Subcontract Report

NREL/SR-540-45597

June 2010

Investigation of Nitro-Organic 

Compounds in Diesel Engine 

Exhaust

Final Report

February 2007 – April 2008

John Dane and Kent J. Voorhees

Colorado School of Mines

Department of Chemistry and Geochemistry

Golden, Colorado
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Subcontract Report

NREL/SR-540-45597

June 2010

Investigation of Nitro-Organic 

Compounds in Diesel Engine 

Exhaust

Final Report

February 2007 – April 2008

John Dane and Kent J. Voorhees

Colorado School of Mines

Department of Chemistry and Geochemistry

Golden, Colorado

NREL Technical Monitor: Matthew Ratcliff

Prepared under Subcontract No. NEV-7-77395-01
NOTICE

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i

Acknowledgment

Work described in this report is supported by the U.S. Department of Energy (DOE) Vehicle 

Technologies Program under the Nonpetroleum-Based Fuels task. This task is managed by 

Kevin Stork at DOE and by Robert McCormick at the National Renewable Energy Laboratory.
ii

Executive Summary

Diesel particle filters (DPF) dramatically reduce the level of particulate matter (PM) emitted by 

diesel engines. There has not, however, been much research to verify that unregulated organic 

pollutants associated with diesel PM are also reduced by the use of DPFs. The U.S. Department 

of Energy’s National Renewable Energy Laboratory recently upgraded its ReFUEL engine and 

vehicle testing facility’s capabilities to speciate unregulated gas-phase emissions. To 

complement this capability, the laboratory contracted with the Colorado School of Mines to 

study the effects of soy biodiesel fuel and a DPF on emissions of polycyclic aromatic 

hydrocarbons (PAH) and nitro-polycyclic aromatic hydrocarbons (NPAH). These are related 

types of harmful but unregulated emissions associated with PM from diesel engines.

In this study, the Colorado School of Mines developed procedures to sample diesel PM 

emissions from raw and diluted exhaust, with and without a DPF. They also developed improved 

procedures for extracting PAH and NPAH from the PM and quantifying those compounds with a 

gas chromatograph-electron monochromator mass spectrometer. While the study found the DPF 

generally reduced PAH emissions by 1 to 3 orders of magnitude, PAH conversion was lowest in 

the case of B100, suggesting that PAHs were actually being formed in the DPF. This finding 

warrants further investigation. 

Orders of magnitude reductions were also generally found for NPAH emissions exiting the DPF. 

However, the conversion of 1-nitropyrene through the DPF was less than 50% for all fuels. 

Because 1-nitropyrene has been shown to be mutagenic and carcinogenic, and because the DPF 

may concentrate condensable organics on a larger number of smaller particles, this could be a 

very significant concern. Differences in NPAHs between raw and dilution-tunnel PM samples 

suggest that chemical reactions continue through the raw exhaust system or occur during 

dilution. The apparent net effect is to reduce the diversity of NPAH compounds and in particular 

increase the amount of 1-nitropyrene.
iii

Acronyms and Abbreviations

AVL powertrain engineering and test equipment manufacturer

B100 100% biodiesel diesel fuel

B20 20% biodiesel diesel fuel 

Cert certification diesel fuel

CSM Colorado School of Mines 

DCM dichloromethane 

DNPH dinitrophenyl hydrazine

DOC diesel oxidation catalyst 

DPF diesel particle filter 

DPF-out exhaust down-stream of installed DPF

ECD electron capture detectors 

EI electron ionization

EI− negative ion electron ionization 

EI+ positive ion electron ionization 

EM electron monochromator 

EM-MS electron monochromator mass spectrometry

Engine-out exhaust without DPF installed 

EPA Environmental Protection Agency 

FAME fatty acid methyl ester

GC gas chromatography

GC/EM-MS GC-MS instrument including trochoidal EM

GC-MS gas chromatograph-mass spectrometry 

HPLC high-pressure liquid chromatography

JEOL EM-MS instrument manufacturer

MFC mass flow controller 

NCI negative-ion chemical ionization

NIST National Institute of Science and Technology 

NPAH nitro-polycyclic aromatic hydrocarbons 

NREL National Renewable Energy Laboratory

PAH polycyclic aromatic hydrocarbons

PM particulate matter 

PTFE polytetrafluoroethylene 

ReFUEL NREL’s Renewable Fuels and Lubricants Laboratory

Rel Int relative intensity

SIM selected ion monitoring 

SPE solid-phase extraction

TIC total ion current

URG Name of PM filter-holder vendor
iv

Table of Contents

EXECUTIVE SUMMARY ................................................................................................ ii

1. INTRODUCTION .......................................................................................................... 1

2. GC/ELECTRON MONOCHROMATOR-MASS SPECTROMETRY ......................... 3

2.1 Background............................................................................................................... 3

2.2 Instrumentation ......................................................................................................... 4

3. METHOD DEVELOPMENT......................................................................................... 5

3.1 Filter Experiments..................................................................................................... 5

3.2 PM Filter Conditioning and Weighing ..................................................................... 6

3.3 Solvent Purities......................................................................................................... 9

3.4 PAH and NPAH Standard Studies............................................................................ 9

3.5 Detection of Ethyl Nitrite........................................................................................ 14

3.6 Solvent Extraction Studies...................................................................................... 15

3.7 Solid-Phase Extraction Studies............................................................................... 17

3.8 Evaporation Procedure............................................................................................ 19

3.9 Complete Engine-out Sample Preparation Procedure............................................. 20

3.10 Complete DPF-out Sample Preparation Procedure............................................... 21

3.11 Engine Testing Procedure ..................................................................................... 21

3.12 Raw Exhaust Sampling......................................................................................... 22

3.13 Dilute Exhaust Sampling ...................................................................................... 23

4. RESULTS AND DISCUSSIONS................................................................................. 24

4.1 Raw Exhaust Gravimetric Data .............................................................................. 24

4.2 Results for Engine-out Raw Exhaust...................................................................... 25

4.3 Results for DPF-out Raw Exhaust.......................................................................... 31

4.4 Dilute Exhaust Gravimetric Analysis ..................................................................... 34

4.5 Results for Engine-out Dilute Exhaust ................................................................... 35

4.6 Results for DPF-out Dilute Exhaust ....................................................................... 41

5. CONCLUSIONS AND FUTURE RESEARCH .......................................................... 46

6. REFERENCES ............................................................................................................. 48
1 

1. Introduction 

The National Renewable Energy Laboratory (NREL) Renewable Fuels and Lubricants 

(ReFUEL) facility is an established leader in the field of advanced heavy-duty diesel vehicle and 

engine testing. The rapid development of advanced combustion cycles, exhaust aftertreatment 

systems, and alternative fuels has made it imperative to expand the technical capabilities of this 

facility for determining whether any of these new technologies have unintended consequences 

when it comes to the pollutants that are produced in engine exhaust. 

One area of particular interest is the generation of nonregulated organic compounds by diesel 

combustion. These compounds may impact the environment in detrimental ways that are not 

accounted for by the Environmental Protection Agency (EPA) or the engine manufacturers. 

Diesel particle filters (DPF) have recently been integrated into all new diesel vehicle exhaust 

systems to significantly lower the particulate matter (PM) emitted from the engine. This 

reduction of PM is significant because a number of particularly harmful unregulated pollutants—

including analogs of polycyclic aromatic hydrocarbons, the main focus of this study—reside in 

this phase of the exhaust. As a result, the assumption (without supporting research data) has been 

that these pollutants are also significantly reduced, particularly since the PM weight is reduced 

by over an order of magnitude. As for the gas-phase portion of the post-DPF exhaust, the 

production of unregulated volatile and semi-volatile compounds is also not well understood. 

Because of this lack of information for both gas and particle phases, there is concern that DPFs 

or other exhaust aftertreatment technologies could have negative unintended consequences that 

produce increased levels of nonregulated pollutants. 

ReFUEL has recently expanded its capabilities to include monitoring unregulated volatile and 

semi-volatile pollutants in the engine exhaust gas for both a DPF configuration (termed DPFout) and a non-DPF configuration (termed Engine-out). Additionally, the sampling scenario was 

expanded from diluted exhaust to also include raw exhaust immediately downstream from the 

engine. The sampling techniques for these configurations utilize evacuated, surface-passivated 

canisters for hydrocarbons and dinitrophenyl hydrazine (DNPH) cartridges for trapping 

aldehydes and ketones. The canister samples are then analyzed off-line by gas-chromatograph 

(GC) mass spectrometry (MS), and the DNPH cartridges are analyzed by high-pressure liquid 

chromatography (HPLC). The results for these analyses typically focus on volatile and semivolatile organics that have molecular weights ranging from 30 to 170 amu. 

These improvements to the ReFUEL testing capability do not, however, address all potential 

diesel pollutants. Parallel to these gas-phase efforts, NREL subcontracted the Colorado School of 

Mines (CSM) Mass Spectrometry Laboratory to research the nonregulated pollutants found in 

the particle phase produced from both non-DPF and DPF exhaust configurations. Initially, the 

goal for this research was to develop PM sampling and sample preparation extraction techniques 

that focused on nitro-polycyclic aromatic hydrocarbons (NPAH). Subsequently, the research 

expanded to also include identifying all non-nitrated polycyclic aromatic hydrocarbons (PAH) 

present in the PM. The objective was to develop a clearer understanding of the connection 

between these closely related classes of compounds by generating both PAH and NPAH data for 

each sample. Furthermore, the CSM research would demonstrate the versatility of a specialized 

GC-MS instrument that features a unique trochoidal electron monochromator (EM). This 

instrument (termed GC/EM-MS) enables highly selective detection of molecules with high 
2 

electron affinity, such as NPAHs, which have molecular weights ranging from 123 amu to at 

least 247 amu. Additionally, PAHs produce strong molecular ion signals during standard electron 

ionization (EI+), providing easy identifications for these compounds. The PAHs identified 

during this type of analysis range in mass from 128 amu to at least 202 amu. 

The overall scientific goal of the CSM research, in conjunction with the ongoing research 

conducted at NREL, was to develop a more comprehensive characterization of the organic 

compounds present in heavy-duty diesel engine exhaust. Additionally, this information includes 

the determination of the chemical changes brought about by the use of different fuel blends 

(certification diesel, B20 diesel, and B100 diesel) and the use of a DPF during an advanced 

combustion test cycle. In particular, the DPF-out data would provide new information to a 

portion of the exhaust, particularly for the particle phase, that has not been well characterized in 

previous research. 

This report covers all of the research that was conducted during the CSM subcontract period 

from February 2007 through April 2008. Section 2 discusses the GC/EM-MS utilized during the 

research and provides background information for this system. Section 3 discusses preliminary 

experiments that were conducted to determine the best PM collection filter, extraction 

techniques, and evaporation techniques. Section 4 provides a discussion of the results from both 

the raw and dilute exhaust PM samples. The final section discusses conclusions derived from this 

research project. 
3

2. GC/Electron Monochromator-Mass Spectrometry

2.1 Background 

Over the last 15 years, EM-MS has gained considerable interest for detecting electrophilic 

compounds because it offers the ionization stability of electron capture detectors (ECD) and the 

mass spectral information produced by negative-ion chemical ionization (NCI)-MS. 

Furthermore, EM-MS has the capability of controlling the ionization fragmentation that occurs 

for a given electrophilic analyte, which adds a degree of selectivity and specificity that is not 

realized by either ECD or NCI-MS. A schematic for the underlying design of the EM system is 

shown in Figure 2-1. 

eExit Deflector

Deflector

Anode 1

Anode 2

E

B

Pierce Element

Filament

eExit Deflector

Deflector

Anode 1

Anode 2

E

B

Pierce Element

Filament

Figure 2-1. Schematic of trochoidal electron monochromator

This EM design works by using electrons emitted from a standard tungsten filament and focusing 

them using a Pierce element (a cone-shaped region) into an anode region that further collimates 

the electrons into a deflection region. The deflector region is defined by crossed magnetic (B)

and electric fields (E), which cause the electrons to move with a trochoidal (spiraling) motion.1

 

The magnetic field remains stationary, so the electron energy separation is made by adjusting the 

electric field settings. When these settings are adjusted, each electron in the beam is deflected at 

a right angle to both fields (magnetic and electric) according to their kinetic energy. When the 

magnitude of these electron deflections are controlled using the electric field parameters, only 

electrons with a particular kinetic energy are emitted through the offset exit aperture. This results 

in an electron beam energy (used for ionization) that can be precisely controlled to within 0.4 eV 

with beam intensities only slightly below those observed for conventional electron ionization 

(EI) sources.2

 

When the EM is set for low-energy (0−10 eV) ionization, the net effect is the capture of an 

electron of the proper energy, termed resonance energy, by electrophilic compounds. There are 

two types of electron capture processes utilized for the analysis of electrophilic compounds. The 

first ionization process is described as pure electron capture using an electron energy of ~0 eV 

(Equation I). The second ionization process is called dissociative electron capture and utilizes 

electron energies that can range from 0.1 to 10 eV (Equation II). In this scenario, the electron is 
4

captured by the molecule but then imparts enough energy into the molecule to induce 

fragmentation in very specific ways, depending on the molecular constituents and the energy 

chosen for ionization.

