Recommended Best Practice for 

Quantifying Speciated Organic Gas 

Emissions from Aircraft Equipped with 

Turbofan, Turbojet, and Turboprop 

Engines 

Version 1.0 
Recommended Best Practice for 


Quantifying Speciated Organic Gas 


Emissions from Aircraft Equipped with 


Turbofan, Turbojet, and Turboprop 


Engines


Version 1.0 

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 
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 Iovinelli, 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 

CSSI’s Contract DTFAWA-05-C-00044, Technical Directive Memorandum B-002-011. 
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.
 3 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 
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. 

5

 See www.FAA.gov/regulations_policies/policy_guidance/envir_policy/ and www.EPA.gov/otaq/aviation.htm 6

 USEPA. SPECIATE Version 4.0 (www.epa.gov/ttn/chief/software/speciate/index.html), December 2006. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 
ACRONYMS AND ABBREVIATIONS
 

AEE 

APEX 

ASPM 

CAA 

CAEP 

CARB 

CAS 

DoD 

EDMS 

EPA 

FAA 

FID 

HAPs 

HC 

ICAO 

IRIS 

JETS 

kg 

LTO 

NASA 

NEI 

NMOG 

OG 

OTAQ 

QAPP 

RBP 

SAPRC99 

SPECIATE 

TAC 

TAF 

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 Ionization 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 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 
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 SPECIATED OG 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. Page 

1 Groups of OGs ..............................................................................................................10 
 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice i 
1.0 INTRODUCTION
 

This document presents an Purpose of this 

approach for quantification of 

speciated organic gas (OG) Recommended Best Practice (RBP) 

To provide a uniform approach to, and technical 

emissions, including hazardous air 

support for, the preparation of speciated gas-phase 

pollutants (HAPs), from HC inventories (including HAPs) from aircraft 

commercial aircraft equipped with 

equipped with turbofan, turbojet, and turboprop turbofan, turbojet, and turboprop 

engines.

1,2,3,4

 The preparation of an 

engines. 

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 database

5

, 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.html), December 2006. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 1 
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 2 
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 gasphase 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 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 3 
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/regulations_policies/policy_guidance/envir_policy/ 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. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 4 
Table 1. Speciated Gas-Phase OG Profile for Aircraft Equipped with
 

Turbofan, Turbojet, and Turboprop Engines.

c
 

Compound CAS 

Registry No.

a 

Mass 

Fraction

 Compound CAS 

Registry No.

