.3.1-1. Summer average, maximum, and minimum ME concentrations (ppbv) of 

BTEX, 1,3-BD, HCHO, CH3CHO, EtOH, MTBE, and CO (ppmv) .............................. 1-7 

Table 1.3.2-1A. Correlation coefficients (R2) and associated statistic for relationships of 

time-integrated measurements with continuous methods (NMVOC and CO) for 3 

cities, without ME3 and ME7 ........................................................................................ 1-21 

Table 1.3.2-1B. Correlation coefficients (R2) and associated statistic for relationships of 

time-integrated measurements with continuous methods (NMVOC and CO) for 

ME3 and ME7 in 3 cities............................................................................................... 1-22 

Table 1.3.2-2. Summary of the reconstructed 1-minute data (ppbv), Summer ......................... 1-23 

Table 1.3.2-3. Summary of the reconstructed 1-min data (ppbv), Winter................................. 1-24 

Table 1.3.2-4. Summary of the 5-minute canister data (ppbv) .................................................. 1-25 

Table 1.3.4-1. Average, minimum, and maximum ambient temperatures and RH ................... 1-35 

Table 2-1. Conventional gasoline versus reformulated gasoline RFG (from EPA OMS 

web page http://www.epa.gov/OMSWWW/rfgnew.htm, updated by S. Romanow, 

OMS)................................................................................................................................ 2-5 

Table 2-2. Summary of sample collections in urban MEs........................................................... 2-6 

Table 2-3. Mass ratios of MTBE to benzene in Houston by ME. ............................................... 2-7 

Table 2-4. Mass ratios of MTBE to benzene in vehicle exhaust, gasoline vapor and liquid 

gasoline. ........................................................................................................................... 2-8 

Table 2-5. Fractional contributions of evaporative emissions to total motor vehicles 

emissions in Houston by ME. .......................................................................................... 2-9 

Table 3-1. Summary of sample collections in urban microenvironments................................... 3-5 

Table 3-2. Average and standard deviation in ratios of the time-integrated CO from 

canister samples to the corresponding hourly CO from regional ambient air 

monitoring sites for Houston, Atlanta and Chicago by season and 

microenvironment............................................................................................................ 3-6 

Table 3-3. Average and standard deviations in ratios of BTEX and 1,3-BD from timeintegrated canister samples to the corresponding hourly automated GC data from 

the ambient air monitoring sites in Houston.................................................................... 3-7 

ix
Table 3-4. Houston benzene ME/ambient ratio comparison with HAPEM benzene ME 

factors............................................................................................................................... 3-8 

Table 4.2-1. Summary of vehicles used....................................................................................... 4-2 

Table 4.2-2. Protocol for attached garage experiments. .............................................................. 4-3 

Table 4.3-1. Summary of properties for the six test fuels............................................................ 4-5 

Table 4.3-2. Regulated and Hot Soak Emissions from the Ford F-150, Summer 2002. ............. 4-6 

Table 4.3-3. Regulated and Hot Soak Emissions from the Ford F-150, Winter 2005................. 4-6 

Table 4.3-4. Regulated and Hot Soak Emissions from the Toyota Camry, Summer 2002 ......... 4-6 

Table 4.3-5. Regulated and Hot Soak Emissions from the Toyota Camry, Winter 2005............ 4-6 

Table 4.3-6. Summary of Background Concentrations in Kitchen and Garage. Units are 

ppbv, except as noted....................................................................................................... 4-7 

Table 4.3-7. Summary of Test Concentration Ranges in Kitchen and Garage. Units are 

ppbv, except as noted....................................................................................................... 4-8 

Table 4.3-8. Seasonal Impact on Observed Maximum Concentrations (Units are ppbv, 

except as noted)................................................................................................................ 4-8 

Table 4.3-9. Seasonal Impact on Observed Maximum Concentrations (Units are ppbv, 

except as noted), Normal Mode Vehicles Only............................................................... 4-8 

Table 4.3-10. Seasonal Impact on Observed Average Concentrations (Units are ppbv, 

except as noted), Normal Mode Vehicles Only............................................................... 4-8 

Table 4.3-11. Effect of Fuel and Operational Mode of the Sedan on Observed Levels in 

the Kitchen and Garage (Units are ppbv, except as noted).............................................. 4-9 

Table 4.3-12. Effect of Fuel and Operational Mode of the Truck on Observed Levels in 

the Kitchen and Garage (Units are ppbv, except as noted).............................................. 4-9 

Table 5.2-1. Protocol for Trailing Vehicle Tests......................................................................... 5-3 

Table 5.3-1. Summary of Summer and Winter Background Concentrations.............................. 5-6 

Table 5.3-2. Summary of Test Concentrations for Summer, Winter and Overall. Units are 

ppbv, except CO as noted. ............................................................................................... 5-7 

Table 5.3-3. Summary of Concentrations Observed During Idle Tests. Units are ppbv 

except CO as noted. ....................................................................................................... 5-12 

Table 5.3.4. Effect of Vehicle, Fuel, and Operational Mode. Units are ppbv, except CO as 

noted. Number of measurements = n ............................................................................. 5-13 

Table 5.3-5. Influence of high emitting vehicles and each fuel on trailing vehicle in-cabin 

concentrations. Units are ppbv except CO as noted. ..................................................... 5-14 

Table 5.3-6. Summary of Seasonal Differences in the High Emitter Samples.......................... 5-14 

Table 5.3-7. Comparison of High and Low In-cabin Ventilation Conditions, Winter 2005 

only. Units are ppbv except CO as noted....................................................................... 5-15 

x
EXECUTIVE SUMMARY 

This study evaluated the upper-end distribution of inhalation exposures to evaporative 

and combustion emissions from conventional and oxygenated-gasoline. This final report 

describes the measurement methods and protocol used in the study and summarizes the 

validation and initial analysis of the assembled database. The main findings and conclusions are 

emphasized in this final report and additional details and descriptions of the data are provided in 

several supporting appendices. 

Introduction and Background 

The 211b Research Group is an unincorporated group of USA fuel and fuel additive 

manufacturers affiliated by contractual obligation to meet the testing requirements of Section 

211(b) (2) and 211(e) of Clean Air Act. The American Petroleum Institute (API) manages the 

required work on behalf of the 211b Research Group. 

Mobile source air toxics (MSAT) may pose an adverse health risk, especially in 

microenvironments with high exposures to vehicle exhaust or evaporative emissions. Although 

programs such as reformulated gasoline (RFG) are intended to reduce the emissions of MSAT 

and ozone precursors, uncertainties remain regarding population exposures associated with both 

oxygenate-gasoline blends and conventional gasoline. Accordingly, the EPA issued requirements 

for a test program in accordance with the Alternative Tier 2 provisions of the fuels and fuel 

additives (F/FA) regulations, which are required pursuant to Section 211 of the Clean Air Act. 

To satisfy those testing requirements, API contracted with a research team consisting of the 

Desert Research Institute (DRI), Southwest Research Institute (SwRI), Lovelace Respiratory 

Research Institute (LRRI), and TRJ Environmental, Inc (TRJ) to conduct a study of the high-end 

distribution of inhalation exposures to evaporative and combustion emissions of conventional 

and oxygenated-gasoline (MTBE-gasoline, and ethanol-gasoline). 

The results of this study provide data that will allow estimation of the upper-end of the 

frequency of annual average inhalation exposures to evaporative and combustion emissions of 

gasoline and oxygenated-gasoline. EPA may accomplish this by using the scripted exposures in 

high-end microenvironments with EPA regulatory exposure models, such as the Hazardous Air 

Pollutant Exposure Model (HAPEM). HAPEM is a screening-level exposure model for assessing 

average long-term inhalation exposure of the general population, or specific sub-populations, 

over spatial scales ranging from urban to national. The information from this study will permit 

sensitivity analyses to determine the range of these exposures, especially during heavy traffic, in 

residential and public parking garages and during refueling. The study also provides data for 

determining the relative proportion of evaporative versus combustion emissions in higher 

exposure microenvironments. 

The specific objectives of the study are to provide information allowing EPA to: 

• Quantify personal exposures to motor vehicle gasoline evaporative and combustion 

emissions in microenvironments (MEs) representing the upper end of the population 

exposure frequency distribution (99th + percentile) of such exposures; 

ES-1 
ES-2 

• Determine quantitative relationships between personal exposures in selected MEs and 

fixed site measurements in these MEs and at nearby air monitoring stations; 

• Determine how personal exposures differ among cities and seasons in which methyl tbutyl ether (MTBE)- and ethanol (EtOH)-gasolines are used compared with a city where 

oxygenated fuels are not used.; 

• Extrapolate study data to other cities and other oxygenated fuels; 

• Apportion the relative contributions of vehicle fuel combustion versus evaporative 

emissions to personal exposures in high-end MEs; 

• Determine the relationship between vehicle tailpipe and evaporative emissions and 

exposure levels in a trailing vehicle cabin and in a residence with an attached garage. 

Experimental Methods and Approach 

The study was conducted in several phases. First, DRI evaluated the suitability of 

available measurement methods for meeting the technical objectives of the study. These methods 

included continuous and time-integrated measurements of carbon monoxide (CO), total volatile 

organic compounds (VOC), and the following MSAT species: benzene, toluene, ethylbenzene 

and xylenes (BTEX), 1,3-butadiene (1,3-BD), methyl tertiary butyl ether (MTBE), formaldehyde 

and acetaldehyde. Exposure measurements included well-established time-integrated methods 

for measurements of hydrocarbons and carbonyl compounds. These samples provide data of 

known precision and accuracy for each chemical species of interest during each exposure 

measurement, which typically covered a 20 to 40 min period. Several continuous and semicontinuous methods were used to provide time-resolved data ranging from 1 to 10 minutes. 

Continuous exposure measurements included benzene, toluene, ethylbenzene, and xylenes 

(BTEX) by a portable mass spectrometer (MS), carbon monoxide (CO) by a portable 

electrochemical analyzer and by a nondispersive infrared (NDIR) analyzer, and estimates of total 

volatile organic compounds by a portable photoionization detector (PID). Semi-continuous 

measurements of BTEX were also obtained from analysis of solid phase microextraction (SPME) 

fibers. 

Because exposure levels in most microenvironments were expected to vary with time, the 

measurement protocol included continuous measurements of target species with time resolution 

of 1 minute or less. This requirement necessitated the use of instruments such as the Kore 

MS200 and the Alpha Omega formaldehyde analyzer, which have not previously been proven 

for such application and did not perform sufficiently well in field conditions during the pilot 

studies. Furthermore, there are no acceptable continuous methods for 1,3-butadiene, MTBE, 

ethanol, acetaldehyde or nonmethane hydrocarbons (NMHC) that could be used in portable 

modes of operation with adequate sensitivity. Therefore, our sampling strategy consists of a 

three-tier approach shown in Table E-1, which lists the overlapping measurement methods used 

in the Section 211(B) Tier 2 High-End Exposure Screening Study and their intended application. 
ES-3 

Table E-1. Measurement methods used in the Section 211(B) Tier 2 High-End Exposure Screening Study. Data aspecific methods are classified as reference, confirmatory, and surrogate. 

Continuous Semi-Cont Integrated 

Method T15 CO NDIR CO ppbRAE MS200 HCHO SPME Canister DNApplicable Environments outdoor and 

in-cabin 

all outdoor and 

in-cabin 

higher end MEs 

outdoor All all all 

Time Resolution 1 min seconds seconds 1 min 1 min 10 min 20-40&5 min 20-40 Detection Limits 0.1 ppm 0.04 ppm 1 ppb 1-3 ppbv 1 ppbv 0.2 ppbv 0.05 ppbC 0.1 pData Application 1 S S S C C C R R 

CO SC SC RPID SC 2BTEX S (a) S (a) SC (c) C C R 1,3-Butadiene S (a) S (a) S (c) R MTBE S (a) S (a) S (c) C R Formaldehyde S (b) S (b) S (d) C R Acetaldehye S (b) S (b) S (d) R Ethanol S (e) S (e) S (f) NMHC S (a) S (a) S (c) R 

1. Category of data application include surrogate (S), confirmatory (C) reference (R), and surrogate compounds or signal (SC) 2. Sum of molecules ionizable at 10.6 eV and detected by photoionization detector. S (a). Time series will be reconstructed from the canister/CO ratio for exhaust-dominated samples. S (b). Time series will be reconstructed from the DNPH/CO ratio for exhaust-dominated samples except outdoor daytime samples. S (c). Time series will be reconstructed from the canister/PID ratio for exhaust- or evap-dominated samples in outdoor MEs. S (d). Time series will be reconstructed from the DNPH/PID ratio for exhaust-dominated samples except outdoor daytime samples. S (e). Time series will be reconstructed from the solid adsorbent/CO ratio for exhaust-dominated samples. S (f). Time series will be reconstructed from the solid adsorbent/PID ratio for exhaust and evap-dominated samples. 
The measurements are classified in one of three tiers: reference, surrogate, and 

confirmatory. The base set or “reference” (R) measurements consist of three well-established 

time-integrated measurements. These include: canister sampling and analysis by gas 

chromatography with flame ionization detection for CO, BTEX, 1,3-butadiene, MTBE, and 

nonmethane hydrocarbons (NMHC); 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling and 

analysis by high performance liquid chromatography with UV detection for formaldehyde and 

acetaldehyde; and solid adsorbent sampling and analysis of ethanol by gas chromatography with 

mass spectrometry. These three methods combined measure all species of interest over the entire 

sampling period within each microenvironment. Although these integrated methods do not 

characterize peak exposures in microenvironments with highly varying exposure levels, they 

serve several other purposes. They provide a basis for validating continuous and semi-continuous 

data. They also provide a basis for deriving correlations between the time-integrated values with 

time averages of continuous data from the CO and PID instruments. Thus the continuous data 

were used as “surrogates” (S) for reconstructing the time series of specific MSAT based on these 

correlations. For example, data for BTEX, 1,3-butadiene, and MTBE from the canister 

measurements were correlated to continuous CO and PID data to reconstruct their time series in 

exhaust-dominated environments. In a similar manner, the time series of formaldehyde was 

reconstructed from the correlation of the integrated DNPH samples with CO. Outdoor afternoon 

samples were excluded due to potential contributions of carbonyl compounds formed from 

atmospheric reactions of hydrocarbons. Table E-1 shows other correlations that can be used in 

this manner. Two pilot studies were conducted in Reno, NV to test the proposed measurement 

methods under field conditions and to refine the exposure protocols. Two experimental 

approaches were used in the main study. 

Controlled Exposure Measurements in San Antonio

First, DRI and SwRI conducted exposure measurements in San Antonio under controlled 

conditions to establish quantitative relationships between vehicle tailpipe and evaporative 

emissions and exposure levels in two specific microenvironments, a trailing vehicle cabin and in 

a residence with an attached garage. The two vehicles (2.2L 4-cylinder 1993 Toyota Camry and 

a 5.0L V8 1995 Ford F150 Pickup truck) used in these controlled exposure experiments were 

tested at the SwRI laboratory for FTP (Federal Test Procedure) exhaust and hot soak evaporative 

emissions (Merritt, 2005). The tests were performed with the vehicles in normal and in 

malfunction condition while operating on summer and winter grade fuels from Houston, Atlanta 

and Chicago in summer 2002 and winter 2005. Measured FTP exhaust NMHC emission rates for 

the sedan and truck averaged 0.21 and 0.31 g/mi, respectively, in normal mode. Both emission 

rates are below the certified emission standards. The induced malfunctions raised NMHC 

emission rates by a factor of 16.7 for the sedan to 3.58 g/mi and factor of 7.0 for the truck to 2.20 

g/mi. Differences in NMHC emission rates among the three regional fuels were not significant. 

The p values of the regression between Atlanta and Houston and Atlanta and Chicago fuels were 

0.07 and 0.08, respectively for normal mode and 0.01 and 0.04, respectively for malfunction 

mode. The percent relative standard deviations of the NMHC emission rates for the sedan and 

truck were 15% and 14%, respectively, in normal mode and 3% and 6%, respectively with the 

induced malfunctions. 

The two test vehicles in normal operation and with induced malfunction were used to 

determine exposure in a cabin of a third vehicle which trailed the test vehicle. During each test, 

the trailing vehicle was driven behind the test vehicle over a travel loop of several miles in a 

ES-4 
rural area south of San Antonio. Measurements were made during the first 10 minutes without 

the test vehicle in order to established background exposure levels. Each trailing vehicle run 

included three scenarios (based on the proximity to the leading vehicle: far, near, and passing) 

for each low and high speed (30 mph and 60 mph) according to a prescribed schedule. Separate 

integrated samples were collected for background and separate periods corresponding to the 

driving and idle portions of each test for each fuel (i.e., Atlanta, Houston and Chicago) and 

emission condition (i.e., normal and malfunction mode). Data from the integrated reference 

methods showed observable relationships between exhaust emission rates and in-cabin exposures 

in a trailing vehicle. 

The same two test vehicles (with and without malfunctions) were used to determine 

indoor exposure in a home with an attached residential garage. The vehicles were parked in a 

closed garage also containing a gasoline powered lawnmower and gasoline storage container 

filled with the test fuels, with in-garage and adjacent room monitoring conducted before, during 

and after the vehicle cool-down period. Time-integrated canister and cartridge samples were 

collected for each test (one in the garage and one in the adjacent room). A set of continuous and 

semi-continuous measurements by serial 10 minute average solid phase micro-extraction 

(SPME) sampling were made during test period of two hours. 

Personal Exposures in Houston, Chicago and Atlanta

In the second approach, DRI measured personal exposures in selected MEs representing 

the upper end of the frequency distribution of potential population exposures. The study was 

conducted in Houston, TX, Chicago, IL and Atlanta, GA where MTBE-gasoline, ethanolgasoline and conventional gasoline are used, respectively. These cities also satisfy additional 

requirements of the study for ongoing ambient air monitoring programs and geographic and 

climatologic diversity among the three cities. Sampling was performed during winter and 

summer and under conditions that were conducive to higher exposures within each ME (e.g., 

downwind, low wind speeds, rush hour traffic). Continuous measurements included both NDIR 

and electrochemical CO, two PIDs and in-cabin and fuel tank skin temperature. From 3 to 5 

time-integrated canister and DNPH cartridge samples were collected for the following twelve 

microenvironments; 

 

• ME1-cabin exposure in congested freeway during commute, 

• ME2-cabin exposure in urban canyon, 

• ME3-cabin exposure during refueling, 

• ME4-cabin exposure in underground garage, 

• ME5-cabin exposure at toll plaza, 

• ME6- cabin exposure in on-road tunnel (Houston and Chicago only), 

• ME7-outside exposure during refueling, 

• ME8-outdoor exposure at busy street, 

• ME9-outdoor exposure at bus stop, 

• ME10-outdoor exposure at surface parking lot during and after event, 

• ME11-outside exposure in underground garage, 12-outdoor exposure at toll plaza, 

• ME13-cabin exposure following a high emitter (Atlanta only) 

ES-5 
In addition, 5-minute integrated canister samples were collected for ME6, ME7, ME10, and 

ME13 during peak exposures that corresponded to collection of breath samples. 

Exposure Protocol and Study Plan, and Study Schedule 

The Exposure Protocol and Study Plan was developed and refined based upon results of 

the pilot studies and initial field measurements during summer 2002. The following chronology 

describes the main stages in the study and development of the Study Plan. 

• First Pilot Study. Prior to the main field studies, DRI and LRRI conducted a 5-day pilot 

study in Reno, NV, during February 2002 to test alternative measurement approaches 

under field conditions similar to those that were encountered in the main study (Zielinska 

et al., 2002c). DRI and LRRI also evaluated the stability of the designated VOC species 

in breath and urine samples. Based upon the result of this pilot study, the exposure 

protocols and measurement methods, sampling and analytical procedures were refined 

and proposed in the June 13, 2002 Exposure Protocol and Study Plan (Zielinska et al., 

2002a). 

• Summer 2002 Field Studies. The field measurements in San Antonio, Houston, and 

Atlanta were completed in adherence to the June 2002 protocol during summer 2002. 

These data were presented in three separate reports: Interim Data Report (Zielinska et al., 

2002b), Summer 2002 Atlanta Field Study Report (Zielinska et al., 2003a) and Summer 

2002 San Antonio and Houston Field Study Report (Zielinska et al., 2004a). The work in 

Chicago in the summer of 2002 was postponed, pending further evaluation of the 

measurement protocol and assessment of the data collected in 2002. 

• Second Pilot Study. The second pilot study in Reno was conducted to refine the exposure 

protocol and further evaluate the surrogate approach and SPME measurements (Zielinska 

et al., 2003c). Several improvements were implemented in the mobile sampling platform 

during this time. Additional changes were incorporated into the final version of Exposure 

Protocol and Study Plan (Zielinska et al., 2003d) based upon discussions between EPA 

and DRI on the results of these reports. The final study protocol approved by the U.S. 

EPA is included in the Appendix A of this Final Report. 

• The final version of the protocol was applied to the summer 2003 and winter 2004/5 field 

study in Atlanta, Chicago and Houston and in the winter 2005 in San Antonio. A data 

report was previously prepared for the summer 2003 field study in Atlanta and Chicago 

(Zielinska et al. 2004b). 

API Section 211(B) Tier-2 Exposure Database 

The data have been organized into four data files (API Data_Continuous.xls, API 

Data_SPME.xls, API Data_Time-integrated.xls and API Data_Reconstructed.xls) containing the 

continuous, SPME, time-integrated and reconstructed exposure data. All files include data fields 

describing the sample collection conditions (e.g.; microenvironment, fuel type, test mode) as 

well as data flags indicating problems with the analytical or sample collection methods. Tables 

ES-6 
explaining the meaning of each data field are also included with each file. The files are supplied 

in Excel workbook format for convenience, but have been formatted to be compatible with 

common database software (the value -99 is used for missing data points, and time is in hhmm 

text format) 

The time-integrated data contains speciation results from canister, DNPH cartridge, and 

TENAX adsorbent tubes, plus time-averaged values of pollutants and environmental parameters 

that were measured continuously during the batch sample collection periods. Within the timeintegrated data file there are 4 sub-categories that are presented separately due to the differing 

number of experimental variables for each type: 1) microenvironment exposure measurements 

from the three cities, 2) breath samples collected from subjects participating in 4 of the 

microenvironments, 3) residence with attached garage, and 4) trailing vehicle exposure tests. 

The SPME data is assembled in essentially the same manner as the time-integrated data, 

but contains only the BTEX hydrocarbon compounds and uses some different sample descriptors 

where necessary to identify which portion of each test the sample was collected. The same 

sample IDs are used to facilitate comparison of the two sampling methods. 

The third data file contains 1-minute averages of the pollutants and environmental 

parameters that were measured continuously during the microenvironment exposure tests in the 3 

cities. Data were typically logged every 10 seconds during testing, but to reduce measurement 

noise, make the data set more manageable, and reduce the effect of minor timing discrepancies 

between instruments due to imperfect clock synchronization or differences in sample line 

residence time, the data was time averaged by minute. Each data record in this file has both a 

time/date stamp and an identification code that relates it to the corresponding time-integrated 

sample. Data flags are given to identify any missing or invalid data for each minute. Due to the 

large size of this file, the various sample descriptors have not been included but these can be 

derived from the identification code as described in the included key. 

The fourth data file contains 1-min reconstructed data for benzene, 1,3-butadiane and 

formaldehyde based on PID and NDIR CO continuous data, as described in Chapter 1 of this 

report. Both full time integrated canister and DNPH-carbonyl samples and 5-min canister 

samples collected over a peak exposure in selected MEs, are included. 

Study Findings 

Quantification of Personal Exposures to Motor Vehicle Emissions in High Exposure 

Microenvironments in Atlanta, Houston and Chicago during Summer and Winter (Chapter 1) 

• Since different fuels were used in each of the tree cities, only combined effect of city/fuel 

was examined in this study. 

• Day-to-day variations in high-end (99th + percentile) benzene, 1,3-butadiene, 

formaldehyde, and CO concentrations in different MEs were substantial and independent 

of city and season, probably related to the activity and emission rates of sources in the 

given MEs which differ from day to day. 

ES-7 
ES-8 

• With the exception of refueling, exposure levels were generally lower in outdoor MEs 

and higher in enclosed MEs. 

• The 20-min average exposures to benzene during refueling ranged up to few hundred 

ppbv and showed substantial day-to-day variability. 

• In-cabin exposures during on-road vehicle operation were less variable than in-cabin 

exposures in garages and toll plazas. 

• Exposure levels of BTEX species were highest in refueling MEs, which are dominated by 

evaporative emissions whereas exposures to CO, formaldehyde, and 1,3-butadiene were 

highest in cold-start dominated MEs. 

• BTEX and 1,3-butadiene measured by the time-integrated canister method correlated 

well with continuous PID and CO measurements, respectively, in all MEs except 

refueling. Correlation of formaldehyde with continuous CO was weak, probably due to 

photochemical production of this compound. 

• Continuous PID and CO (NDIR) data can be used to reconstruct 1-minute time series for 

benzene and 1,3-BD, respectively, provided that the averaged continuous measurements 

are above the detection limits of the instruments (25 ppbv and 0.5 ppmv, respectively). 

CO data can also be used to reconstruct 1-minute formaldehyde data; however, less 

reliably so due to poorer correlation between these species. 

• Reconstructed 1-minute time-series data for benzene and 1,3-butadiene, averaged over 

five minutes, correlated well with the corresponding 5-minute canister samples after 

excluding the Houston refueling ME data, which were distorted by high concentrations of 

MTBE. 

• The concentrations of benzene and 1,3-butadiene measured in post peak exposure breath 

samples closely tracked the corresponding microenvironmental 1-minute maximum 

reconstructed surrogate values. 

• Increases in concentrations of measured species occur in all breath samples that were 

collected within a minute of a peak exposure. In Atlanta and Chicago, the highest breath 

concentrations of BTEX and 1,3-BD were observed in ME7 (refueling) and ME11 

(underground garage), respectively. In Houston, high concentrations of MTBE were 

measured in ME7. 

Figure E-1 shows the distribution of reconstructed 1-min BTEX concentrations in high-end MEs 

in Atlanta in Summer. One-min time resolution reflects the high short-time peak concentrations 

necessary to characterize 99th + percentile exposure. The Atlanta winter distribution as well as 

Houston and Chicago MEs look very similar. 

Figure E-2 A and B shows the comparison of 1,3-butadiane, benzene, formaldehyde and CO 

averaged concentrations in three cities in Summer and Winter, respectively. 
2.4

132

9.2

14.2

9.8

40.0 25.8

7.3

97.6

5.8 9.4

24.3

172.

1.4

65

10.1

1.3

583

18.0 3.1

304

17.5

0.6

25

3.7

2.2

2454

13.3 0.8

58

5.1

2.6

80

7.0

2.1

98

14.1

60.1

465

152.

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME8_9 ME10 ME11 

0

20406080

100120

2.4

132

9.2

1.4

65

10.1

1.3

583

18.0 3.1

304

17.5

0.6

25

3.7

2.2

2454

13.3 0.8

58

5.1

2.6

80

7.0

2.1

98

14.1

60.1

465

152.

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME8_9 ME10 ME11 

0

20406080

100120

14.2

9.8

40.0 25.8

7.3

97.6

5.8 9.4

24.3

172.

2.4

132

9.2

1.4

65

10.1

1.3

583

18.0 3.1

304

17.5

0.6

25

3.7

2.2

2454

13.3 0.8

58

5.1

2.6

80

7.0

2.1

98

14.1

60.1

465

152.

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME8_9 ME10 ME11 

0

20406080

100120

14.2

9.8

40.0 25.8

7.3

97.6

5.8 9.4

24.3

172.

1. In-Cabin Congested Freeway 5. In-Cabin Toll Plaza 10. Outdoor Surface Parking2. In-Cabin Urban Canyon 7. Outdoor Refueling 11. Outdoor Underground Garage

3. In-Cabin Refueling 8. Sidewalk 12. Outdoor Toll Plaza

4. In-Cabin Underground Garage 9. Sidewalk/Bus Stop 13. Following High Emitters

Figure E-1. Distribution of reconstructed 1-min BTEX exposures in high-end Atlanta MEs. Edges of the box = firs

black line = median; red line = average. Minimum and maximum values (ppbv) are shown at the bottom and top o

covers 99.3% of the data distribution. Filled circles > 3 times the box interval, empty circle are within that intervalthe percentage of data distribution. 

ES-9 
Benzene

0

20406080

100120140

1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppbv

Houston Atlanta Chicago

1,3-Butadiene

02468

10

1 2 3 4 5 6 7 8 9 

ME

ppbv

Houston Atlanta Chicago

Formaldehyde

05

101520253035

1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppbv

Houston Atlanta Chicago

CO

02468

10121416

1 2 3 4 5 6 7 8 9 

ME

ppm

Houston Atlanta Chicago

Figure E-2A. Comparison of average concentrations of benzene, 1,3-BD, HCHO and CO in three cities in Summe

ES-10 
Formaldehyde

05

10152025

1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppbv

Houston Atlanta Chicago

CO

05

101520

1 2 3 4 5 6 7 8 9 10 

ME

ppm

Houston Atlanta Chicago

Benzene

0

102030405060

1 2 3 4 5 6 7 8 9 10 11 12 13

M E

ppbv

Houston Atlanta Chicago

1,3-Butadiene

02468

1012

1 2 3 4 5 6 7 8 9 10 

M E

ppbv

Houston Atlanta Chicago

ES-11 

Figure E-2B. Comparison of average concentrations of benzene, 1,3-BD, HCHO and CO in three cities in Winter
ES-12 

Relative Contributions of Vehicle Evaporative and Exhaust Emissions to Concentrations of 

Volatile Air Toxics in High Exposure Microenvironments (Chapter 2)

• MTBE/benzene ratios were used to estimate the relative contributions of evaporative and 

exhaust emissions to MSAT. This basis for this approach is that the proportion of MTBE 

in exhaust is reduced during combustion relative to its proportion in the fuel while 

benzene is enriched in exhaust relative to its proportion in the fuel due to toluene and 

xylene dealkylation. Consequently, MTBE to benzene ratios are substantially lower in 

exhaust than in liquid fuel or headspace vapors. Exposures at the two refueling MEs (3 & 

7) were dominated by evaporative emissions as expected, with MTBE/benzene ratios in 

Houston of 20 to 30. Ratios for all other MEs were between 1 and 4. 

• The fractional contribution of evaporative and exhaust emission were estimated for each 

ME based on exhaust MTBE/benzene ratios from several dynamometer exhaust tests and 

on-road tunnel measurements and evaporative MTBE/benzene ratios for the SwRI SHED 

tests and composition of gasoline headspace vapor. Exposures during refueling (ME3, 

ME7) are 100% due to evaporative emissions within the uncertainties associated with the 

measurements and method. All other MEs are dominated by tailpipe emissions with 

fractional evaporative contributions < 10%. 

Figure E-3 shows the MTBE/benzene ratio and contribution of evaporative emissions in Houston 

MEs 

Quantitative Relationships Between Levels of Volatile Air Toxics and Carbon Monoxide 

Measured in High-End Exposure Microenvironments and at Nearby Air Quality Monitoring 

Stations (Chapter 3)

• MEs in close proximity to running vehicle engines have enhanced CO relative to ambient 

levels at nearby air quality monitoring sites with enrichment ratios approaching 40 where 

ventilation is limited, as in underground garages. Average in-cabin CO/ambient ratios in 

congested freeway traffic range from 2-9. ME locations less proximate to operating 

vehicles, such as gas stations and urban sidewalks, have CO/ambient ratios of 0.5-2. 