AB + e- → [AB-·

AB + e

]* (~0 eV) (I)

- → [AB-·

]* → A·+ BBy combining the EM-MS with a GC, this technique has the capability of producing data that 

contains molecular mass information, selected ion data for the controlled formation of fragment 

ions from specific functional groups, and GC retention time information.

(0.1 to 10 eV) (II)

Of particular importance to NPAH analysis is the fact that nitro-aromatic compounds produce 

nitro group anions (m/z 46) using the dissociative resonance energy of ~3.5 eV.3 This particular 

ion is unique in negative ion analysis, which allows for the differentiation of nitro-containing 

compounds from the background. Once the presence of these compounds is confirmed, the 

ionization energy is then lowered to ~0 eV, and the molecular radical anion is produced for 

further identification. Using GC/EM-MS allows a selective (EM ionization energy selection), 

specific (nitro group anion uniqueness), and sensitive technique to be created for NPAH analysis.

Additionally, the GC/EM-MS offers the versatility of generating positive ion electron ionization 

(EI+) by simply increasing ionization energy to 25 eV, enabling the analysis of other

nonelectrophilic compounds such as PAHs in this research.

2.2 Instrumentation

A JEOL trochoidal EM interfaced to a JEOL MStation JMS-700T high-resolution magnetic 

sector mass spectrometer equipped with an Agilent 6890 GC was used for all spectrometric 

analyses. The EM system can generate ionization energies from 0 to 25 eV with a resolution of 

±0.4 eV. Electron energy resolution and tuning for negative ion analysis were conducted using 

nitrobenzene as the calibration standard. Perfluorokerosene was used as the ionization energy 

calibration standard for all positive ion analyses. Each nitro-aromatic compound detected in the 

PM samples was identified through selected ion monitoring (SIM) of the m/z 46 ion and the 

molecular ions, while each PAH was identified through SIM of their molecular ions.

The Agilent 6890 GC had an on-column injection port installed that was programmed to remain 

3oC above the GC oven temperature throughout each analysis. With the utilization of this oncolumn injection system, the choice was made to use an Integra-Guard RTX-5Sil MS analytical 

column (30 m x 0.25 mm ID x 0.25 μm). This type of GC column has an integrated 10 m guard 

column that protects the analytical portion of the column from the needle and the liquid samples, 

which can greatly accelerate the deterioration of the column phase. For each sample analysis, 

the GC oven was programmed using the following temperature profile: 

Isothermal at 100oC for 1 min

Programmed at 10oC/min to 190oC

Isothermal at 190oC for 2 min

Programmed at 5oC/min to 240oC

Isothermal at 240oC for 1 min

Programmed at 10oC/min to 310oC

Isothermal at 310oC for 2 min.
5

3. Method Development

3.1 Filter Experiments

During the early stages of the CSM project, a PM sampling filter was chosen that had two 

features. First, the filter had to be robust enough to handle an extraction utilizing

dichloromethane. Second, based on the early direction of the research toward raw exhaust 

sampling, the filter had to withstand much higher temperatures than the typical 150°C–220°C

dilution-tunnel temperatures. As a result, work was done to find an optimal filter to satisfy these 

two constraints.

As a starting point, Pall Teflo filters (Pall part R2PL047) were tested because they were the filter 

of choice for gravimetric PM testing at the ReFUEL laboratory. However, these filters are 

typically used for collecting PM during dilution tunnel experiments and consist of a 

polymethylpentene outer ring with a polytetrafluoroethylene (PTFE) filter through the middle

(47 mm diameter, 1 μm pore size). The problems with these filters were twofold in that they 

cannot withstand dichloromethane extraction (see Figure 3-1) and, according to the 

manufacturer, PTFE filters are typically useful up to no more than 220oC. Based on this 

information, other types of filter membranes were investigated. 

Figure 3-1. Teflo filter (a) before and (b) after dichloromethane extraction

(Credit: John Dane, Colorado School of Mines; used with permission)

The best fit for the CSM project was determined to be 47 mm Pall Tissuquartz heat-treated filters 

(Pall part 7202). These filters are composed of pure quartz fibers, do not contain binder, and 

have been heat-treated to remove all organic contaminants. Because of these attributes, they

provided the best option for withstanding both the dichloromethane solvent extraction and the 

high raw exhaust temperatures (up to 1100oC with flow rates as high as 73 L/min/cm2) while 

providing a clean substrate for collecting the PM. Additionally, the Tissuquartz filters efficiently 

collect 99.9% of all particles with ≥0.3 μm diameter, which is also an improvement over the 1 

μm capacity of the Teflo filters. Follow up solvent tests showed that these filters were 

impervious to degradation during extraction with dichloromethane. Furthermore, these 

(a) (b)
6

extractions showed that the filters were indeed free of contaminants detectable by GC/EM-MS. 

As a result, no pre-extraction was necessary prior to their use for sampling diesel exhaust. 

3.2 PM Filter Conditioning and Weighing

The ReFUEL facility has a dedicated clean room/environmental chamber. It is a Class-1000 

clean room with precise control over the temperature and humidity (temperature: 22°C ± 1°C 

and dew point: 9.5°C ± 1°C). This room was used for all filter handling, conditioning, and 

weighing during this research. The Sartorius SC2 microbalance found within the lab features a 

readability of 0.1 μg (a federal requirement) and features static control, a barcode reader for filter 

identification and tracking, and a computer interface for data acquisition. This balance is 

installed on a specially designed table that eliminates variation in the measurement due to 

vibration. Additionally, the features of this clean room were designed to ensure that the room’s

air flow is compatible with the microbalance. Figure 3-2 contains photographs of the laboratory 

and the microbalance. 

Figure 3-2. Photographs of the clean room exterior and the microbalance (Credit: NREL ReFUEL 

Laboratory photos)

All of the Tissuquartz filters were placed into separate petri dishes and allowed to equilibrate 

overnight to the clean room environment. The method for handling and weighing the filters was 

as follows:

1. Weigh a warm-up filter with similar weight to sample filters 

- Repeat until there is 0.0025 mg agreement between subsequent weighings

- This step is used to warm up the microbalance electromagnetic coil

2. Once the microbalance is warmed up, weigh a standard calibration weight (100 mg in this 

case) to determine the absolute accuracy of the balance

3. Weigh a reference filter with a weight similar to that of sample filters

4. Measure two subsequent weights for each Tissuquartz filter

- Must be 0.0025 mg agreement between these weighings or this step must be 

repeated

5. Repeat step 4 for next filter

6. After every four measurements (2 samples), the standard 100 mg weight must be 

measured to ensure balance accuracy

- The standard deviation of these measurements cannot exceed 0.25 μg or all previous 

weighings must be redone

PM Conditioning / Weigh Room PM Microbalance
7

7. After every eight measurements (4 samples), the reference filter must be weighed to 

ensure that there are no environmental effects causing changes in filter weights

- The average change in weight cannot exceed 10 μg or all previous weighings 

must be redone within that session

8. Repeat steps 4 through 7 until all filter weights have been obtained.

Several important aspects not mentioned above were also a part of the procedure. First, between 

every weighing, the balance was allowed to sit for 2 minutes before taring it back to zero. 

Second, the filters were passed through the static control device prior to placing them on the 

balance. If this step was not included, the microbalance drifted erratically while the filter was on 

the balance and never settled on a particular weight. Finally, the filter or calibration weight was

left on the microbalance for 2 minutes before the value was recorded in the computer. Once each 

weighing was completed, the filters were placed back in the petri dishes and stored in the clean 

room until they were utilized for collecting the PM samples. 

After testing (sample acquisition), the filters were then allowed to equilibrate in the clean room 

for a minimum of 1 hour. In most cases, this time period was expanded to overnight (16−20 

hours). Once the allotted time had passed, the weighing procedures described above were 

repeated for these sample filters. The results were then compared with the clean filter weights,

and gravimetric data for each PM sample were calculated. Subsequently, the samples were 

transferred from the ReFUEL facility to the CSM laboratory and stored in a refrigerator until 

extraction and analysis could be carried out.

During the course of the research, it was determined that the PM samples would require UV 

protection throughout the process of weighing and transferring the samples from the ReFUEL 

facility to the CSM laboratory. Nitro-polycyclic aromatic hydrocarbons are susceptible to 

photodegradation while under UV radiation, so countermeasures had to be taken to protect the 

integrity of the samples. As a result, several options were investigated to determine the best 

scenario for protecting these samples. The first course of action was to look at amber petri

dishes, which like amber glass, would provide UV protection to the samples. Amber Dynalab 

petri dishes were the only mass-produced plastic (polystyrene) dishes available in this color. 

Although these dishes appeared to offer UV protection, the vendor could not guarantee this 

information. As a result, their UV filtering capabilities were investigated utilizing CSM’s 

Thermo Electron Evolution 300 UV-Visible Spectrometer to scan from 190 nm–1100 nm, which 

covers the full region of UV and visible radiation. 

A comparison of the UV-Vis spectra from the amber jar glass (a traditional UV filter) and the 

amber petri dish is shown in Figure 3-3. While the petri dishes had the ability to filter the UV C 

radiation (190–280 nm), the UV A and UV B (280–400 nm) radiation passed through with 

minimal filtration. Clearly these results showed that this type of petri dish was insufficient for 

protecting the NPAHs found within the samples. Without other amber petri dish options 

immediately available, it was decided that for transport purposes, enclosing the petri dishes in a 

cardboard container would be sufficient for transferring the samples from ReFUEL to CSM.
8

Figure 3-3. UV-visible spectrum for (a) the amber jar glass and (b) the amber petri dish

Because each sample would spend at least a few hours in the clean room prior to and during 

weighing, the next logical option was to find ways to eliminate the UV radiation inside this 

room. The best option was to find a UV-filtering acrylic plastic that could be placed over the 

exterior windows of the room and in front of the lights. A local plastics vendor (Plasticare, 

Englewood, Colo.) had an acrylic that seemed to offer the best option for accomplishing this 

goal. This Ultraviolet Filtering Museum Quality Material (Cyro, Rockaway, N.J.) is used by 

galleries to protect art from UV radiation. The UV-filtering component is fabricated into the 

acrylic sheets and cannot be scratched off the surface. Additionally, the manufacturer states that 

this material has the capability of filtering out 98% of the UV radiation. To verify these claims, a 

small piece of this UV-filtering acrylic was tested in the UV-Vis spectrometer. Figure 3-4 shows 

the resulting absorbance spectrum.

Uv-Vis Amber Petri Dish

0

1

2

3

4

5

190 290 390 490 590 690 790 890 990 1090

Wavelength (nm)

Absorbance

UV C UV A

UV B

V I S I B L E

b)

Uv-Vis Amber Bottle

0

1

2

3

4

5

6

190 290 390 490 590 690 790 890 990 1090

Wavelength (nm)

Absorbance

UV C UV A

UV B

V I S I B L E

a)

99.99% Filtering

99.99% Filtering

99.9% Filtering
9

Figure 3-4. UV-Visible spectrum for the UV filtering acrylic

The results above show that this acrylic filters UV radiation to the manufacturer’s specifications, 

if not slightly better. After this analysis, the acrylic was installed over the clean room window, 

door windows, and overhead lights to prevent the samples from photodegrading while they were 

in this room. Additionally, because the room was now 98% UV free, special handling procedures 

were not necessary for transferring the samples to and from the microbalance. 

3.3 Solvent Purities

All solvents utilized for extraction and sample analysis were tested for impurities that could 

produce interfering impurity peaks in the negative ion (0 eV) pure electron capture GC/EM-MS 

analyses. These solvent tests were critical because every solvent utilized during this research is 

concentrated from a larger volume (up to 300 mL) to a lower volume (100–200 μL) at some 

point during the course of the extraction/cleanup process. As a result, each solvent was tested by 

concentrating it under flowing nitrogen from the maximum possible volume utilized during 

sample preparation to 100 μL. The solvents that showed no interfering impurities during the 

subsequent GC/EM-MS analyses were these:

Malinkrodt UltimAR Dichloromethane

Malinkrodt UltimAR Toluene

Pharmco/Aaper HPLC/ACS Grade Toluene

Pharmco/Aaper n-Pentane Trace Grade Pentane.

3.4 PAH and NPAH Standard Studies

A complete range of PAH and NPAH standards that represent the majority of possible 

compounds found in diesel exhaust PM samples was purchased for this research. Table 3-1 lists 

the 13 PAH standards that were acquired by CSM during this project. Table 3-2 lists all 58 

NPAH standards utilized during the analyses. 

