Randy L. Vander Wal

Penn State University, University Park, Pennsylvania

Victoria M. Bryg

The Universities Space Research Association

National Center for Space Exploration Research, Cleveland, Ohio

Chemistry Characterization of Jet Aircraft Engine

Particulate by XPS: Results From APEX III

NASA/CR—2014-218293

June 2014
NASA STI Program . . . in Profi le

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientifi c and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Offi cer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major signifi cant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of signifi cant 

scientifi c and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientifi c 

and technical fi ndings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientifi c and 

technical fi ndings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientifi c and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientifi c, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientifi c and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question to help@sti.nasa.gov

• Fax your question to the NASA STI 

Information Desk at 443–757–5803

• Phone the NASA STI Information Desk at

 443–757–5802

• Write to:

 STI Information Desk

NASA Center for AeroSpace Information

 7115 Standard Drive

 Hanover, MD 21076–1320
Randy L. Vander Wal

Penn State University, University Park, Pennsylvania

Victoria M. Bryg

The Universities Space Research Association

National Center for Space Exploration Research, Cleveland, Ohio

Chemistry Characterization of Jet Aircraft Engine

Particulate by XPS: Results From APEX III

NASA/CR—2014-218293

June 2014

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared under Grant NNX09AD42A
Acknowledgments

This work was supported under the Subsonic Fixed Wing Program, Topic A.2.2—Emissions Reduction Program, Subtopic A.2.2.2 

Fundamental Experiments, through grant NNX09AD42A with Penn State University. The authors gratefully acknowledge the 

contributions by Chung-Hsuan Huang (Penn State, EME Dept. graduate student) to the manuscript preparation and discussions. 

The manuscript was written through contributions of all authors. All authors have given approval to the fi nal version of the 

manuscript. These authors contributed equally.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by NASA technical management OR expert reviewer(s).
NASA/CR—2014-218293 1 

Chemistry Characterization of Jet Aircraft Engine Particulate by 

XPS: Results From APEX III 

Randy L. Vander Wal 

Penn State University 

University Park, Pennsylvania 16802 

Victoria M. Bryg 

The Universities Space Research Association 

National Center for Space Exploration Research 

Cleveland, Ohio 44135 

Abstract 

This paper reports XPS analysis of jet exhaust particulate from a B737, Lear, ERJ, and A300 aircraft 

during the APEX III NASA led field campaign. Carbon hybridization and bonding chemistry are 

identified by high-resolution scans about the C1s core-shell region. Significant organic content as gauged 

by the sp3

/sp2 ratio is found across engines and platforms. Polar oxygen functional groups include 

carboxylic, carbonyl and phenol with combined content of 20 percent or more. By lower resolution 

survey scans various elements including transition metals are identified along with lighter elements such 

as S, N, and O in the form of oxides. Burning additives within lubricants are probable sources of Na, Ba, 

Ca, Zn, P and possibly Sn. Elements present and their percentages varied significantly across all engines, 

not revealing any trend or identifiable cause for the differences, though the origin is likely the same for 

the same element when observed. This finding suggests that their presence can be used as a tracer for 

identifying soots from aircraft engines as well as diagnostic for monitoring engine performance and wear. 

Introduction 

Soot chemistry is relevant to its environmental interaction and impact on human health (Pope et al. 

2002). Soot can contain heteroelements. These may arise from the fuel, lube oil, engine wear or by the 

combustion process (Timko et al. 2010). Elemental content and concentration depends upon the 

contribution and partitioning of these sources to soot. Hence, their presence serves as a potential 

diagnostic and also is a potential means of apportionment. Heteroelements can participate in surface 

reactions (Countless et al. 1980). For example, Fe can generate reactive oxygen species, such as OH by 

the well-known Fenton reaction (Kennedy 2007). 

Soot chemistry also pertains to oxygen functionality and organic content. In absence of condensed 

sulfate and volatile compounds, oxygen groups determine the acidity of the carbon surface and 

correspondingly its hydrophilic properties (Gysel et al. 2003). Three nominal classes, hydroxyl, carbonyl 

and carboxylic acid groups are the characteristic groups as distinguished by wet analytical methods 

(Boehm 1994). Therein it is quite logical to use the same group identification by XPS (Okpalugo et al. 

2005). Soot chemistry also includes the carbon hybridization state, namely sp2

 versus sp3 (Lascovich et al. 

