Mobile Source Air Toxics (MSATs):
Assessing Project-Level Impacts
Song Bai, Ph.D.
Douglas Eisinger, Ph.D.
Deb Niemeier, Ph.D.
UC Davis-Caltrans Air Quality Project
Presented at the 2007 CAPCOA Health Conference:
Understanding and Addressing Health Impacts of
Air Pollution on Communities
Carson, California
September 19, 2007
UC Davis-Caltrans Air Quality Project
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Acknowledgments
The study team received valuable assistance from:
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Mike Brady, Caltrans
Michael Claggett, FHWA
David Ipps, Caltrans
Jeff Long, California Air Resources Board
Jean Mazur, FHWA
Dilip Patel, California Air Resources Board
Dennis Wade, California Air Resources Board
Peng Wu, University of California, Davis
UC Davis-Caltrans Air Quality Project
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Motivation
Mobile Source Air Toxics (MSAT)
• February 2006, FHWA interim MSAT guidance
• EPA’s original six priority MSATs:
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–
–
–
–
–
Diesel PM
Benzene
1,3-butadiene
Acetaldehyde
Formaldehyde
Acrolein
• Lack of project-level MSAT analysis protocol for
California
UC Davis-Caltrans Air Quality Project
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Outline
• Analysis methods and new spreadsheet tool
• Example freeway widening project
• Results for benzene and diesel PM
– Build vs. no-build – surprising findings
– Main reasons results occurred
– EMFAC2002 vs. EMFAC2007
• Conclusions and future research
UC Davis-Caltrans Air Quality Project
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Analysis Methods Overview:
MSAT emissions = emission factors × traffic activity
• Obtain TOG and PM emission factors from EMFAC
• Obtain MSAT speciation factors from California ARB
• Obtain traffic activity data from Caltrans
UC Davis-Caltrans Air Quality Project
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MSAT Spreadsheet Tool
Obtain
EMFAC
emission
factors
Calculate
composite
emission
factors
Apply MSAT
speciation
factors
Calculate
emissions
based on
activity
UC Davis-Caltrans Air Quality Project
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Southern CA freeway example
Existing:
3 Mixed Flow
(MF) lanes each
direction
Proposed:
• 4 MF + 1 HOV
• 4 MF + 2 HOV
• 5 MF + 1 HOV
UC Davis-Caltrans Air Quality Project
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Analysis Explored Freeway With Substantial
Daily Traffic Activity (Volume)
2004
Base Case (3 MF)
2030
184,000
increase
n/a
No-Build (3 MF)
225,000
22%
4 MF + 1 HOV
291,000
58%
4 MF + 2 HOV
302,000
64%
5 MF + 1 HOV
313,000
70%
UC Davis-Caltrans Air Quality Project
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2004 vs. Future: Overall Reductions (No-Build)
• By 2013: Benzene drops 44%
• By 2030: Benzene drops 83%
EMFAC2002 Results
Project MSAT Scenario Comparison - Benzene
14000
Benzene (grams/day)
12000
11380
10000
8000
7308
6412
6502
6597
6000
4000
1960
2045
2092
2030 No-Build
2030 Build 1
2030 Build 2
2081
2000
0
Existing (2004) 2013 No-Build
2013 Build 1
UC Davis-Caltrans
Air Quality
Project2013 Build 2
2013 Build 3
2030 Build 3 9
2004 vs. Future: Overall Reductions (No-Build)
• By 2013: DPM drops 5%
• By 2030: DPM drops 30%
EMFAC2002 Results
Project MSAT Scenario Comparison - Diesel PM
12000
10465
Diesel PM (grams/day)
10000
9981
10308
9789
9709
8000
7365
6982
6924
2030 Build 1
2030 Build 2
6923
6000
4000
2000
0
Existing (2004) 2013 No-Build
2013 Build 1
UC Davis-Caltrans
Air Quality
Project2013 Build 2
2013 Build 3
2030 No-Build
2030 Build 10
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Benzene and DPM Results: EMFAC2002
2030 No-Build (3 MF) vs. Build (4 MF + 2 HOV)
• Benzene increases 7%
• DPM decreases 6%
Benzene Comparison
(grams/day)
DPM Comparison
(grams/day)
2400
8000
2000
6000
1600
1200
4000
1960
2092
7365
6924
800
2000
400
0
0
2030 No-build (3MF)
2030 Build (4MF+2HOV)
UC Davis-Caltrans Air Quality Project
2030 No-build (3MF)
2030 Build (4MF+2HOV)
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Why Are Benzene Emissions Higher in Build Case?