Uv-Vis of UV Filter Acrylic

0

1

2

3

4

5

6

190 290 390 490 590 690 790 890 990 1090

Wavelength (nm)

Absorbance

UV C UV A

UV B

V I S I B L E

99.99% Filtering

99.9% Filtering
10

Table 3-1. List of PAH Standards

naphthalene phenanthrene

biphenyl fluoranthene

acenaphthene pyrene

acenaphthylene chrysene

fluorene benzo[c]phenanthrene

dibenzofuran benzo[a]pyrene

anthracene

Table 3-2. List of NPAH Standards

nitrobenzene 5-nitroquinoline 2-nitrodibenzothiophene

2-nitrotoluene 6-nitroquinoline 2,8-dinitrodibenzothiophene

3-nitrotoluene 2-nitrobiphenyl 6-nitro-3,4-benzocoumarin

4-nitrotoluene 3-nitrobiphenyl 2-nitrofluoranthene

2,4-dinitrotoluene 4-nitrobiphenyl 3-nitrofluoranthene

2,6-dinitrotoluene 2,2'-dinitrobiphenyl 1-nitropyrene

2-nitrophenol 2,4'-dinitrobiphenyl 2-nitropyrene

3-nitrophenol 4,4'-dinitrobiphenyl 4-nitropyrene

4-nitrophenol 4,4"-dinitro-p-terphenyl 1,3-dinitropyrene

2,4-dinitrophenol 5-nitroacenaphthene 1,6-dinitropyrene

2-nitro-1-naphthol 2-nitrofluorene 1,8-dinitropyrene

4,6-dinitro-o-cresol 2,7-dinitrofluorene 2,7-dinitro-9-fluorenone

2-nitro-m-xylene 3-nitrodibenzofuran 6-nitrochrysene

4-nitro-m-xylene 2-nitroanthracene 6,12-dinitrochrysene

5-nitro-m-xylene 9-nitroanthracene 7-nitrobenz[a]anthracene

1-nitronaphthalene 9,10-dinitroanthracene 5-nitrobenz[c]phenanthrene

2-nitronaphthalene 3-nitrophenanthrene 1-nitrobenzo[a]pyrene

1,3-dinitronaphthalene 4-nitrophenanthrene 3-nitrobenzo[a]pyrene

1,5-dinitronaphthalene 9-nitrophenanthrene 6-nitrobenz[a]pyrene

1,8-dinitronaphthalene 

Along with the standards shown in Tables 3-1 and 3-2, it was also necessary to obtain PAH and 

NPAH internal standards that were isotopically labeled. This type of standard is spiked into each

sample prior to sample extraction and then used during sample analysis to determine analyte 

recoveries. Table 3-3 lists the deuterium-labeled PAHs and NPAHs acquired for this project. 
11

Table 3-3. List of PAH and NPAH Internal Standards

PAH NPAH

naphthalene-d8 nitrobenzene-d5

acenaphthene-d10 1-nitronaphthalene-d7

phenanthrene-d10 1,5-dinitronaphthalene-d6

anthracene-d10 4-nitrobiphenyl-d9

chrysene-d12 9-nitroanthracene-d9

3-nitrofluoranthene-d9

1-nitropyrene-d9

Next, a 13-component PAH standard test mixture was tested using electron capture (0 eV) 

negative ion (EI-) analysis and EI+ (25 eV) analysis. The EI- analysis did not show a strong 

signal for any of the PAHs (3.5 ng), while the EI+ analysis total ion current (TIC) gas 

chromatogram showed distinctive peaks for each of the 13 PAH compounds (see Figure 3-5) at 

this same concentration. Each peak is labeled with a number, and the corresponding compound is 

listed in Table 3-4. The peaks prior to naphthalene are toluene (sample solvent), which was 

mostly cut from the spectrum by delaying the detection time, and isomers of xylene, an impurity 

found in the toluene. Subsequently, a pure 58-component NPAH standard mixture was analyzed 

using the EI- dissociative electron capture (3.5 eV) to preferentially generate the NO2

- (m/z 46). 

Figure 3-6 shows the m/z 46 SIM for this mixture. Each peak is labeled with a number, and the 

corresponding compound is listed in Table 3-5. 

13 Component PAH Standard Mixture 

Positive Ion TIC

0 5 10 15 20 25 30

Time (min)

Rel. Int.

1

2

3 4

5

6

7 8 9

10

11

12

13

Figure 3-5. Positive ion TIC chromatogram for the PAH standard mixture (displayed as relative 

intensity)
12

Table 3-4. List of PAH Standards in Figure 3-5 and their Corresponding Peak Numbers

Peak # PAH Ret. Time (min)

1 naphthalene 6.76

2 biphenyl 9.02

3 acenaphthylene 10.02

4 acenaphthene 10.45

5 dibenzofuran 10.91

6 fluorene 11.94

7 phenanthrene 15.42

8 anthracene 15.62

9 fluoranthene 20.47

10 pyrene 21.43

11 benzo[c]phenanthrene 25.82

12 chrysene 26.69

13 benzo[a]pyrene 30.55

Figure 3-6. Nitro (m/z 46) chromatogram for the NPAH standard mixture
13

Table 3-.5. List of NPAH Standards in Figure 3-6 and their Corresponding Peak Numbers

Peak 

# NPAH Compound

Ret. 

Time 

(min)

Peak 

# NPAH Compound

Ret. 

Time 

(min)

1 nitrobenzene 3.98 30 2,4'-dinitrobiphenyl 18.43

2 2-nitrophenol 4.36 31 9-nitrophenanthrene 19.07

3 2-nitrotoluene 4.61 32 2-nitrodibenzothiophene 19.58

4 2-nitro-m-xylene 4.83 33 3-nitrophenanthrene 19.86

5 3-nitrotoluene 4.99 34 2-nitroanthracene 20.64

6 4-nitrotoluene 5.19 35 9,10-dinitroanthracene 20.90

7 4-nitro-m-xylene 5.93 36 dinitrobiphenyl impurity 21.15

8 5-nitro-m-xylene 6.16 37 6-nitro-3,4-benzocoumarin 21.47

9 2,6-dinitrotoluene 7.84 38 4,4'-dinitrobiphenyl 21.66

10 3-nitrophenol 8.01 39 2-nitrofluoranthene 24.45

11 4-nitrophenol 8.65 40 3-nitrofluoranthene 24.49

12 2,4-dinitrotoluene 8.73 41 4-nitropyrene 24.71

13 5-nitroquinoline 9.47 42 1-nitropyrene 25.25

14 1-nitronaphthalene 9.66 43 2-nitropyrene 25.52

15 2-nitronaphthalene 10.15 44 2,7-dinitrofluorene 25.88

16 6-nitroquinoline 10.28 45 2,7-Dinitro-9-fluorenone 26.10

17 2-nitrobiphenyl 10.61 46 2,8-dinitrodibenzothiophene 27.07

18 3-nitrobiphenyl 12.58 47 7-nitrobenz[a]anthracene 27.40

19 4-nitrobiphenyl 13.08 48 5-nitrobenzo[c]phenanthrene 27.76

20 1,5-dinitronaphthalene 14.46 49 6-nitrochrysene 28.26

21 3-nitroacenaphthene 14.52 50 1,3-dinitropyrene 28.93

22 1,3-dinitronaphthalene 15.00 51 1,6-dinitropyrene 29.41

23 3-nitrodibenzofuran 15.34 52 1,8-dinitropyrene 29.74

24 5-nitroacenaphthene 15.67 53 6-nitrobenz[a]pyrene 30.96

25 2,2'-dinitrobiphenyl 16.40 54 6,12-dinitrochrysene 31.01

26 2-nitrofluorene 17.36 55 4,4'-dinitro-p-terphenyl 31.82

27 4-nitrophenanthrene 17.70 56 dinitrochrysene impurity 31.98

28 9-nitroanthracene 17.79 57 1-/3-nitrobenzo[a]pyrene 32.44

29 1,8-dinitronaphthalene 18.08 58 1-/3-nitrobenzo[a]pyrene 32.56

Next, the PAH and NPAH internal standards mixtures were analyzed by the GC/EM-MS. 

Representative two-ring (naphthalene-d8), three-ring (phenanthrene-d10), and four-ring 

(chrysene-d12) PAHs were chosen for the internal standard mixture spiked into each sample. 

Figure 3-7 shows the labeled TIC for the PAH standards spiked into each sample. As for the 

NPAHs, the mixture evolved from a three-component mixture to a five-component mixture. 

Early in this research, it was important to imitate the work that had been previously done by 

Havey et al., which used only a 3-component NPAH mixture (1-nitronaphthalene-d7, 1,5-

dinitronaphthalene-d6, 1-nitropyrene-d9).4,5 However, despite the fact that this mixture was 

useful for assessing the recoveries of two-ring, four-ring, and dinitro NPAHs, it did not account 

for all ring types. As a result, the internal standard solution was adjusted to include a single-ring 
14

(nitrobenzene-d5) and three-ring (9-nitroanthracene-d9) NPAH. Figure 3-8 shows the labeled m/z

46 chromatogram for the NPAH internal standards spiked into the samples. It is important to 

note that these additional standards were not added until midway through the project. Because of 

this, some early studies presented in this report will not include all five NPAH standards. 

Naphthalene-d8

Phenanthrene-d10

Chrysene-d12

Figure 3-7. Positive-ion TIC chromatogram for the deuterated PAH standard mixture

1-nitronaphthalene-d7

9-nitroanthracene-d9

nitrobenzene-d5

1,5-dinitronaphthalene-d6

1-nitropyrene-d9

Figure 3-8. Nitro (m/z 46) chromatogram for deuterated NPAH standard mixture

3.5 Detection of Ethyl Nitrite

An early task for the CSM project was to evaluate the detection of ethyl nitrite and acetaldehyde 

using the GC/EM-MS. Although these compounds would be in the gas phase, it was thought that 

if the EM provided a better detection scenario, then a trapping/desorption scenario would be 

investigated for the diesel exhaust samples. The findings of these studies showed that there was a 

distinctive m/z 75 for the ethyl nitrite molecular ion and an m/z 44 for the acetaldehyde molecular 
15

ion (see Figure 3-9). However, both compounds were observed to co-elute even when utilizing a 

starting temperature at or slightly below room temperature (15oC−25oC). As a result, the full scan 

data produced overlapping spectra, making it difficult to determine which ions were

contributions from acetaldehyde and which were from ethyl nitrite. Despite this situation, these 

compounds, even when utilizing pure electron capture, produce fragment ions that can also be 

utilized for identification purposes. The positive result of this study was that, as predicted, 

compounds without aromatic systems produce EI- full-scan spectra that include both molecular

radical ions and fragment ions, unlike aromatic systems such as NPAHs, which almost 

exclusively produce molecular ions at 0 eV ionization. If this area is to be studied further using 

the GC/EM-MS, it will be necessary to invest in a cryogenic GC oven cooling system and/or in a 

60 m capillary GC column. 

Figure 3-9. Full-scan mass spectrum of acetaldehyde and ethyl nitrite utilizing pure electron 

capture ionization

3.6 Solvent Extraction Studies

An area that warranted further investigation, based on the article by Havey et al., was the solvent 

extraction method utilized to extract the NPAHs out of the PM and into the dichloromethane 

solution. This earlier research had shown that using a shaker table did not provide an efficient

extraction of the heavier NPAHs from the PM, as shown by the poor recoveries (5%) of 1-

nitropyrene-d9.

4

 As a result, two other scenarios were investigated that provided a more rigorous 

extraction method, sonication and Soxhlet extraction. To test these two methods, two 

certification (Cert) diesel PM samples were spiked with internal standards. Sample #1 was 

sonicated for approximately 1 hour in 25 mL of dichloromethane; Sample #2 was placed in a 

EI+ Fullscan Spectrum

m/z

30 35 40 45 50 55 60 65 70 75 80

Rel. Int.

Negative Ion Electron 

Ionization Full-Scan 

Spectrum
16

Soxhlet apparatus with 200 mL of dichloromethane that was cycled 63 times. Afterward, each 

sample was analyzed using the GC/EM-MS to monitor the molecular ions for 3-

nitrofluoranthene-d9 and 1-nitropyrene-d9 (see Figure 3-10).

Figure 3-10. Molecular ion chromatogram for the PM sample that was (a) sonicated and (b) Soxhlet 

extracted

A comparison of these chromatograms clearly shows that Soxhlet extraction produces superior 

recovery of the two NPAH compounds. Our speculation for the poor recovery observed for the 

sonicated sample was that the diesel soot has a morphology that has a significant affinity toward 

the larger NPAHs, especially when compared with the solvent. To address this problem, it would 

likely require a number of sonication extractions with fresh solvent (similar to each cycle during 

a Soxhlet extraction) to help break up the soot and extract these compounds out of the PM. 

Rather than spend time devising a multiple sonication extraction method, the decision was made 

to use the Soxhlet extraction process for all future samples. 

