United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-83-106 Dec. 1983
oEPA Project Summary
Exhaust Emissions from a
Diesel Engine
Terence H. Risby
Studies were performed using (1)
diesel particles collected from the undi-
luted exhaust of a single-cylinder en-
gine, operated at constant speed and
load, using a binary pure hydrocarbon
fuel with air or gas mixture oxidizers,
and (2) diesel particles collected from
the diluted exhaust of a multicylinder
engine operated on a commercial fuel.
The physicochemical properties of the
particles were determined by static and
dynamic methods. The organic adsorb-
ate was characterized by gas chroma-
tography and mass spectrometry and
by microbial testing protocols. Electron
paramagnetic resonance spectrometry
and high performance liquid chroma-
tography were used to study reactivity
of the organic adsorbate.
The particles collected from the ex-
haust of diesel engines operated on a
1:1 mixture of 2,2,4-trimethylpentane
and n-tetradecane and on commercial
fuels contained similar compounds in
their organic adsorbates. The nitrogen
in these compounds is derived mainly
from the oxidizer (air).
Diesel particles have high surface
areas and reactivities; this results in the
efficient collection of organic adsorb-
ates. The heats of adsorption of the
organic adsorbates on the surface of
diesel particles are sufficiently large
that these molecules are not released
into the biological solvents used in
microbial testing protocols testing for
cytotoxic effects.
The microbial mutagenic activities of
the organic adsorbates found on the
surface of both types of diesel particles
are comparable. These microbial muta-
genic activities can be attributed mainly
to the presence of nitrated polynuclear
aromatic hydrocarbons.
This Project Summary was developed
by EPA's Environmental Sciences Re-
search Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
A number of studies have been per-
formed on the organic extracts of collected
diesel engine paniculate matter. These
studies indicated that the organics associ-
ated with this particulate matter have
biologic activity. However, the source of
this activity was not identified. Attempts
to define the origin and nature of the
compounds responsible for these effects
and the ultimate implication of this activity
were confounded by the complexity of the
diesel fuel. Although a variety of extrac-
tion systems were used to study tbp
carbon particulate, its basic character
was unknown.
This study was undertaken to define
the surface character of the carbon partic-
ulate matter emitted from diesel engines
and to identify combustion products by
using pure fuel and oxidizer components
to simplify the emissions. The use of
controlled pure components aids product
identification by limiting the number of
possibilities and interferences from fuel
compounds. A wide variety of analytical
techniques, such as gas chromatography,
gas chromatography/chemical ionization
mass spectrometry, and high perform-
ance liquid chromatography, were used
to chemically identify the products. The
Ames test and the Comptestwere used to
measure biologic activity.
The study was divided into four main
components. Three of the components
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were engineering, design, and operation
of the engine using various fuels and
oxidants; chemical analysis of the ad-
sorbed organics on the particulate matter;
and biologic assay of the particulate and
associated organics. The fourth compo-
nent, physical chemical characterization
of the particulate matter, was treated
separately, although particulate matter
generated by the other components was
one of the three types of particulate
studied. Very few studies have attempted
to accurately define the physical chemis-
try of particles in diesel exhaust.
As a result of this study, nine papers
were published in peer-reviewed jour-
nals. The final project report incorporates
information in those papers and may
provide more detail on some aspects of
the study.
Procedure
An AVCO-Lycoming Bernard W-51
industrial diesel engine was used for the
study. The small, single cylinder, four-
stroke, air-cooled direct-injected diesel
engine was operated at 2,400 r/min on a
1:1 mixture of 2,2,4-trimethylpentane
and n-tetradecane. This pure fuel had a
measured cetane number of 53.4. A
synthetic lubricant, polyalkyleneglycol
(UCON LB 525, Union Carbide), was used
for the engine and was maintained at
60°C.
The engine emissions were mixed and
a continuous aliquot of approximately
17% was taken. This aliquot was cooled
through a heat exchanger to below 52°C
and filtered to remove the particulate
carbon monoxide, carbon dioxide, oxygen,
NO/NO,, and hydrocarbons were meas-
ured. A constant flow was maintained by
a series of pumps and meters, and the
particles were collected on Teflon coated,
gloaa fiber filters.
