FEDERAL LAND MANAGERS' AIR QUALITY RELATED VALUES WORKGROUP (FLAG)
PHASE I REPORT
(December 2000)
Appendices
A. Glossary
The list below contains definitions for some of the terms used in the FLAG Phase I Report. These terms are defined in the sense that they relate to the work of the Federal Land Managers (FLMs) in protecting air resources.
For terms whose definition is lengthy or complex, the associated Code of Federal Regulations (CFR) section or other reference is cited.
AIR QUALITY RELATED VALUE (AQRV). A resource, as identified by the FLM 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 FLM for a particular area.
ADVERSE IMPACT ON AN AQRV. An unacceptable effect, as identified by an FLM, that results from current, or would result from predicted, deterioration of air quality in a Federal Class I or Class II area. A determination of unacceptable effect shall be made on a case-by-case basis for each area taking into account existing air quality conditions. It should be based on a demonstration that the current or predicted deterioration of air quality will cause or contribute to a diminishment of the area's national significance, impairment of the structure and functioning of the area's ecosystem, or impairment of the quality of the visitor experience in the area.
ADVERSE IMPACT ON VISIBILITY. Visibility impairment which interferes with the management, protection, preservation, or enjoyment of a visitor's visual experience of a Federal Class I or Class II area. This determination must be made on a case-by-case basis taking into account the geographic extent, intensity, duration, frequency and time of visibility impairments, and how these factors correlate with (1) times of visitor use of the Class I area, and (2) the frequency and timing of natural conditions that reduce visibility. This term does not include effects on integral vistas. [40 CFR §51.301(a)]
ABSORPTION. The process by which incident light is removed from the atmosphere and retained by a particle.
ABSORPTION COEFFICIENT. A number that is proportional to the "amount" of light removed from a sight path by absorption per unit distance.
ACIDIFICATION. The decrease of acid neutralizing capacity in water or base saturation in soil caused by natural or anthropogenic processes.
AEROSOL. A mixture of microscopic solid or liquid particles in a gaseous medium. Smoke, haze, and fog are aerosol examples.
AIRSHED. A geographic area that, because of topography, meteorology, and/or climate, is frequently affected by the same air mass.
AOT40. Sum of all hourly average concentrations after subtracting 40 ppb from each hourly value.
BACT (BEST AVAILABLE CONTROL TECHNOLOGY). The control level (or control measures) required for sources subject to PSD. (See 40 CFR §52.21(b)(12), or 40 CFR §51.166(b)(12)).
CLASS I AREA. As defined in the Clean Air Act, the following areas that were in existence as of August 7, 1977: national parks over 6,000 acres, national wilderness areas and national memorial parks over 5,000 acres, and international parks.
CRITICAL LOAD. The concentration of air pollution above which a specific deleterious effect may occur.
CUMULATIVE EFFECT. The impact on an AQRV resulting from the total pollutant loading from all sources including the contributing effects of known and reasonably foreseeable new and modified sources of air pollution. A single source may cause individually minor, but cumulatively significant, effects on AQRVs.
DAMAGE. Any reduction in the intended use or value of a biological or physical resource. For example, economic production, ecological structure or function, aesthetic value, or biological or genetic diversity that may be altered by a pollutant.
EMISSION OFFSET. A Federally enforceable reduction in emissions from an existing source that mitigates the impacts of a proposed new or modified source on AQRVs, PSD increments, and/or NAAQS. Also, Federally enforceable reductions in actual emissions from existing sources in a nonattainment area such that the total allowable emissions from a new or modified source and existing sources will be sufficiently less than the total emissions from existing sources before the application for a permit to construct so as to represent reasonable further progress towards attainment of the NAAQS. (See 42 U.S.C. § 7503(a)(1)(A))
EXTINCTION. The attenuation of light due to scattering and absorption as it passes through a medium.
FUGITIVE EMISSIONS. Emissions which do not pass through a stack, chimney, vent, or other functionally equivalent opening.
FEDERAL LAND MANAGER (FLM). The Secretary of the Department with authority over such lands. [40 CFR §51.166(b)(24)] The FLM for the Department of the Interior has been delegated to the Assistant Secretary for Fish and Wildlife and Parks; the FLM for the Department of Agriculture has been delegated to the Forest Service, and has been redelegated to the Regional Forester or individual Forest Supervisor.
FLUX Gaseous uptake into plant tissue.
GREEN LINE. The total pollutant loading (contributions from existing and proposed sources) below which there is a very high degree of certainty that no AQRV will be adversely affected.
HAZE. An atmospheric aerosol of sufficient concentration to be visible. The particles are so small that they cannot be seen individually, but are still effective attenuating light and reducing visual range.
HYDROCARBONS. Compounds containing only hydrogen and carbon. Examples: methane, benzene, and decane.
HYGROSCOPIC. Readily absorbing moisture, as from the atmosphere.
INJURY. Any physical or biological response to pollutants, such as a change in metabolism, reduced photosynthesis, leaf necrosis, premature leaf drop, or chlorosis.
LAER (LOWEST ACHIEVABLE EMISSIONS RATE). The control level required of a source subject to nonattainment review. (See 40 CFR §51.165(a)(1)(xiii))
LIMIT OF ACCEPTABLE CHANGE. The amount of change that could occur without significantly altering an AQRV or sensitive receptor.
MICROMETER. A unit of length equal to one millionth of a meter; the unit of measure for particle size.
MIE THEORY. A complex mathematical model that allows the computation of the amount of energy (light) scattered by spherical particles.
N100. Number of hourly average concentrations ≥100 ppb.