Further Soxhlet extraction testing revealed that the affinity of 1-nitropyrene and chrysene for the 

PM is much stronger than was originally anticipated, even with the choice of an improved 

extraction technique. Additionally, this affinity increased as more Cert diesel was incorporated 

into the fuel. Table 3-6 demonstrates this trend for chrysene-d12 and 1-nitropyrene-d9 by showing 

recoveries for a set of Cert, B20 (20% biodiesel), and B100 (100% biodiesel) Engine-out

samples when utilizing only a minimum of 30 (max 60) cycles per sample. 
17

Table 3-6. Comparison of Chrysene-D12 and 1-Nitropyrene-D9 Recoveries Prior to Optimizing the 

Number of Soxhlet Extraction Cycles

Cert B20 B100

chrysene-d12 32% ± 5 41% ± 7 73% ± 12

1-nitropyrene-d9 50% ± 2 78% ± 4 86% ± 3

As a result, the number of extraction cycles was increased to over 200 for each sample in order 

to ensure that these compounds were completely extracted from the PM. Table 3-7 shows the 

improved recoveries for chrysene-d12 and 1-nitropyrene-d9 from the PM of each fuel type. Based 

on these results, the 200 cycle Soxhlet extraction scenario was utilized during the PM sample 

preparation process.

Table 3-7. Comparison of Chrysene-D12 and 1-Nitropyrene-D9 Recoveries after Optimizing the 

Number of Soxhlet Extraction Cycles

Cert B20 B100

chrysene-d12 74% ± 7 62% ± 11 87% ± 22

1-nitropyrene-d9 85% ± 14 86% ± 14 92% ± 11

3.7 Solid-Phase Extraction Studies

Early in the project, it was determined that it would be necessary to add an additional step to the 

extraction process in order to further clean the Engine-out samples. Without additional cleanup, 

these PM samples produced noisy, rising baselines in each molecular ion and TIC

chromatogram. As a result, an amino solid phase extraction (NH2 SPE) process was incorporated 

into the Engine-out sample preparation in order to remove any polar constituents extracted from 

the PM. These components tend to create the most problems for chromatography and signal 

suppression. The extraction scenario was based upon previous work conducted at CSM.

5

 To 

streamline the NH2 SPE method development, we utilized steps described in Analytical SolidPhase Extraction by James S. Fritz, which outlines techniques for developing SPE methods.

6 

The technique developed here is based upon prefabricated 25 mL Alltech ultra-clean cartridges 

containing 1.5 g of amino phase. It is worth mentioning that the DPF-out samples did not require 

this SPE scenario; these samples were sufficiently clean after Soxhlet extraction for analysis of 

PAHs and NPAHs. 

Overall, several NH2 SPE scenarios were investigated before a final method was settled upon. 

Each of the methods investigated was based upon NPAH research conducted previously7, 8 but 

was designed to simplify the process. However, after investigating these other methods, it was 

determined that only a slight modification from the original technique was necessary to 

streamline the extraction process. First, the hexane was replaced with pentane to increase the 

evaporation rate achievable during sample concentration. Second, the solvent ratio was adjusted

from 18:82 dichloromethane/hexane to 20:80 dichloromethane/pentane to simplify the solvent

volume selections. The final SPE method utilized on each sample was as follows:
18

o Prepare sample solution

• Make 10 mL dichloromethane sample solution into a 20:80 mixture by adding 

40 mL of pentane

o Prepare 75 mL of 20:80 dichloromethane/pentane solution for use during SPE by 

combining 15 mL of dichloromethane with 60 mL of pentane

o Prepare 1.5 g ultra-clean NH2 SPE (eliminates contaminants from phase synthesis) 

• Pass 10 mL pentane through cartridge, draining to just above NH2 phase

• Pass 10 mL of 20:80 dichloromethane/pentane through cartridge, draining to 

just above NH2 phase

o Pass sample solution through the phase

• Pass all 50 mL of sample solution through phase, again draining to just above 

NH2 phase

o Pass 50 mL of pure 20:80 dichloromethane/pentane through phase, this time draining 

completely

• Evaporate sample under flowing nitrogen to 200 μL (see exact procedure in

Section 3.9).

Representative internal standard recoveries for the PM samples, which also reflect the use of the 

Soxhlet extraction procedure discussed in Section 3.5, are shown below in Table 3-8. All of the 

internal standards except naphthalene-d8 (which is fairly volatile) showed recoveries of greater 

than 50%. These results, which include the improved Soxhlet extraction method discussed 

above, represent a significant improvement over the 5% recovery of 1-nitropyrene-d9 reported by 

Havey et al.4,5

Table 3-8. PAH and NPAH Internal Standard Recoveries

PAH Recovery

naphthalene-d8 31.4%

phenanthrene-d10 72.0%

chrysene-d12 78.6%

NPAH Recovery

1-nitronaphthalene-d7 50.0%

1,5-dinitronaphthalene-d6 86.1%

9-nitroanthracene-d9 76.1%

1-nitropyrene-d9 92.0%
19

3.8 Evaporation Procedure

Over the course of this research, one common effect consistently observed, no matter how much 

optimization was done to the extraction and cleanup procedure, was the low recovery of the 

smaller, most volatile components found within the samples (i.e., nitrobenzene-d5, naphthalened8, and nitronaphthalene-d7). The most obvious process to account for these losses was the 

concentration and evaporation that occurred during the cleanup procedure. To test this 

hypothesis, experiments were done to determine an optimal evaporation procedure that would

limit the loss of these compounds. The initial evaporation method was as follows:

o Evaporate 200−300 mL Soxhlet solution under gently flowing nitrogen to between 3 

and 10 mL

o Dilute sample back up to exactly 10 mL with dichloromethane

o Conduct amino solid phase extraction

o Spike sample (~100 mL) with 3 mL of toluene for volume regulation

• DCM/pentane evaporates too quickly under flowing nitrogen, so toluene is 

added to help regulate this evaporation rate

o Evaporate sample to between 1 and 3 mL

o Transfer sample to 2 mL amber vial and continue evaporation

o Once sample transfer is complete, rinse jar with two 1 mL portions of toluene and add 

these rinses to amber vial

o Continue evaporation under flowing nitrogen to less than 100 μL 

o Dilute solution back up to exactly 100 μL with toluene using a pipetter to determine 

the final volume.

This procedure required a significant amount of focus because there were several areas where 

mistakes could be made that would lead to complete solvent evaporation. The most difficult 

aspect to control was the step in which the volume is evaporated below 100 μL. Ideally, the goal

was to go slightly below this 100 μL volume, but at such a small volume, it was difficult to 

achieve this optimal situation. The problems would multiply when more than one sample was 

being prepared at a time. 

Consequently, several steps were added to improve control of the evaporation, resulting in higher

recoveries for the volatile analytes within the samples. First, all evaporation steps were done in 

an ice bath to slow down the solvent evaporation while retaining the volatile analytes in solution. 

Second, all final volumes at various stages of the evaporation process were controlled by 

monitoring the weight of the solution. In this way, exact volumes could be monitored and 

achieved. Finally, the target final volume for the sample solution was increased from 100 μL to 

200 μL, making it less likely that the sample would be evaporated completely. Table 3-9 shows 

the volatile internal standard recoveries for an evaporation test conducted using these techniques. 
20

Table 3-9. Volatile Internal Standard Recoveries for an Evaporation Test

Deuterated PAH Recovery

naphthalene-d8 73%

nitrobenzene-d5 75%

1-nitronaphthalene-d7 67%

These data show that this procedure improved recoveries for these volatile components when 

compared with the recovery tables shown previously. Therefore, this technique was utilized 

during the sample preparation process.

3.9 Complete Engine-out Sample Preparation Procedure

The following is a complete description of the final sample preparation procedure for the Engineout samples, as determined by the development work described above.

o Spike weighed PM sample with 20 μL of the 250 pg/μL NPAH and 20 μL of the 2.5 

ng/μL PAH internal standard mixtures

o Place sample in Soxhlet apparatus with 200 mL of dichloromethane (DCM) in round 

bottom flask

o Cycle DCM through sample a minimum of 200 times

o Evaporate the solution in an ice bath under gently flowing nitrogen to ~100 mL

o Pour sample into amber jar and rinse flask twice with 20 mL of DCM

o Pour rinses into the sample amber jar

o Evaporate sample in an ice bath under flowing nitrogen to ~13 g

o Dilute sample back up to 10 mL (13.277 g) with DCM

o Make this sample solution into a 20:80 DCM/pentane mixture by adding 

40 mL of pentane

o Prepare 75 mL of 20:80 DCM/pentane solution for use during SPE 

• 15 mL DCM to 60 mL of pentane

o Pass 10 mL pentane through cartridge, draining to just above NH2 phase

o Pass 10 mL of 20:80 DCM/pentane through cartridge, draining to just above NH2

phase

o Pass all 50 mL of sample solution through phase, again draining to just above the 

NH2 phase

o Pass 50 mL of pure 20:80 DCM/pentane through phase, this time draining completely

o Spike sample with 3 mL of toluene for volume regulation

o Evaporate sample in an ice bath under flowing nitrogen to 2–3 g

o Transfer sample to amber vial and continue evaporation in an ice bath under flowing 

nitrogen
21

o Once sample transfer is complete, rinse jar with two 1-mL portions of toluene and 

add these rinses to amber vial

o Evaporate sample to just below 0.1733 g

o Dilute solution back up to 0.1733 g (200 μL) with toluene.

3.10 Complete DPF-out Sample Preparation Procedure

For the DPF-out samples, the following is a complete description of the final preparation 

procedure for these samples. 

o Spike weighed PM sample with 20 μL of the 250 pg/μL NPAH and 20 μL of the 2.5 

ng/μL PAH internal standard mixtures

o Place sample in Soxhlet apparatus with 200 mL of DCM in round bottom flask

o Cycle DCM through sample a minimum of 60 times

o Evaporate the solution under gently flowing nitrogen while sitting in an ice bath to 

~100 mL

o Pour sample into amber jar and rinse flask twice with 20 mL of DCM

o Pour rinses into the sample amber jar

o Spike sample with 3 mL of toluene for volume regulation

o Evaporate sample in an ice bath under flowing nitrogen to 2–3 g

o Transfer sample to amber vial and continue evaporation in an ice bath under flowing 

nitrogen 

o Once sample transfer is complete, rinse jar with two 1-mL portions of toluene and 

add these rinses to amber vial

o Evaporate sample to just below 0.1733 g

o Dilute solution back up to 0.1733 g (200 μL) with toluene.

3.11 Engine Testing Procedure 

All of the PM samples collected during this project were generated from a 2002 model year 

Cummins ISB diesel engine with exhaust gas recirculation. Additionally, the test procedure 

chosen for the engine was an AVL 8-Mode test, which is a steady-state engine test procedure 

designed to closely correlate with the exhaust emission results obtained for the U.S. FTP heavyduty engine transient cycle.9

 Table 3-10 shows the parameters utilized for this test procedure. 

The sample time periods reflect the weightings applied to regulated emissions measurements 

from the AVL 8-Mode test and are based on a total of 30 minutes of sample collection.
22

Table 3-10. AVL 8-Mode Test

Mode % Engine 

Speed *

% 

Load

Time 

(min)

1 0 0 12.5

2 11 25 2.25

3 21 63 1.03

4 32 84 1.18

5 100 18 3.00

6 95 40 3.73

7 95 69 3.65

8 89 95 2.62

* Normalized speed: 0% = low idle, 100 % = rated speed

Experiments in this report referred to as Engine-out were performed without a combined diesel 

oxidation catalyst (DOC) and diesel particle filter (DPF) installed in the exhaust system. Separate 

experiments were performed with the DOC/DPF installed, and are referred to as DPF-out. The 

sampling location for the raw exhaust experiments was therefore always the same. Likewise, the 

diluted exhaust experiments used a common (but obviously separate) sampling port. The purpose 

of the DOC is to catalytically oxidize the vapor phase hydrocarbons to CO2 and H2O. It also 

converts NO to NO2 for use by the DPF to oxidize PM. 

3.12 Raw Exhaust Sampling

Raw exhaust PM sampling is not commonly done within the engine testing community. As a 

result, a collection system for this type of sampling had to be designed for collecting Engine-out 

and DPF-out samples prior to the dilution tunnel. The mass flow controller (MFC) and pump 

associated with the regulated emissions bench at ReFUEL were used to control the sampling 

flow. Additionally, URG (Chapel Hill, N.C.) single-stage stainless steel filter holders at ReFUEL 

were incorporated into the sampling system to hold the Tissuquartz filters. Otherwise, the system 

was custom built and consisted of a sample probe, interconnecting stainless steel tubing, a filter 

holder, and the MFC bench. A PM sampling system schematic is shown in Figure 3-11. 

Raw Exhaust 

From Engine

Dilution 

Tunnel

MFC

Sample 

Probe

Condensation 

Trap

Exhaust Temp. 

Thermocouple Heat Trace and 

Insulation

Filter Holder

Sanitary Flange

Raw Exhaust 

From Engine

Dilution 

Tunnel

MFC

Sample 

Probe

Condensation 

Trap

Exhaust Temp. 

