Recommended Best Practice for
Quantifying Speciated Organic Gas
Emissions from Aircraft Equipped with
Turbofan, Turbojet, and Turboprop
Engines
Version LO
United States
Environmental Protection
Agency
-------
Recommended Best Practice for
Quantifying Speciated Organic Gas
Emissions from Aircraft Equipped with
Turbofan, Turbojet, and Turboprop
Engines
Version LO
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-09-901
May 2009
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ACKNOWLEDGEMENTS
The Federal Aviation Administration (FAA) Office of Environment and Energy (AEE) and the
U.S. Environmental Protection Agency (EPA) Office of Transportation Air Quality (OTAQ)
would like to acknowledge the following agencies and individuals for their contribution to this
document:
FAA - Ralph lovinelli, Mohan Gupta, Carl Ma, and Ed McQueen
EPA - Bryan Manning, Rich Cook, Kent Helmer, Ken Petche, John Kinsey,
Rich Wilcox, Kathryn Sergeant, Marion Hoyer, Laurel Driver, and Suzanne
King
California Air Resources Board - Steve Francis, Paul Allen, Wenli Yang, and
Steve Church
Aerodyne Research, Inc. - Rick Miake-Lye and Scott Herndon
Montana State University - Berk Knighton
KB Environmental Sciences, Inc. - Carrol Bryant, Mike Ratte, Paul Sanford,
and Mike Kenney
This document was prepared for the Federal Aviation Administration, Office of Environment
and Energy by KB Environmental Sciences Inc. with assistance from CSSI Inc. in support of
CSSFs Contract DTFAWA-05-C-00044, Technical Directive Memorandum B-002-011.
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EXECUTIVE SUMMARY
This document presents an approach to, and technical support for, the quantification of organic
gas (OG) emissions including hazardous air pollutants (HAPs) from aircraft equipped with
turbofan, turbojet and turboprop engines.1'2'3 This Recommended Best Practice (RBP) was
produced through an inter-agency partnership and collaborative effort between the Federal
Aviation Administration (FAA) Office of Environment and Energy (AEE) and the U. S.
Environmental Protection Agency (EPA) Office of Transportation Air Quality (OTAQ).4 At the
onset of the endeavor, the agencies agreed that the method used to quantify speciated OG
emissions from aircraft engines should be:
Nationally consistent,
Supported by scientific data,
Representative of today's flying fleet (to the extent possible), and
A "living" process to reflect the state-of-the-science as new data becomes available.
Central to this RBP is the preparation of a revised speciation profile to identify most of the
individual OG species that comprise the OG emissions from aircraft equipped with turbofan,
turbojet, and turboprop engines (it should be noted that approximately 29 percent of the total
amount of OG emissions from the tested engines remain characterized as unidentified). This new
profile is based on recent field measurement campaigns and is considered representative of
today's modern aircraft engines. The new profile (SPECIATE profile #5565), to be incorporated
in to the next revision of EPA's SPECIATE (Version 4.0) database, is recommended as a
replacement for all prior speciation profiles identified for aircraft and is the preferred profile that
should be used to characterize gas-phase speciated OG emissions from aircraft equipped with
turbofan, turbojet and turboprop engines.
The new speciation profile identifies 77 individual compounds, including 15 that are recognized
by section 112 of the Clean Air Act as being hazardous air pollutants (HAPs). Two additional
compounds also have potential toxic characteristics according to EPA's Integrated Risk
Information System (IRIS) database. While future research will further define the unidentified
component, in the interim, the unidentified mass has been generically characterized as longer
carbon chain species (see Section 2.1 of this report) for air quality modeling practitioners that use
chemical mechanisms such as the Statewide Air Pollution Research Center 1999 (SAPRC99),
Carbon Bond 4, Carbon Bond 5, and the RADM-2 models.
It is important to acknowledge that the measurement of air emissions associated with aircraft
engines is an evolving process that is still under development. This is especially relevant to the
speciation of aircraft-related OG for which there is appreciably less experience, data, and
1 This document does not address and/or provide speciation profiles for polynuclear aromatic hydrocarbons
(PAH)/volatile organic compounds (VOC) or PAH/particulate matter.
2 Although direct emission measurements from turboprop engines are not available at this time, it is recognized that
turboprop engines operate with the same kerosene based fuels and have similar combustor temperature and pressures
as the tested engines.
This effort/document focuses on kerosene fueled turbofan, turbojet, and turboprop engines. Other engine types,
including piston engines and those in auxiliary power units and ground service equipment, are not included in the
analysis.
4 EPA's Office of Research Development (ORD)/National Risk Management Research Laboratory (NRMRL) also
participated in the development and review of this material.
Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice
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information, when compared to other criteria pollutants or air pollutant emissions from other
mobile sources (e.g., motor vehicles).
The FAA and EPA have agreed to continue further development of speciated OG from aircraft
engines as new scientific information becomes available. Because this effort is a "living"
methodology, air quality practitioners should verify that they have the most recent version of this
document (by date and version number on the cover) and associated speciated profile before
preparing an aircraft HAPs emissions inventory. New information and speciation profile will be
posted on both FAA's and EPA's websites.5 In addition, EPA's next revision to the SPECIATE
database will incorporate this information.6
It is also important to acknowledge that there are currently no Federal regulatory guidelines
specific to HAPs emissions from aircraft engines and, while the methodology discussed in this
document is useful for disclosure, reporting, and comparative purposes, it does not provide
results that are directly comparable to any regulatory or enforceable air quality standards.
See www.FAA.gov/regulationsjolicies/policv guidance/envir_policv/ and www.EPA. gov/otaq/aviation.htm
USEPA. SPECIATE Version 4.0 (www.epa.gov/ttn/chief/software/speciate/index.html), December 2006.
Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice
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ACRONYMS AND ABBREVIATIONS
AEE
APEX
ASPM
CAA
CAEP
CARS
CAS
DoD
EDMS
EPA
FAA
FID
HAPs
HC
ICAO
IRIS
JETS
kg
LTO
NASA
NEI
NMOG
OG
OTAQ
QAPP
RBP
SAPRC99
SPECIATE
TAC
TAP
TAP
THC
TIM
TOG
VOC
FAA Office of Environment and Energy
Aircraft Particle Emissions Experiment
Aviation System Performance Metrics (database)
Clean Air Act
Committee on Aviation Environmental Protection
California Air Resources Board
Chemical Abstracts Service
U.S. Department of Defense
Emissions and Dispersion Modeling System
U.S. Environmental Protection Agency
Federal Aviation Administration
Flame lonization Detector
Hazardous air pollutants
Hydrocarbon
International Civil Aviation Organization
Integrated Risk Information System
Jet Emission Testing for Speciation
Kilogram
Landing-takeoff cycle
National Aeronautics and Space Administration
National Emission Inventory
Non-methane organic gas
Organic gas
Office of Transportation Air Quality
Quality Assurance Plan
Recommended Best Practice
Statewide Air Pollution Research Center 1999
U.S. EPA data system of speciation profiles
Toxic air contaminant
Terminal Area Forecast
Toxic air pollutant
Total hydrocarbons
Time in mode
Total organic gases
Volatile organic compounds
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TABLE OF CONTENTS
Executive Summary
Acronyms and Abbreviations
Page
1.0 INTRODUCTION 1
1.1 Background Information 1
1.2 Approach 2
1.3 Regulatory Context 3
2.0 SPECIATEDOG PROFILE 4
2.1 Representation of Unidentified Mass 6
2.2 SPECIATE Database Rating 6
3.0 CONVERSION FACTORS 9
4.0 EMISSION INVENTORIES 13
4.1 Aircraft Operational Data 13
4.2 Calculating THC, NMOG, or VOC Emissions 13
4.3 Converting to TOG 15
4.4 Applying Speciation Profile Data 16
4.5 Presentation of Results 16
List of References
LIST OF TABLES
No. Page
1 Speciated Gas-Phase OG Profile for Aircraft Equipped with
Turbofan, Turbojet, and Turboprop Engines 5
2 Unidentified Mass Species Assignment 6
3 Overall Profile Quality Ratings 7
4 Conversion Factors 11
5 Example Aircraft Operational Data 14
6 Example Fuel Flow Rates/Emission Indices 14
7 Example THC Estimate 15
8 Example Speciated OG Emission Levels 16
9 Example Format for Reporting Speciated OG 17
LIST OF FIGURES
Figure No.
Groups of OGs 10
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1.0 INTRODUCTION
This document presents an I ~ ~~.
, f .. .. f Purpose of this
approach for quantification of ^_ /-T.UU\
, , /-/-v/->\ Recommended Best Practice (RBP)
speciated organic gas (OG) _ ., .,, u* j* u i
. . i j- u j To provide a uniform approach to, and technical
emissions, including hazardous air ^c ^ J c *. j i
.. /TT A-r. \ r- support tor, the preparation or speciated gas-phase
pollutants (HAPs), from . ' .,.,,. TTA^ n.
i « j vi HC inventories (including HAPs) from aircraft
commercial aircraft equipped with . > > \ c i j 1
n rr equipped with turbofan, turbojet, and turboprop
turbofan, turbojet, and turboprop
engines.
engines. ' ' ' The preparation of an
emissions inventory (an accounting of pollutant mass emissions from a source over a specific
time interval) is the preferred approach for quantifying emissions from aircraft equipped with
turbofan, turbojet, and turboprop engines. The aircraft-related speciation profile discussed in
this document will also be used to update the speciated OG profile for aircraft equipment
with turbofan, turbojet, and turboprop engines in the SPECIATE database5, the U.S.
Environmental Protection Agency's (EPA's) multi-sector repository for such data.
The focus of this document is only on aircraft equipped with turbofan, turbojet, and
turboprop engines. The Federal Aviation Administration (FAA) intends to separately publish
information that will address other airport-related sources (including other piston-powered
aircraft engines). In these separate efforts, information will be provided for sources such as
ground service equipment (includes vehicles such as aircraft tugs, baggage tugs, fuel trucks,
maintenance vehicles, and other miscellaneous vehicles used to support aircraft operations),
ground access vehicles (includes motor vehicles used by passengers, employees, freight
operators, and other persons to enter and leave an airport such as shuttles, taxis, rental cars,
and privately-owned vehicles), fuel storage and transfer facilities, stationary support services,
and construction activities.
1.1 Background Information
The National Aeronautics and Space Administration (NASA), EPA, the Department of
Defense (DoD), and FAA collaboratively sponsored three separate commercial aircraft
engine exhaust measurement campaigns in 2004 and 2005, known as the Aircraft Particle
Emission experiments (APEX1, APEX2, and APEX3). In addition, California Air
Resources Board co-sponsored, as well as initiated, the JETS/APEX2 campaign (JETS (Jet
Emission Testing for Speciation) is a California Air Resources Board (CARB) acronym).
1 In this document, the term "hazardous air pollutants" and the accompanying acronym "HAPs" mean the same
as "air toxics", "toxic air contaminants" or "TACs", and "toxic air pollutants" or "TAPs".
2 This document does not address and/or provide speciation profiles for polycyclic aromatic hydrocarbons
(PAH)/volatile organic compounds (VOC) or PAH/particulate matter.
3 Although direct emission measurements from turboprop engines are not available at this time, it is recognized
that turboprop engines operate on the same kerosene based fuels, and have similar combustor temperature and
pressures as the tested engines.
4
This effort/document focuses on kerosene fueled turbofan, turbojet, and turboprop engines. Other engine
types, including piston engines, and those in auxiliary power units and ground service equipment, are not
included in the analysis.
5 USEPA. SPECIATE Version 4.0 (www.epa.gov/ttn/chief/software/speciate/index.htmlX December 2006.
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The three campaigns were designed to evaluate the effects of engine thrust and fuel type on
the levels of particulate matter and gaseous emissions from commercial aircraft engines, and
specific measurements were made for speciated OG, including HAPs.
