Aircraft Engine Speciated Organic Gases: 

Speciation of Unburned Organic Gases 

in Aircraft Exhaust 
Aircraft Engine Speciated Organic Gases: 


Speciation of Unburned Organic Gases 


in Aircraft Exhaust


Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

and


AEE-300 - Emissions Division


Office of Environment and Energy


Federal Aviation Administration


EPA-420-R-09-902 

May 2009 
1 Aircraft Engine Speciated Organic Gases: 

2 Speciation of Unburned Organic Gases in Aircraft Exhaust 

3 

4 W.B. Knighton, S.C. Herndon, and R.C. Miake-Lye 

5 

6 

7 Purpose and Scope: The FAA and EPA are evaluating the methodology to quantify 

8 Hazardous Air Pollutants (HAPs) emissions from commercial aircraft engines, to be used 

9 when an aircraft HAPs emissions inventory is requested. Central to the methodology is a 

10 singular HAPs speciation profile. The final HAPs speciation profile will be: 

11 

12 − Nationally consistent, 

13 − Supported by state-of-the-science data, 

14 − Representative of today’s commercial aircraft fleet, and 

15 − “Living” to continue to reflect the state-of-the-science as studies are 

16 conducted and new data becomes available. 

17 

18 A second outcome of this effort is to evaluate and, if necessary, update the factors needed 

19 to convert between total unburned hydrocarbons (HC), volatile organic compounds 

20 (VOC), and total organic gases (TOG). 

21 

22 The scope of this work is to update the current HAPs profile that exists for commercial 

23 aircraft engines, using recent HAPs measurements conducted on more modern 

24 commercial aircraft engines. The original HAPs profile has been in existence unchanged 

25 for over 2 decades, based upon a single 1984 measurement campaign by Spicer et al.

1

 To 

26 support the update of the existing HAPs profile, consolidated data from Spicer and more 

27 recent measurements (EXCAVATE, APEX) will be investigated and discussed in this 

28 document. Important questions to address in this scope of work are: how to combine all 

29 of the data sets into a single profile given the various methods used to collect the 

30 samples; and how to address combustor technologies, etc. not yet tested. We still have 

31 very limited data to work with at this time, which limits the conclusions we can make, so 

32 it is necessary to be mindful of these questions as new HAPs data becomes available in 

33 the future and we endeavor to update this methodology. 

34 

35 Introduction: Aircraft gas turbine engines are designed to burn their hydrocarbon (HC) 

36 fuel efficiently, since any inefficiency translates into carrying more fuel, a greater take37 off weight, and a steeply rising cost of operation as efficiency decreases. Because most 

38 of the fuel is consumed at higher power settings and most of the operational time is spent 

39 at cruise, for power settings of cruise and above most engines convert significantly more 

1

 HAPs profile No. 1098 in EPA’s SPECIATE database. http://www.epa.gov/ttn/chief/software/speciate/index.html 

Composite profile developed from data for a CFM-56 jet engine fired with JP-5 fuel at idle, 30% thrust and 

80% thrust. Data collected by GC/MS and DNPH analyses were combined according to average LTO 

cycle times obtained from AP-42. Spicer, C. W., et al., Battelle Columbus Laboratories, Composition and 

Photochemical Reactivity of Turbine Engine Exhaust, Report No. ESL-TR-84-28, Prepared for Air Force 

Engineering and Services Center (RDVS), Tyndall AFB, FL, September 1984. 
Technical Support Document 

1 than 99% of the fuel through complete combustion to carbon dioxide (CO2) and water 

2 (H2O). At idle conditions, much less fuel is consumed and, in the interest of maintaining 

3 stable combustion at lower power conditions, some sacrifice in combustion efficiency 

4 occurs even though this inefficiency is still only a percent or so. Any combustion 

5 inefficiency of HC fuel will result in emissions of some combination of CO and 

6 incompletely oxidized HCs, as well as some carbonaceous particles. 

7 

8 From the point of view of understanding the combustion process, knowing the 

9 combustion efficiency is important since any HC emission represents an inefficiency in 

10 converting fuel to CO2 and H2O. In order to understand the environmental impact of the 

11 emissions, it is important to quantify the amounts of the emitted species, especially those 

12 that are deemed highly toxic or carcinogenic. The US EPA considers a number of HCs 

13 (among other pollutants) as HAPs, and quantification of levels of these species takes on a 

14 special importance. This report will discuss the emissions of HAPs from aircraft engines 

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and how the speciation of the HC emissions relates to levels of the various HAPs present 

in aircraft exhaust.

2

 Since the concentrations of HCs and HAPs are highest in the exhaust 

17 at low power conditions, the emphasis will be on measurements under such conditions. 

18 

19 Components of PM emissions from aviation engines may also be classified as Hazardous 

20 Air Pollutants, but PM emissions are measured and analyzed very differently than 

21 gaseous emissions, and are not discussed in this document. Much work is currently being 

22 directed at identifying measurement approaches and resolving sampling issues for 

23 aviation gas turbine engine PM emissions (e.g. the APEX and related campaigns), and 

24 data characterizing PM emissions from a variety of commercial aircraft gas turbine 

25 engines is being accumulated. 

26 

27 Background: Several studies have attempted to document the speciation of the HCs 

28 emitted from aircraft engines. Most notably, in the 1980s Spicer et al. (Spicer, Holdren et 

29 al. 1994) performed a series of studies on a set of military engines using a variety of 

30 analytical techniques to quantify a wide range of HCs. Subsequently Gerstle et al. 

31 (Gerstle, Virag et al. 1999) examined another set of military aircraft, with a similar set of 

32 analytical techniques. Most recently, a set of studies initiated by NASA called Aircraft 

33 Particle Emissions eXperiment (APEX), and supported by a wide range of sponsors 

34 (NASA, FAA, CARB, EPA, DoD ...) has focused attention on commercial aircraft 

35 Particulate Matter (PM) emissions (Wey 2004; Onasch, Jayne et al. 2006; Wey, 

36 Anderson et al. 2006; Lobo, Hagen et al. 2007), using a wide range of analytical 

37 techniques. These studies also included HC gaseous emissions analysis. Some of the 

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techniques employed in APEX1-3 overlap with the earlier tests, but also some more 

advanced (faster time response/higher sensitivity) techniques were used during APEX.

3 

2

 It should be noted that because a compound is considered hazardous it does not imply health or welfare 

effects at current levels, or that it is appropriate to adopt controls to limit the emissions of such a compound 

from turbine engine aircraft or their fuels. 3

 APEX was the collaborative research effort of NASA, EPA, DoD, and the FAA. The main objective of 

the APEX research was to characterize both gaseous and particulate emissions to advance the 

understanding of emissions from commercial aircraft engines. APEX1 was conducted in April of 2004 with 

a NASA-owned DC-8 aircraft equipped with CFM-56-2C1 engines. APEX2 was conducted in August 

2005 for typical in-use aircraft engines (CFM56 engines on B737 aircraft), APEX3 testing was conducted 

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1 The range of experiments and the variety of techniques employed can be used to provide 

2 greater confidence in the HAPs emissions measurement data, and to allow assessment of 

3 which results can be verified by multiple techniques. In addition, one engine type, a 

4 CFM56 (a high bypass turbofan engine), was part of both the Spicer and APEX studies, 

5 so that a most direct cross comparison can be made.

4 

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7 The comprehensive measurements of Spicer et al. (Spicer, Holdren et al. 1994) have 

8 provided valuable data for the CFM56-3 and the TF-39 (forerunner to the General 

9 Electric CF6 class of high bypass turbofan engines).

5

 These measurements were 

10 conducted using a mixture of on-line instrumentation and canister sampling with off-line 

11 analysis developed from a prolific program of military engine emissions characterization. 

