GLOSSARY OF TERMINOLOGY USED
BY THE WRAP
Aerosol: Solid particles
or liquid droplets that are small enough to be suspended in the
air. Aerosols cause most of the light
extinction responsible for haze on the Colorado Plateau.
Area source: Many small
sources of air pollution in which the contribution of each source
is relatively small, but combined may be a significant source of
air pollution. A city can be an area source (although large facilities
within the city could release enough air pollution to warrant their
analysis individually as a point source).
BART: Best Available Retrofit Technology,
a process under the CAA to evaluate the need and, if warranted,
install the most effective pollution controls on an already existing
air pollution source.
Forecast Scenario: A computer model used by the
Grand Canyon Visibility Transport Commission to estimate future
haze-causing pollution and economics. The GCVTC based
this scenario on current technologies, existing laws, and a
variety of assumptions about how quickly various kinds of pollution
sources will be retired and the type of facilities that will
replace them. It is an extension of current policies, and allows
comparisons with other air pollution management scenarios the GCVTC may
CAA/CAAA: The Clean Air Act,
and the Clean Air Act Amendments.
National air pollution control is based on the Clean Air Act, passed
in 1970. Congress amended the Clean Air Act in 1977 (adding many
visibility sections that the GCVTC is addressing), and in
1990 (when it required creation of the GCVTC, assigned tribal
governments power under the CAA similar to those of the states).
Class I site/area: In
1977, Congress identified 158 national parks, wilderness areas,
international parks and other areas that were to receive the most
stringent protection from increases in air pollution. It also set
a visibility goal for these areas to protect them from future human-caused
haze, and to eliminate existing human-caused haze, and required reasonable
progress toward that goal.
Colorado Plateau: A
high, semi-arid tableland in southeast Utah, northern Arizona,
northwest New Mexico, and western Colorado. The unique erosional
forms of the Plateau are world famous.
CNG: Compressed Natural Gas,
a relatively clean-burning fossil fuel.
EC/OC: Elemental Carbon
(such as soot, often the result of fire and diesel engines) and
carbon combined with other elements to form complex compounds,
often given off by plants and most human activities.
Fine Mass Particulates: Aerosols that
are smaller than 2.5 micrometers in diameter. (A micrometer is
one millionth of a meter, a human hair is about 70 micrometers
GCVTC: The Grand Canyon Visibility Transport Commission,
composed of the governors of eight western states (AZ, CA, CO,
NM, NV, OR, UT, WY), five tribes (Acoma, Hopi, Hualapai, Navajo),
four federal land managers (Bureau of Land Management, U.S. Fish
and Wildlife Service, U.S. Forest Service, National Park Service),
the Columbia River Inter-Tribal Fish Commission, and the Environmental
Protection Agency. The states and tribes vote, the other GCVTC
members do not. The Commission was established to recommend methods
to preserve and improve visibility on the Colorado Plateau.
Congress required establishment of the GCVTC through the Clean
Air Act Amendments of 1990.
HC: Hydrocarbons. A group of
chemicals containing hydrogen and carbon that often contribute
to air pollution as OC's or VOC's.
They are involved in forming ozone, and some hydrocarbons are toxic.
Term often used interchangeably with VOCs.
Hopi Point: An
important air quality monitoring site on the South Rim of the Grand
Canyon in Grand Canyon National Park.
IAS: Integrated Assessment System,
a computer model created by the GCVTC to
generate information about future visibility and economic trends
under a variety of pollution control scenarios.
IMPROVE: Interagency Monitoring
of Protected Visual Environments,
a group of federal agencies using a common set of standards to
monitor visibility across the United States. Other nations have
also adopted portions or all of the IMPROVE monitoring techniques.
