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Instructions,
| Glossary of Terms used in Inhalation Toxicology, Aerosol Measurement, and Pulmonary Biology Note that more than one reference may be used for a term. See references below. Aerodynamic Diameter - The diameter of a unit-density sphere having the same terminal settling velocity as the particle in question. It is used to predict where in the respiratory tract such particles will deposit.1 Aerodynamic (equivalent) diameter - diameter of a unit-density sphere having the same gravitational-settling velocity as the particle in question.1 Aerodynamic diameter takes into account the shape, roughness, and aerodynamic drag of the particle. Used for movement of particles through a gas.2 Aerodynamic particle sizer - A particle spectrometer that uses an acceleration system to differentiate particles by aerodynamic diameter and a laser velocimeter to detect particles.1 Aerosol - An assembly of liquid or solid particles suspended in a gaseous medium long enough to be observed and measured; generally, about 0.001 - 100 um in size.1 Absorption - A process whereby gas or vapor molecules are transferred to the liquid phase.1 Adsorption - Transfer of gas or vapor molecules from the surrounding gas to a solid surface.1 Agglomerate - A group of particles held together by van der Waals forces or surface tension.1 Alveolar - Part of the respiratory system in which gas exchange occurs; alveoli are small sacs at the end of the bronchioles lined on the gas side by Types 1 and 2 epithelial cells. Ambient air - surrounding air1 Anisoaxial sampling -Sampling conditions in which the air flowing into an inlet has a different direction from the ambient air flow.1 Atomizer - A device used to produce droplets by mechanical disruption of a bulk liquid.1 Bimodal size distribution - Particle size distribution with two distinct maxima.1 Bioaerosol - an aerosol of solid or liquid particles consisting of, or containing, biologically-viable organisms (viruses, bacteria, allergans, fungi, etc.), with size ranging from sub-micrometer to greater than 100um.3 Bipolar ion field - Region in which ions of both polarities exist.1 Boltzmann charge distribution - Residual or minimum charge distribution on particles after exposure to a bipolar ion field .1 Boundary Layer - Region of flow near the bounding surface, where the flow is dominated by friction forces resulting in reduced flow velocity.1 Breathing zone sample - A sample taken as close as possible to the point at which the subject inhales air; represents a subject's inhaled air.1 Brunauer-Emmett-Teller (BET) - An approach to measure the surface area of particles. The amount of material required to cover the particles with a single layer of molecules. It may be done with low-temperature adsorption of nitrogen or an inert gas from the vapor phase.4 Bronchoalveolar lavage fluid (BALF) - the fluid obtained by washing out the lungs for cytologic and enzymatic analyses. Brownian Motion - Random motion of particles due to collisions with gas molecules.1 Bubble meter - a tube with a defined volume into which bubbles are injected to measure flow rate.1 Capillary pore filter - a filter consisting of a solid membrane with an array of cylindrical holes of uniform size penetrating the membrane.1 Cascade impactor - a device that uses a series of impaction stages with decreasing particle cut size so that particles can be separated into relatively narrow intervals of aerodynamic diameter; used for measuring the aerodynamic size distribution of an aerosol.1 Concentration - Amount of a given test article in a given volume of air (e.g., mg/L, mg/m3, pr ppm) Can also be in water or other material. Condensation - A physical process with more vapor molecules arriving at particle's surface than leaving the surface, resulting in a net growth of the particle.1 Condensation nuclei counter - A device in which submicrometer-sized particles are grown by vapor supersaturation to a larger size and are detected by light scattering. 1 Critical orifice - A very small hole through which there will be constant airflow with even higher head pressure after a sufficient pressure drop across the orifice causes sonic flow. Cutoff particle diameter - Median diameter of a range of particle sizes which will impact on a stage of a cascade impactor; also call 50% cut point, d50, or the effective cutoff diameter.1 Cyclone - A device in which particles are removed by centrifugal forces in a cyclonic path.1 Dust - an aerosol consisting of solid particles made airborne by the mechanical disintegration of bulk solid material (e.g., during cutting, crushing, grinding, abrasion, transportation, etc.), with sizes ranging from as low as sub-micrometer (um) to over 100um. Dependent upon particles being airborne. Fine Particle- Particles less than about 2 um in size, consisting of particles in the nuclei and accumulation modes; term used in describing atmospheric aerosols.1 Filter - A porous membrane or mat of fibers used to collect