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Section I
Introduction
This document describes the results and findings of Airport reactive or absorptive losses in the sampling probe are described
Cooperative Research Program (ACRP) Project 02-03a, which in Appendix C. The data collected at the airport fence line
characterized the emissions of gaseous hazardous air pollutants (a mix of aircraft emissions and terminal area emissions) and
(HAPs) from idling aircraft engines during three measure- its potential implications are described in Appendix D. The
ment campaigns. The document begins with a discussion of analytical methods used to characterize the engine exhaust and
the motivation for this project, and a summary of the test plan quality assurance procedures are collected in Appendix E.
and approach is presented in Section II. Section III examines The aircraft exhaust matrix potentially consists of thousands
the effect of fuel flow on emissions. A method for scaling of specific molecules containing carbon, hydrogen, oxygen,
emission indices to reference values is described in order to nitrogen, and sulfur. Sets and subsets of these emitted com-
enable data comparison of different engine technologies and pounds are denoted by various terms. A variety of terms have
different volatile organic compounds (VOCs). The relationship been used to describe the species of interest in this docu-
between emissions and ambient temperature is discussed in ment, including volatile organic compounds, hydrocarbons,
Section IV. unburned hydrocarbons, and partially burned hydrocarbons.
Data from this project, as well as from other complemen- Every attempt has been made in this document to keep
tary projects, have been used to develop a model for emission the language concise and accurate. An important observation
estimates when the engine is operating at near-idle power. drawn from this work and previous measurements is that
The variability observed in the on-wing characterization of trends with near-idle engine state and ambient temperature in
multiple engines will be discussed in the context of overall one volatile organic compound also apply to the compounds
measurement uncertainty. Section V discusses a straight in the other classifications.
forward estimation tool that is based on the analysis of mea-
sured data trends. The estimation tool has direct applicability · A hazardous air pollutant (HAP) is defined by the U.S.
for quantifying emission levels in scenario evaluations and Environmental Protection Agency (EPA) as a compound
airport inventory modeling. The temperature and fuel flow that causes or may cause cancer or other serious health
corrections described here have been applied to a series of effects. EPA lists 187 compounds as HAPs, 15 of which have
digital flight data records collected from in-use operations. been identified in aircraft exhaust.
Additional findings that occurred beyond the initial project · A hydrocarbon (HC) is a chemical compound that contains
statement are also summarized. only carbon and hydrogen.
Section VI includes a discussion of the apparent engine · An unburned hydrocarbon (UHC) refers to the total gas
warm-up effect, the near-idle hydrocarbon emission profile, phase organic carbon content in the exhaust as measured
and the effect of fuel properties on emissions. Section VII by a flame ionization detector. This is the measurement
provides a discussion of the relevance of the project findings reported by ICAO.
to airport practice. · A volatile organic compound (VOC) is defined by EPA as an
Appendix A describes the results of the testing conducted organic compound that participates in atmospheric photo
for this project. The test matrix and test procedures developed chemical reactions. Originally, a VOC was defined based
specifically for the question of addressing near-idle emissions only on volatility, but the current definition makes the term
for on-wing engine testing are described in Appendix B. inaccurate for describing the collection of gas phase organic
The methods employed for sampling specific VOCs without compounds present in aircraft exhaust. Because the term
