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A2LA	The American Association for Laboratory Accreditation (A2LA) is a nonprofit, non-governmental, public service, membership society. The mission of A2LA is to provide comprehensive services in laboratory accreditation and laboratory-related training. Services are available to any type of organization, be it private or government. Laboratory accreditation is based on internationally accepted criteria for competence (ISO/IEC 17025:2005). A2LA also offers programs for accreditation of inspection bodies, proficiency testing providers, reference material producers and product certification bodies. The fundamental goals of A2LA are to: • Establish and maintain global acceptance of A2LA accreditation services for the accredited bodies and their accredited data recognition and establish and maintain effective international and domestic Mutual Recognition Arrangements; • Establish and maintain programs to meet existing and emerging needs for accreditation services in the marketplace. • Increase market share and expand into new areas consistent with our non-profit status and/or expand market opportunities and customer base; • Improve the productivity and effectiveness of the A2LA management system to ensure and enhance the quality of customer services and accreditations; • Establish and maintain beneficial relationships with peers, laboratories, users and other stakeholders to enhance the value of A2LA accreditation; • Provide continual improvement opportunities for participants in the administration of A2LA, including staff, assessors, advisory committee members, Council members and Board members.
Accuracy	The extent to which results of a calculation or the readings of an instrument approach the true values of the calculated or measured quantities.
AERMOD	AERMOD is the next generation air dispersion modeling system and consists of 3 components - AERMOD (air dispersion model), AERMET (meteorological data preprocessor) and AERMAP (terrain preprocessor). On November 9th, 2005 AERMOD was promulgated by EPA. AERMOD should be used for appropriate modeling applications as a replacement for the ISC model. During the one year period after the promulgation date, protocols for modeling analyses using ISC may still be approved at the discretion of the reviewing authority. After this one year transition period, AERMOD will become the primary model for near-field modeling analyses, replacing the ISC model.
Air Toxic	A generic term referring to a harmful chemical or group of chemicals in the air. Typically, substances that are especially harmful to health, such as those considered under EPA's hazardous air pollutant program or California's AB 1807 toxic air contaminant program, are considered to be air toxics. Technically, any compound that is in the air and has the potential to produce adverse health effects is an air toxic.
AQRV	A resource as identified by the Federal Land Manager for one or more federal areas, that may be adversely affected by a change in air quality. The resource may include visibility or a specific scenic, cultural, physical, biological, ecological, or recreational resource identified by the Federal Land Manager for a particular area.
BACT	(Best Available Control Technology) The most up-to-date methods, systems, techniques, and production processes available to achieve the greatest feasible emission reductions for given regulated air pollutants and processes. BACT is a requirement of NSR (New Source Review) and PSD (Prevention of Significant Deterioration).
Biogenic Sources	Natural sources of air pollution (ex: Isoprene emitted from plants, Ammonia emitted from the soil, etc.)
CALPUFF	CALPUFF is an advanced non-steady-state meteorological and air quality modeling system developed and distributed by Earth Tech, Inc. The model has been adopted by the U.S. Environmental Protection Agency (U.S. EPA) in its Guideline on Air Quality Models as the preferred model for assessing long range transport of pollutants and their impacts on Federal Class I areas and on a case-by-case basis for certain near-field applications involving complex meteorological conditions. The modeling system consists of three main components and a set of preprocessing and postprocessing programs. The main components of the modeling system are CALMET (a diagnostic 3-dimensional meteorological model), CALPUFF (an air quality dispersion model), and CALPOST (a postprocessing package).
Carbonyl Cartridge	Commonly used sampling technique based on reacting airborne carbonyls with 2,4-dinitrophenylhydrazine (2,4-DNPH) coated on an adsorbent cartridge followed by separation and analysis of the hydrazone derivative by high performance liquid chromatography (HPLC) with ultraviolet (UV) detection.
Certified Consulting Meteorologist	The Certified Consulting Meteorologist (CCM) is a professional meteorologist who has an in-depth understanding of the atmosphere and its behavior. Services and products provided by CCMs are founded upon their abilities to apply this specialized knowledge to a broad range of related activities, issues, and inquiries. The essential attribute of the CCM is a specialized knowledge of the field, combined with broad experience, an integrated concept of service, and a clear and unwavering adherence to the rules of professional conduct and service.