12 This work chose to report values as ppmC present in the exhaust. The data labeled ‘idle’ 

13 in this work was conducted at nominal ‘ground idle’ and does not reflect the ICAO 

14 definition of idle, also called 7% of rated thrust. The Spicer et al. work finds that 40% of 

15 the organic gas mass is accounted for by the compounds, ethene, formaldehyde, propene, 

16 ethyne and methane. 

17 

18 In a report to the US Air Force, Gerstle and co-workers (Gerstle, Virag et al. 1999) 

19 reported HC emission rates for several engines not included in the ICAO databank, as 

20 well as some emissions from auxiliary power units. Some of the military engines 

21 addressed in this study represent older engine technologies that are no longer represented 

22 in the commercial fleet and, as such, there may be issues regarding combustion 

23 efficiencies at low power conditions that may cause significant differences in emissions 

24 due to raw fuel contributions to the HCs emissions at low power (personal 

25 communication Will Dodds, GE, and KBE, February 2007 et seq.). 

26 

27 A more recent series of measurements have focused on commercial engines. NASA’s 

28 interest in charactering the emissions from commercial engines in dedicated engine tests 

29 was demonstrated during the EXCAVATE campaign. Anderson et al. (Anderson, Chen 

30 et al. 2006) measured the speciated organic gas emissions from a Rolls-Royce RB211­

31 535-E4 engine (another high bypass turbofan engine) for two different fuel sulfur levels. 

32 A very comprehensive program continued with the APEX-1 campaign (Wey, Anderson 

33 et al. 2006) within which HAPs characterization was conducted with high time response 

34 on-line organic gas speciation using infrared fingerprint absorption spectroscopy and 

35 chemical ionization mass spectrometry for a CFM56-2C1 (Knighton, Rogers et al. 2007; 

in October and November of 2005 spanning a range of engines from a small business jet, through a modern 

regional turbofan, a single-aisle transport turbofan, to a large high bypass ratio turbo fan, representing five 

different engine types, some measuring more than one example. In all studies, exhaust plumes were 

sampled at the engine exit plane and several downstream measurement locations. 4

 CFM56 and the CFM logo are for CFM International, which is a joint company of Snecma and General 

Electric. Snecma is a French manufacturer of engines for commercial and military aircraft, and space 

vehicles. 5

 The General Electric TF-39 was the first high bypass turbofan engine, and it was developed for the Air 

Force back in 1965 for a new transport aircraft. Turbofan engines with a bypass ratio of 5 or greater are 

considered to be high bypass turbofan engines (Cumpsty, N., Jet Propulsion, Cambridge University Press, 

2002, p. 46.). Bypass ratio is the ratio between the mass flow rate of the air drawn in by the fan, but 

bypassing the engine core, to the mass flow rate passing through the engine core (Cumpsty, loc. cit.). 

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1 Yelvington, Herndon et al. 2007). Time integrated LTO cycle data were also collected at 

2 

3 

the same time (Kinsey et al, document in preparation). An analysis of the JETS/APEX-2 

(Lobo et al., 2007)6 and APEX-3 datasets is forthcoming (Timko et al., in preparation). 

4 

5 In all of the APEX dedicated engine tests, measurements were made at both the engine 

6 exit plane and in the plume at a downstream location (nominally 30 m for an intermediate 

7 engine size such as a CFM56). It is important to note that the measured HC profile is 

8 relatively consistent regardless of measurement location. In the ensembles of data 

9 presented below, all of the various distances, fuels, and power conditions below 30% of 

10 rated thrust are combined in demonstrating the tight correlations among HC emissions. 

11 Further, in the airport studies discussed next, much further downwind measurements also 

12 indicated no change in the relative concentrations of species, although as the exhaust 

13 continues to dilute, the species present as very small fractions of the total profile begin to 

14 fall below detection limits as distances increase further from the emission source. 

15 

16 In addition to dedicated engine tests, sampling from airports during routing operation 

17 have also provided useful data for HAPs emissions. Using analysis of wind-advected 

18 plumes sampled at Boston Logan International Airport, selected speciated organic gas 

19 emissions were characterized from in-use aircraft (Herndon, Rogers et al. 2006). 

20 Schürmann et al. (Schürmann, Schäfer et al. 2007) also measured volatile organic 

21 compounds using canister sampling of diluted exhaust in an operational taxiway area. 

22 They found that refueling activity altered the profile of hydrocarbons considerably. An 

23 analysis of the wind advected data collected at the Oakland GRE and taxiway/runway 

24 sampling is forthcoming (Herndon et al., in preparation). 

25 

26 All of the studies indicate that a wide range of combustion-related emissions are present 

27 in aircraft exhaust. Despite the long list of species present, a ranking of the species by 

28 concentration indicates that 15-20 species represent most (95% or more) of the emissions 

29 on the basis of concentration. A greater number of species are present at a fraction of a 

30 percent or smaller of the total concentration. Of the overall speciated mixture, a number 

31 of species can be considered HAPs, while another set may be significant to the overall 

32 level of VOC emissions but data indicating toxicity are lacking. 

33 

34 An important point to note is that no instrument measures all of the HC emissions. The 

35 fast time response instrument (Proton Transfer Reaction Mass Spectrometer: PTR-MS) 

36 used for HC measurements in APEX was focused on measuring relevant HAPs, and as 

37 such was not capable of measuring alkanes or acetylene. Since the PTR-MS is capable of 

38 measuring a wide range of HCs other than alkanes and acetylene, the measurement focus 

39 was on a list of species that were measurable by the PTR-MS, identified EPA HAPs 

40 species, and present in aircraft exhaust. Formaldehyde and ethylene were also not 

41 measurable with the PTR-MS, but were measured separately in APEX using IR 

42 techniques (Tunable Infrared Laser Absorption Spectroscopy: TILDAS). In the Spicer 

6

 Additional data reported from JETS/APEX2, taken by the UC Riverside team, was not used to develop 

the jet aircraft speciation profile, because the compromised sampling system for that data source prevented 

a complete and high-confidence organic compound data set from being assembled from the UC Riverside 

data. 

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studies, a wide range of techniques was used, but no measurement of methanol was 

attempted, and none of the trimethylbenzenes nor several of C9-C11 aromatic species 

were identified with the techniques employed therein. In many of the studies, a Flame 

Ionization Detector (FID) was used to quantify the total “unburned hydrocarbons” 

(UHCs), but this is an imperfect estimation of the total emissions due to the FID’s nonuniform response to different carbon-containing compounds. All this is to note that, 

while these several data sets provide very useful data on many individual compounds and 

their relationship to one another, arriving at an estimate of a total quantity by mass or by 

concentration is dependent on which species are included in the total. And, the measured 

species are determined by what measurement techniques have been employed. 

Data Comparison: The most direct intercomparison between the earlier studies and the 

recent APEX mission is accomplished through the overlap with the CFM56 engine. 

Table 1 reproduces Spicer’s speciation data for this engine (Spicer, Holdren et al. 1994) 

ranked in order of decreasing concentration. The first column lists the species present in 

the highest concentration, which represent about 95% of the total speciated non methane 

hydrocarbon (NMHC) emissions on a concentration basis as measured by Spicer. The 

highlighted species indicate those species measured by Spicer that were also quantified in 

APEX by PTR-MS (yellow) or TILDAS (green). In the first column, only acetylene and 

ethane are not highlighted. In subsequent columns, the sum of which represents 5% of 

the Spicer emissions concentration, a number of other alkanes also are not highlighted. 