1991). Alkyl groups, as substituent groups on aromatic units and other hydrocarbon fragments from either 

fuel or oil can contribute to the latter (Yu et al. 1991). Secondary condensation of volatiles can contribute 

to both, and can usually be distinguished via TEM from the “solid” particle as a coating, or appear as a 

flattened droplet if formed as an independent secondary aerosol (Russell et al. 2002). Both aspects of 

surface chemistry impact atmospheric longevity of the soot, its propensity to condense gases such as SO3

and NO2 and to coalesce with other aerosols (Choi and Leu 1998). 

 
NASA/CR—2014-218293 2 

To-date, reports on the chemistry aircraft exhaust particulate matter (PM) emission from full-scale 

engines (as opposed to sector or model combustors) burning actual fuels are few. Early work reported 

elemental speciation for PM from a CFM56-2C1 engine with a recent study analyzing soot collected from 

the NASA-DC-8 jet for element content (Kinsey and Hays 2011). Limited analysis has also been 

performed on particulate collected in chase experiments (Wuebbles et al. 2007). Performed relatively 

recently, these studies summarize the relatively few studies to-date. 

Thus far most emphasis has been upon physical characterization of engine PM. Field campaigns with 

multiple teams have measured PM size and number distributions, with others calculating mass emission 

indices as function of power and fuel type (Wey et al. 2006). Specific techniques have included scanning 

mobility particle sizer (SMPS), aerosol mass spectrometers (AM), providing electric and aerodynamic 

mobilities, respectively, tapered element oscillator measurement (TEOM) for total PM mass and 

absorption for black carbon determination in an aethalometer or multi-angle absorption photometer 

(MAAP) instrument. 

Characterization of actual aircraft engine PM is difficult; little is available and sampling opportunities 

from real systems few. Yet significant public exposure occurs at airports, and particularly for ground 

support personnel. On tarmacs, boarding ramps, and open terminals, if exhaust is smelled, likely soot, 

concurrent with emission is breathed. Therein the objective of this study was to obtain PM samples across 

a variety of jet engine platforms to compare the chemical composition of the combustion-generated 

particulate (solid and volatile) at realistic engine conditions, and contribute to existing data. 

The goal of this study was analysis of a spectrum of soot for the aforementioned aspects of chemistry. 

With paucity of such data from real operating aircraft, this subset of analyses conducted on soot collected 

during the field campaign provides a baseline for the consistency or variability of these different chemical 

measures of jet engine PM. Given the varied aspects each with their own relevance, XPS was selected for 

its applicability to each. 

Experimental 

PM emissions are historically measured as the fuel emission index (EI), being the percent of PM mass 

per unit (mass) of fuel consumed. Filter based measurements have shown EI to peak at low and high 

engine thrust. The former is due to poor efficiency at idle operation (4 to 7 percent power) and the latter 

due to amount of fuel consumed at takeoff (85 to 100 percent power). These two modes are the primary 

operational regimes of jet engines at and near ground level, i.e., at airports, and hence are the operational 

regimes producing the PM exposure to travelers and the surrounding neighborhood. These are the thrust 

levels as which soot chemistry is characterized across a variety of jet engine platforms. Also these powers 

produce the majority of ground and near-ground level soot emissions. Samples were collected during the 

APEX III field campaign in the fall of 2005 at the NASA-Glenn Research Facility in Cleveland Ohio, 

immediately adjacent to the Cleveland Hopkins International Airport. This geographic proximity 

facilitated “loans” of the varied aircraft, with fuel, Jet-A, by Continental Airlines, coordinated by Hopkins 

personnel.

XPS measurements were performed on soot collected on quartz filters (at ambient temperature). 

These filters were type GF 10 used for absorption in a MAAP, manufactured by Thermo Electron. Further 

details may be found in a NASA Technical Memorandum for APEX I (Wey et al. 2006). 