• The mean ratio of in-vehicle exposures on congested freeways (ME #1) to ambient levels 

at a monitoring station of 9.8 ± 3.8 ratio for Houston exceed the HAPEM5 median 

proximity factor of 4.9 (triangular distribution mode:range 1.9:0-14.3) and HAPEM4 

proximity factor of 6.9 for this ME (Rosenbaum, 2005; Long & Johnson, 2004), although 

by less than expected. 

Figure E-4 shows the mean ratios of ME concentrations to corresponding hourly measurements 

at the regional air monitoring station in Houston. 
Evaporative Emissions Contrib

0.00.20.40.60.81.0

1 2 3 4 5 6 7 8 

ME

Fraction

MTBE/benzene

0

20406080

1 2 3 4 5 6 7 8 9 10 11 12

ME

Ratio

summerwinter

 1. In-vehicle congested freeway 5. In-vehicle toll plaza 9. Outdoor bus stop 2. In-vehicle urban canyon 6. In-vehicle road tunnel 10. Outdoor surface parking  3. In-vehicle refueling 7. Outdoor refueling 11. Outdoor underground garage

 4. In-vehicle underground garage 8. Outdoor sidewalk 12. Outdoor toll plaza

Figure E-3. MTBE/benzene ratio and contribution of evaporative emissions in Houston MEs 

ES-13 
Houston- Summer

1

10

100

1000

10000

1 2 3 4 5 6 7 8 9 10 11 12

Microenvironment

ME/Station Ratio

BenzeneToluenem&p-Xylenes

Houston - Winte

1

10

100

1000

10000

1 2 3 4 5 6 7 

Microenviro

ME/Station Ratio

 1. In-vehicle congested freeway 5. In-vehicle toll plaza 9. Outdoor bus stop 2. In-vehicle urban canyon 6. In-vehicle road tunnel 10. Outdoor surface parking  3. In-vehicle refueling 7. Outdoor refueling 11. Outdoor underground garage

 4. In-vehicle underground garage 8. Outdoor sidewalk 12. Outdoor toll plaza

ES-14 

Figure E-4. Mean ratios of ME concentrations to corresponding hourly measurements at the regional air monitorin
Relationship of Attached Garage and Home Exposures to Fuel Type and Emission Levels of 

Garaged Sources (Chapter 4)

• Two target components, formaldehyde and ethanol, had high kitchen background values 

indicating indoor sources of these compounds. Average kitchen formaldehyde levels 

were higher in summer than winter, probably due to enhanced off-gassing of building 

materials and/or penetration of ambient photochemical formaldehyde. 

• Kitchen BTEX, MTBE and CO species are higher in winter than summer. The exception 

is toluene which shows a minimal difference that actually averages higher in summer for 

normal mode vehicles. This is consistent with indoor toluene emissions from paints, 

adhesives, cleaning, and personal care products. 

• MTBE and ethanol are highest for fuels containing those species, as anticipated. 

• FTP exhaust and SHED evaporative emissions were tested for each vehicle, fuel, and 

emissions mode, and compared to observed levels in the garage. Neither canister nor 

SPME samples show strong (r2

=0.003 and 0.005, respectively) correlations with hot soak 

emissions, although cold-stabilized FTP Bag 2 benzene appears reasonably correlated 

(r2= 0.4) to the cold-start SPME. 

• Correlations of kitchen levels with garage concentrations were weak (r2 generally below 

0.1) and could not be used to predict kitchen exposures from garage levels. 

Figure E-5 shows the effect of fuel and vehicle operational mode (i.e. normal or malfunction) on 

observed concentrations of 1,3-butadiene, BTEX, MTBE, formaldehyde, ethanol and CO in the 

kitchen. 

Effect of Ventilation, Proximity, and Emission Levels on In-Cabin Exposures of Trailing Vehicle 

(Chapter 5)

• Summer and winter in-cabin values were similar in magnitude with the exception of 

formaldehyde which was higher in the summer, possibly due to higher photochemical 

activity and higher temperatures that led to more off-gassing of formaldehyde in the 

vehicle cabin interior. 

• Trailing vehicle cabin values were larger than background values (as measured during the 

first 10 min run without the test vehicle) except for formaldehyde which was actually 

lower than background in winter tests. 

• Idle test sample values were on average twice those encountered in driving tests, 

suggesting that proximity and proximity duration may substantially impact in-cabin 

trailing vehicle concentrations. 

ES-15 
• Average in-cabin levels were affected by both state of maintenance of the vehicle and 

fuel composition. Use of Atlanta fuel resulted in higher BTEX concentrations in the 

trailing vehicle cabin, which is consistent with higher aromatic contents of Atlanta fuel, 

especially in summer. Similarly BTEX concentrations were consistently higher during 

the summer, which is also in concert with higher aromatic contents of summer fuels, 

especially for Atlanta. Averaging over the fuels and vehicles, the high emitter mode 

resulted in 2.2 times higher in-cabin exposure levels for the trailing vehicle than the 

normal emitter mode except for HCHO which was relatively unchanged from 

background. 

• Trailing vehicle ventilation status affected in-cabin values; the concentrations observed 

by continuous PID and CO monitors were more variable under high ventilation. This may 

be rationalized as the vehicle moving into and out of the exhaust plume of the leading 

vehicle with in-cabin values changing rapidly under high ventilation; whereas under low 

ventilation, in-cabin concentrations trapped as the vents were closed stayed relatively 

constant during the remainder of low ventilation conditions. 

• Trailing vehicle tests indicated that the largest impact on in-cabin values came from the 

emissions mode (normal or malfunction) of the leading vehicle. 

Table E-2 shows the effects of changing vehicle, fuel and operational mode (i.e. normal or 

malfunction) on observed concentrations of 1,3-butadiene, BTEX, MTBE, formaldehyde, 

ethanol and CO in the trailing vehicle cabin. 

ES-16 
0

5

10

15

20

25

30

35

40

45

50

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

compound

ppbv

Atlanta-N

Atlanta-F

Houston-N

Houston-F

Chicago-N

Chicago-F

339,542

Figure E-6. The effect of fuel and vehicle operation mode (i.e. normal or malfunction) on 

observed concentrations in the kitchen 

Table E-2. The effects of changing vehicle, fuel and operational mode (i.e. normal or 

malfunction) on observed concentrations in the trailing vehicle cabin. 

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Formal

Truck only 0.42 1.14 2.06 0.38 1.24 0.52 0.15 1.08 4.23

Car only 0.59 1.13 1.87 0.33 1.11 0.45 0.53 1.42 6.13

Atl fuel only 0.53 1.44 2.79 0.51 1.66 0.68 0.14 1.41 5.99

Hou fuel only 0.56 1.05 1.63 0.35 1.19 0.50 1.28 1.10 5.88

Chi fuel only 0.48 0.87 1.32 0.20 0.66 0.28 0.03 1.22 4.20

Normal only 0.06 0.46 1.05 0.21 0.73 0.31 0.16 0.41 5.21

High emitter only 1.01 1.85 2.92 0.52 1.64 0.67 0.56 2.18 5.35

St Dev high emitter only 26% 35% 40% 43% 43% 45% 199% 42% 55%

ES-17 
Evaluation of Measurement Method’s Performance 

 The integrated canister and DNPH sampling methods produced nearly 100 percent data 

capture of high quality data as confirmed by internal consistency checks. However, some 

challenges were encountered in applying two continuous confirmatory measurements, the Kore 

MS200 and formaldehyde analyzers. In most of the MEs, the MS200 had vacuum problems, 

most probably due to the high humidity in Houston, Chicago and Atlanta, and did not produce 

useful data. The instrument performed much better during first and second Pilot Study in Reno, 

probably because of much lower humidity. Although the formaldehyde analyzer was upgraded, 

it still required extensive user intervention and did not run reliably under the conditions 

encountered. The sensitivity of the instrument to environmental noise associated with driving 

limited its utility under mobile sampling. With proper operation and better characterization of 

instrument performance, the supplemental continuous formaldehyde analyzer may prove useful 

for ambient monitoring at fixed location. 

 The SPME also had excellent data capture, as did the continuous instruments for CO and 

PID. The two PIDs were compared both in controlled tests and collocated during the MEs. In 

both cases, they tracked each other quite well. Differences appear to be due to an offset in one 

unit, and a slightly different response speed between the two units. The NDIR CO and 

electrochemical CO (Langan T15) instruments compared favorably, usually within 1 ppm. The 

detailed description of data quality and QA/QC procedures are presented in Appendix H. 

Conclusions 

Exposure levels are directly related to the activity and emission rates of sources in the 

microenvironment and inversely related to the distance between sources of emissions and the 

measurement location and extent of dilution of emissions, which are a function of meteorological 

conditions and the presence of physical obstruction that inhibit dispersion. All of these factors 

contribute to the large temporal and spatial variations in pollutant exposures that exist within 

each of the microenvironments. Testing at SwRI showed that the differences in exhaust and 

evaporative emission rates among the three regional fuels were not statistically significant except 

for MTBE. With the exception of MTBE, the small differences due to fuel formulation are 

masked by the large variations of exposure levels within each of the microenvironments. 

The information from control exposure experiments in San Antonio provided useful 

context for interpreting the varying exposures in the high-end microenvironments in Atlanta, 

Houston and Chicago. We found that the results of the trailing vehicle experiments were 

qualitatively consistent with our observations in the three cities. In-cabin exposure levels even in 

congested traffic were on the order of a factor of two higher than background. Congested stopand-go conditions resulted in some increase in exposure levels due to shorter gaps between 

vehicles and highest on-road exposures were measured when following high emitters. In-cabin 

exposures during low ventilation conditions were relatively constant and retained the levels at 

the time ventilation was cut off. 

Evaporative emissions were the only substantial components of high-end ME exposures 

during vehicle refueling operations, where they are dominant. Since refueling MEs had the 

highest relative levels of these components, they constituted the peak exposures, although overall 

the average population time spent in these high end MEs is likely the shortest. The contributions 

ES-18 
of evaporative emissions for all other MEs were typically about 5% of the total measured 

exposures. Results were similar for both seasons, although evaporative contributions during 

refueling were marginally less during summer, possibly due to more rapid dispersion of vapors 

and evaporation of fuel spilled during each refueling test at higher summer temperatures. These 

results suggest that the contemporary Houston vehicle fleet contained relatively few carbureted 

or leaking vehicles given that evaporative emissions were not a substantial source in the nonrefueling MEs tested. Refueling emissions released from pressurized fuel systems and spilled 

fuels appeared to be the primary source of peak evaporative exposures. The lack of a seasonal 

variability in the evaporative contribution was also consistent with this supposition. Although it 

was not feasible to try to distinguish further between liquid and headspace vapor contributions by 

the method used, the extremely low MTBE/benzene ratios observed for the roadway, sidewalk, 

and parking MEs strongly suggest that the impact from leaking liquid gasoline emissions were 

minor. 

HAPEM5 proximity factors may need to be adjusted since they were based on a 1998 

scoping study where measurements ‘highlighted trailing behind heavy duty diesel vehicles and 

diesel city buses when possible’. Houston ME/ambient ratio comparisons also generally exceed 

the other HAPEM factors. Refueling ratios (ME3, ME7) for benzene were higher than the 

corresponding HAPEM factors as expected, given the refueling protocol provisions maximizing 

exposure discussed above and below. Concentrations of exhaust compounds such as CO and 1,3-

butadiene were enhanced under reduced ventilation situations. 

It must be recognized that the various microenvironments were selected with a goal to 

capture the 99th percentile exposure levels within each type of microenvironment, as prescribed 

by EPA and API. We also selected specific sampling times and locations with the greatest 

potential for higher exposures. These selections were based on considerations of various 

emission surrogates such as traffic counts, diurnal variations in average highway speeds, length 

of queues at toll plazas, number of cars refueling or entering and exiting parking garages. 

Surrogates of dispersion included wind roses and diurnal variations in temperature. 

Measurements in microenvironments with unrestricted dispersion were made in the early 

morning or evening during calm conditions and minimal vertical mixing. In moderate wind 

conditions, we drove parallel to the prevailing wind to reduce the impact of cross winds. Thus, 

the ranges of exposures determined in this study are skewed toward the higher end of the 

distribution of exposures for each microenvironment. 

References 

Long, T. and T. Johnson (2004). Development of Penetration and Proximity Microenvironment 

Factor Distributions for the HAPEM5 in Support of the 1999 National-Scale Air Toxics 

Assessment (NATA). Memorandum prepared by TRJ Environmental, Inc. for the U.S. 

Environmental Protection Agency, Research Triangle Park, NC, April 5, 2004 

Merritt, P. (2005). Evaporative and Tailpipe Emissions Support for S211b Tier 2 Exposure 

Study. Final report submitted by Southwest Research Institute to Desert Research 

Institute on July 29, 2005. 

ES-19 
Rosenbaum, A. (2005). The HAPEM5 User’s Guide. Report prepared by ICF Consulting for the 

U.S. Environmental Protection Agency, Research Triangle Park, NC, March 2005. 

Zielinska, B., E. M. Fujita, J.C. Sagebiel, D. E. Campbell, L.R. Smith, T. Johnson (2002a). 

Exposure Protocol and Study Plan for the Section 211 (B) Tier 2 High End Exposure 

Screening Study of Baseline and Oxygenated Gasoline. Prepared for American Petroleum 

Institute, 1220 L Street, Washington, DC 20005-4007. June 13, 2002 

Zielinska, B., E. M. Fujita, J. C. Sagebiel, D. E. Campbell, J. McDonald (2002b). Interim Data 

Report for Section 211 (B) Tier 2 High-End Exposure Screening Study of Baseline and 

Oxygenated Gasoline. Prepared for American Petroleum Institute, 1220 L Street, 

Washington, DC 20005-4007. November 15, 2002. 

Zielinska, B, J. Sagebiel, E. Fujita, D. Campbell, J. McDonald, T.J. Kelly, and D. W. Joseph 

(2002c). Section 211(B) Tier 2 High-End Exposure Screening Study of Baseline and 

Oxygenated Gasoline-Pilot Study. Prepared for American Petroleum Institute, 1220 L 

Street, Washington, DC 20005-4007. June 13, 2002 

Zielinska, B, E.M. Fujita, and J.C. Sagebiel (2003a). Section 211 (B) Tier 2 High End Exposure 

Screening Study of Baseline and Oxygenated Gasoline-Summer 2002 Atlanta Field Study 

on Baseline Gasoline. Prepared for American Petroleum Institute, 1220 L. Street, 

Washington, DC 2005-4070. March 13, 2003. 

Zielinska, B., J.C. Sagebiel, D. Campbell, D. Ceballos, M. McDaniel, and E.M. Fujita (2003b). 

Section 211 (B) Tier 2 High End Exposure Screening Study of Baseline and Oxygenated 

Gasoline-2nd Reno Pilot Study. Prepared for American Petroleum Institute, 1220 L 

Street, Washington, DC 20005-4007. June 13, 2003 

Zielinska, B., E. M. Fujita, J.C. Sagebiel, D. E. Campbell, L.R. Smith, T. Johnson (2003d). 

Exposure Protocol and Study Plan for the Section 211 (B) Tier 2 High End Exposure 

Screening Study of Baseline and Oxygenated Gasoline. Prepared for American Petroleum 

Institute, 1220 L Street, Washington, DC 20005-4007. Final Version. October 1, 2003 

Zielinska, B., J.C. Sagebiel, D. Campbell, E.M. Fujita (2004a). Section 211 (B) Tier 2 High End 

Exposure Screening Study if Baseline and Oxygenated Gasoline-Summer 2002 San 

Antonio and Houston Field Studies. Prepared for American Petroleum Institute, 1220 L. 

Street, Washington, DC 2005-4070. March 5, 2004. 

Zielinska, B., J.C. Sagebiel, D. Campbell, E.M. Fujita (2004b). Section 211 (B) Tier 2 High End 

Exposure Screening Study if Baseline and Oxygenated Gasoline-Summer 2003 Chicago 

and Atlanta Field Studies. Prepared for American Petroleum Institute, 1220 L. Street, 

Washington, DC 2005-4070. July 5, 2004. 

ES-20 
1. Quantification of Personal Exposures to Motor Vehicle Emissions in High 

Exposure Microenvironments in Atlanta, Houston, and Chicago during 

Summer and Winter. 

1.1 Introduction 

 Gasoline-powered vehicles emit a portion of ozone-forming volatile organic compounds 

(VOC) and mobile source air toxics (MSAT) in the urban areas of the country. Elevated 

exposures to gasoline-related MSAT have been reported in certain microenvironments (MEs), 

such as in vehicle cabins during commuting on congested roadways (Batterman et al., 2002; 

Chan et al. 1991; Rodes et al., 1998; Fedoruk and Kerger 2003; Weisel et al., 1992; Jo and Park, 

1999), refueling (Vayghani and Weisel 1999; Vainitalo et al., 1999; Lindstrom and Pliel, 1996) 

or in urban canyons (Rodes et al., 1998; Chan et al. 1991). 

 Although oxygenated fuel and reformulated gasoline (RFG) programs are intended to 

reduce the emissions of ozone precursors and MSAT , uncertainties remain regarding the 

population exposures associated with oxygenated and conventional gasoline. Accordingly, in 

2001 EPA issued testing requirements under Alternative Tier 2 provisions of the fuel and fuel 

additive (F/FA) health effects testing regulations, required pursuant to Section 211(b) of the 

Clean Air Act. 

 The population exposure study reported here targets conventional gasoline and two 

oxygenated blends containing methyl tertiary butyl ether (MTBE) and ethanol (EtOH) and 

conducts studies in prospective high-end microenvironments (MEs) likely associated with the 

most-exposed populations. Personal exposures are quantified in selected MEs representing the 

upper end of the frequency distribution of potential population exposures. The studies take place 

in cities that have ongoing ambient air monitoring programs, located in hot and cold parts of the 

country, using one of the three target fuels. Sampling was performed during winter and summer 

seasons and under conditions (e.g., downwind, low wind speeds, rush hour traffic, fuel spillage, 

trailing high emission vehicles) thought to maximize exposure within each ME. The same 

sampling protocols (e.g., location, duration, cabin ventilation) were used in both seasons 

whenever possible. A number of fuel emission and exhaust components [carbon monoxide (CO), 

carbon dioxide (CO2), benzene, toluene, ethylbenzene, xylenes (BTEX), MTBE, 1,3-butadiene 

(1,3-BD), EtOH, formaldehyde (HCHO), and acetaldehyde (CH3CHO)] were measured within 

thirteen MEs in personal breathing zones, and in breath immediately after measured peak 

exposures. The results of these microenvironmental studies were intended to include the upperend (99+th percentile) of the frequency of annual average inhalation exposures to evaporative and 

combustion emissions from the three targeted gasolines. The study also estimates the relative 

proportion of evaporative and combustion emissions by ME in breathing zone air. 

1-1
The specific objectives of the study are to provide information allowing EPA to: 

• Quantify personal exposures to motor vehicle gasoline evaporative and combustion 

emissions in MEs representing the upper end of the population exposure frequency 

distribution (99+th centile) of such exposures; 

• Determine quantitative relationships between personal exposures in selected MEs and 

fixed site measurements in these MEs and at nearby air monitoring stations; 

• Determine how personal exposures differ across seasons and cities using the three target 

fuels (conventional-, MTBE-, and EtOH-gasoline); 

• Extrapolate study data to other cities and other oxygenated fuels; and 

• Apportion the relative contributions of vehicle fuel combustion vs. evaporative emissions 

to personal exposures in high-end MEs. 

1.2 Experimental 

1.2.1 Selection of Microenvironments 

 Houston (TX), Chicago (IL) and Atlanta (GA) were selected as the study sites. These 

cities have ongoing ambient monitoring programs and dispense MTBE-RFG, EtOH-RFG, and 

conventional gasoline formulations, respectively. One of the goals of the project was to sample 

high-end MEs, plausibly characterized in the upper 99+th percentile of exposures to 

exhaust/evaporative emissions from gasoline-fueled vehicles. Selection of high-end MEs1

 was 

made in consultation with EPA and independent peer reviewers according to the selection 

criteria described in the Exposure Protocol and Study Plan (Zielinska et al, 2003a) included in 

Appendix A. Table 1.2.1-1 lists the MEs chosen along with the number of replicate 

measurements taken in each ME, whether biomarker (breath) measurements were taken for that 

ME, and the sampling time spent in each ME. 

 

1

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin 

toll plaza; ME6: In-cabin roadway tunnel; ME7: Out-of-cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; 

ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; ME12: Outside toll plaza; ME13: In-cabin trailing high-emitter 

vehicle 

1-2
Table 1.2.1-1. Microenvironmental Sampling. 

ME # ME Description Replica

tes 

Biomar

ker 

SamplingTime 

(min)** 

1 In-Cabin Congested Freeway 5 40 (20 H and 20 L) 

2 In-Cabin Urban Canyon 3 40(20 H and 20 L) 

3 In-Cabin Refueling 5 20 (10 H and 10 L) 

4 In-Cabin Underground Garage 5 40 (20 H and 20 L) 

5 In-Cabin Toll Plaza 3 40 (20 H and 20 L) 

6* In-Cabin Roadway Tunnel 5 yes 40 (20 H and 20 L) 

7 Out-of-Cabin Refueling 5 yes 20 

8 Out-of-Cabin Sidewalk 3 40 

8/9 Out-of-Cabin Sidewalk/Bus Stop 3 40 

10 Out-of-Cabin Surface Parking 3 40 

11 Out-of-Cabin Underground Garage 5 yes 40 

12 Outdoor Toll Plaza 3 40 

13* In-Cabin Trailing High-Emitting 

Vehicles 

5 yes 40 (20 H and 20 L) 

 *ME6 was sampled in Houston & Chicago and ME13 in Atlanta 

 ** H refers to high ventilation and L to low ventilation conditions (see Monitoring 

 Methods below) 

 The ME number refers to the same type of ME in each city studied. Since ME6 refers to a 

roadway tunnel and a suitable tunnel was not found in Atlanta, ME13 (following a high emitting 

vehicle) was substituted. 

 Prior to selecting specific ME locations, Desert Research Institute (DRI) personnel 

surveyed potential high-end MEs in each city. The objectives of these surveys with portable gas 

analyzers were to determine the suitability of candidate sampling locations with respect to 

access, maximal exposure levels, and the variability of these exposures. The sampling period in 

each ME was selected to coincide with maximum activity level (i.e., emissions and exposure) as 

described in the Protocol (Appendix A). In the absence of data on the range of actual emission 

component exposures in various MEs in each city, we considered available surrogate parameters 

for emission and dispersion to select locations and sampling periods with the greatest potential 

for maximal exposures. These emission surrogates included diurnal traffic counts, variations in 

highway speeds, length of queues at toll plazas, concurrent numbers of cars refueling, and count 

rates entering and exiting parking garages. Surrogates for dispersion included diurnal wind roses 

and variations in temperature. Where possible we drove parallel to the prevailing wind direction 

to reduce the impact of cross winds and sampled downwind of the nearest emission sources. Our 

sampling strategy also recognized that vehicle exhaust emissions are significantly higher for 

identified high emitting vehicles and all vehicles during cold starts (e.g., at parking lots, 

underground garages, and service stations) and accelerations (e.g., at toll plazas, roadway 

intersections). All of these factors are important in understanding the high-end perspective of 

sampling and the temporal and spatial variations that exist within these high-end MEs. 

1-3
1.2.2 Monitoring Methods 

Instrumented Van. All in-cabin and out-of-cabin exposure measurements were performed 

with the mobile sampling van, a 1996 Chrysler Minivan, DRI-modified for on-road and 

stationary sampling. The power system included two banks of rechargeable AGM gel batteries 

with minimal H2 out-gassing during either charge or discharge. Each bank had a 1750 watt 

inverter for 110v AC power and direct connections for 12v DC, giving maximum flexibility. The 

suspension of the vehicle was upgraded to support the additional battery and instrument weight. 

Seats were removed and replaced with an adjustable equipment racks. For refueling experiments, 

a second fuel pump was installed to facilitate prompt removal of fuel. In-cabin and exterior 

temperature and relative humidity sensors were installed along with an additional sensor 

measuring fuel tank temperature. The data acquisition system has eight analog-to-digital inputs 

to record instrument outputs, which include a global positioning satellite (GPS) sensor, and 

compiles spatially-located data into a single database. All in-cabin equipment was manifolded to 

sample from a point in the driver's breathing zone. This manifold inlet could also be extended 

outside for stationary sampling purposes (e.g., into the subject breathing zone during refueling 

tests). Infiltration of outside air was adjusted by opening or closing windows in the front and rear 

of the cabin and switching the heating/AC system from vent to recirculate. In this manner two 

ventilation modes, high (all open) and low (all closed), were included in all in-cabin tests. 

Equipment Cart. For sidewalk, bus stop and outdoor toll plaza tests, sampling equipment 

was placed on a cart that was pushed along the sidewalk of a busy street in an urban canyon 

(ME8), patrolled a bus stop sidewalk at a high traffic density intersection (ME9) or was stationed 

next to a toll booth during rush hour traffic (ME12). Sampling inlets were positioned in the 

subject breathing zone. Detailed protocols for sampling in each ME are described in the 

Exposure Protocol and Study Plan (Zielinska et al, 2003a), included in Appendix A. 

Measurements in each ME were repeated three to five times for each city-season as noted in 

Table 1.2.1-1. 

Sampling and Analysis Methods. Three approaches were used to measure targeted 

compounds in the high-end MEs: (1) reference method time-integrated samplers to quantify 

concentrations over 20-40 minute sampling periods; (2) continuous surrogate method monitors to 

determine short-term concentration variations over 10-60 second sampling periods; and (3) 

supplemental methods to provide additional short-term surrogate concentration estimates over 

intermediate time frames of several minutes. Supplemental methods included newer methods that 

have not been fully adapted or ruggedized for field use. The supplemental methods provide 

independent checks and periodic corroboration of the surrogate approach used to estimate timeseries values for species not directly measured by the surrogate methods. 

1. The reference methods include passive and pressurized whole-air canister samplers used 

to collect ambient and breath CO, CO2, BTEX, MTBE, and 1,3-BD; acidified 2,4-

dinitrophenylhydrazine (DNPH) cartridges to collect HCHO and CH3CHO; and a multibed (TenaxTA-Carbotrap-Carbosieve) solid adsorbent tube for ambient EtOH (Chicago 

only). After collection, these samples are sent to the DRI Organic Analytical Laboratory 

for analysis. Canister CO and CO2 are chromatographed and converted to methane for 

analysis by flame ionization detection (GC/FID); BTEX, MTBE, and 1,3-BD are 

quantified by capillary GC/FID [GC/mass spectrometry (MS) for breath samples] using a 

separate system (Zielinska et al, 1998). The DNPH cartridges are eluted with acetonitrile 

1-4
and aldehydes analyzed by high performance liquid chromatography (LC) with 

photodiode array ultraviolet (UV) detection of their hydrazone derivatives. The multi-bed 

sorption tubes are thermally desorbed into a GC and quantified by MS. These methods 

are basically standard TO-15, -11A, and -17 EPA procedures with some improvements 

incorporated by DRI as described in Appendix B.

2. The surrogate methods include both active non-dispersive infrared (NDIR) and passive 

T-15 Langan electrochemical cell devices for CO, and an active photo-ionization detector 

(PID) for volatile organic compounds (VOCs) with ionization potentials below 10.6 eV 

(principally olefins and aromatic species). These continuous instruments respond to 

concentration changes within a few seconds and provide sensitive proportionate measures 

of the short-term variability of exhaust and evaporative species quantified by the timeintegrated reference methods. Surrogate methods are used to generate normalized 

continuous time-series of concentrations for BTEX, MTBE, EtOH, 1,3-BD, and the 

aldehydes quantified by the reference methods.

3. The supplemental methods include both active continuous BTEX and HCHO instruments 

with several minute response times and a passive microextraction fiber sampling a 

flowing analyte stream for BTEX over a 10-minute period. The continuous BTEX 

monitor, a Kore MS200, quantifies species diffusing through its semi-permeable 

membrane inlet by 70eV electron impact ionization and time-of-flight MS. The HCHO 

instrument bubbles ambient air into a flowing aqueous 2,4-pentanedione and ammonia 

reagent to produce a HCHO-specific product, 3,5-diacetyl-1,4-dihydrolutidene, that is 

quantified by UV fluorescence. The 75 um film solid phase microextraction 

carboxen/polydimethylsiloxane (SPME-CAR/PDMS) fiber is passively exposed in a 

flowing air stream for 10 minutes, retracted into its syringe holder, and promptly injected 

into a GC with PID/FID detection optimized for BTEX quantification. 

All sampling and analysis methods are described in detail in Appendix B. In addition, 

the validation of the SPME method is described in detail in Appendix C. Quality Assurance 

procedures are described in Appendix H. 

1.2.3 Exposure Biomarkers 

Breath measurements were used as exposure biomarkers in four high-end MEs: out-ofvehicle cabin refueling (ME7); parking in an underground garage (ME11); driving through a 

roadway tunnel (ME6); and trailing a high emitting vehicle (ME13). The test subject took three 

breath samples. One sample was taken before initiating ME sampling; the second, ten seconds 

immediately after completing the active refueling task or within a minute of experiencing a 

measured peak exposure in the other three MEs, and a third, immediately following the second. 

The 3rd sample was analyzed if there was a problem with the second sample. The subject used a 

1-liter evacuated canister, placing its inlet tube into his mouth and breathing smoothly and 

regularly through the mouth around the tube until a resting tidal breathing pattern was 

established. At the end of a normal tidal exhalation, the subject closed his mouth around the 

tube, opened the canister valve expelling his expiratory reserve and filled the canister, collecting 

one liter of the expiratory reserve. When the canister was filled, the technician closed the canister 

valve to capture the sample (Pleil and Lindstrom, 2002; Lindstrom and Pleil, 1996). All breath 

samples were analyzed by GC/MS for BTEX, MTBE, 1,3-BD, and EtOH as described by Pleil 

1-5
1-6

and Lindstrom (2002); CO2 was methanized and quantified by GC/FID. Four subjects, labeled as 

1, 2, 3, and 4 in the time- integrated database, were utilized for breath sample measurements. 

1.3 Results and Discussion 

This section summarizes the distributions of high-end exposure levels observed for each 

ME by city and season. These exposure levels are examined as 20 to 40 minute averages from 

the integrated reference measurements, 5-10 minute averages from the surrogate data as 

corroborated by the supplemental measures, and as peak exposures using the one minute 

reconstructed surrogate time series. 

1.3.1 Variation of day-to-day exposures by ME in each city 

Table 1.3.1-1 and 1.3.1-2 summarize the three city, summer-winter, 20-40 minute 

average, maximum, and minimum ME canister levels of CO, benzene, and sum of BTEX and the 

HCHO and CH3CHO values from DNPH cartridges. Average, maximum, and minimum in/outcabin temperature and relative humidity (T/ RH) values are also listed. In-cabin T/RH values are 

in parentheses. Figures 1.3.1-1 through 1.3.1-6 show the day-to-day variations in benzene, 1,3-

BD, HCHO, and CO concentrations. 

In general, exposure levels should be proportionate to the number of sources and their 

emission rates in the ME and inverse to increasing distance to the emission source and the extent 

of emissions dilution. Dilution is a function of meteorology and the presence of physical 

obstructions that may inhibit emissions dispersion. With the exception of refueling activities, we 

generally find that exposure levels are lower in outdoor environments and higher in enclosed 

environments. However, substantial variations exist among outdoor environments with respect to 

proximity to emission sources and the magnitude of their emissions. For example, the 40-minute 

average exposures for most urban canyon sidewalk/bus stop samples are on the order of a 1-2 

ppbv for benzene, whereas benzene exposures on outdoor surface parking lots or toll plaza 

aprons are usually higher. Refueling samples range up to few hundred ppbv benzene over 20 

minute sampling times and show substantial day-to-day variability. In-cabin exposures during 

vehicle roadway operation show more consistency sample to sample and more temporal 

uniformity than the other MEs. 

