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Characterization of Fine Particulate Matter
Produced by Combustion of Residual Fuel Oil
Gerald P. Huffman a , Frank E. Huggins a , Naresh Shah a , Robert Huggins a , William P.
Linak b , C. Andrew Miller b , Ronald J. Pugmire c , Henk L.C. Meuzelaar c , Mohindar S.
Seehra d & A. Manivannan d
a Consortium for Fossil Fuel Liquefaction Science , University of Kentucky , Lexington ,
Kentucky , USA
b U.S. Environmental Protection Agency, National Risk Management Research
Laboratory , Research Triangle Park , North Carolina , USA
c Department of Chemical and Fuels Engineering , University of Utah , Salt Lake City ,
Utah , USA
d Physics Department , West Virginia University , Morgantown , West Virginia , USA
Published online: 27 Dec 2011.
To cite this article: Gerald P. Huffman , Frank E. Huggins , Naresh Shah , Robert Huggins , William P. Linak , C. Andrew
Miller , Ronald J. Pugmire , Henk L.C. Meuzelaar , Mohindar S. Seehra & A. Manivannan (2000) Characterization of Fine
Particulate Matter Produced by Combustion of Residual Fuel Oil, Journal of the Air & Waste Management Association,
50:7, 1106-1114, DOI: 10.1080/10473289.2000.10464157
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Huffman et al.
TECHNICAL PAPER
ISSN 1047-3289 J. Air & Waste Manage. Assoc. 50:1106-1114
Copyright 2000 Air & Waste Management Association
Characterization of Fine Particulate Matter Produced by
Combustion of Residual Fuel Oil
Gerald P. Huffman, Frank E. Huggins, Naresh Shah, and Robert Huggins
Consortium for Fossil Fuel Liquefaction Science, University of Kentucky, Lexington, Kentucky
William P. Linak and C. Andrew Miller
U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Research Triangle
Park, North Carolina
Ronald J. Pugmire and Henk L.C. Meuzelaar
Department of Chemical and Fuels Engineering, University of Utah, Salt Lake City, Utah
Mohindar S. Seehra and A. Manivannan
Physics Department, West Virginia University, Morgantown, West Virginia
ABSTRACT
Cu, Zn, and As K-edges and at the Pb L-edge. Deconvolution
of the X-ray absorption near edge structure (XANES) region
of the S spectra established that the dominant molecular
forms of S present were sulfate (26–84% of total S) and
thiophene (13–39% of total S). Sulfate was greater in the
PM2.5 samples than in the PM2.5+ samples. Inorganic sulfides
and elemental sulfur were present in lower percentages. The
Ni XANES spectra from all of the samples agreed fairly well
with that of NiSO4, while most of the V spectra closely re-
sembled that of vanadyl sulfate (VO•SO4•xH2O). The other
metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present
predominantly as sulfates. Arsenic was present as an arsen-
ate (As+5). X-ray diffraction patterns of the PM2.5 fraction
exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca,
etc.) superimposed on broad peaks due to amorphous car-
bons. All of the samples contain a significant organic com-
ponent, with the loss on ignition (LOI) ranging from 64 to
87% for the PM2.5 fraction and from 88 to 97% for the PM2.5+
fraction. Based on 13C nuclear magnetic resonance (NMR)
analysis, the carbon is predominantly condensed in graphitic
structures. Aliphatic structure was detected in only one of
seven samples examined.
Combustion experiments were carried out on four different
residual fuel oils in a 732-kW boiler. PM emission samples
were separated aerodynamically by a cyclone into fractions
that were nominally less than and greater than 2.5 µm in
diameter. However, examination of several of the samples
by computer-controlled scanning electron microscopy
(CCSEM) revealed that part of the PM2.5 fraction consists of
carbonaceous cenospheres and vesicular particles that range
up to 10 µm in diameter. X-ray absorption fine structure
(XAFS) spectroscopy data were obtained at the S, V, Ni, Fe,
IMPLICATIONS
Regulations on PM2.5 should be based on the best scien-
tific data, particularly with regard to characterization. Al-
though there are many analytical techniques for deter-
mining the elemental composition of PM2.5, information
on molecular structure and microstructure is difficult to
obtain. This paper presents the results of an investigation
of the structure of PM2.5 from combustion of residual oil
using a variety of analytical techniques (XAFS spectros-
copy, CCSEM, 13C NMR, inductively coupled plasma/
mass spectrometry [ICP/MS], and X-ray diffraction [XRD]).