In the summer of 2007, the FAA and EPA formed a partnership and began a joint effort to
use this newly acquired information and data to develop uniform protocols and methods to
quantify the level of OG and HAPs from commercial aircraft. At the onset, the agencies
agreed that the protocols and methods should be:
Nationally consistent,
Supported by scientific data,
Representative of today's flying fleet to the extent possible, and
A "living" process to reflect the state-of-the-science as new data becomes available.
The procedures that the FAA and EPA used to develop the uniform protocols and methods
discussed in this document are outlined in the FAA/EPA Quality Assurance Project Plan
(QAPP) for the Development of a Commercial Aircraft Hazardous Air Pollutants Emission
Inventory Methodology [FAA/EPA, 2008]. In addition, the technical details and scientific
information are available in a Technical Support Document [Knighton, Herndon, Miake-Lye,
2009]. Electronic copies of these documents are available on both FAA's and EPA's
websites.6
1.2 Approach
It is important to acknowledge that the measurement of pollutant emissions in aircraft
exhaust is an evolving science. In fact, new aircraft engine exhaust measurement campaigns
and modeling studies are currently underway and more are planned in the future. This is
especially relevant to aircraft-related speciated OG for which there is appreciably less
experience, data, and information, when compared to criteria air pollutants (e.g., carbon
monoxide and nitrogen oxides) and other mobile air pollutant sources (e.g., ground service
equipment, motor vehicles).
Two guiding principles were followed during the course of this endeavor to develop uniform
protocols and methods for quantifying aircraft-related gas-phase speciated OGs, while
considering the current limitations and uncertainties associated with these specialized
pollutants.
First, the RBP should reflect the current state-of-the-science. The FAA and EPA recognize
that even though the amount of aircraft engine emission test data is growing, the amount is
still limited and there are research gaps that need to be addressed. However, by publishing
this document, the FAA and EPA are establishing an initial and nationally-consistent
approach for preparing speciated OG and HAPs emission inventories. While this is the case,
air quality practitioners must recognize that the topic of speciating aircraft-related OG is
6 See www.FAA.gov/regulations policies/policy guidance/envir policy/ and www.EPA. gov/otaq/aviation.htm
Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice
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relatively new and therefore in an evolutionary science. As a result, this RBP will be updated
as scientific advancements are made.
Second, even though there is still some uncertainty related to gas-phase speciated OG
emissions from commercial aircraft, there is an immediate and growing need for an accurate,
up-to-date, and consistent method for estimating these emissions. Therefore, this document
makes the best use of what is presently known about aircraft OGs with the expectation that
this RBP may need to be updated as new information and data are available.
1.3 Regulatory Context
There are presently no Federal regulatory guidelines that address aircraft engine-related gas-
phase OG species or HAPs emissions. By definition, aircraft are not subject to the
regulations of Section 112 of the Federal Clean Air Act (CAA).7 That said, there are 15
common HAPs detected in measurable concentrations in aircraft engine exhaust, and these
HAPs are also listed in Section 112 of the CAA. These pollutants are 1,3 butadiene,
acetaldehyde, acrolein, benzene, ethylbenzene, formaldehyde, isopropylbenzene, methanol,
m-xylene and p-xylene, naphthalene, o-xylene, phenol, propionaldehyde, styrene, and
toluene. EPA's Integrated Risk Information System (IRIS)8 identifies two additional
hazardous compounds measured in the exhaust from turbofan, turbojet, and turboprop
engines: benzaldehyde and 2-methyl-naphthalene.
7 Only major stationary sources are regulated by Section 112 of the CAA.
8 EPA's IRIS (Integrated Risk Information System) is a compilation of electronic reports on specific substances
found in the environment and their potential to cause human health effects, http://cfpub.epa.gov/ncea/iris/index.cfm
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2.0 SPECIATED OG PROFILE
The initial speciation profile for use in the quantification of the level of OGs/HAPs emitted
from aircraft equipped with turbofan, turbojet, and turboprop engines are provided in Table 1
and in a companion spreadsheet to this document (posted mutually on FAA's and EPA's
websites).9 Because the intent of the FAA/EPA is to update the profile as additional data
becomes available, air quality practitioners should verify that they have the most recent
profile before beginning an evaluation.
The development of the recommended FAA/EPA speciation profile (provided in Table 1) is
discussed in a Technical Support Document entitled Aircraft Engine Speciated Organic
Gases: Speciation of Unburned Organic Gases in Aircraft Exhaust [Knighton, Herndon,
Miake-Lye, 2009]. The most noteworthy findings of this effort are stated below:
The current speciation profile chosen to represent organic gas emissions from aircraft
engines is #109810 in the SPECIATE database, and was derived from a publication by
Spicer et al. in 1994. This profile included data from a military variant of the CFM56
commercial engine.11 Comparisons of data from Spicer's measurements for the
CFM-56 and several of the CFM-56 engines measured in the APEX programs
indicate that, with few exceptions, the Spicer and APEX data exhibit an overall
agreement for species where the results of measurements are available. Notably, and
again with few exceptions, all of the data are within one standard deviation of the
measurements to the unit line (i.e., the unity line represents perfect agreement).
The results of a comparison of Spicer's measurements for the CFM-56 and the APEX
measurements for three models of the CFM-56 also provide strong support that
speciated OG profile data are invariant across engine technologies for the commercial
engines tested.
Results of both studies (i.e., Spicer and APEX) indicate that at engine power
conditions substantially higher than approximately 15 to 30 percent thrust, the engine
combustion efficiency is close to 100 percent. Measurement of many OGs becomes
difficult or impossible due to limitations of the instrument detection levels (the OG
concentration is too small to measure). Therefore, the total amount of aircraft OG in
an aircraft landing-takeoff cycle (LTO) is dominated by the OG emitted at low power
settings (30 percent thrust or less).