Mm-1: A measurement unit used for light
extinction, the higher the value, the hazier the air
LEV/ZEV: Low Emission Vehicle/Zero Emission Vehicle,
motor vehicle classifications referring to their tailpipe release
of air pollution. Today's ZEV's are generally battery powered,
but may use hydrogen fuel cells and other energy sources in the
Light extinction: The "loss" of
light as it travels through the air. Light can be truly lost by
being absorbed by gases and aerosols in
the air. Light can also be "lost" as it scatters off
gases and aerosols.
LNG: Liquefied Natural Gas,
a relatively clean-burning fossil fuel.
LPG: Liquefied Petroleum Gas,
a relatively clean-burning fossil fuel such as propane.
megameters, a measurement unit used for light
extinction, the higher the value, the hazier the air
MMA: Maximum Management Alternative,
an computer model used to estimate
the maximum visibility improvements possible regardless of the
cost of the pollution controls used. The MMA was used for comparisons,
rather than as a policy option.
Mobile source: A
pollution source that moves. Mobile sources are often divided into
road sources, including cars, trucks, buses, and motorcycles, and
non-road sources like trains, planes, boats, lawnmowers, etc.
Modeling: The use of a
computer to mimic reality and predict the future behavior of the
subject under study. Models of complex subjects like visibility
are often limited by the raw data available and the capacity of
the computer itself. The GCVTC's IAS is a computer model
of regional air quality for the Colorado
Plateau and uses information from throughout western North
NAAQS: National Ambient Air Quality Standards,
levels of air pollution set by the U.S. Environmental Protection
Agency to protect public health and welfare. Standards are set
for ozone (O3), carbon monoxide (CO), sulfur
dioxide (SO2), nitrogen dioxide (NO2), lead (Pb), and particulates (solid aerosols).
Non-attainment area: A
geographic region where concentrations of a particular air pollutant
exceed the NAAQS. A particular location
may be non-attainment for more than one pollutant.
mixture of nitrogen dioxide and other nitrogen oxide gases. Nitrogen
is the most common gas in the atmosphere. In high temperature and/or
high pressure burning (as in an engine), the air's nitrogen is
broken down and combined with oxygen, forming unstable or reactive
NOx gases. Nitrogen dioxide (NO2)
is yellowish brown, and thus contributes directly to haze. All
the NOx gases react in the air to form haze-causing aerosols and
NPS: National Park Service,
a federal agency charged with protecting the natural and cultural
resources and the processes that create and sustain them, in the
National Park System.
New Source Review: A
review of a new facility that has the potential to emit air pollutants
in amounts specified by law. The review is done to establish the
impact of the pollution, and the options available to control that
OC: Organic Carbon,
complex carbon-containing compounds often emitted by plants and
many human activities. OC2.5 is organic carbon
of 2.5 micrometers of less.
PAC: Public Advisory Committee,
established by the GCVTC to represent a broad range of public
interests. Members are drawn from all levels of government, business,
industry, environmental organizations, academia, and private citizens.
The GCVTC Commissioners charged the
PAC with developing consensus recommendations for managing visibility.
material small enough to remain suspended in the air.
PM2.5: Aerosols with
a diameter smaller than 2.5 micrometers, the most effective size
range to create haze (a micrometer, or micron, is one millionth
of a meter, an inch is 25,400 micrometers long).
PM10: Aerosols with
a diameter smaller than 10 micrometers, on which the EPA has based
current NAAQS. Larger aerosols in this size range (larger
than 2.5 micrometers) are less effective in creating haze than
the smaller ones. In addition to creating haze, higher concentrations
of PM10 can also cause irritation of the
throat and lungs, cancers, and early death.
Point source: A specific
source of air pollution.
Prescribed fire: Fires
in wildland areas that are allowed to burn under prescribed conditions.
The "prescription" reflects ecosystem management goals,
ability to control the fire, and air quality concerns.
Prescribed natural fire: A
fire started by natural processes (usually lightning) and allowed
to burn as long as it meets prescribed
PSD: Prevention of Significant Deterioration.