Thermocouple Heat Trace and 

Insulation

Filter Holder

Sanitary Flange

Raw Exhaust 

From Engine

Dilution 

Tunnel

MFC

Sample 

Probe

Condensation 

Trap

Exhaust Temp. 

Thermocouple Heat Trace and 

Insulation

Filter Holder

Sanitary Flange

Figure 3-11. Schematic of sampling apparatus
23

Several heat tracing configurations were tried, and the best scenario involved keeping the 

exhaust temperature through the filter between 180°F and 350°F. Using a temperature any lower 

than 180°F would result in significant water condensation in the lines leading to the filter; using 

a temperature any higher than 350°F would result in the decomposition of the Delrin filter 

cassette used to hold the Tissuquartz filters in place within the filter holder. The exhaust flow 

rate through the filter was chosen to be 30 L/min for the DPF-out samples and 20 L/min for the 

Engine-out samples, based on the need to maximize the amount of PM while keeping the 

temperature in the appropriate temperature range. Also, the line into the filter was heat-traced at 

a setting of 212°F and insulated to help keep the temperature in the appropriate range. A photo of 

the sample setup is shown in Figure 3-12.

Figure 3-12. Photo of sampling apparatus (Credit: NREL ReFUEL Laboratory photos)

The sampling position in the exhaust stream was not changed for the Engine-out and DPF-out 

samples. Instead, the DPF was incorporated (or not) into the exhaust stream prior to the sample 

port. The Engine-out samples were collected from the exhaust stream when the DPF was not 

included in the system, while the DPF-out samples were collected with the DPF incorporated 

into the system. Additionally, each PM sample was collected onto a new Tissuquartz filter per 

the engine test.

3.13 Dilute Exhaust Sampling

The dilute exhaust samples were collected using ReFUEL’s conventional PM sampling system. 

This system includes a sample probe installed in the dilution tunnel, the URG stainless steel filter 

holder, and the MFC bench. These PM samples, both Engine-out and DPF-out, were all collected 

using a flow rate of 60 L/min. Each Engine-out PM sample was collected onto a separate 

Tissuquartz filter per engine run. However, each DPF-out sample filter represented a triplicate of 

runs for each fuel type to maximize the amount of PM collected for analysis purposes. In this 

case, the final PAH and NPAH levels were then calculated by dividing the total value by 3 to 

determine the per-run value.
24

4. Results and Discussion

4.1 Raw Exhaust Gravimetric Data

The DPF-out PM samples were collected during the early stages of testing so only two fuel types 

(Cert and B20) were collected. The Engine-out samples, however, consisted of a complete set of 

PM samples representing all three fuel samples (Cert, B20, B100). All samples were collected 

using the apparatus and flow rates described in Section 3.12. Table 4-1 lists the DPF-out samples 

collected during this sampling period. Table 4-2 lists the Engine-out samples collected. 

Table 4-1. Raw Exhaust DPF-out PM Samples

Run # Filter # Fuel

PM 

Mass 

(mg)

Run # Filter # Fuel

PM 

Mass 

(mg)

4 3 Cert 0.2608 11 8 B20 0.1350

6 4 Cert 0.2655 12 9 B20 0.1345

7 5 Cert 0.1840 13 10 B20 0.1070

8 6 Cert 0.0708

9 7 Cert 0.0909

Table 4-2. Raw Exhaust Engine-out PM Samples

Run # Filter # Fuel

PM 

Mass 

(mg)

Run # Filter # Fuel

PM 

Mass 

(mg)

14 11 B20 2.8228 21 17 Cert 4.3728

15 12 B20 2.6323 22 18 Cert 4.0315

16 13 B20 2.7166 23 19 Cert 4.3268

18 14 Cert 3.5685 25 20 B100 1.3388

19 15 Cert 3.3557 26/27 21 B100 1.1494

20 16 Cert 3.3030 28 22 B100 1.3110

After these samples were collected, they were then subjected to the cleanup processes described 

in Sections 3.9 and 3.10 but without the increased extraction period (only 60 cycles/sample) or 

the improved evaporation procedure. These samples were collected early during the subcontract

period, prior to the integration of these procedures into the overall sample preparation process. 

Note that the Engine-out gravimetric data collected during this section of the research are 

imperfect because the Tissuquartz filters ripped during the 8-Mode test. The cause was traced to 

the last three modes in the AVL test cycle in which the engine was reaching a steady state. 

While the engine is reaching a steady state, the pump for drawing the exhaust through the 

Tissuquartz filters is turned off. Because there was no valve between the filter and the engine 

exhaust, the filter would experience an oscillating pressure that would cause it to tear toward the 

exhaust stream. Then when the pump flow was turned on during sampling, the filter was pulled 

back into place on the stainless steel support plate at the back of the filter holder. While this 

would prevent soot from passing into the region beyond the filter, pieces of the filter could be 

seen on the inside of the exhaust inlet side of the filter holder. As a result, a significant error 
25

could be associated with the sample weights, since the levels observed for each PM sample are in 

the milligram range to begin with. All three modes tested (Modes 6, 7, and 8) showed a tendency 

toward this filter tearing scenario. The sampling apparatus and procedure were developed during

DPF-out sampling. Unfortunately, the problem of tearing Tissuquartz filters arose subsequently 

during Engine-out testing; that problem had not occurred while the DPF was being used. 

Apparently, the DPF dampens the oscillating pressures experienced by the Tissuquartz filters. 

Since the problem was not realized until after the DPF-out samples had been collected, an

opportunity to overcome this problem was not available.

4.2 Results for Engine-out Raw Exhaust 

First, the Engine-out PM samples were analyzed for nitro compounds utilizing GC/EM-MS. The 

m/z 46 SIM chromatograms for the Cert, B20, and B100 PM samples are shown in Figure 4-1. 

These chromatograms show the nitro compounds that are present in each sample and provide a 

starting point for the rest of the NPAH analyses. Overall, the chromatograms showed a number 

of similar features, which demonstrated the presence of common nitro compounds found within 

each sample. 

Comparison of Nitro Compounds in PM

(m/z 46 Chromatogram)

0 5 10 15 20 25 30

Time (min)

Rel. Int.

Cert

B20

B100

Figure 4-1. Nitro (m/z 46) chromatograms for each raw exhaust Engine-out PM sample (displayed 

as relative intensity) 

Note that the large peak at approximately 18 minutes in the Cert chromatogram was identified as 

a contaminant that was introduced into the sample at the CSM laboratory. As a result, this feature 

can be ignored as a contribution from the PM samples. As for the peaks observed in the B100 

chromatogram with retention times between 24 and 28 minutes, these peaks did not match any of 

the 58 NPAH standards available at the CSM laboratory. Additionally, these peaks were also 

observed, to a much lesser extent, in the B20 samples, which seems to suggest a connection to 

the biodiesel itself. Moreover, these peaks were at elution times that indicate the presence of 

higher molecular weight compounds. It is interesting that the detection of these heavier unknown 

compounds is inconsistent with the results from this study and other studies, in which an overall 
26

decrease in all NPAH levels is observed as the amount of biodiesel is increased in the fuel. 

Further investigation of these peaks is discussed later in this section. 

Once the nitro compounds had been preliminarily identified through their retention times in the 

m/z 46 chromatogram, the next step was to verify and quantify these compounds using their 

molecular ions. Several representative NPAHs (1- and 2-nitronaphthalene, 9-nitroanthracene, 3-

nitrophenanthrene, and 1-nitropyrene) were selected for quantitation purposes. Figures 4-2 and 

4-3 show the molecular ion chromatograms for 9-nitroanthracene and 1-nitropyrene, 

respectively. These chromatograms illustrate qualitatively that there is a trend toward lower 

concentrations of these species as more biodiesel is incorporated into the fuel. 

Comparison of 9-Nitroanthracene

(m/z 223 Chromatogram) 

17.5 17.7 17.9 Time (min) 18.1 18.3 18.5 18.7 Rel. Int.

Cert

B20

B100

Figure 4-2. The molecular ion chromatograms (m/z 223) for 9-nitroanthracene

Comparison of 1-Nitropyrene Analyses

(m/z 247 Chromatograms)

24.4 24.6 24.8 25 25.2 25.4 25.6 25.8 26

Time (min)

Rel. Int.

Cert

B20

B100

Figure 4-3. The molecular ion chromatograms (m/z 247) for 1-nitropyrene
27

Table 4-3 shows the total amount (average of 3 replicates) for each NPAH measured from each 

fuel type, with the measurement error expressed as the standard deviation. These results illustrate 

that as more biodiesel is incorporated into the fuel, lower levels of NPAHs are present in the 

exhaust. However, when these levels are related back to the total amount of PM present, this 

trend does not hold. Table 4-4 shows the NPAH levels as they relate to the amount of PM 

present for each sample. 

Table 4-3. Raw Exhaust Engine-out NPAH Quantities for each Fuel (ng/sample)

Cert 

(ng/sample)

B20 

(ng/sample)

B100 

(ng/sample)

1-nitronaphthalene 0.87 ± 0.04 0.20 ± 0.05 0.14 ± 0.02

2-nitronaphthalene 3.9 ± 0.2 1.0 ± 0.2 0.65 ± 0.19

9-nitroanthracene

9-nitrophenanthrene

9.6 ± 1.5

ND

1.2 ± 0.2

ND

0.45 ± 0.05

ND

3-nitrophenanthrene

3-nitrofluoranthene

1.3 ± 0.4

ND

0.28 ± 0.01

ND

0.25 ± 0.03

T

1-nitropyrene

TOTAL

2.1 ± 0.4

17.8

1.2 ± 0.3

3.9

0.54 ± 0.13

2.03

 ND: not detected; T: trace

Table 4-4. Raw Exhaust Engine-out NPAH Quantities for each Fuel (ng/mg PM)

Cert 

(ng/mg)

B20 

(ng/mg)

B100 

(ng/mg)

1-nitronaphthalene 0.20 ± 0.02 0.08 ± 0.02 0.11 ± 0.01

2-nitronaphthalene 0.90 ± 0.07 0.37 ± 0.07 0.51 ± 0.14

9-nitroanthracene

9-nitrophenanthrene

2.3 ± 0.4

ND

0.46 ± 0.15

ND

0.36 ± 0.03

ND

3-nitrophenanthrene

3-nitrofluoranthene

0.31 ± 0.11

ND

0.10 ± 0.01

ND

0.20 ± 0.01

T

1-nitropyrene

TOTAL

0.12 ± 0.03

3.8

0.39 ± 0.02

1.40

0.43 ± 0.09

1.61

 ND: not detected; T: trace

The data in Table 4-4 do not show a clear pattern between the fuel type and NPAH levels present 

per PM amount. The total NPAH in the B20 samples is roughly half that from Cert samples, but 

the B100 samples had higher total NPAH per milligram of PM than the B20 samples. In the case 

of 1-nitropyrene, the B100 and B20 samples actually had higher amounts per milligram than the 

Cert diesel samples. While these results were unexpected, the cause is possibly related to the 

filter tearing situation that was discussed in Section 4.1. If the sampling system was improved to 

eliminate this problem, these numbers would likely change. The B100 samples had particularly 

bad oscillating pressure across the PM filters because the exhaust gas recirculation controls shut

down for brief periods during the later modes, which would in turn cause the engine to lose 

power for brief periods of time during the testing period. 
28

The samples were then analyzed for PAHs using EI+ (25 eV) in conjunction with molecular ion 

information obtained for each compound. These molecular ion chromatograms were then used to 

quantify the levels for each PAH. Figures 4-4 and 4-5 show the molecular ion chromatograms for

phenanthrene, anthracene, fluoranthene, and pyrene. Each chromatogram qualitatively shows a 

trend toward lower concentrations as more biodiesel was incorporated into the fuel. 

Comparison of Phenanthrene and Anthracene

(m/z 178 Chromatogram)

10 11 12 13 14

Time (min)

Rel. Int.

Cert

B20

B100

Figure 4-4. The molecular ion chromatograms (m/z 178) for phenanthrene and anthracene

Comparison of Fluoranthene and Pyrene

(m/z 202 Chromatogram)

15 16 17 18 19 20 Time (min)

Rel. Int.

Cert

B20

B100

Figure 4-5. The molecular ion chromatograms (m/z 202) for fluoranthene and pyrene
29

Along with the four PAHs shown in the above chromatograms, naphthalene was also selected for 

quantitation purposes. Table 4-5 shows the total PAH quantity obtained from each PM sample

(average of three replicates). The data quantitatively show that as more biodiesel is incorporated 

into the fuel, smaller amounts of PAHs are produced during the combustion process, just as for 

NPAHs. Table 4-6 shows the PAH levels as they relate to the milligram amount of PM present in 

each sample. Similar to the NPAHs, there is a drop of about 50% in total PAH amount from Cert 

to B20. However, within the error of the measurements there is no difference in total PAHs 

between B100 and B20 samples, and naphthalene appears to actually increase from B20 to B100.