9 See www.FAA.gov/regulationsjolicies/policv guidance/envir_policv/ and www.EPA. gov/otaq/aviation.htm.
10 The results of this effort will be incorporated into the SPECIATE database as profile #5565.
11 The CFM56 is a high bypass turbofan engine. 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.). CFM56 and the CFM logo represent CFM International, a joint company of Snecma and General
Electric. Snecma is a French manufacturer of engines for commercial and military aircraft, and space vehicles.
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Table 1. Speciated Gas-Phase OG Profile for Aircraft Equipped with
Turbofan, Turbojet, and Turboprop Engines/
Compound
1,2,3 -trimethylbenzene
1 ,2,4-trimethylbenzene
1,3,5 -trimethylbenzene
1,3 -butadiene"1
1-decene
1-heptene
1-hexene
1 -methyl naphthalene
1-nonene
1-octene
1-pentene
2-methyl- 1 -butene
2-methyl- 1 -pentene
2-methyl-2-butene
2-methyl-naphthalene e
2-methylpentane
3 -methyl- 1 -butene
4-methyl- 1 -pentene
acetaldehyde d
acetone
acetylene
acrolein d
benzaldehyde e
benzene d
butyraldehyde
c!4-alkane
cl5-alkane
c!6-alkane
cl8-alkane
c4-benzene +
c3-aroald
c5-benzene + c4-aroald
cis-2-butene
cis-2-pentene
crotonaldehyde
dimethylnapthalenes
ethane
ethylbenzene d
ethylenef
formaldehyde d'f
CAS
Registry No.a
526-73-8
95-63-6
108-67-8
106-99-0
872-05-9
25339-56-4
592-41-6
90-12-0
124-11-8
25377-83-7
109-67-1
563-46-2
763-29-1
513-35-9
91-57-6
107-83-5
563-45-1
691-37-2
75-07-0
67-64-1
74-86-2
107-02-8
100-52-7
71-43-2
123-72-8
No CAS
No CAS
No CAS
No CAS
No CAS
No CAS
590-18-1
627-20-3
4170-30-3
28804-88-8
74-84-0
100-41-4
74-85-1
50-00-0
Mass
Fraction
0.00106
0.00350
0.00054
0.01687
0.00185
0.00438
0.00736
0.00247
0.00246
0.00276
0.00776
0.00140
0.00034
0.00185
0.00206
0.00408
0.00112
0.00069
0.04272
0.00369
0.03939
0.02449
0.00470
0.01681
0.00119
0.00186
0.00177
0.00146
0.00002
0.00656
0.00324
0.00210
0.00276
0.01033
0.00090
0.00521
0.00174
0.15461
0.12310
Compound
glyoxal
isobutene/ 1 -butene
isopropylbenzene d
isovaleraldehyde
methacrolein
methanol d
methylglyoxal
m-ethyltoluene
m-tolualdehyde
m-xylene and
p-xylene d
naphthalene d
n-decane
n-dodecane
n-heptadecane
n-heptane
n-hexadecane
n-nonane
n-octane
n-pentadecane
n-pentane
n-propylbenzene
n-tetradecane
n-tridecane
n-undecane
o-ethyltoluene
o-tolualdehyde
o-xylene d
p-ethyltoluene
p-tolualdehyde
phenol d
propane
propionaldehyde d
propylene
styrene d
toluene d
trans-2-hexene
trans-2-pentene
valeraldehyde
unidentified b
CAS
Registry No.a
107-22-2
106-98-9
98-82-8
590-86-3
78-85-3
67-56-1
78-98-8
620-14-4
620-23-5
108-38-3 /
106-42-3
91-20-3
124-18-5
112-40-3
629-78-7
142-82-5
544-76-3
111-84-2
111-65-9
629-62-9
109-66-0
103-65-1
629-59-4
629-50-5
1120-21-4
611-14-3
529-20-4
95-47-6
622-96-8
104-87-0
108-95-2
74-98-6
123-38-6
115-07-1
100-42-5
108-88-3
4050-45-7
646-04-8
110-62-3
NA
Sum of all compounds
Mass
Fraction
0.01816
0.01754
0.00003
0.00032
0.00429
0.01805
0.01503
0.00154
0.00278
0.00282
0.00541
0.00320
0.00462
0.00009
0.00064
0.00049
0.00062
0.00062
0.00173
0.00198
0.00053
0.00416
0.00535
0.00444
0.00065
0.00230
0.00166
0.00064
0.00048
0.00726
0.00078
0.00727
0.04534
0.00309
0.00642
0.00030
0.00359
0.00245
0.29213
1.00000
a CAS = Chemical Abstracts Service
b See discussion of unidentified species in Section 2.1 of this report.
0 For commercial, military, general aviation, and air taxi aircraft equipped with turbofan, turbojet, and turboprop engines.
d Identified as a HAP in Section 112 of the CAA (shaded above).
e Identified in IRIS as having toxic characteristics (shaded above).
f Values were adjusted from those shown in the Technical Support Document to account for rounding and to facilitate
inclusion of the data in the SPECIATE database (where the required sum of the values is 1.00000).
Note: Values in this table may be revised in the future as additional engine data are available.
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2.1 Representation of Unidentified Mass
Table 1 shows that approximately 29 percent of the OG mass associated with the exhaust
from the tested commercial aircraft engines is presently unidentified. Future research by
both the FAA and EPA may provide better quantification and definition of the currently
unidentified mass. In the interim, the unidentified mass has been generically identified as
longer carbon chain species not included in the measured OG species listed in Table 1.
These longer carbon chain species, identified in Table 2, are based on scientific judgment
from the APEX principal investigators, the EPA, and the FAA.