A program established under the Clean Air Act Amendments of 1977,
whose goal is to prevent major increases in air pollution in areas
with cleaner air. The program sets the tightest limits on pollution
increases from large point sources in Class
Rayleigh Scattering: The natural scattering of
light caused by nitrogen and oxygen in the atmosphere which
makes the sky look blue. Also called "blue sky."
Reasonable progress: Reasonable
progress refers to progress in reducing human-caused haze in Class
I areas under the national visibility goal. The Clean
Air Act indicates that "reasonable" should consider
the cost of reducing air pollution emissions, the time necessary,
the energy and non-air quality environmental impacts of reducing
emissions, and the remaining useful life of any existing air pollution
source considered for these reductions. The GCVTC Public
Advisory Committee has developed the following definition: "Reasonable
progress towards the national visibility goal is achieving continuous
emission reductions necessary to reduce existing impairment and
attain steady improvement of visibility in mandatory Class I areas,
and managing emissions growth so as to prevent perceptible degradation
of clean air days."
dust: Fine and coarse dust stirred up from paved
or dirt surfaces by the passage of vehicles. The dust may include
soil particles, tire rubber, soot, and other materials.
Regional cap: A limit
on the amount of specific air pollutants that can be released in
a defined geographic area, or a limit on the amount of a specific
air pollutant that is allowed to be in the air in a defined geographic
ROG: Reactive Organic Gases,
typically hydrocarbons (HC), but include
SIP/TIP: State Implementation Plan/Tribal Implementation Plan,
plans devised by states and tribes to carry out their responsibilities
under the Clean Air Act. SIP's and TIP's must be approved by the
U.S. Environmental Protection Agency and include public review.
SOx, sulfates: Compounds composed of oxygen and
sulfur. Burning fuels, manufacturing paper, or smelting rock
containing sulfur produces sulfur dioxide gas (SO2)
which is converted in the air to other sulfur oxides (SOx)
or haze-causing aerosols (sulfates).
Source: Where air pollutants
are released. Sources are usually classified as point, mobile,
or area sources.
Source attribution: Determining
how much a single source contributes
to air pollution.
Stationary source: An
air pollution source that remains
in one place (generally a business or industrial facility).
Species: A term used to
refer to types of pollutants.
TIP/SIP: Tribal Implementation Plan/State Implementation Plan,
plans devised by states and tribes to meet requirements of the
Clean Air Act as defined by the U.S. Environmental Protection Agency.
Trading program: In
air quality management, a plan under which some limit is set on
the amount of an air pollutant that can be released into the air.
If a facility releases less than its limit, it may trade or sell
the ability to release "unused" amount of air pollutant
to another facility, so the second facility can release more than
Transfer coefficient: In
computer modeling of air quality,
a geographic area is divided into "cells." Transfer coefficients
are mathematical formulas that tell the computer how much air pollution
to "move" from one cell to another. Determining a transfer
coefficient requires the computer model designer to consider wind
directions, chemical changes to the air pollutants as they travel,
loss of pollutants from the air, and other factors.
device that measures light extinction by
shining a light beam of known brightness through the air and measuring
how much is lost when the beam reaches a receiver, usually about
4 miles away.
Urban plume/plume blight: An
urban plume is the "cloud" (either visible or invisible)
of air pollution blown downwind of an urban area. Plume blight
is a distinct band or layer of visible air pollution, often from
a single pollution source.
Visibility impairment: The
loss of clarity in the air that results when gases or aerosols scatter
and absorb light. We usually see visibility impairment as a general
haze or a distinct plume.
VMT: Vehicle Miles Traveled.
This number is a measure of vehicle usage and is used to calculate
the air pollution produced by mobile
sources, such as passenger cars, tailpipe emissions and
or road dust.
VOC: Volatile Organic Compound.
A carbon-containing material that evaporates, such as gasoline,
some paints, solvents, dry cleaning fluids, and the like. VOC's
contribute to ozone formation and may form OC aerosols.