The results demonstrate that these techniques provide a
rather complete analysis of the molecular structure of both
the inorganic and organic components of PM2.5. Improved
information is also obtained on particle size distributions,
composition ranges, and morphologies. Since both health
effects and source apportionment of PM2.5 are closely re-
lated to such parameters, this type of information should
be valuable to regulatory authorities and industry.
INTRODUCTION
The U.S. Environmental Protection Agency (EPA) currently
is considering new regulations for fine airborne particulate
matter less than 2.5 µm in diameter (PM2.5). Such regula-
tions should be based on the best scientific data, particu-
larly with regard to fine particle characterization. Although
there are many analytical techniques for determining the
1106 Journal of the Air & Waste Management Association
Volume 50 July 2000

Huffman et al.
elemental composition of PM2.5, there has been relatively
little research on its molecular structure and microstruc-
ture. Many scientists believe that both the effects on hu-
man health and the source apportionment of PM2.5 are
closely related to parameters such as particle size distri-
butions and morphology and the valence and solubility
of critical elements. It is therefore essential to identify and
evaluate analytical methods that can provide such struc-
tural information.
Four residual fuel oils were combusted, with sulfur
contents ranging from 0.53 to 2.33 wt %. The ultimate
analyses of these oils, together with the concentrations of
the metals of interest for this paper, are given in Table 1.
Table 2 contains the loss on ignition (LOI) and metal con-
centrations for the PM2.5 and PM2.5+ fractions. The metal
analyses were performed using acid digestion and ICP/MS.10
Although burnout was fairly complete (> 99.7%), the inor-
ganic content of the oils was quite low (0.02–0.10 wt %
ash), and the LOI results indicate that the dominant ele-
ment of the ROFA is carbon (64–87 wt % for PM2.5 and 88–
97 wt % for PM2.5+). V is present at relatively large
concentrations (~0.5–5 wt %); Ni, Fe, and Zn are present at
moderate concentrations (~0.1–0.5 wt %); and several met-
als (Pb, As, Cr, Cu, Mn, Sb, and Cd) are present at concen-
trations that are rather low (~20–1000 ppm) but could still
be significant for health considerations. The metals are typi-
cally more concentrated in the PM2.5 samples than in the
PM2.5+ samples by factors from ~3 to 6.
X-ray absorption fine structure (XAFS) spectroscopy is
a synchrotron radiation-based technique that is uniquely
well-suited to characterization of the molecular structure
of individual elements in complex materials. In previous
research, we have used XAFS spectroscopy to determine
the molecular forms of environmentally important ele-
ments (e.g., S, Cl, As, Cr, Hg, Ni, etc.) in coal, oil, fly ash,
and sorbents.1-7 Our initial investigations of PM indicate
that XAFS will also be a powerful tool in this area.8,9
In the current work, XAFS spectroscopy and a num-
ber of additional analytical techniques were applied to a
suite of residual oil fly ash (ROFA) samples separated aero-
dynamically into PM2.5 and PM2.5+ fractions. Briefly, the
characterization data obtained included
XAFS SPECTROSCOPY RESULTS
The samples were investigated by XAFS spectroscopy at
the Stanford Synchrotron Radiation Laboratory (Menlo
Park, CA) and the National Synchrotron Light Source at
Brookhaven National Laboratory (Upton, Long Island,
NY). All measurements were carried out in the fluores-
cent mode using either a Lytle detector or a multi-element
Ge array detector, as described elsewhere.1-4 The X-ray ab-
sorption near edge structure (XANES) regions of the spec-
tra were analyzed by deconvolution, derivative, and
comparative analysis methods, as discussed in earlier pa-
pers.1-7 The results for the elements investigated to date
are summarized below.