As it could be expected, MTBE and the BTEX species show the highest concentrations in 

refueling MEs dominated by evaporative emissions whereas CO, HCHO and 1,3-BD are highest 

in cold-start dominated MEs (underground garage, roadway tunnel, toll plaza, surface parking). 

Several Houston refueling 1,3-BD values had to be invalidated due to the interferences stemming 

from elevated MTBE concentrations in these MEs. MTBE decomposes slightly (on the order of 

1 – 5%) at GC injector temperatures forming isobutene (2-methylpropene), a decomposition 

product that elutes just prior to 1,3-BD on the DB-1 (or equivalent) chromatographic column. 

When concentrations of isobutene are much higher than 1,3-BD, they tail into the butadiene peak 

biasing its apparent concentration upward. This interference was confirmed by GC/MS. As noted 

in Tables 1.3.1-1 and 1.3.1-2, one value for ME3 and two for ME7 were invalidated in summer 

samples and one value for ME3 and four for ME7 in winter samples. 
Table 1.3.1-1. Summer average, maximum, and minimum ME concentrations (ppbv) of BTEX, 1,3-BD, HCHO, 

MTBE, and CO (ppmv) Atlanta (Conventional Fuel)ME ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 ME12 ME13 Replicates 5 3 5 5 3 5 3 3 3 5 3 5 1,3-butadiene Ave. 1.7 0.3 0.6 3.6 0.3 0.3 0.2 0.1 1.3 3.6 0.7 1.0 

Min. 1.2 0.1 0.1 1.2 0.0 0.1 0.1 0.0 0.4 1.2 0.5 0.7 Max. 2.2 0.4 2.1 7.3 0.7 0.6 0.2 0.4 2.2 6.2 0.8 1.1 

Benzene Ave. 6.8 2.0 12.3 20.4 2.4 25.9 1.0 1.6 4.6 28.1 3.6 6.0 

Min. 4.2 1.4 5.8 6.0 1.7 6.2 0.9 1.4 1.6 17.7 3.0 3.7 Max. 9.3 2.4 22.9 40.3 3.7 74.2 1.1 1.8 9.0 35.3 3.9 9.3 

Toluene Ave. 13.6 4.2 30.6 63.2 4.2 43.7 2.5 4.1 9.8 76.5 5.3 18.0 

Min. 8.4 2.4 15.7 19.7 3.1 10.5 2.4 3.6 3.3 49.2 4.9 9.1 Max. 21.2 5.4 43.0 122.6 6.2 104.1 2.8 4.7 19.4 93.6 5.6 37.6 

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon loop; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6

1-7

Ethylbenzene Ave. 2.2 0.7 4.1 9.9 0.7 4.6 0.4 0.7 2.0 12.8 0.8 2.6 

Min. 1.5 0.4 1.8 3.4 0.5 1.1 0.4 0.6 0.6 8.2 0.8 1.6 Max. 3.5 0.9 5.1 18.7 1.0 8.7 0.5 0.9 4.0 17.2 0.9 4.8 

Xylene Ave. 8.7 2.9 15.2 37.0 2.6 17.1 1.8 3.0 8.0 48.8 3.6 10.3 

Min. 5.5 1.6 6.6 12.5 1.5 4.4 1.8 2.6 2.9 30.9 3.4 6.1 Max. 13.7 3.7 18.5 69.2 3.9 29.2 1.9 3.8 15.5 63.4 3.9 19.1 

Formaldehyde Ave. 6.6 6.7 9.3 25.7 5.1 10.0 10.7 11.2 12.8 33.2 7.6 8.6 

Min. 3.9 5.0 5.5 15.4 4.4 7.2 9.6 10.5 8.8 22.2 7.0 7.3 Max. 8.4 8.5 11.1 32.3 6.2 11.5 11.3 12.5 19.7 50.6 8.3 11.1 

Acetaldehyde Ave. 6.6 4.6 4.3 10.8 2.8 3.4 2.7 3.0 4.0 12.2 2.4 5.2 

Min. 2.0 3.5 1.2 7.3 2.1 1.1 2.5 2.1 2.5 7.4 1.5 4.4 Max. 18.6 6.5 5.9 15.1 3.4 5.1 3.1 4.0 6.8 20.9 3.5 6.7 

CO canister Ave. 6.1 1.4 0.7 8.5 2.1 0.6 0.8 1.1 2.7 14.5 3.1 4.0 

Min. 3.7 0.7 0.4 1.7 2.0 0.2 0.7 1.0 0.8 9.8 2.8 2.3 Max. 11.7 2.1 1.4 16.2 2.4 1.2 1.0 1.1 5.6 20.0 3.5 6.2 

Temp  ̊C Ave. (22.3) (27.2) (31.7) 27.8 32.3 (24.6) 

(in-cabin) Min. (21.2) (19.6) (30.5) 22.1 31.0 (23.6) 

Max. (23.9) (33.6) (33.8) 30.4 33.8 (25.6) 

RH, % Ave. (57.8) (60.0) (51.8) 65.3 47.4 (48.8) (in-cabin) Min. (56.0) (43.0) (46.0) 56.0 41.0 (46.0) 

Max. (59.0) (73.0) (60.0) 86.0 51.0 (54.0) 

Note: Urban canyon loop for Atlanta: Peachtree Street NW, Forsyth-Carnegie, Spring Street NW, and Harris Street

Out-of-cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground g

ME13: In-cabin trailing high-emitter vehicle 
Chicago (Oxygenated Fuel - Ethanol)

ME ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 1,3-butadiene Ave. 0.4 0.5 0.1 2.4 0.3 1.3 0.1 0.3 0.3 0.6 1.4 0.5 

Min. 0.2 0.3 0.0 1.5 0.2 1.2 0.0 0.3 0.1 0.4 0.2 0.3 Max. 0.5 1.0 0.1 4.0 0.3 1.6 0.3 0.4 0.4 0.9 2.6 0.8 

Benzene Ave. 2.7 2.9 2.1 8.9 1.5 5.8 4.9 2.5 1.7 3.3 5.1 3.1 

Min. 1.7 1.6 0.5 5.6 1.4 4.2 0.6 1.8 1.3 1.8 1.2 2.6 

Max. 4.9 5.2 4.6 12.2 1.5 8.7 11.4 3.6 2.2 5.7 8.2 3.4 

Toluene Ave. 4.8 4.7 6.6 23.3 2.8 15.0 11.2 3.4 2.4 7.5 11.8 3.6 

Min. 2.4 2.6 1.4 13.6 2.3 6.7 0.7 2.0 1.5 3.5 3.4 2.6 Max. 9.3 7.5 18.6 37.8 3.3 25.5 27.3 6.1 3.5 13.6 18.4 4.3 

Ethylbenzene Ave. 0.8 0.7 1.7 3.3 0.4 1.9 1.4 0.6 0.5 0.8 2.0 0.6 

Min. 0.4 0.3 0.2 1.8 0.3 1.4 0.1 0.4 0.3 0.7 0.6 0.4 

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon loop; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6

1-8

Max. 1.3 1.2 7.2 4.5 0.5 2.8 2.6 0.9 0.8 1.1 3.0 0.7 

Xylene Ave. 3.1 2.7 7.2 13.4 1.7 6.6 5.9 2.1 1.8 3.2 7.8 2.3 

Min. 1.6 1.2 0.9 6.9 1.4 5.1 0.5 1.4 1.1 2.7 2.2 1.9 Max. 5.1 4.5 29.8 17.1 2.0 9.4 10.2 3.4 3.0 4.0 12.1 2.8 

Formaldehyde Ave. 7.7 5.5 10.5 16.1 5.9 8.9 11.7 6.2 6.1 6.7 10.5 8.8 

Min. 5.4 4.6 8.4 10.7 5.3 8.0 3.4 3.8 3.7 5.9 5.8 6.2 Max. 9.4 7.3 13.7 26.7 6.5 10.1 24.6 7.6 7.8 8.1 14.1 11.6 

Acetaldehyde Ave. 6.3 7.7 6.3 10.9 5.1 8.4 4.5 3.8 3.7 3.4 6.5 5.4 

Min. 3.6 4.1 2.8 8.1 4.5 7.4 2.5 3.7 2.2 2.5 3.4 3.8 

Max. 8.6 14.7 9.4 15.0 5.8 8.8 6.1 4.0 4.5 4.4 8.3 7.8 

CO canister Ave. 2.2 1.7 0.4 5.3 1.4 5.1 0.6 1.0 1.4 1.2 3.1 3.0 

Min. 1.5 1.3 0.3 4.0 1.1 4.0 0.3 0.8 0.9 1.0 0.6 2.5 Max. 3.0 2.4 0.6 8.2 1.6 7.1 0.7 1.2 1.7 1.8 5.1 3.7 

EtOH Ave. 6.7 10.5 13.0 15.4 5.7 20.6 28.3 0.0 0.8 1.3 12.2 3.1 

Min. 0.0 4.9 0.0 0.0 0.7 12.5 0.0 0.0 0.0 0.0 0.0 0.0 Max. 12.1 20.0 36.7 30.4 10.4 29.4 115.4 0.0 2.4 3.8 42.1 4.9 

Temp  ̊C Ave. (23.3) (22.3) (28.3) (26.8) (21.0) (21.7) 26.7 25.0 26.0 22.6 27.3 31.5 

(in-cabin) Min. (21.2) (21.9) (25.6) (25.9) (20.3) (20.2) 23.5 23.4 24.5 20.7 22.7 30.2 

Max. (25.8) (23.2) (30.2) (28.4) (21.4) (25.0) 28.8 26.5 27.8 24.6 29.7 33.5 

RH, % Ave. (51.6) (44.7) (51.5) (60.2) (56.0) (53.0) 58.2 54.3 52.7 69.7 56.0 42.3 (in-cabin) Min. (46.0) (41.0) (45.0) (55.0) (53.0) (50.0) 49.0 53.0 50.0 66.0 45.0 30.0 

Max. (55.0) (48.0) (63.0) (65.0) (60.0) (57.0) 67.0 56.0 55.0 73.0 66.0 56.0 

Note: Urban canyon loop for Chicago: Lake Street, Wabash Avenue, Van Buren Street, and State Street

Out-of-cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground g

ME13: In-cabin trailing high-emitter vehicle 
Houston (Oxygenated Fuel – MTBE)

ME ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 1,3-butadiene Ave. 0.7 0.4 0.6* 1.7 0.9 1.4 1.2* 0.3 0.1 0.4 1.6 0.9 

Min. 0.3 0.3 0.3 0.2 0.6 0.8 0.5 0.2 0.1 0.3 0.5 0.4 Max. 1.0 0.5 0.7* 4.5 1.2 2.8 2.1* 0.5 0.2 0.5 2.9 1.4 

Benzene Ave. 1.9 1.4 52.6 5.1 2.5 3.7 130.7 1.4 0.6 1.6 5.4 3.2 

Min. 1.3 1.2 5.6 1.0 1.9 2.5 13.3 0.7 0.3 1.0 2.3 1.3 

Max. 2.7 1.9 175.1 11.1 3.1 7.1 281.9 2.6 0.7 1.9 9.8 5.0 

Toluene Ave. 3.4 2.7 80.3 11.5 4.6 6.6 183.0 3.3 1.0 2.7 12.0 5.8 

Min. 2.1 2.2 15.9 2.5 3.0 4.1 27.4 1.7 0.7 1.9 5.6 1.7 

Max. 4.2 3.3 277.5 22.7 5.5 13.7 425.6 4.4 1.3 3.1 19.4 12.2 

Ethylbenzene Ave. 0.6 0.5 10.6 2.4 0.9 1.3 21.0 0.7 0.2 0.7 2.6 1.3 

Min. 0.4 0.5 2.6 0.6 0.6 0.9 3.5 0.3 0.1 0.5 1.1 0.3 

Max. 0.7 0.7 35.0 5.2 1.1 2.5 50.8 1.3 0.2 0.8 4.5 2.9 

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon loop; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6

1-9Xylene Ave. 2.6 2.3 35.7 9.3 3.8 5.4 71.5 2.7 0.9 2.6 10.1 5.6 Min. 1.7 2.0 10.2 2.5 2.6 3.8 10.2 1.1 0.6 1.8 4.5 1.3 

Max. 3.4 2.8 110.2 18.5 4.4 10.3 143.0 5.1 1.0 3.2 16.8 12.2 

Formaldehyde Ave. 5.9 4.3 5.2 6.8 6.5 5.8 7.3 5.5 4.1 5.3 8.4 7.3 

Min. 3.4 2.9 4.1 4.9 4.4 5.2 4.5 4.9 2.7 4.5 6.0 5.1 

Max. 10.9 5.1 7.7 8.1 8.9 6.2 10.2 6.4 6.4 5.8 10.1 10.0 

Acetaldehyde Ave. 0.7 0.6 0.8 0.8 0.8 0.7 1.0 0.7 0.5 0.7 1.0 0.8 

Min. 0.5 0.4 0.7 0.6 0.6 0.6 0.7 0.6 0.4 0.6 0.7 0.6 Max. 1.2 0.6 1.1 0.9 1.0 0.7 1.3 0.8 0.8 0.7 1.1 1.1 

CO canister Ave. 1.7 1.5 1.0 2.9 1.7 2.7 0.6 0.6 0.5 0.8 3.1 2.5 

Min. 1.2 0.9 0.7 0.5 1.7 1.8 0.3 0.5 0.4 0.5 1.1 1.8 Max. 2.1 2.6 1.6 7.0 1.8 4.5 0.8 0.6 0.7 1.1 6.2 3.2 

MTBE Ave. 2.8 1.3 1325.5 11.2 5.6 8.8 3129 2.9 1.3 2.6 12.2 8.7 

Min. 2.1 0.8 79.8 4.8 3.7 5.1 414.3 1.3 1.2 2.1 6.3 1.5 

Max. 3.8 1.7 4284.1 18.8 7.9 16.5 5767 5.4 1.4 2.9 23.7 20.1 

Temp  ̊C Ave. (23.7) (24.5) (28.2) (28.3) (22.5) (24.5) 33.1 31.1 31.4 31.7 28.1 30.0 

(in-cabin) Min. (22.9) (23.5) (26.0) (24.0) (21.3) (23.3) 28.4 28.5 27.9 28.5 21.8 29.5 

Max. (25.2) (25.7) 30.9 (33.6) (24.7) (25.6) 35.0 33.4 33.6 36.5 37.1 30.4 

RH, % Ave. (54.8) (47.0) (47.6) (47.0) (55.3) (50.2) 53.6 58.3 58.7 58.0 48.8 67.5 (in-cabin) Min. (50.0) (42.0) (41.0) (36.0) (53.0) (47.0) 47.0 41.0 48.0 40.0 41.0 65.0 

Max. (62.0) (51.0) (58.0) (57.0) (57.0) (57.0) 70.0 75.0 77.0 69.0 58.0 70.0 

Note: Urban canyon for Houston: Louisiana , Clay, Walker, and Smith Streets *For 1,3-BD in Houston, one extreme value for ME3 and two for ME7 

Out-of-cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground g

ME13: In-cabin trailing high-emitter vehicle 
Table 1.3.1-2. Winter average, maximum, and minimum ME concentrations (ppbv) of BTEX, 1,3-BD, HCHO, C

MTBE, and CO (ppmv) Atlanta (Conventional Fuel)ME ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 ME12 ME13 Replicates 5 3 5 5 3 6 3 3 3 5 3 5 1,3-BD Ave. 0.6 0.3 0.4 4.1 0.3 1.5 0.2 0.2 0.7 4.0 0.4 1.6 

Min. 0.3 0.0 0.1 1.7 0.2 0.2 0.1 0.1 0.3 1.0 0.3 0.9 Max. 0.8 0.4 0.7 7.9 0.5 3.6 0.3 0.3 1.5 6.3 0.5 2.8 

Benzene Ave. 2.6 1.4 8.4 26.4 1.4 38.5 0.9 1.0 3.5 21.0 2.4 6.7 

Min. 1.9 0.3 1.6 6.1 1.1 10.0 0.7 0.6 1.3 3.2 1.6 3.5 

Max. 3.5 2.3 17.6 49.9 1.7 99.4 1.2 1.3 6.4 28.6 3.2 11.1 

Toluene Ave. 5.3 4.0 14.5 60.5 3.5 58.8 1.5 1.8 8.7 53.0 3.7 17.7 

Min. 3.7 0.8 4.0 14.5 2.2 23.3 1.0 1.2 2.8 7.1 2.2 9.1 

Max. 7.3 6.5 26.4 112.7 4.5 125.1 2.5 2.7 15.4 87.4 6.0 33.5 

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon loop; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6

1-10

Ethylbenzene Ave. 1.0 0.8 1.7 11.5 0.6 4.8 0.3 0.3 1.5 9.7 0.6 2.8 

Min. 0.7 0.1 0.5 2.5 0.5 2.7 0.2 0.2 0.5 1.4 0.4 1.5 

Max. 1.5 1.4 2.6 22.1 0.9 7.4 0.4 0.5 2.7 15.0 1.0 5.4 

 Xylene Ave. 4.4 3.2 6.4 42.6 2.6 17.2 1.1 1.3 5.7 37.2 2.4 11.4 

Min. 3.0 0.4 2.2 9.7 2.0 10.2 0.8 0.9 2.0 5.4 1.5 6.0 

Max. 6.2 5.7 9.3 79.7 3.7 26.4 1.6 1.8 10.5 58.5 3.8 22.1 

Formaldehyde Ave. 6.2 8.6 21.9 19.6 4.6 3.4 2.6 2.0 5.0 11.4 3.4 8.4 

Min. 2.6 5.1 4.1 5.6 3.3 2.3 1.4 1.1 3.4 4.0 3.0 5.7 Max. 8.0 12.4 89.1 28.1 6.0 5.0 4.1 3.1 6.2 15.7 3.7 10.4 

Acetaldehyde Ave. 2.8 2.9 5.4 8.2 2.0 2.0 1.7 1.5 2.3 6.8 2.5 4.3 

Min. 0.9 2.5 1.5 4.2 1.1 1.1 1.5 0.9 1.3 2.8 1.7 3.6 

Max. 5.6 3.5 17.4 12.0 3.1 2.6 2.1 1.9 2.9 9.8 3.0 5.2 

CO canister Ave. 2.6 1.5 0.8 17.7 1.2 1.2 0.8 0.9 1.9 13.2 2.4 5.7 

Min. 2.0 1.3 0.5 4.3 0.9 0.4 0.7 0.6 0.9 2.9 1.5 2.7 

Max. 3.2 1.8 1.4 36.1 1.5 2.2 1.0 1.1 3.9 21.9 2.8 9.0 

Temp  ̊C Ave. (21.3) (24.6) (17.9) (21.1) (22.8) 10.1 4.8 3.8 10.6 14.5 9.4 (22.2) 

(in-cabin) Min. (15.2) (23.1) (15.0) (14.0) (20.6) 5.9 4.1 1.2 5.1 5.5 6.0 (17.9) 

Max. (28.4) (25.8) (20.2) (24.6) (24.0) 16.7 5.5 5.7 14.2 19.4 15.3 (26.4) 

RH, % Ave. (35.0) (32.3) (40.4) (41.8) (31.0) 54.8 58.0 63.0 52.0 47.4 55.7 (37.2) (in-cabin) Min. (21.0) (28.0) (28.0) (30.0) (27.0) 41.0 45.0 45.0 38.0 26.0 22.0 (23.0) 

Max. (48.0) (36.0) (56.0) (47.0) (34.0) 81.0 71.0 73.0 63.0 65.0 77.0 (50.0) 

Out-of-cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground g

ME13: In-cabin trailing high-emitter vehicle 
Chicago (Oxygenated Fuel - Ethanol)

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 

1,3-BD Ave. 0.6 0.4 2.8 4.4 0.2 0.5 0.7 0.3 0.3 0.5 2.4 0.3 

Min. 0.2 0.2 0.0 1.6 0.1 0.4 0.2 0.2 0.2 0.1 1.3 0.2 

Max. 1.2 0.6 13.2 7.7 0.2 0.9 1.2 0.5 0.3 0.8 3.2 0.4 

Benzene Ave. 1.2 1.3 5.2 16.4 0.7 2.3 20.4 1.0 1.0 1.8 12.9 1.2 

Min. 0.5 1.0 0.2 5.7 0.7 1.4 1.4 0.9 0.9 0.6 5.6 0.9 

Max. 2.2 1.6 12.9 24.2 0.8 4.8 39.1 1.2 1.1 2.9 20.7 1.9 

Toluene Ave. 1.8 2.5 4.6 29.0 1.1 3.1 13.8 1.4 1.2 2.9 22.7 1.3 

Min. 0.5 2.0 1.2 10.8 1.0 1.8 2.1 1.2 1.1 0.9 12.3 0.9 Max. 3.1 2.9 8.9 39.1 1.3 6.5 26.6 1.8 1.4 4.9 36.4 2.0 

Ethylbenzene Ave. 0.5 0.4 0.6 5.5 0.2 0.6 1.4 0.3 0.3 0.6 4.4 0.3 

Min. 0.2 0.3 0.0 1.9 0.1 0.4 0.5 0.2 0.2 0.2 2.3 0.2 

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon loop; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6

1-11

Max. 0.8 0.5 1.4 7.6 0.2 1.4 3.0 0.4 0.3 1.0 7.4 0.4 

Xylene Ave. 1.9 1.5 2.8 22.7 0.8 2.5 6.9 1.1 0.9 2.3 18.3 1.1 

Min. 0.9 1.2 0.2 7.5 0.7 1.4 1.9 0.8 0.9 0.7 10.3 0.8 Max. 3.6 1.8 6.0 31.2 0.9 5.2 15.7 1.4 1.0 3.8 29.5 1.8 

Formaldehyde Ave. 7.2 4.6 4.3 13.9 2.8 5.3 3.2 2.9 3.5 4.4 9.1 3.0 

Min. 2.1 3.2 2.3 7.2 1.8 2.9 1.8 2.5 2.8 3.3 2.9 2.5 

Max. 21.5 6.0 7.7 18.2 3.5 7.8 4.3 3.2 4.2 5.9 15.3 3.6 

Acetaldehyde Ave. 5.0 3.1 3.6 12.7 2.3 3.8 2.8 2.1 2.5 2.5 7.6 2.2 

Min. 1.1 2.4 2.4 5.9 1.4 1.5 2.0 1.6 2.1 1.4 1.6 2.0 

Max. 16.8 4.5 7.4 17.7 2.9 6.9 3.8 2.7 3.1 3.8 12.8 2.6 

CO canister Ave. 1.5 1.0 0.4 12.0 0.9 2.2 0.7 0.9 0.9 1.7 11.0 1.7 

Min. 1.1 0.4 0.4 4.5 0.8 1.7 0.2 0.7 0.8 0.6 3.8 1.3 

Max. 2.1 1.4 0.5 18.4 1.0 3.4 1.8 1.1 1.0 2.7 16.8 2.0 

EtOH Ave. 6.8 2.1 5.1 1.4 4.3 1.6 2.2 1.8 4.0 3.3 3.7 0.9 

Min. 1.6 0.0 2.8 0.1 1.4 0.0 0.0 0.0 0.0 1.3 1.9 0.0 

Max. 12.3 3.1 9.8 2.6 7.9 2.7 4.8 3.9 8.0 5.9 6.0 2.3 

Temp  ̊C Ave. (21.5) (22.8) (17.3) (21.6) (22.6) (20.9) 1.6 4.9 6.5 6.4 (17.0) 1.9 

(in-cabin) Min. (18.1) (21.3) (11.2) (15.9) (21.6) (16.3) -3.3 1.3 2.1 4.1 (13.6) 0.0 

Max. (30.6) (24.8) (19.8) (24.7) (23.5) (24.7) 6.6 9.5 12.3 8.7 (22.1) 4.6 

RH, % Ave. (19.2) (23.7) (22.0) (37.5) (17.7) (24.8) 44.7 46.3 42.7 37.0 (41.4) 53.0 (in-cabin) Min. (9.0) (21.0) (13.0) (25.0) (13.0) (14.0) 32.0 32.0 27.0 32.0 (29.0) 25.0 

Max. (25.0) (25.0) (32.0) (60.0) (21.0) (41.0) 62.0 62.0 60.0 42.0 (61.0) 77.0 

Out-of-cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground g

ME13: In-cabin trailing high-emitter vehicle 
Houston (Oxygenated Fuel - MTBE)

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12 

1,3-BD Ave. 0.4 1.2 1.8* 3.8 0.5 1.1 1.9* 0.1 0.2 1.7 2.7 0.8 

Min. 0.3 0.4 0.4 0.4 0.4 0.1 1.9* 0.1 0.1 0.2 0.4 0.5 Max. 0.6 2.7 3.6 5.7 0.6 2.3 1.9* 0.2 0.2 4.3 4.3 1.3 

Benzene Ave. 1.4 3.7 17.7 10.6 1.7 2.7 55.0 0.5 0.6 5.0 7.8 2.5 

Min. 1.1 1.4 2.3 1.6 1.4 0.7 7.7 0.5 0.4 1.5 1.4 1.8 Max. 2.0 8.2 56.6 14.5 2.1 4.2 97.7 0.7 0.8 11.9 13.7 3.8 

Toluene Ave. 3.0 6.5 25.6 21.8 3.6 4.6 64.3 0.8 1.1 10.5 17.3 4.2 

Min. 2.3 2.9 4.2 4.2 3.2 1.6 10.9 0.7 0.8 3.5 3.1 2.7 

Max. 5.2 13.4 69.7 30.9 3.8 6.7 106.0 1.0 1.4 21.7 31.4 6.3 

Ethylbenzene Ave. 0.7 1.4 2.4 4.3 0.8 0.9 4.5 0.2 0.3 1.9 3.3 0.8 

Min. 0.5 0.7 0.7 1.1 0.7 0.4 1.8 0.2 0.2 0.7 0.7 0.5 

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon loop; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6

1-12

Max. 1.1 2.6 4.4 5.9 0.8 1.4 8.0 0.2 0.3 4.3 5.8 1.2 

Xylene Ave. 3.4 6.3 10.9 17.6 3.5 4.4 18.7 0.8 1.1 8.1 13.9 3.6 

Min. 2.5 3.3 3.6 5.5 3.5 1.5 4.4 0.7 0.7 3.4 3.7 2.1 Max. 5.9 11.5 18.4 24.7 3.6 6.9 35.2 1.0 1.4 17.5 25.0 6.3 

Formaldehyde Ave. 4.5 8.2 7.1 10.5 3.8 7.6 5.7 2.1 2.5 4.0 5.7 5.0 

Min. 3.0 4.7 4.6 7.9 2.7 5.4 3.5 1.9 2.0 1.2 2.9 4.0 

Max. 5.1 12.6 8.4 12.1 4.5 8.8 10.6 2.3 3.1 7.6 8.6 6.1 

Acetaldehyde Ave. 1.9 4.3 6.5 5.3 1.9 4.4 5.3 1.7 1.7 4.5 3.4 2.0 

Min. 1.2 2.5 3.5 4.7 1.5 2.6 3.2 1.4 1.2 3.4 1.0 1.8 

Max. 2.4 7.0 9.2 5.9 2.2 6.1 10.0 1.9 1.9 5.7 4.9 2.4 

CO canister Ave. 1.4 3.7 1.2 7.8 1.8 2.9 1.0 0.4 0.5 3.4 6.0 2.7 

Min. 0.9 1.4 0.5 1.1 1.6 0.8 0.3 0.3 0.4 0.7 1.1 1.7 

Max. 1.6 6.9 2.7 12.5 2.1 5.5 2.6 0.5 0.7 8.4 9.8 4.5 

MTBE Ave. 3.9 10.2 890.6 25.4 4.2 7.3 2568.9 0.5 0.7 15.1 26.0 6.7 

Min. 1.4 2.6 23.3 1.8 3.2 3.3 347.8 0.5 0.6 6.5 2.7 2.6 

Max. 8.1 25.3 3135.3 68.1 4.8 10.4 5629.9 0.6 0.8 20.9 63.6 13.2 

Temp  ̊C Ave. (22.3) (22.9) (21.6) (22.6) (21.0) (22.4) 15.7 9.8 11.4 17.1 15.5 14.9 

(in-cabin) Min. (18.0) (20.4) (19.3) (19.9) (19.1) (19.9) 10.9 7.2 7.9 13.4 10.3 7.9 

Max. (26.5) (24.3) (23.4) (25.2) (22.2) (24.8) 20.9 12.2 14.7 21.0 18.6 20.2 

RH, % Ave. (41.2) (36.7) (52.0) (54.2) (49.3) (46.0) 67.0 61.0 55.3 63.0 69.6 77.7 (in-cabin) Min. (29.0) (33.0) (37.0) (36.0) (43.0) (34.0) 55.0 53.0 46.0 48.0 43.0 70.0 

Max. (58.0) (42.0) (61.0) (69.0) (56.0) (54.0) 77.0 71.0 67.0 76.0 87.0 83.0 

*Note: For 1,3-BD in Houston, one extreme value for ME3 and four for ME7 were invalidated

Out-of-cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground g

ME13: In-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-13Microenvironments

ppbv

Atlanta, Summer 2002-2003

1,3 - Butadiene

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 ME12 

0

0.81.62.43.2

4

4.85.66.47.2

8

Microenvironment

ppbv

Atlanta, Summer 2002-2003

Benzene

ME1 ME2 ME3 ME

4

ME5

ME7

ME8

ME9 ME10 ME11 ME12 ME13

08

162432404856647280

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppm

CO

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 ME12 ME13

0

2468

101214161820

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppbv

Formaldehyde

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 ME12 

0

5

10152025303540455055

MaximumMinimum75%25%MedianOutliersExtremes

Figure 1.3.1-1. Time-integrated exposure levels in different MEs in Atlanta, Summer 2002 and 2003 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
Microenvironment

ppbv

Atlanta, Winter 2004

Benzene

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 ME12 ME13

0

102030405060708090

100

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppbv

Atlanta, Winter 2004

1,3-Butadiane

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 

0

0.81.62.43.2

4

4.85.66.47.2

8

MaximumMinimum75%25%MedianOutliersExtremes

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-14 Microenvironment

ppm

CO

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 ME12 ME13

0

48

1216202428323640

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppb

Formaldehyde

ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME9 ME10 ME11 M

0

369

12151821242730

Figure 1.3.1-2. Time-integrated exposure levels in different MEs in Atlanta, Winter 2004 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-15

Microenvironments

ppbv

Chicago, Summer 2003

Benzene

Microenvironments

ppbv

Chicago, Summer 2003

1, 3-

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 M

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

1.5

3

4.5

6

7.5

9

10.5

12

13.5

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironments

ppbv

Formaldehyde

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME1

0369

121518212427

MaxMin75%25%MedOutExtr

Microenvironments

ppm

CO

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

0.81.62.43.2

4

4.85.66.47.2

8

8.8

MaximumMinimum75%25%MedianOutliersExtremes

Figure 1.3.1-3. Time-integrated exposure levels in different MEs in Chicago, Summer 2003 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-16 Microenvironment

Microenvironment

ppbv

Chicago, Winter 2004.xls

Benzene

Microenvironments

ppbv

Chicago, Winter 2004

1,3-Butadiene

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

0.81.62.43.2

4

4.85.66.47.2

8

MaximMinim75%25%MediaOutlieExtre

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

48

1216202428323640

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppm

CO

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

02468

101214161820

MaximumMinimum75%25%MedianOutliersExtremes

ppbv

Formaldehyde

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

2468

101214161820

MaximumMinimum75%25%MedianOutliersExtremes

Figure 1.3.1-4. Time-integrated exposure levels in different MEs in Chicago, Winter 2004 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-17

Microenvironments

ppbv

Houston, Summer 2004

1,3-Butadiane

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppbv

Houston, Summer 2004

Benzene

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

306090

120150180210240270300

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppm

CO

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

123456789

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppbv

Formaldehyde

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

1.5

3

4.5

6

7.5

9

10.5

12

MaximumMinimum75%25%MedianOutliersExtremes

Figure 1.3.1-5. Time-integrated exposure levels in different MEs in Houston, Summer 2004 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; M

gh-emitter vehicle 

Microenvironments

ppbv

Houston, Winter 2005

1,3-Butadiane

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME1

0

0.61.21.82.4

3

3.64.24.85.4

6

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppm

CO

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

1.5

3

4.5

6

7.5

9

10.5

12

13.5

MaximumMinimum75%25%MedianOutliersExtremes

Microenvironment

ppbv

Formaldehyde

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 M

0

1.5

3

4.5

6

7.5

9

10.5

12

13.5

MaximumMinimum75%25%MedianOutliersExtremes

Figure 1.3.1-6. Time-integrated exposure levels in different MEs in Houston, Winter 2005 

Microenvironment

Houston, Winter 2005

Benzene

ME1In-cabin trailing hi

1-18

ppbv

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

102030405060708090

100

MaximumMinimum75%25%MedianOutliersExtremes
1.3.2 Distribution of exposures within MEs in each city (1-minute time series) 

The study protocol (Appendix A) specifies a sampling period of 20 (ME3/ME7) to 40 

minutes beginning at the top of the hour to correlate with the local air quality monitoring 

network sampling periods. Because large variations are expected within these time frames in 

exposures for most MEs, the protocol includes continuous measurements of target species with 

time resolutions of about a minute. The supplemental Kore MS200 MS (deployed for BTEX) 

and Alpha Omega HCHO analyzer used to measure these species at 1-minute resolutions directly 

had not been earlier proven under such field conditions and only worked well intermittently. 

