School Bus Emissions StudySAE Paper 2003-01-1381
Plus Cancer Potency Analysis
9th Diesel Engine Emission Reduction Conference Newport, Rhode Island
August 24-28, 2003
Warren J. SlodowskeManger Environmental Staff
International Truck and Engine Corporation
Authors• International Truck and
Engine Corporation– Warren Slodowske, Bill
Trestrail, Angelita Cook, William Bunn
• Lapin & Associates– Charles Lapin
Acknowledgements
• Southwest Research Institute– Terry Ullman– Lawrence Smith– Joseph Anthony
• ConocoPhillips– Charles R. Clark– Joe Kaufman– Kenneth Wright
Study Rationale
• Determine the validity of CARB’s claim that there are 41 TACs associated with current diesel exhaust.
• Determine the validity of the claim that natural gas school buses emit fewer toxics than low emitting diesel buses
Study Objectives• Evaluate school buses currently in use• Compare three engine configurations:
conventional diesel (CD), low-emitting diesel (LED), and compressed natural gas (CNG)
• Use a chassis dynamometer, real world test cycle
• Look at regulated emissions and over 300 chemicals
• Compare toxic potency weighted emissions
Diesel School Bus• 1998 American
Transport Chassis • 2001 International 8.7 L
Engine• Used for conventional &
low emitting diesel (LED) configurations
• Changes for conventional diesel configuration:– Remove Engelhard DPF– Reset low NOx ECM
Engelhard Catalyzed Diesel Particulate Filter for Low Emitting Diesel
CNG School Bus• 2000 Blue Bird
Chassis• 2000 John Deere
8.1 L Engine• No aftertreatment • Assumed same test
weight and road load
Why no aftertreatment on CNG Bus?
• Unable to find CNG school bus of the required configuration equipped with aftertreatment. None being purchased.
• SCAQMD Rule 1195 favors the purchase CNG buses without aftertreatment over low emitting diesel
Diesel Fuel
13.37.6PNAs, wt%
47.547.7CetaneNumber
33.130.9Aromatics, wt%
37114Sulfur, ppm
ConventionalUltra-Low Sulfur
CNG Fuel Composition
88.1Methane Number (CARB)
1039Heating value (BTU/ft3)
3.47Nitrogen
2.11Propane
0.10Ethylene
4.11Ethane
90.21Methane
Mole %Component
City Suburban Heavy Vehicle Cycle
•Three tests for each configuration with three consecutive cycles per test
0
5
10
15
20
25
30
35
40
45
50
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800Time (sec.)
Spee
d (m
ph)
Sample Collection
Ambient Background for THC, NMHC, CO, CO2, NOx, PM, Individual hydrocarbons
PM, SOF, SO4
Aldehydes, methanol, cyanide, chromium
Chlorobenzenes Metals
THC, NMHC NO, NOx
Individual HC, CO, CO2
Butadiene
PAH, Dioxins, Furans, SVOL
Air Quality Emissions
0
2
4
6
8
10
12
14
16
18
20
NOx NO NO2 PM x 100 SOF x 100 SO4 x10000
THC NMHC CH4 CO CO2/100
g/m
ile
Low Emitting DieselConventional DieselCNG
Engine Certification Data
0.01
3.0
Low Emitting Diesel
0.050.09PM (g/hp-hr)
2.63.9NOx(g/hp-hr)
CNGConventional Diesel
• CNG’s high NOx emission surprising given its low NOx certification.
21 Toxic Air Contaminants Were Not Found
• Aniline • Antimony compounds • Arsenic • Beryllium compounds • Cadmium • Chlorine (chloride)• Chlorobenzene and
derivatives • Chromium compounds• Cobalt compounds • Ethylbenzene• Inorganic lead
• Manganese • Mercury • 4-Nitrobiphenyl • Nickel • Selenium • Styrene • Xylene isomers and mixtures • o-Xylenes• p-Xylenes• m-Xylenes
Toxic Air Contaminants (TACs)
0246
81012
Acetal
dehy
de /10
Acrolei
n
Benze
ne
Biphen
yl x1
0
Bis [2-et
hylhex
yl]ph
thalat
e x1,0
00Buta
diene
, 1,3-
Cresol
isomers
x10
Cyanid
e com
poun
ds x1
0
di-n-B
utylph
thalat
e x1,00
0
Dioxins &
furans
x10,0
00,000
mg/
mile
Low Emitting DieselConventional DieselCNG
Toxic Air Contaminants (continued)
0123456789
Formaldeh
yde /
100
Hexane
Methan
ol /10
Methyl
ethyl
ketone
x10
Naphtha
lene x
10Phe
nol x
10Pho
spho
rus x1
0
POM (PAHs+
deriva
tives
)Prop
ionalde
hyde
Toluene
mg/
mile
Low Emitting DieselConventional DieselCNG
TACs Statistically Same Across All Three Engine Configurations
1) Bis[2-ethylhexyl]phthalate2) Cyanide compounds3) Total Dioxins and Furans4) Hexane5) Phosphorus
TACs Statistically Same Between LED and CNG
1) Biphenyl2) 1,3-Butadiene3) Cresol isomers4) Di-n-butylphthalate5) Methanol
6) Naphthalene7) Phenol8) Polycyclic Organic
Matter (PAH+derivatives)
9) Toluene
TACs Where CNG is Statistically Higher than LED
1) Acetaldehyde2) Acrolein3) Benzene4) Formaldehyde5) Methyl Ethyl Ketone6) Propionaldehyde
TACs Where LED is Statistically Higher than CNG
Statistical Ranking Where Only CD and CNG Emissions Differ
CNGCDMethanol
CDCNGPOM (PAH+derv.)