These species, not measured by PTR-MS or TILDAS, represent about 1.4% of Spicer’s 

total, and are not typically considered HAPs. It is worth noting that, of the species noted 

in the “EPA 14” and “FAA 10” HAPs lists that were developed based on relevant HC 

emissions from aviation engines (URS and FAA 2003), all of those species are in the 

highlighted (measured in both studies) elements of Table 1. 

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1 Table 1. NMHC emission ratios for the CFM56-3 engine reported by Spicer et al. listed 

2 in decreasing magnitude. The first column represents 95% of the emissions on a molar 

3 basis. Green highlighted cells indicate compounds that are measured by TILDAS. Yellow 

4 highlighted cells indicate compounds that are quantified by the PTR-MS. 

Compound ER 

(mmole/mole) Compound ER (mmole/mole) Compound ER (mmole/mole) 

ethylene 0.77 acetone 0.0089 1-nonene 0.0027 

formaldehyde 0.572 C5-ene 0.0072 propane 0.0025 

acetylene 0.211 2-methylpentane 0.0066 1-CH3-naphthalene 0.0024 

propene 0.151 benzaldehyde 0.0062 hexanal 0.0023 

acetaldehyde 0.135 1-heptene 0.0061 C5-cyclohexane 0.0023 

acrolein 0.061 naphthalene 0.0059 ethylbenzene 0.0023 

1-butene 0.044 C5-ene 0.0055 C4-benzene 0.0023 

glyoxal 0.044 cis-2-butene 0.0052 o-xylene 0.0022 

1,3-butadiene 0.044 styrene 0.0041 2-CH3-naphthalene 0.0020 

benzene 0.03 n-undecane 0.0040 C5-benzene 0.0020 

methylglyoxal 0.029 n-pentane 0.0038 1-decene 0.0018 

ethane 0.024 n-dodecane 0.0038 C13-alkane 0.0014 

butanal/crotona 

ldehyde 0.019 m,p-xylene 0.0037 C14-alkane 0.0013 

propanal 0.017 2-methyl-2-butene 0.0037 n-heptane 0.0009 

1-pentene 0.015 1-octene 0.0034 n-octane 0.0008 

1-hexene 0.012 n-decane 0.0031 n-nonane 0.0007 

toluene 0.0097 phenol 0.0029 C12-C18 alkanes 0.0045 

6 

7 The highlighted sections in Table 1 indicate that comparisons can be made for the 

8 measurements of those species measured for Spicer’s CFM56 and the several CFM56 

9 engines measured in APEX. Those comparisons are listed in Table 2 as mass ratios, 

10 expressed as ratios of Emission Indices (EIs). The EI of a species is the mass of that 

11 species emitted in grams, divided by the mass of fuel consumed in kilograms (species 

12 g/kg fuel). The unhighlighted elements in Table 1 indicate that the APEX PTR

13 MS/TILDAS data set is missing those elements and no direct comparison can be made 

14 and are thus not included as rows in Table 2. The unhighlighted elements in Table 1 

15 represent approximately 12% of the concentration in Spicer’s list. 

16 

17 

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1 Table 2. Compound EIs normalized to formaldehyde (EIx/EIHCHO) for low engine powers 

2 (4-15% rated thrust) evaluated as the slopes of plots of EI(x) vs EI(HCHO) 

Compound APEX 1 

EIx/EIHCHO 

APEX 2 

EIx/EIHCHO 

APEX 3 

EIx/EIHCHO 

Spicer et al. 

EIx/EIHCHO 

Methanol 0.18 0.14 0.12 --

Propene 0.36 0.39 0.38 0.37 

Acetaldehyde 0.32 0.36 0.36 0.35 

Butene + Acrolein 0.30 0.45 0.48 0.36 

Acetone + Propanal + 

Glyoxal 0.18 0.16 0.20 0.24 

Benzene 0.15 0.17 0.16 0.14 

Toluene 0.056 0.082 0.073 0.052 

mass 107 0.088 0.138 0.103 0.089 

mass 121 0.074 0.119 0.085 --

mass 135 0.035 0.074 0.051 --

mass 149 0.014 0.038 0.027 --

Naphthalene 0.018 0.034 0.020 0.044 

Methylnaphthalenes 0.009 0.023 0.016 0.037 

Dimethylnaphthalenes 0.0026 0.011 0.0083 --

Phenol 0.063 0.064 0.050 0.016 

Styrene 0.020 0.035 0.023 0.025 

Acetic acid 0.16 0.057 0.084 --

3 propene – quantified assuming that 68% all of the ion intensity measured at m/z43 originated originates
 

4 from propene.
 

5 butene + acrolein – quantified assuming the m/z 57 signal is distributed as reported by Spicer et al. 45%
 

6 butenes and 55% acrolein.
 

7 acetone + propanal + gyloxal – quantified assuming the m/z 59 signal is distributed as reported by Spicer
 

8 et al. 12% acetone, 25% propanal and 63% glyoxal.
 

9 Mass 107 – quantified as p-xylene and represents the sum of o,m,p-xylene, ethyl benzene & benzaldehyde
 

10 Mass 121 – quantified as 1,2,4-trimethylbenzene and represents the sum of C9H12 and C8H8O 
 

11 Mass 135 – quantified using a single rate constant and represents the sum of C10H14 and C9H10O 
 

12 Mass 149 – quantified using a single rate constant and represents the sum of C11H16 and C10H12O 
 

13 

14 However, as is noted by the first row of Table 2, Spicer did not measure methanol, which 

15 is approximately 5% of Spicer’s total concentration, which would increase the HC total 

16 by that amount. There are also several other aromatic species listed in Table 2, which 

17 were not identified in the Spicer analysis. While these compounds would fall into the 

18 second two columns of Table 1 if they were included, and thus represent only a percent 

19 or so of the total concentration profile, they do represent a significant number of aromatic 

20 compounds. These several differences in the lists of species measured in these 

21 measurement studies highlight the uncertainty in working with any “total” emissions 

22 level: the “total” is only a sum of whatever species are included in the “total”. 

23 

24 A longer list of species measured in the APEX campaigns but not measured by Spicer is 

25 included in the accompanying spreadsheet. In that spreadsheet, the additional species are 

26 color coded by blue (from PTR-MS) and yellow (from EPA’s set of integrating 

27 measurements, Kinsey et al, manuscript in preparation). 

28 

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This spreadsheet also provides a normalized emission profile. This profile was 

developed based on Spicer’s original speciation and carbon balance. Adjustments and 

additions were made, based on the new data available (all APEX1-3 data discussed in this 

report), but the measured species continue to make use of the original carbon balance. 

Thus, because of the longer list of species now quantified, these refinements to the 

speciation profile result in a decrease of the unidentified emitted mass from about 35% in 

the original Spicer work (34% if methane were included, but as discussed below, Spicer 

has shown elsewhere that the methane measurement was due to background methane and 

should not be included in the sum) to about 29% due to the additionally identified species 

and refinements to phenol and butyraldehyde/crotonaldehyde. Separate analysis of the 

total HC emissions by independent measurements during the APEX1-3 campaigns (J. 

Kinsey, personal communication) used time-integrated sampling over a range of power 

conditions. Because that approach is distinguished from the single power points 

measured by Spicer and the data presented here, precise agreement would not be 

expected due to different dependence on background levels and related data analysis 

issues. However, despite these potential differences, similar ratios of the sum of 

identified to the total HC mass were calculated using the time integrated measurements in 

APEX1-3 as compared to those of this revised profile, giving increased confidence in the 

overall HC mass balance presented with these data. 