Furthermore, there were no acceptable continuous methods for 1,3-BD, MTBE, EtOH, 

CH3CHO, or non-methane VOCs (NMVOC) that could be used in portable modes of operation 

with the necessary sensitivity. Accordingly, our sampling strategy consisted of a three-tiered 

approach classified as reference, surrogate, and confirmatory measurements. The base set or 

reference (R) measurements consist of three well-established time-integrated methods (canisters, 

DNPH, and solid adsorbent cartridges) as described in Section 1.2.2. These three methods 

together measure all species of interest over the 20-40 minute sampling periods within each ME 

and had excellent data capture rates. Although the integrated methods do not characterize shortterm peak exposures in MEs with highly varying exposure levels, they provide a basis for 

quantifying and deriving correlations between the integrated values and continuous surrogate (S) 

measures, such as the CO and PID NMVOC monitors, in order to reconstruct short-term time 

series. For example, data for BTEX, and 1, 3-BD from the canister measurements can be used to 

normalize continuous CO and NMVOC traces taken over the same periods to construct 

component time series in exhaust-dominated environments. In a similar manner, the time series 

of HCHO values can be reconstructed from the correlation of the integrated DNPH samples with 

continuous CO measures. 

Tables 1.3.2-1A and 1.3.2-1B list correlation coefficients (R2), slopes, P-values and 

performance statistic for correlations of benzene, 1,3-BD, HCHO, and CO measured from 

canisters with NMVOC PID and continuous CO, measured by NDIR, for all ME with exception 

of ME3 and ME7, and for ME3 and ME7 only, respectively. It can be seen from Table 1.3.2-1A 

that 1,3-BD correlates with CO somewhat better than with NMVOC so continuous CO values 

were used for reconstructing 1-minute time series for 1,3-BD for all MEs with exception of 

refueling experiments (ME3 and ME7). However, for refueling MEs (Table1.3.2-1B), the 

correlations are worse, although the correlations of benzene with NMVOC are still statistically 

significant for all three cities. The correlations of 1,3-BD with NMVOC PID and CO_NDIR are 

not statistically significant, since neither 1,3-BD, nor CO is abundant in evaporative emissions. 

Thus, the calculation of 1-min time series for 1,3-BD in ME3 and ME7 is not valid for 

evaporative gasoline exposure. However, these species are often measured at some gas stations, 

since they originate from exhaust emissions of higher-emitting vehicles. In addition, HCHO does 

not correlate very well with CO probably due to the photochemical production of this compound 

in outdoor MEs. 

The reconstructed 1-minute peak exposures were calculated based on the method used in 

the Atlanta Summer 2002 and Atlanta and Chicago Summer 2003 (Zielinska et al, 2003b, 2004b) 

reports. The NMVOC PID time series was used to reconstruct benzene values (the remaining 

TEX species follow the benzene time series) and the CO time series was used to reconstruct 

HCHO and 1,3-BD values. No CO and NMVOC data were used where the average CO or 

1-19
1-20

NMVOC was below the approximate detection limit of the instruments (0.5 ppmv and 25 ppbv, 

respectively). In each case the approach was the same. The mean value of the compound to be 

reconstructed was multiplied by the ratio of the surrogate mean to the instantaneous reading. For 

example, to produce the 1st minute value for benzene, the mean benzene canister value was 

multiplied by the 1st minute NMVOC reading divided by the mean NMVOC reading. For HCHO 

and 1,3-BD, the NDIR CO value was used for all cases where it was available and valid. 

A summary of the reconstructed data is presented in Tables 1.3.2-2 and 1.3.2-3 for 

benzene, 1,3-BD and HCHO (the complete data set is submitted in electronic form) for summer 

and winter, respectively. The average maximum and minimum values for each ME in each city 

and season are shown. The reconstructed time series are graphically presented in Figure 1.3.2-1 

through 1.3.2-3 for selected MEs to illustrate the variability of exposure. 

For in-cabin exposures in Figure 1.3.2-1 and upper part of Figure 1.3.2-2, the first 20 

minutes of measurement was carried out under high ventilation conditions (i.e. window open, air 

recirculation off), whereas for the remaining 20 minutes at low ventilation (i.e. window closed, 

air conditioning or heating on, air recirculation on). As can be seen, the second 20 minutes of 

measurement are less variable. In addition, the concentration of benzene is rising steadily for this 

latter sampling period, reflecting the rising NMVOC signal, probably due to accumulation of 

outgasing emissions from vehicle cabin material and the breath of people present in the vehicle 

cabin. 

For refueling experiments (in-cabin ME3 and active out-of-cabin refueling ME7) the 

highest exposures occurred during the active refueling performed during the second 10 minutes 

of the sampling period. The highest concentrations are observed for BTEX species as expected 

from evaporative and spillage emissions during active refueling. HCHO and 1,3-BD present in 

exhaust emissions are lower and usually not correlated with benzene, as can be seen for ME3 in 

Fig. 1.3.2-2. 

As shown in Figure 1.3.2-3, outdoor exposures (ME8, ME9 and ME12) are usually low 

and less variable. HCHO seems higher than benzene and 1,3-BD as is also evident from Figures 

1.3.1-1 to 1.3.1-6 and Tables 1.3.1-1 and -2. On the other hand, outdoor surface parking (ME10) 

and out-of-cabin underground garage (ME11) MEs show much higher variability corresponding 

to vehicles exiting the parking lots after the game (ME10) or at the end of a work day (ME11). 

We collected 5-minute canister samples at peak of exposures for ME7, ME11, and ME6 

in Houston and Chicago and ME13 in Atlanta. Table 1.3.2-4 shows the average concentrations of 

BTEX, 1,3-BD and MTBE for these selected samples (full data set provided in electronic form). 

Figures 1.3.2-4 show the correlations for benzene and 1,3-BD, respectively, quantified from 

these 5-minute canisters and averaged over corresponding 5-minute surrogate 1-minute 

measurements. ME7 values for Houston were removed from these correlations since high MTBE 

levels distort NMVOC PID signal correlation to benzene. An obvious outlier from Atlanta (ME7, 

summer) was also removed. As seen from these figures, correlations are reasonable, especially 

for benzene (R2 = 0.87). 
Table 1.3.2-1A. Correlation coefficients (R2) and associated statistic for relationships of time-integrated measure

continuous methods (NMVOC and CO) for 3 cities, without ME3 and ME7 

PID CO_NDIR 

r2 Slope Intercept df Fstat Fcrit P-value r2 Slope Intercept df F- stat 

Atlanta Benzene 0.88 7.36 2.38 88 675 3.9 0.00% 1,3-BD 0.55 31.05 20.29 88 107 3.9 0.00% 0.68 2.43 1.25 41 88 Formaldehyde 0.39 0.35 1.79 41 27 CO_can 0.93 0.90 -0.01 41 514 Chicago Benzene 0.82 7.86 -0.85 87 406 4.0 0.00% 1,3-BD 0.61 25.55 6.33 87 136 4.0 0.00% 0.70 2.35 0.82 46 106 Formaldehyde 0.20 0.38 0.65 46 11 

1-21

CO_can 0.94 0.95 -0.07 46 687 Houston Benzene 0.70 9.02 26.16 71 162 4.0 0.00% 1,3-BD 0.70 24.86 28.75 71 169 4.0 0.00% 0.81 2.00 0.11 43 181 Formaldehyde 0.29 0.70 -1.37 43 18 CO_can 0.88 1.08 -0.38 43 309 

Notes: F-stat = performance statistic for regression slope of 2-tailed paired data: Critical F-value for 95% confidence is sho

P-value = probability that correlation is not significant df = degrees of freedom (number of data pairs - 2) 
Table 1.3.2-1B. Correlation coefficients (R2) and associated statistic for relationships of time-integrated measure

continuous methods (NMVOC and CO) for ME3 and ME7 in 3 cities 

PID CO_NDIR 

r2 Slope Intercept df Fstat Fcrit P-value r2 Slope Intercept df F- st

Atlanta 

Benzene 0.57 12.15 1274.84 53 70 4.0 0.00% 1,3-BD 0.34 159.97 729.81 47 5 4.0 2.47% 0.06 -0.03 0.55 12 1 Formaldehyde 0.01 0.02 1.09 2 1 CO_can 0.41 0.58 0.59 2 2 Chicago Benzene 0.96 15.76 -4.47 25 590 4.2 0.00% 1,3-BD 0.04 43.11 238.60 25 1 4.2 30.37% insufficient data available Formaldehyde insufficient data available CO_can insufficient data available Houston Benzene 0.52 10.94 2896.65 27 30 4.2 0.00% 1,3-BD 0.22 116.19 1878.18 19 5 4.4 3.36% 0.01 0.01 0.92 5 1 Formaldehyde 0.42 -0.22 2.72 3 2 CO_can 0.75 0.78 -0.08 3 11 

1-22

Notes: F-stat = performance statistic for regression slope of 2-tailed paired data: Critical F-value for 95% confidence is sho

P-value = probability that correlation is not significant df = degrees of freedom (number of data pairs - 2) 
Table 1.3.2-2. Summary of the reconstructed 1-minute data (ppbv), Summer 

City ME Benzene 1,3-BD HCHO 

min max min max min max 

A 01 0.00 47.38 0.00 16.59 0.00 34.25 

A 02 

A 03 0.00 103.60 0.00 0.67 0.00 29.42 

A 04 0.00 49.48 0.00 8.20 0.00 92.53 

A 05 

A 07 0.00 976.35 

A 08 

A 09 

A 10 0.95 18.57 0.00 8.55 0.00 75.30 

A 11 7.68 51.30 0.90 9.19 12.82 70.80 

A 12 1.62 11.57 0.31 3.40 3.79 29.95 

A 13 0.00 253.74 0.00 19.14 0.00 141.72 

C 01 0.00 31.98 0.01 0.85 0.00 13.56 

C 02 0.00 11.42 0.01 1.75 0.11 13.09 

C 03 0.00 30.18 

C 04 0.50 15.39 0.74 4.61 3.64 35.66 

C 05 0.80 0.00 17.55 

C 06 0.10 65.31 0.20 11.65 1.13 64.03 

C 07 0.00 111.01 

C 08 0.29 0.40 3.81 7.65 

C 09 0.15 0.45 3.66 7.85 

C 10 0.01 2.14 0.04 14.25 

C 11 0.20 20.73 0.09 4.11 0.00 25.99 

C 12 0.31 0.77 6.15 11.60 

H 01 0.95 6.89 0.06 9.25 0.50 47.92 

H 02 0.82 2.02 0.03 7.95 0.27 78.24 

H 03 0.00 1346.97 0.23 3.66 1.67 26.55 

H 04 2.09 13.44 0.48 6.00 1.86 23.44 

H 05 1.19 4.04 0.14 2.80 0.63 26.49 

H 06 1.31 16.95 0.12 6.23 0.89 25.61 

H 07 0.00 1948.10 2.85 45.79 

H 08 0.27 2.80 0.00 0.68 0.00 17.17 

H 09 0.18 0.87 0.04 0.43 1.20 17.69 

H 10 0.90 5.71 0.11 3.93 1.47 50.49 

H 11 1.88 15.71 0.14 6.08 1.13 53.69 

H 12 0.85 17.54 0.08 2.74 0.95 13.09 

1-23
Table 1.3.2-3. Summary of the reconstructed 1-min data (ppbv), Winter 

City ME Benzene 13-BD Formaldehyde 

min max min max min max 

A 01 0.02 1.28 0.25 15.70 

A 02 1.60 3.87 0.07 1.34 0.82 15.71 

A 03 0.59 107.31 

A 04 2.71 67.30 0.07 13.32 0.22 43.93 

A 05 0.02 1.98 0.24 17.49 

A 07 0.00 1080.63 3.44 19.02 

A 08 0.74 2.17 0.23 0.41 3.15 5.69 

A 09 1.06 1.81 0.27 0.53 2.48 4.79 

A 10 3.11 13.55 0.08 3.07 1.35 41.48 

A 11 1.66 49.76 0.05 17.32 0.21 50.86 

A 12 0.81 6.53 0.17 1.33 1.11 11.75 

A 13 0.53 33.96 0.05 6.36 0.20 42.78 

C 01 0.17 1.20 0.07 7.40 0.26 64.35 

C 02 

C 03 0.00 98.94 

C 04 3.72 31.25 0.97 8.97 4.45 25.70 

C 05 0.04 0.72 0.65 11.37 

C 06 0.13 8.53 0.06 1.63 0.45 14.92 

C 07 0.00 511.90 0.58 4.57 0.86 6.75 

C 08 0.10 1.71 0.94 10.07 

C 09 0.00 0.53 0.00 8.02 

C 10 0.07 2.54 0.47 18.27 

C 11 3.01 33.48 0.11 5.63 0.45 26.76 

C 12 0.00 0.65 0.00 8.87 

H 01 0.60 6.34 0.06 3.13 0.58 23.47 

H 02 0.82 13.93 

H 03 0.47 335.71 0.11 1.86 0.74 12.11 

H 04 1.22 17.85 0.11 6.57 2.40 33.89 

H 05 0.67 3.25 0.07 1.68 0.69 16.77 

H 06 0.46 7.77 0.01 4.72 0.15 23.07 

H 07 0.15 1203.84 0.25 20.29 

H 08 0.35 0.62 

H 09 0.28 1.06 

H 10 1.16 32.64 0.08 12.89 0.13 22.73 

H 11 3.71 18.66 1.23 12.10 2.41 16.98 

H 12 1.43 3.76 

1-24
Table 1.3.2-4. Summary of the 5-minute canister data (ppbv) 

City Atlanta, Summer Atlanta, Winter 

ME 7 11 13 7 11 13 

Replicates 5 5 4 6 5 5 

1,3-BD Ave. 1.53 5.39 1.20 6.48 7.23 1.79 

Min. 0.04 3.97 0.79 0.78 0.51 0.48 

Max. 4.09 7.50 1.90 15.47 10.13 2.72 

Benzene Ave. 163.98 33.26 6.30 89.52 27.95 8.11 

Min. 3.06 24.80 4.36 13.52 1.51 1.90 

Max. 475.82 45.07 10.34 256.31 42.40 16.02 

Toluene Ave. 253.17 94.52 15.30 139.88 70.84 29.44 

Min. 8.90 68.88 10.97 48.39 3.94 4.62 

Max. 649.81 126.79 20.41 360.24 113.45 67.34 

Ethylbenzene Ave. 23.15 16.06 2.42 8.82 11.89 3.91 

Min. 1.45 11.89 1.89 3.86 0.64 0.69 

Max. 57.14 22.88 2.93 20.24 19.79 8.50 

Xylene Ave. 79.33 62.04 9.60 29.86 48.27 17.52 

Min. 6.21 44.84 7.39 15.90 2.69 3.01 

Max. 202.27 87.73 12.72 64.24 77.88 38.85 

City Chicago, Summer Chicago, Winter 

ME 6 7 11 6 7 11 

Replicates 5 5 5 5 4 4 

1,3-BD Ave. 1.51 0.21 2.33 0.73 2.19 4.00 

Min. 0.94 0.03 0.80 0.51 1.44 1.79 

Max. 2.66 0.39 3.01 1.45 2.74 5.75 

Benzene Ave. 8.87 13.56 7.75 2.22 84.25 12.00 

Min. 4.11 0.56 2.50 1.59 24.98 6.15 

Max. 24.00 37.23 10.00 3.94 160.53 17.32 

Toluene Ave. 25.53 22.74 19.40 3.56 56.51 23.92 

Min. 5.87 0.57 5.57 2.14 32.96 12.82 

Max. 78.10 61.34 25.73 6.48 100.48 36.75 

Ethylbenzene Ave. 2.69 2.77 3.31 0.59 6.11 4.03 

Min. 1.23 0.11 1.17 0.36 2.12 2.01 

Max. 6.80 6.78 4.63 1.04 11.90 6.00 

Xylene Ave. 9.43 11.19 12.74 2.89 25.92 18.75 

Min. 4.83 0.38 4.35 1.67 9.31 9.43 

Max. 23.42 26.91 18.57 5.33 51.91 27.41 

1-25
1-26

City Houston, Summer Houston, Winter 

ME 6 7 11 6 7 11 

Replicates 4 5 5 5 5 5 

1,3-BD Ave. 4.55 4.04 4.22 1.79 76.11 3.18 

Min. 1.24 1.36 0.55 0.81 13.03 0.39 

Max. 10.07 6.72 12.85 3.18 174.21 5.15 

Benzene Ave. 12.51 918.86 11.05 4.32 379.48 9.47 

Min. 4.17 181.85 1.99 2.53 49.61 1.91 

Max. 27.86 2429.61 26.71 7.91 607.22 16.60 

Toluene Ave. 21.28 815.73 27.31 7.30 420.64 19.84 

Min. 6.59 360.54 4.79 4.98 64.85 2.98 

Max. 50.32 1142.43 62.52 13.52 835.98 38.04 

Ethylbenzene Ave. 4.25 94.58 5.34 1.32 23.92 3.85 

Min. 1.47 44.53 1.12 0.85 4.22 0.50 

Max. 10.08 135.65 13.00 2.70 51.83 7.59 

Xylene Ave. 5.31 368.47 6.40 5.78 100.90 16.07 

Min. 6.74 132.36 4.38 4.13 16.87 2.14 

Max. 11.78 553.69 15.03 10.98 205.55 32.78 

MTBE Ave. 36.50 26977.95 30.06 15.28 9705.27 32.96 

Min. 13.65 3319.53 5.71 5.47 2019.60 14.29 

Max. 67.35 61643.39 48.23 39.34 15484.50 65.53 
ME1, Houston Summer 2004

02468

101214

0708

0710

0712

0714

0716

0718

0720

0722

0724

0726

0728

0730

0732

0734

0736

0738

0740

0742

0744

0746

0748

ppbv

benz_pid bud13_co form_co

ME2, Atlanta Winter 2004

0.00.51.01.52.02.53.03.54.04.5

0745

0746

0747

0748

0749

0750

0751

0752

0753

0754

0755

0756

0757

0758

0759

0800

0801

0802

0803

0804

0805

0806

0807

0808

0809

0810

0811

0812

0813

0814

0815

0816

Benzene, 1,3-BD, ppbv

benz_pid 13-BD_co Form_co

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-27ME4, Atlanta Summer 2003 051015202530 1720 1723 1726 1729 1732 1735 1738 1741 1744 1747 1750 1753 1756 1759

ppbv

benz_pid 13-BD_co Form_co

ME5, Houston Summer 2004

02468

10

0705

0707

0709

0711

0713

0715

0717

0719

0721

0723

0725

0727

0729

0731

ppbv

benz_pid bud13_co f

Figure 1.3.2-1. 1-Minute time series for in-cabin exposures: ME1 (congested freeway), ME2 (urban canyon); M

garage) and ME5 (toll plaza) 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-28

ME6, Houston Summer 2004

02468

1012141618

0747

0749

0751

0753

0755

0757

0759

0801

0803

0805

0807

0809

0811

0813

0815

0817

0819

0821

0823

0825

0827

ppbv

benz_pid bud13_co form_co

ME13, Atlanta Winter 2004

05

101520253035

1131

1133

1135

1137

1139

1141

1143

1145

1147

1149

1151

1153

1155

1157

1159

1201

ppbv

benz_pid 13-BD_co Form_c

ME3, Chicago, Winter 2004

0

20406080

100120

1330 1332 1334 1336 1338 1340 1342 1344 1346 1348 1350

ppb

benz_pid 13BD_co Form_co

ME7, Houston Summer 2004

0

500

1000150020002500

1248

1249

1250

1251

1252

1253

1254

1255

1256

1257

1258

1259

1300

1301

1302

 ppbv

bud13_co form_co benz_p

Figure 1.3.2-2. 1-Minute time series for in-cabin exposures: ME6 (tunnel); ME13 (following high-emitting vehi

refueling) and out-of-cabin refueling, ME7 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-29

ME8, Atlanta Winter 2004

0123456

1155

1157

1159

1201

1203

1205

1207

1209

1211

1213

1215

1217

1219

1221

1223

1225

1227

1229

1231

1233

ppbv

benz_pid 13-BD_co Form_co

ME10, Chicago, Summer 2003

05

10152025

2100

2101

2102

2103

2104

2105

2106

2107

2108

2109

2110

2111

2112

2113

2114

2115

2116

2117

2118

2119

2120

2121

2122

2123

2124

2125

2126

2127

2128

2129

2130

2131

2132

2133

2134

2135

2136

2137

2138

2139

2140

2141

2142

2143

Benzene, 1,3-BD,ppb

benz_pid bud13_co form_co

Me11, Houston Summer 2004

05

10152025

1620

1622

1624

1626

1628

1630

1632

1634

1636

1638

1640

1642

1644

1646

1648

1650

1652

1654

1656

1658

1700

ppbv

benz_pid bud13_co form_co

ME12, Chicago Winter 2004

01234567

1616

1618

1620

1622

1624

1626

1628

1630

1632

1634

1636

1638

1640

1642

ppbv

benz_pid 13BD_co F

Figure 1.3.2-3. 1-Minute time series for out-of cabin outdoor exposures:ME8 (sidewalk); ME10 (surface parking

(underground garage) and ME12 (toll plaza) 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
1,3-Butadiane - No ME7 

02468

101214

024

5-min Ave Sur

5-min Can

ME1In-cabin trailing hi

1-30

: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; M

gh-emitter vehicle 

Figure 1.3.2-4. Correlations between 5-minute canister samples and surrogate 1-minute values, averaged over cominutes. 

Benzene - No ME7 in Houston

y = 1.0955x - 2.7164

R2 = 0.8747

0

50

100150200250300350400450500

0 50 100 150 200 250 300 350

5-Min Ave Surrogates

5-Min Can
1-31

1.3.3 Oxygenated and conventional gasoline (difference between cities) 

 The MTBE and EtOH concentration variability by ME in Houston and Chicago is shown 

in Figure 1.3.3-1. The complete data are provided in electronic form. Although MTBE is 

measured in all Houston MEs, the concentrations recorded during refueling are relatively high, in 

the range of a few ppmv. In contrast, Chicago ethanol concentrations are lower, especially during 

winter time. We generally use the same gas station in each city (absent problems with the gas 

station manager) and we select a station with high traffic close to a major freeway. For example, 

the gas station in Houston was situated next to Tollway 8 and was always very busy. 

 The high concentrations of MTBE during refueling in Houston caused occasional 

problems with 1,3-BD quantification in canister samples as discussed at Section 1.3.1. In 

addition, MTBE PID response changed the slope of canister benzene and NMVOC PID 

regressions in Houston MEs from those observed in Chicago and Atlanta, as shown in Table 

1.3.2-1. However, when ME3 and ME7 data are removed from correlations, the slopes are more 

consistent among the three cities. 

 Figures 1.3.3-2 and -3 show comparisons of average benzene, 1,3-BD, HCHO, and CO 

concentrations by ME in the three cities by season. Tables 1.3.1-1 and 1.3.1-2 provide the data 

for all species measured with the time-integrated methods. For refueling MEs, the highest 

benzene concentrations are observed in Houston, in both seasons. However, for underground 

garage MEs, Atlanta shows the highest concentrations of benzene, HCHO, and CO. It is however 

not clear whether these findings result from the different fuels, choice of specific ME locations, 

or the greater variability of high-end ME exposures in general. 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-32

ppbv

Houston, Summer 2004

MTBE

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

600

120018002400300036004200480054006000

MaximumMinimum75%25%MedianOutliersExtremes

ppbv

Houston, Winter 2005

MTBE

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

600

120018002400300036004200480054006000

MaximumMinimum75%25%MedianOutliersExtremes

ppbv

Chicago, Summer 2003

Ethanol

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

153045607590

105120

MaximumMinimum75%25%MedianOutliersExtremes

ppbv

Chicago, Winter 2004

Ethanol

ME1 ME2 ME3 ME4 ME5 ME6 ME7 ME8 ME9 ME10 ME11 ME12

0

1.5

3

4.5

6

7.5

9

10.5

12

13.5

MaximumMinimum75%25%MedianOutliersExtremes

Figure 1.3.3-1. MTBE and EtOH concentrations in Houston and Chicago, respectively..Note different y-axis scaland Winter 

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
Benzene

0

20406080

100120140

1 2 3 4 5 6 7 8 9 10 11 12 13

ppbv

Houston Atlanta Chicago

1,3-Butadiene

0123456789

1 2 3 4 5 6 7 8 

ppbv

Houston Atlanta Ch

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-33 Formaldehyde 05101520253035 1 2 3 4 5 6 7 8 9 10 11 12 13

ppbv

Houston Atlanta Chicago

CO

02468

10121416

1 2 3 4 5 6 7 8 

ppm

Houston Atlanta C

Figure 1.3.3-2. Comparison of benzene, 1,3-BD, HCHO, and CO average concentrations in three cities in Summ

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
ME1

In-cabin trailing hi

1-34

: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; M

gh-emitter vehicle 

Benzene

0

102030405060

0 1 2 3 4 5 6 7 8 9 10 11 12 13

M E

ppbv

Atlanta Chicago Houston

1,3-Butadiene

02468

1012

0 1 2 3 4 5 6 7 8 9 10 

ME

ppbv

Atlanta Chicago Houston

Formaldehyde

05

10152025

0 1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppbv

Atlanta Chicago Houston

CO

05

101520

0 1 2 3 4 5 6 7 8 

ME

ppm

Atlanta Chicago Housto

Figure 1.3.3-3. Comparison of benzene, 1,3-BD, HCHO, and CO average concentrations in three cities in Winter 
1.3.4 Effect of meteorology on exposure 

As shown in Figures 1.3.3-1 through 1.3.3-6 the highest day-to-day variations in in-cabin 

or out-of-cabin exposures occur during refueling, in ME3 and ME7. ME4 and ME11 relate to 

exposures in an underground garage so these MEs are not subject to different meteorological 

conditions. However, wind speed and direction play an important role in refueling MEs. As a 

general rule, we performed refueling experiments under calm conditions (wind speeds ≤ 4 mph). 

Also, it was usually possible to find a pump location that was relatively sheltered from the direct 

influences of the wind. Subjects generally stood downwind during refueling tests. As a result, 

correlations of wind speed and concentrations in the refueling MEs were weak. For example, 

summer ME7 BTEX levels were highest in Chicago with a steady wind speed of 2-3 mph and 

lowest at variable wind speeds of 1-3 mph. 

Table 1.3.4-1 lists average outdoor ambient temperatures and relative humidity by ME, 

city, and season. The detailed data recorded during each test are provided in electronic form. 