(1) XAFS analysis of the molecular structure of S, V,
Ni, Fe, Cu, Zn, Pb, and As;
(2) computer-controlled scanning electron micros-
copy (CCSEM) analysis of particle size, composi-
tion, and morphology;
(3) 13C nuclear magnetic resonance (NMR) analysis
of the molecular structure of carbon, the domi-
nant element;
(4) X-ray diffraction (XRD) identification of crystal-
line phases; and
(5) inductively coupled plasma/mass spectrometry
(ICP/MS) determination of metal concentrations.
Sulfur
Typical S K-edge XANES spectra of ROFA PM2.5 and PM2.5+
samples are shown in Figure 1. The spectra are deconvoluted
by a least-squares computer analysis into a series of peaks
(50% Lorentzian–50% Gaussian) and two rounded arctan-
gent step functions, as discussed elsewhere.1,2 Most of the
peaks represent 1s→3p transitions of photoelectrons ex-
cited from the K-shell by X-ray absorption. Both the posi-
tion and relative intensity of these peaks vary significantly
with the electronic state of the S atom, increasing with
increasing valence. By using calibration data generated from
mixtures of standard compounds, the peak area percent-
ages can be translated into percentages of the total S con-
tained in different molecular forms.1,2
COMBUSTION PROCEDURE
The combustion experiments were carried out in a North
American three-pass fire tube package boiler, which is a
practical, commercially available heavy fuel oil combus-
tion unit. A detailed description of this boiler is given
elsewhere.10 Samples were separated aerodynamically by
a cyclone into PM2.5 and PM2.5+ fractions. The sampling
system consists of a large dilution sampler capable of
isokinetically sampling 0.28 m3/min (10 ft3/min) of flue
gas using a Source Assessment Sampling System (SASS)
cyclone. Details on the construction and operation of this
sampling system are available elsewhere.11 The SASS cy-
clone produces 50 and 95% collection efficiencies at ap-
proximately 1.8 and 2.5 µm diameters, respectively. The
resulting PM is collected on large (65-cm) Teflon (DuPont)-
coated glass fiber filters, transferred to sampling jars, and
made available for analysis.
The results of this analysis for the ROFA PM samples
are summarized in Table 3. The dominant molecular forms
of S observed are sulfate and thiophenic S. Sulfate was
greater in the PM2.5 samples than in the PM2.5+ samples,
reflecting the greater degree of carbon burnout for the
Volume 50 July 2000
Journal of the Air & Waste Management Association 1107

Huffman et al.
Table 1. Analysis of the four fuel oils examined.
No. 5 Oil
Low Sulfur
No. 6 Oil
Medium Sulfur
No. 6 Oil
High Sulfur
No. 6 Oil
Ultimate Analysis, wt %
Carbon
Hydrogen
Nitrogen
Sulfur
86.36
10.82
0.33
1.73
0.34
0.35
0.07
86.00
11.29
0.43
0.53
1.24
0.50
0.02
86.48
10.98
0.43
0.93
0.67
0.50
0.03
85.49
10.36
0.35
2.33
0.92
0.50
0.10
Oxygen*
Moisture
Ash
Elemental Analysis, µg/g
Arsenic
Beryllium
Cadmium
Chromium
Copper
Iron
2
< 1
0.1
0.5
4
0.2
< 0.3
0.50
1.08
0.56
23
0.2
< 0.3
0.60
0.96
0.78
19
0.1
< 0.3
0.60
1.05
3.5
50
3
21
Lead
0.80
0.06
17
0.58
0.12
22
4.5
Mercury
Nickel
–
0.10
30
34
< 2
180
39
Selenium
Vanadium
Zinc
< 0.1
35
< 0.1
70
< 0.1
220
74
4.11
3.70
Figure 1. Typical deconvolution of S K-edge XANES spectra of ROFA
PM2.5 and PM2.5+
.