XPS Instrument and Analysis 

The PHI 500 Series XPS is a conventional dual anode X-ray source (Mg & Al) with a 200 

hemispherical electron energy analyzer and a multi-channel detector. Analyzer electronics have an energy 

scan range of 0 to 4800 eV with a resolution of 0.025 eV minimum step size, and the lens is an OmniFocus III (Physical Electronics Inc. (PHI). The mono-chromatic Al X-ray source has a variable energy 

range of 4 kV to 15 kV with 300 W power in continuous operation. The sample stage can be moved and 

focused in three dimensions. 
NASA/CR—2014-218293 3 

XPS was performed on each sample using both a survey scan for all elements plus a multi-plex (high 

resolution) scan for carbon (and usually oxygen). The percent of each element, determined by the survey 

scan was measured to 0.1 percent was measured using a semi-quantitative program associated with the 

XPS software. The data was collected by a MATLAB (The Mathworks, Inc., Natick, MA) computer 

routine. 

A high-resolution (multi-plex) scan was run for carbon, with a minimum of 10 sweeps and 7 cycles. 

The resultant high resolution C1s peak was curve fit using Gauss-Lorenz peaks and a Shirley fit. Because 

the carbon 1s peak was the peak of interest, attention was focused on this peak: its breadth, displacement 

and asymmetry. Soots were examined to determine if the carbon 1s peak had identifiable sub-peaks as 

established by a curve fitting routine attached to the XPS software. Any sample charging was taken into 

account by using the neutralizer during acquisition. The default limits to this program used a FWHM of 

1.0 and a (%) Gaussian component of 20. An effort was made to fit a peak for the leading edge 

(~283eV+) of the curve and locate larger peaks with a minimum peak broadening. The exception to this 

was the area where the plasmon peaks are found, usually 286 eV. This area was often broad and poorly 

defined relative to baseline. Peak deconvolution was performed via the same MATLAB program after 

setting the background parameters. Peak assignments were made per the NIST compilation (NIST 

database), allowing for shifts due to sample charging. Precision of reported percentages of the different 

C1s components is judged to be ~5 percent as +1s, this measure being based upon examination of 

residuals expressing goodness of fit upon variation of peak position or width. 

Results and Discussions 

Chemical Composition, Surface Chemistry, and Carbon Bonding State 

As an analytical tool, XPS is of particular value in providing three complimentary chemistry 

measures of carbonaceous aerosol: elemental composition, surface chemistry and carbon bonding. 

Though a commercial fuel with up to 300 ppm sulfur content was used in all tests. 

Variability in engine design have the potential to create very conditions for soot formation and 

oxidation. Examination of the soot chemistry by hetero-element content and carbon bonding can identify 

the impact or not, of engine differences. A secondary consideration is how different are such soots from 

common laboratory flame. Similarity would permit transfer of knowledge between the laboratory and 

actual systems whereas differences would point to the future need for individual studies at full scale. 

Elemental Composition 

In XPS a survey scan generally covers a very broad energy range in which element signatures are 

identified on the basis of the emitted photoelectron kinetic energy, as shown in Figure 1, for each of the 

four jet soots. Common to all soots is the significant content of N, S, and Na. 

In the case of highly refined jet fuel (kerosene), light elements such as N and O will not arise from the 

fuel but rather from the air-supported combustion. Additional high resolution scans over the S2p, N1s and 

O1s regions confirm these elements to be in the form of oxides (Wey et al. 2006). The high N content 

suggests significant exposure and adsorption of NOx species (Prince et al. 2002). NO or NO2 could 

undergo radical addition to p bonds or to vacancies and edge sites in aromatic systems and the carbon 

lamella comprising the soot surface. Reaction will form—NO- intermediates on carbon, as is known by 

oxidation studies (Jeguirim et al. 2005), but NO2 may not be prevalent relative to NO at exhaust 

temperatures. Alternatively surface oxygen groups (observed in the C1s scanned region) could participate 

in bonding with NO and NO2 to again form surface bound nitrogen oxides (Seisel et al. 2005). No sulfur 

was detected in elemental form either but rather, consistent with N, in the form of oxides. Its adsorption is 

also attributed to bonding with surface oxygen groups. The role that water may play in facilitating 

adsorption of nitrate or sulfate compounds is not addressed by these measurements. Moreover these 

interpretations do not preclude the possibility that sulfur species yet may act as seed nuclei for soot 
NASA/CR—2014-218293 4 

Figure 1.—The XPS global survey scan of A300, ERJ, Lear, and B737 derived soot. 

(Karcher 1998), where at the particle core the (elemental) S would not be detectable. Other elements such 

as alkalis (e.g., Na) can arise from pre-treatment of the fuel by supported catalysts or absorbents, or may 

simply be the counter ion of organic or inorganic salts. The sum total of these factors determines the 

elemental composition of the soot. 