While the unidentified species mass has been reduced through this process, the 

composition of that unidentified mass remains an uncertainty. In the original Spicer 

profile, which used gas chromatography and various HC capture techniques, the 

unidentified mass could possibly include contributions from some of the species that 

were specifically identified. In other words, based on the original Spicer work, one could 

argue that some of the identified species may have been present in larger amounts than 

were reported because they may have also been contributing to the unidentified mass. 

That would be a result of some mass “sticking” to a GC column or a HC capture medium. 

The new additional data reduces that uncertainty considerably, since independent realtime data were collected which largely corroborated the Spicer profile. The combination 

of the original and new data provide good evidence that the identified species contribute 

to the profile at the levels measured and have little or no contribution to the unidentified 

HC mass fraction. 

Table 2 compares the concentration of the particular species of interest to that of 

formaldehyde, which is one of the most prevalent emissions and serves as a useful 

reference species. This is done, rather than directly compare concentrations, since the 

combustion efficiency is highly dependent on precise fuel flow and power settings at low 

engine powers, with ambient temperature also having a significant impact on emission 

levels (Yelvington, et al.). Since engine operating point, ambient temperature, and 

related details are all slightly different from test to test, the combustion efficiency is also 

likely to vary from data set to data set. However, the relationship of the various 

emissions to each other is quite constant even though their levels may go up and down 

together. 

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Figure 1 shows that this is true not only for the CFM56 measured in APEX1 and 

discussed by Yelvington et al. but it is also true for the several CFM56 engines measured 

in JETS/APEX2 and, indeed, is equally true for the wider range of different commercial 

engine types measured in APEX3. In fact, not only is it true that the speciation is 

invariant as a specific engine varies power and combustion efficiency, but for the range 

of commercial engines measured in APEX1-3 and the range of standard jet fuels used 

through those tests, the relationship between the various HC emissions, (i.e. the 

speciation profile shown here as individual species plotted versus formaldehyde, HCHO), 

is also invariant across these different commercial engine types: all of the curves lie 

essentially on top of one another. The invariance of the speciation profile across power 

settings, ambient temperature, and engine types for commercial engines is very useful 

for interpreting HAPs emissions from commercial engines. 

The range of fuels used in the diverse set of tests presented in Figure 1 suggests that fuel 

also has a minimal impact on the speciation profile. Fuel sulfur and aromatic content 

spanned a range of values across these tests, particularly when the APEX1 fuel sulfur 

additions are included. However dramatic changes in the hydrocarbon composition of 

the fuel, as might be encountered using alternative fuels like Fischer-Tropsch or bio

fuels, have not been explored in the set of data presented here. 

The correlation of each of the individual species versus formaldehyde plotted in Figure 1 

show that, for the three APEX campaigns, there are very tight correlations for the several 

species plotted. Species present in greater concentration (propene and acetaldehyde) 

have a tighter correlation than species at lower concentrations (benzene and, especially, 

naphthalene, which is a PAH and may begin condensing on PM emissions soon after 

leaving the engine, which might affect its gas phase concentration). 

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Figure 1. Correlation scatter plots of selected HC vs. HCHO emission indices measured 

on the 1-meter probe under low power, 4-15% rated thrust. 

Table 2 provides the comparison between the speciation profile measured by Spicer and 

that from PTR-MS/TILDAS from APEX. The three data columns from APEX cover the 

CFM56-2C1 measured in APEX1, the several CFM56-3 and -7 engines measured in 

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APEX2, and an average over the set of engines (excluding the AE3007 for this analysis) 

measured in APEX3. For many species, especially those at larger concentration ratios, 

the variation among the various tests is no greater than the variation between APEX and 

Spicer. The speciation for these species appears to be very robust. Some of the more 

minor species show more significant variation, which may be partly due to measurement 

uncertainty and may be partly due to sensitivity to other variables such as minor fuel 

composition variations and so forth. It is worth noting that many of these smaller 

contributors represent less than 1% of the speciated concentration mixture. 

One species of particular note is phenol. The APEX series of measurements indicate a 

concentration ratio three times higher than that of Spicer. That is the largest 

disagreement in Table 2 (excluding cases where a Spicer measurement is not available), 

and deserves further comment. While phenol represents only about 0.1% of the 

speciation concentration profile, it does represent a test of the ability to measure a minor 

species accurately. While further analysis might be warranted, phenol was measured by 

Spicer using canister capture to deliver the sample to the gas chromatographic 

measurement system. Given the significant differences indicated for this compound, wall 

losses might be suggested as a possible explanation for this unique discrepancy in the HC 

speciation. 

The overall agreement between the Spicer and the APEX speciation profiles is shown in 

Figure 2. This is a direct comparison of the overall APEX speciation profile to that of 

Spicer for those species where the measurements are available in both studies. Except for 

phenol and the combination of acetone, propanal, and glyoxal (which, unlike phenol, is 

still within 2 sigma), all of the data are within the standard deviation of the measurements 

themselves to the unit line (the unity line represents perfect agreement). 

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0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0 0.2 0.4 0.6 

Spicer et al. 

EI(x)/EI(HCHO) 

propene 

acetaldehyde 

butene + acrolein 

acetone+propanal+glyoxal 

benzene 

toluene 

mass 107 

naphthalene 

methylnaphthalenes 

phenol 

styrene 

unit line 

1 

2 Figure 2. Correlation plot of normalized compound EIs derived from the APEX 

3 experiments versus that reported by Spicer et al. APEX data is derived from the slopes of 

4 the plots of EI(x) versus EI(HCHO) for data obtained at low power 4% - 15% rated 

5 thrust on the 1-meter probe. Error bars reflect the standard deviation of the three 

6 measurements. 

7 

8 The comparison of the various PTR-MS/TILDAS measurements across different engines 

9 in APEX3 provides strong support that the speciation profile is invariant across engine 

10 technologies for commercial engines. A similar question could be posed for the various 

11 military engines measured by Spicer and Gerstle. Initial analysis (data not shown here: 

12 KBE) indicates that there is much agreement between some of the relative amounts of 

13 relevant HAPs. Detailed analysis of the TF39 (a forerunner to the GE CF-6 engine) 

14 measured by Spicer is shown in Figure 3 comparing the speciation profiles for the TF39 

15 with that of the CFM56 measured by Spicer, in analogy to what was shown in Figure 2 

16 between the many engines of APEX1-3 and the Spicer CFM56-3. The speciation profiles 

17 for these two engines measured by Spicer, which received the careful analysis required 

18 for archival publication (Spicer et al. 1994), also support the contention that the 

19 speciation profile from aviation gas turbine engines is invariant across engine types. 

20 

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y = 1.3892x 

R2

 = 0.9457 

0.001 

0.010 

0.100 

1.000 

10.000 

0.001 0.010 0.100 1.000 10.000 

CFM-56 

EI(x)/EI(HCHO) 

All data 

oxygenates 

alkanes 

1 

2 Figure 3. Correlation plot of normalized compound EIs for the TF39 vs. CFM56 engines 

3 at ground idle derived from the measurements reported by Spicer et al. 

4 

5 Discussion: The emissions of organic gases are controlled by combustion efficiency. 

6 The ICAO datasheets show a very clear trend of decreasing UHC emission indices from 

7 idle and approach to climb-out and take-off. There are strong dependences of the 

8 magnitude of UHC emissions between different engine models in the ICAO databank. 