Note: * Determined by difference.
The S in the PM2.5 of the ROFA from a high S residual oil
burned in a second furnace, where carbon burnout was
much more complete, was 100% sulfate.
smaller particles. Additional components, including el-
emental S and inorganic sulfides, are present in lower
percentages. The origin of the elemental S is not clear.
Table 2. Metal concentrations and enrichment ratios of PM2.5 and PM 2.5+ samples (µg/g).
Low Sulfur No. 6 Oil
2.5 2.5+ 2.5/2.5+
Medium Sulfur No. 6 Oil
High Sulfur No. 6 Oil
2.5 2.5+ 2.5/2.5+
No. 5 oil
2.5
2.5+ 2.5/2.5+
2.5
2.5+ 2.5/2.5+
Antimony
Arsenic
23.4
49.9
0.40
0.50
32.6
123
4.90
11.0
0.10
0.21
27.5
33.8
1410
21.5
428
4.8
4.5
4.0
2.4
1.2
3.6
3.6
5.3
3.4
2.7
5.6
3.2
4.9
0.7
24.2
49.8
0.47
1.26
44.7
159
2.9
4.9
8.3
10
48.6
35.9
0.46
19.3
60.2
1050
3850
990
8.20
8.60
0.15
1.84
41.3
222
5.9
4.2
3.1
11
34.5
18.7
0.44
2.75
60.5
233
4.86
1.70
0.20
0.69
33.3
58.1
1110
–
7.1
11
Beryllium
Cadmium
Chromium
Copper
0.11
0.46
46.9
36.8
1510
22.4
436
4.3
2.7
1.0
4.3
3.0
7.3
3.3
2.3
6.1
4.7
4.4
0.8
2.2
4.0
1.8
4.0
3.8
–
1.5
4.7
1.7
11
Iron
5100
114
4460
164
2300
94.2
2220
42.8
2270
19900
2740
969
4220
–
Lead
Magnesium
Manganese
Nickel
1450
93.3
4840
14700
1600
658
1450
84.5
7470
35300
1840
790
6190
73.2
8020
58900
21000
866
2.9
1.7
3.5
3.0
7.7
0.9
1770
89.9
10600
58600
2750
641
101
18
34.1
863
37.1
1230
7560
422
23.6
2200
13000
6530
883
3.8
4.8
4.5
0.4
0.7
Vanadium
Zinc
4510
328
LOI, mg/g
903
978
1108 Journal of the Air & Waste Management Association
Volume 50 July 2000

Huffman et al.
Vanadium
The molecular forms of the metals investigated in this
study were identified by comparing the XANES spectra
and the first derivative of the XANES spectra of the ROFA
samples to those of standard compounds. The standard
compound suite included most of the oxides, sulfates, and
sulfides of each metal investigated.
Most of the V XANES and first derivative XANES spec-
tra from both the PM2.5 and PM2.5+ fractions closely re-
semble the spectrum of vanadyl sulfate (VO•SO4•xH2O).
This is brought out most clearly by the distinctive first
derivative of the XANES spectrum, which exhibits peaks
in nearly identical positions and with similar intensities
to the first derivative of the XANES spectrum of
VO•SO4•3H2O reported by Wong et al.12 and also mea-
sured in this study. Typical V XANES and first derivative
spectra from a PM2.5 sample are shown in Figure 2. The
spectra of several samples also indicate the presence of
minor amounts of oxide, probably V2O5.
Energy, eV
Nickel
The Ni XANES and first derivative spectra from the PM
samples (see Figure 3) were found to agree well with those
of NiSO4. For ease of comparison, the absorption scale for
all spectra has been normalized to the same arbitrary unit
of intensity. Similar XAFS results were obtained for Ni in
an earlier investigation of ROFA5 by the authors. There is
again evidence of a small amount of oxide (NiO) in one
of the PM2.5 samples (low S No. 6), both in the first deriva-
tive spectrum and in the radial structure function obtained
by Fourier analysis of the XAFS spectrum.