Soot, particularly as produced by engines, often contains metals in addition to carbon (Kinsey and 

Hays 2011). Transition or heavier metals may arise from jet engine materials. Al is used in inlet ducts and 

Al2O3 is a bond coat material for thermal barrier coatings that are primarily composed of yittria (Y2O3) 

stabilized zirconia (ZrO2) (Clarke and Phillopot 2005; Van Ben et al. 2010; Stover and Funke 1999). 

Elements such as Sr or Ba may be added to the ceramic for stability while transition elements such as Ni 

or Co are found in the underlying bond coat and are constituents of turbine fan blades (Stover and Funke 

1999). Cr is a common stainless steel alloy element, e.g., used in stainless steel bearings. The presence of 

any of these elements would be indicative either of erosion, wear of these coatings or exposure of 

underlying alloys. The fact that such elements are present in the PM2.5 allows for source identification 

and illustrates XPS as a valuable diagnostic tool for monitoring engine health. 

However, most of the elements can be attributed to lube oil additives (Kinsey and Hays 2011). 

Additives are substances formulated for improvement of the anti-friction, chemical and physical 

properties of base oils (mineral, synthetic, vegetable or animal) that enhance lubricant performance and 

extend equipment lifetime (Denis et al. 2000; Kashiki and Oshima 1971; Booser 1988). Combinations of 

different additives and their quantities are determined by the lubricant type (e.g., engine, gear or hydraulic 

oils) and the specific operating conditions (temperature, load, component, materials, environment, etc.). 

Additive content may reach 30 percent. 

Additives serve a number of functions (Denis et al. 2000; Kashiki and Oshima 1971; Booser 1988). 

Tin may be present as an oil additive, usually in conjunction with lubricants containing molybdenum 

compounds, though it can also be used as an overlay for flashing of components. Barium compounds 

serve as corrosion and rust inhibitors; detergent; antismoke additive in fuels. Zinc dithiophosphate (ZDP) 

or dialky-dithiophosphate (ZDDP) are antiwear, antioxidant, and corrosion inhibitors. Sodium (Na) and 

barium (Ba) are associated with detergents that neutralize strong acids, produced during the combustion 

process. Phenolates, sulphonates and phosphonates of alkaline and alkaline-earth elements, such as 

calcium (Ca), magnesium (Mg), sodium (Na) or barium (Ba) are used as detergents in lubricants. The 
NASA/CR—2014-218293 5 

absence of phosphorous (P) is surprising since it is often used in tri-cresyl phosphate as an anti-wear 

additive that prevents direct metal to metal contact. Other organic additives include anti-oxidants, (e.g., 

alkyl sulfides, aromatic sulfides, aromatic amines, and phenols), rust and corrosion inhibitors, (e.g., 

organic acids, esters and amino-acid derivatives), and polymeric pour point depressants and anti-foaming 

additives such as silicon-based organics. 

It is likely that combustion of the S- N- or Si-atoms containing compounds contribute to the oxides of 

these elements for those engines and associated PM in which other lube-oil elements were detected. 

Related work has found oil to contribute to secondary organics by overboard venting of the recirculation 

system through the engine nacelle (Yu et al. 2010) and also by fragmentation patterns of hydrocarbons of 

vented vapors within the core flow exhaust (Yu et al. 2012). Yet fragmentation patterns, under exhaust 

flow conditions can be masked given the vast array of other organics produced by incomplete 

combustion. Hetero-elements and their oxidation state as incurred by surface adsorption of vented oil or 

by full combustion of oil from leaking seals can provide a definitive signature. 

Elemental content appears specific to each soot and associated engine. The distribution of metals 

depends upon engine age and maintenance. Those elements whose origin is the fuel, such as sulfur (S) 

and nitrogen (N) are omni-present as is the nitrogen arising from combustion produced NOx. However a 

particular pattern or specific ratio is not apparent. 

