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Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2008. Research Needs Associated with Particulate Emissions at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14160.
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Page 33
Page 34
Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2008. Research Needs Associated with Particulate Emissions at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14160.
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Page 34

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33 Advected plume—wind-transported exhaust plume, subject to local meteorological conditions Aircraft gas turbine engine1—any gas turbine engine used for aircraft propulsion or for power generation on an aircraft, including those commonly called turbojet, turbofan, turboprop, or turboshaft type engines Black carbon—nonvolatile diesel particulate matter, often used inter- changeably with soot or elemental carbon (see below), although it is most often used when discussing optical properties Classical aerodynamic diameter1—diameter of an equivalent unit den- sity sphere with the same settling velocity in still air as the particle in question Coarse particle2—particle with a classical aerodynamic diameter be- tween 2.5 and 10 μm Deposition—an airborne pollutant that reaches the ground by force of gravity, rain, or by attaching to other particles EIm1—Emission Index (mass), the mass of emissions of a given con- stituent per thousand mass units of fuel burned (e.g., g/kg fuel); also total mass of particulate emissions in the same units Elemental carbon1—often referred to as EC and frequently used inter- changeably with black carbon and soot, although it is most often used when referring to chemical properties; the refractory carbon found in combustion-generated particulate matter; the portion of a sample of combustion-generated particulate matter that remains after volatile components have been removed; also known as graphitic carbon Engine exit plane—any point within the area of the engine exhaust nozzle at an axial distance within 0.5 diameters (or equivalent, if not circular) downstream from the outer edge of the nozzle Fine particle2—particle with a classical aerodynamic diameter less than 2.5 μm Geometric mean2—the nth root of the product of n numbers HAPs—hazardous air pollutants, 188 pollutants that the Clean Air Act Amendments of 1990 required EPA to regulate; also referred to as “air toxics”; the complete list of pollutants can be found in Appen- dix C: The Clean Air Act Amendments of 1990 List of Hazardous Air Pollutants and on the EPA website: http://www.epa.gov/ttn/atw/ orig189.html; for the purpose of this report, particulate matter, while hazardous and potentially toxic, are not included in the definition of HAPs (See also related report ACRP 02-03, Aircraft and Airport-Related Hazardous Air Pollutants: Research Needs and Analysis) Line loss—percent of particles lost during transit through a given sam- ple line; particle loss mechanisms include impaction, diffusion, settling (gravitational), and thermophoresis (thermodiffusion) Lognormal3—a normal distribution that is the distribution of the logarithm of a random variable Normal distribution2—a probability density function that approximates the distribution of many random variables (as the proportion of out- comes of a particular sort in a large number of independent repeti- tions of an experiment in which the probabilities remain constant from trial to trial) and that has the form f(x) = (1/(σ<sqroot>2π)) e(−1/2[(x - µ)/σ]2 where µ is the mean and σ is the standard deviation Nonroad—mobile emission sources not commonly operated on pub- lic roadways such as airport ground support equipment, lawn mowers, etc. Nonvolatile particles1—particles that exist at engine exit plane tem- perature and pressure conditions Nucleation4—the process of initial formation of a particle from vapor; this process is usually facilitated by the presence of small particles called condensation nuclei, which serve as sites for condensation Organic carbon2—often referred to as OC, is a major component of particulate carbon and is composed of many compounds, most of which partition between the gas and aerosol phases at ambient con- ditions and are referred to as semi-volatile organic compounds (SVOC) (EPA) Parameterization—to express in terms of statistically representative characteristics Parts per million (ppmv) —the unit volume concentration of a gas per million unit volumes of the gas mixture of which it is part; also applicable to mass measurements as referred to as ppmm1 Photochemical—the interaction of atoms, molecules, and light PM10, PM2.5, PM1.0—regulatory designations of particulate matter less than or equal to 10 micrometers, 2.5 micrometers, and 1.0 microm- eters, respectively, in diameter; these measures are similar to the terms coarse, fine, and ultrafine, respectively Primary particle—a particle that is emitted directly from the source Refractory—resistant to heat: nonvolatile Glossary 1 Definition from Society of Automotive Engineers, Aerospace Information Report 5892, copyright © 2007, Society of Automotive Engineers. 2 Definition from http://www.epa.gov/pmdesignations/faq.htm. 3 Definition from Merriam-Webster Online Dictionary, copyright © 2005, Merriam- Webster, Inc. 4 Definition from Baron P.A. and Willeke K. (eds) Aerosol Measurement Princi- ples, Techniques and Applications, 2nd ed., John Wiley and Sons, New York, 2001.

Secondary particle—a particle that forms as the result of a chemical reac- tion or other means by combining with other elements after leaving the source Smoke—Small gas-borne solid particles, including but not limited to black carbonaceous material from the burning of fuel, which in suf- ficient concentration create visible opacity Smoke number (SN)—the dimensionless term quantifying smoke emission; SN increases with smoke density and is rated on a scale from 0 to 100; SN is evaluated for a sample size of 16.2 kg of exhaust gas/m2 (0.0239 lb/in2) of filter area Soot—nonvolatile diesel particulate matter, also referred to as black carbon or elemental carbon (see above) Total carbon1—the sum of elemental carbon and organic carbon Transients—a momentary or temporary variation in a variable of interest, e.g., engine power, ambient pressure, temperature Ultrafine particles—particles with a classical aerodynamic diameter of less than 0.1 μm Volatile particles1—particles formed from condensable gases after the exhaust has been cooled to below engine exit conditions 34

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TRB’s Airport Cooperative Research Program (ACRP) Report 6: Research Needs Associated with Particulate Emissions at Airports examines the state of industry research on aviation-related particulate matter emissions and explores knowledge gaps that existing research has not yet bridged.

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