1) The document analyzes how gasoline vehicle exhaust VOC speciation profiles vary with temperature, focusing on measurements from vehicles tested over different driving cycles and temperatures. 2) Key results show significant decreases in emissions of most VOCs, especially aromatics and alkanes, at higher temperatures due to improved catalyst efficiency. 3) MSAT fractions and ozone-forming potential also decrease substantially at 75°F compared to lower temperatures, with implications for air quality modeling of temperature effects.

1. Effects of Temperature on
Gasoline Exhaust VOC speciation
Anirban Roy1, Darrell Sonntag2, Charles Schenk2,
Joseph McDonald2, Rich Cook2, Catherine Yanca2,
David Hawkins2, Yunsoo Choi1
1 University of Houston
2 USEPA, Ann Arbor
USEPA’s Annual Emissions Inventory Conference
April 16th, San Diego

2. The VOC ozone problem
• VOC major contributor to ozone in urban regions, which
are NOx-saturated i.e. VOC sensitive.
Choi et al., 2012
NOx-sensitiveVOC-sensitive
What drives ozone?

3. Motor Vehicle VOC emissions
• Two urban counties – New York (NYC-Manhattan) and Harris (Houston)
• Major contributor to urban VOC emissions.
• Gasoline VOCs- comprise of Mobile Source Air Toxics (MSATs)
• Gasoline dominates the split for both emission cases.
New York, NY Harris, TX
0
5
10
15
20
25
30
VOC,ktonsperyear
Gasoline
Diesel
New York, NY Harris, TX
0
1
2
3
4
5
6
MSATVOCs,ktonsperyear
Gasoline
Diesel
(a) Total VOCs (b) MSATs
USEPA NEI, 2011

4. Temperature dependence of VOC emissions
Total hydrocarbons vs. T
Temperature Catalytic efficiency Emissions
Stump et al.

5. Motivation for current work
• Previous studies focused on total hydrocarbons and
MSATS at different temperatures.
• Little quantification of uncertainty in emission factors
• No comprehensive evaluation of speciation profiles -
imperative for air quality modeling.
• This work intends to build on previous work to develop
comprehensive temperature dependent speciation
profiles.

6. Key questions
• How do the speciation profiles for gasoline exhaust vary
under temperature?
• What is the uncertainty in the emission factors for species
classes?
• How does the MSAT content (both species and total) in
VOCs vary with temperature?
• What implications do the results have for air quality
modeling?

7. Vehicle fleet
• Driving conditions
• FTP (urban conditions)
• US-06 (aggressive highway)
Temperatures
• 0 oF
• 20oF
• 75oF
Name Year Technology Standard Mileage Configuration
Buick Lucerne 2010 MPFI Tier 2/Bin 4 22000 3.9L V-6
Honda Accord 2010 MPFI Tier 2/Bin 5 24000 2.4L I-4
Jeep Patriot 2010 MPFI Tier 2/Bin 5 22000 2.0L I-4
Kia Forte EX 2010 MPFI Tier 2/Bin 5 25000 2.0L I-4
Mazda 6 2010 MPFI Tier 2/Bin 5 24000 2.5L I-4
Mitsubishi Galant 2010 MPFI Tier 2/Bin 5 38000 2.4L I-4

8. Additional details
• Testing done at the USEPA’s OTAQ premises.
• All vehicles used 10% ethanol by volume.
• 160 compounds, grouped into following species classes
Aromatics
Alkanes
Cyclic Alkanes
Alkenes
Alkynes
Ethers
Aldehydes
Ketones
• Methane evaluated separately
• FTP – 3 phases: Cold Start, Running and Hot Start.
• Cold Start evaluated separately

9. Bootstrap Method
• Example with FTP Cold Start at 0oF.
• Distribution of means from random sampling.
• Uncertainty shown by 95% confidence interval.
0 1 2 3
0.0
0.1
0.2
0.3
0.4
0.5
Relativefrequency
Aromatics EF, g mi
-1
Draw Sample
Calculate Mean
Repeat 1000 times
0.8 1.0 1.2 1.4 1.6 1.8 2.0
0.00
0.05
0.10
0.15
0.20
Relativefrequency
Aromatics EFs, g mi
-1
0.6 0.8 1.0 1.2 1.4 1.6 1.8
0.0
0.2
0.4
0.6
0.8
1.0
95% C.I
Mean
Percentile
Aromatics EFs, g mi
-1

10. FTP Composite Emissions: Monte Carlo method
0.43*Cold Start+Running+0.57*Hot Start
Means, Cold Start Means, Running Means, Hot Start
0.1 0.2 0.3 0.4
0
20
40
60
80
100
Percentile
Composite Aromatics EFs, g mi
-1