Surface Oxygen Groups 

Figure 2 summarizes the peak intensities associated with the Lear soot at 100 and 7 percent power 

levels, as extracted by deconvolution of the nominal C1s scans. Surface oxygen groups are inherent to 

partial oxidation of the carbon surface and include phenolic (-OH), carbonyl (-C = O) and carboxylic acid 

(C-OOH) groups. The concentration of different functionalities represents a composite picture of the 

oxidative environment experienced by the soot particle in its post-growth environment. Species such as 

CO2, H2O and in particular NO2 can all partially oxidize the soot particle. Across this range of species and 

temperature, the surface oxygen concentrations are the steady-state levels resulting from surface oxidation 

processes and are not reflective of the rate or degree of oxidation. However to the extent that the postcombustion environments of different (engine) sources differ in temperature and chemical environment, 

Figure 2.—Summary of peak intensities of C1s peak deconvolution from 

Lear 100 and 7 percent derived soot. 
NASA/CR—2014-218293 6 

the identities and concentrations of these oxygen groups can also vary (Braun et al. 2008). It is interesting 

to note that with but a couple small exceptions, the carboxylic and especially the phenol concentrations 

uniformly are larger at lower engine power (85 or 65 percent) than at 100 percent. Across the jet engines 

observed in this study at equivalent power levels, the concentrations for these groups are similar. They are 

also equivalent to measurements made on soots from power plants and diesel exhaust particulate (Kinsey 

and Hays 2011). Therein these groups do not necessarily provide a robust signature distinguishing jet 

engine soots. 

Nevertheless the significant concentration of these groups suggests that the emitted soot is far from 

hydrophobic, but rather quite hydrophilic. If as first order the carbon bonded to the oxygen functional 

groups is taken as the fractional monolayer coverage, relatively to purposefully assembled SAMs or even 

ordinary hydroxylated glass with less than 10 percent surface silanols, the soot should readily adsorb 

water and other polar compounds such as NOx and SOx. While no such films were observed in TEM, the 

evaporation of physically adsorbed species is likely in the high vacuum of such instruments. For this same 

reason the phenolic content is attributed to C-OH, and not bound water. Contributions from S-H or N-H, 

though coinciding with this energy region are not considered plausible given the combustion origin of the 

soot. 

Carbon Chemical State 

As illustrated in Figure 2, a dramatic change in sp2/sp3 content occurs between 100 and 7 percent 

power levels for the Lear soot. A similar shift in content is observed in the B737 soot between 100 and 

55 percent power levels. These and results for other soots are summarized in Table 1. In each case the 

change reflects varied combustion environments at the different power levels. Soot is considered to be 

composed of both elemental and organic carbon (Matuschek et al. 2007). The main carbon C1s peak may 

be resolved into one or two peaks by deconvolution. The main position at approximately 284.5 eV 

corresponds to the sp2

 carbon while the peak centered near 285.4 eV may be interpreted as originating 

from sp3

 hybridized carbon (Titantah and Lamoen 2005; Gilham et al. 2008). These two types of carbon 

bonding are integral to the overall soot nanostructure, representing the elemental and organic carbon, 

respectively. The amount and spatial relationship of these different hybridized components are intimately 

linked to the soot formation process. Nascent fuel composition, gas-phase pyrolysis processes and 

exposure to elevated temperature all play a role in determining the split between these components. 

Of particular interest for the Lear soot at 7 percent power is the high sp3

/sp2 ratio, approximately 

1:1.5, indicating significant organic content. A similar ratio of ~1.9, which indicates a significant organic 

content was found for the B737 soot, but at 55 percent power. It is not surprising that the organic content 

increases at lower power levels. Operating off optimal design, mixing is incomplete and combustion 

uncompleted. Fuel pyrolysis products becomes incorporated and retained within the soot. But for the ERJ 

and A300 soots, organic content exhibits the opposite trend, decreasing with decreasing power. Unburnt 

hydrocarbons in the exhaust stream can also condense upon the surfaces of the soot where they act as seed 

nuclei. Yet the HRTEM images did not reveal an organic coating upon the soot particles nor any liquidlike droplets upon the TEM grid used for direct capture—for any of the soots. In fact the TEM showed 