9 The Yelvington et al. result from APEX-1 (Yelvington, Herndon et al. 2007) shows there 

10 is a strong dependence of the emissions of HCHO on temperature; that emissions 

11 

12 

increase at colder ambient temperatures, particularly for ground idle. This dependence is 

greater than estimated in the Boeing Fuel Flow Method-27

 correction (DuBois and 

13 Paynter 2006). 

14 

15 Despite these strong dependences of the magnitude of UHC emissions on various factors, 

16 a remarkable and simplifying result is that the relative profile of organic gas emissions 

17 near idle does not have any such significant dependence, as presented in Figure 1. This 

18 has been demonstrated for various engines to be valid for conditions from ground idle up 

19 to ~15% of rated thrust. This invariant speciation profile demonstrates that despite large 

20 variations in the total amount of emissions, the ratio of benzene to ethylene, for example, 

21 is a relatively constant value among different conditions and engines. 

22 

7

 The Boeing Fuel Flow Method is a theory-based means of obtaining estimated emissions data at power 

conditions other than the ICAO specified power points by interpolating ICAO certification data. 

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1 One HC emission of particular note is methane (CH4). This compound was measured by 

2 Spicer, but not in more recent studies. While methane is present in the exhaust of aircraft 

3 engines, it is present at levels below ambient levels for most power conditions (Spicer, 

4 Holdren et al. 1992, Wiesen et al, 1994, Vay et al., 1998). Indeed, in that reference 

5 Spicer notes “At power levels above idle, the exhaust is depleted in methane compared 

6 with the incoming air used for combustion. The methane concentrations observed in the 

7 engine exhaust are consistent with partial combustion of the atmospheric methane present 

8 in the inlet air, although some methane production during combustion cannot be ruled 

9 out.” At idle the methane values in the exhaust during the Spicer were consistent with 

10 ambient levels, so any methane production must have been small enough to be within the 

11 experimental uncertainty or was balanced by methane consumption. Methane is not 

12 

13 

considered to be a significant emission from aircraft gas turbine engines burning Jet A, 

and is not included in the profile information provided here.

8 

14 

15 At engine power conditions significantly higher that ~15% rated thrust, the engine 

16 combustion efficiency is so close to 100% that measurement of many HCs becomes 

17 difficult or impossible due to instrument detection levels for diluted exhaust gases (either 

18 with 1 m dilution probes or downwind sampling): the HC concentrations are too small to 

19 measure. Thus, when considering the total emissions contribution from a given aircraft 

20 operation, the amount of HCs is dominated by the low power conditions. Since the total 

21 emissions burden is the product of an emission index (g pollutant/kg fuel) times the fuel 

22 flow rate (kg fuel/sec) times the time in mode for that power condition, even the high fuel 

23 flow rates of take-off and climb-out cannot compensate for the very small emission 

24 indices for HCs and the short times in the take-off and climb-out power conditions. 

25 

26 The dominance of the low power conditions in determining the overall HC emission 

27 loading suggests that any changes to the HAPs profile above 15% power will have 

28 limited impact on the net HAPs loading. Since the emissions levels become too small to 

29 measure for many of the smallest percentage HAPs in the profile, a bound can be placed 

30 on how much their fractional contribution to the HAPs profile might be increasing as 

31 power increases. In lieu of specific data for these very small levels, a default of retaining 

32 the same profile as power increases beyond 15% could be suggested, which would be 

33 used for those powers above which the smallest contributors can be measured. An 

34 analysis of the potential errors introduced in using this default could be performed, 

35 however Figure 4 suggests that the limits of detection of the instruments, in combination 

36 with the rapidly decreasing overall HC emissions, will limit the overall uncertainties in 

37 the overall HC loading when using a low power HAPs profile. 

38 

39 Figure 4 demonstrates the relative importance of the elements of an LTO cycle by 

40 accounting for times in mode and emission indices for UHCs from the ICAO databank 

41 for a CFM56-3C1 engine (two engines for a 737-300). The LTO cycle in the figure 

42 reflects times in mode reported in the Boston Logan Airport 2005 Environmental Data 

8

 When using this speciation profile in concert with reported certification HC emission indices, it is worth 

noting that ICAO CAEP Annex 16 Vol II makes no account for corrections to measured HCs due to 

ambient methane concentrations when reporting FID measurements for certification. Presumably ambient 

methane levels may be included in the certification FID measurements of EI HC unless otherwise noted. 

05/27/09 14
 
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1 Report (Wilkins 2007). Essentially, it is a modestly adjusted set of times but the same 

2 power conditions as a standard ICAO LTO cycle. Whatever the variation in the 

3 speciation profile at the higher powers, the lower EIs at the high powers preclude a 

4 significant impact on the total emissions burden from the complete LTO cycle, at least in 

5 this first attempt to assess the speciated emissions. Variation in the HC speciation profile 

6 at higher powers are unlikely to have a significant impact on airport air-quality modeling 

7 or to risk assessment from the compounds that are HAPs. 

8 

9 

10 

11 Figure 4. Emission Rate vs. Time in Mode. The estimated emission rate, coupling fuel 

12 flow and emission index for UHC for a CFM56-3C1. The LTO profile begins and ends 

13 with a 7.5 minute APU interval. In this figure the apparent area of the ‘boxes’ reflect the 

14 total emissions magnitude for the defined modes. 

15 

16 Relationship of Dedicated Engine Tests to Airport Measurements: Dedicated engine 

17 tests allow control of the engine operation. However emissions at airports are due to 

18 airplanes being operated as required to satisfy airline requirements. Table 3 compares 

19 normalized emission ratios (Species concentration/Formaldehyde concentration) for 

20 several APEX measurements and for advected plumes measured at Boston Logan, 

21 Zurich, and Oakland airports. While greater uncertainties might be expected in the 

22 advected plumes measured in a non-interference basis at airports, there is very good 

23 agreement between the emissions ratios measured in these disparate studies. In the 

24 advected plumes (last column) the error bars represent the width of the distribution of 

25 results. This uncertainty can be taken as an upper limit on the real variability in these 

26 ratios. When the detailed analysis of the instrumental contribution to this noise is 

27 complete, it will likely narrow the range of species variability, as opposed to instrument 

05/27/09 15
 
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1 noise. This is possible because the observed distribution in this sample is nearly
 

2 Gaussian. 
 

3 
 

4 Table 3. Speciated VOC Index Ratio (HCHO relative) 
 

Compound Spicer 

et al. APEX-1 Logan EXC Zurich APEX-2 OAK 

Staged Advected 

HCHO 1 1 1 *

1 1 

Acetaldehyde 0.35 0.24 0.26 0.37 0.31±0.09 

C2H4 1.26 0.78 1* 1* 0.76 0.85±0.3 

Propene 0.36 0.31 0.32 0.32 0.45 0.42±0.2 

Butenes+Acrolein 0.36 0.45 0.25 0.45 0.26& 0.49 

Pentenes 0.11 0.31 0.11 

Benzene 0.14 0.14 0.11 0.08 0.11 0.18 0.15±0.08 

Toluene 0.05 0.06 0.06 0.01 0.13 0.09 

1-ring Aromatics 0.28 0.48 0.3 - 0.39 0.73 

Styrene 0.03 0.03 0.04 0.04 

Naphthalene 0.04 0.01 0.04 

5 Table Notes:
 

6 All values are in units of grams of VOC per gram of HCHO, except for the EXCAVATE
 

7 column, which is grams of VOC per gram of C2H4. 
 

8 *The EXCAVATE and Zurich datasets have been normalized by the emission index for ethene
 

9 in lieu of formaldehyde.
 

10 &The Zurich tabulation for Butenes+Acrolein assumes the ratio of Acrolein to the sum of the 

11 butene isomers is that found in Spicer et al. 