CDCNGPhenol
CDCNGNaphthalene
CDCNGCresol isomers
CNGCD1,3-Butadiene
CDCNGBiphenyl
HigherLower
"Concentrate on what cannot lie. The evidence..." -- Gil Grissom
Toxic Potency Weighted Emissions
PAH Emissions: Potency Adjusted & Relative to CD, Individual PAHs
0
10
20
30
40
50
60
70
80
90
100
CD LED CNGug B
AP e
quiv
alen
ts/m
ile re
lativ
e to
CD
= 1
00
benzo(a)anthracene chrysene
benzo(b)fluoranthene benzo(k)fluoranthene
benzo(a)pyrene indeno (123-cd)pyrene
dibenz(ah)anthrancene nitropyrene
(Calculations adapted from “Draft Staff Report. Procedure for Calculating Toxic Risk Reduction from Vehicle Emissions” SCAQMD, 11/2000)
Relative Cancer Potency Weighted Emissions
Cancer Potency Weighted Emissions = ∑(emission ratei)(unit risk factori)
6.6 8.2
100
0
10
20
30
40
50
60
70
80
90
100
Low Emitting Diesel Conventional Diesel CNG
Canc
er P
oten
cy W
eigh
ted
Emis
sion
s R
elat
ive
to C
NG =
100
(Calculations adapted from “Draft Staff Report. Procedure for Calculating Toxic Risk Reduction fromVehicle Emissions” SCAQMD, 11/2000)
Relative Cancer Potency Weighted Emissions Details
0.000010.00010.00006 DHEP
8.2
0.03
0.004
0.6
3.4
0
4.1
Conventional Diesel
1006.6 Total
0.0090.0004 PAHs
0.010.01 Dioxins
1.60.2 Acetaldehyde
3.20 Benzene
19.35.6Butadiene, 1,3-
75.80.8 Formaldehyde
CNGLow Emitting Diesel
(Calculations adapted from “Draft Staff Report. Procedure for Calculating Toxic Risk Reduction from
Vehicle Emissions” SCAQMD, 11/2000)
Comparison to Other Recent Studies
• CARB and BP compared diesel and CNG fueled transit buses
• CARB transit bus study– CNG w/ and w/o oxidation catalyst
• BP transit bus study– Evaluated the effect of different diesel fuels
• Both used several different test cycles, Central Business District reported here. Results similar with other cycles.
Cancer Potency Weighted Emissions: Chemical Species Approach
Diesels no trap Diesels w/trap CNG no after treatment CNG oxycat
0
1
2
3
4
5
6
CARB_BP
Conve
ntiona
l dies
el SB
ECD1 No C
at_BP
ECD1 Oxy_
Cat_ARB
ECD1 CRT_B
PECD1 C
RT_ARB
ECD CRT_BP
Low em
itting d
iesel SB
CNG.2000
_BP
CNG.2001
_BP
CNG_1_ARB
CNG_2_ARB
CNG_3_ARB
CNG scho
ol bus
DDCw/OxCat_
ARB
CMw/OxC
at_ARB
Can
cer P
oten
cy W
eigh
ted
Emis
sion
s (u
rf x
ug/
mile
)
Acetaldehyde Benzene Butadiene, 1,3- Formaldehyde(Calculations adapted from “Draft Staff Report. Procedure for Calculating Toxic Risk Reduction from Vehicle Emissions” SCAQMD, 11/2000)
Summary• For 8 of the eleven air quality emissions, low-
emitting diesel was lower than CNG• Of the 41 Toxic Air Contaminants (TACs)
identified by CARB to be in diesel exhaust, 21 were not found
• Of the 20 TACs found, in no case was CNG lower than the low-emitting diesel
• Conventional diesel had 12 of 20 TACs below or equivalent to CNG
• Potency weighted emissions were higher for CNG
Conclusions
1) Don’t assume modern diesel emits 41 toxics!!
2) Don’t assume natural gas is less toxic than modern diesel!!
“Do not assume anything, clear your mind must be”
Yoda, Star Wars Episode II