TABLE 1.—SUMMARY OF C1S PEAK DECONVOLUTION COMPONENTS ACROSS SOOTS 

PRODUCED BY THE DIFFERENT AIRCRAFT 

 ERJ - 

100% 

ERJ - 

85% 

Lear -

100% 

Lear - 

85% 

Lear - 

7% 

B737 - 

100% 

B737 - 

65% 

A300 - 

85% 

A300 -

65% 

Csp2 6.63 6.72 49.72 12.87 23.28 36.21 ----- 8.51 15.27 

Csp3 69.53 56.58 24.82 58.34 43.62 37.5 41.87 67.78 47.75 

C-OH 10.49 22.49 15.75 18.53 22.61 15.39 34.29 13.21 23.4 

C = O 5.1 6.33 5.13 ----- 3.29 1.84 12.31 4.75 11 

COOH 8.25 7.88 4.59 10.26 7.2 9.17 10.62 5.77 ----- 
NASA/CR—2014-218293 7 

that the particle surfaces were at least as structured if not more so than the core, ruling out a surface 

specific origin. This absence of visible organic material coupled with the evident oxidation of the particle 

suggests the organic content of the soot is matrix bound. And since it is unlikely to be trapped organics 

(again the HRTEM image does not suggest this), it is more likely in the form of alkyl groups as 

substituents on aromatic units (Cain et al. 2010). 

Addendum 

During the preparation of this article a complimentary one appeared in ES&T. Using X-ray (induced) 

fluorescence (XRF), PM elemental content was assessed from the three APEX campaigns. Collected on 

Teflon filters, exhaust plume samples from seven commercial turbofan engine models were collected on 

the ground at a distance of 30 m behind the engine exit. 

For the aircraft and engines in APEX III results are available for only 2 of the 5 aircraft, the ERJ145 

and the A300 jets. This limited overlap and different sampling position hinders comparisons. Our samples 

were not analyzed by XRF nor was HRTEM applied to those 2 PM samples. To note is that by XRF 

indicated high elemental sulfur content (54 percent for the ERJ and 89 percent for the A300, of total PM 

emission index) with 50 percent for both engines of the water soluble ion emission being sulfate. Such a 

high content suggests that sulfate aerosol served as the particle nuclei and/or coalesced with aggregates. 

Either case should be evident by TEM. Neither case was noted in our studies and samples. As known, 

sampling as distances of 30 m is a widely accepted practice that allows for the formation of volatile PM 

while maintaining plume integrity (Kinsey and Hays 2011; Onasch et al. 2009). A second point of 

commonality was the EC/OC determination using the prescribed NIOSH thermo-optical reflectance 

method on pre-fired quartz filters. No direct point of comparison is available, other than that the 

EC/OC ratio varies from less than 0.5 to well above 2.0 across the suite of engines for power levels 30 to 

40 percent. Our values, denoted as sp2

/sp3 inferred by XPS for full power operation are plausible, given 

this range (Kinsey and Hays 2011). 

Conclusions 

Techniques such as XPS and XRF excel in analyzing PM, particularly aerosols. Both techniques can 

analyze for elements including Na and above with 0.1 atomic percent detection limits. XPS is more 

sensitive than ion chromatography and can capture a broader range of elements in variable oxidation 

states. However it is strictly a surface sensitive technique, with penetration/probe depths in carbonaceous 

materials of only a few nanometers. For nanoscale materials such as soot, this outer surface band actually 

access ~20 percent of the particle volume, hence some volumetric portion of the particle is probed. Unlike 

ICP requiring gram quantities for carbon-based materials, XPS can analyze milligram—10 mg quantities, 

with similar accuracy and no sample preparation—certainly not the difficult sample digestion required by 

ICP for carbon. 

XPS identified a suite of elements within the jet engine soots. The high fuel sulfur content led to soots 

with high sulfur contents (Onasch et al. 2009). Lube oil contributed elements such as Ca, Zn, and P by 

additives. Transition metals arose from chemical and/or mechanical wear. Light metals such as Al or Mg 

are integral to many engine components while Al, Ba, Y, and Zr are elements of bond coats on turbine fan 

blades. Alkali elements, particularly Na are the counter ion to organic salts within fuels. The presence and 

concentration of any particular element appears to be very dependent upon the specific engine and 

maintenance. 

XPS also provides complimentary information regarding carbon bonding and surface chemistry. A 

near-surface sensitive measure of these characteristics is well suited for gauging environmental 

consequences of carbonaceous PM. Most combustion-generated soot possesses surface oxygen groups. 

Mainly in the form of –OH, hydroxyl groups, being the most stable thermodynamically, they are 

considered to arise by exposure to hot oxidizing gases such as H2O and primarily O2. Variable in 

percentage, the combined content relative to (unoxidized) carbon can extend to 20 percent, or more. It is 
NASA/CR—2014-218293 8 

plausible that the extended time within the hot combustion exhaust leads to such concentrations before 

collection. 