Table 1.3.4-1. Average, minimum, and maximum ambient temperatures and RH 

City Season ME Replicate Temperature ( oC) RH (%) 

ave min max ave min max 

A S 1 5 27.6 27 29 58.4 56 60 

A S 2 3 24.3 22 27 42.6 33 63 

A S 3 5 32.0 26 37 61.8 44 74 

A S 4 5 32.2 31 33 52.2 46 61 

A S 5 3 24.2 22 26 49.9 36 72 

A S 7 5 29.5 22 34 63.0 57 86 

A S 8 3 33.7 29 39 41.0 29 65 

A S 9 3 33.7 29 39 41.0 29 65 

A S 10 3 31.9 22 41 42.6 20 69 

A S 11 5 33.2 32 35 47.8 42 51 

A S 12 3 27.1 24 32 58.8 42 77 

A S 13 5 41.2 37 46 49.4 47 54 

C S 1 5 27.0 26 28 52.2 46 55 

C S 2 3 25.0 24 26 45.7 42 49 

C S 3 6 30.5 24 35 51.8 45 63 

C S 4 5 26.4 23 28 60.8 56 66 

C S 5 3 29.7 26 33 56.7 54 61 

C S 6 5 30.0 29 31 53.4 50 57 

C S 7 5 28.6 24 31 59.0 50 68 

C S 8 3 25.0 23 27 55.0 54 56 

C S 9 3 26.3 25 28 53.3 51 55 

C S 10 3 21.0 20 23 70.3 67 73 

C S 11 5 28.4 22 33 56.6 46 67 

C S 12 3 31.7 30 34 43.0 31 57 

H S 1 5 33.8 30 37 55.6 51 63 

1-35
City Season ME Replicate Temperature ( oC) RH (%) 

ave min max ave min max 

H S 3 5 36.8 30 41 48.6 42 59 

H S 4 5 31.0 30 33 43.0 37 53 

H S 5 3 29.3 29 30 56.0 54 58 

H S 6 5 37.8 32 42 51.0 48 57 

H S 7 5 36.6 29 40 54.0 48 70 

H S 8 3 31.0 28 33 59.3 42 76 

H S 9 3 31.7 28 34 59.3 49 78 

H S 10 3 36.0 27 53 58.0 40 69 

H S 11 5 31.8 27 35 49.6 41 59 

H S 12 3 30.0 30 30 68.0 66 70 

A W 1 5 12.2 4 27 35.4 21 49 

A W 2 3 10.0 7 13 33.0 29 37 

A W 3 5 11.8 7 18 40.8 29 56 

A W 4 5 15.2 9 19 42.0 30 47 

A W 5 3 13.3 7 17 31.0 27 34 

A W 7 6 10.7 7 17 55.8 42 82 

A W 8 3 3.7 1 6 64.3 45 76 

A W 9 3 3.7 1 6 63.3 45 73 

A W 10 3 10.3 7 15 52.7 38 64 

A W 11 5 15.4 8 21 47.8 27 64 

A W 12 3 9.3 6 15 55.7 22 77 

A W 13 5 14.2 4 26 37.2 23 50 

C W 1 5 7.0 0 12 19.8 10 26 

C W 2 3 6.7 4 9 24.0 21 26 

C W 3 5 6.3 4 11 22.0 14 32 

C W 4 5 11.4 13 16 30.2 26 60 

C W 5 3 7.0 3 10 18.0 13 22 

C W 6 5 6.8 3 10 25.0 14 42 

C W 7 5 6.9 2 9 27.0 32 63 

C W 8 3 4.7 1 9 46.7 32 63 

C W 9 3 6.3 2 12 43.3 28 61 

C W 10 3 6.0 1 9 37.3 32 42 

C W 11 5 13.6 11 15 42.0 30 62 

C W 12 3 2.0 0 5 53.7 25 78 

H W 1 5 14.8 9 24 41.6 30 59 

H W 2 3 14.7 9 21 37.3 34 43 

H W 3 5 16.2 10 23 52.8 38 62 

H W 4 5 15.6 10 19 54.4 36 69 

H W 5 3 15.0 8 20 49.7 44 56 

H W 6 5 22.4 14 25 46.6 34 55 

H W 7 5 15.8 10 22 67.6 56 77 

H W 8 3 9.7 7 12 61.0 53 71 

H W 9 3 11.7 8 15 56.0 47 67 

H W 10 3 16.3 14 21 63.3 48 76 

H W 11 5 15.4 9 19 69.8 43 87 

H W 12 3 15.0 8 20 78.0 70 83 

1-36
1-37

1.3.5 Comparison of summer and winter exposures 

Figures 1.3.5-1 through 1.3.5-3 shows the differences between exposures in each city 

during the summer and winter seasons. For Chicago, the concentrations of benzene, 1,3-BD, and 

CO are higher in the underground garage (ME4 and ME11) during winter season. The same is 

true for ME3 and ME7, although CO concentrations are low and comparable for these refueling 

MEs, as expected. However, HCHO is clearly higher during the summer season in all MEs, 

perhaps a result of photochemical formation of this compound. In Houston, benzene is clearly 

much higher in refueling MEs in summer. However, for ME4 and ME11, winter concentrations 

are also marginally higher for benzene, 1,3-BD and CO. HCHO is less consistent, but clearly 

higher in summer in outdoor MEs (8, 9, 10, and 12). For Atlanta, the differences are not very 

large between winter and summer seasons, and not very consistent between different species and 

MEs. However, HCHO is clearly higher in summer in outdoor MEs (7, 8, 9, 10, and 12). 
Atlanta, 1,3-But

012345

0 1 2 3 4 5 6 

ME

ppbv

1,3-BD_S 

Atlanta, Benzene

0

1020304050

0 1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppbv

Benzene_S Benzene_W

ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-38Atlanta, Formalde

05101520253035 0 1 2 3 4 5 6 7 

ME

ppbv

Formal_S F

Atlanta, CO

05

101520

0 1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppmv

CO_S CO_W

Figure 1.3.5-1. Time integrated average exposure levels in different MEs in Atlanta in Summer and Winter seaso

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

1-39

Chicago, Benzene

05

10152025

0 1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppbv

Benzene_S Benzene_W

Chicago, 1,3-Butadiane

012345

0 1 2 3 4 5 6 7 8 

ME

ppbv

1,3-BD_S 1,3-BD_W

Chicago, CO

02468

101214

0 1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppmv

CO_S CO_W

Chicago, Formaldehyde

02468

1012141618

0 1 2 3 4 5 6 7 8 

ME

ppbv

Formal_S Formal_

Figure 1.3.5-2. Time integrated average exposure levels in different MEs in Chicago in Summer and Winter seas

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; MIn-cabin trailing high-emitter vehicle 
Houston, 1,3-Butadia

01234

0 1 2 3 4 5 6 7 8 

ME

ppbv

1,3-BD_S 1,3-BD

Houston, Formaldehy

02468

1012

0 1 2 3 4 5 6 7 

ME

ppbv

Formal_S Form

ME1In-cabin trailing hi

1-40

: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; M

gh-emitter vehicle 

Figure 1.3.5-3. Time integrated average exposure levels in different MEs in Houston in Summer and Winter seas

Houston, CO

02468

10

0 1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppmv

CO_S CO_W

Houston, Benzene

0

20406080

100120140

0 1 2 3 4 5 6 7 8 9 10 11 12 13

ME

ppbv

Benzene_S Benzene_W
1-41

1.3.6 Correlations to breath concentrations 

Figures 1.3.6-1 and 1.3.6-2 shows the average concentrations of BTEX, 1,3-BD, MTBE, 

EtOH and CO2 measured in pre- and a post-peak exposure breath for three MEs in each city and 

season. Detailed data are submitted in the electronic form. As it can be seen from these figures, a 

considerable increase in concentrations of measured species occurs in all cases immediately after 

a peak exposure. In Atlanta and Chicago, the highest breath concentrations of BTEX and 1,3-BD 

were observed in ME7 (refueling) and ME11 (underground garage). In Houston, high 

concentrations of MTBE were measured in ME7 in summer and winter. Although high 

concentrations of EtOH were measured in breath in all Chicago MEs, it is not clear if this is due 

wholly to the presence of EtOH in Chicago fuel, since pre-exposure breath concentrations were 

occasionally higher than the post-exposure concentrations. Subjects were cautioned against 

consuming alcoholic beverages or using alcoholic personal care products prior to breath testing 

but EtOH may also be a metabolic product for certain other food types. For example, it has been 

reported (Turner et al., 2006) that increased ethanol levels were observed in the breath of healthy 

individuals if sweet drinks/food had been consumed within 2 hr prior to providing breath 

samples. 

Figure 1.3.6-3 (upper panel) shows the correlations between 1-minute maximum 

surrogate values for benzene and 1,3-BD and post-exposure breath concentrations of these 

species. The correlation is somewhat better for 1,3-BD (R2

 = 0.46) than for benzene (R2 = 0.26); 

however, benzene concentrations in these MEs are much higher than breath concentrations. As 

shown in the lower panel of Figure 1.3.6-3, both benzene and 1,3-BD concentrations in breath 

track well these compound concentrations in all MEs. Note that the logarithmic scale was used 

for benzene and that no ME3 and ME7 data were included in 1,3-BD correlations for Houston. 

Also, some 1-minute surrogate 1,3-BD and benzene values are missing for certain MEs. As 

explained in Section 1.3.2, if the CO or NMVOC values were below the approximate detection 

limits of the continuous CO and PID instruments (0.5 ppmv and 25 ppbv, respectively), no 1-min 

surrogate data were calculated. Data used for these plots are submitted in electronic form. 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; M

1-42

Atlanta, Summer 2003

0

1020304050

ME7pre ME7post ME11pre ME11post ME13pre ME13post

ppbv

0123456

% CO2

bud13 benze tolue etbzmp_xyl o_xyl CO2 %

Chicago, Sum

02468

10121416

ME6pre ME6post ME7pre 

ppbv

bud13 benze mp_xyl o_xyl 

Houston, Summer 2004

0

100200300400500600

ME6-pre ME6-

post

ME11-

pre

ME11-

post

ME7-pre ME7-

post

ppbv

012345

% CO2

bud13 mtbe benze tolueetbz mp_xyl o_xyl CO2 (%)

05

10152025

ME6-pre ME6-post ME11-pre ME11-post

ppbv

012345

% CO2

Chicago

02468

101214

ME6pre ME6post ME7

BTEX, ppb

BT

Figure 1.3.6-1. Average breath BTEX, 1,3-BD, MTBE, EtOH, and CO2 concentrations in three cities in Summer In-cabin trailing high-emitter vehicle 
ME1: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; M

1-43

Atlanta, Winter 2004

05

1015202530354045

ME7-pre ME7-post ME11-pre ME11-post ME13-pre ME13-post

ppbv

1234567

CO2 %

budi13 benze tolue etbzmp_xyl o_xyl CO2_percen

Chicago, W

05

101520253035

ME6-pre ME6-post ME7-pre 

ppbv

budi13 benze mp_xyl o_xyl 

Houston, Winter 2005

0

20406080

100120

ME6-pre ME6-post ME11-pre ME11-post ME7-pre ME7-post

ppbv

0123456

CO2 %

budi13 benze tolue etbzmp_xyl o_xyl mtbe CO2_percen

02468

1012141618

ME6-pre ME6-post ME11-pre ME11-post

ppbv

0123456

CO2 %

Chicago, Wi

05

1015202530

ME6-pre ME6-post ME7-pre M

BTEX, ppbv

BTEX 

Figure 1.3.6-2. Average breath BTEX, 1,3-BD, MTBE, EtOH, and CO2 concentrations in three cities in Winter In-cabin trailing high-emitter vehicle 
1,3-Butadiane

02468

1012

0 2 4 6 8 

1-min max

Peak Breath

1,3-Butadian

02468

101214

AS11B_1B

AS11B_3B

AS13B_1B

AS13B_5B

AW11B_2B

AW11B_4B

AW13B_1B

CS06B_1B

CS06B_3B

CS11B_2B

CS11B_4B

CW06B_1B

CW06B_3B

CW06B_5B

CW11B1B

1-Min Max

1,3-BD_1min 1,

ME1In-cabin trailing hi

1-44

: In-cabin congested freeway; ME2: In-cabin urban canyon; ME3: In-cabin refueling; ME4: In-cabin underground garage; ME5: In-cabin toll plaza; ME6: In-cab

cabin refueling; ME8:Out-of-cabin sidewalk; ME9: Out-of-cabin sidewalk/bus stop; ME10: Out-of-cabin surface parking; ME11: Out-of-cabin underground garage; M

gh-emitter vehicle 

Figure 1.3.6-3. Correlations between 1-minute surrogate benzene and 1,3-BD max values and post-exposure brea(upper panel) and comparison of these concentrations in different ME and cities (lower panel) 

Benzene

01

10

100

1000

10000

AS07M_1

AS07M_3

AS07M_5

AS11M_2

AS11M_4

AS13M_1

AS13M_5

AW07M_2

AW07M_4

AW07M_6

AW11M_2

AW11M_4

AW13M_1

AW13M_3

AW13M_5

CS06M_2

CS06M_4

CS07M_2

CS11M_2

CS11M_4

CW06M_5

CW07M_4

CW11M_1

CW11M_4

HS06M_2

HS06M_4

HS07M_1

HS07M_3

HS07M_5

HS11M_3

HS11M_5

HW06M_2

HW06M_4

HW07M_1

HW07M_3

HW07M_5

HW11M_3

HW11M_5

benz_1min benz_breath

Benzene

y = 0.0105x + 4.7492

R2 = 0.2314

05

10152025303540

0 500 1000 1500 2000 2500

1-min max

Peak Breath
1.4 Conclusions 

 Summary findings related to the three city study are as follows: 

• Day-to-day variations in high-end (99+th percentile) benzene, 1,3-BD, HCHO, and 

CO concentrations in different MEs are substantial and independent of city and 

season, but related to the activity and emission rates of sources in the given MEs 

which differ from day to day. 

• With the exception of refueling, exposure levels are generally lower in outdoor MEs 

and higher in enclosed MEs. 

• The 20-min average refueling benzene exposures range up to few hundred ppbv and 

show substantial day-to-day variability. 

• In-cabin exposures during on-road vehicle operation are more consistent and uniform 

than for other in-cabin MEs. 

• BTEX species show the highest concentrations in refueling MEs dominated by 

evaporative emissions whereas CO, HCHO, and 1,3-BD are the highest in the coldstart dominated MEs. 

• BTEX and 1,3-BD measured by time-integrated canister method show good 

correlations with continuous NMVOC and CO measurements, respectively. HCHO 

correlation with continuous CO is modest, probably due to photochemical production 

of this compound. 

• Continuous NMVOC (PID) and CO (NDIR) data can be used to reconstruct 1-minute 

time series for benzene and 1,3-BD, respectively, provided that the averaged 

continuous measurements are above the detection limits of the instruments (25 ppbv 

and 0.5 ppmv, respectively). CO data can also be used to reconstruct 1-minute HCHO 

data; however, less reliably so due to poorer correlation between these species. 

• Reconstructed 1-minute time-series data for benzene and 1,3-BD, averaged over the 

five minute time frame corresponding to the collection of 5-minute canister samples, 

correlate well after excluding the Houston refueling ME with relatively high TVOC 

levels that distort typical correlation coefficients and elevated MTBE levels which 

bias 1,3-BD measurements. 

• The concentrations of benzene and 1,3-BD measured in post peak exposure breath 

samples track corresponding ME 1-minute maximum reconstructed surrogate values 

well. 

• Increases in concentrations of measured species occur in all breath samples collected 

within a minute of a peak exposure. In Atlanta and Chicago, the highest breath 

concentrations of BTEX and 1,3-BD were observed in ME7 (refueling) and ME11 

(underground garage), respectively. In Houston, high concentrations of MTBE were 

measured in ME7. 

• The largest differences in benzene, 1,3-BD, and CO concentrations between summer 

and winter seasons are observed in Chicago, consistent with the largest ambient 

temperature differences for this city. These concentrations are higher in winter. For 

Atlanta and Houston such differences are less pronounced. HCHO is consistently 

higher in summer season in outdoor environments, probably due to the photochemical 

production of this compound. 

1-45
1.5 References 

Batterman, S. S, Peng C-y, Braun, J. (2002). Levels and composition of volatile organic 

compounds on commuting routes in Detroit, Michigan. Atmos. Environ., 36:6013-6030. 

Chan, C-C., H. Ozkaynak, J. D. Spengler and L. Sheldon (1991). Driver exposure to volatile 

organic compounds, CO ozone, NO2 under different driving conditions. Environ. Sci. 

Technol., 25: 964-972. 

Fedoruk, M.J. and Kerger, B.D. (2003). Measurements of volatile organic compounds inside 

automobiles. Journal of Exposure Analysis and Environmental Epidemiology, 13:31-41 

Lindstrom A.B. and J.D. Pleil (1996). Alveolar Breath Sampling and Analysis to Assess 

Exposures to Methyl Tertiary Butyl Ether (MTBE) During Motor Vehicle Refueling. J. 

Air & Waste Manage. Assoc., 46:676-682. 

Pleil, J. D.and A. Lindstrom (2002). A review of the USEPA’s single breath canister (SBC) 

method for exhaled volatile organic biomarkers. Biomarkers, 7:189-208. 

Rodes, C., L. Sheldon,, D. Whitaker, et al., (1998). Measuring Concentrations of Selected Air 

Pollutants Inside California Vehicles. Final report, ARB Contract # 95-339. California 

Air Resources Board. 

Turner, C., P. Spanel and D. Smith (2006). A longitudinal study of ethanol and acetaldehyde in 

the exhaled breath of healthy volunteers using selected-ion flow-tube mass spectrometry. 

Rapid Commun. Mass Spectrom., 20:61-68. 

Vayghani, S. A. and C. Weisel (1999). The MTBE air concentrations in the cabin of automobiles 

while fueling. Journal of Exposure Analysis and Environmental Epidemiology, 9:261-

267. 

Weisel, C., N. J. Lawryk, P. J. Lioy (1992). Exposure to emissions from gasoline within 

automobile cabins. J. Expo Anal Environ Epidem, 2(1):79-96. 

Zielinska, B., E. Fujita, J. Sagebiel, G. Harshfield, E. Uberna, T. Hayes, and F. Keene (1998). 

Arizona Hazardous Air Pollutants Monitoring Program. J. Air Waste Manage. Assoc.,

48:1038-1050. 

Zielinska, B., E. M. Fujita, J.C. Sagebiel, D. E. Campbell, L.R. Smith, T. Johnson (2003a). 

Exposure Protocol and Study Plan for the Section 211 (B) Tier 2 High End Exposure 

Screening Study of Baseline and Oxygenated Gasoline. Prepared for American Petroleum 

Institute, 1220 L Street, Washington, DC 20005-4007. Final Version. October 1, 2003. 

Zielinska, B, E.M. Fujita, and J.C. Sagebiel (2003b). Section 211 (B) Tier 2 High End Exposure 

Screening Study of Baseline and Oxygenated Gasoline-Summer 2002 Atlanta Field Study 

on Baseline Gasoline. Prepared for American Petroleum Institute, 1220 L. Street, 

Washington, DC 2005-4070. March 13, 2003. 

Zielinska, B, J.C. Sagebiel, D.Campbell and E.M. Fujita, (2004a). Section 211 (B) Tier 2 High 

End Exposure Screening Study of Baseline and Oxygenated Gasoline-Summer 2003 

Chicago and Atlanta Field Study on Baseline Gasoline. Prepared for American Petroleum 

Institute, 1220 L. Street, Washington, DC 2005-4070. March 13, 2003. 

1-46
2. Relative Contributions of Vehicle Evaporative and Exhaust Emission to 

Concentrations of Volatile Air Toxics in High Exposure 

Microenvironments in Houston 

2.1 Introduction 

The Desert Research Institute (DRI) conducted measurements to quantify exposures to 

automotive emissions in microenvironments representing the upper-end (> 99th percentile) of the 

distribution of inhalation exposures to evaporative and exhaust emissions of conventional- and 

oxygenated-gasoline. The study was conducted as part of the Section 211(b) Tier 2 High-End 

Exposure Study of Conventional and Oxygenated Gasoline. DRI and SwRI conducted 

measurements under controlled conditions to establish quantitative relationships between tailpipe 

and evaporative emission rates to exposure levels in a vehicle cabin and attached residential 

garage. Field exposures also were measured in several high-end exposure microenvironments in 

Atlanta, Chicago, and Houston during winter and summer. Target species (TVOC, CO, BTEX, 

HCHO,1,3-BD, MTBE, EtOH) were measured within microenvironments, breathing zones, and 

breath. This section apportions the relative contributions of fuel combustion and evaporative 

emissions to exposures measured various high-end microenvironments, based on differing 

abundances of MTBE and benzene in exhaust and evaporative emissions. This particular analysis 

approach was applied to the exposure data from Houston because it is the only city included in 

the Section 211(b) exposure screening study to use MTBE as the oxygenated additive. 

Federal reformulated gasoline (RFG) was introduced in 1995 in nine metropolitan areas 

of the United States that were not in attainment of the ambient air quality standard for ozone. The 

RFG program is implemented year-round in these areas as an emission reduction program to 

control ambient ozone and mobile source air toxics (MSAT). Non-oxygenated conventional 

gasoline was used in Atlanta during the period of study. Ethanol was used to oxygenate 

reformulated gasoline in Chicago and MTBE in the Houston area. Table 2-1 summarizes the 

major differences in fuel composition between conventional and RFG. Exhaust emissions 

include a mixture of un-combusted fuel components (e.g., BTEX, MTBE, EtOH, TVOC) and 

species produced during combustion (e.g., benzene, 1,3-BD, HCHO, CO). The relative 

abundances of combustion by-products in the exhaust profile vary with emission control 

technology, level of vehicle maintenance, and operating mode. 

Liquid gasoline contains many target compounds (BTEX, MTBE, EtOH, TVOC) in 

common with gasoline-vehicle exhaust. Gasoline headspace vapor, vapor in equilibrium with 

liquid gasoline, also contains these combustion compounds but is enriched in the more volatile 

species such as benzene, MTBE, and EtOH. Composite liquid and headspace vapor profiles 

across different brands and grades of gasoline were developed in conjunction with the Tuscarora, 

Fort McHenry, and SOS on-road exhaust experiments, for the Auto-Oil program, COAST, the 

Paso del Norte Study, and the 1995/96 RFG Study (Zielinska et al., 1997). Gasoline 

compositions were also determine for western Washington (Fujita et al., 1997c), Austin (Fujita, 

et al. 1999a), San Francisco Bay Area (Kirchstetter et al., 1999), Houston (Fujita et. al., 2001), 

and Los Angeles (Fujita et al, 1997; Fujita et al., 2003). 

2-1
There are several sources of evaporative emissions including hot soak emissions driven 

by residual engine heat following cessation of vehicle operation, diurnal emissions associated 

with fuel tank ‘breathing’ during diurnal temperature and barometric pressure cycling, running 

losses resulting from fuel tank radiant heating by roadways or from injector fuel recirculation 

during vehicles operation, resting losses from gasoline permeation through rubber and plastic 

components of the fuel lines, and simple fuel system leakage. From an analysis of ambient air 

samples and reconciliation with VOC source profiles, Pierson et al. (1999) conclude that 71 ± 

9% of motor vehicle VOC emissions are emitted from tailpipes, 17 ± 6% result from non-tailpipe 

liquid fuel emissions (fuel system leakage) , and 12 ± 4% are due to headspace vapor emissions. 

2.2 Experimental Approach 

The profiles for vehicle exhaust, liquid gasoline, and gasoline headspace vapor include 

many of the same species but notable differences in the ratio of species, a difference that can be 

used to apportion tailpipe and evaporative emission source strengths. The proportion of MTBE in 

exhaust is reduced during combustion relative to its proportion in the fuel. Conversely, benzene 

is enriched in exhaust relative to its proportion in the fuel due to toluene and xylene dealkylation. 

Consequently, MTBE to benzene ratios are substantially lower in exhaust than in liquid fuel or 

headspace vapors. MTBE and benzene were measured in all microenvironments in Houston as 

well as in fuel and vehicle exhaust samples. The fractional evaporative contribution, X, was 

estimated using following formula. 

X = (RME - REXH)/ (RVAP - REXH) 

RME is the measured microenvironmental MTBE/benzene ratio, REXH is the exhaust 

MTBE/benzene ratio, and RVAP is the evaporative MTBE/benzene vapor ratio; either of whole 

gasoline or headspace vapor depending upon type of evaporative emissions expected in a 

particular ME (e.g., whole liquid gasoline for hot soak, leaks, or spills and headspace vapors if 

refueling). Some MEs are influenced by a combination of whole gasoline and headspace vapor 

emissions. 

For the present study, the Southwest Research Institute (SwRI) procured two test vehicles 

and determined their evaporative/tailpipe emissions in the normal/malfunction modes using the 

three test fuels. The test vehicles, a sedan and full-sized V8 truck, were chosen within the 1993-

1996 model years from vehicles with 90,000-110,000 odometer miles. The chosen 1993 Toyota 

Camry (2.2L 4-cylinder engine) and 1995 Ford F150 Pickup truck (5.0L V8 engine) were 

operated in normal, as purchased, modes and in “high emitter” modes with the catalytic 

converter removed and emission levels above 2 grams per mile NMHC as measured on the FTP 

driving cycle. While converter removal sufficed for the F150 truck, a calibrated manifold leak 

was also needed to achieve the ≥ 2g/mile Camry emissions. SwRI determined dynamometer FTP 

emissions for each vehicle with all three fuels in the two emission modes (24 tests). Emission 

control components could be reproducibly adjusted to represent normal and reasonable high-end 

approximations (≥ 2g/mile) of real world exhaust emissions. 

The FTP exhaust emission test uses the 1372 second Urban Dynamometer Driving 

Schedule (UDDS) that is divided into cold/start transient 505 (Bag 1) and cold stabilized 867 

2-2
(Bag 2) second segments. This portion of the FTP is followed by a 10-minute soak and a hot/start 

transient 505 (Bag 3) test. The FTP evaporative emission test includes one hour Diurnal Heat 

Build (DHB) and Hot Soak Loss (HSL) tests. THC/VOC emissions are recorded during the HSL 

segment of the test. Prior to the FTP cold-start exhaust test, the DHB is conducted by fueling the 

test vehicle to 40 percent of tank capacity with fuel < 55°F, attaching a heating blanket outside 

the fuel tank, placing a thermocouple in the tank fuel, hooking it up to computer control, and 

beginning the test as fuel reaches 60°F (increasing at 0.4°F per minute for the 60-minute test to a 

84°F final temperature). In the HSL segment, conducted immediately following exhaust 

emission testing, the vehicle is driven into an evaporative emission enclosure and allowed to 

“soak” in the enclosure for one hour. THC/VOC emissions are measured at the beginning and 

end of the one-hour segment and hot soak evaporative emissions are calculated. 

Test fuel samples were subject to standard tests for Reid Vapor Pressure (RVP), 

distillation range, Specific Gravity, Sulfur, Benzene, HC Category (saturates, olefins, aromatics), 

Oxygenated species (MTBE/EtOH), carbon weight percent, hydrogen weight percent, oxygen 

weight percent, and octane number. Gasoline headspace vapor compositions were predicted from 

the measured composition of liquid gasoline using the Raoult’s Law method described by 

Kirchstetter et al. (1999). This method is based on the proportionality between the compound 

headspace partial pressure and its liquid mole fraction times the vapor pressure of the pure 

species. The individual vapor pressures are determined using the Wagner equation (Reid et al. 

1987). 

DRI measured seasonal in-cabin breathing zone exposures for urban roadways and other 

high-end MEs in Houston (6/3-7/9/04; 2/1-2/8/05), Chicago (8/5-8/20/03; 3/3-3/17/04), and 

Atlanta (7/28-8/8/02; 8/23-9/3/03; 2/10-2/29/04) using a combination of time-integrated samples 

and continuous instruments listed in Table 2-2. Three replicate exposure measurements were 

made for low variability MEs and five for MEs with higher variability (i.e., ME13-trailing high 

emitting vehicles, ME11-underground garages, and ME7-outdoor refueling). Measurements in 

each ME were taken over a period of 20-40 minutes beginning at the top of the hour. Shorter 

sampling times were used for refueling events and parking garage exits after sporting events. 

Sampling and analytical methods are described in Section 1 of the report and in the study plan 

(Zielinska et al., 2003). 

2.3 Results 

The measured MTBE/benzene ratios are summarized in Table 2-3 for the Houston MEs. 

Exposures at the two refueling MEs (3 & 7) were dominated by evaporative emissions as 

expected, with MTBE/benzene ratios of 20 to 30. Ratios for all other MEs were between 1 and 4. 

The exhaust, headspace, and liquid fuel MTBE/benzene ratios measured in this and other recent 

studies are shown in Table 2-4. MTBE/benzene exhaust ratios among the dynamometer tests 

average slightly less than 1 with the tunnel ratios nearer 2, possibly due to the added running loss 

emissions in tunnels. The MTBE/benzene ratios in liquid gasoline and vapor are similar, 

averaging 15-20. Ratios for the SwRI SHED tests vary somewhat with calculated headspace 

compositions and values from earlier listed studies. 

2-3
The estimated fractional contributions of evaporative emissions to total motor vehicles 

emissions for the various Houston MEs, using the above method, are summarized in Table 2-5 

and Figure 2-1. Uncertainties are the standard deviation of the ratios calculated from replicate 

test measurements for each ME (represents the variability of ratio within observed sample set). 

Exposures during refueling (ME3, ME7) are 100% due to evaporative emissions within the 

uncertainties associated with the measurements and method. All other MEs are dominated by 

tailpipe emissions with fractional evaporative contributions < 10%. 

2.4 Conclusions 

The results presented in Table 2-5 indicate that evaporative emissions are only substantial 

components of high end ME exposures during vehicle refueling operations, where they are 

dominant. Since refueling MEs have the highest relative levels of these components (see sections 

1 and 3), they constitute the peak exposures, although overall the average population time spent 

in these high end MEs is likely the shortest. The contribution of evaporative emissions for all 

other MEs was typically about 5% of the total measured exposure. Results were similar for both 

seasons, although evaporative contributions during refueling were marginally less during 

summer, possibly due to more rapid dispersion of vapors and evaporation of fuel spilled during 

each refueling test at higher summer temperatures. The clear distinction in evaporative 

contribution between refueling and non-refueling MEs, along with the relative consistency in 

MTBE/benzene ratios shown in Table 2.4, gives some confidence in the approach. 

These results suggest that the contemporary Houston vehicle fleet contains relatively few 

carbureted or leaking vehicles given that evaporative emissions are not a substantial source in the 

non-refueling MEs tested. Refueling emissions released from pressurized fuel systems and 

spilled fuels appear to be the primary source of peak evaporative exposures. The lack of a 

seasonal variability in the evaporative contribution is also consistent with this supposition. 

Although it was not feasible to try to distinguish further between liquid and headspace vapor 

contributions by the method used, the extremely low MTBE/benzene ratios observed for the 

roadway, sidewalk, and parking MEs suggest that the contributions of emissions from leaking 

liquid gasoline is relatively small. 

The contributions of exhaust and evaporative emissions to ambient volatile air toxics were 

estimated for Houston only since it is the only city among the three in the study with oxygenated 

gasoline containing MTBE. While the contributions of evaporative emissions relative to exhaust 

emissions may vary with differences in average prevailing meteorological conditions, such 

differences are unlikely to result in significantly different conclusions in other cities with regard 

to the relative contributions of exhaust and evaporative emissions to ambient concentrations of 

volatile air toxics. It must also be noted that the vehicle used in this study for the refueling tests 

was a 1996 vehicle. All vehicles prior to the 1998 model year do not have onboard refueling 

vapor recovery (ORVR) systems, and therefore higher refueling emissions. Although refueling 

stations in Houston had Stage II vapor recovery systems, the ORVR system also reduces vapor 

losses when the fuel cap is opened by lowering the internal pressure of the fuel tank. The 

implementation of ORVR systems may further reduce the relative contributions of evaporative 

emissions. 

2-4
Table 2-1. Conventional gasoline versus reformulated gasoline RFG (from EPA OTAQ web 

page http://www.epa.gov/OMSWWW/rfgnew.htm, updated by S. Romanow, OTAQ). 

 Fuel Parameter Values (national basis) 

 Conventional Gasoline Gasohol

Oxyfuel 

(2.7% wt)

 "Summer" 

Phase I RFG 

 Averagea Rangeb Average Average Averagee 

 8.7-S 6.9-15.1 9.7-S 8.7-S 7.0-7.9f 

 11.5-W 11.5-W 11.5-W 

 T50 (°F) 207 141-251 202 205 199 

 T90 (°F) 332 286-369 316 318 325 

 Aromatics (volume %) 28.6 6.1-52.2 23.9 25.8 22.3 

 Olefins (volume %) 10.8 0.4-29.9 8.7 8.5 12.5 

 Benzene (volume %) 1.60 0.1-5.18 1.60 1.60 0.64 

 Sulfur (ppm) 338 10-1170 305 313 269 

 MTBEd

 (volume %) -- 0.1-13.8 -- 15 11g 

 EtOHd (volume %) -- 0.1-10.4 10 7.7 10h 

 RVPc (PSI) 

a As defined in the Clean Air Act. 

b 1990 Motor Vehicle Manufacturer’s Association (MVMA) survey. 

c Winter (W) Reid Vapor Pressure (RVP) higher than Summer (S) to maintain vehicle performance. 

d Oxygenate concentrations shown are for separate batches of fuel; combinations of both methyl tertiary butyl ether 

(MTBE) and ethanol (EtOH) in the same blend can never be above 15 volume percent total. 

e Except as noted, values in this column are volume-weighted average based on preliminary analysis of a portion of 

1996 RFG batch reporting data submitted to EPA by refineries and importers. Numbers are subject to change. 

f The lower RVP number is average for RFG designated for sale in VOC Control Region 1; the higher RVP number 

for VOC Control Region 2. In general, Region 1 areas are to the south and/or west. 

g This is a “typical” value for an RFG batch containing MTBE as the sole oxygenate; this provides about 2% 

oxygen by weight. 

h This is a “typical” value for an RFG batch containing ethanol. Ethanol is not combined with other oxygenates in 

VOCcontrolled RFG. There are economic incentives for blending ethanol at this level, which provides about 3.5% 

oxygen by weight 

i. T(50) and T(90) refers to temperatures at which 50% and 90%, respectively, of gasoline volume is distilled. 