Table 2. Unidentified Mass Species Assignment
Species
C-10 paraffins
C-10 olefms
decanal
dodecenal
Total
CAS
No CAS
No CAS
112-31-2
1127 1786
Mass
Fraction
0.14608
0.05843
0.05843
0.02922
0.29213
Both FAA and EPA recognize that the advanced atmospheric photochemical models used to
simulate the transport, dispersion, and reactivity of aircraft engine emissions will benefit
from the best available accounting of OGs. For the purpose of photochemical and other
related modeling efforts, the EPA and FAA recommend the "best fit" speciation of the
unidentified mass listed in Table 2 (recognizing that other assignments may be appropriate
depending on the modeling effort provided assignments do not repeat or overlap with already
identified species). This unidentified mass species assignment is recommended for use in
existing chemical mechanisms such as the Statewide Air Pollution Research Center 1999
(SAPRC99), Carbon Bond 4, Carbon Bond 5, RADM-2 and other atmospheric chemistry
models.
2.2 SPECIATE Database Rating
In the support documentation for the SPECIATE database, EPA explains the rating criteria
developed for adding new profiles to the database. The aircraft engine speciation profile
listed in Table 1 will also reside in EPA's SPECIATE database, as the FAA and EPA
preferred profile for speciating OG emissions from aircraft equipped with turbofan, turbojet,
and turboprop engines. The profile will replace and supersede all prior profiles.
The EPA rates all SPECIATE profiles using criteria to describe the confidence, data quality
and robustness. These ratings assess the quality of the entire dataset used to generate a given
profile, rather than each specific pollutant within the profile. These criteria are
presented/discussed on the following page:
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V-rating (profile vintage) is based on the vintage of the profile which reflects
measurement technology and methodology:
- After year 2000 score = 5
- 1996-2000 score = 4
- 1991-1995 score = 3
- 1980-1990 score = 2
- For profiles before year 1980 - score = 1
The speciation profile presented in Table 1 was assigned a V-rating of "5" because the
profile is based on measurement techniques that were used and methodologies that have
been accepted after the year 2000.
D-rating (number of samples) is given a "4" (excellent) to "1" (poor) rating. This
category is rated based on the number of samples:
- Number of samples greater than 10 score = 4
- 5-9 samples score = 3
- 3-4 and composite samples score = 2
- 1-2 or unknown number of samples score = 1
The speciation profile presented in Table 1 has been assigned a D-rating of "4" because the
profile is based on more than 10 samples (the multiple Spicer and APEX testing for CFM-56
engines).
Final Score = (V-rating) x (D-rating). Profile quality is then rated from A
(excellent) to E (poor) as shown in Table 3.
Table 3. Overall Profile Quality Ratings
Final Score Ranges
17-20
13-16
9-12
5-8
<5
Profile Quality
A
B
C
D
E
The final profile quality rating for the speciation profile in Table 1 is 20, or "A".
J-rating (expert judgment) is given a "5" (excellent) to "1" (poor) rating. This
value is based on the information underlying each profile including, but not
limited to:
o Profile composition;
o Relative ratios of species within the profile;
o Sum of the speciated mass fractions;
o Confidence in investigator/group collecting the data; and
o Supporting documentation.
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EPA does not provide objective rules on how to assign the J-rating. This inherently
qualitative value has been assigned by the principal investigators of the profile (Aerodyne
Research, Inc. and EPA's Office of Research Development-National Risk Management
Research Laboratory) with input from the participants on this project.
The speciation profile in Table 1 has been assigned a J-rating of "5" (excellent).
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3.0 CONVERSION FACTORS
OG emissions are defined a variety of ways depending on the reason for the analysis (e.g.,
preparation of an emissions inventory or photochemical analysis), the modeling need, and/or
the regulatory context. The definitions include total organic gases (TOG)18, non-methane
OGs (NMOG), total HC (THC), and volatile organic compounds (VOC). The individual and
groups of OGs included in each defined set/subset of gases are described in the following and
illustrated on Figure 1:
TOG -TOG is defined by CARB as compounds of carbon, excluding carbon
monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and
ammonium carbonate. TOG includes all organic gas compounds emitted to the
atmosphere, including the low reactivity compounds (e.g., methane, ethane, various
chlorinated fluorocarbons, acetone, perchloroethylene, volatile methyl siloxanes, and
oxygenated OG).
NMOG - As implied, NMOGs include all organic compounds except methane which
is the most common OG and a greenhouse gas that is sometimes excluded from the
analysis of organic compounds.
THC - Organic compounds in exhaust, as measured by a flame ionization detector
(FID) per the International Civil Aviation Organization's (ICAO's) Annex 16.19
Notably, a FID does not accurately measure all of the mass of oxygenated OG, which
influences the abundances of specific chemical compounds relative to the total in the
measured exhaust. This is important because these abundances dictate the amounts of
each speciated compound in the exhaust plume
VOC - VOC is defined by EPA as any compound of carbon that participates in
atmospheric photochemical reactions. For aircraft, this is further defined as exhaust
TOG corrected to exclude the mass of methane, ethane, and acetone and to fully
on
account for the mass of formaldehyde and acetaldehyde [U.S. EPA 2007]. Notably,
additional compounds are excluded/exempt from this group of OG when sources
other than aircraft engines are being considered. VOC also excludes carbon
monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and
ammonium carbonate.
18 Also referred to as total organic compounds (TOC) when discussed in an air quality context.
19 ICAO's Annex 16 addresses protection of the environment from the effect of aircraft noise and aircraft engine
emissions.
20 Per the EPA definition of VOC at http://www.epa. gov/ttn/naaqs/ozone/ozonetech/def voc.htm
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This graphic illustrates the following relationships between
these "groups" of organic gases: TOG, NMOG. THC, and
VOC.
TOG includes all compounds
If hydrocarbons are measured by a FID, not all
the mass of acetone and oxygenated
hydrocarbons are measured. The mass that is
measured is known as THC.
If methane is removed from TOG, the collective
remaining gases are known as NMOG.
If methane, acetone, and ethane are removed
from TOG, the collective remaining compounds
are known as VOC.