Energy, eV
Figure 2. Distinctive V K-edge XANES (top) and first derivative spectra
(bottom) for the ROFA PM2.5 samples identify vanadyl sulfate
(VOSO4•xH2O) as the dominant molecular form of vanadium.
standard compounds. One PM2.5 sample (low S No. 6) con-
tains a small amount of iron oxide, probably Fe3O4.
Iron
Copper, Zinc, and Lead
The Fe XANES and the first derivatives of the Fe XANES of
the ROFA PM samples (see Figure 4) agree well with those
of ferric sulfate, Fe2(SO4)3, indicating that it is the domi-
nant iron compound in both the PM2.5 and PM2.5+ samples.
This conclusion was reached by comparing the spectra for
the ROFA PM samples with those of numerous iron-based
Although fewer samples have been examined, and the
data are of somewhat lower quality because of lower con-
centrations, it appears that sulfates are the dominant
phases detected by the XANES spectra for these metals
also. The phases tentatively identified are CuSO4•xH2O,
ZnSO4, and PbSO4.
Table 3. XANES results for the percentages of the total sulfur contained in different molecular forms in ROFA PM samples.
Sample
PM Size (µm)
Sulfate
Thiophene
Elemental S
Inorganic Sulfide
Other Forms
No. 5 Oil
< 2.5
> 2.5
< 2.5
> 2.5
< 2.5
> 2.5
< 2.5
> 2.5
55
32
84
58
73
55
54
26
24
37
14
34
13
35
29
39
5
8
–
6
6
6
5
9
11
19
–
5
4
2
2
8
3
1
–
No. 5 Oil
Low S No. 6 Oil
Low S No. 6 Oil
Med. S No. 6 Oil
Med. S No. 6 Oil
High S No. 6 Oil
High S No. 6 Oil
–
–
–
11
26
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Journal of the Air & Waste Management Association 1109

Huffman et al.
Arsenic
The As XANES spectra establish that the
arsenic is present as an arsenate (As+5)
but do not identify the specific phase.
A discussion of the identification of ar-
senic valence states from XANES spec-
tra can be found in refs 3 and 4.
CCSEM DATA
The principles of CCSEM have been sum-
marized in numerous previous papers.
Briefly, as the electron beam is rastered
across the sample, the back-scattered
electron intensity is measured and com-
pared to a preset discriminator level to
detect particles. When a particle is de-
tected, the stepping density of the elec-
tron beam is increased by a factor of 256
and the cross-sectional area, maximum
and minimum diameters, and energy
dispersive X-ray (EDX) spectrum of the
particle are measured. Details of the
measurement procedure are summarized
elsewhere.13-15 With a well-prepared
sample, it is possible to measure the size
and approximate composition of about
1000 particles in several hours. In the
current studies, the CCSEM examination
was carried out on PM samples dispersed
on nucleopore filters, prepared as dis-
cussed elsewhere.13 For the current PM
Figure 3. Ni XANES and first derivative spectra for the ROFA PM2.5 indicate that the dominant Ni
phase is NiSO4. The spectra are normalized to unit step height for easy comparison.
samples, C was by far the dominant element detected in
the EDX spectra, while S was detected in most particles at
concentrations of ~1–10%. Since EDX collection times were
only 5 sec per particle, V, Ni, and other metals were de-
tected only as minor components of selected particles.