Table 4-5. Raw Exhaust Engine-out PAH Quantities for each Fuel (ng/sample)

Cert 

(ng/sample)

B20 

(ng/sample)

B100 

(ng/sample)

naphthalene 240 ± 70 63 ± 4 40 ± 2

phenanthrene 130 ± 10 58 ± 3 24 ± 4

anthracene 23 ± 3 12 ± 1 3.5 ± 0.3

fluoranthene 190 ± 40 62 ± 14 22 ± 5

pyrene

TOTAL

310 ± 30

853

94 ± 22

289

31 ± 8

121

Table 4-6. Raw Exhaust Engine-out PAH Quantities for each Fuel (ng/mg PM)

Cert 

(ng/mg)

B20 

(ng/mg)

B100 

(ng/mg)

naphthalene 55.6 ± 15.3 23.1 ± 0.9 31.5 ± 1.9

phenanthrene 31.3 ± 3.5 21.4 ± 0.7 18.6 ± 1.8

anthracene 5.5 ± 0.6 4.4 ± 0.3 2.7 ± 0.1

fluoranthene 45.5 ± 11.6 22.9 ± 5.7 17.5 ± 3.4

pyrene

TOTAL

 72.7 ± 8.9

210.6

 34.5 ± 9.0

106.3

24.7 ± 4.8

95.0

A comparison of the NPAH levels (Table 4-3) with the PAH levels (Table 4-5) shows that all of 

the NPAH levels (except 9-nitroanthracene) were observed to be approximately two orders of 

magnitude below the observed levels for the corresponding PAH. In the case of 9-

nitroanthracene, this compound was consistently at or below one order of magnitude under the 

relative concentration of anthracene. There seems to be a much closer relationship between these 

two compounds than there is for any of the other compounds.

As previously mentioned, the large late eluting nitro peaks were a surprising result observed in 

the B100 samples and warranted further investigation in an attempt to narrow down the identity 

of these compounds. Figure 4-6 shows a B100 nitro (m/z 46) chromatogram again, this time 

highlighting these unknown peaks.
30

B100 m/z 46 Chromatogram

23 24 25 26 27 28 29 30

Time (min)

Rel. Int.

Figure 4-6. Nitro (m/z 46) chromatograms for a raw exhaust Engine-out B100 PM sample

All of the B100 raw exhaust Engine-out samples showed the presence of these unknown 

compounds. Additionally, the B20 Engine-out samples showed a much smaller presence of these 

compounds, while the Cert diesel exhaust did not show any peaks in this retention time region. 

All of this information indicates that these unknown compounds are most likely associated in 

some way with the soy biodiesel. Consequently, the biodiesel samples (which had the highest 

concentrations) were investigated further in an effort to identify these unknown nitro peaks. The 

EI+ full-scan (m/z 100-400) TICs generated in August 2007 (during the PAH analysis) were 

scrutinized more closely in order to see if any ions generated during this 26- to 27-minute

timeframe could be associated with the nitro peak retention times. Figure 4-7 shows the TIC for 

a B100 Engine-out raw exhaust sample. 

B100 TIC Engine-out Raw Exhaust

m/z 100-400

23 24 25 26 27 28 29 30

Time (min)

Rel. Int.

Figure 4-7. EI+ TIC (m/z 100−400) chromatogram for the Engine-out B100 raw exhaust PM samples
31

Based on the TIC, no obvious peaks were observed that could be related to the unknown peaks. 

However, by reconstructing the SIM plots from the ions in this time region, it was found that the 

first large peak at 26.2 minutes had only an m/z 351 associated with it. The middle, large peak at 

26.4 minutes had ions of m/z 125, 143, and 365 associated with it. The third large peak at 26.7 

minutes had ions of m/z 143, 339, and 382 associated with it. Using these masses as search 

parameters, the National Institute of Science and Technology (NIST) database did not show any 

possible matches for these compounds. Additionally, even with baseline subtraction to eliminate 

background ions, the full scan spectrum for each compound had a number of background ions 

present that disrupted the NIST database search. 

The peaks in Figure 4-6 could possibly relate to the engine losing power during Mode 7 for the 

B20/B100 samples. If so, they may arise from lube oil entering the combustion chamber. 

However, the current evidence suggests they are likely some sort of long-chain nitro compounds 

produced by the incomplete combustion of the soy biodiesel. If future raw Engine-out B100 PM 

samples show the presence of these compounds, more effort should be focused on identifying 

these unknown nitro peaks.

4.3 Results for DPF-out Raw Exhaust

The DPF-out samples were analyzed using the GC/EM-MS by monitoring the samples for nitrocompounds. To do this, the instrument was set to monitor the nitro ion (NO2

-

) using an ionization 

energy of 3.5 eV (EI-) that selectively fragments this portion from the NPAH molecules. The m/z

46 SIM chromatograms for the Cert and B20 PM samples are shown in Figure 4-8. These 

chromatograms show all of the nitro compounds that are present in each sample and provide a 

starting point for the rest of the NPAH analyses. 

Figure 4-8. Nitro (m/z 46) chromatograms for the raw exhaust DPF-out Cert and B20 PM samples

(displayed as relative intensity)

Overall, the chromatograms showed a number of similar features and demonstrate the presence 

of common nitro compounds found within each sample. Each of the internal standard NPAH 

peaks has also been indicated in Figure 4-8 to clarify its position in the chromatogram. As for the 

peak at approximately 17 minutes, this was identified earlier as a contaminant that was also 

present in the Engine-out samples.

Comparison of Nitro Compounds in PM 

(m/z 46 Chromatograms)

0 5 10 15 20 25 30

Time (min)

Rel. Int.

Cert

B20

1-nitronaphthalene-d7

1,5-dinitronaphthalene-d6

1-nitropyrene-d9

contaminant
32

The majority of the nitro compounds eluted between 3 and 15 minutes; when compared to the 58 

component NPAH mixture, this indicates that these compounds are single- and double-ring nitroaromatics. Figure 4-9 shows a magnified view of this time region.

Figure 4-9. Magnified nitro (m/z 46) chromatograms from the raw exhaust DPF-out Cert and B20 

PM samples

The very largest peaks observed at ~5 minutes, ~5.8 minutes, and ~12.8 minutes in these postDPF exhaust samples are 4-nitrotoluene, 5-nitro-m-xylene, and 3-nitrobiphenyl, respectively. 

Table 4-7 lists all of the single and double-ring nitro-aromatics qualitatively identified from both 

Cert and B20. The quantities for each compound cannot be accurately reported for these samples 

because of large standard deviations in the peak areas. Because the PM levels were so low, even 

the smallest variation in engine conditions, DPF loading, or other factors could account for the 

changes in both PM and NPAH levels present in these samples.

Table 4-7. Nitro-aromatics Identified in the Raw Exhaust DPF-out PM Samples from Cert and B20

Compound

nitrobenzene

2-nitrotoluene

3-nitrotoluene

4-nitrotoluene

2-nitro-m-xylene

5-nitro-m-xylene

3-nitrobiphenyl

1-nitronaphthalene

2-nitronaphthalene

Comparison of Nitro Compounds in PM 

(m/z 46 Chromatograms)

2 4 6 8 10 12 14 16

Time (min)

Rel. Int.

Cert

B20

nitrobenzene

1-nitronaphthalene-d7

4-nitrotoluene

5-nitro-m-xylene

3-nitrobiphenyl 1,5-dinitronaphthalene-d6
33

Along with the identified compounds, there were also a number of unidentified nitro peaks 

observed in Figure 4-9 that could not be associated with any of the 58 NPAH standards. Because 

of their early retention times, the hypothesis is that these compounds are also single-ring (and 

possibly double-ring) nitro-aromatics that possibly have larger side chains than the methyl 

groups found in nitrotoluene and nitro-m-xylene. A negative ion full-scan analysis (m/z 40−400) 

did not provide any additional information for these samples. Compounding this problem is the 

fact that the smaller single-ring nitro-aromatics do not form molecular ions very efficiently and 

tend to fragment more easily than the larger aromatic systems, even when using the near 0 eV 

ionization energy. As for the two small, late eluting peaks between 27.3 and 27.5 minutes in 

Figure 4-8, these nitro peaks did not correlate with any of the available NPAH standards. 

A PAH analysis for the DPF-out samples was performed by setting the GC/EM-MS system for 

EI+ full-scan (m/z 100−400). Figure 4-10 shows the TIC for both the certification diesel and the 

B20 diesel samples. Qualitatively, the chromatograms show the number and type of compounds 

that are similar for these fuels. Generally, the B20 samples qualitatively showed lower levels of 

each compound. Within these chromatograms, only peaks that could be associated with PAHs 

were identified (although the full-scan information for each peak is available and could be 

analyzed for peak identities). Only three PAHs (naphthalene, acenaphthene, and phenanthrene) 

were observed in both the Cert and B20 diesel PM samples. To demonstrate the presence of the 

phenanthrene in the samples, Figure 4-11 shows the m/z 178 (molecular ion) SIM for the Cert

diesel and the B20 diesel PM samples. Again, no actual quantities could be associated with these 

samples because of the significant fluctuations in values (>50% deviations), which are likely 

connected to the PM weight variations. Further work investigating samples like these will be 

necessary before conclusive information can be determined about PAH and NPAH levels in 

DPF-out samples.

Figure 4-10. Comparison of the TIC for the raw exhaust DPF-out Cert and B20 PM samples

TIC Comparison Between Cert and B20

0 5 10 15 20 25 30

Time (min)

Rel. Int.

Cert

B20

naphthalene

acenaphthene

phenanthrene
34

Comparison of Phenanthrene Levels

10.5 11 11.5 12 12.5

Time (min)

Rel. Int.

Cert

B20

Figure 4-11. Comparison of the m/z 178 (phenanthrene molecular ion) for the raw exhaust DPF-out

Cert and B20 PM samples

4.4 Dilute Exhaust Gravimetric Analysis

The Engine-out and DPF-out PM samples were collected for the Cert, B20, and B100 fuels using 

the sampling procedure described in Section 3.13. Table 4-8 shows a list of the Engine-out 

samples collected during this sampling period. Subsequently, the DPF was placed into the 

exhaust system and the DPF-out samples were collected. Table 4-9 shows a list of these DPF-out 

samples collected. Each PM sample listed in Table 4-9 represents three cumulative 30-minute

runs, which was done to maximize the amount of PM collected for each analysis. After the 

samples were collected, they were then subjected to the complete cleanup processes described in 

Sections 3.9 and 3.10. 

Table 4-8. Dilute Exhaust Engine-out PM Samples

Run Filename Filter # Fuel PM Mass (mg)

1-29-08 Toxics Cert 01 24 Cert 3.0903

1-30-08 Toxics Cert 02 25 Cert 3.0046

1-30-08 Toxics Cert 03 26 Cert 2.9576

2-1-08 Toxics Cert 04 34 Cert 3.0212

1-30-08 Toxics B20 01 27 B20 2.4445

1-30-08 Toxics B20 02 28 B20 2.3985

1-31-08 Toxics B20 03 29 B20 2.3247

2-1-08 Toxics B20 04 35 B20 2.6768

1-31-08 Toxics B100 01 30 B100 1.3445

1-31-08 Toxics B100 02 31 B100 1.371

1-31-08 Toxics B100 03 32 B100 1.376

2-1-08 Toxics B100 04 33 B100 1.2732

3-18-08 Toxics B100 07 38 B100 1.2031

3-18-08 Toxics B100 08 39 B100 1.389

3-18-08 Toxics B100 09 40 B100 1.5256
35

Table 4-9. Dilute Exhaust DPF-out PM Samples

Run Filename Filter # Fuel PM Wt. (mg)

4-8-08 Toxics DPF Cert 01

4-8-08 Toxics DPF Cert 02 41 Cert 0.1503

4-8-08 Toxics DPF Cert 03

4-9-08 Toxics DPF B20 01

4-9-08 Toxics DPF B20 02 43 B20 0.4932

4-9-08 Toxics DPF B20 03

4-10-08 Toxics DPF B100 01

4-10-08 Toxics DPF B100 02 44 B100 0.4507

4-10-08 Toxics DPF B100 03

Note that the Cert DPF-out PM sample mass was much lower than that of the B20 and B100

samples, which is just the opposite of what was anticipated for these samples. However, this 

sample was allowed to equilibrate in the ReFUEL Mass Lab clean room environment for only

~1.5 hours, while the other two samples (B20 and B100) were allowed to equilibrate overnight. 

The hypothesis is that 1.5 hours was not a sufficient time period for equilibration, and that if the 

sample had been left in the Mass Lab overnight prior to weighing, it would have reached 

equilibrium with the humidity there and shown a heavier final weight (absorption of water). 

Future investigation is necessary to corroborate or disprove this hypothesis.

4.5 Results for Engine-out Dilute Exhaust 

The Engine-out PM samples were first analyzed for nitro compounds utilizing GC/EM-MS. The 

m/z 46 SIM chromatograms for the Cert, B20, and B100 PM samples are shown in Figure 4-12. 