Climatologies	The description and scientific study of climate. Descriptive climatology deals with the observed geographic or temporal distribution of meteorological observations over a specified period of time. Scientific climatology addresses the nature and controls of the earth's climate and the causes of climate variability and change on all timescales. The modern treatment of the nature and theory of climate, as opposed to a purely descriptive account, must deal with the dynamics of the entire atmosphere–ocean–land surface climate system, in terms of its internal interactions and its response to external factors, for example, incoming solar radiation. Applied climatology addresses the climate factors involved in a broad range of problems relating to the planning, design, operations, and other decision-making activities of climate sensitive sectors of modern society.
Cloud Cover	That portion of the sky cover that is attributed to clouds, usually measured in tenths or eighths of sky covered.
CO	(Carbon Monoxide) A colorless, odorless gas resulting from the incomplete combustion of fossil fuels. Over 80% of the CO emitted in urban areas is contributed by motor vehicles. CO interferes with the blood's ability to carry oxygen to the body's tissues and results in numerous adverse health effects. CO is a criteria air pollutant.
Criteria Pollutants	Pollutants that can injure health, harm the environment, and cause property damage. In 1997, the criteria pollutants in the United States were: Carbon monoxide (CO) Lead (Pb) Nitrogen dioxide (NO2) Ozone (O3) Particulate matter with aerodynamic size less than or equal to 10 μm (PM-10) Sulfur dioxide (SO2).
Delta Temperature	The difference between temperature measurements taken at two significant levels above the ground. Temperatures at 2, 10 and 50 meters are commonly used. Used in conjunction with solar radiation and wind speed data, stability class approximations can be derived.
Deposition	Processes by which traces gases or particles are transferred from the atmosphere to the surface of the earth. Atmospheric deposition is usually divided into two categories, wet deposition and dry deposition, depending on the phase of the material during the deposition process. Thus, in wet deposition, the gas or particle is first incorporated into a droplet and is then transferred to the surface via precipitation. In dry deposition, the gas or particle is transported to ground level, where it is adsorbed onto a surface. The surface can be the ocean, soil, vegetation, buildings, etc. Note that the surface involved in the dry deposition may be wet or dry—the “dry” in dry deposition refers only to the phase of the material being deposited.
Dispersion	Dispersion can be the result of molecular diffusion, turbulent mixing, and mean wind shear. The displacement or advection of polluted air by the mean wind is usually called transport rather than dispersion. The amount of dispersion is usually described statistically by the standard deviation (σx, σy and σz) of pollutant particle locations (x, y, z) from the pollutant puff center-of-mass for isolated short releases such as explosions, or from the plume centerline for continuous emissions such as from a smokestack. For a plume, the local Cartesian coordinate system can be aligned with the x axis pointing in the mean wind direction at plume centerline height, allowing the crosswind and vertical dispersion to be described by σy and σz, respectively.
Evaporation	The physical process by which a liquid or solid is transformed to the gaseous state; the opposite of condensation. Evaporation is usually restricted in use to the change of water from liquid to gas, while sublimation is used for the change from solid to gas. According to the kinetic theory of gases, evaporation occurs when liquid molecules escape into the vapor phase as a result of the chance acquisition of above-average, outward-directed, translational velocities at a time when they happen to lie within about one mean free path below the effective liquid surface. It is conventionally stated that evaporation into a gas ceases when the gas reaches saturation. In reality, net evaporation does cease, but only because the numbers of molecules escaping from and returning to the liquid are equal, that is, evaporation is counteracted by condensation. Because the molecules that escape the condensed phase have above-average energies, those left behind have below-average energies, which is manifested by a decrease in temperature of the condensed phase (unless compensated for by energy transfer from the surroundings).
GPS	A navigation system based on a constellation of 24 low earth-orbiting satellites having highly accurate clocks and the computational capacity to triangulate positions near the earth's surface. Developed by the U.S. Department of Defense, the system has the capability of determining position to an accuracy of 10–100 m. If systems at two locations are used with long integration times, positions may be determined within millimeters of a known reference position.