11. Temperature dependence of mean emission factors
(a) FTP (b) US-06
• Significant decrease with temperature due to increasing catalyst
efficiency.
• US-06 emissions significantly lower than FTP-Composite.
0
1000
2000
3000
4000
75
o
F20
o
F0
o
F75
o
F20
o
F0
o
F
Composites
Cold Start
TOGEFs,mgmi
-1
0
10
20
30
40
50
20
o
F 75
o
F0
o
F
Methane
Ketones
Aldehydes
Alcohols
Ethers
Alkynes
Alkenes
Cyclic Alkanes
Alkanes
Aromatics
TOGEFs,mgmi
-1

12. Uncertainty in mean emission factors
• Example with FTP composite emissions, units in mg mi-1.
• Broadly factor of 2, uncertainty.
0 oF 20 oF 75 oF
Aromatics 265 (188-356) 51 (76-99) 12 (9-15)
Alkanes 256 (189-317) 61 (46-74) 8 (7-10)
Cyclic Alkanes 41 (25-59) 11 (7-14) 1.1 (0.8-1.3)
Alkenes 125 (100-150) 36 (26-46) 5 (4-6)
Alkynes 19 (14-24) 3.3 (2.3-4.3) 0.4 (0.2-0.6)
Alcohols 54 (39-69) 18 (10-28) 7 (2-13)
Aldehydes 9 (8-11) 7 (6-8) 3 (4-11)
Ketones 1.2 (1-1.3) 1.7 (1-2.5) 0.6 (0.5-0.7)
Methane 34 (29-39) 12 (9-14) 5 (3-7)

13. What influences composite emissions?
• Two scenarios:
• CASE 1 : Cold Start dominates by orders of magnitude.
• Applicable to most hydrocarbons at all temperatures.
• CASE 2: Hot Start and Running comparable to Cold Start.
• Applicable to all oxygenates - alcohols, aldehydes and ketones.
Cold
Start
HotStart
Running
10
0
10
1
10
2
10
3
AromaticsEFs,mgmi
-1
(a) FTP, 0F
Cold
Start
H
otStart
Running
0
2
4
6
8
10
AlcoholEFs,mgmi
-1
(b) FTP, 75F

14. Speciation profiles
• Significant increases seen in speciation for alcohols, aldehydes and methane.
• Alkanes show definitive decrease with temperature for both Cold Start and composite
phases of the FTP cycle.
• Aromatics significantly fall with temperature for the US-06 cycle.
Cold
Start,0F
Cold
Start,20F
Cold
Start,75F
Com
posite,0F
Com
posite,20F
Com
posite,75F
US-06,0F
US-06,20F
US-06,75F
0
20
40
60
80
100 US-06Composites, FTPCold Start, FTP
Weight%TOG
Methane
Ketones
Aldehydes
Alcohols
Ethers
Alkynes
Alkenes
Cyclic Alkanes
Alkanes
Aromatics

15. MSAT fraction in TOG profile
• Three distinct patterns.
• FTP, Cold Start – MSAT fraction increases marginally with temperature.
Speciation constant.
• FTP, Composite – Substantial change in MSAT fraction and speciation.
• US06- MSAT fraction unchanged, substantial change in speciation.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
US06
75F75F20F 20F0F0F
FTP, CompositeFTP, Cold Start
75F20F0F
MSATfractioninTOG
Other MSATs
Ethanol
Benzene, Toluene,
Ethyl benzene, Xylene (BTEX)

16. Ozone forming potential: the Carter MIR scale
• US-06: definitive changes with temperature, especially at 75oF.
• Weaker trends for FTP-Composite profiles.
• Need detailed air quality modeling representing varying NOx
conditions to accurately understand the impacts.
C
old
Start,0F
Cold
Start,20F
Cold
Start,75F
Com
posite,0F
Com
posite,20F
Com
posite,75F
US06,0F
US06,20F
US06,75F
0
1
2
3
4
Ozoneformed,tons/day
http://www.cert.ucr.edu/~carter/emitdb/
Ozone potential = VOC mass fraction x MIR x emission rate ( 1 ton/day)

17. Conclusions
• Significant difference in speciation across temperatures and
driving conditions.
• Cold Start emissions were the dominant FTP phase for
most hydrocarbons, greater by at least 2 orders of
magnitude than Running and Hot Start emissions .
• For alcohols and carbonyls, Cold Start, Running and Hot
Start emissions were comparable.
• Three distinct patterns for MSAT fractions with temperature.
Cold Start: Marginal change in MSAT fraction, speciation unchanged
Composite : Significant change in MSAT fraction and speciation
US06: Marginal change in MSAT fraction, significant for speciation
• Ozone forming potential decreased at 75oF for Composite
and US-06 profiles.

18. Future directions
• Speciation results will be available at the USEPA’s
SPECIATE database for the next version.
• Use these profiles to inform and update MOVES model to
build motor vehicle emissions inventories.

19. Acknowledgements
• University of Houston-College of Natural Sciences and
Mathematics for funding.

20. ?