Some preliminary CCSEM data for two ROFA PM2.5
samples are shown in Table 4 and Figure 5. The data are
considered to be preliminary, because preparation of sat-
isfactory SEM specimens for these samples has proven to
be difficult, and we are still refining our procedures. Con-
sequently, the current data, while informative, should be
considered qualitative in nature. Table 4 indicates the three
major classes of particles identified and the average com-
position of those classes based on the EDX spectra. Better
information can be obtained regarding particle composi-
tion by the use of binary and ternary composition dia-
grams,13 such as the C–S diagram for the medium S No. 6
PM2.5 sample shown in Figure 5a. This diagram includes all
particles for which C + S was greater than 80%. It illustrates
that the carbon-rich char particles contain a range of S
concentrations, from 0 to approximately 20%, with peaks
in the 0–2% and the 6–10% ranges. The particle size
distribution for all of the particles analyzed for the low S
No. 6 PM2.5 sample is shown in Figure 5b. It is seen that a
significant percentage of the particles classified aerody-
namically as PM2.5 by the cyclone separator are in fact
greater than 2.5 µm in diameter. Many of these appear to
be cenospherical, vesicular carbon particles, such as those
shown in Figure 6. The arrows in Figure 6 indicate inor-
ganic particles rich in V and S, some of which also con-
tain Ca, Al, and Si. These particles presumably consist
primarily of vanadyl sulfate. It is worth noting that this
type of configuration, small particle transition metal
phases on a highly porous carbon support, could act as a
good catalyst for chemical reactions. This type of micro-
structure is frequently observed in the ROFA PM2.5.
NMR DATA
There has been extensive use of 13C NMR in examining the
molecular structure of carbon in a wide range of materials.
It is perhaps the best method of measuring the relative
percentages of aromatic and aliphatic carbon in organic
materials and can provide detailed information on the ex-
tended carbon skeletal structure and bonding groups.
1110 Journal of the Air & Waste Management Association
Volume 50 July 2000

Huffman et al.
content of the samples was very low, and
hence, no useful data were obtained us-
ing this experimental technique. Proton
spectra taken on several samples verified
the very low H/C ratios for all but the
PM2.5 sample derived from combustion
of the high S No. 6 oil. The 13C NMR
spectra were then acquired by using
block decay with a pulse repetition rate
of 10 sec and accumulating between
17,000 and 25,000 scans. Six of the seven
samples examined exhibited spectra es-
sentially identical to that shown in Fig-
ure 7 for the low S No. 6 oil PM2.5 sample.
These spectra indicate that the carbon
in these samples is predominantly con-
densed in graphitic structures. Second
moment (line width) measurements are
uniform at ~75 ppm (full width at half
height [FW/HH]) for all six of the
samples. However, the second moment
for the high S No. 6 PM2.5 sample indi-
cates a much narrower aromatic band
(peak at ~120 ppm, FW/HH = 45 ppm),
and the spectrum clearly shows the pres-
ence of aliphatic structure (peak at
~20ppm).
Energy, eV
Energy, eV
XRD DATA
The XRD experiments were carried out
using a Wide Angle X-Ray Diffracto-meter
Figure 4. Fe XANES and first derivative spectra indicate that Fe2(SO4)3 is the dominant Fe
compound in ROFA PM2.5. The spectra are normalized to unit step height for easy comparison.
(Rigaku Model D/Max) employing CuKα
radiation (λ = 1.5418 Å). The data were
Detailed discussion of the methodology involved in such
analyses is given elsewhere.16 Four of the PM2.5 and three of
the PM2.5+ ROFA samples were examined by 13C NMR. Cross-
polarization experiments suggested that the proton
taken in the step-scan mode using 0.04° steps and 30-sec
collection time at each step. The data were analyzed using a
Jade software package and the Joint Commision of Power
Diffraction Standards (JCPDS) data files.
Table 4. CCSEM results for two PM2.5 samples. Composition in atomic %.
Medium S #6 PM2.5 – 689 particles.
Classes
C/S Rich
C Rich
Number
Number %
61.4
C
S
10
2
Al
1
Si
1
423
222
35
83
94
59
32.0
1
1
Al/Si Rich
Others
5.3
2
11
26
9
1.3
Low S #6 PM2.5 – 522 particles.