particles from the air.1 Filter, glass fiber - Made with combination of finely spun borosilicate glass fibers with a binder and compressed into a thin mat; exhibit low water uptake, low head loss, and high capture efficiency for particles larger than 0.3 um. Specified by EPA for measuring total suspended particulate matter in the National Air Sampling Network.2 Fume - an aerosol consisting of small solid particles produced by the condensation of vapors or gaseous combustion products. Usually, such particles are aggregates made up from large numbers of very small primary particles, with the individual units having dimensions of the order of a few nanometers (nm) and upwards although less than 1um.3 Geometric standard deviation - A measure of dispersion in a lognormal distribution (always greater than or equal to 1.0).1 Impactor - A device in which aerosol particles with sufficiently high inertia in a deflected air stream are impacted onto a surface.1 Impinger - A device in which particles are removed by impacting the aerosol particles into a liquid.1 Inhalable - Fraction of an aerosol that can enter the human respiratory system.1 Inhalable particles - Those materials that are deposited anywhere in the respiratory tract. Jet nebulizer - A nebulizer employing air pressure to aerosolize a bulk liquid.1 LALN - Lung associated lymph nodes. Laminar flow - Gas flow with a smooth, nonturbulent pattern of streamlines, with no streamline looping back on itself; usually occurs at very low Reynolds numbers.1 LC50 - The statistically derived median lethal concentration, it is the concentration of a test material that can be expected to cause 50% mortality in a group of test animals for a given duration. Usually associated with an exposure duration, e.g. 4-hour LC50. Lognormal size distribution - Particle size distribution characterized by a bell-shaped or Gaussian distribution shape when plotted on a logarithmic-size scale.1 Lower respiratory tract - Those structures of the respiratory tract below the larynx. Mass (equivalent) diameter - diameter of a sphere composed of the particle bulk material with no voids that has the same mass as the particle in question.1 Mass median aerodynamic diameter - (MMAD) - The geometric mean aerodynamic diameter. Fifty per cent of the particles by weight will be smaller that the MMAD, 50% will be larger. Minute volume - The average volume of air (or gas) inspired or exhaled per minute. For physiological evaluations, expired minute volume is usually expressed as BTPS conditions. For calculating estimated doses, inspired minute volumes are usually expressed as ATPD. Expired minute volumes are slightly less than inspired minute volumes. Mist - A liquid particle aerosol, typically formed by physical shearing of liquids, such as in nebulization, spraying, or bubbling.1 Mobility (equivalent) diameter - Diameter of a spherical particle with the same dynamic mobility as the particle in question1 Monodisperse Distribution - A distribution of particles with a single size or a small range of sizes.1 Nasopharyngeal compartment - A portion of the respiratory tract between the epiglottis and the anterior nares.1 Nebulizer - A device in which droplet aerosols are produced by dispersion of a bulk liquid.1 Nominal Concentration - A gross estimate of exposure concentration based upon test material usage. The total amount of test material used during a given exposure day divided by the total volume of air passed through the chamber during the exposure. Normal distribution - particle size distribution characterized by a bell-shaped or Gaussian distribution shape when plotted on a linear scale.1 Orifice meter - A device used to measure flow rate in a duct by measuring the pressure drop across a calibrated constriction.1 Also known as a variable pressure meter; the flow rate is a function of the pressure drop across a constriction (orifice) in the flow stream and the size of the orifice.2 Open-face sampler - A filter cassette sampler with the inlet approximately the same size as the filter.1 Particle - A small discrete object, often having a density approaching the intrinsic density of the bulk material; it may be chemically homogeneous or contain a variety of chemical species; it may consist of solid or liquid materials or both.1 Poisson distribution - Mathematical function relating the number of particles in a given volume element to the average concentration of randomly distributed particles in the entire volume.1 PM10 - Common global sampling convention that quantifies the mass of particulate air pollution in the environment. The PM10 convention collect particles in the ulrafine range. Most PM10 is derived from combustion sources. Pulmonary Compartment - Portion of the respiratory tract in which gas exchange occurs (including alveoli and respiratory bronchioles)1 RD50 - The concentration of a test article which will depress the respiration rate of mice by 50%. Relaxation Time - Time for a particle to reach 1/e of its final velocity from an initial velocity