These chromatograms show the nitro compounds that are present in each sample and provide a 

starting point for the rest of the NPAH analyses. Overall, the chromatograms showed a number 

of similar features, which demonstrated the presence of common nitro compounds found within 

each sample. The first thing that was quite apparent from these chromatograms was that they 

were very different from the raw exhaust Engine-out results shown previously. The raw exhaust 

Engine-out nitro chromatogram in Figure 4-1 is shown again here in Figure 4-13. 
36 

Comparison of Nitro Compounds in PM

(m/z 46 Chromatograms)

0 5 10 15 20 25 30

Time (min)

Rel. Int.

Cert

B20

B100

Figure 4-12. Nitro (m/z 46) chromatograms for each dilute exhaust Engine-out PM sample 

(displayed as relative intensity) 

Comparison of Nitro Compounds in PM

(m/z 46 Chromatogram)

0 5 10 15 20 25 30

Time (min)

Rel. Int.

Cert

B20

B100

Figure 4-13. Nitro (m/z 46) chromatograms for each raw exhaust Engine-out PM sample 

Evidently, collecting the PM samples from the dilution tunnel had a significant impact on the 

nitro-compounds present and the levels at which they are found in the PM. These results appear 

to indicate that the chemistry of NPAH formation is still occurring as the exhaust leaves the 

engine and moves into the dilution tunnel. It is interesting that the dilution tunnel samples appear 

cleaner in that there is less diversity among the nitro compounds present. However, the Cert and 

B20 dilute exhaust samples show much larger quantities of 1-nitropyrene (retention time 25.3 

minutes) than those found in the raw exhaust. Apparently, there is a driving force that is focusing 
37

the NPAHs associated with PM from a relatively large number in the raw exhaust to just a 

handful of compounds as the exhaust moves into the dilution tunnel and cools. To the best of our 

knowledge, this is new information and may warrant further investigation. It should be noted 

however, that the raw exhaust PM samples may be more susceptible to sampling artifacts from 

exposure to higher NO2 concentrations, possibly leading to the formation of additional nitro 

compounds.10

Fundamentally, these dilution tunnel samples are much more representative of PM that would be 

emitted into the environment. Additionally, because these dilution tunnel samples were collected 

using conventional diesel PM collection procedures, the results shown in Figure 4-12 provide 

information that can be compared with that in other reports utilizing the same engine testing 

procedure. Once the nitro compounds had been preliminarily identified through their retention 

times in the m/z 46 chromatogram, the next step was to verify and quantify these compounds 

using their molecular ions. Figures 4-14 and 4-15 show the molecular ion chromatograms for 9-

nitroanthracene and 1-nitropyrene, respectively. These chromatograms illustrate qualitatively 

that there is a trend towards lower concentrations as more biodiesel is incorporated into the fuel. 

Figure 4-14. The molecular ion chromatograms (m/z 223) for 9-nitroanthracene

Comparison of 9-Nitroanthracene 

(m/z 223 Chromatograms)

17 17.2 17.4 17.6 17.8 18 18.2 18.4 18.6 18.8 19

Time (min)

Rel. Int.

Cert

B20

B100
38

Figure 4-15. The molecular ion (m/z 247) chromatograms for 1-nitropyrene

Table 4-10 shows the total amount of each NPAH produced as it relates to a given fuel type. 

These results illustrate that as more biodiesel is incorporated into the fuel, smaller amounts of 

NPAHs are present in the PM, presumably because lower levels of NPAHs are produced during 

the combustion process. Table 4-11 shows the results of these NPAH levels as they relate back to 

the PM levels produced by each fuel. The nitrophenanthrenes and 3-nitrofluoranthene generally 

showed that the concentration per amount of soot is consistent for all fuel types. In other words, 

the average concentration for each of these compounds is generally within the standard deviation 

for each fuel type. The other compounds listed in Table 4-11 trend toward less NPAH per 

milligram as more biodiesel is incorporated into the fuel. 

Table 4-10. Diluted exhaust Engine-out NPAH quantities for each fuel (ng/sample)

Cert 

(ng/sample)

B20 

(ng/sample)

B100 

(ng/sample)

1-nitronaphthalene 0.95 ± 0.20 0.49 ± 0.18 0.23 ± 0.04

2-nitronaphthalene 4.33 ± 0.84 3.01 ± 0.0.37 0.73 ± 0.18

9-nitroanthracene 30.1 ± 5.3 18.6 ± 3.4 7.37 ± 1.89

9-nitrophenanthrene 11.8 ± 4.2 8.69 ± 1.33 5.18 ± 0.37

3-nitrophenanthrene 2.41 ± 0.48 1.51 ± 0.24 1.03 ± 0.37

3-nitrofluoranthene 2.44 ± 0.78 1.13 ± 0.22 0.66 ± 0.16

1-nitropyrene

TOTAL

123.4 ± 47.5

175.4

60.5 ± 11.9

93.9

26.8 ± 3.8

42.0

Comparison of 1-Nitropyrene 

(m/z 247 chromatograms)

24.7 24.9 25.1 25.3 25.5 25.7 25.9

Time (min)

Rel. Int.

Cert

B20

B100
39

Table 4-11. Diluted exhaust Engine-out NPAH quantities for each fuel (ng/mg PM)

Cert (ng/mg) B20 (ng/mg) B100 (ng/mg)

1-nitronaphthalene 0.32 ± 0.07 0.20 ± 0.07 0.18 ± 0.03

2-nitronaphthalene 1.44 ± 0.30 1.26 ± 0.14 0.57 ± 0.17

9-nitroanthracene 9.96 ± 1.51 7.76 ± 1.22 5.63 ± 1.22

9-nitrophenanthrene 3.89 ± 1.33 3.63 ± 0.47 4.00 ± 0.44

3-nitrophenanthrene 0.80 ± 0.14 0.63 ± 0.09 0.80 ± 0.34

3-nitrofluoranthene 0.80 ± 0.25 0.47 ± 0.08 0.52 ± 0.15

1-nitropyrene

TOTAL

40.8 ± 15.3

58.0

25.3 ± 4.4

39.2

20.6 ± 1.9

32.3

Analyses for PAHs were performed using EI+ (25 eV) in conjunction with molecular ion 

information obtained for each compound. These molecular ion chromatograms were then used to 

quantify the levels for each PAH. Figures 4-16 and 4-17 show the molecular ion chromatograms 

for phenanthrene, anthracene, fluoranthene and pyrene. Each chromatogram qualitatively shows 

a trend toward lower concentrations as more biodiesel was incorporated into the fuel. 

Comparison of Phenanthrene and Anthracene 

(m/z 178 Chromatograms)

11 11.5 12 12.5 13

Time (min)

Rel. Int.

Cert

B20

B100

Figure 4-16. The molecular ion chromatograms (m/z 178) for phenanthrene and anthracene
40

Comparison of Fluoranthene and Pyrene 

(m/z 202 Chromatograms)

15 16 17 18 19 20 Time (min) Rel. Int.

Cert

B20

B100

Figure 4-17. The molecular ion chromatograms (m/z 202) for fluoranthene and pyrene

Along with the four PAHs shown in the above chromatograms, several other PAHs were also 

selected for quantitation purposes. Table 4-12 shows the overall quantity of PAH produced by 

each fuel. Table 4-13 shows each PAH quantity as it relates to the amount of PM collected for 

each sample. 

Table 4-12. Diluted Exhaust Engine-out PAH Quantities for each Fuel (ng/sample)

Cert 

(ng/sample) B20 (ng/sample) B100 (ng/sample)

naphthalene 82.7 ± 15.0 62.4 ± 8.9 171.1 ± 47.5

biphenyl 16.4 ± 4.6 16.6 ± 0.4 21.9 ± 7.1

acenaphthylene 2.0 ± 0.3 1.9 ± 0.6 1.8 ± 0.3

fluorene 12.9 ± 1.2 8.4 ± 1.39 2.7 ± 0.5

phenanthrene 890.8 ± 154.6 529.9 ± 66.9 89.4 ± 16.7

anthracene 57.7 ± 6.5 35.5 ± 2.3 2.0 ± 0.4

fluoranthene 822.1 ± 177.2 594.9 ± 217.2 186.9 ± 38.2

pyrene 536.5 ± 143.7 332.0 ± 112.5 130.8 ± 23.4

benzo[c]phenanthrene 13.2 ± 5.1 9.0 ± 2.6 4.2 ± 1.2

chrysene

TOTAL

19.2 ± 6.9

2453.5

17.7 ± 5.4

1608.3

9.2 ± 3.3

620.0
41

Table 4-13. Diluted Exhaust Engine-out PAH Quantities for each Fuel (ng/mg PM)

Cert (ng/mg) B20 (ng/mg) B100 (ng/mg)

naphthalene 29.8 ± 6.4 25.3 ± 2.2 113.3 ± 18.6

biphenyl 6.7 ± 2.8 6.8 ± 0.4 15.9 ± 5.4

acenaphthylene 0.8 ± 0.3 0.8 ± 0.2 1.3 ± 0.2

fluorene 4.7 ± 0.8 3.4 ± 0.4 2.0 ± 0.6

phenanthrene 275.9 ± 53.2 216.9 ± 38.1 67.4 ± 14.9

anthracene 18.0 ± 2.8 14.5 ± 1.6 1.4 ± 0.2

fluoranthene 306.5 ± 81.7 246.0 ± 98.5 135.7 ± 38.7

pyrene 194.3 ± 52.3 137.2 ± 52.1 95.0 ± 16.2

benzo[c]phenanthrene 5.0 ± 1.8 3.7 ± 1.2 3.0 ± 1.1

chrysene

TOTAL

6.8 ± 1.9

848.5

7.2 ± 2.2

661.8

6.8 ± 3.3

441.8

For the three-ring and higher PAHs, the data quantitatively show that as more biodiesel is 

incorporated into the fuel, smaller amounts of these larger PAHs are present per milligram of PM 

produced. However, for the double-ring PAHs, naphthalene and biphenyl, the B100 samples 

showed a higher concentration of these compounds. This scenario is probably related to the fuel 

properties themselves in that the biodiesel and Cert diesel have fundamentally different chemical 

properties. Soy biodiesel consists of straight-chain fatty acid methyl esters (FAMEs), including 

significant amounts of double and triple unsaturations in the molecules that probably provide the 

genesis for the formation of smaller double-ring PAHs. Cert diesel is a petroleum fuel that 

consists of aromatic constituents that provide better precursors to the formation of the larger 

three- and four-ring PAHs than the FAMEs. The results shown in Table 4-12 and Table 4-13

seem to corroborate this hypothesis.

4.6 Results for DPF-out Dilute Exhaust

These samples were collected in the final days of the subcontract period with the assumption that 

the gravimetric data would most likely be the only useful data generated for these experiments. 

The DPF-out exhaust produces such low levels of actual PM that it seemed unlikely that these 

samples would produce NPAH or PAH signals. Additionally, with the dilution tunnel factored 

into the sampling, this situation presented an even less likely scenario for detecting these 

compounds, even after focusing the three 30-minute runs for each fuel onto a single Tissuquartz 

filter. At most, the expectation was to observe the smaller single-ring and double-ring NPAHs 

and PAHs. However, upon analysis of the PM for nitro-compounds using the GC/EM-MS, some 

unexpected results were observed for these samples. Figure 4-18 shows the nitro chromatogram 

for each fuel sample. 
42

0 5 10 15 20 25 30

Time(min)

Rel. Int.

Cert

B20

B100

1-Nitropyrene

Nitrobenzene

Comparison of DPF-out Nitro Compounds

(m/z = 46 chromatograms)

Figure 4-18. Nitro (m/z 46) chromatograms for each DPF-out PM sample

(displayed as relative intensity)

The particularly interesting aspect of these chromatograms is the large peak observed at ~25.2 

minutes in the Cert and B20 chromatogram (and to a much lesser extent in the B100 sample),

which was identified as 1-nitropyrene. These results were very surprising in that the magnitude 

of these peaks indicated a significant presence of this compound in the DPF-out samples. The 

Cert and B20 chromatograms are largely free of other NPAHs, indicating that the DPF 

preferentially forms this compound over all other nitro-aromatics. This result is very surprising 

given the low level of PM present in the exhaust. 

Despite the fact that the B100 sample showed less 1-nitropyrene and other larger NPAHs, it did 

show an increased number of the smaller, single- and double-ring nitro-aromatics (pre-15

minutes). Figure 4-19 shows a magnified view of the 3- to 20-minute time region for the three 

samples, with the internal standards labeled on the chromatogram. It is interesting that the 

majority of these compounds could not be correlated to the 58 NPAH standards available in the 

laboratory despite the fact that they were clearly nitro compounds. Additionally, the large peak at 

approximately 9 minutes in the B100 sample was not comparable to the NPAH standards. These

unidentified peaks are most likely alkyl nitro-aromatic compounds (e.g., ethyl or propyl 

nitrobenzenes or nitronaphthalenes) based on their retention times. More work using full-scan

analysis will be necessary to identify these unknown nitro compounds.
43

3 5 7 9 11 13 15 17 19

Time(min)

Rel. Int.