Classes
C/S Rich
C Rich
Number
Number %
58.4
C
S
11
1
Al
1
Si
1
310
177
20
82
94
60
36.7
2
0
Al/Si Rich
Others
3.6
4
12
21
15
1.3
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Journal of the Air & Waste Management Association 1111

Huffman et al.
Figure 5a. CCSEM C–S distribution for medium S No. 6 PM2.5
.
Figure 5b. CCSEM particle size distribution for low S No. 6 PM2.5
.
Figure 6. Highly vesicular carbon rich char particles. The arrows point
Typical X-ray diffractograms are shown in Figure 8
for the PM2.5 from the No. 5 oil and the PM2.5 and PM2.5+
from the high S No. 6 oil. The diffractograms consist of
sharp lines superposed on two broad peaks at 2θ = 26°
and 44°. The broad peaks are due to amorphous carbon.17
The sharp lines are due to inorganic compounds and have
been identified as sulfates and sulfites of Zn, V, Ni, Pb, Fe,
Ca, and Cu. The identified compounds are CaSO4,
Zn4SO4(OH)6•5H2O, Zn(SO3)2.5H2O, VOSO4, NiSO4•6H2O,
PbS2O3, Fe3(SO4)4•14H2O, ZnSO4•xH2O, Ca(SO4)•2H2O,
and Cu2SO4. Qualitatively, the intensities of the lines are
largest for samples obtained from the high S No. 6 oil
and for the PM2.5 fraction of No. 5 oil (BL5FH). This is
understandable, since the high sulfur content would tend
to produce higher levels of the sulfates. Generally, PM2.5
fractions tend to have higher concentrations of the sul-
fates as compared to the PM2.5+ fractions, as illustrated
by the comparison of the diffractograms for the PM2.5
and PM2.5+ fractions from high S No. 6 oil in Figure 8. For
the PM2.5 fraction from the No. 5 oil, the intensities of
the lines are the largest of all the samples, but only weak
lines due to CaSO4 are observed for the PM2.5+ fraction. A
more complete summary of all the XRD data has been
given elsewhere.18
to inorganic particles on the particle surfaces, rich in V and S.
SUMMARY AND CONCLUSIONS
The structure of PM2.5 and PM2.5+ from the combustion
of several residual fuel oils in a commercial boiler has
Figure 7. 13C NMR spectra of PM2.5 from ROFA. Only the low S No. 6
PM2.5 sample shows any aliphatic structure (top spectrum).
1112 Journal of the Air & Waste Management Association
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Huffman et al.
Figure 8. Typical X-ray diffractograms of PM2.5 and PM2.5+ samples from ROFA.
been characterized by a range of analytical techniques.
XAFS spectroscopy was used to investigate the molecu-
lar structure of S, a number of metals (V, Ni, Fe, Zn, Cu,
and Pb), and As. Deconvolution of the S XANES spectra
revealed that the dominant molecular forms of S ob-
served were sulfate and thiophenic S. Sulfate was greater
in the PM2.5 samples than in the PM2.5+ samples, reflect-
ing the greater degree of carbon burnout for the smaller
particles. Sulfates were identified by XAFS as the domi-
nant metal compounds (VOSO4•xH2O, NiSO4, Fe2(SO4)3,
etc.). Arsenic was present as an arsenate (As+5). XRD also
identified a number of metal sulfates and sulfites, in-
cluding CaSO4. CCSEM measurement of the particle size
distributions of two PM2.5 samples established that a
significant percentage of particles exceeded 2.5 µm in
diameter. Many of these were vesicular, cenospherical
carbon char particles. The surfaces of these highly po-
rous carbon particles were decorated with small (~1–3
µm) metal sulfate particles. This structure is similar to
that of a supported catalyst and suggests that such par-
ticles might play a role in the formation of radicals in the
lung. Based on 13C NMR, the carbon in the PM was pre-
dominantly graphitic or soot-like in structure, with only
one sample exhibiting an aliphatic component.