12 The APEX-2, Staged aircraft column represents the average result for ‘ground-idle’ including 

13 the following engines; 3 CFM56-7B22, 1 CFM56-3B1, 2 CFM56-3B2. 

14 Tabulated values in the OAK Advected column represent Gaussian fits to the distribution of 

15 measured compound to HCHO ratios. The error bar is one Gaussian width. 

16 

17 Next Step Recommendations: First, recent work has reinforced the overall speciation for 

18 commercial engine as measured by Spicer for the CFM56-3 engine. Both in comparison 

19 to the TF39 measured by Spicer and the wider range of commercial engines in APEX1-3, 

20 this speciation profile is insensitive to engine type, engine power condition, and ambient 

21 conditions, even though those parameters significantly impact the total amount of UHCs 

22 (or VOCs or total HCs, however one wants to add up a total). Other measurements 

23 (Gerstle and airport advected plume studies) are also consistent with the general 

24 invariance, near idle, of this speciation. 

25 

26 Several modest uncertainties are present, particularly for species that are present in small 

27 quantities. These may be due to measurement uncertainties, or due to actual variations in 

28 emissions numbers themselves. Modest dependences on fuel composition or other 

29 unknown parameters may cause some of this variation. Most of these variations are 

30 within the uncertainties between studies or engines. One notable exception is the 

31 significant variation associated with phenol. The APEX studies all agree with one 

32 another for phenol, while Spicer is significantly lower. Wall losses in the canister 

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sampling done by Spicer are a possible explanation for such a loss, but additional studies 

may be warranted to resolve this discrepancy. 

For future work, two remaining questions should be kept in mind. 

1.	 On which set of species do we need to focus to further refine the HAPs profile? 

(E.g.: [1] phenol discrepancy, [2] methanol and the several aromatics and long list 

of species present at a fraction of a percent of total mass not measured by Spicer 

et al., [3] questions regarding acrolein/butene etc.) 

2.	 What is our approach to evaluating (and possibly revising) the UHC-to-VOC-toTOG conversions? 

With the completion of this analysis of Spicer and APEX data, we can offer the 

speciation profile provided in the accompanying spreadsheet for inclusion into the EPA’s 

SPECIATE database. 

Cited References: 

Anderson, B. E., G. Chen and D. R. Blake (2006). "Hydrocarbon emissions from a 

modern commercial airliner." Atmospheric Environ. 40(19): 3601-3612. 

DuBois, D. and G. C. Paynter (2006). ""Fuel Flow Method2" for Estimating Aircraft 

Emissions." SAE Technical Paper Series 2006-01-1987. 

Gerstle, T., P. Virag and M. Wade (1999). "Aircraft Engine and Auxiliary Power Unit 

Emission Testing: Vol. 1." United States Air Force: IERA RS-BR-TR-1999-0006. 

Herndon, S. C., T. Rogers, E. J. Dunlea, R. C. Miake-Lye and B. Knighton (2006). 

"Hydrocarbon emissions from in-use commercial aircraft during airport operations." 

Environmental Science and Technology 40(14): 4406 - 4413. 

Kinsey, J. S., Y. Dong, and D. C. Williams (in preparation 2008). "Characterization of 

Emissions from Commercial Aircraft Engines during the Aircraft Particle Emissions 

eXperiment (APEX)", U. S. Environmental Protection Agency, Office of Research and 

Development, National Risk Management Research Laboratory, Research Triangle Park, 

NC. 

Knighton, W. B., T. Rogers, C. C. Wey, B. E. Anderson, S. C. Herndon, P. E. Yelvington 

and R. C. Miake-Lye (2007). "Application of Proton Transfer Reaction Mass 

Spectrometry (PTR-MS) for Measurement of Volatile Organic Trace Gas Emissions 

From Aircraft." Journal of Propulsion and Power 23: 949-958. 

Lobo, P., P. D. Whitefield, D. E. Hagen, S. C. Herndon, J. T. Jayne, E. C. Wood, W. B. 

Knighton, M. J. Northway, R. C. Miake-Lye, D. Cocker, A. Sawant, H. Agrawal and J. 

Wayne Miller (2007). "The development of exhaust speciation profiles for commercial 

jet engines." Final Report, Contract No. 04-344, California Air Resources Board, 

Sacramento, CA, October 31, 2007. 

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Lobo, P., D. E. Hagen, P. D. Whitefield and D. J. Alofs (2007). "Physical 

characterization of aerosol emissions from a Commercial Gas Turbine Engine." Journal 

of Propulsion and Power 23: 919-929. 

Onasch, T. B., J. T. Jayne, S. C. Herndon, P. Mortimer, D. R. Worsnop and R. C. MiakeLye (2006). "Chemical Properties of Aircraft Engine Exhaust Aerosols Sampled During 

APEX." NASA/TM-2006-214382 ARL_TR_3903: Appendix J. 

Schürmann, G., K. Schäfer, C. Jahn, H. Hoffmann, M. Bauerfeind, E. Fleuti and B. 

Rappenglück (2007). "The impact of NOx, CO and VOC emissions in the air quality of 

Zurich Airport." Atmospheric Environ. 41: 103-118. 

Spicer, C. W., M. W. Holdren, R. M. Riggin and T. F. Lyon (1994). "Chemical 

composition and photochemical reactivity of exhaust from aircraft turbine engines." Ann. 

Geophysicae 12: 944-955. 

Spicer, C. W., M. W. Holdren, D. L. Smith, D. P. Hughes and M. D. Smith (1992). 

"Chemical composition of exhaust from aircraft turbine engines." Journal of Engineering 

for Gas Turbines and Power 114(1): 111-117. 

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

Canagaratna, R. C. Miake-Lye and W. Berk Knighton (manuscript in prepartion, 2008). 

"Gas Turbine Engine Emissions Part 1. Hydrocarbons and Nitrogen Oxides" Aerodyne 

Research, Inc., Billerica, MA. 

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

Herndon, E. Wood and R. C. Miake-Lye (manuscript in prepartion, 2008). "Gas Turbine 

Engine Emissions Part 2. Chemical Properties of Particulate Matter" Aerodyne Research, 

Inc., Billerica, MA. 

URS and FAA (2003). Select resource materials and annotated bibliography on the topic 

of hazardous air pollutants (HAPs) associated with aircraft, airports and aviation. 

Technical Directive Memorandum: D01-010, CSSI Contract: DTFA 01-99-Y-01002. 

Wey, C. C. (2004). Overview of the Aircraft Particle Emissions eXperiment (APEX) 

Program. Aircraft Particle Emissions Workshop, Cleveland, OH. 

Vay, S.A., B.E. Anderson, G. W. Sachse, J. E. Collins, Jr., J. R. Podolske, C. H. Twohy, 

B. Gandrud, K. R. Chan, S. L. Baughcum, H. A. Wallio. (1998) DC-8-based 

observations of aircraft CO, CH4, N2O, and H2O(g) emission indices during SUCCESS. 

Geophysical Research Letters 25 1717-1720. 

Wey, C. C., B. E. Anderson, et al. (2006). "Aircraft Particle Emissions eXperiment 

(APEX)." NASA/TM-2006-214382 ARL-TR-3903. 

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Wiesen, P. J., J. Kleffmann, R. Kurtenbach, K.H. Becker. (1994) Nitrous Oxide and 

Methane Emissions form Aero Engines. Geophysical Research Letters 21 2027-2030. 

Wilkins, J. (2007). Description of the 2005 Boston Logan Airport Environmental Data 

Report. S. Herndon. Boston: LTO times compiled from actual data collected at the airport 

during 2005. 