2-5
Table 2-2. Summary of sample collections in urban MEs 

ME # ME Description Replicates Biomarker

5 min 

Canister

Sampling Time 

(min)

1 In-Cabin Congested Freeway 5 40

2 In-Cabin Urban Canyon 3 40

3 In-Cabin Refueling 5 20

4 In-Cabin Underground Garage 5 40

5 In-Cabin Toll Plaza 3 40

6* Roadway Tunnel 5 40

7 Outdoor Refueling 5 yes yes 20

8 Sidewalk 3 40

8/9 Sidewalk/Bus Stop 3 40

10 Outdoor Surface Parking 3 40

11 Outdoor Underground Garage 5 yes yes 40

12 Outdoor Toll Plaza 3 40

13* In-cabin Trailing High-Emitting Vehicles 5 yes yes 40

*ME13 was substituted for ME6 in Atlanta and Chicago.

2-6
Table 2-3. Mass ratios of MTBE to benzene in Houston by ME. 

2-7 

Microenvironment ME Summer Winter

Freeway 1 1.72 ± 0.49 2.88 ± 1.33

Urban Canyon 2 1.10 ± 0.41 2.56 ± 0.80

In-Cabin Refueling 3 24.91 ± 12.19 41.96 ± 21.35

In-Cabin Underground Garage 4 3.22 ± 1.49 2.35 ± 1.78

In-Cabin Toll Plaza 5 2.49 ± 0.77 2.99 ± 1.14

Tunnel 6 2.74 ± 0.42 5.33 ± 6.63

Outdoor Refueling 7 28.82 ± 12.01 55.77 ± 26.83

Sidew 19 1.15 ± 0.06

Bus 13 1.31 ± 0.18

Su 6.93 ± 6.57

Out 37 3.30 ± 1.50

Out 81 2.78 ± 1.18

alk 8 2.34 ± 0.

 Stop 9 2.87 ± 1.

rface Parking 10 1.94 ± 0.36

door Underground Garage 11 2.60 ± 0.

door Toll Plaza 12 2.48 ± 1.
2-8

Table 2-4. Mass ratios of MTBE to benzene in vehicle exhaust, gasoline vapor and liquid gasoline. 

Test Set Fuel Year Average Stdev ReRatios in LDGV Exhaust

CRPAQS/GDS dyno exhaust Los Angeles 2001 0.62 1.35 Fitz 

CRPAQS/GDS dyno warm-starts Los Angeles 2001 0.43 1.43 Fitz 

CRPAQS/GDS dyno hi-em Los Angeles 2001 1.11 3.17 Fitz 

SWRI FTP - summer Houston 2004 0.44 0.24 Me

SWRI FTP - winter Houston 2005 1.40 0.55 Me

SWRI FTP- normal Houston 2004 and 2005 0.60 0.45 Me

SWRI FTP- malfunction Houston 2004 and 2005 1.24 0.71 Me

Ratios in Tunnel and Roadway Samples

WEO3 on-road Los Angeles 2000 2.96 1.03 Fujita et al.2003

LA tunnels-corrected for running loss Los Angeles 1995 and 1996 0.32 0.99 Fujita 

LA tunnels, uncorrected Los Angeles 1995 and 1996 1.69 0.54 Fujita API houston tunnel (ME6) Houston 2004 and 2005 3.36 1.35 T

Ratio in Gasoline Vapor

LA vapor Los Angeles 1995 16.63 Fujita 

WEO3 vapor Los Angeles 2000 44.98 Fujita et al.2003SWRI shed - malfunction Houston 2004 and 2005 20.52 29.20 Me

SWRI shed - malfunction, outlier removed Houston 2004 and 2005 5.93 1.60 Meestimated from fuel content - summer Houston 2004 32.8 Me

estimated from fuel content - winter Houston 2005 43.9 Me

Ratios in Liquid Gasoline

LA gasoline - 1995 RFG Los Angeles 1995 11.79 Fujita 

WEO3 gasoline Los Angeles 2000 19.56 5.23 Fujita et al.2003gds gasoline Los Angeles 2001 17.15 5.49 Ga

API gasoline - summer Houston 2004 13.28 Me

API gasoline - winter Houston 2004 17.87 Me
Table 2-5. Fractional contributions of evaporative emissions to total motor vehicles emissions in 

Houston by ME. 

Microenvironment ME Summer Winter

Freeway 1 0.04 ± 0.02 0.03 ± 0.03

Urban Canyon 2 0.02 ± 0.01 0.03 ± 0.02

In-Cabin Refueling 3 0.76 ± 0.38 0.95 ± 0.50

In-Cabin Underground Garage 4 0.09 ± 0.05 0.02 ± 0.04

In-Cabin Toll Plaza 5 0.06 ± 0.02 0.04 ± 0.03

Tunnel 6 0.07 ± 0.01 0.09 ± 0.16

Outdoor Refueling 7 0.88 ± 0.37 1.28 ± 0.63

Sidewalk 8 0.06 ± 0.01 -0.01 ± 0.00

Bus Stop 9 0.08 ± 0.04 0.00 ± 0.00

Surface Parking 10 0.05 ± 0.01 0.13 ± 0.15

Outdoor Underground Garage 11 0.07 ± 0.01 0.04 ± 0.04

Outdoor Toll Plaza 12 0.06 ± 0.06 0.03 ± 0.03

Evaporative Emissions Contribution

0.0

0.5

1.0

1.5

2.0

1 2 3 4 5 6 7 8 9 10 11 12

ME

Fraction

summer

winter

Figure 2-1.Fractional contributions of evaporative emissions to total motor vehicles emissions in 

Houston by ME. 

2-9
2.5 References 

Fujita, E.M., Z. Lu, L. Sheetz, G. Harshfield, T. Hayes, and B. Zielinska (1997c). Hydrocarbon 

Source Apportionment in Western Washington. Report prepared for the State of 

Washington Department of Ecology, Lacy, WA, September, 1997. 

Fujita, E.M., R.E. Keislar, J.L. Bowen, W. Goliff, F. Zhang, L.H. Sheetz, M.D. Keith, J.C. 

Sagebiel, and B. Zielinska (1999a). 1998 Central Texas On-Road Hydrocarbon Study. 

Final report prepared for the Texas Department of Transportation, Austin, TX under 

subcontract to PBS&J, Austin, TX, March, 1999. 

Fujita E.M. (2001). Hydrocarbon Source Apportionment for the 1996 Paso del Norte Ozone 

Study. Science of the Total Environment, 276:171-184. 

Fujita, E.M., D.E. Campbell, B. Zielinska, J.C. Sagebiel, J.L. Bowen, W. Goliff, W.R. 

Stockwell, and D.R. Lawson (2003a). Diurnal and Weekday Variations in Source 

Contributions of Ozone Precursors in California’s South Coast Air Basin. J. Air & Waste 

Manage. Assoc. 53:844-863. 

Fujita, E.M. and D. Campbell (2003b). Validation and Application Protocol for Source 

Apportionment of Photochemical Assessment Monitoring Stations (PAMS) Ambient 

Volatile Organic Compound (VOC) Data. Final report prepared for the U.S. 

Environmental Protection Agency under EPA Star Grant #GR826237-01-0, August 31, 

2003. 

Gabele, P. Support of the Gasoline/Diesel Particulate Matter Split Study. Final report submitted 

by U.S. Environmental Protection Agency to Department of Energy through Interagency 

Agreement (IAG) No. DE-AI04-2001AL67138, March 17, 2003. 

Kirchstetter, T.W., B.C. Singer, R.A. Harley, G.R. Kendall, and J.M. Hesson (1999). Impact of 

California Reformulated Gasoline on Motor Vehicle Emissions: 2. Volatile Organic 

Compound Speciation and Reactivity. Environ. Sci. Technol., 33:329-336. 

Pierson, W., E. Schorran, E. Fujita, J. Sagebiel, D. Lawson, and R. Tanner (1999). Assessment 

of Non-Tailpipe Hydrocarbon Emissions from Motor Vehicles. J. Air Waste Manage. 

Assoc., 49: 498-519. 

Reid, R.C., J.M. Prausnitz and B.E. Poling (1987). Composition of Vapor Emitted from a 

Vehicle Gasoline Tank During Refueling. SAE Technical Paper Series, paper no. 

860086. 

Zielinska, B. E.M. Fujita, and J.C. Sagebiel, D. Campbell, L.R. Smith and T. Johnson (2003). 

Exposure Protocol and Study Plan for the Section 211 (B) Tier 2 High End Exposure 

Screening Study of Baseline and Oxygenated Gasoline. Prepared for American Petroleum 

Institute, 1220 L. Street, Washington, DC 20005-4007. Final Version. October 1, 2003.

2-10
3. Determination of the Quantitative Relationships between Levels of 

Volatile Air Toxics and Carbon Monoxide Measured In High End 

Microenvironments and At Nearby Air Quality Monitoring Stations 

3.1 Introduction 

The U.S. Environmental Protection Agency conducts national-scale assessments of air 

toxics in order to set program priorities, characterize risks, and track progress towards achieving 

the goals of the national air toxics program as established by the 1990 Clean Air Act 

Amendments (CAAA). As part of the National Air Toxics Assessment (NATA), EPA conducted 

a national screening-level assessment for 1996 and 1999 to characterize the potential risks 

associated with inhalation exposures to 33 air toxics and diesel particulates. The screening-level 

assessment estimated outdoor air toxics concentrations across the US and related these 

concentrations to population exposures. 

The Assessment System for Population Exposure Nationwide (ASPEN) model was used 

by EPA to estimate outdoor air toxics concentrations across for every census tract in the 

continental United States, Puerto Rico and the Virgin Islands. To enable the simulation of a large 

number of air toxics nationwide, a number of simplified approaches are incorporated into the 

model. The model uses a simplified approach to simulate atmospheric chemistry such as reactive 

decay and secondary formation (production of an air toxics compound due to chemical reactions 

in the atmosphere). A uniform background concentration is added for some pollutants for which 

information is available to compensate because the model simulates only pollutant transport 

within 50 kilometers of any individual source. For those air toxics with high levels of 

background concentrations, the model’s ability to predict ambient concentrations are greatly 

impacted by the accuracy of background estimates. Past comparisons with limited monitoring 

data show that the modeled air toxics concentrations are generally within two orders of 

magnitude of measured concentrations. 

For the exposure-modeling portion of the analysis, EPA used the Hazardous Air Pollutant 

Exposure Model (HAPEM). The HAPEM modeling approach simulates the movements of 

various population groups through zones of varying air quality. Each zone is defined by a 

geographic location (typically a census tract) and a microenvironment (ME). The patterns of 

movements among the zones are determined by diary-derived activity data and commuting data 

acquired from the U.S. census. Ambient concentrations are estimated by the ASPEN dispersion 

model based on local emissions and meteorological data. The pollutant concentration in a 

specific ME is estimated as a function of the ambient concentration by a linear expression 

containing three terms that vary with ME: the penetration factor (the indoor/outdoor ratio in the 

absence of indoor sources), the additive factor (accounts for contribution of indoor sources), and 

the proximity factor (accounts for distance to specific outdoor sources such as roadways). 

Estimates for these factors for 33 HAPS have been obtained from various field studies and from 

previous modeling exercises. In general, there is a high degree of uncertainty associated with 

HAPEM exposure estimates because of the limited data available for estimating the ME factors 

(Rosenbaum, 2005). 

3-1
The DRI conducted measurements quantifying exposures to automotive emissions in 

microenvironments (MEs) representing the upper-end (> 99th percentile) of the distribution of 

inhalation exposures to evaporative and exhaust emissions of conventional and oxygenatedgasoline. The study was conducted as part of the Section 211(b) Tier 2 High-End Exposure 

Screening Study of Baseline and Oxygenated Gasoline. DRI and SwRI conducted measurements 

under controlled conditions to establish quantitative relationships between tailpipe and 

evaporative emission rates to exposure levels in a vehicle cabin and attached residential garage. 

Field exposures also were measured in several high-end exposure MEs in Atlanta, Chicago, and 

Houston during winter and summer. Target species (TVOC, CO, BTEX, HCHO,1,3-BD, MTBE, 

EtOH) were measured within MEs, breathing zones, and breath. This section examines the 

quantitative relationships between CO exposure levels in these MEs to the corresponding fixed 

site measurements at nearby air monitoring stations. These comparisons are extended for 

Houston to volatile organic mobile source air toxics, which was the only city among the three 

with available data. These relationships are compared to the HAPEM proximity factors (Long 

and Johnson, 2004) that were used in the National Air Toxics Assessments. 

3.2 Experimental 

DRI measured seasonal in-cabin breathing zone exposures for urban roadways and other 

high-end MEs in Houston (6/3-7/9/04; 2/1-2/8/05), Chicago (8/5-8/20/03; 3/3-3/17/04), and 

Atlanta (7/28-8/8/02; 8/23-9/3/03; 2/10-2/29/04) using a combination of time-integrated samples 

and continuous instruments for thirteen different MEs listed in Table 3-1. Three replicate 

exposure measurements were made for low variability MEs and five for MEs with higher 

variability (i.e., ME13-trailing high emitting vehicles, ME11-underground garages, and ME7-

outdoor refueling). Measurements in each ME were taken over a period of 20-40 minutes 

beginning at the top of the hour. Shorter sampling times were used for refueling events and 

parking garage exits after sporting events. 

The integrated samples included whole-air canister samples for CO, BTEX, MTBE, and 

1,3-BD, acidified 2,4-diphenylhydrazine (DNPH) cartridges for HCHO and CH3CHO, and a 

multi-bed (TenaxTA-Carbotrap-Carbosieve) solid adsorbent tube for EtOH. Continuous 

measurements included both non-dispersive infrared (NDIR) and passive electrochemical 

(Langan T-15) devices for CO and an active photo-ionization detector (PID) for TVOC with an 

ionization potential below 10.6 eV (principally olefins and aromatic species). Sampling and 

analytical methods are described in Section 1 and in the study plan (Zielinska et al., 2003). 

Ambient CO and VOC data were retrieved from EPA’s Air Quality System (AQS) for the 

specific periods of the field study in each city and compared to the ME measurements. The 

ambient monitoring and ME locations are mapped for each city in Figures 3-1a to 3-1c although 

some ME locations are overlapped by adjacent MEs. AQS VOC data were not available for 

Atlanta; incomplete data were available for a single site (Northbrook, IL) in Chicago located 20 

miles N/NW of city center that is unlikely representative of urban Chicago. Speciated hourly 

GC/FID VOC data were available from two sites in Houston for both summer and winter. All 

sites reporting CO and VOC data within each metropolitan area were averaged together for the 

purposes of comparison. The average CO and benzene concentrations did not show substantial 

spatial variation within each city. 

3-2
3.3 Results and Discussion 

Exposure levels are directly related to source emission rates in the ME and inversely 

related to source distance and the extent of dilution, itself a function of meteorology and any 

physical obstructions that inhibit dilution. Hourly values from air quality monitoring stations in 

urban areas typically represent neighborhood scale exposure levels while 20-40 minute measures 

from MEs listed in Table 3-1 are intended to represent the high end exposures exceeding the 99th 

percentile. Consequently, the tabulated ME ratios reflect exposures scripted to reflect ‘worstcase’ conditions rather than population-average ME factors for these locations. Such information 

should be used solely to evaluate extreme exposures and not misinterpreted as ‘typical’ ME 

exposures encountered by the general population. 

Quantitative relationships for CO between ME measures and fixed site measurements at 

nearby air monitoring stations are examined first. CO is non-reactive and commonly measured 

year-round as a primary mobile source emission that is generally correlated with BTEX and 1,3-

BD. Table 3-2 shows the averages and standard deviations of the ratios of time-integrated CO 

from canister samples to the corresponding hourly CO from the ambient air monitoring stations 

in Houston, Atlanta, and Chicago by season and ME. As expected, the ratios are higher in MEs 

that are nearer to operating vehicle engines, especially in underground garages where dispersion 

of pollutants is limited. The average ratios for in-cabin exposures in congested freeway traffic 

ranged from 2 to 9 with lower ratios in the winter. Ratios were highest in Atlanta and lowest in 

Chicago. The seasonal and city-specific differences hold for most of the other MEs. Notable 

exceptions to the seasonal differences are the underground garages where the ratios are higher in 

the winter in all three cities, most likely due to the higher cold-start emissions. Garage size, 

ventilation, and spatial-temporal vehicle activity patterns account for the variance differences 

between underground garages. The garage in Atlanta is smaller, less ventilated, and more used 

than the garages in Houston or Chicago. While CO is a good exhaust species tracer, correlation 

with evaporative emissions is less. ME/ambient ratios are generally lower for CO than most of 

the other pollutants. This is most likely due to higher urban background levels of CO. 

Table 3-3 shows average Houston BTEX and 1,3-BD ME/ambient ratios (± SD), i.e., the 

time-integrated canister value to the corresponding hourly monitoring station GC/FID value. In 

contrast to CO, BTEX ME/ambient ratios are substantially higher for refueling (ME 3, ME 7). 

The BTEX ratios are closer to corresponding ratios derived for CO during winter but higher 

during summer. Since 1,3-BD is an exhaust species, the relative variation of ME/ambient ratios 

is similar to CO. 1,3-BD measures in MEs with high MTBE were invalid due to interferences 

(see Section 1). 

The integrated exposure measurements are 20-40 minute averages. Continuous CO and 

VOC PID measurements show higher peak (1-5 minutes) exposures. Continuous instruments 

provide sensitive proportionate measures of short-term target species variability since continuous 

time-averaged traces are well correlated to the corresponding time-integrated measurements. 

Consequently, the normalized continuous CO or VOC PID measures were used to reconstruct 1-

minute time-series concentrations for specific components. Either CO or VOC PID traces are 

suitable surrogates in exhaust-dominated MEs; VOC PID values are suitable surrogates in 

evaporative emissions-dominated MEs such as refueling. Reconstructed time-series and ranges 

3-3
of estimated 1-minute values are summarized in Section 1. Figures 3-2a through 3-2c show 20-

40 minute average and maximal estimated 1-minute values for benzene, 1,3-BD, and HCHO, 

respectively. Short-term exposures from evaporative-dominated ME3 and ME7 range more 

widely than those from other exhaust-dominated MEs. 

3.4 Conclusions 

MEs in close proximity to running vehicle engines have enhanced CO relative to ambient 

levels with enrichment ratios approaching 40 where ventilation is limited, as in underground 

garages. Average in-cabin CO/ambient ratios in congested freeway traffic range from 2-9 with 

lower winter ratios. ME locations less proximate to operating vehicles, such as gas stations and 

urban sidewalks, have CO/ambient ratios of 0.5-2. 

The Houston benzene ME1/ambient ratio of 9.8 ± 3.8 for exceed the HAPEM5 median 

proximity factor of 4.9 (triangular distribution mode:range 1.9:0-14.3) and HAPEM4 proximity 

factor of 6.9 for this ME (Rosenbaum, 2005; Long and Johnson, 2004), although by less than 

expected. The HAPEM4 factors may be elevated compared to present conditions since 

measurements occurred before 1991 when benzene fuel levels and roadway fleet emissions were 

higher than today. HAPEM5 proximity factors may also need to be adjusted since they were 

based on a 1998 scoping study where measurements ‘highlighted trailing behind heavy duty 

diesel vehicles and diesel city buses when possible’. Houston ME/ambient ratio comparisons 

also generally exceed the other HAPEM factors listed in Table 3-4. Refueling ratios (ME3, ME7) 

for benzene were substantially higher than the corresponding HAPEM factors also as expected. 

Concentrations of exhaust compounds such as CO and 1,3-BD were enhanced under reduced 

ventilation situations. 

3.5 References 

Rosenbaum, A. (2005). The HAPEM5 User’s Guide. Report prepared by ICF Consulting for the 

U.S. Environmental Protection Agency, Research Triangle Park, NC, March 2005. 

Long, T. and T. Johnson (2004). Development of Penetration and Proximity Microenvironment 

Factor Distributions for the HAPEM5 in Support of the 1999 National-Scale Air Toxics 

Assessment (NATA). Memorandum prepared by TRJ Environmental, Inc. for the U.S. 

Environmental Protection Agency, Research Triangle Park, NC, April 5, 2004. 

Zielinska, B. E.M. Fujita, and J.C. Sagebiel, D. Campbell, L.R. Smith and T. Johnson (2003). 

Exposure Protocol and Study Plan for the Section 211 (B) Tier 2 High End Exposure 

Screening Study of Baseline and Oxygenated Gasoline. Prepared for American Petroleum 

Institute, 1220 L. Street, Washington, DC 20005-4007. Final Version. October 1, 2003. 

3-4
Table 3-1. Summary of sample collections in urban microenvironments 

3-5

ME # ME Description Replicates Biomarker

5 min 

Canister

Sampling Time 

(min)

1 In-Cabin Congested Freeway 5 40

2 In-Cabin Urban Canyon 3 40

3 In-Cabin Refueling 5 20

4 In-Cabin Underground Garage 5 40

5 In-Cabin Toll Plaza 3 40

6* Roadway Tunnel 5 40

7 Outdoor Refueling 5 yes yes 20

8 Sidewalk 3 40

8/9 Sidewalk/Bus Stop 3 40

3 40

5 yes yes 40

3 40

1 5 yes yes 40

*M

10 Outdoor Surface Parking

11 Outdoor Underground Garage

12 Outdoor Toll Plaza

3* In-cabin Trailing High-Emitting Vehicles

E13 was substituted for ME6 in Atlanta and Chicago.
Table 3-2. Average and standard deviation in ratios of the time-integrated CO from canister samples to the corres

from regional ambient air monitoring sites for Houston, Atlanta and Chicago by season and microenvironment. 

Summer Winter

 Microenvironment Houston Atlanta Chicago Houston Atlanta 

1 Congested Freeway, In-Cabin 4.6 ± 1.0 9.1 ± 6.5 2.6 ± 0.4 4.0 ± 1.0 5.4 ± 1.9 2 Urban Canyon, In-Cabin 5.2 ± 2.5 3.9 ± 3.9 2.9 ± 1.4 12.1 ± 10.9 2.7 ± 5.6 3 Refueling, In-Cabin 3.6 ± 0.9 1.4 ± 2.7 0.7 ± 0.3 4.1 ± 3.2 1.3 ± 0.6 4 Underground Garage, In-Cabin 8.4 ± 8.0 16.9 ± 0.8 7.9 ± 3.4 21.4 ± 12.5 38.8 ± 0.2 5 Toll Plaza, In-Cabin 4.1 ± 1.0 6.4 ± 0.0 1.6 ± 0.5 3.6 ± 0.6 2.7 ± 0.0 6 Tunnel, In-Cabin 8.4 ± 1.7 6.3 ± 1.5 9.7 ± 5.2 

7 Refueling, Outdoor 1.9 ± 0.8 1.2 ± 1.8 0.9 ± 0.3 3.3 ± 2.5 2.1 ± 1.4 8 Sidewalk 1.9 ± 0.5 1.9 ± 0.5 1.1 ± 0.2 1.3 ± 0.6 1.9 ± 0.9 9 Sidewalk/BusStop 1.5 ± 0.3 2.4 ± 0.3 1.6 ± 0.6 1.8 ± 0.1 1.9 ± 0.2 

10 Surf Parking, Outdoor 3.3 ± 1.2 5.3 ± 0.7 2.1 ± 1.3 4.7 ± 2.9 3.3 ± 0.6 11 Underground Garage, Outdoor 8.6 ± 7.4 26.8 ± 3.6 3.9 ± 2.3 17.1 ± 11.2 32.9 ± 2.0 12 Toll Plaza, Outdoor 7.6 ± 2.7 6.5 ± 8.8 3.2 ± 0.2 6.2 ± 4.3 7.4 ± 16.5 13 Following High Emitter, In-Cabin 8.4 ± 2.6 12.0 ± 4.2

3-6
Table 3-3. Average and standard deviations in ratios of BTEX and 1,3-BD from time-integrated canister samples 

hourly automated GC data from the ambient air monitoring sites in Houston. 

 Microenvironment Benzene Toluene Etbenzene m&p-Xylene o-Xyl

Summer

1 Congested Freeway, In-Cabin 9.8 ± 3.8 7.8 ± 1.9 5.4 ± 1.8 5.2 ± 0.6 6.6 ± 

2 Urban Canyon, In-Cabin 7.4 ± 3.0 6.8 ± 1.1 5.6 ± 3.3 5.6 ± 1.4 5.8 ± 

3 Refueling, In-Cabin 565 ± 791 446 ± 666 140 ± 188 115 ± 136 117 ± 4 Underground Garage, In-Cabin 19.4 ± 13.9 17.2 ± 15.0 16.0 ± 13.7 14.2 ± 12.8 17.1 ± 5 Toll Plaza, In-Cabin 9.1 ± 4.4 7.8 ± 3.6 6.8 ± 4.9 6.2 ± 3.4 7.1 ± 

6 Tunnel, In-Cabin 25.9 ± 14.1 12.4 ± 6.8 7.8 ± 2.9 7.5 ± 2.7 8.9 ± 

7 Refueling, Outdoor 1312 ± 1811 974 ± 1356 335 ± 479 219 ± 227 197 ± 8 Sidewalk 15.4 ± 10.6 10.6 ± 4.4 12.5 ± 15.3 11.9 ± 14.0 14.2 ± 9 Sidewalk/BusStop 4.7 ± 2.0 2.9 ± 1.3 1.8 ± 0.4 1.9 ± 0.5 2.3 ± 

10 Surf Parking, Outdoor 11.5 ± 5.5 8.3 ± 2.8 7.4 ± 2.1 6.7 ± 3.1 7.0 ± 11 Underground Garage, Outdoor 16.7 ± 5.3 15.7 ± 7.2 13.8 ± 7.2 11.1 ± 7.2 14.4 ± 

12 Toll Plaza, Outdoor 14.7 ± 8.5 11.3 ± 10.2 9.2 ± 8.3 8.5 ± 7.6 11.0 ± 

Winter

1 Congested Freeway, In-Cabin 4.6 ± 1.6 6.4 ± 3.7 6.4 ± 3.0 8.8 ± 5.2 9.7 ± 

2 Urban Canyon, In-Cabin 17.0 ± 21.7 22.7 ± 27.7 22.1 ± 26.4 31.1 ± 36.9 26.7 ± 3 Refueling, In-Cabin 35.0 ± 25.4 36.5 ± 27.2 22.7 ± 18.2 25.3 ± 19.2 24.2 ± 4 Underground Garage, In-Cabin 37.2 ± 15.8 32.3 ± 12.9 24.0 ± 9.4 23.2 ± 8.5 25.0 ± 5 Toll Plaza, In-Cabin 3.5 ± 1.7 3.7 ± 1.5 4.3 ± 1.7 4.6 ± 2.0 5.3 ± 

6 Tunnel, In-Cabin 8.5 ± 6.7 9.0 ± 6.9 7.0 ± 4.5 8.9 ± 6.4 9.9 ± 

7 Refueling, Outdoor 160 ± 148 119 ± 92 49.1 ± 39.2 56.1 ± 54.3 44.6 ± 8 Sidewalk 2.8 ± 0.8 2.6 ± 1.0 2.7 ± 0.7 3.6 ± 1.7 3.7 ± 

9 Sidewalk/BusStop 3.3 ± 0.3 3.6 ± 0.3 3.5 ± 1.1 4.2 ± 0.7 4.3 ± 

10 Surf Parking, Outdoor 4.3 ± 3.0 7.5 ± 6.4 5.7 ± 2.9 6.1 ± 2.1 6.0 ± 

11 Underground Garage, Outdoor 28.3 ± 16.5 25.0 ± 13.0 20.8 ± 11.3 21.9 ± 11.1 22.9 ± 

12 Toll Plaza, Outdoor 4.8 ± 0.7 4.5 ± 1.4 4.5 ± 1.8 4.9 ± 1.6 5.4 ± 

3-7
Table 3-4. Houston benzene ME/ambient ratio comparison with HAPEM benzene ME factors 

ME Summer Winter HAPEM4 

PROX 

HAPEM5 PROX Distribution (mode;median) 

HARa

1 Congested Freeway, In-Cabin 9.8 4.6 5.2, 6.9* Triangular 1.9; 4.9 0-12 Urban Canyon, In-Cabin 7.4 17 4.4 Triangular 1.9; 4.9 0-13 Refueling, In-Cabin 565 35 4.4 Triangular 1.6; 2.7 0-74 Underground Garage, In-Cabin 19 37 1.0 Triangular 1.6; 2.7 0-75 Toll Plaza, In-Cabin 9.1 3.5 4.4 Triangular 1.9; 4.9 0-16 Tunnel, In-Cabin 26 8.5 4.4 Triangular 1.9; 4.9 0-17 Refueling, Outdoors 1300 160 4.4 Triangular 1.6; 2.7 0-78 Sidewalk 15 2.8 4.4 Triangular 1.6; 2.7 0-79 Sidewalk, BusStop 4.7 3.3 4.4 Triangular 1.6; 2.7 0-710 Surface Parking, Outdoors 12 4.3 4.4 Triangular 1.6; 2.7 0-711 Underground Garage, Outdoors 17 28 1.0 Triangular 1.6; 2.7 0-712 Toll Plaza, Outdoors 15 4.8 4.4 Triangular 1.6; 2.7 0-7* truck, car 

3-8
Figure 3.1a. Location of ME sampling and fixed monitoring stations in Chicago Metro Area. 

3-9
Figure 3.1b. Location of ME sampling and fixed monitoring stations in Houston Metro Area. 

3-10
3-11

Figure 3.1c. Location of ME sampling and fixed monitoring stations in Atlanta Metro Area. 
Benzene - Estimated Average 1-minute Concentrations

0

20

40

60

80

100

120

140

01020304050708091011121301020304050708091011121301020304050607080910111213010203040506070809101112010203040506070809101112010203040506070809101112

Summer Winter Summer Winter Summer Winter

Atlanta Chicago Houston

Conc (ppbv)

Benzene - Estimated Maximum 1-minute Concentrations

0

500

1000

1500

2000

2500

01020304050708091011121301020304050708091011121301020304050607080910111213010203040506070809101112010203040506070809101112010203040506070809101112

Summer Winter Summer Winter Summer Winter

Atlanta Chicago Houston

Conc (ppbv)

Figure 3-2a. Comparison of average versus the maximum 1-minute benzene levels by 

city, season and microenvironment. 

3-12 
1,3-Butadiene - Estimated Average 1-minute Concentrations

0

1

2

3

4

5

01020304050708091011121301020304050708091011121301020304050607080910111213010203040506070809101112010203040506070809101112010203040506070809101112

Summer Winter Summer Winter Summer Winter

Atlanta Chicago Houston

Conc (ppbv)

1,3-Butadiene - Estimated Maximum 1-minute Concentrations

0

5

10

15

20

25

01020304050708091011121301020304050708091011121301020304050607080910111213010203040506070809101112010203040506070809101112010203040506070809101112

Summer Winter Summer Winter Summer Winter

Atlanta Chicago Houston

Conc (ppbv)

Figure 3-2b. Comparison of average versus the maximum 1-minute 1,3-butadiene levels 

by city, season and microenvironment. 