or from rest when subjected to an external force; an indicator of a particle's ability to adjust to changes in flow velocity.1 Reserve air volume - air retained in the deepest part of the lung where there is insignificant convection.3 Respirable fraction - Fraction of aerosol that can reach the gas exchange region of the human respiratory system.1 Respirable particles - Those materials that are deposited in the gas-exchange region of the lung. Respiratory rate - The average rate of breathing; e.g., breaths per minute. Respiratory tract - Composed of the conducting airway including the nose, mouth, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli. Reynolds number - Flow similitude parameter, expressed as the ratio of the inertial force of the gas to the friction force of the gas moving over the surface of an object; flow Reynolds number the gas flow in a tube and parricle Reynolds number describes the gas flow around a particle. 1 Rotameter - A device used to measure the flow rate of a gas, as indicated by the height of a float centered in a vertical tapered tube.1 Slip correction factor - A factor which allows slip flow behavior to be calculated using continuum gas flow equations.1 Slip flow regime - Transition between free molecular flow and continuum gas flow.1 Smoke - an aerosol of solid or liquid particles usually resulting from incomplete combustion, usually in the form of aggregated very small primary particles.3 Snell's law - Fundamental principle in optics that the sines of the angles of incidence and refraction are in a constant ratio to one another.1 Space charge - Charged particles within an aerosol may interact with one another by virtue of the Coulomb-type forces which bring about mutual attraction or repulsion depending on whether particle charges are of the same or opposite polarities; net result integrated over the whole cloud of particles is an internal electric field ultimately resulting in deposition onto solid surfaces.3 Spray - An aerosol of relatively large liquid droplets produced by the mechanical disruption of bulk liquid material, with sizes upwards of a few micrometers.3 Stokes diameter - Diameter of a spherical particle with the same density and settling velocity as the particle in question.1 Stokes' law flow - Flow around a body under the influence of viscous, but not inertial forces. 1 Stokes' number - Ratio of a particle's stopping distance to a characteristic dimension; generally used as an indicator of similitude in particle behavior in a given aerosol flow configuration.1 Stokes' regime - Condition for which Stokes' law applies. 1 Stopping Distance - Product of relaxation time and the initial particle velocity; an indicator of a particle's ability to adjust to directional changes in aerosol flow.1 Tidal volume - volume of air convected in and out during the breathing cycle.(as opposed to reserve air volume)3 UFP - ultrafine particles - particles less than 100 nm in diameter that are a variable and heterogeneous component of environmental air pollution (PM10). They are derived from primary combustion sources. Vapor pressure - Partial pressure of a liquid's vapor required to maintain the vapor in equilibrium with the condensed liquid or solid; also referred to as saturation vapor pressure.1 Vertical elutriator - A vertical channel that gravitationally retains or removes particles above a given size or size range and emits the remaining airborne particles.1 Vena contracta - Flow contraction with flow separation from the wall, usually occurring after constriction of a flow channel or just downstream of the entry point of an inlet.1 Venturi meter - A device used to measure flow rate in a duct by measuring the pressure drop across a calibrated streamlined constriction.1 Virtual impactor - A device in which particles are removed by impacting them through a virtual surface into a stagnant volume, or a volume with a slowly moving airflow, so that large particles remain in this volume while smaller particles are deflected with the bulk of the original air flow; the dichotomous impactor is a frequently used virtual impactor.1 Vital Capacity - Maximum volume of gas that can be exhaled from the lung after maximum inhalation.1 Wall loss- Deposition of particles in a sampler on surfaces other than those designed for particle collection.1 References: 1- Aerosol Measurement: Principles, Techniques and Applications. Edited by Klaus Willeke and Paul A. Baron. Van Nostrand Reinhold, New York, 1993. 2- Fundamentals of Aerosol Sampling. Gregory D. Wight. Lewis Publishers, CRC Press, 1994. 3- Aerosol Science for Industrial Hygienists. James H. Vincent. Pergamon Press, Elsevier Science, Inc., Tarrytown, NY, 1995. 4- Casarett and Doull's "The Basic Science of Poisons" (Second Edition). Editors: John Doull, Curtis D. Klassen and Mary O. Amdur. 1980. Macmillan Publishing Co., Inc. New York, London
In preparation by Susan G. Shami, ScD sshami@mindsspring.com 08/28/2006 05:41 PM -0500
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