Yelvington, P. E., S. C. Herndon, J. C. Wormhoudt, J. T. Jayne, R. C. Miake-Lye, W. B. 

Knighton and C. C. Wey (2007). "Chemical Speciation of Hydrocarbon Emissions from a 

Commercial Aircraft Engine." Journal of Propulsion and Power 23: 912-918. 

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1 Aircraft Engine Speciated Organic Gases: 

2 Speciation Profile Spreadsheet 

3 

4 R.C. Miake-Lye 

5 

6 Introduction: A numerical spreadsheet

9

 was developed that used both the Spicer data and 

7 APEX data to formulate a speciated profile of HC emissions, as discussed in the main 

8 body of this report. These several pages that follow are a description of the process used 

9 to develop that spreadsheet and an explanation of how the equations are used to provide 

10 the resulting calculated quantities. The spreadsheet (in Microsoft Excel format) is 

11 intended to accompany this documentation, with its data and imbedded equations. 

12 

13 The initial formulation of the spreadsheet was based on the several data sources (Spicer, 

14 and APEX, including both ARI/MSU and EPA contributions). These data sources are 

15 listed in columns, with the rows representing the numerous species measured by the 

16 several investigators. These data are combined to provide a single profile, as described 

17 more fully in the main body of the report. Below, the approach for that combination will 

18 be described. 

19 

20 After the profile was finalized, with many new species added and a few adjustments of 

21 specific species values from the original Spicer speciation, several additional quantities 

22 were calculated. The calculations are all imbedded in the spreadsheet, via the equations 

23 used to generate the quantities in the labeled cells, and the rationale behind the 

24 calculations will be presented below. The types of calculations are primarily directed at 

25 understanding how the speciated profile relates to the total amount of HCs emitted, which 

26 requires some assumptions since no measurement can quantify with complete certainty 

27 all of the HC emissions. As part of developing that understanding, calculations were also 

28 made to address questions of 1) how the limited measurements (such as that from a 

29 Flame Ionization Detector or FID, as used in certification testing) can be corrected to 

30 approximate the full HC complement and 2) how to convert HC emissions expressed in 

31 terms of methane mass equivalents, the reporting convention for HC EIs measured with a 

32 FID, into an estimate of the actual total mass of the full speciation profile, including 

33 unmeasured species. These calculations are all described below, as well. 

34 

35 An abbreviated version of the speciation spreadsheet is reproduced in Table 4 below. 

36 Species that have no mass fraction that are included in the spreadsheet for completeness 

37 are not included in Table 4. Also, the only columns from the spreadsheet that are shown 

38 in Table 4 are the profile species with non-zero mass fractions, their molecular mass and 

39 formula numbers, and the profile mass fraction. In the last two rows of Table 4, the 

40 fractions of the total profile mass represented by the identified species (71%) and that 

41 represented by the unidentified mass (29%) are listed, based on the total mass estimates 

42 given by Spicer and refined with the new measurements, and supported by the EPA 

9

 The accompanying Microsoft Excel filename is FAA-EPA_TSD_Speciated_HC_Aircraft_04AUG08.xls and 

all references to columns, rows, or cells can be found in the worksheet titled “Data Summary”. 

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6 

APEX data as discussed in the main report. The approach for calculating these quantities 

is discussed below. 

Table 4. Aircraft Profile Speciation 

Species Molecular 

Weight 

Formula Mass Fraction 

C H O 

Ethylene 28 2 4 0.15459 

Acetylene 26 2 2 0.03939 

Ethane 30 2 6 0.00521 

Propylene 42 3 6 0.04534 

Propane 44 3 8 0.00078 

Isobutene/1-Butene 56 4 8 0.01754 

1,3-Butadiene 54 4 6 0.01687 

cis-2-Butene 56 4 8 0.00210 

3-Methyl-1-butene 70 5 10 0.00112 

1-Pentene 70 5 10 0.00776 

2-Methyl-1-butene 70 5 10 0.00140 

n-Pentane 72 5 12 0.00198 

trans-2-Pentene 70 5 10 0.00359 

cis-2-Pentene 70 5 10 0.00276 

2-Methyl-2-butene 70 5 10 0.00185 

4-Methyl-1-pentene 84 6 12 0.00069 

2-Methylpentane 86 6 14 0.00408 

2-Methyl-1-pentene 84 6 12 0.00034 

1-Hexene 84 6 12 0.00736 

trans-2-Hexene 84 6 12 0.00030 

Benzene 78 6 6 0.01681 

1-Heptene 98 7 14 0.00438 

n-Heptane 100 7 16 0.00064 

Toluene 92 7 8 0.00642 

1-Octene 112 8 16 0.00276 

n-Octane 114 8 18 0.00062 

Ethylbenzene 106 8 10 0.00174 

m-Xylene/p-Xylene 106 8 10 0.00282 

Styrene 104 8 8 0.00309 

o-Xylene 106 8 10 0.00166 

1-Nonene 126 9 18 0.00246 

n-Nonane 128 9 20 0.00062 

Isopropylbenzene 120 9 12 0.00003 

n-Propylbenzene 120 9 12 0.00053 

m-Ethyltoluene 120 9 12 0.00154 

p-Ethyltoluene 120 9 12 0.00064 

1,3,5-Trimethylbenzene 120 9 12 0.00054 

o-Ethyltoluene 120 9 12 0.00065 

1,2,4-Trimethylbenzene 120 9 12 0.00350 

1-Decene 140 10 20 0.00185 

n-Decane 142 10 22 0.00320 

1,2,3-Trimethylbenzene 120 9 12 0.00106 

n-Undecane 156 11 24 0.00444 

n-Dodecane 170 12 26 0.00462 

n-Tridecane 184 13 28 0.00535 

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C14-alkane 198 14 30 0.00186 

C15-alkane 212 15 32 0.00177 

n-tetradecane 198 14 30 0.00416 

C16-alkane 226 16 34 0.00146 

n-pentadecane 212 15 32 0.00173 

n-hexadecane 226 16 34 0.00049 

C18-alkane 254 18 38 0.00002 

n-heptadecane 240 17 36 0.00009 

phenol 94 6 6 1 0.00726 

naphthalene 128 10 8 0.00541 

2-methyl naphthalene 142 11 10 0.00206 

1-methyl naphthalene 142 11 10 0.00247 

dimethylnapthalenes 156 12 12 0.00090 

C4-Benzene + C3-aroald 134 10 14 0.00656 

C5-Benzene+C4-aroald 148 11 16 0.00324 

Methanol 32 1 4 1 0.01805 

Formaldehyde (FAD) 30 1 2 1 0.12308 

Acetaldehyde (AAD) 44 2 4 1 0.04272 

Acetone 58 3 6 1 0.00369 

Propionaldehyde 58 3 6 1 0.00727 

Crotonaldehyde 70 4 6 1 0.01033 

Butyraldehyde 72 4 8 1 0.00119 

Benzaldehyde 106 7 6 1 0.00470 

Isovaleraldehyde 86 5 10 1 0.00032 

Valeraldehyde 86 5 10 1 0.00245 

o-Tolualdehyde 120 8 8 1 0.00230 

m-Tolualdehyde 120 8 8 1 0.00278 

p-Tolualdehyde 120 8 8 1 0.00048 

Methacrolein 70 4 6 1 0.00429 

Glyoxal 58 2 2 2 0.01816 

Methylglyoxal 72 3 4 2 0.01503 

acrolein 56 3 4 1 0.02449 

Sum of all identified species 0.70787 

Unidentified mass 0.29213 

1 

2 Development of the Profile: As described in the main report, most of the species 

3 contributions measured by Spicer were supported by the APEX measurements. So, the 

4 data columns in the spreadsheet (not included in Table 4 above) show values for each 

5 measured species, in separate columns for each data source. If the data from APEX were 

6 not significantly different from Spicer’s, the value from Spicer’s column was used. This 

7 was true for almost all of the species measured by Spicer. The two exceptions were 

8 phenol and butyraldehyde (also called butanal). In these two cases, the more recent 

9 APEX data were used to update the values for those species. Then, additional species 

10 from either the ARI/MSU team (color coded blue in the spreadsheet) or from EPA 

11 (yellow) were also added to the species list and their contributions quantified. All of 

12 these quantifications are first entered into the spreadsheet as column L as ratios of 

13 emission indices of the species in question to the emission index of formaldehyde. 