Growing Seasons	Generally, the period of the year during which the temperature of cultivated vegetation (i.e., the temperature of the vegetal microclimate) remains sufficiently high to allow plant growth. This is an important concept in agricultural climatology, but it suffers greatly from vagueness and complexity. The growing season is highly variable due to plant varieties as related to temperature sensitivity. Currently, the most common measure of this period, “the average length of growing season,” is defined as the number of days between the average dates of the last killing frost (see frost) in spring and the first killing frost of autumn. The lack of a positive, practical definition for (and means of determining) a “killing” frost seriously limits the scientific usefulness of this measure. To provide some economic significance, the effective growing season is defined as the length of growing season that prevails in 80% of the years. Another measure, the frost-free season, is defined as the interval between the last and first occurrences of 32°F temperatures in spring and fall. This may be observed exactly, but its relationship to the local microclimate is variable and nonspecific, and it does not consider differences in types of vegetation. Still a fourth measure, the vegetative period or vegetation season, attempts to allow for the greater microclimatic temperature range and for the general growth retardation by cold temperatures, and is defined as the summer period confined between occurrences of 42°F (or 41°F or 43°F) temperatures. At best, any of the above is an index of growing season length, rather than a direct measure of it. Basically, the growing season (and “killing frost”) should be defined biologically rather than meteorologically and should consider the detailed microclimate, plant resistance to frost, growth rate versus temperature, and probably other factors.
ISCST	The Industrial Source Complex - Short Term regulatory air dispersion model (ISCST3) is a Gaussian plume model and is widely used to assess pollution concentration and/or deposition flux on receptors from a wide variety of sources.
Isohyetal	Map depicting contours of equal precipitation amounts recorded during a specific time period.
Long-range Forecasts	A forecast of weather conditions for a period extending beyond three or more days from the day of issuance.
Meteorology	Meteorology is the scientific study of the atmosphere that focuses on weather processes and forecasting. Meteorological phenomena are observable weather events which illuminate and are explained by the science of meteorology. Those events are bound by the variables that exist in Earth's atmosphere. They are temperature, pressure, water vapor, and the gradients and interactions of each variable, and how they change in time. The majority of Earth's observed weather is located in the troposphere.
Micrometeorological	The study of weather conditions on a small scale, as in the area immediately around a building, smokestack, or mountain.
NAAQS	Standards set by the federal EPA for the maximum levels of air pollutants which can exist in the outdoor air without unacceptable effects on human health or the public welfare.
Net Radiation	The difference between downward and upward (total) radiation; net flux of all radiation. Derived using an instrument that measures the net flux of downward and upward total (solar and terrestrial) radiation through a horizontal surface.
NEXRAD	1. Acronym for Next Generation Weather Radar program, a joint program of the U.S. Departments of Commerce, Defense, and Transportation during the 1980s and 1990s to develop and deploy a network of operational Doppler weather radars. 2. The popular name for the radar itself, the WSR-88D weather radar, which became the operational network radar for the U.S. National Weather Service, U.S. Air Force, and Federal Aviation Administration during the early and middle 1990s. The nominal transmitted wavelength of the WSR-88D is 10.5 cm (S band) and the nominal circular beamwidth is 0.95°.
NIST	National Institute of Standards and Technology
Nowcasting	A short-term weather forecast, generally for the next few hours. The U.S. National Weather Service specifies zero to three hours, though up to six hours may be used by some.
NSR	(New Source Review) A program used in development of permits for new or modified industrial facilities which are in a non-attainment area, and which emit non-attainment criteria air pollutants. The two major requirements of NSR are Best Available Control Technology and Emission Offset.
OCR	optical character recognition
Oxides of Nitrogen	A general term pertaining to compounds of nitric oxide (NO), nitrogen dioxide (NO2), and other oxides of nitrogen. Nitrogen oxides are typically created during combustion processes, and are major contributors to smog formation and acid deposition. NO2 is a criteria air pollutant, and may result in numerous adverse health effects.
Ozone	A strong smelling, pale blue, reactive toxic chemical gas consisting of three oxygen atoms. It is a product of the photochemical process involving the sun's energy. Ozone exists in the upper atmosphere ozone layer as well as at the earth's surface. Ozone at the earth's surface causes numerous adverse health effects and is a criteria air pollutant. It is a major component of smog.
Permit	Written authorization from a government agency (e.g., an air quality management district) that allows for the construction and/or operation of an emissions generating facility or its equipment within certain specified limits.
PM10	(Particulate Matter) A major air pollutant consisting of tiny solid or liquid particles of soot, dust, smoke, fumes, and mists. The size of the particles (10 microns or smaller, about 0.0004 inches or less) allows them to easily enter the air sacs deep in the lungs where they may be deposited to result in adverse health effects. PM-10 also causes visibility reduction and is a criteria air pollutant.
Precipitation	All liquid or solid phase aqueous particles that originate in the atmosphere and fall to the earth's surface. The amount, usually expressed in millimeters or inches of liquid water depth, of the water substance that has fallen at a given point over a specified period of time. As this is usually measured in a fixed rain gauge, small amounts of dew, frost, rime, etc., may be included in the total. The more common term rainfall is also used in this total sense to include not only amounts of rain, but also the water equivalents of frozen precipitation. For obvious reasons, precipitation is the preferred general term.