Of particular interest is the sp2

/sp3 carbon bonding content, revealing that the soot is has significant 

organic content. Comparison to HRTEM images revealed no coating nor liquid-like droplets, suggesting 

that the organic content is matrix distributed. To note is that there does not appear to be a uniform trend in 

the sp2

/sp3 with engine power. This may be understood or at least rationalized by the origin of the soot 

being from fuel-rich regions, or pockets where mixing is incomplete before combustion ceases or is 

quenched. How such regions vary across engines and with power level is unknown, but is likely different. 

Of value is that XPS can provide such measurements on microgram quantities of PM. 

In summary, soot from jet engines operating at low and high power levels appears to be hydrophilic, 

acts to concentrate sulfur and nitrogen oxides, and may contain varied percentages of elements associated 

with lube oil—namely the metals from the organo-metallic additives. The impact to air quality 

surrounding airports can be assessed based on measured emission indices and jet operations, motivated by 

its chemically active nature as identified here. 

Abbreviations 

NASA National Aeronautics and Space Administration 

TEM transmission electron microscopy 

XPS X-ray photoelectron spectroscopy 

References 

Boehm H.P. (1994). Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 

32:759-769. 

Booser, E. R. (1988). CRC handbook of lubrication, General Electric, U.S. 

Braun, A., Huggins, F. E., Kubatova, A., Wirick, S., Maricq, M. M., Mun, B. S., McDonald, J. D., Kelly, 

K. E., Shah, N., Huffman, G. P. (2008). Toward distinguishing woodsmoke and diesel exhaust in 

ambient particulate matter. Environ. Sci. Technol. 42:374-380. 

Cain, J. P., Gassman, P. L., Wang, H., Laskin, A. (2010). Micro-FTIR study of soot chemical 

composition – evidence of aliphatic hydrocarbons on nascent soot surfaces. Phys. Chem. Chem. Phys. 

12:5206-5218. 

Choi, W., Leu, M-T. (1998). Nitric acid uptake and decomposition on black carbon (soot) surfaces: Its 

implications for the upper troposphere and lower stratosphere. J. Phys. Chem. A 102:7618-7630. 

Clarke, D. R., Phillpot, S. R. (2005). Thermal barrier coating materials. Mater. Today 8:22-29. 

Countless, R. J., Wolff, G. T., Cadle, S. H. (1980). The Denver winter aerosol: A comprehensive 

chemical characterization. JAPCA. 30:1194-1200. 

Denis J., Briant J., Hipeaux J-C. (2000). Lubricant properties analysis and testing; Editions Technip 

(Industrial Lubrication and Tribology): Paris. Vol. 52. 

Gilham, R. J. J., Spencer, S. J., Buterfield, D., Seah, M. P., Quincey, P. G. (2008). On the applicability of 

XPS for quantitative total organic and elemental carbon analysis of airborne particulate matter. Atmos. 

Environ. 42:3888-3891. 

Gysel, M., Nyeki, S., Weingartner, E., Baltensperger, U., Giebl, H., Hitzenberger, R., Petzold, A., 

Wilson, C. W. (2003). Properties of jet engine combustion particles during the PartEmis experiment. 

Hygroscopicity at subsaturated conditions. Geophys. Res. Lett. 30:1566-1569. 

Jeguirim, M., Tschamber, V., Brilhac, J. F., Ehrburger, P. (2005). Oxidation mechanism of carbon black 

by NO2: Effect of water vapour. Fuel 84:1949-1956. 

Karcher B. (1998). On the potential importance of sulfur-induced activation of soot particles in nascent jet 

aircraft exhaust plumes. Atmos. Res. 46:293-305. 
NASA/CR—2014-218293 9 

Kashiki M., Oshima S. (1971). Determination of calcium, barium and zinc in lubricating oils by atomic 

absorption spectrometry. Anal. Chim. Acta. 55:436-438. 

Kennedy, I. M. (2007). The health effects of combustion generated aerosol. Proc. Combust. Inst. 31:2757-

2770. 

Kinsey, J. S., Hays, M. D. (2011). Chemical characterization of the fine particle emissions from 

commercial aircraft engines during the aircraft particle emissions experiment (APEX) 1 to 3. Environ. 

Sci. Technol. 45:3415-3421. 