3-13 
Formaldehyde - Estimated Average 1-minute Concentrations

0

10

20

30

40

01020304050708091011121301020304050708091011121301020304050607080910111213010203040506070809101112010203040506070809101112010203040506070809101112

Summer Winter Summer Winter Summer Winter

Atlanta Chicago Houston

Conc (ppbv)

Formaldehyde - Estimated Maximum 1-minute Concentrations

0

20

40

60

80

100

120

140

160

01020304050708091011121301020304050708091011121301020304050607080910111213010203040506070809101112010203040506070809101112010203040506070809101112

Summer Winter Summer Winter Summer Winter

Atlanta Chicago Houston

Conc (ppbv)

Figure 3-2c. Comparison of average versus the maximum 1-minute formaldehyde levels 

by city, season and microenvironment. 

3-14 
4. Relationships of Attached Garage and Home Exposures to Fuel 

Type and Emission Levels of Garage Sources 

4.1 Introduction 

This chapter describes experiments to determine relationships between measured 

fuel and exhaust components in the attached garage, adjacent room (kitchen), and 

garaged vehicle emission levels. The same vehicles, fuels and vehicle malfunctions used 

here are used in Chapter 5 to explore the effects of ventilation, proximity, and leading 

vehicle emission levels on trailing vehicle in-cabin exposures. These measurements are 

also described in the executive summary and Chapter 1. 

Measurements were performed during June-July 2002 and February-March 2005 

in San Antonio, TX on a sedan and a pickup truck using either non-oxygenated 

conventional gasoline, gasohol (E10), or an MTBE-oxygenated gasoline. The vehicles 

were tested in both a normal emissions mode and a malfunctioning high emitter mode 

where emissions were adjusted to exceed 2 grams of non-methane hydrocarbons 

(NMHC) per mile as measured by the Federal Test Procedure (FTP). 

4.2 Experimental 

Methods and procedures specific to the attached garage experiments are 

summarized below. Sampling and analyses methods are described in Chapter 1 and 

Appendix B. 

4.2.1 Vehicles and Vehicle Test Methods 

The Southwest Research Institute (SwRI) procured two test vehicles and 

determined their evaporative/tailpipe emissions in the normal/malfunction modes using 

the three test fuels. The test vehicles, a sedan and full-sized V8 truck, were chosen within 

the 1993-1996 model years from vehicles with 90,000-110,000 odometer miles. The 

chosen 1993 Toyota Camry (2.2L 4-cylinder engine) and 1995 Ford F150 Pickup truck 

(5.0L V8 engine) were operated in normal, as purchased, modes and in “high emitter” 

modes with the catalytic converter removed and emission levels above 2 grams per mile 

NMHC as measured on the FTP driving cycle. While converter removal sufficed for the 

F150 truck, a calibrated manifold leak was also needed to achieve the ≥ 2g/mile Camry 

emissions. SwRI determined dynamometer FTP emissions for each vehicle with all three 

fuels in the two emission modes (24 tests). Emission control components could be 

reproducibly adjusted to represent normal and reasonable high-end approximations (≥

2g/mile) of real world exhaust emissions. The vehicle properties are summarized in Table 

4.2-1 and included in the SwRI report (Appendix F). 

4-1
Table 4.2-1. Summary of vehicles used. 

Vehicle Make Model Year Engine Malfunction 

Truck Ford F150 1995 5.0 L V8 Removed Catalyst. 

Sedan Toyota Camry 1993 2.2 L 4 

cylinder 

Removed Catalyst and added 

leak to manifold. 

Regulated exhaust emissions (THC, NMHC, CO, NOx), fuel economy, and 

specific VOCs (MTBE, EtOH, BTEX, 1,3-BD, HCHO) were determined in 

dynamometer FTP tests. During hot-soak SHED tests, THC and specific VOCs (minus 

HCHO) were also determined. 

The FTP exhaust emission test uses the 1372 second Urban Dynamometer 

Driving Schedule (UDDS) that is divided into cold/start transient 505 (Bag 1) and cold 

stabilized 867 (Bag 2) second segments. This portion of the FTP is followed by a 10-

minute soak and a hot/start transient 505 (Bag 3) test. The FTP evaporative emission test 

includes one hour Diurnal Heat Build (DHB) and Hot Soak Loss (HSL) tests. THC/VOC 

emissions are recorded during the HSL segment of the test. Prior to the FTP cold-start 

exhaust test, the DHB is conducted by fueling the test vehicle to 40 percent of tank 

capacity with fuel < 55°F, attaching a heating blanket outside the fuel tank, placing a 

thermocouple in the tank fuel, hooking it up to computer control, and beginning the test 

as fuel reaches 60°F (increasing at 0.4°F per minute for the 60-minute test to a 84°F final 

temperature). 

In the HSL segment, conducted immediately following exhaust emission testing, 

the vehicle is driven into an evaporative emission enclosure and allowed to “soak” in the 

enclosure for one hour. THC/VOC emissions are measured at the beginning and end of 

the one-hour segment and hot soak evaporative emissions are calculated. 

4.2.2 Fuel Testing 

Test fuel samples were subject to standard tests for Reid Vapor Pressure (RVP), 

distillation range, Specific Gravity, Sulfur, Benzene, HC Category (saturates, olefins, 

aromatics), Oxygenated species (MTBE/EtOH), carbon weight percent, hydrogen weight 

percent, oxygen weight percent, and octane number. These results are presented in Table 

4.3-1. 

4.2.3 Test House 

Fuel component levels were measured in the garage and in a room (kitchen) 

adjacent to an attached garage using the fuels and test vehicles in normal and high emitter 

modes. Appendix I shows the layout of the house. The double garage contained an active 

ceiling fan that minimized emissions stratification and hot spots within the garage. The 

garage also contained a plastic gasoline container and gasoline-powered lawnmower 

filled with the test fuels. The exhaust fan over the kitchen’s stove was not used during the 

4-2
experiments. However, the central air conditioning was active during the summer tests. 

Garage and kitchen monitoring was conducted according to the scenarios described in 

Table 4.2-2. Window and door openings, of the garage vehicle door, the kitchen door 

between the garage and kitchen, and kitchen window were scripted. Time-integrated 

canister, DNPH and solid adsorbent (for EtOH) cartridges, and SPME samples were 

collected for each test. EtOH was measured for Chicago fuel only. Continuous or semicontinuous measurements were also operated during the exposure periods. Measurements 

were taken over scripted 30-minute scenario intervals through collocated sampling inlets 

at breathing height (1.5 m) a meter distant from nearby walls in the kitchen and 

unventilated garage. Continuous PID TVOC and Langan CO instruments sampled from 

the kitchen before (background) and during 2002 tests. For the winter 2005 samples, a 

second PID TVOC and the NDIR CO instrument were used to monitor the garage 

continuously. In the summer 2002 samples, the continuous MS200 BTEX and A-Ω

HCHO monitors sampled cyclically through collocated inlets in the garage and kitchen 

every 10 minutes. 

A half-filled two-gallon plastic gasoline storage container with vent opened was 

placed adjacent to a fueled lawnmower, with gas tank half filled, against the center of the 

rear garage wall common with the kitchen. The container and lawnmower filled with the 

appropriate fuel were placed in the garage one day before the series of vehicle tests for 

that fuel began and remained there over the duration of the tests. Scenario conditions 

were changed every 30 minutes over the 3-hour protocol as described in the Table 4.2-2. 

Ambient garage temperatures were recorded each 30 minutes. Tests were conducted 

daily (excluding weekends) over a two week period. 

Table 4.2-2. Protocol for attached garage experiments. 

Condition Time 

(min) 

Garage 

Door 

Kitchen 

Door 

Kitchen 

Window 

Inlet 

Location

Continuous 

Instruments

SPME Integrated 

Canisters/ 

Cartridges 

10 garage yes 

10 kitchen yes 

Background 

No vehicle, 

but lawn 

mower & gas 10 

closed closed closed 

garage yes 

2 2 

10 kitchen yes 

10 garage yes 

Hot soak 

vehicle, 

lawnmower, 

& gas 10 

closed 

opened 1 

min 

& closed

closed 

kitchen yes 

2 

10 garage yes 

10 kitchen yes 

Cooling 

vehicle, 

lawnmower, 

& gas 10 

closed closed closed 

garage yes 

2 

10 kitchen yes 

10 garage yes 

Cold vehicle, 

lawnmower, 

& gas 

10 

closed closed open 

kitchen yes 

2 

2 

4-3
Condition Time 

(min) 

Garage 

Door 

Kitchen 

Door 

Kitchen 

Window 

Inlet 

Location

Continuous 

Instruments

SPME Integrated 

Canisters/ 

Cartridges 

10 garage yes 

10 kitchen yes 

Cold start, 

idling, 

lawnmower, 

& gas 10 

open opened 1 

min 

& closed

closed 

garage yes 

2 

10 kitchen yes

10 garage yes

No vehicle, 

but 

lawnmower, 

& gas 10 

closed closed closed 

kitchen yes

2 

The first scenario condition, background, assesses levels in the kitchen and garage 

prior to the beginning of vehicle testing. In the garage, background will include emissions 

from the gasoline container and lawn mower. The hot soak condition should most closely 

reflect the hot soak SHED tests performed by SwRI. In this condition, the exposure 

scenario is that of a person coming home from shopping and conveying purchases 

through the kitchen-garage door into the home, allowing some enhanced air exchange 

between the garage and the kitchen. The next condition, cooling vehicle, reflects a period 

where the trapped garage air remains in the kitchen. The cold vehicle condition is 

performed with the kitchen window open to allow outside fresh air exchange within the 

kitchen (keeping the garage door closed). The cold start condition simulates a person 

warming up his car in an open garage prior to leaving; the kitchen door is open for one 

minute to account for the extra trips to and from the vehicle. The vehicle is started and 

then idled for the entire 30 minutes. The final condition, no vehicle, represents kitchen 

exposures after the vehicle has left. One integrated canister and cartridge samples were 

collected over background test and another one over all five phases of the garage 

experiments, as shown in Table 4.2-2. 

4.3 Results 

4.3.1 Fuel Analyses 

The results of the fuel analyses are presented in Table 4.3-1. Fewer tests were run 

on the Summer 2002 fuels. 

The results confirm that there was no oxygenate in the Atlanta conventional fuel, 

that MTBE was present in the Houston fuel, and that ethanol was present in the Chicago 

fuel. Across seasons total aromatics were similar in the oxygenated fuels but higher in the 

conventional fuel. Benzene levels range from 0.5-1.2 % with the conventional summer 

fuel highest. The Reid Vapor Pressure (RVP) is higher in the winter fuels to ensure cold 

start reliability. 

4-4
Table 4.3-1. Summary of properties for the six test fuels. 

O2 Total wt% = total oxygen weight % 

MeOH = methanol; EtOH = ethanol 

4.3.2 Vehicle Regulated and Hot Soak Emissions 

 The vehicle emission tests were conducted as described in Section 4.2. The details 

of these tests are described in the SwRI Report, attached in Appendix F. Tables 4.3-2 

through 4.3-5 show the measured regulated exhaust and hot soak emissions from the test 

vehicles for summer and winter test fuels. The FTP results show that all emissions 

increased and the high emitter target of ≥ 2 grams NMHC per mile was achieved. 

4-5
 Table 4.3-2. Regulated and Hot Soak Emissions from the Ford F-150, Summer 2002. 

Table 4.3-3. Regulated and Hot Soak Emissions from the Ford F-150, Winter 2005. 

Table 4.3-4. Regulated and Hot Soak Emissions from the Toyota Camry, Summer 2002 

Table 4.3-5. Regulated and Hot Soak Emissions from the Toyota Camry, Winter 2005 

4-6
4.3.3 Garage and Kitchen Exhaust/Evaporative Fuel Component Levels 

This section summarizes emission component concentrations observed in the 

kitchen and attached garage. As discussed in Chapter 1, measured 1,3-BD levels are 

biased upwards in the presence of high MTBE concentrations. In addition, a single 

garage sample (sedan with gasohol in normal mode) was invalidated. The sample 

contained high anomalous levels of BTEX, BTEX/1,3-BD and BTEX/CO ratios were 25- 

and 88-fold higher, respectively, in the normal mode than the high emitter tests, 

suggesting an anomalous source of BTEX such as an unrecorded garage fuel spill. 

BTEX and 1,3-butadiane data presented in Tables 4.3-6 to 4.3-12 are from the 

canister samples and ethanol is from the sorbent cartridges, as described in Chapter 1 and 

Appendix B.. 

4.3.3.1 Background and Overall Concentrations 

The background samples, taken before the vehicle was brought into the garage, 

are presented in Table 4.3-6 for both the average (top section, separated for summer and 

winter) and ranges of the data. Note that the max-min ranges denote the single highest 

values for each species individually across tests. Gaps indicate missing samples. Both 

HCHO and EtOH show relatively higher levels in the kitchen. HCHO off-gases from 

residential furnishings and construction materials. EtOH is emitted from people, foods, 

cleaning & personal care products, domestic garbage, and alcoholic beverages. 

Table 4.3-6. Summary of Background Concentrations in Kitchen and Garage. Units are 

ppbv, except as noted. 

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

Kitchen Backgrounds

Summer 0.08 1.70 6.50 0.67 2.30 1.05 0.42 0.35 49.83 1215.58

Winter 0.21 3.93 7.47 4.82 7.47 4.32 1.31 0.87 13.51

Garage Backgrounds

Summer 0.02 2.68 8.87 0.92 3.25 1.14 0.20 0.15 20.29

Winter 0.12 2.29 5.40 0.85 3.13 1.21 1.11 0.78 7.70

Kitchen, all

Min 0.02 0.73 3.33 0.37 1.25 0.50 0.00 0.15 5.50 53.

Max 1.33 11.76 15.49 38.21 32.27 24.64 6.16 5.29 106.63 2194.10

Garage, all

Min 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.85 0.

Max 0.90 11.47 25.72 3.19 11.33 4.27 3.78 7.01 35.63 1475.60

60

90

Budi13 = 1,3BD; Benze = benzene; Tolue = toluene, Mp_xyl = m,p-xylene; o_xyl = o-xylene, 

Formal = formaldehyde; EtOH = ethanol 

The ranges of all samples taken during the vehicle-related scenario portions are presented 

in Table 4.3-7. As expected, the lower concentrations stem from normal mode vehicles 

and higher levels from the high emitter mode. 

4-7
Table 4.3-7. Summary of Test Concentration Ranges in Kitchen and Garage. Units are 

ppbv, except as noted. 

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

Kitchen, all

Min 0.02 0.18 2.49 0.25 0.78 0.43 0.00 0.00 0.00 158.

Max 1.64 11.17 15.58 3.02 9.06 5.12 13.27 10.85 95.59 670.20

Garage, all

Min 0.03 1.33 2.48 0.39 1.25 0.51 0.00 0.20 0.00 5.

Max 36.35 65.44 93.67 18.23 50.72 19.36 185.63 39.16 174.20 27.70

80

80

Budi13 = 1,3BD; Benze = benzene; Tolue = toluene, Mp_xyl = m,p-xylene; o_xyl = o-xylene, 

Formal = formaldehyde; EtOH = ethanol 

4.3.3.2 Seasonal Impacts 

 

Seasonal max trends are inconsistent. Table 4.3-8 shows that differences seen in 

the kitchen are smaller than in the garage. The garage has higher exhaust 1.3-BD and 

HCHO in the summer, but lower CO values than in the winter. 

Table 4.3-8. Seasonal Impact on Observed Maximum Concentrations (Units are ppbv, 

except as noted). 

. Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

Kitchen Max-S 1.42 7.77 14.64 1.84 6.44 2.98 10.49 1.62 95.59 670.20

Max-W 1.64 11.17 15.58 3.02 9.06 5.12 13.27 10.85 54.78

Garage Max-S 36.35 65.44 93.67 18.23 50.72 19.36 93.63 28.60 174.20 27.70

Max-W 8.47 24.68 34.61 6.05 22.78 8.04 185.63 39.16 54.78

Budi13 = 1,3BD; Benze = benzene; Tolue = toluene, Mp_xyl = m,p-xylene; o_xyl = o-xylene, 

Formal = formaldehyde; EtOH = ethanol 

 Tables 4.3-9 and 4.3-10 provide max and average values for normal mode 

vehicles only. The maximum values for the normal vehicles are generally lower with 

winter mean values higher than summer. 

Table 4.3-9. Seasonal Impact on Observed Maximum Concentrations (Units are ppbv, 

except as noted), Normal Mode Vehicles Only. 

Normal Only Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

Kitchen Max-S 0.29 4.87 14.35 1.80 6.44 2.48 1.59 0.81 95.59 519.70

Max-W 1.55 11.17 14.80 2.76 8.50 3.44 13.27 3.07 31.31

Garage Max-S 4.76 21.02 48.73 6.99 19.92 7.73 8.95 3.86 58.53 27.70

Max-W 8.47 24.68 34.61 6.05 22.78 8.04 185.63 39.16 54.78

Table 4.3-10. Seasonal Impact on Observed Average Concentrations (Units are ppbv, 

except as noted), Normal Mode Vehicles Only. 

4-8
Normal Only Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

Kitchen Ave-S 0.16 3.25 11.54 1.39 4.58 1.97 0.56 0.39 53.33 339.25

Ave-W 0.43 4.38 7.24 1.31 4.12 1.72 3.76 0.92 14.54

Garage Ave-S 1.87 8.72 20.36 3.06 8.67 3.51 2.47 1.82 26.44 17.35

Ave-W 2.35 8.15 14.44 2.54 9.00 3.39 36.64 6.45 18.72

4.3.3.3 Fuel and Vehicle Effects 

This section addresses fuel, vehicle, and operational mode separately for all 

seasons. For the sedan, Table 4.3-11 indicates highest mean MTBE values for Houston 

fuel and EtOH for Chicago, as expected, with high-emitter/malfunction effects strongest 

in the garage. 

Table 4.3-11. Effect of Fuel and Operational Mode of the Sedan on Observed Levels in 

the Kitchen and Garage (Units are ppbv, except as noted). 

. Location Fuel Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

Normal Garage Atlanta 0.55 2.40 6.09 0.98 3.24 1.38 0.82 0.31 7.16

Houston 0.95 3.56 9.78 1.51 5.20 2.08 10.81 0.56 22.25

Chicago 1.19 3.40 8.29 1.39 4.91 2.06 0.48 0.45 11.75 27.70

Kitchen Atlanta 0.06 2.01 8.42 1.03 3.61 1.45 0.10 0.10 63.45

Houston 0.24 2.82 7.49 1.10 3.69 1.59 3.35 0.52 24.01

Chicago 0.06 3.82 8.45 1.26 4.40 1.91 0.27 0.29 13.38 158.80

Malfunction Garage Atlanta 1.42 26.80 44.40 4.03 13.08 4.86 16.67 6.27 23.35

Houston 2.54 12.45 25.68 4.20 14.11 5.53 49.97 13.29 30.72

Chicago 1.92 9.54 11.26 1.65 5.64 2.18 1.13 12.16 13.08 19.00

Kitchen Atlanta 0.86 9.13 15.11 2.06 6.47 2.92 0.35 5.59 21.99

Houston 0.23 4.14 9.68 1.74 5.42 2.65 10.19 1.30 26.19

Chicago 0.23 2.81 6.04 1.03 3.51 1.53 0.30 0.76 25.93 670.20

Budi13 = 1,3BD; Benze = benzene; Tolue = toluene, Mp_xyl = m,p-xylene; o_xyl = o-xylene, 

Formal = formaldehyde; EtOH = ethanol 

For the truck, Table 4.3-12 indicates lesser fuel impacts on normal mode garage 

levels than for the sedan. For the malfunction mode, Houston fuel garage values exceed 

those of the other two fuels. 

Table 4.3-12. Effect of Fuel and Operational Mode of the Truck on Observed Levels in 

the Kitchen and Garage (Units are ppbv, except as noted). 

. Location Fuel Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

Normal Garage Atlanta 2.40 11.28 26.45 3.79 11.05 4.32 0.44 2.13 38.17

Houston 1.39 9.69 24.99 3.83 11.12 4.46 10.46 2.15 38.12

Chicago 2.55 9.64 15.61 2.99 8.56 3.41 1.74 2.87 0.00 7.00

Kitchen Atlanta 0.12 1.65 8.23 0.83 2.58 1.04 0.10 0.28 35.68

Houston 0.37 4.57 9.68 1.62 4.85 2.28 7.20 0.82 45.47

Chicago 0.92 8.02 14.08 2.27 6.97 2.78 1.95 1.94 21.61 519.70

Malfunction Garage Atlanta 3.74 16.19 26.42 3.87 12.22 4.58 0.38 8.03 45.11

Houston 22.41 45.06 64.14 12.14 36.75 13.70 139.63 33.88 114.49

Chicago 2.73 7.72 11.55 1.85 5.87 2.16 0.06 2.52 32.96 5.80

Kitchen Atlanta 0.24 3.25 7.65 1.99 5.67 3.15 0.13 0.68 42.56

Houston 0.80 4.23 9.05 1.42 4.25 1.89 4.57 1.33 52.72

Chicago 0.11 4.11 7.29 1.45 4.67 1.92 0.03 0.28 29.37 414.10

4-9
 Figure 4.3-1 illustrates the effect of fuel and mode (N-normal, F-malfunction) on 

mean garage values averaged across vehicle and season. Figure 4.3-2 shows the kitchen 

values. Both figures report relatively high 1,3-BD values for the Houston fuel high 

emitter mode. Since both are also associated with high MTBE values, these 1,3-BD 

values are suspect as discussed earlier and in Chapter 1. The same caveat applies to 

Figures 4.3-3 and 4.3-4. 

0

10

20

30

40

50

60

70

80

90

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

compound

ppbv

Atlanta-N

Atlanta-F

Houston-N

Houston-F

Chicago-N

Chicago-F

Figure 4.3-1. Effect of fuel and mode on observed concentrations in the garage. The 

legend “N” is normal and “F” is malfunction. The 1,3-BD value for Houston-F is suspect. 

4-10
0

5

10

15

20

25

30

35

40

45

50

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

compound

ppbv

Atlanta-N

Atlanta-F

Houston-N

Houston-F

Chicago-N

Chicago-F

339,542

Figure 4.3-2. Effect of fuel and mode on observed concentrations in the kitchen. The 

legend “N” is normal and “F” is malfunction. The 1,3-BD value for Houston-F is suspect. 

The kitchen concentrations are dominated by HCHO and EtOH, but high 

background levels indicate kitchen sources rather than the garaged vehicles. 

The effect in the garage is expected to be more directly correlated with the 

vehicle. Figure 4.3-3 shows the concentrations seen in the garage only for the sedan, 

looking at the effect of the fuel and operational mode. The same presentation for the truck 

only is in Figure 4.3-4. 

4-11
0

10

20

30

40

50

60

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

compound

Garage, ppbv

Atlanta-N

Atlanta-F

Houston-N

Houston-F

Chicago-N

Chicago-F

Figure 4.3-3. Effect of fuel and mode on observed sedan garage levels. The legend “N” is 

normal and “F” is malfunction. The 1,3-BD level for Houston-F is suspect, see text. 

0

20

40

60

80

100

120

140

160

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO,ppm Formal EtOH

compound

Garage, ppbv

Atlanta-N

Atlanta-F

Houston-N

Houston-F

Chicago-N

Chicago-F

Figure 4.3-4. Effect of fuel and mode on observed truck garage levels. The legend “N” is 

normal and “F” is malfunction. The 1,3-BD level for Houston-F is suspect, see text. 

4-12
4-13

Comparison of 1,3-BD, BTEX and CO background concentrations with garage 

and kitchen concentrations for each test is shown in Figure 4.3-5 and Figure 4.3-6 for 

Summer 2002 and Winter 2005, respectively. In general, these figures indicate 

compound range rankings of garage » kitchen ~ background, especially for vehicle in the 

normal mode. For vehicles in high emitting mode, the increase in kitchen levels could be 

seen. In Winter 2005, a few high background samples were observed, possibly due to a 

prolonged storage of a plastic gasoline container in the garage. 
0

50

100150200250300350400

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

K-BACKG

G -BACKG

K-TE S T

G -TE S T

ppbv

budi13 mtbe benze tolue etbz mp_xyl o_xyl CO

Toyota, norm al 

Toyota, m alfunction

Atlanta (Baseline) Fuel

Truck, norm al 

Truck, m alfunction 

Toyota, norm al 

Toyota, norm al 

Truck, m alfunction Toyota, 

m alfunction

Toyota, m alfunctio

Truck, norm al 

Houston (M TBE) Fuel

Chicago (Ethan

Figure 4.3-5. Concentrations of 1,3-butadiene, MTBE and BTEX and CO as measured from canisters in the garagkitchen in Summer 2002 

4-14
4-15

0

50

100150200250300

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

K-TEST

G-TEST

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

G-TEST

K-TEST

G-BACKG

K-BACKG

ppbv

budi13 mtbe benze tolue etbz mp_xyl o_xyl CO_ppm

Atlanta (Baseline) Fuel

Toyota, 

normal Toyota, 

malfunction

Truck, 

normal 

Truck, 

malfunction 

Houston (M TBE) Fuel

Toyota, 

normal 

Toyota, 

malfunction Truck, normal 

Truck, 

malfunction 

Ch

Toyota, 

normal T

ma

M

M

Figure 4.3-6. Concentrations of 1,3-butadiene, MTBE and BTEX (A) and CO (B) as measured from canisters in th

adjacent kitchen in Winter 2005. M=sample missing or invalid. 
4.3.3.4 Comparison with Emissions Data 

 There are five distinct garage scenario phases after the background sample as described 

in Table 4.2-2. The first phase, hot soak, is best compared to the hot soak SHED test run by 

SwRI. Benzene canister values are compared in Figure 4.3-7. While there does not appear to be a 

strong correlation, the canister samples collected in the garage average over all five scenarios, 

not only hot soak. The high outlying points come from the truck in high emitter mode and are 

expected to be high. SPME samples taken every half-hour correspond better with the phases of 

the experiment. Benzene winter SPME values for hot soak phase are compared with SHED 

values in Figure 4.3-8A (all samples) and 4.3-8B (outliers removed). Although the correlation is 

not very good for all samples (A), it improves after removing two outliers from the truck in high 

emitter mode (B). The high emitting vehicles are generally not stable and the SHED results may 

be very different from the garage, due to different time and location. 

 

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140 160

SHED results, mg

Garage, ppbv

Figure 4.3-7. Comparison of SHED results with the observed canister concentration in the garage 

for benzene. 

0

5

10

15

20

25

30

35

0 20 40 60 80 100 120 140 160

SHED, mg

Garage hot soak, ppbv (by SPME)

y = 0.1317x + 4.8305

R2

 = 0.4323

0

5

10

15

20

25

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0

SHED, MG

Garage hot soak, ppbv (SPME)

A B

Figure 4.3-8. Comparison of the SHED results with the observed SPME hot soak concentration 

in the garage for benzene A: all data, B: two outliers removed. 

4-16
Cold start 1,3-BD and benzene canister values can be compared to the FTP Bag 1 data in Figures 

4.3-9 and 4.3-10, respectively. Garage 1,3-BD values appear insensitive to FTP levels. It is 

possible that this may reflect another 1,3-BD analytical challenge from NO2 scavenging in the 

FTP sample; the high point in Figure 4.3-7 is also suspect since 1,3-BD occurs concurrent with 

high MTBE levels. The Figure 4.3-8 garage benzene scatter is similar to 1,3-BD and also appears 

insensitive to FTP levels; however, benzene is stable in canisters and these values should be 

accurate. Figure 4.3-11 compares garage SPME cold start values to FTP Bag 2 values. This 

comparison trends upwards with garage values increasing with increasing FTP emissions, 

although not strongly. 

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80

FTP Bag 1, mg/mi

Garage, ppbv

Figure 4.3-9. Comparison of FTP Bag 1 emissions and observed garage levels of 1,3-BD. 

4-17
0

10

20

30

40

50

60

70

0 50 100 150 200 250

FTP Bag 1, mg/mi

Garage, ppbv

Figure 4.3-10. Comparison of FTP Bag 1 benzene emissions and observed garage levels. 

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

FTP Bag 1, mg/mi

Garage, cold start, ppbv (by SPME)

Figure 4.3-11. Comparison of hot soak FTP Bag 1 benzene emissions and observed SPME 

garage values. 

4-18
4.3.3.5 Relationships of Garage and Kitchen Concentrations 

 Kitchen values would be expected to increase with increasing garage levels from vehicle 

and fuel container sources. Based on their high background levels, EtOH and HCHO would not 

be good candidates for tests. Three other species 1,3-BD, CO, and benzene are plotted in Figures 

4.3-12, 4.3-13 and 4.3-14, respectively. 

 Figure 4.3-12A shows a weak 1,3-BD trend which seems to be driven mostly by outliers 

associated with high level MTBE interference. As explained in Chapter 1 (page 1-6) elevated 

MTBE concentrations biases measured 1,3-BD levels upwards, due to the thermal decomposition 

of MTBE (in the order of 1 to 5 %) in a GC injector. The removal of two outliers (for the truck 

with MTBE fuel in malfunction mode) eliminates any correlation between garage and kitchen 

concentrations (Figure 4.3-12B). 

 Figure 4.3-13 trends toward a CO insensitivity to garage concentrations. The high value 

occurred for the sedan in malfunction mode; the continuous data show a 100 ppm CO spike at 

the beginning of the cold-start phase that may have penetrated through a briefly opened kitchen 

door. Figure 4.3-14 shows that there is no correlations between kitchen and garage benzene 

concentrations. However, it has to be pointed out that these kitchen – benzene correlations are 

shown for the time-integrated canister samples that were collected over 2.5 hr duration of the 

experiment. During this time several 30-min scenarios were executed, as shown in Table 4-2.2. 

The differences in ventilation conditions between garage and kitchen are the most probably 

responsible for the lack of correlations between species measured from canisters. 

y = 0.0298x + 0.2539

R2

 = 0.2034

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 10 20 30 40

y = 0.0141x + 0.2965

R2

 = 0.002

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0123456

Garage Concentrations, ppbv

Kitchen Concentrations, ppbv

B

Garage Concentration, ppbv

Kitchen Concentration,ppbv

A

Figure 4.3-12. Comparison of garage and kitchen concentrations for 1,3-BD. A – all data, Bwith two outliers removed (see text). 

4-19
y = 0.04x + 0.84

R2

 = 0.05

0

2

4

6

8

10

12

0 10 20 30 40 5

Garage Concentration, ppbv

Kitchen Concentration,ppbv

0

 

Figure 4.3-13. Comparison of garage and kitchen concentrations of carbon monoxide. 

y = 0.04x + 3.61

R2

 = 0.06

0

2

4

6

8

10

12

0 20 40 60

Garage Concentration, ppbv

Kitchen Concentration,ppbv

80

Figure 4.3-14. Comparison of garage and kitchen concentrations of benzene. 

4-20
4.4 Discussion 

 The objective of this section was to test the effects of attached garage on indoor home 

levels of fuel and exhaust components. The experiment simulates common activities such as 

coming home with a warm car or leaving home after starting a cold vehicle. 

 Various parameters are assessed in section 4.3 to determine their effects on air levels in 

the adjacent room (here a kitchen) connecting to the garage. Two target components, HCHO and 

EtOH, had high kitchen background values indicating indoor sources of these materials. 

Average HCHO levels were higher in summer than winter, consistent with enhanced off-gassing 

of building materials and/or penetration of ambient photochemical HCHO. It has been also 

reported (Reiss et al, 1995; Wang and Morrison, 2006; Weschler, 2006) that a larger fraction of 

indoor HCHO and other oxygenated-low molecular weight hydrocarbons can result from 

heterogeneous processes. Ozone originating from outdoors can be deposited onto indoor surfaces 

and react with different materials to produce low molecular weight organic acids and aldehydes. 