A series of different air oxidizing sys-
tems containing 5 or 10% excess oxygen
and 10% excess nitrogen were used. A
special nitrogen free blend of 18.9%
oxygen, 20.7% argon, and 50.4% carbon
dioxide was chosen to simulate the
physical characteristics of air. In all cases,
the amount of oxygen relative to the
amount of fuel (oxygen/fuel ratio) was
held constant and the volume of gas used
was adjusted to conform to the percent-
age composition, i.e., supercharging.
Filter samples were collected until 0.1
to 0.2 gram of particulate was obtained
(10 to 20 minutes). Filters were dessicated
to equilibrium, weighed, and stored in a
refrigerator. They were protected from
light.
Organic extracts of the particulate were
prepared by methylene chloride extraction
for 24 hours at two cycles per hour. The
extract was reduced to dryness using a
rotating evaporator and purging with dry
nitrogen or argon. The extract was stored
in vials and refrigerated. It was protected
from light.
Extracts were analyzed by gas chromatog-
raphy (GC), gas chromatography/chemi-
cal ionization mass spectrometry (GC/
MS), and high performance liquid chroma-
tography (HPLC) with MS identification.
The gas chromatograph used a 0.25 mm
i.d. borosilicate glass column (WCOT)
coated with SE-54 with either a flame
ionization or a nitrogen specif icthermonic
detector. Nitrogen or helium was used as
the carrier gas, as appropriate. The
column was temperature programmed
for 100° to 300°C at 2°C/minute.
The gas chromatograph for the GC/MS
system was similarly configured. The
chemical ionization mass spectrometer
(CIMS) was operated in both the positive
and negative ionization mode with auto-
matic computer controlled data collection.
Some comparison runs were made on a
different system using electron impact
ionization and similar GC systems. The
spectra obtained from these systems were
compared with those at the National
Bureau of Standards MS Library.
HPLC was used for fraction separation
before analysis using a 5-//m silica
column with a multisolvent program: n-
hexane programmed to 100% dichloro-
methane in 10 minutes and then pro-
grammed to 100% acetonitrile in 10
minutes. A 254-nm ultraviolet (UV)detec-
tor was used. Fractions were collected,
evaporated to dryness, and analyzed on
the CIMS using a programmable direct
insertion probe.
Environmental Protection Agency (EPA)
personnel analyzed for nitropyrene using
HPLC with on column reduction to amino-
pyrene and fluorescence detection. Bio-
logical testing was conducted on the
soluble organic extracts of the particulate
matter and on the total particulate. Two
microbiological assays were used in this
study: the Ames test and the Comptest.
The Ames test was conducted with tester
strains TA98 and TA100 with and without
S9 metabolic activation, according to the
standard procedures developed by Dr.
Ames. The Comptest was conducted on
Bacillus subtilis RUB827 and RUB818
wild type (as reported by R. E. Yasbin in
Environ. Mutagen., 1981).
The diesel particulate collected during
tests was examined with respect to its
physical chemistry and compared to diesel
particulate collected from a diesel engine
operating on conventional cycles using
full-boiling-range (regular) number two
diesel fuel and commercial lubricating oil.
A graphitized carbon black fuel (Spheron
6) was chosen as a reference.
Particle size was measured by electron
microscopy (EM) and the external surface
area was calculated. Bulk and helium
densities were determined when suffi-
cient sample was available. Brunauer,
Emmett, and Teller (BET) surface areas
were calculated with nitrogen (16.2
AVmolecule), benzene (40 AVmolecule),
and n-hexane (51 AVmolecule). A num-
ber of preconditioning regimes were
followed to vary the activation tempera-
ture and other conditions. GC was used to
determine the isoteric heats of adsorption
for a wide variety of compounds. Addi-
tional efforts were made to define the
surface character of the particulate matter
using electron paramagnetic resonance
spectrometry with and without UV radi-
ation.
Results
Engine Operation, Chemical
Analysis, and Biologic Assay
Use of the nitrogen free oxidizer results
in reduced power and delayed ignition.
No oxides of nitrogen were present in the
exhaust, and total hydrocarbons and
particulates were reduced 40 to 30%.
When nitrogen was present, carbon
monoxide and total hydrocarbons de-
creased as the percentage of oxygen
increased. The nitric oxides increased to a
maximum at 25% oxygen and then de-
creased slightly. The total amount of
particulate decreased with increasing
oxygen while the percentage of soluble
organics increased.
