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3 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