Lascovich, J. C., Giorgi, R., Scaglione, S. (1991). Evaluation of the sp2/sp3 ratio in amorphous carbon 

structure by XPS and XANES. Appl. Surf. Sci. 47:17-21. 

Matuschek, G., Karg, E., Schroppel, A., Schulz, H., Schmid, O. (2007). Chemical investigation of eight 

different types of carbonaceous particles using thermoanalytical techniques. Environ. Sci. Technol. 

41:8406-8411. 

NIST X-ray Photoelectron Spectroscopy Database; http://srdata.nist.gov/xps/. 

Okpalugo, T. I. T., Papkonstantinou, P., Murphy, H., McLaughlin, J., Brown, N. M. D. (2005). High 

resolution XPS characterization of chemical functionalized MWNTs and SWNTs. Carbon 43:153-161. 

Onasch, T. B., Jayne, J. T., Herndon, S., Worsnop, D. R., Miake-Lye, R. C., Mortimer, I. P., Anderson, B. 

E. (2009). Chemical properties of aircraft engine particulate exhaust emissions. J. Propul. Power 

25:1121-1137. 

Pope, C. A., Burnett, R. T., Thun, M.J., Calle, E. E., Krewski, D., Ito, K., Thurston, G. D. (2002). Lung 

cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution; JAMA. 

287:1132-1141. 

Prince, A. P., Wade, J. L., Grassian V. H., Kleiber P. D., Young M. A. (2002). Heterogeneous reactions 

of soot aerosols with nitrogen dioxide and nitric acid: atmospheric chamber and Knudsen cell studies. 

Atmos. Environ. 36:5729-5740. 

Russell, L. M., Maria, S. F., Myneni, S. C. B. (2002). Mapping organic coatings on atmospheric particles. 

Geophys. Res. Lett. 29:26-1-26-4. 

Seisel, S., Pashkova, A., Lian, Y., Zellner, R. (2005). Water uptake on mineral dust and soot: A 

fundamental view of the hydrophilicity of atmospheric particles? Faraday Discuss. 130:437-451. 

Stover, D., Funke, C. (1999). Directions of the development of thermal barrier coatings in energy 

applications. J. Mater. Process. Technol. 92-93:195-202. 

Timko, M. T., Onasch, T. B., Northway, M. J., Jayne, J. T., Canagaratna, M. R., Herndon, S. C., Wood, 

E. C., Miake-Lye, R. C., Knighton, W. B. (2010). Gas turbine engine emissions-Part II: Chemical 

properties of particulate matter. J. Eng. Gas Turbine Power 132:061505-14. 

Titantah, J. T., Lamoen, D. (2005). sp3/sp2 characterization of carbon materials from first-principles 

calculations: X-ray photoelectron versus high energy electron energy-loss spectroscopy techniques. 

Carbon 43:1311-1316. 

Van Ben, R., Jarligo, M. O., Steinke, T., Mack, D. E., Stover, D. (2010). Overview on advanced thermal 

barrier coatings. Surf. Coat. Technol. 205:938-942. 

Wey, C. C., Anderson, B. E., Hudgins, C., Wey, C., Li-Jones, X., Winstead, E., Thornhill, L. K., Lobo, 

P., Hagen, D., Whitefield, P., Yelvington, P. E., Herndon, S. C., Onasch, T. B., Miake-Lye, R. C., 

Wormhoudt, J., Knighton, W. B., Howard, R., Bryant, D. (2006). Aircraft particle emissions experiment 

(APEX), NASA TM-2006-214382. 

Wuebbles, D., Gupta, M., Ko, M. (2007). Evaluating the impacts of aviation on climate change. Trans. 

Am. Geophys. Union 88:157-168. 

Yu, Z., Herndon, S. C., Ziemba, L. D., Timko, M. T., Liscinsky, D. S., Anderson, B. E., Miake-Lye, R. C. 

(2012). Identification of lubrication oil in the particulate matter emissions from engine exhaust of inservice commercial. Environ. Sci. Technol. 46:9630-9637. 

Yu, Z., Liscinsky, D. S., Winstead, E. L., True, B. S., Timko, M. T., Bhargava, A., Herndon, S. C., 

Miake-Lye, R. C., Anderson, B. E. (2010). Characterization of lubrication oil emissions from aircraft 

engines. Environ. Sci. Technol. 44:9530-9534.