Precision	The quality of being exactly defined. Sometimes indicated by the minimum number of significant digits required for an adequate representation of a quantity. Not the same as accuracy but often confused as such. A measurement having small random error is said to have high precision; a measurement having small systematic error or bias is said to have high accuracy.
Pressure	The pressure exerted by the atmosphere as a consequence of gravitational attraction exerted upon the “column” of air lying directly above the point in question. As with any gas, the pressure exerted by the atmosphere is ultimately explainable in terms of bombardment by gas molecules; it is independent of the orientation of the surface on which it acts. Atmospheric pressure is one of the basic meteorological elements. It is measured by many varieties of barometer and is expressed in several unit systems. The most common unit used is the millibar (1 millibar equals 1000 dynes cm−2). Unique to the science of meteorology is the use of inches (or millimeters) of mercury, that is, the height of a column of mercury that exactly balances the weight of the column of atmosphere the base of which coincides with that of the mercury column.
PSD	Prevention of Significant Deterioration (PSD): A permitting program for new and modified stationary sources of air pollution located in an area that attains or is unclassified for national ambient air quality standards (NAAQS). The PSD program is designed to ensure that air quality does not degrade beyond those air quality standards or beyond specified incremental amounts. The PSD permitting process requires new and modified facilities above a specified size threshold to be carefully reviewed prior to construction for air quality impacts. PSD also requires those facilities to apply BACT to minimize emissions of air pollutants. A public notification process is conducted prior to issuance of final PSD permits.
Qualified Environmental Professional	The QEP is a multi-media, multi-disciplinary, fully accredited credential that requires environmental professionals to see "the big picture" and to have the skills and knowledge to solve "real world problems". Through the QEP certification, environmental professionals demonstrate the breadth and depth of their knowledge and experience. They also agree to abide by IPEP's Code of Ethics. The QEP is distinguished from other certifications by its cross-disciplinary nature, its qualifying education prerequisites, its rigorous application and examination process, and by its continuing education requirements for recertification. The QEP establishes standards for the environmental professional and provides a career track for new professionals entering the field. It does not take the place of specialized certifications or registrations, but rather is a unique credential that serves to link and coordinate environmental practice. The QEP is committed to: • A strict code of ethics. • High standards of environmental practice. • Ongoing professional development. • Contributing to community and profession. The QEP has demonstrated: • Ability to solve complex environmental problems. • Awareness of multi-media impacts. • Broad based, multi-disciplinary understanding of environmental issues. • In-depth knowledge in your area of professional practice.
Quantitative Precipitation Forecasts	A prediction of the amount of precipitation that will fall at a given location in a given time interval.
Relative Humidity	The ratio of the vapor pressure to the saturation vapor pressure with respect to water. This quantity is alternatively defined by the World Meteorological Organization as the ratio of the mixing ratio to the saturation mixing ratio. These two definitions yield almost identical numerical values. Relative humidity is usually expressed in percent and can be computed from psychrometric data. Unless specified otherwise, relative humidity is reported with respect to water rather than ice because most hygrometers are sensitive to relative humidity with respect to water even at subfreezing temperatures, and because the air can easily become supersaturated with respect to ice, which would require three digits in coded messages for relative humidity with respect to ice.
Return Period	Also called recurrence interval. The average time until the next occurrence of a defined event. When the time to the next occurrence has a geometric distribution, the return period is equal to the inverse of probability of the event occurring in the next time period, that is, T = 1/P, where T is the return period, in number of time intervals, and P is the probability of the next event's occurrence in a given time interval.
Sigma Theta	The standard deviation of wind direction. Provides an indication of the variability of the wind direction. Used in calculations of atmospheric stability.
Snow Depth	A measurement of the depth of snow on the ground made either since the snow began falling or since a previous observation. The total accumulation is equivalent to the total snow depth during a storm, or after any single snowstorm or series of storms. Snow accumulation can vary due to settling and melting and will therefore vary depending on how often it is measured. For example, if new snow is measured every hour during a relatively long duration storm, it is likely that the summed accumulations may exceed a total snow accumulation measured only once at the end of the storm.
SO2	(Sulfur Dioxide) A strong smelling, colorless gas that is formed by the combustion of fossil fuels. Power plants, which may use coal or oil high in sulfur content, can be major sources of SO2. SO2 and other sulfur oxides contribute to the problem of acid deposition. SO2 is a criteria pollutant.