The current study is part of a more general investiga-
tion of petroleum-derived PM2.5. Future work, in addition
to further characterization of the current samples, will
include characterization of diesel emissions and PM
Volume 50 July 2000
Journal of the Air & Waste Management Association 1113

Huffman et al.
14. Huggins, F.E.; Kosmack, D.A.; Huffman, G.P.; Lee, R.J. Coal
Mineralogies by SEM Automatic Image Analysis. In Scanning Electron
Microscopy, Vol. I; SEM Inc., AMF O’Hare: Chicago, IL, 1980; pp 531-
540.
samples collected on filters from the ambient atmosphere
in appropriate locations.
15. Huffman, G.P.; Huggins, F.E.; Shah, N. Prog. Energy Combust. Sci. 1990,
16(4), 293-302.
16. Solum, M.S.; Pugmire, R.J.; Grant, D.M. Energy & Fuels 1989, 3, 187-
193.
17. Babu, V.S.; Farinash, L.; Seehra, M.S. J. Mater. Res. 1995, 10, 1075.
18. Manivannan, A.; Seehra, M. S. ACS Fuel Division Preprints, in press.
ACKNOWLEDGMENTS
Support of this research under U.S. Department of Energy
(DOE) Fossil Energy/National Petroleum Technology Of-
fice (FE/NPTO) contract No. DE-AC26-99BC15220 is grate-
fully acknowledged. The XAFS experiments were
conducted at the Stanford Synchrotron Radiation Labo-
ratory and the National Synchrotron Light Source, which
are also supported by the DOE.
REFERENCES
1. Huffman, G.P.; Mitra, S.; Huggins, F.E.; Shah, N.; Vaidya, S.; Lu, F.
Energy & Fuels 1991, 5, 574-581.
About the Authors
2. Mehdi Taghiei, M.; Huggins, F.E.; Shah, N.; Huffman, G.P. Energy &
Fuels 1992, 6, 293-300.
3. Huffman, G.P.; Huggins, F.E.; Shah, N.; Zhao, J. Fuel Processing Technol.
1994, 39, 47-62.
4. Huggins, F.E.; Huffman, G.P. Int. J. Coal Geology 1996, 32, 31-53.
5. Galbreath, K.C.; Zygarlicke, C.J.; Toman, D.L.; Huggins, F.E.; Huffman,
G.P. Energy & Fuels 1998, 12(4), 818-822.
6. Huggins, F.E.; Najih, M.; Huffman, G.P. Fuel 1999, 78, 233-242.
7. Huggins, F.E.; Huffman, G.P.; Dunham, G.E.; Senior, C.L. Energy &
Fuels 1999, 13, 114-121.
8. Huggins, F.E.; Huffman, G.P.; Robertson, J.D. ACS, Environ. Chem. Div.
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Srinivasachar, S.; Peterson, T.; Wendt, J.; Gallagher, N.; Bool, L.;
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Gerald P. Huffman is the director of the Consortium for Fos-
sil Fuel Liquefaction Science, a research center of the Uni-
versity of Kentucky (UK), and a research professor of Chemi-
cal and Materials Engineering. Frank E. Huggins and Naresh
Shah are research professors of Chemical and Materials
Engineering at UK. Robert Huggins is a student who was
formerly engaged in research at UK. William P. Linak and C.
Andrew Miller are scientists at the Environmental Protec-
tion Agency National Risk Management Research Labora-
tory at Research Triangle Park, NC. Ronald J. Pugmire is
associate vice president for research and Henk Meuzelaar
is director of the Micro Analytical Research Center and re-
search professor at the Department of Chemical and Fuel
Science Engineering, respectively, at the University of Utah
in Salt Lake City, UT. Mohindar Seehra and A. Manivannan
are professor and postdoctoral research associate, respec-
tively, in the Physics Department at West Virginia University
in Morgantown, WV.
1114 Journal of the Air & Waste Management Association
Volume 50 July 2000