Non-Methane
Organic Gas
(NMOG)
Ail other organic gases
Figure 1
Groups of OGs
Total
Organic Gas .. .--?
(TOG)
All other organic gases
Oxygenated '
/Organic Compounds
-. -
/""Other
( Excluded/'
\ Exempts/
Other
Excluded/'
Exempts
Oxygenated .
.Organic Compounds,
' as measured by a FID (which
measures cncfgsnates wi'ffl a
reduced sensitivity}
" see 40 CFR 51.100 for Us of
other excluded organic compounds
dea because they have ftegiigiblB
photochemical reactivity}
;' Methane ';
Total
/ Hydrocarbons*
(THC)
All other organic gases
Oxygenated
'Organic Compounds*1'
Volatile {
Organic
Compounds**
(VOC)
All other organic gases
Other
Excluded/
Exempts
Acetone* i /
Oxygenated
/Organic Compounds,
" Other \
Excluded/')
".Exempts**7
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Unlike emissions from other transportation sources, international certification standards
require that OG emissions from newly certified aircraft engines be reported in units of
methane equivalency.21 As part of the effort to develop an approach to quantifying
individual OG and HAPs species, the OG, in methane equivalency, is converted to TOG
according to the average molecular weight of the entire specific profile (discussed in more
detail in the Technical Support Document) listed in Table 1. The derivations of conversion
factors for various types of defined OGs are discussed in a companion spreadsheet to this
document that is entitled Aircraft Engine Speciated Hydrocarbons: Speciation Profile
Spreadsheet [Miake-Lye, 2008]. The factors for converting THC to TOG, VOC to TOG and
factors to/from the other groups of organic compounds are provided in Table 4.
Table 4. Conversion Factors"
THC to
TOG
1.16
VOC to
TOG
1.01
THC to
NMOG
1.16
THC to
VOC
1.15
NMOG to
TOG
1.00
TOG to
VOC
0.99
TOG to
NMOG
1.00
a For the purpose of reporting, application, and comparison, the units for the compounds in this
table are referenced as follows: THC measured as methane equivalent (following procedures
established by ICAO's Committee on Aviation Environmental Protection (CAEP)) , TOG as
TOG, VOC as VOC, and NMOG as NMOG (see Technical Support Document for additional
information).
Source: Aircraft Engine Speciated Hydrocarbons: Speciation Profile Spreadsheet, Miake-Lye,
2008.
It should be noted that the conversion factors in Table 4 supersede all factors previously
published by the EPA for aircraft. These conversion factors are needed because the EPA
National Emissions Inventory (NEI) reports emissions as VOC, rather than THC, which is
the mass of hydrocarbons measured by a Flame lonization Detector (FID). The FID does not
accurately measure the mass of some compounds, such as formaldehyde and acetaldehyde
(oxygenated OGs). VOC as defined above excludes methane. The turbine engine aircraft
emissions profile presented in this RBP does not include methane. When a detailed
quantification of methane is made in the future, the measured levels will be used to better
identify all of the emissions that occur at low power. It is worth noting, however, that
consumption of methane at high powers more than compensates for production of this
compound at low powers, so the net budget of methane will indicate consumption and it will
not be an important aircraft engine emission. Regardless, quantifying the amount of methane
in aircraft engine exhaust will provide a more complete speciation of idle emissions.
Previously there were slightly different profiles for commercial, military, air taxi and general
aviation turbine engine aircraft, due to different time in mode (TIM) estimates. Currently, it
is recommended that one profile be used for all aircraft equipped with turbofan, turbojet, and
turboprop engines, regardless of aircraft classification. A key difference between the old and
new profiles is that while methane was previously assumed to be about 9 percent of
hydrocarbon exhaust, methane is no longer considered to be an emission from aircraft gas
turbine engines burning Jet A at higher power settings and is, in fact, consumed in net at
these higher powers. This is an area of continuing scientific researchthe results of which
Procedures in the Emissions Certification of Aircraft Engines, Annex 16, Volume II, International Civil
Aviation Organization, www.icao.int
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will clarify if methane emissions are significant at lower power settings and should thereby
be considered in fully speciating the low power emissions profile. FAA and EPA agree to re-
visit the development of an organic profile that reflects these developments as the data
becomes available. [Knighton, Herndon, Miake-Lye, 2008].
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4.0 EMISSION INVENTORIES
This section describes the recommended steps to prepare an emission inventory of speciated
OGs, including HAPs, for commercial, military, general aviation, and air taxi aircraft that are
equipped with turbofan, turbojet, and turboprop engines. The emission inventories discussed
in this document provide an estimation of the speciated OG and HAPs associated with
aircraft activity. The results of the aircraft engine-related emission inventories are typically
expressed in units of pounds per day or tons per year for each pollutant.22
4.1 Aircraft Operational Data
The aircraft operational characteristics that are of primary significance for preparation of an
emissions inventory of ground-based pollutants and pollutants below the atmospheric mixing
height are:
The number of aircraft operations (i.e., landings and takeoffs) by aircraft type,
The type and number of aircraft engines, and
Times-in-mode for each of the aircraft operational modes (i.e., approach, taxi-in, taxi-
T\ 1A
out, idle (delay), takeoff, and climbout) within the atmospheric mixing zone. '
Some of this data are available from airport planning and design documents. Certain data
(i.e., times-in-mode for the landing/take off cycle) may also be acquired from aircraft
performance manuals, airport-specific data, and the FAA's Aviation System Performance
Metrics (ASPM) database, Terminal Area Forecast (TAP) and/or Emissions and Dispersion
Modeling System (EDMS) model.