14 Column L is titled “Revised Ratios” since these are the EI ratios of the individual species 

15 to formaldehyde accounting for both Spicer and the more recent APEX data. 

16 

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Mass Fractions of Identified and Unidentified Species: Since the ratios of EIs are really 

mass ratios (EIs are mass ratios of the species to mass fuel burn, so ratioing EIs divides 

one EI by another and the fuel burn divides out), this column is a set of 

species:formaldehyde mass ratios. This is not useful for general application, since 

formaldehyde emissions are not generally measured or known. To be most generally 

useful, a profile for the full complement of species was desired. This could be done for 

the identified species, but there may be some HC species which contribute to the mass 

but which could not be identified. 

In order to attempt to account for all of the HC species, including those not identified, 

Spicer’s data was reviewed. Spicer attempted to do a complete carbon balance, based on 

the suite of instruments employed and accounting for corrections for sensitivities. With 

the set of species measured by Spicer, an estimate was made for the mass of the identified 

species and for those that were not identified. For the present purposes, we have taken 

Spicer’s values to be correct for the unidentified species based on his measurements. We 

have also compared to the time-integrated LTO cycle HC data taken by EPA, which were 

taken under a different set of measurement protocols (integrating over power settings, 

including engine start, and the corresponding different effects of backgrounds) and have 

determined that the APEX EPA data is largely consistent with the Spicer data set (see 

main report). 

So Spicer’s unidentified mass fraction was taken as a starting point. However, the 

additional species included in APEX actually reduced this unidentified list and 

unidentified mass. And the adjustments of phenol and butyraldehyde must also be 

accounted for. So, in calculating column K of the spreadsheet (reproduced for non-zero 

mass fraction species in Table 4 above), the original species in Spicer’s profile were 

summed (see cell K7 in the spreadsheet). In the equation in cell K7, the phenol and 

butyraldehyde values were individually reset to Spicer’s original values rather than use 

the new “Revised Ratio” values in column L, and the sum was set to Spicer’s original 

identified mass fraction so that Spicer’s carbon balance could be used, albeit with the 

unidentified mass reduced due to the newly added species. (Note that Spicer quotes his 

numbers in terms of parts per million carbon (ppmC) concentrations. However, within 

the limits of accuracy of these calculations, the fractions of ppmC reported for identified 

and unidentified are equivalent to the masses identified and unidentified in that the 

mass/carbon for the two fractions, identified and unidentified, is not significantly 

different for these two fractions.) 

With the sum calculated and set equal to the Spicer’s identified mass fraction, the 

individual mass ratios in column L can be scaled such that they can be referenced to a 

total given by Spicer’s carbon balance. Cell K7 of the spreadsheet takes the sum and 

uses Spicer’s identified mass fraction, to give a scaling factor for each identified species 

in the “Revised Ratios” column (L) to give the resulting profile in column K. Because 

more species are now identified, the sum of the identified profile now comes to 70.8% of 

the total HC mass (cell K119). The new additions to the list represent 6.4 of the total HC 

mass (cell K120), while phenol and butyraldehyde adjust things a little as well from 

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Spicer’s original identified mass. The unidentified mass represents 29.2% of the total 

mass in this new profile (K126). 

Determining Effective Mass of Total Profile and Corrections for FID response: Since 

certification data from commercial engines are available, such data are often used for 

estimating HC emissions. Unfortunately, there are two problems with that certification 

data. The measurement device prescribed for this measurement uses a FID, which 

essentially “counts carbon atoms”. This raises two problems. One is that the FID does 

not count carbon atoms that have an oxygen atom attached, and so is not equally sensitive 

to all HC species. Second, since the measurement is “counting carbons”, it keeps track of 

a concentration and there is no direct indication of the mass of the species in question. 

(Mass is determined by the amount of hydrogen and oxygen in the molecule in addition 

to the number of carbons.) For the certification numbers, a mass/carbon based on the 

methane molecule (molecular mass 16.04) is used by convention. This is purely an 

assumption and has not been based on measurements to date, as far as the authors know. 

These two problems can be addressed with the detailed profile provided in column K. 

For the known species, the mass/carbon can be calculated, since both the number of 

carbons and the molecular mass are known (given in Table 4 above and in spreadsheet 

columns D and H, as well as hydrogen and oxygen numbers provided in columns I and J). 

From the individual mass/carbon numbers and the mass fractions in column K, the massweighted mass/carbon can be calculated for the identified profile. In order to correct the 

mass for the total profile, one would need to have the mass-weighted mass/carbon for the 

complete profile. Since we do not have the molecular masses and formulas for the 

unidentified species (because they are unidentified), that calculation cannot be done 

rigorously. Thus, an estimate of the mass/carbon for the full profile is required. 

In order to estimate the mass/carbon for the full profile, the mass/carbon was examined 

for two classes of species in the identified species. The first class represents those 

species present at greater than 1% of the total HC mass in column K. This includes many 

light oxygenated HCs, which have a large oxygen contribution to their total mass. The 

mass/carbon for these light species is not likely to be similar to those larger HC in the 

unidentified mass contributions. These light species have a mass/carbon of 17.6 (cell 

C130). The remaining species in the identified list have a mass/carbon of 14.4 (cell 

C132), which is likely closer to what might be expected for the larger, partially oxidized 

species in the unidentified component. Any deviation from 14.4 for the unidentified, 

while not expected to be large, is also devalued by the modest (29%) contribution of the 

unidentified to the total. This argument indicates that a good estimate for the 

mass/carbon for the full profile can be calculated using this approach. Thus, assigning 

14.4 to the unidentified and combining with the identified, gives a total mass/carbon for 

the full profile of 15.97 (cell C137). (This is surprisingly close to the original convention 

of using methane’s molecular mass of 16.04.) 

The problem of the FID’s lack of sensitivity to carbons bound to oxygen can also be 

rectified by the profile information. By a similar approach to calculating the massweighted mass/carbon, the mass-weighted C/H/O ratios for the various profile 

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components discussed above can be calculated. These are included in cells EFG130, 

EFG132, and EFG137. By ratioing to carbon, in cells EFG131, EFG133, and EFG138, 

the number of oxygens/carbon can be determined. Since each carbon effectively cancels 

out the measurement of one carbon by the FID, the FID response for the full profile can 

be estimated by subtracting cell G138 from cell E138 (or 1.00 – 0.1365). The FID 

response is then 0.8635 of the total carbon number, or the correction for the FID’s lack of 

sensitivity due to oxygen containing molecules is 1.16 times the FID output. 

To summarize: 

To correct for the FID response to account for the oxygen content, multiply the FID 

measurement by 1.16. 

To make use of the best estimate of the actual molecular masses of the HC species 

instead of using the equivalent methane convention, multiply the FID measurement by 

15.97/16.04 = 0.996. 

The net total correction is 1.16 times 0.996 = 1.16. 

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