The concentrations of these species are higher during the summer when more ozone penetrates 

indoors. 

 Tables 4.3-8 to 4.3-10 show a seasonal impact where kitchen BTEX, MTBE and CO 

species are higher in winter than summer. The exception is toluene which shows a minimal 

difference that actually averages higher in summer for normal mode vehicles. This is consistent 

with indoor toluene emissions from paints, adhesives, cleaning, and personal care products. 

Tables 4.3-8 and 4.3-9 focus on normal mode vehicles to remove the variability of high emitter 

modes in assessing the seasonal effect. Since many species higher in the winter come from both 

evaporative and exhaust emissions, it is possible that winter enhanced fuel RVP contributes to 

the apparent seasonal effect. In addition, a large number of studies have shown that home air 

exchange rates are typically lower during the winter. This would result in longer residence times 

(thus accumulation) of pollutants generated in the garage and further infiltration to the kitchen 

area. 

 Tables 4.3-10 and 4.3-12 show vehicle data separately for each fuel. MTBE and ethanol 

are highest for fuels containing those species, as anticipated. Otherwise, there is not a strong fuel 

effect across vehicles. 

 FTP exhaust and SHED evaporative emissions were tested for each vehicle, fuel, and 

emissions mode, and compared to observed levels in the garage. These comparisons are 

challenging in that canisters integrate across hours covering not only hot soak, adjustments to the 

air exchange, and cold start. Concurrent SPME samples are collected for each condition. 

However, neither canister nor SPME samples show strong correlations with hot soak emissions 

(Figures 4.3-5 to 4.3-8), although cold-stabilized FTP Bag 2 benzene appears reasonably 

correlated to the cold-start SPME (Figure 4.3-9). 

 Correlations of kitchen levels with garage concentrations are presented in Figures 4.3-12 

to 4.3-14. These plots evidence weak correlations and could not be used to predict kitchen 

exposures from garage levels. 1,3-BD (Figure 4.3-12) and benzene (Figure 4.3-14) may trend 

weakly upwards, with kitchen levels increasing with garage levels; however CO (Figure 4.3-13) 

4-21
does not. Tables 4.3-6 and 4.3-7 indicate (HCHO & EtOH excepted) compound range rankings 

of garage » kitchen ~ background, especially for vehicle in the normal mode. For vehicles in 

high emitting mode, the increase in kitchen levels is seen from Figures 4.3-5 and 4.3-6. 

4.5 References: 

Reiss, R., Ryan, P., Tibbetts, S. E., and Koutrakis, P., Measurement of Organic Acids, 

Aldehydes, and Ketones in Residential Environments and their Relationship to Ozone, Journal of 

the Air and Waste Management Association, 45, 811 (1995). 

Wang, H., G.C. Morrison. Ozone-initiated secondary emission rates of aldehydes from indoor 

surfaces in four homes. ES&T 40: 5262-68 (2006) 

Weschler, C.J. Ozone’s impact on public health: contributions from indoor exposures to ozone 

and products of ozone-initiated chemistry. Environ.Health Perspective 141: 1489-96 (2006). 

4-22
5. Effect of Ventilation, Proximity, and Emission Levels on In-Cabin 

Exposures of Trailing Vehicle. 

5.1 Introduction 

 This chapter describes experiments designed to determine the relationships 

between ventilation, proximity, fuel, and emission levels of a leading vehicle on in-cabin 

exposures within a trailing vehicle. The same vehicles, fuels and induced malfunctions 

used for this chapter are used for Chapter 4. These measurements are part of the program 

described in the executive summary and Chapter 1. 

 As in the preceding chapter, the vehicles used are a sedan and a pickup truck; the 

fuels used are either a conventional fuel (without oxygenate), an ethanol fuel, or an 

MTBE fuel. The vehicles are tested in a normal and induced-malfunction mode with nonmethane hydrocarbon (NMHC) emissions of about 2 g/mile by Federal Test Procedure 

(FTP). 

 The experiments were performed in summer (June-July 2002) and winter 

(February-March 2005). 

5.2 Experimental 

 The Southwest Research Institute (SwRI) procured two test vehicles and 

determined their evaporative/tailpipe emissions in the normal/malfunction modes using 

the three test fuels. The test vehicles, a sedan and full-sized V8 truck, were chosen within 

the 1993-1996 model years from vehicles with 90,000-110,000 odometer miles. The 

chosen 1993 Toyota Camry (2.2L 4-cylinder engine) and 1995 Ford F150 Pickup truck 

(5.0L V8 engine) were operated in normal, as purchased, modes and in “high emitter” 

modes with the catalytic converter removed and emission levels above 2 grams per mile 

NMHC as measured on the FTP driving cycle. While converter removal sufficed for the 

F150 truck, a calibrated manifold leak was also needed to achieve the 2g/mile Camry 

emissions. SwRI determined dynamometer FTP emissions for each vehicle with all three 

fuels in the two emission modes (24 tests). Emission control components could be 

reproducibly adjusted to represent normal and reasonable high-end approximations (2 

g/mile) of real world exhaust emissions. Test vehicle evaporative emissions were also 

measured for test fuels in the two emission modes as reported in Chapter 4. 

 Regulated exhaust emissions (THC, NMHC, CO, NOx), fuel economy, and 

specific VOCs (MTBE, EtOH, BTEX, 1,3-BD, HCHO) were determined in the 

dynamometer FTP tests. During hot-soak SHED tests, THC and specific VOCs (minus 

HCHO) were determined. 

 The FTP exhaust emission test uses the 1372 second Urban Dynamometer 

Driving Schedule (UDDS) that is divided into cold/start transient 505 (Bag 1) and cold 

stabilized 867 (Bag 2) second segments. This portion of the FTP is followed by a 10-

minute soak and a hot/start transient 505 (Bag 3) test. The FTP evaporative emission test 

5-1
includes one hour Diurnal Heat Build (DHB) and Hot Soak Loss (HSL) tests. THC/VOC 

emissions are recorded during the HSL segment of the test. Prior to the FTP cold-start 

exhaust test, the DHB is conducted by fueling the test vehicle to 40 percent of tank 

capacity with fuel < 55°F, attaching a heating blanket outside the fuel tank, placing a 

thermocouple in the tank fuel, hooking it up to computer control, and beginning the test 

as fuel reaches 60°F (increasing at 0.4°F per minute for the 60-minute test to a 84°F final 

temperature). 

 In the HSL segment, conducted immediately following exhaust emission testing, 

the vehicle is driven into an evaporative emission enclosure and allowed to “soak” in the 

enclosure for one hour. THC/VOC emissions are measured at the beginning and end of 

the one-hour segment and hot soak evaporative emissions are calculated. 

5.2.1 Fuel Testing 

 Test fuel samples were subject to standard tests for Reid Vapor Pressure (RVP), 

distillation range, Specific Gravity, Sulfur, Benzene, HC Category (saturates, olefins, 

aromatics), Oxygenated species (MTBE/EtOH), carbon weight percent, hydrogen weight 

percent, oxygen weight percent, and octane number. These results are presented in 

Chapter 4, Table 4.3-1. 

5.2.2 Relationship between Exhaust Emission Rates and In-Cabin Exposure - 

Trailing Vehicle Test 

5.2.2.1 Test Protocol 

 The two test vehicles were used as characterized sources of measured in-cabin 

exposures for an instrumented trailing vehicle. SwRI procured a 1996 Chrysler Minivan 

which DRI instrumented as the trailing vehicle (described in Chapter 1) that was driven 

behind the test vehicles over a remote, paved, two-lane, farm-to-market roadway loop 

(described below) for test periods up to 3 hours. Initial measurements made absent the 

test vehicles established background levels. Trailing vehicle tests then implemented far, 

near, and passing scenarios at low (30 mph) and high speeds (60 mph) as noted in Table 

5.2-1. During 'far' scenarios, ‘safe’ vehicle spacing (defined as one car length - 10 feet - 

for each 10 mph) was maintained. During the 'near' scenario, the trailing vehicle 

tailgated the lead vehicle, following at a close distance deemed 'safe' by the professional 

drivers under prevailing traffic and meteorological conditions. During the “passing” 

scenario, the trailing vehicle split its time between tailgating the lead vehicle and 

‘passing,’ immediately behind the lead vehicle but in the adjacent lane. A final idling test 

was conducted while the trailing vehicle was parked on the road shoulder downwind and 

closely behind the parked idling lead vehicle. High (10 min) and low (10 min) ventilation 

conditions were used during all (including idling) tests. 

 Table 5.2-1 details the trailing vehicle protocol. Trailing vehicle in-cabin TVOC 

[ppbRAE-PID (photoionization detector)], CO (Langan T15), BTEX (Kore200MS), and 

HCHO (A-Ω) were continuously monitored. Integrated VOC/NMHC (canister), 

5-2
HCHO/CH3CHO (DNPH cartridge), and EtOH (sorbent tube – EtOH fuel only) samples 

were also collected. SPME BTEX samples were collected every 10 min. Appendix B 

describes sampling and analytical methods in detail. 

 The trailing vehicle tests were conducted south of San Antonio, TX on county 

roads 462 and 2779 off IH 35 in the vicinity of Moore, Big Foot, and Jones Mound, 

Texas. The position of the trailing vehicle was recorded continuously by a Garmin 12XL 

GPS unit recording in UTM using NAD83/WGS84. Speed and direction of the vehicle 

between any two points can be located on a map as illustrated in the June 19, 2002 test 

Figures 5.2-1, -2. The mapping software also contains a digital elevation model that 

creates elevation profiles as shown in Figure 5.2-3. The change in elevation over the 

14.5-mile driving route is approximately 100 feet. 

Table 5.2-1. Protocol for Trailing Vehicle Tests 

Time 

Min. 

Speed 

Mph 

Ventilation 

Setting Distance Notes 

Continuous 

Instruments 

SPME Time 

Integrated 

10 high high background Y 1 1 

10 low high far Y 1 

10 low high near Y 1 

10 low high passing Y 1 

10 high high far Y 1 

10 high high near Y 1 

10 high high passing Y 1 

10 low low far Y 1 

10 low low near Y 1 

10 low low passing Y 1 

10 high low far Y 1 

10 high low near Y 1 

10 high low passing Y 1 

One sample 

in Summer 

2002. 

Two 

samples, at 

high/low 

ventilation, 

for Winter 

2005. 

10 idle low adjacent Y 1 

10 idle high adjacent 

Vehicles:Toyota 

Camry and Ford 

Pick-up truck, in 

normal and 

malfunction mode. 

Fuels: Atlanta 

(conventional), 

Houston (MTBE), 

Chicago (ethanol) 

Y 1 

1 

5-3
Figure 5.2-1. Map of Driving Test Location near San Antonio. The blue markers indicate 

the location of the driving tests. 

5-4
Figure 5.2-2. Map of Driving Test Location near Moore, TX. 

Figure 5.2-3. Elevation Profile of the Driving Route near Moore, TX. 

5-5
5.3 Results 

 An initial summary of the trailing vehicle study findings, averaging across all 

vehicles, emission modes, and fuels, is presented below. The lead vehicles and fuels are 

the same as described in Chapter 4; Section 4.3.1 presents the fuel analyses and Section 

4.3.2 the FTP exhaust and evaporative vehicle emissions tests. 

 Note the protocol changes between Summer 2002 and Winter 2005 tests: in the 

Summer tests only half the sample days were begun with a background sample; in the 

Winter tests separate in-cabin samples were taken for the high ventilation and low 

ventilation measurements as detailed in Table 5.2-1. 

5.3.1 Background and Overall Concentrations 

 The background sample results from the summer and winter samples are 

presented in Table 5.3-1. The percent standard deviations are relatively low, suggesting 

that the backgrounds are relatively stable. The MTBE deviations are highest likely 

because this compound is principally present only in the Houston fuel. Background 

MTBE ranged from 0 to 0.21 ppbv. There was only one EtOH background measurement 

for the Summer 2002 (261 ppb) and three valid measurements for Winter 2005. The high 

2002 EtOH value could be connected with the presence of four people in the vehicle 

cabin and/or the presence of the continuous formaldehyde analyzer. The winter values 

range from 9 to 44 ppb and seem to be more reliable. 

Table 5.3-1. Summary of Summer and Winter Background Concentrations. 

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Formal EtOH

Mean Summer (n=6) 0.02 0.27 0.44 0.07 0.17 0.11 0.06 0.13 5.80 2

% std dev 53% 26% 15% 24% 46% 48% 131% 18% 84% (n=1)

Mean Winter (n=12) 0.03 0.33 0.60 0.12 0.43 0.19 0.07 0.22 5.76 22.07

% std dev 47% 43% 68% 62% 65% 69% 107% 36% 61% 88%

Mean all 0.03 0.31 0.55 0.10 0.35 0.16 0.07 0.19 5.78 81.

% std dev 50% 40% 62% 62% 77% 71% 111% 40% 67% 147%

61

80

Budi13 = 1,3BD; Benze = benzene; Tolue = toluene, Mp_xyl = m,p-xylene; o_xyl = o-xylene, 

Formal = formaldehyde; EtOH = ethanol 

 In Figure 5.3-1 the values for formaldehyde are divided by 10 to fit on the same 

scale as the rest of the species and the EtOH values are not shown. Generally speaking 

the in-cabin background values are < 1 ppbv, with the exception of HCHO and EtOH, 

and relatively consistent from summer to winter. 

 In-cabin HCHO measurements likely included contributions from photochemical 

formation from ambient VOCs and in-cabin fabric component degassing of this species. 

As mentioned in Chapter 1 and 4, EtOH may be emitted from people (as a metabolic 

product for certain food types), foods, cleaning& personal care products, etc. 

5-6
5-7

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Forma

Concentration, ppbv or ppm

l/10

Mean Summer (n=6) Mean Winter (n=12)

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Formal EtOH

Mean Summer (n=11) 0.50 1.17 2.01 0.36 1.07 0.49 0.38 0.85 6.78 2308.07

% std dev 111% 84% 70% 79% 77% 76% 269% 87% 50% 102%

Mean Winter (n=22) 0.48 1.01 1.75 0.32 1.11 0.43 0.31 1.36 4.32 1.49

% std dev 105% 81% 81% 85% 81% 84% 219% 91% 84% 48%

Mean all 0.49 1.06 1.84 0.33 1.10 0.45 0.34 1.19 5.14 770.35

% std dev 105% 81% 76% 82% 79% 80% 238% 93% 72% 214%

Figure 5.3-1. Comparison of Summer and Winter Background Concentrations with 

Standard Deviations. HCHO is divided by 10 for scale. 

 Mean concentrations over all tests are presented in Table 5.3-2. Standard 

deviations are expressed as a percent of test value. As with the background 

concentrations, MTBE likely shows the greatest variability since it was prominent in only 

one fuel. Also, EtOH Summer 2002 measurements (3 values) are most probably artifact, 

whereas Winter 2005 data (6 measurements) seem to be much more reliable. 

Table 5.3-2. Summary of Test Concentrations for Summer, Winter and Overall. Units are 

ppbv, except CO as noted. 

Budi13 = 1,3BD; Benze = benzene; Tolue = toluene, Mp_xyl = m,p-xylene; o_xyl = o-xylene, 

Formal = formaldehyde; EtOH = ethanol 

 Figure 5.3-2 and 5.3-3 shows the CO, MTBE and BTEX concentrations for each 

test in the Summer 2002 and Winter 2005, respectively. 
0

102030405060

BACKG.

TEST

IDLE

TEST

IDLE

TEST

IDLE

BACKG.

TEST

IDLE

BACKG.

TEST

IDLE

TEST

IDLE

TEST

IDLE

TEST

IDLE

BACKG.

TEST

IDLE

BACKG.

TEST

ppbv

budi13 mtbe benze tolue etbz mp_xyl o_xyl CO

Truck, m alfunction

Toyota, norm al 

Toyta, m alfunction

Truck, norm al 

Toyota m alfunction 

Truck m alfunctio

Toyota norm al 

Toyota, m alfunction 

Toyota, norm al 

(M )

Truck, norm al 

Atlanta (Baseline) Fuel Houston (MTBE) Fuel Chicago (Ethanol) 

Figure 5-3-2. Concentrations of 1,3-BD, MTBE and BTEX (A) and CO (B) as measured in the cabin of the traili

2002 

5-8
5-9

05

1015202530354045

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

TEST_LV

IDLE

BACKG

TEST_HV

ppbv

budi13 mtbe benze tolue etbz mp_xyl o_xyl CO_pp

Atlanta (Baseline) Fuel

Toyota, 

normal 

Toyota, 

malfunctio

Truck normal

Truck malfunction

Toyota, normal 

Toyota, malfunctio

M

Truck normal

Truck malfunction

Houston (MTBE) Fuel

Toyota, 

normal 

Toymalf

C

Figure 5-3-3. Concentrations of 1,3-BD, MTBE and BTEX and CO as measured in the cabin of the trailing vehi
Figure 5.3-4 compares summer and winter concentrations which, like background, are 

similar (EtOH data not shown). 

0

1

2

3

4

5

6

7

8

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Formal

Concentration, ppbv or ppm

Mean Summer (n=11) Mean Winter (n=22)

Figure 5.3-4. Comparison of Summer and Winter Concentrations for the Trailing tests. 

 Summer background and test values, excluding HCHO and EtOH, are compared 

in Figure 5.3-5. Test values show a substantial increase over background. Correlating all 

summer species except HCHO and EtOH against their background values gives a slope 

of 0.24 (r-square = 0.93). 

 Winter background and test values are presented in Figure 5.3-6, omitting HCHO 

and EtOH. The observation that the winter HCHO values were, on average, lower than 

background values suggests that most of the HCHO observed was not coming from the 

lead vehicle but possibly from photochemical or off-gassing sources (e.g., fabrics) inside 

the trailing vehicle. EtOH background values were higher than test values, which suggest 

some initial off-gassing of EtOH in the vehicle cabin (since background sample was 

collected at the beginning of each experiment). The correlation of all winter species 

values except HCHO and EtOH against their background values had a slope of 0.31 (rsquare = 0.73). 

5-10
0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm

Concentration, ppbv or ppm

Summer Background Summer Tests

Figure 5.3-5. Comparison of Summer Background and Test Values. 

0

1

1

2

2

3

3

4

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm

Concentration, ppbv or ppm

Winter Background Winter Tests

Figure 5.3-6. Comparison of Winter Background and Test Values. 

 

5-11
 Table 5.3-3 presents the concentrations and percent standard deviations observed 

during the idle tests. These values showed more of a range and larger deviations than 

either the background or the driving tests. HCHO again appears to be an outlier with the 

lowest deviation of any of the species, likely indicating that this species is not coming 

predominantly from the upwind lead vehicle. EtOH values for Summer 2002 (3 

measurements) are most probably artifact and the Winter 2005 values (4 measurements) 

are more realistic. Since the main difference between the Summer 2002 and Winter 2005 

experiments was the absence of the continuous formaldehyde and MS200 KORE mass 

spectrometer in the trailing vehicle, it is possible that one of these instruments (most 

probably the continuous formaldehyde analyzer, since it is based on the wet method) was 

out-gassing EtOH. 

Table 5.3-3. Summary of Concentrations Observed During Idle Tests. Units are ppbv 

except CO as noted. 

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Formal EtOH

Mean Summer (n=11) 1.55 3.67 4.84 0.80 2.42 1.00 1.48 2.13 8.71 1030.68

% std dev 138% 114% 101% 106% 106% 99% 195% 156% 53% 59%

Mean Winter (n=22) 0.66 2.63 3.07 0.48 1.70 0.65 0.44 3.17 6.46 3.86

% std dev 162% 140% 140% 116% 117% 101% 200% 119% 42% 61%

Mean all 1.14 3.19 4.03 0.65 2.09 0.84 1.00 2.61 7.68 517.

% std dev 154% 123% 115% 112% 110% 102% 222% 134% 52% 131%

27

Budi13 = 1,3BD; Benze = benzene; Tolue = toluene, Mp_xyl = m,p-xylene; o_xyl = o-xylene, 

Formal = formaldehyde; EtOH = ethanol 

5.3.2 Vehicle and Fuel Effects 

 The preceding section assessed overall mean concentrations in the trailing vehicle 

cabin, averaging across vehicles, emission modes and fuels; this section will separately 

consider these parameters. 

 Table 5.3-4 details the effects of changing vehicle, fuel, and emission mode. 

 The first two rows distinguish the truck and the car, averaged over all fuels and 

modes. These values are very similar, showing little effect of the vehicle by itself. 

 The next three rows distinguish the fuels, averaging over the vehicles and modes. 

The Atlanta fuel results in higher BTEX concentrations in the trailing vehicle cabin, 

which is consistent with higher aromatic contents of Atlanta fuel, especially in summer 

(see Table 4.3-1). 

 The next two rows distinguish the normal and high emitter modes, averaging over 

the vehicles and fuels. The values clearly differ, with the high emitter mode values much 

higher than for the normal emitter mode. 

 The last line in this table presents the percent standard deviations of the high 

emitter values that are very similar, with the anticipated exception of MTBE which is 

larger due to its predominant occurrence in only one of the three fuels. 

5-12
 Figure 5.3-7 presents the effect of normal versus high emitter vehicle on the 

trailing vehicle in-cabin concentrations in a scatter plot for all species except HCHO and 

EtOH. Cabin levels of HCHO and EtOH were omitted since in-cabin upholstery and 

occupant sources of these compounds predominate penetration of outdoor levels. The 

slope indicates that in-cabin values measured during trailing the vehicle in high emitter 

mode are about twice those found for the normal mode. Since lead vehicles in these tests 

are converted between ‘normal’ and ‘high emitter’ states by disabling control devices, not 

by mis-tuning the engines or opening fuel line leaks, exhaust emissions should remain 

roughly proportionate between both operational modes. 

Table 5.3.4. Effect of Vehicle, Fuel, and Operational Mode. Units are ppbv, except CO as 

noted. Number of measurements = n 

Vehicle, Fuel & 

Mode 

Budi13 Benze Tolue Etbz Mp_xy

lene 

o_xyl MTB

E 

CO, 

ppm 

Form

-al. 

Truck only (n=12) 0.42 1.14 2.06 0.38 1.24 0.52 0.15 1.08 4.23

Car only (n=12) 0.59 1.13 1.87 0.33 1.11 0.45 0.53 1.42 6.13

Atl fuel only (n=8) 0.53 1.44 2.79 0.51 1.66 0.68 0.14 1.41 5.99

Hou fuel only (n=8) 0.56 1.05 1.63 0.35 1.19 0.50 1.28 1.10 5.88

Chi fuel only (n=8) 0.48 0.87 1.32 0.20 0.66 0.28 0.03 1.22 4.20

Normal only (n=12) 0.06 0.46 1.05 0.21 0.73 0.31 0.16 0.41 5.21

High emitter only 

(n=12) 

1.01 1.85 2.92 0.52 1.64 0.67 0.56 2.18 5.35

St Dev high emitter 

only 

26% 35% 40% 43% 43% 45% 199% 42% 55%

y = 2.2228x + 0.4798

R2

 = 0.6929

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Normal Emitter

High Emitter

Figure 5.3-7. Scatter plot of Normal Emitter and High Emitter Mean In-cabin Values for 

all species except HCHO and EtOH. 

5-13
 Looking at the high emitter mode only, Table 5.3-5 presents high emitter mean incabin values for each fuel separately. MTBE values present the clearest difference. This 

is expected based on the fuel composition. The other species show relatively little 

difference. EtOH values are not shown, due to the Summer 2002 artifact. 

Table 5.3-5. Influence of high emitting vehicles and each fuel on trailing vehicle in-cabin 

concentrations. Units are ppbv except CO as noted. 

Mode, Fuel Budi13 Benze Tolue Etbz Mp_x

ylene 

o_xyl MTBE CO, 

ppm 

Formal 

High Emiter, 

Atlanta (n=4) 

1.02 2.35 3.97 0.67 2.12 0.85 0.03 2.48 5.04

High Emiter, 

Houston (n=4) 

1.18 1.76 2.65 0.61 1.98 0.82 2.63 1.82 5.81

High Emiter, 

Chicago (n=4) 

0.91 1.40 2.02 0.31 0.98 0.42 0.06 2.08 5.42

 The high emitter values, averaged across fuels, are presented in Table 5.3-6 

separated by season. HCHO has the largest difference, summer > winter, which is likely 

due to more rapid photochemical reactions or in-cabin off gassing rates during the 

summer. In addition, BTEX concentrations are consistently higher during the summer, 

which is consistent with higher aromatic contents of summer fuels, especially for Atlanta 

(see Table 4.3-1). 

Table 5.3-6. Summary of Seasonal Differences in the High Emitter Samples. 

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Formal

Summer High 1.05 2.07 3.31 0.58 1.75 0.77 0.78 1.48 8.11

Winter High 0.98 1.74 2.73 0.48 1.58 0.62 0.45 2.54 3.96

5.3.3 Trailing Vehicle Effects 

 In the winter 2005 tests, separate canisters were collected for the high and low 

cabin ventilation portions of the tests; in the summer 2002 tests, only a single canister 

was collected integrating these two periods. Table 5.3-7 shows the average values from 

the high and low ventilation winter 2005 canisters. Their values are similar across 

seasons. Table 5.3-7 shows that although mean canister (integrated) in-cabin values were 

similar under high and low ventilation conditions, the range of concentrations observed 

by continuous PID monitor was much larger under high ventilation conditions, as 

illustrated in Figure 5.3-8. The high ventilation condition continues up to 60 min and is 

then switched to low ventilation for the remaining 60 min. The outdoor ppbRAE-PID 

shows generally lower values and the two indoor peaks in the first 60 min are associated 

with the “near” tailgating portion of the driving sequence. The outdoor PID2 shows 

generally lower values that the indoor PID1, since it was mounted on the aerial on the 

right side of the van, thus its inlet was mostly opposite to the truck’s tailpipe (that was 

situated on the left side of the truck). 

5-14
ME0 - IN-CABIN TRUCK MAL BASE HV TEST 2/25 8:56

0

10

20

30

40

50

60

70

80

0 30 60 90

elapsed time (min)

PID

120

PID1 PID2

Figure 5.3-8. Time Series of In-Cabin (PID1) and Outside (PID2) PID Values. The first 

60 min are under high ventilation conditions (0-60 min) and the next 60 min (60-120 

min) are under low ventilation conditions. 

Table 5.3-7. Comparison of High and Low In-cabin Ventilation Conditions, Winter 2005 

only. Units are ppbv except CO as noted. 

Budi13 Benze Tolue Etbz Mp_xyl O_xyl MTBE CO, ppm Formal

High Vent only 0.46 1.06 2.00 0.37 1.25 0.51 0.32 1.32 4.40

Low Vent only 0.55 1.06 1.69 0.30 1.08 0.41 0.33 1.52 4.46

5-15
5.3.4 Comparison with FTP Data 

 The driving tests were all conducted while the vehicle was in a hot stabilized 

operating condition. The FTP test phase most comparable is phase 2 (Bag 2) and this 

section will examine the correlation of the Bag 2 components with observed values in the 

driving tests. 

 Figure 5.3-9 correlates Bag 2 and the trailing vehicle benzene values. There is a 

trend of increasing cabin benzene concentrations with increasing benzene FTP emissions 

(R2=0.64). Figure 5.3-10 presents the same correlation for MTBE although there are 

fewer data points since only the Houston fuel contained substantial concentrations of 

MTBE. Figure 5.3-11 illustrates the same correlation for 1,3-BD. Unlike benzene and 

MTBE, 1,3-BD is primarily an exhaust component. The 1,3-BD plot shows the same 

correlation (R2

 =0.62) between the FTP emission level and the resulting trailing vehicle 

cabin concentration as benzene. The correlations are driven mostly by the vehicles in 

malfunction modes, since only these vehicle emissions result in significant concentrations 

in the trailing vehicle cabin. 

 

y = 0.02x + 0.55

R2

 = 0.64

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 20 40 60 80 100 120 14

FTP Bag 2 mg/mi

Trailing Veh, ppbv

0

Malfunction

Normal

Figure 5.3-9. Comparison of FTP Bag 2 Benzene Emissions to In-cabin Concentration in 

the Trailing Vehicle. 

5-16
y = 0.0367x + 0.5247

R2

 = 0.5041

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120 140

FTP Bag 2 mg/mi

Trailing Veh, ppbv

Malfunction

Normal

Figure 5.3-10. Comparison of FTP Bag 2 MTBE emissions to in-cabin concentrations in 

the trailing vehicle. 

y = 0.02x + 0.26

R2

 = 0.62

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 10 20 30 40 5

FTP Bag 2 mg/mi

Trailing Veh, ppbv

0

Malfunction

Normal

Figure 5.3-11. Comparison of FTP Bag 2 1,3-BD Emissions to In-cabin Concentrations 

in the Trailing Vehicle. 

5-17
5.4 Discussion 

 The overall objective of this section is to assess the various effects that might 

impact trailing vehicle in-cabin levels of leading vehicle emissions. A rural test site with 

very little traffic was chosen to minimize non-lead vehicle influences on measured incabin values. Background samples were taken prior to the driving tests to quantify other 

possible sources. Measured component backgrounds were low and consistent from 

summer to winter although HCHO backgrounds were relatively high, suggesting in-cabin 

sources. 

 Summer and winter in-cabin values were similar in magnitude with the exception 

of HCHO which was higher in the summer, possibly due to higher photochemical activity 

and higher temperatures that led to more HCHO off-gassing of the vehicle cabin interior. 

EtOH values in Summer 2002 are much higher than in Winter 2005, most probably due 

to the off-gassing effect of the continuous formaldehyde analyzer that was located in the 

trailing vehicle cabin for Summer 2002 measurements. 

 Trailing vehicle cabin values were substantially larger than background values 

except for HCHO which was actually lower than background in winter tests. Idle test 

sample values were on average twice those encountered in driving tests, suggesting that 

proximity and proximity duration may substantially impact in-cabin trailing vehicle 

concentrations. 

 Average in-cabin levels were little affected by different vehicles or fuels except 

for an MTBE fuel effect. However, averaging over the fuels and vehicles, the high 

emitter mode resulted in much higher trailing vehicle in-cabin values than the normal 

emitter mode, on average 2.2 times higher; except for HCHO which was relatively 

unchanged from background. Similarly, the season had no strong effect upon the trailing 

vehicle concentrations. 

 Trailing vehicle ventilation status also affected in-cabin values. Although mean 

canister (integrated) in-cabin values were similar under high and low ventilation 

conditions, the range of concentrations observed by continuous PID and CO monitors 

was much larger under high ventilation. This may be rationalized as the vehicle moving 

into and out of the exhaust plume of the leading vehicle with in-cabin values changing 

rapidly under high ventilation; whereas under low ventilation, in-cabin concentrations 

trapped as the vents were closed stayed relatively constant during the remainder of low 

ventilation conditions. 

 Trailing vehicle tests indicated that the largest impact on in-cabin values came 

from the emissions mode of the leading vehicle. Emissions observed in Bag 2 of the FTP 

tests were compared to the observed trailing vehicle levels of benzene, MTBE and 1,3-

BD. Benzene and MTBE have both exhaust and evaporative emissions while 1,3-BD is 

only emitted in exhaust. In-cabin benzene and MTBE levels appear to correlate with FTP 

emissions, however, 1,3-BD does not but correlates with other in-cabin species. 

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APPENDIX A 

APPENDIX B 

APPENDIX C 

APPENDIX D 

APPENDIX E 

APPENDIX F 

APPENDIX G 

APPENDIX H 

APPENDIX I 

1