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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