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33 APPENDIX B Glossary of Terms Advected plume--wind-transported exhaust plume, sub- impaction, diffusion, settling (gravitational), and ther- jected to local meteorological conditions. mophoresis (thermodiffusion). Aircraft gas turbine engine1--any gas turbine engine used Lognormal3--a normal distribution of the logarithm of a for aircraft propulsion or for power generation on an air- random variable. craft, including those commonly called turbojet, turbofan, Mass-based emission index--the mass of emissions of a turboprop, or turboshaft type engines. given constituent per thousand mass units of fuel burned Classical aerodynamic diameter1--the diameter of an equiv- (e.g., g/kg fuel); also total mass of particulate emissions in alent unit density sphere with the same settling velocity in the same units. still air as the particle in question. Normal distribution2--a probability density function that Coarse particle2--particle with a classical aerodynamic di- approximates the distribution of many random variables ameter between 2.5 and 10 m. (as the proportion of outcomes of a particular sort in a large Deposition--an airborne pollutant that reaches the number of independent repetitions of an experiment in ground by force of gravity, rain, or attaching to other which the probabilities remain constant from trial to trial) particles. and that has the form f(x) = (1/( 2 ))e(-1/2[(x - )/]2) where Elemental carbon--the refractory carbon found in is the mean and is the standard deviation. combustion-generated particulate matter; also known as Nonroad--mobile emission sources not commonly operated graphitic carbon. on public roadways such as airport ground support equip- Engine exit plane--any point within the area of the engine ment, lawn mowers, etc. exhaust nozzle at an axial distance within 0.5 diameters Non-volatile particles1--particles that exist at engine exit (or equivalent, if not circular) downstream from the outer plane temperature and pressure conditions. edge of the nozzle. Nucleation4--the process of initial formation of a particle Fine particle2--particle with a classical aerodynamic diame- from vapor. This process is usually facilitated by the pres- ter less than 2.5 m. ence of small particles called condensation nuclei, which Geometric mean2--the nth root of the product of n numbers. serve as sites for condensation. HAPs - Hazardous air pollutants--188 pollutants that the Organic carbon--often abbreviated as OC, is a major com- Clean Air Act Amendments of 1990 required the EPA to ponent of particulate carbon and is composed of many regulate. For the complete list of pollutants see Appendix C: compounds most of which partition between the gas and The Clean Air Act Amendments of 1990 List of Hazardous aerosol phases at ambient conditions. Air Pollutants found on the EPA website: http://www.epa. Parameterization--expression in terms of statistically repre- gov/ttn/atw/orig189.html. sentative characteristics. Line loss--percent of particles lost during transit through Parts per million (ppm)--the unit volume concentration of a given sample line. Particle loss mechanisms include a gas per million unit volumes of the gas mixture of which 3 Definition from Merriam-Webster Online Dictionary, copyright 2005 by 1 Definition from Society of Automotive Engineers Aerospace Information Re- Merriam-Webster, Incorporated. port 5892, copyright 2007, Society of Automotive Engineers. 4 Definition from Baron P.A. and Willeke K. (eds), Aerosol Measurement Princi- 2 Definition from ples, Techniques and Applications, 2nd ed., John Wiley & Sons, New York, 2001.

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34 it is part; also applicable to mass measurements as referred using the SAE Aerospace Recommended Practice1179. to as ppmm. SN increases with smoke density and is rated on a scale Photochemical--the interaction of atoms, molecules, and from 0 to 100. SN is evaluated for a sample size of 16.2 kg light. of exhaust gas/m2 (0.0239 lb/in2) of filter area. PM10, PM2.5--regulatory designations of particulate matter less Soluble mass fraction--the fraction of the aerosol mass that than or equal to 10 m, and 2.5 m, respectively, in diame- is soluble in water. ter; these measures are similar to the terms coarse, and fine, SUMMA canister--an airtight, stainless-steel vessel whose respectively. internal surface has been passivated using a SUMMA Primary particle--a particle that is emitted directly from the process, which combines an electro-polishing step with source. chemical deactivation, to produce a surface that is chemi- Refractory--resistant to heat: non-volatile. cally inert. Secondary particle--a particle that forms as the result of a Total carbon1--the sum of elemental carbon and organic chemical reaction or other means by combining with other carbon. elements after leaving the source. These particles form on the Transients--a momentary or temporary variation in a vari- timescales of minutes to days and may continue to form in able of interest (e.g., engine power, ambient pressure, air masses moving hundreds of kilometers from the source. temperature). Smoke--small gas-borne solid particles, including but not Ultrafine particles--particles with a classical aerodynamic limited to black carbonaceous material from the burning of diameter of less than 1.0 m. fuel, which in sufficient concentration create visible opacity. Volatile particles1--particles formed from condensable Smoke number--often abbreviated as SN, the dimensionless gases after the exhaust has been cooled to below engine term quantifying smoke emission and is determined exit conditions.