4.2 Calculating THC, VOC, or NMOG Emissions
For each unique aircraft/engine combination, air quality practitioners will first prepare an
emissions inventory for THC, VOC, or NMOG emissions. The inventories can be prepared
using either the FAA's EDMS model or by manual calculation using the EDMS database or
ICAO's Engine Exhaust Emissions Databank.25
For commercial aircraft, the easiest way to obtain an estimate of these emissions is to use
FAA's EDMS model. For demonstrative purposes, the following example shows how to
obtain an estimate of THC emissions using ICAO data. Estimates of THC are calculated
22 The emission inventory results can also be expressed in metric system equivalents (e.g., kilograms per day).
23 The time spent in the approach and climbout modes of the landing/take-off cycle is directly related to the
height of the "mixing zone." The mixing zone is the layer of the earth's atmosphere where air is completely
mixed and pollutants emitted anywhere within the layer will be carried down to the ground level. The height of
the mixing zone for a given location typically varies by season and time of day.
24 Aircraft also emit OG during "start-up". These emissions are will be addressed through future research and
included in updates to this document (including updates to the speciation profile at the time such an update is
appropriate.
25 The ICAO Engine Exhaust Emissions Databank is available at
http://www.caa.co.uk/defaultaspx?catid=702&pagetype=90 .
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based on the amount of fuel consumed by an aircraft in each of the aircraft operational modes
and engine-specific THC emission indices (specific to each aircraft operational mode).
4.2.1 Example THC Calculation
An air quality practitioner is charged with speciating aircraft-related THC emissions for an
Airbus A320-100 equipped with two CFM56-5A1 turbofan engines. Over the period of
interest, the A320-100 performs 1,000 operations (500 landing-takeoff cycles). Based on the
configuration of the airport and field surveys, each aircraft has an average combined taxi/idle
(delay) time of 26 minutes per landing-takeoff cycle (a taxi in time of 7 minutes and a taxi-
out time, including delay, of 19 minutes). This aircraft and operational data are summarized
in Table 5.
Table 5. Example Aircraft Operational Data
Aircraft
Engine
Number
of
Engines
Number of Operations3
Taxi Time
(Minutes)
In
Out
Airbus A320-100 CFM56-5A1
1,000
19
1,000 operations equals 500 landing-takeoff cycles or 500 arrivals and 500 departures.
The fuel flow rates and THC emission indices for the CFM56-5 Al are provided in Table 6.
Table 6: Example Fuel Flow Rates/Emission Indices
Data
Fuel Flow Rate
(kilograms/second)
THC Emission Indices
(grams/kilogram of fuel)
Aircraft Operational Mode
Takeoff
1.05100
0.2300
Climbout
0.86200
0.2300
Approach
0.29100
0.4000
Idle
0.10110
1.4000
Assuming a scenario specific atmospheric mixing height26 and using the aircraft operational
data (i.e., number of arrivals, number of departures, times-in-mode) and the base data (i.e.,
fuel flow rates and THC emission indices), the THC emissions, by aircraft operational mode
is calculated, are calculated, and then summed for each mode, as detailed in Equations No. 1
and 2.27
The national default atmospheric mixing height is 3,000 feet. Site-specific data should be used when such
data is readily available.
27 Notably, HAPs emissions are greatest during the taxi and idle aircraft operational modes and emissions
attributable to the approach and climbout modes will vary depending on the scenario specific atmospheric
mixing height.
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Equation No. 1:
Fuel Consumption By Aircraft Operational Mode
Fuel Flow Rate for Operational Mode (kg/sec) x Time-in-Mode (sees)
Total Fuel Consumption/Engine for Operational Mode (kg)
Equation No. 2:
THC Emissions By Aircraft Operational Mode
Total Fuel Consumption for Operational Mode (kg) x THC Emission Indices (g/1000 kg of fuel) x
Number of Engines x Number of Operations x kg/1000 g
= THC Emissions by Mode (kg)
For the A320 aircraft example, the fuel flow rate and THC emission indices are provided in
Table 7. The estimated level of THC from each of the aircraft operational modes and the
THC for all of the A320 activity (all 1,000 operations or 500 landing-takeoff cycles) is also
provided. As shown, the level of THC varies substantially depending on the aircraft
operational mode with emissions being the highest during the taxi in and taxi out modes and
the lowest during approach, takeoff, and climbout.
Table 7. Example THC Estimate
Fuel Flow Rate
(Per Engine)3
Modeb
Approach
Taxi In
Taxi Out
Takeoff
Climbout
Total
Rate
(kg/sec)
0.29100
0.10110
0.10110
1.05100
0.86200
~
Time
in
Mode
(rnins)3
4.12
7.00
19.00
1.51
0.53
~
Fuel
Consumption
(Per Engine
Per Operation
-kg)
71.935
42.562
115.254
95.221
27.412
~
THC
Emission
Indices
(g/kg Fuel
Consumed)3
0.40
1.40
1.40
0.23
0.23
~
Number of
Engines
2
2
2
2
2
~
Operations
500
500
500
500
500
~
THC (kg)
28.77
59.45
161.36
21.90
6.30
277.78
a Obtained from FAA's EDMS databases.
b This example does not include data and/or assumptions for auxiliary power units.
As shown in Table 7, 277.78 kg of THC emissions are estimated to result from the
operations performed by the Airbus A320-100.
4.3 Converting to TOG
As previously stated, the profile data in Table 1 should be applied to inventories of TOG to
obtain estimates of individual (speciated) OGs. Before applying the profile data to an
estimate of THC emissions (or NMOG or VOC), the THC must first be converted to TOG.
This application is detailed in Equation No. 3.
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Equation No. 3:
Conversion to TOG
THC Emissions (kg) x TOG Conversion Factor = TOG (kg)
As shown in Table 4, the THC to TOG conversion factor is 1.16. Therefore, the amount of
TOG emitted by the A320 aircraft in this example is an estimated 322.22 kg.
4.4 Applying Speciation Profile Data
To speciate TOG emissions, an air quality practitioner should obtain the latest OG speciation
profile (from Table 1 or from the FAA/EPA websites). To derive the emission rates for an
individual OG, the mass fractions in the profiles are multiplied by the total amount of TOG.
The calculation for obtaining the estimated emission rate for an individual OG and/or HAP is
provided in Equation No. 4.