• Benzene from non-diesel increases
– Limited EF improvement due to speed
– Large VMT increase (35%)
– High HOV lane speed (emission factor increases)
Benzene Comparison
2030 No-build (3 MF)
2030 Build (4 MF + 2 HOV)
Benzene Emissions (gram)
1800
Increased
VMT
1500
1200
900
Speed
improvement
Reduced
travel time
600
300
0
Diesel Exhaust
Non-diesel Exhaust
(using g/mile factors)
(using g/mile factors)
UC Davis-Caltrans Air Quality Project
Non-diesel Evaporative
Running Loss
(using g/minute factors)
Daily Total
(sum of exhaust and
evaporative benzene)
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Why Are DPM Emissions Lower in Build Case?
• Speed improvements overwhelm VMT increase
– VMT increases only 15% (not as much as non-diesel)
– Speed improvement lowers emission factors 15-25%
DPM Comparison - VMT
2030 No-build (3MF)
DPM Comparison - Emission Factors
2030 Build (4MF+2HOV)
80000
2030 No-build (3MF)
2030 Build (4MF+2HOV)
0.10
0.08
60000
0.06
40000
0.04
20000
0.02
0
0.00
Peak time
Off-peak time
UC Davis-Caltrans Air Quality Project
Peak time
Off-peak time
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Benzene and DPM Results: EMFAC2002
(Results Shown Previously – Focus on DPM)
• Benzene increases 7%
• DPM decreases 6%
Benzene Comparison
(grams/day)
DPM Comparison
(grams/day)
2400
8000
2000
6000
1600
1200
4000
1960
2092
7365
6924
800
2000
400
0
0
2030 No-build (3MF)
2030 Build (4MF+2HOV)
UC Davis-Caltrans Air Quality Project
2030 No-build (3MF)
2030 Build (4MF+2HOV)
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Same slide as last one, except for EMFAC2007
• Benzene increases 9%
• DPM increases 17%
Big Shift from
EMFAC2002
Benzene Comparison
(grams/day)
DPM Comparison
(grams/day)
2400
8000
2000
6000
1600
1200
2052
2244
7998
4000
6856
800
2000
400
0
0
2030 No-build (3MF)
2030 Build (4MF+2HOV)
UC Davis-Caltrans Air Quality Project
2030 No-build (3MF)
2030 Build (4MF+2HOV)
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EMFAC2002 vs. EMFAC2007
Differences Affecting Diesel PM
Speed Corrections
DPM Emission Factors: EMFAC2002 vs. EMFAC2007
EMFAC2002
EMFAC2007
0.25
DPM (grams/mile)
0.2
0.15
0.1
0.05
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
speed bin
EMFAC2007 - 50 vs. 35 mph: 9% > g/mi emissions
EMFAC2002 - 50 vs. 35 mph: 23% < g/mi emissions
UC Davis-Caltrans Air Quality Project
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Speed correction: which is closer to reality?
EMFAC2002
DPM SCFs: EMFAC2002 vs EMFAC2007
3.5
3.5
EMFAC2007
3.0
3.0
2.5
2.5
SCF (normalized by UDDS)
SCF
EMFAC2002
2.0
1.5
2.0
1.5
1.0
1.0
0.5
0.5
0.0
0.0
0
10
20
30
40
50
60
70
0
10
20
30
40
50
60
Speed (MPH)
Speed (MPH)
UCD: 1984 - 87
UCD Diesel PM SCFs
UCD: 1998-02
EMFAC 2002 SCF
SCF curves: UCD model seems closer to EMFAC2002 than EMFAC2007
Key question: at high speeds, are DPM emissions going up or down?
UC Davis-Caltrans Air Quality Project
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Conclusions and Future Research
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MSAT emissions drop over time
Project outcomes can vary by MSAT
Results hinge on traffic volumes and speeds
Example results – vary by project and model !
Next steps…
• Investigate MSAT speciation factors
• Test sensitivity to speeds and volumes
• Continue to compare EMFAC2002 vs. EMFAC2007
UC Davis-Caltrans Air Quality Project
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Questions or Comments?
UC Davis-Caltrans Air Quality Project
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EMFAC2002 vs. EMFAC2007
Another Look at Differences Affecting Diesel PM
• Diesel VMT proportion changes
(40.6% in EMFAC2002; 29.4% in EMFAC2007)
EMFAC2002 Model
GAS VMT Proportions
EMFAC2007 Model
DSL VMT Proportions
GAS VMT Proportions
12%
12%
10%
10%
8%
8%
6%
6%
4%
4%
2%
2%
0%
DSL VMT Proportions
0%
MDV
LHD1
LHD2
MHD
UC Davis-Caltrans Air Quality Project
HHD
MDV
LHD1
LHD2
MHD
HHD
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