Forty-five organic compounds were
detected on the particulate matter by GC;
10 of these compounds could not be
positively identified, although an estima-
tion of molecular weight was possible
from the CIMS. Twenty polynuclear aro-
matic compounds, ranging from naphtha-
lene to benzo(ghi)perylene, were detected
as well as 11 compounds containing
oxygen: two furans, two quinones, and
seven carbonyl compounds. The fuel
component n-tetradecane, phthalate
anhydride, benzo(c)cinnoline, and nitro-
pyrene were also seen.
The oxidizing system variation influ-
enced the chemical composition of the
particulate. When the nitrogen free oxi-
dizer was used, the oxides of nitrogen
decreased from an average of 470 ppm to
-------
less than 1 ppm. Most of the nitrogen
containing compounds were eliminated,
and those remaining were at concentra-
tions that were too low to identify. The
components identified from the runs
using the air oxidizer were very similar to
those seen from regular diesel fuel even
though only a two-component mixture
was used.
The presence of 1 -nitropyrene was not
correlated with the presence of either
nitric oxide or nitrogen dioxide, and it was
not related to the presence of pyrene in
the sample. Furthermore, no overall
relationship existed between 1-nitropy-
rene and the amount of total particulate.
This finding is different from previous
observations of particulate matter that
was collected from experiments using the
nitrogen free oxidizer and exposed to a
stream of nitrogen dioxide and water
vapor. In these experiments, the amount
of 1-nitropyrene increased as the concen-
tration of nitrogen dioxide increased.
The results from the chemical analysis
are consistent with the biologic activity
results, which correlate well with the
amount of nitropyrene present in the
nitrogen containing systems. Very few
nitropyrenes were present in the nitrogen
free case and almost no biologic activity
was detected. When nitrogen dioxide was
added to these particles, a large step
increase in activity occurred, and increas-
ing nitrogen dioxide caused a gradual
increase in activity. No significant in-
crease occurred in any of the tests that
involved biologic activation (+S9) and in
many cases, the results were lower. This
result indicates that the activity was direct
acting. The amount of nitropyrene in the
system could not account for the activity
observed; therefore, other compounds
must cause the additional activity.
A 10- to 20-fold increase in activity
occurred between the nitrogen free and
air oxidant cases. Toxicity also increased
but was not severe enougri to interfere
with any tests. Very similar results were
seen from the Comptest. The fuels and
lubricants used showed no activity in any
system.
Attempts were made to test the unex-
tracted particles; however, no positive
results were obtained. These results were
compared to test resultsfrom unextracted
particles collected from an identical en-
gine operated on regular diesel fuel and
lubricant with air oxidant. These tests
were slightly positive in strains TA98 and
TA100 at similar levels to those seen for
the organic extracts of the particles
sbtained from the nitrogen free oxidizer.
Physical Chemical
Characterization
The resultsfrom the EM and BET(nitro-
gen) tests are summarized in Table 1. The
roughness factor is the ratio of the two
area determinations and may be taken as
an indication of porosity. In this case, the
diesel particles from regularfuel are much
less porous than the carbon black
(Spheron 6) particles.
The engine particulates from the regu-
lar diesel fuel and from the pure fuel
exhibited distinct differences. The surface
area and the type of adsorption for both
types of particulate were strongly depend-
ent upon temperature of activation and
only reached the value shown in Table 1
after activation and degasing at 400°C. At
lower temperatures, the surface of the
regular fuel particulate appeared to be
already covered and not subject to classi-
cal adsorption. This idea was further
supported by a net weight loss of 17.5%,
which is approximately the amount of
material that can be extracted by using
Table 1. EM and BET Test Data
dichloromethane. In contrast, the particu-
late matter from the pure fuel studies
showed the largest surface area initially
and this area was reduced on each suc-
cessive run with benzene or hexane.
Higher activation temperatures up to
400°C temporarily increased the area but
not to the original levels, possibly indi-
cating some very strongly adsorbed mate-
rial that could not be removed under the
described conditions.
Heats of adsorption showed a similar
phenomenon. This response indicated
that the surface of the particulate from
the diesel engine using regular fuel was
already covered and that after 400°C
activation, a fresh surface was exposed
and normal monolayer coverage occurred.
