1
Definitions/Glossary of Terms

As noted in the Preface, this book is concerned with air pollution control equipment and as such, this chapter primarily addresses air pollution control equipment‐related terms. It has been written not only for academic use in colleges, and universities but also for both engineers and scientists who work in the air pollution control equipment field. This glossary may be used whenever and wherever information is needed about words and/or terms in air pollution.

Some additional points deserve mentioning:

1. Each definition avoids technical jargon.
2. No mathematical equations – in any form – are employed in the definition. In some instances, where necessary, common scientific and engineering units have been included.
3. Only keywords or terms used in practice are provided, as is the case in preparing a text, particularly a dictionary, the problems of what to include and what to omit have been particularly difficult.
4. Only one spelling is used for words with multiple accepted spellings, e.g., modeling versus modeling.
5. Some important acronyms are also included with a one‐sentence definition.
6. As with nearly every glossary, the terms have been alphabetized.

This chapter defines many – but not all – of the terms that the reader will encounter in this book. The following list is therefore not a complete glossary of all terms that appear in this field. It should also be noted that many of the terms have come to mean slightly different things to different people; this will become evident as one delves deeper into the literature.1–3

1.1 Glossary of Terms

Absolute humidity.

The amount of water vapor present in a unit mass of air, which is usually expressed in kg water vapor/kg dry air or lb water vapor/lb dry air.

Absolute pressure.

The actual pressure exerted on a surface that is measured relative to zero pressure; it equals the gauge pressure plus the atmospheric pressure.

Absolute temperature.

The temperature expressed in degrees of Kelvin or Rankine.

Absorbate.

A substance that is taken up and retained by an absorbent.

Absorbent.

Any substance that takes in or absorbs other substances.

Absorber.

A device in which a gas is absorbed by contact with a liquid.

Absorption.

The process in which one material (the absorbent) takes up and retains another (the absorbate) to form a homogeneous solution; it often involves the use of a liquid to remove certain gas components from a gaseous mixture.

Actual cubic feet per minute (acfm).

A unit of flow rate measured under actual pressure and temperature conditions.

Acute (risk).

Risks associated with short periods of time. For health risk, it usually represents short exposures to high concentrations of an agent.

Adiabatic.

A term used to describe a system in which no gain or loss of heat is allowed to occur.

Adiabatic flame temperature.

The maximum temperature that a combustion system can reach.

Adiabatic lapse rate.

The rate at which the temperature of a moving air parcel decreases in the atmosphere as height above the surface increases when no heat is added or subtracted from the moving air parcel; the adiabatic lapse rate is 10 °C/km.

Adsorbent.

A substance (e.g., activated carbon, activated alumina, silica gel) that has the ability to condense or hold molecules of other substances on its surface.

Adsorber.

An apparatus in which molecules of gas or liquid are retained on the surface of an adsorbent.

Adsorption.

The physical or chemical bonding of molecules of gas, liquid, or dissolved solid to the external or internal (if porous) surface of a solid (adsorbent); it is an advanced method of treating waste that is employed to remove odor, color, or organic matter from a system.

Afterburner.

A secondary burner is located so that combustion gases from the primary incinerator are further burned to remove smoke, odors, and other pollutants.

Agent.

A biological, physical, or chemical entity capable of causing disease or adverse health effects.

Alpha (α) particle.

A positively charged helium nucleus (i.e., two protons and two neutrons) that is emitted spontaneously from the decay of radioactive elements.

Amines.

Organic compound related to ammonia.

Ammonia.

An alkaline gas composed of hydrogen and nitrogen; it has a strong odor when present in high concentrations.

Asphyxiant.

A vapor or gas that has little or no positive toxic effect but that can bring about unconsciousness and death by replacing air and thus depriving an organism of oxygen.

Aspirator.

A hydraulic device that creates a negative pressure by forcing liquid through a restriction, thus increasing the velocity head.

Atmosphere.

The general volume of air above the earth; it is the lower portion of the atmosphere in which pollution must be controlled.

Atmospheric dispersion.

The mixing of a gas or vapor (usually from a discharge point) with air in the lower atmosphere. The mixing is the result of convective motion and turbulent eddies.

Atmospheric stability.

A measure of the degree of atmospheric turbulence, often defined in terms of the vertical temperature gradient in the lower atmosphere.

Atomic fission.

The breaking down of a large atom into smaller atoms or elements, involving the liberation of heat, gamma rays, alpha particles, and beta particles.

Audit.

The examination of something with the intent to check, verify, or inspect a particular subject matter.

Auto‐ignition temperature.

The lowest temperature at which a flammable gas in the air will ignite without an ignition source.

Auto‐ignition.

The starting of a fire without the addition of an external source such as a flame, spark, or heat.

Average rate of death (ROD).

The average number of fatalities that can be expected per unit time (usually on an annual basis) from all possible risks and/or incidents.

Baffle.

A flow‐regulating device usually consisting of a plate placed horizontally across a pipe or channel to restrict or divert the passage of a fluid, usually used for the purpose of providing a uniformly dispersed flow.

Ball joint.

A flexible pipe joint formed in the shape of a ball or a sphere.

Ball valve.

A nonreturn valve consisting of a ball resting on a cylindrical seat within a fluid passageway or pipe.

Barometric pressure.

The pressure of the ambient air in the atmosphere at a particular point on or above the surface of the earth.

Basic event.

A fault tree event (FTE) that is sufficiently basic that no further explanation or development of additional events is necessary.

Batch process.

A process that is not continuous; its operations are carried out with discrete quantities of material added and removed from it at appropriate time intervals.

Benzene.

Aromatic hydrocarbon formerly used in paints and varnishes, but now considered toxic for this purpose.

Beta (β) particle.

A charged particle emitted from a radioactive atomic nucleus; it has moderate penetrative power and is able to damage living tissue.

Bias.

The systematic distortion of data; it is the tendency of a sample to be unrepresentative of all the cases involved in a study.

Bleeding.

The gradual release of material and/or reduction of pressure from a system or process (e.g., by a valve or leak).

Blowdown.

The cyclic or constant removal of a portion of any process flow to maintain the constituents of the flow at a desired level.

Blower.

A fan employed to force or move air or gas under pressure.

Brownian movement.

The constant, random movement of small, suspended particles due to collisions with other molecules.

Buffer.

A solution containing both a weak acid and its conjugate weak base, which is employed to stabilize the pH value in a solution, and anything that acts to diminish and/or regulate changes in a system or process.

Bulk sample.

A small portion of material that is collected and sent to a laboratory for analysis.

Bulk density.

The mass per unit volume of a solid in a mixture such as a packed bed or soil mass; unlike the real solid particle density, the pore space is included in the volume for this calculation.

Burning.

The chemical combination of oxygen and a fuel such as carbon, hydrogen, hydrocarbon, or other substances that combine with oxygen.

Butterfly damper.

A plate or blade installed in a duct, flue, breeching, or stack that rotates on an axis to regulate the flow of gases.

Butterfly valve.

A flow control valve containing a disk supported by a shaft on which it rotates.

Bypass.

The avoiding...