Equation No. 4:
Computing Speciated Aircraft OG Emissions Using TOG
TOG (kg) x Speciation Profile j (mass fraction) = OGj (kg)
Where: i = OG of interest
For illustrative purposes, Table 8 provides the OG emission estimate for the A320 example
for three individual OG/HAPs (the table does not include all of the speciated OGs in Table
1). The three OGs/HAPs are ethylene, formaldehyde, and toluene.
Table 8. Example Speciated OG Emission Levels
Aircraft Type
A320-100
Engine Type
/No. of
Engines
CFM-56 / 2
TOG
(kg)
322.22
OG
ethylene
formaldehyde
toluene
Speciation
Profile
(mass fraction)
0.15459
0.12308
0.00642
OG Emission
Inventory
(kg)
49.81
39.66
2.09
As shown in Table 8, the estimated emission rates for ethylene, formaldehyde, and toluene
emissions are approximately 50, 40, and 2 kg, respectively, for the A320 example.
4.5 Presentation of Results
The emissions inventory provides an estimate of the amount of aircraft-related HAPs emitted
in the timeframe of the inventory. For consistency with emission inventories that are
prepared for the EPA criteria air pollutants, the results should be expressed in units of tons or
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pounds per year or pounds per day or as equivalent metric system units. Because the output
data can be overly complex and voluminous, the data are most conveniently presented in
tabular form. Table 9 provides a sample table format for presenting the aircraft-related
OG/HAP emission estimates. The format of Table 1 (including CAS Registry numbers) may
also be used.
Table 9. Example Format for Reporting Speciated OGs
Year
2008
OG
ethylene
formaldehyde
toluene
Estimated
Emissions
(kg)
50
40
2
Depending on the purpose and scope of the assessment, the results can be further segregated
by analysis year, airport operational level or project alternative. For reviewing purposes, the
emission estimation results should be accompanied by 1) a summary explanation of how the
assessment was conducted (information and data sources, major assumptions, computational
methods), 2) how the results are interpreted or compared (between alternatives or compared
to any applicable significance criteria) and 3) any noteworthy limitations to the
understanding and application of the outcome(s).
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LIST OF REFERENCES
CAA, 1977, 42 U.S.C. 7401 to 771q, Clean Air Act.
CARB, 2000, FACT SHEET #1: Development of Organic Emission Estimates For
California's Emission Inventory and Air Quality Models, August.
CARB, 2000, Statewide Air Pollution Research Center 1999 Mechanism (SAPRC99), May.
FAA, 2007, Emissions and Dispersion Modeling System (EDMS) User's Manual, FAA Office of
Environment and Energy, prepared by CSSI, Inc., January.
FAA and U.S. EPA, 2008, Quality Assurance Project Plan for the Development of a Commercial
Aircraft Hazardous Air Pollutants Emission Inventory Methodology, prepared by KB
Environmental Sciences, Inc., March 31.
Gery et al, 1988, 1989. Carbon Bond IV Mechanism (CB4).
ICAO, Annex 16, Volume II - Aircraft Engine Emissions.
Knighton, W. B., Herndon, S.C., and Miake-Lye, R.C. (2009). Aircraft Engine Speciated
Organic Gases: Speciation of Unburned Organic Gases in Aircraft Exhaust.
Lobo, P., et al., 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.
Stockwell, Regional Atmospheric Chemistry Mechanism (RADM-2), 1997.
Systems Applications International, An Updated Photochemical Mechanism for Modeling Urban
and Regional Air Quality: Carbon Bond, Version 5 (CB-V), December 4, 2002.
USAF, 1984, Composition and Photochemical Reactivity of Turbine Engine Exhaust, prepared
by Battelle Laboratories, prepared for the Air Force Engineering and Services Center,
September.
USAF, 1987'a, Aircraft Emissions Characterization: TF41-A2, TF30-P103, and TF30-P109
Engines, December (Spicer et. al.)
USAF, 1987b, Aircraft Emissions Characterization: TF33-P3, TF33-P7, and J79 (Smokeless)
Engines, August (Spicer et.al)
USAF, 1990, Aircraft Emissions Characterization: F101 andFllO Engines, March (Spicer et.al)
USAF, 1994, Developing an Emission Factor for Hazardous Air Pollutants for an F-16 Using
JP-8Fuel, U.S. Air Force, September 1994
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USAF, 1999a, Aircraft Engine and Auxiliary Power Unit Emissions Testing; Volume 1,
Executive Summary. U.S. Air Force, March 1999 (Gerstle, Virag, Wade, Kimm)
USAF, 1999b, Aircraft Engine and Auxiliary Power Unit Emissions Testing; Volume 2, Detailed
Sampling Approach and Results. March 1999 (Gerstle, Virag, Wade, Kimm)
USAF, 1999c, Aircraft Engine and Auxiliary Power Unit Emissions Testing; Volume 3,
Particulate Matter Results, U.S. Air Force, March 1999 (Gerstle, Virag, Wade, Kimm)
USAF, 2002, Aircraft Engine and Auxiliary Power Unit Emissions Testing: Final Report.
Addendum. F199-PW-100 Engine Emissions Testing Report, June 2002 (Gerstle, Virag,
Wade, Kimm)
U.S. EPA, 2000, Compilation of Air Pollutant Emission Factors., AP-42, November.
Wey, C. C. et al, 2006. Aircraft particle emissions experiment (APEX). NASA TM-2006-
214382, September.
U.S. EPA, 2006, SPECIATE 4.0, Speciation Database Development Documentation, Final
Report, November.
U.S. EPA, 2007, Converting Aircraft Total Hydrocarbons (THC) to VOC, Memorandum from
Rich Cook to Bryan Manning, National Vehicle and Fuel Emissions Laboratory, Office of
Transportation and Air Quality, June 27.
U.S. EPA. Integrated Risk Information System (IRIS). [Online] Available
http://cfpub.epa.gov/ncea/iris/index.cfm. June 2, 2008.
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