Cert

B20

B100

1-Nitronaphthalene-d7

Nitrobenzene

Comparison of DPF-out Nitro Compounds

(m/z = 46 chromatograms)

1,5-Dinitronaphthalene-d6

1-Nitroanthracene-d9

Figure 4-19. Magnified nitro (m/z 46) chromatograms for each DPF-out PM sample

Once the nitro compounds had been preliminarily identified through their retention times in the 

m/z 46 chromatogram, the next step was to verify and quantify these compounds using their 

molecular ions. Figure 4-20 shows the molecular ion chromatograms for 1-nitropyrene. These

chromatograms illustrate qualitatively that there is a trend toward lower concentrations as more 

biodiesel is incorporated into the fuel. 

24.7 24.9 25.1 25.3 25.5 25.7 25.9

Time(min)

Rel. Int.

Cert

B20

B100

Comparison of 1-Nitropyrene

Figure 4-20. The molecular ion (m/z 247) chromatograms for 1-nitropyrene

Table 4-14 shows the total quantitative results for each fuel type for the three largest (four-ring) 

identifiable NPAHs. These results illustrate that as more biodiesel is incorporated into the fuel, 

lower levels of four-ring NPAHs are present in the PM, presumably because lower levels of fourring NPAHs are produced during the combustion process. 
44

Table 4-14. Diluted Exhaust DPF-out NPAH Quantities for each Fuel (ng/sample)

Cert 

(ng/sample)

B20 

(ng/sample)

B100 

(ng/sample)

3-nitrofluoranthene 0.07 0.06 0.05

1-nitropyrene 80.3 53.5 15.0

4-nitropyrene 0.20 0.19 0.16

Normally, the next step would be to look at the relationship between these NPAH amounts and 

the PM masses for each sample. However, the PM mass reported for the Cert sample in Section 

4.4 was far below the weights of the other samples for reasons that were explained previously. 

As a result, the data cannot be reliably reported at this time. The DPF-out data for the 1-

nitropyrene are quite high, and in fact achieve levels comparable to the Engine-out data obtained 

previously. Table 4-15 shows this comparison between the two exhaust configurations.

Table 4-15. Comparison of 1-nitropyrene Levels between DPF-out and Engine-out Diluted Exhaust

Samples

DPF-out (ng/sample) Engine-out (ng/sample)

Cert Fuel 80.3 123.4 ± 47.5

B20 Fuel 53.5 60.5 ± 11.9

B100 Fuel 15.0 26.8 ± 3.8

These data clearly show that the amount of 1-nitropyrene is largely independent of the amount of 

PM removed from the engine exhaust stream by the DPF. These results were completely 

unanticipated and have not been reported previously. Undoubtedly this finding by itself warrants 

further investigation to determine the reproducibility of these results, particularly since the DPF 

appears to be concentrating the 1-nitropyrene onto quantitatively less PM. Additionally, it is 

expected that DPF-out particles are smaller diameter than Engine-out particles. Thus, the DPF 

system may create a scenario of higher concentrations of 1-nitropyrene on smaller particles. This

in turn may deliver the compound deeper into throat and lung tissues when inhaled, presenting a 

potential health concern because 1-Nitropyrene has been shown to be both mutagenic and

carcinogenic.

11, 12

The samples were analyzed for PAHs using EI+ (25 eV) in conjunction with molecular ion

information obtained for each compound. These molecular ion chromatograms were then used to 

quantify the levels for each PAH. Table 4-16 shows each PAH quantity as it relates to each 

sample. Again, these values were not related back to the PM levels because of the question about 

the Cert sample discussed in Section 4.4.
45

Table 4-16. PAH Quantities for Diluted Exhaust DPF-out for each Fuel (ng/sample)

Cert 

(ng/sample)

B20 

(ng/sample)

B100 

(ng/sample)

naphthalene 28.2 58.4 7.7

biphenyl 3.4 9.6 1.9

acenaphthylene 0.08 0.09 0.10

fluorene ND* ND ND

phenanthrene 1.6 1.7 11.5

anthracene 0.11 0.07 0.12

fluoranthene 2.1 1.8 25.1

pyrene 0.98 0.25 15.1

benzo[c]phenanthrene ND ND ND

chrysene

TOTAL

ND

36.4

ND

71.9

ND

61.5

*ND = not detected

The data did not show any clear trends other than this one: of the three fuels studied, the B100 

samples had the highest levels of phenanthrene, anthracene, fluoranthene, and pyrene. 

Additionally, there does not appear to be a clear numerical link between the fluoranthene and 

pyrene levels observed and the nitrofluoranthene and nitropyrene levels observed in these DPFout samples other than the general trend that, as the PAH level goes higher, the NPAH level goes 

lower. More research in this area is necessary before any clear links can be made among the 

different compounds.

Next, the DPF-out PAH levels for several representative PAHs were compared to the Engine-out 

samples. Table 4-17 shows this comparison between the two exhaust configurations.

Table 4-17. Comparison of Phenanthrene, Fluoranthene, and Pyrene Levels of DPF-Out and 

Engine-out Samples

Fuel 

Type

Exhaust 

Config.

Phenanthrene 

(ng/sample)

Fluoranthene 

(ng/sample)

Pyrene 

(ng/sample)

Cert Engine-out 890.8 ± 154.6 822.1 ± 177.2 536.5 ± 143.7

DPF-out 1.6 2.1 0.98

B20 Engine-out 529.9 ± 66.9 594.9 ± 217.2 332.0 ± 112.5

DPF-out 1.7 1.8 0.25

B100 Engine-out 89.4 ± 16.7 186.9 ± 38.3 130.8 ± 23.4

DPF-out 11.5 25.1 15.1

In all cases, the amount of overall PAH present dropped by approximately an order of magnitude 

or more when the Engine-out samples were compared with the DPF-out samples. However, 

while the Engine-out samples showed the lowest PAH levels for the B100 samples compared 

among the fuels, the B100 DPF-out samples showed the highest PAH levels among the different 

fuels. More research for these types of fuels and exhaust configurations will be necessary to 

determine the reproducibility of these findings. 
46

5. Conclusions and Future Research

This research demonstrated novel approaches in a number of areas for the analysis of PAHs and 

NPAHs produced during diesel combustion. The GC/EM-MS was shown to be a versatile 

technique that allowed for the analysis of both PAHs and NPAHs. In hindsight, because it has 

become clear that this system is sensitive and selective enough for the analysis of these 

compounds, the collected mass of Engine-out PM for all fuel types should be lowered to 

approximately 0.5 mg through the choice of sampling flow rate. This would simplify the sample 

preparation strategy by eliminating the amino solid phase extraction steps, leaving just Soxhlet 

extraction and evaporation. This smaller recommended gravimetric level mimics the dilute DPFout PM samples, which did not need the additional cleanup steps. This simplified scenario would 

not only save time but also eliminate a number of steps that may contribute to the loss of the 

PAHs and NPAHs.

Comparison of the raw and diluted samples shows that the raw exhaust contains a larger variety 

of nitro compounds relative to the dilution tunnel samples. This indicates that chemical changes 

in NPAHs are still occurring in the exhaust gas as it moves from the engine into the dilution 

tunnel. The details of these chemical reactions remain to be determined, but we have 

demonstrated new tools to investigate them. Using this information, new technologies could be 

introduced to limit the formation of these mutagenic and carcinogenic compounds associated 

with the PM. 

While the raw exhaust samples provided interesting new information about NPAH chemistry 

within the exhaust stream, the dilute samples provided a more realistic scenario for determining 

which compounds are actually being emitted into the environment. The DPF-out PM produced 

surprising results with regard to 1-nitropyrene. The fact that this compound was present in the 

DPF-out PM at quantities comparable to those observed in the Engine-out PM samples was 

unexpected, particularly since the DPF lowers the gravimetric amount of PM present in the 

exhaust by over an order of magnitude. This apparent independence from PM level has not been 

reported previously and suggests that the DPF is actually focusing the formation of NPAHs 

almost exclusively toward the 1-nitropyrene compound. This is a concern given the mutagenic 

and carcinogenic nature of this particular NPAH. 

It is interesting that, in concert with the apparent insensitivity of 1-nitropyrene to the DPF, the 

pyrene levels found in the DPF-out samples were much lower (by 3 orders of magnitude in some 

cases) than the pyrene levels observed in the Engine-out samples. If pyrene is a key precursor to 

1-nitropyrene, then one might reasonably expect the two compounds to trend similarly to lower 

concentrations via the DPF. Two possible explanations for the observed divergent trends are as 

follows:

1. 1-nitropyrene is formed by an alternative mechanism to pyrene nitration

2. The measured concentrations of 1-nitropyrene are at or near equilibrium limits exiting the 

DPF.
47

Further engine testing will be necessary to determine the reproducibility of these results, and, if 

these results are indeed reproducible, then more investigations into the mechanisms for the 

formation of 1-nitropyrene may be warranted.
48

6. References

1. Bleakney, W., and J.A. Hipple, Jr. "A New Mass Spectrometer with Improved Focusing 

Properties." Phys. Rev. 53:521-529, 1938.

2. Laramee, J.A., R.B. Cody, and M.L. Deinzer. "Discrete Energy Electron Capture 

Negative Ion Mass Spectrometry." In Encyclopedia of Analytical Chemistry, R.A. 

Meyers, Ed. Chichester: John Wiley and Sons, pp. 11651-11679, 2000.

3. Voorhees, K.J., et al. In Proceedings of 49th ASMS Conference on Mass Spectrometry 

and Allied Topics. Chicago, IL, 2001.

4. Havey, C.D., et al. "Analysis of Nitro-Polycyclic Aromatic Hydrocarbons in 

Conventional Diesel and Fischer-Tropsch Diesel Fuel Emissions Using Electron 

Monochromator-Mass Spectrometry." Anal. Chem. 78:4894-4900, 2006.

5. Havey, C.D., et al. "Theory and Application of Dissociative Electron Capture in 

Molecular Identification." J. Phys. Chem. A. 110(13):4413-4418, 2006.

6. Fritz, J.S., Analytical Solid-Phase Extraction. New York: John Wiley & Sons, Inc., 1999.

7. Bezabeh, D.Z., et al. "Determination of Nitrated Polycyclic Aromatic Hydrocarbons in 

Diesel Particulate-Related Standard Reference Materials by using Gas 

Chromatography/Mass Spectrometry with Negative Ion Chemical Ionization." Anal. and 

Bioanal. Chem. 375(3):381-388, 2003.

8. Dane, A.J., C. Abbas-Hawks, and K.J. Voorhees. Unpublished. Colorado School of 

Mines, 2005.

9. "AVL 8-Mode Heavy-Duty Cycle." Available from 

www.dieselnet.com/standards/cycles/avl_8mode.html, 1997 (rev. 2000); last accessed in 

March 2010.

10. Khalek, I.A. "Nitro-PAH Artifact Investigation." Southwest Research Institute, Project 

No. 10738. Final report to NREL for Subcontract No. ACI-4-44029-01, November 2004. 

11. Chan, P. "National Toxicology Program Technical Report on the Toxicity Studies of 1-

Nitropyrene (CAS No. 5522-43-0) Administered by Inhalation to F344/N Rats." Toxicity 

Report Series 34:1-D2, 1996.

12. Kappers, W.A., et al. "Comparison of Three Different In Vitro Mutation Assays Used for 

the Investigation of Cytochrome P450-Mediated Mutagenicity of Nitro-Polycyclic 

Aromatic Hydrocarbons." Mutation Research 466(2):143-59, 2000.
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4. TITLE AND SUBTITLE

Investigation of Nitro-Organic Compounds in Diesel Engine Exhaust: 

Final Report, February 2007–April 2008

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J. Dane and K.J. Voorhees

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14. ABSTRACT (Maximum 200 Words)

The National Renewable Energy Laboratory upgraded its ReFUEL engine and vehicle testing facility to speciate 

unregulated gas-phase emissions. To complement this capability, the laboratory contracted with the Colorado School 

of Mines (CSM) to study the effects of soy biodiesel fuel and a diesel particle filter (DPF) on emissions of polycyclic 

aromatic hydrocarbons (PAH) and nitro-polycyclic aromatic hydrocarbons (NPAH). CSM developed procedures to 

sample diesel particulate matter (PM) emissions from raw and diluted exhaust, with and without a DPF. They also 

developed improved procedures for extracting PAH and NPAH from the PM and quantifying them with a gas 

chromatograph-electron monochromator mass spectrometer. The study found the DPF generally reduced PAH 

emissions by 1 to 3 orders of magnitude. PAH conversion was lowest for B100, suggesting that PAHs were forming

in the DPF. Orders of magnitude reductions were also found for NPAH emissions exiting the DPF. 

15. SUBJECT TERMS

engine exhaust; biodiesel fuel; particulate matter; diesel particle filter; polycyclic aromatic hydrocarbons; nitro-organic 

compounds; engine testing; fuel tests

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