This normal situation prevailed for the
carbon black and pure fueled diesel
engine particulates.
A dynamic GC method to measure
isoteric heats was employed by using the
particles as the column. The method
allowed use of a wide variety of conditions
and materials. Test results are shown in
Table 2.
Particulate
Source
Pure fuel
Regular fuel
Carbon black (Spheron 6)
Density
g/cm3
-
1.5 -1.8
1.85-2
Diameter
nm
36
26.8
410
Surface Area
Calculated
From (EM)
86.7
116.1
76.9
BET
Surface
103.7
112.2
110
Roughness
Factor
1.2
0.97
1.43
Table 2. Isoteric Heats of Adsorption
Adsorbate
Water
Methanol
Dichloromethane
n-Hexane
1 -Hexane
Benzene
Cyclohexene
Cyclohexane
Ethylbenzene
Acetophenone
Benzaldehyde
n-Octane
Phenol
Naphthalene
Anthracene
Phenanthrene
Heat of
Vaporization
(kcal/mole)
9.72
8.98
_
7.63
7.79
8.15
-
7.83
9.3
11.73
11.66
9.2
11.89
12.31
16.82
14.18
Heat of Adsorption (kcal/mole)
Graphitized
Diesel Particulate Matter Carbon
This Study DPM-EPA Black*
10.3
9.0
8.6
11.4
10.6
12.0
10.2
8.7
15.2
16.1
17.4
15.2
16.4
16.4
-
-
6.9
4.8
5.O
15.0
10.2
12.8
9.7
9.3
8.3
15.1
12.2
8.4
12.2
12.3
11.1
19.0
5.6
5.3
-
10.4
-
9.8
9.1
8.7
12.7
13.0
-
13.4
13.0
17.3
-
-
*These data were obtained from Gas Adsorption Chromatographyf'/f/se/ev, A. V..and Yashin, Y.I.
New York: Plenum Press, 1969).
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Electron paramagnetic studies were
made on all particles to determine surface
character and interactions. In general,
the spin concentrations were similar for
the two diesel particle samples and for
carbon black, as reported in the literature.
The addition of oxygen or nitric oxide
caused an expected decrease in the
signal. Nitrogen dioxide caused no imme-
diate effect but showed a strong increase
with 24-hour exposure, indicating that
reactions leading to paramagnetic species
has occurred. Irradiation by UV light
affected the surface activity; the degree of
effect depended upon conditions and
pressure in the system as well as the
nature of the components. The most
significant change was a 30 to 50%
increase observed when the sample was
maintained in a vacuum.
Conclusions and
Recommendations
Diesel engines operated with pure
component fuels have similar emissions
to vehicles operated with full-boiling-
range diesel fuels. The soluble organic
matter associated with the particulates
from pure component fuels, although
simpler in composition because of the
absence of the multiplicity of fuel com-
ponents, has many of the polynuclear
aromatic compounds and other organic
species that result from full-boiling-range
fuels. The particulates resulting from pure
fuel and from regular fuel also have
similar biologic activity.
Operation of the diesel engine on a
nitrogen free oxidizer demonstrated that
the biologic activity was reduced by over
an Border of magnitude. This biologic
activity was correlated to nitropyrene,
although the concentration of nitropyrene
was insufficient to account for activity.
The amount of nitropyrenes present did
not correlate with the amount of nitrogen
dioxide present. When particles obtained
from the nitrogen free experiments were
exposed to nitrogen dioxide, the amount
of nitropyrene and the biologic activity
increased with increased doses of nitro-
gen dioxide.
The surface character of the particulate
matter generated by the pure component
fuels was similar to that of regular diesel
fuel particulate. Both were comparable tc
carbon black fuel in surf ace area but with
somewhat higher activity for many com-
pounds. The particles were shown tc
have a multilayer coating of organics anc
they were characterized by dissolution ir
the organic coating rather than monolayei
adsorption.
Terence H. Risby is with Division of Environmental Chemistry, Department of
Environmental Health Sciences, The Johns Hopkins University School of
Hygiene and Public Health, Baltimore, MD 21205.
John E. Sigsby is the EPA Project Officer (see below).
The complete report, entitled "Exhaust Emissions from a Diesel Engine," (Order
No. PB 84-122 910; Cost: $13. OO, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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