Summarizing and Interpreting Aircraft Gaseous and Particulate Emissions Data (2008)

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33 Advected plume—wind-transported exhaust plume, sub- jected to local meteorological conditions. Aircraft gas turbine engine1—any gas turbine engine used for aircraft propulsion or for power generation on an air- craft, including those commonly called turbojet, turbofan, turboprop, or turboshaft type engines. Classical aerodynamic diameter1—the diameter of an equiv- alent unit density sphere with the same settling velocity in still air as the particle in question. Coarse particle2—particle with a classical aerodynamic di- ameter between 2.5 and 10 μm. Deposition—an airborne pollutant that reaches the ground by force of gravity, rain, or attaching to other particles. Elemental carbon—the refractory carbon found in combustion-generated particulate matter; 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 diame- ter 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 the EPA to regulate. For the complete list of pollutants see Appendix C: The Clean Air Act Amendments of 1990 List of Hazardous Air Pollutants found on the EPA website: http://www.epa. gov/ttn/atw/orig189.html. Line loss—percent of particles lost during transit through a given sample line. Particle loss mechanisms include impaction, diffusion, settling (gravitational), and ther- mophoresis (thermodiffusion). Lognormal3—a normal distribution of the logarithm of a random variable. Mass-based emission index—the mass of emissions of a given constituent per thousand mass units of fuel burned (e.g., g/kg fuel); also total mass of particulate emissions in the same units. Normal distribution2—a probability density function that approximates the distribution of many random variables (as the proportion of outcomes of a particular sort in a large number of independent repetitions of an experiment in which the probabilities remain constant from trial to trial) and that has the form f(x) = (1/(σ ))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 public roadways such as airport ground support equip- ment, lawn mowers, etc. Non-volatile particles1—particles that exist at engine exit plane temperature and pressure conditions. Nucleation4—the process of initial formation of a particle from vapor. This process is usually facilitated by the pres- ence of small particles called condensation nuclei, which serve as sites for condensation. Organic carbon—often abbreviated as OC, is a major com- ponent of particulate carbon and is composed of many compounds most of which partition between the gas and aerosol phases at ambient conditions. Parameterization—expression in terms of statistically repre- sentative characteristics. Parts per million (ppm)—the unit volume concentration of a gas per million unit volumes of the gas mixture of which 2π A P P E N D I X B Glossary of Terms 1 Definition from Society of Automotive Engineers Aerospace Information Re- port 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 by Merriam-Webster, Incorporated. 4 Definition from Baron P.A. and Willeke K. (eds), Aerosol Measurement Princi- ples, Techniques and Applications, 2nd ed., John Wiley & Sons, New York, 2001.

it is part; also applicable to mass measurements as referred to as ppmm. Photochemical—the interaction of atoms, molecules, and light. PM10, PM2.5—regulatory designations of particulate matter less than or equal to 10 μm, and 2.5 μm, respectively, in diame- ter; these measures are similar to the terms coarse, and fine, respectively. Primary particle—a particle that is emitted directly from the source. Refractory—resistant to heat: non-volatile. Secondary particle—a particle that forms as the result of a chemical reaction or other means by combining with other elements after leaving the source. These particles form on the timescales of minutes to days and may continue to form in air masses moving hundreds of kilometers from the source. Smoke—small gas-borne solid particles, including but not limited to black carbonaceous material from the burning of fuel, which in sufficient concentration create visible opacity. Smoke number—often abbreviated as SN, the dimensionless term quantifying smoke emission and is determined using the SAE Aerospace Recommended Practice–1179. 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. Soluble mass fraction—the fraction of the aerosol mass that is soluble in water. SUMMA canister—an airtight, stainless-steel vessel whose internal surface has been passivated using a SUMMA process, which combines an electro-polishing step with chemical deactivation, to produce a surface that is chemi- cally inert. Total carbon1—the sum of elemental carbon and organic carbon. Transients—a momentary or temporary variation in a vari- able of interest (e.g., engine power, ambient pressure, temperature). Ultrafine particles—particles with a classical aerodynamic diameter of less than 1.0 μm. Volatile particles1—particles formed from condensable gases after the exhaust has been cooled to below engine exit conditions. 34