a 

Mass 

Fraction 

1,2,3-trimethylbenzene 526-73-8 0.00106 glyoxal 107-22-2 0.01816 

1,2,4-trimethylbenzene 95-63-6 0.00350 isobutene/1-butene 106-98-9 0.01754 

1,3,5-trimethylbenzene 108-67-8 0.00054 isopropylbenzene d 98-82-8 0.00003 

1,3-butadiene

d 106-99-0 0.01687 isovaleraldehyde 590-86-3 0.00032 

1-decene 872-05-9 0.00185 methacrolein 78-85-3 0.00429 

1-heptene 25339-56-4 0.00438 methanol d 67-56-1 0.01805 

1-hexene 592-41-6 0.00736 methylglyoxal 78-98-8 0.01503 

1-methyl naphthalene 90-12-0 0.00247 m-ethyltoluene 620-14-4 0.00154 

1-nonene 124-11-8 0.00246 m-tolualdehyde 620-23-5 0.00278 

1-octene 25377-83-7 0.00276 m-xylene and 

p-xylene d 

108-38-3 / 

106-42-3 0.00282 

1-pentene 109-67-1 0.00776 naphthalene d 91-20-3 0.00541 

2-methyl-1-butene 563-46-2 0.00140 n-decane 124-18-5 0.00320 

2-methyl-1-pentene 763-29-1 0.00034 n-dodecane 112-40-3 0.00462 

2-methyl-2-butene 513-35-9 0.00185 n-heptadecane 629-78-7 0.00009 

2-methyl-naphthalene e 91-57-6 0.00206 n-heptane 142-82-5 0.00064 

2-methylpentane 107-83-5 0.00408 n-hexadecane 544-76-3 0.00049 

3-methyl-1-butene 563-45-1 0.00112 n-nonane 111-84-2 0.00062 

4-methyl-1-pentene 691-37-2 0.00069 n-octane 111-65-9 0.00062 

acetaldehyde d 75-07-0 0.04272 n-pentadecane 629-62-9 0.00173 

acetone 67-64-1 0.00369 n-pentane 109-66-0 0.00198 

acetylene 74-86-2 0.03939 n-propylbenzene 103-65-1 0.00053 

acrolein d 107-02-8 0.02449 n-tetradecane 629-59-4 0.00416 

benzaldehyde e 100-52-7 0.00470 n-tridecane 629-50-5 0.00535 

benzene d 71-43-2 0.01681 n-undecane 1120-21-4 0.00444 

butyraldehyde 123-72-8 0.00119 o-ethyltoluene 611-14-3 0.00065 

c14-alkane No CAS 0.00186 o-tolualdehyde 529-20-4 0.00230 

c15-alkane No CAS 0.00177 o-xylene d 95-47-6 0.00166 

c16-alkane No CAS 0.00146 p-ethyltoluene 622-96-8 0.00064 

c18-alkane No CAS 0.00002 p-tolualdehyde 104-87-0 0.00048 

c4-benzene + 

c3-aroald No CAS 0.00656 phenol d 108-95-2 0.00726 

c5-benzene + c4-aroald No CAS 0.00324 propane 74-98-6 0.00078 

cis-2-butene 590-18-1 0.00210 propionaldehyde d 123-38-6 0.00727 

cis-2-pentene 627-20-3 0.00276 propylene 115-07-1 0.04534 

crotonaldehyde 4170-30-3 0.01033 styrene d 100-42-5 0.00309 

dimethylnapthalenes 28804-88-8 0.00090 toluene d 108-88-3 0.00642 

ethane 74-84-0 0.00521 trans-2-hexene 4050-45-7 0.00030 

ethylbenzene d 100-41-4 0.00174 trans-2-pentene 646-04-8 0.00359 

ethylenef 74-85-1 0.15461 valeraldehyde 110-62-3 0.00245 

formaldehyde d,f 50-00-0 0.12310 unidentified b NA 0.29213 

Sum of all compounds 1.00000 a

 CAS = Chemical Abstracts Service
 b

 See discussion of unidentified species in Section 2.1 of this report. 
 c

 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.
 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 5 
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 CAS Mass 

Fraction 

C-10 paraffins No CAS 0.14608 

C-10 olefins No CAS 0.05843 

decanal 112-31-2 0.05843 

dodecenal 1127 1786 0.02922 

Total 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: 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 6 
•	 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 Profile Quality 

17-20 A 

13-16 B 

9-12 C 

5-8 D 

<5 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. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 7 
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). 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 8 
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 

account for the mass of formaldehyde and acetaldehyde [U.S. EPA 2007].

20 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
 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 9 
Figure 1 

Groups of OGs

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 
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

a 

THC to 

TOG 

VOC to 

TOG 

THC to 

NMOG 

THC to 

VOC 

NMOG to 

TOG 

TOG to 

VOC 

TOG to 

NMOG 

1.16 1.01 1.16 1.15 1.00 0.99 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 Ionization 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 research—the results of which 

21 Procedures in the Emissions Certification of Aircraft Engines, Annex 16, Volume II, International Civil 

Aviation Organization. www.icao.int 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 11 
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 revisit the development of an organic profile that reflects these developments as the data 

becomes available. [Knighton, Herndon, Miake-Lye, 2008]. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 12 
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, taxiout, idle (delay), takeoff, and climbout) within the atmospheric mixing zone.

23,24 

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 (TAF) 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/default.aspx?catid=702&pagetype=90 . 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 13 
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 taxiout 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 Operations

a 

Taxi Time 

(Minutes) 

In Out 

Airbus A320-100 CFM56-5A1 2 1,000 7 19 a

 1,000 operations equals 500 landing-takeoff cycles or 500 arrivals and 500 departures. 

The fuel flow rates and THC emission indices for the CFM56-5A1 are provided in Table 6. 

Table 6: Example Fuel Flow Rates/Emission Indices 

Aircraft Operational Mode 

Data Takeoff Climbout Approach Idle 

Fuel Flow Rate 

(kilograms/second) 

1.05100 0.86200 0.29100 0.10110 

THC Emission Indices 

(grams/kilogram of fuel) 

0.2300 0.2300 0.4000 1.4000 

Assuming a scenario specific atmospheric mixing height

26 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 

26 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. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 14 
Equation No. 1:
 

Fuel Consumption By Aircraft Operational Mode
 

Fuel Flow Rate for Operational Mode (kg/sec) x Time-in-Mode (secs) =
 

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)

a Time 

in 

Mode 

(mins)

a 

Fuel 

Consumption 

(Per Engine 

Per Operation 

– kg) 

THC 

Emission 

Indices 

(g/kg Fuel 

Consumed)

a 

Number of 

THC (kg) 

Modeb Rate 

(kg/sec) Engines Operations 

Approach 0.29100 4.12 71.935 0.40 2 500 28.77 

Taxi In 0.10110 7.00 42.562 1.40 2 500 59.45 

Taxi Out 0.10110 19.00 115.254 1.40 2 500 161.36 

Takeoff 1.05100 1.51 95.221 0.23 2 500 21.90 

Climbout 0.86200 0.53 27.412 0.23 2 500 6.30 

Total -- -- -- -- -- -- 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. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 15 
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 Profilei (mass fraction) = OGi (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 

Engine Type 

/ No. of 

Engines 

TOG 

(kg) OG 

Speciation 

Profile 

(mass fraction) 

OG Emission 

Inventory 

(kg) 

ethylene 0.15459 49.81 

A320-100 CFM-56 / 2 322.22 formaldehyde 0.12308 39.66 

toluene 0.00642 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 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 16 
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 

OG 

Estimated 

Emissions 

(kg) 

2008 ethylene 50 

formaldehyde 40 

toluene 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). 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 17 
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, 1987a, 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 and F110 Engines, March (Spicer et.al) 

USAF, 1994, Developing an Emission Factor for Hazardous Air Pollutants for an F-16 Using 

JP-8 Fuel, U.S. Air Force, September 1994 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 18 
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. 

Aircraft Speciated Hydrocarbon Emissions Inventories - Recommended Best Practice 19