Soil Temperature	The temperature measured at a given soil depth, typically at 2, 4, 8, and sometimes 20 and 40 in. Many biological processes, including seed germination, plant emergence, microbial activity, and soil respiration are a function of soil temperature.
Solar Radiation	The total electromagnetic radiation emitted by the sun. To a first approximation, the sun radiates as a blackbody at a temperature of about 5700 K; hence, about 99.9% of its energy output falls within the wavelength interval from 0.15 to 4.0 μm, with peak intensity near 0.5 μm. About one-half of the total energy in the solar beam is contained within the visible spectrum from 0.4 to 0.7 μm, and most of the other half lies in the near-infrared, a small additional portion lying in the ultraviolet.
Sonic Anemometers	An anemometer that measures linear components of the wind vector by determining the effect of the wind on transit times of acoustic pulses transmitted in opposite directions across known paths. 2D sonic anemometers return x and y component wind values while 3D sonic anemometers also return a vertical wind speed component.
Stability	A semiquantitative measure of the mixing capabilities of the lower atmosphere; usually termed the Pasquill– Gifford categories.
Telemetry	The process of measuring a quantity or quantities, transmitting the measured value to a distant station, and there interpreting, indicating, or recording the quantities measured.
Temperature	The quantity measured by a thermometer. Bodies in thermal equilibrium with each other have the same temperature. In gaseous fluid dynamics, temperature represents molecular kinetic energy, which is then consistent with the equation of state and with definitions of pressure as the average force of molecular impacts and density as the total mass of molecules in a volume. For an ideal gas, temperature is the ratio of internal energy to the specific heat capacity at constant volume.
TEOM	The TEOM monitor measures the ambient particulate mass concentration of PM-10, PM-2.5, PM-1 and TSP (total suspended particulate matter) in real time. The monitor is used in ambient air monitoring networks, ambient air research projects, indoor air qualtiy assessment, and exposure studies. The instrument is suitable for a range of other applications requiring time-resolved, mass measurement of the suspended particulate matter concentration. The TEOM operates using a tapered element oscillating mic robalance, which is a patented inertial mass measurement technique for making a direct measurement of the particle mass collected on a filter in real time. The instrument has the USEPA equivalency designation for PM-10 as EQPM-1090-079, and is used extensively by the USEPA and state air monitoring organizations for continuous PM-2.5 monitoring as a correlated acceptable continuous monitor.
Tracer	1. A chemical or thermodynamic property of the flow that is conserved during advection. It can be used to track air-parcel movement and to identify the origins of air masses. Examples are absolute humidity, equivalent potential temperature, radioactivity, and CCN composition. 2. Any substance in the atmosphere that can be used to track the history of an air mass. It can be chemical or radioactive in nature. The main requirement for a tracer is that its lifetime be substantially longer than the transport process under study. An example of an inert chemical tracer is SF6, which is often released during a field experiment and measured at a later time to assess the extent of dilution of the air mass. Chemicals such as methane (CH4) and nitrous oxide (N2O), which are released at the earth's surface and destroyed slowly in the atmosphere, can be used to infer vertical rates of transport. CO released in the boundary layer can be used to trace transport in convection. Radioactive tracers such as 14C and 90Sr have been used to test models of stratospheric circulation. Certain atmospheric gases have also been used as tracers in ocean waters, for example, the chlorofluorocarbons.
Upper Air	In synoptic meteorology and in weather observing, that portion of the atmosphere that is above the lower troposphere. No distinct lower limit is set but the term can be generally applied to the levels above 850 mb.
Vertical Wind Speed	The component of the velocity vector along the local vertical.
Wind Chill	The portion of the cooling of a human body caused by air motion. Air motion accelerates the rate of heat transfer from a human body to the surrounding atmosphere, especially when temperatures are below about 7°C (45°F).
Wind Direction	The direction from which the wind is blowing.
Wind Rose	Any one of a class of diagrams designed to show the distribution of wind direction experienced at a given location over a considerable period; it thus shows the prevailing wind direction. The most common form consists of a circle from which eight or sixteen lines emanate, one for each compass point. The length of each line is proportional to the frequency of wind from that direction, and the frequency of calm conditions is entered in the center. Many variations exist; some indicate the range of wind speeds from each direction; some relate wind directions with other weather occurrences.
Wind Speed	Ratio of the distance covered by the air to the time taken to cover it. The instantaneous speed corresponds to the case of an infinitely small time interval. The mean speed corresponds to the case of a finite time interval. It is one component of wind velocity, the other being wind direction.