NATURAL CONDITIONS. Conditions substantially unaltered by humans or human activities. As applied in the context of visibility, natural conditions include naturally occurring phenomena that reduce visibility as measured in terms of light extinction, visual range, contrast, or coloration.
NATURAL VISIBILITY CONDITIONS. Visibility conditions attributable to Rayleigh scattering and aerosol associated with natural processes.
NEPHELOMETER. An instrument that measures the amount of light scattered.
NITRATES. Those gases and aerosols that have origins in the gas-to-aerosol conversion of nitrogen oxides, e.g., NO2 ; of primary interest are nitric acid and ammonium nitrate. Ammonium nitrate is very hygroscopic so its contribution to visibility impairment is magnified in the presence of water vapor.
NITROGEN DIOXIDE. A gas (N02) consisting of one nitrogen and two oxygen atoms It absorbs blue light and therefore has a reddish-brown color associated with it.
NONATTAINMENT AREA. An area designated by the EPA Administrator pursuant to Section 107(d) of the Clean Air Act as having air quality which does not meet one or more National Ambient Air Quality Standard (NAAQS). For a list of nonattainment areas, see 40 CFR Part 81, Subpart C.
OXIDANT STIPPLE. Small brown or black interveinal necrotic lesions on the adaxial surface of leaf tissue that can be attributed to exposure to ozone.
PHYTOTOXIC. Poisonous to plants.
POST-CONSTRUCTION MONITORING. Monitoring required as a permit condition that the permitting authority considers necessary to determine the effect emissions from a stationary source may have, or are having, on the air quality or on the AQRVs of an area. Such monitoring includes both "ambient" monitoring and "AQRV" monitoring and may involve short-term and long-term measurements made at locations representative of the greatest expected impacts.
PSD INCREMENTS. The maximum increases in ambient pollution concentrations allowed over baselines concentrations. See 40 CFR §51.166 (c) for increments for specific pollutants.
RACT (REASONABLY AVAILABLE CONTROL TECHNOLOGY). The lowest emissions limit that a particular source can meet by the application of control technology that is reasonably available considering technological and economic feasibility.
RAYLEIGH SCATTERING. The scattering of light by particles much smaller than the wavelength of the light, e.g., molecular scattering in the natural atmosphere.
RECONSTRUCTED EXTINCTION. Extinction estimate that results from summing up the product of the mass of each measured particle species and the appropriate absorption or extinction coefficient.
RED LINE. The total pollutant loading (contributions from existing and proposed sources) at which there is a very high degree of certainty that at least one AQRV will be adversely affected.
REGIONAL HAZE VISIBILITY IMPAIRMENT. Any humanly perceptible change in visibility (light extinction, visual range, contrast, coloration) from that which would have existed under natural conditions, caused predominantly by a combination of many sources from, and occurring over, a wide geographic area.
RE-OPENER. A permit condition that requires the permitting authority, at a specified time after permit issuance, to review and revise, if necessary, the permit based on new information such as the findings from post-construction monitoring, updated emissions inventories, updated modeling, research, or information on air pollution effects to terrestrial, aquatic, and visibility resources.
SCATTERING. An interaction of a light with an object (e.g., a fine particle) that causes the light to be redirected in its path.
SCATTERING COEFFICIENT. Measure of the ability of particles to scatter light; measured in number proportional to the "amount" of light scattered per unit distance.
SCREENING LEVEL OR SCREENING LEVEL VALUE (SLV). The concentration or dose of air pollution below which estimated impacts from a proposed new or modified source are considered insignificant. The SLV is dependent on existing air quality and on the condition of the AQRV of concern.
SENSITIVE RECEPTOR. The AQRV, or part thereof, that is the most responsive to, or the most easily affected by the type of air pollution in question. For example, at Great Smoky Mountains National Park, spruce-fir forest is a sensitive receptor of the AQRV flora.
SENSITIVE RECEPTOR INDICATOR. A measurable physical, chemical, biological, or social (e.g., odor) characteristic of a sensitive receptor. For example, for the sensitive receptor, Crater Lake, water clarity is a sensitive receptor indicator.
STATIONARY SOURCE. A source of pollution that is well defined, such as the smokestack of a coal-fired power plant or smelter.
SULFATES. Those aerosols that have origins in the gas-to-aerosol conversion of sulfur dioxide; of primary interest are sulfuric acid and ammonium sulfate. Sulfuric acid and ammonium sulfate are very hygroscopic so their contribution to visibility impairment is magnified in the presence of water vapor.
SULFUR DIOXIDE. A gas (S02) consisting of one sulfur and two oxygen atoms. Of interest because sulfur dioxide converts to an aerosol.
SUM00. The sum of all hourly average concentrations above 0 ppb.
SUM06. The sum of all hourly average concentrations at or above 60 ppb.
TARGET LOAD. The acceptable concentration or dose of an air pollutant that provides a reasonable margin of safety below the critical load. The target load should be achievable under existing conditions.
TRANSMISSOMETER. An instrument that measures the amount of light extinction over a fixed, specified path length.
VISIBILITY IMPAIRMENT. Any humanly perceptible change in visibility (visual range, contrast, coloration) from that which would have existed under natural conditions. [40 CFR §51.301(x)]
VISUAL RANGE. The distance at which a large black object would just disappear from view.
VOLATILE ORGANIC COMPOUND (VOC). Any compound of carbon, except those excluded by EPA, that participates in atmospheric photochemical reactions. (See 40 CFR §51.100(s))
W126. An ozone index that multiplies each specific concentration by a sigmoidal weighted function, then sums all values. Wi = 1/[1 + Me-(A x Ci)] , where M and A are constants 4403 and 126 ppm-1, respectively, wi is the weighting factor for ci, and ci is concentration in ppm.