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Glossary
Absorption of Radiation: The uptake of radiation by a solid a number of layers according to its mixing or chemical char-
body, liquid, or gas. The absorbed energy may be transferred acteristics, generally determined by its thermal properties
or re-emitted. (temperature). The layer nearest the Earth is the troposphere,
which reaches up to an altitude of about 8 km (about 5 mi)
Aerosol: Particulate matter, solid or liquid, larger than a mol-
in the polar regions, and up to 17 km (nearly 11 mi) above
ecule but small enough to remain suspended in the atmo-
the equator. The stratosphere, which reaches to an altitude
sphere. Natural sources include salt particles from sea spray,
of about 50 km (31 mi) lies atop the troposphere. The meso-
dust and clay particles as a result of weathering of rocks, both
sphere extends from 80 to 90 km (50 to 56 mi) atop the strato-
of which are carried upward by the wind. Aerosols can also
sphere, and finally, the thermosphere, or ionosphere, gradually
originate as a result of human activities and are often consid-
diminishes and forms a fuzzy border with outer space. There
ered pollutants. Aerosols are important in the atmosphere as
is relatively little mixing of gases between layers.
nuclei for the condensation of water droplets and ice crystals,
as participants in various chemical cycles, and as absorbers and Aviation Gasoline: All special grades of gasoline for use in
scatterers of solar radiation, thereby influencing the radiation aviation reciprocating engines, as cited in ASTM Specifica-
budget of the Earth's climate system. tion D 910. Includes all refinery products within the gasoline
range that are to be marketed straight or in blends as aviation
Air Carrier: An operator (e.g., airline) in the commercial
gasoline without further processing (any refinery operation
system of air transportation consisting of aircraft that hold
except mechanical blending). Also included are finished com-
certificates of Public Convenience and Necessity issued by the
ponents in the gasoline range, which will be used for blend-
department of transportation to conduct scheduled or non-
ing or compounding into aviation gasoline.
scheduled flights within the country or abroad.
Biodegradable: Material that can be broken down into sim-
Air Pollution: One or more chemicals or substances in high
pler substances (elements and compounds) by bacteria or
enough concentrations in the air to harm humans, other
other decomposers. Paper and most organic wastes such as
animals, vegetation, or materials. Such chemicals or phys-
animal manure are biodegradable.
ical conditions (such as excess heat or noise) are called air
pollutants. Biofuel: Gas or liquid fuel made from plant material (biomass).
Includes wood, wood waste, wood liquors, peat, railroad ties,
Alternative Energy: Energy derived from nontraditional
wood sludge, spent sulfite liquors, agricultural waste, straw,
sources (e.g., compressed natural gas, solar, hydroelectric,
tires, fish oils, tall oil, sludge waste, waste alcohol, municipal
wind).
solid waste, landfill gases, other waste, and ethanol blended
Anthropogenic: Human made. In the context of GHGs, into motor gasoline.
anthropogenic emissions are produced as the result of human
Biomass: Total dry weight of all living organisms that can be
activities.
supported at each tropic level in a food chain. Also, materials
Atmosphere: The mixture of gases surrounding the Earth. that are biological in origin, including organic material (both
The Earth's atmosphere consists of about 79.1% nitrogen (by living and dead) from above and below ground, for exam-
volume), 20.9% oxygen, 0.036% carbon dioxide, and trace ple, trees, crops, grasses, tree litter, roots, and animals and
amounts of other gases. The atmosphere can be divided into animal waste.
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Biomass Energy: Energy produced by combusting biomass Carbon Sinks: Carbon reservoirs and conditions that take in
materials such as wood. The carbon dioxide emitted from and store more carbon (i.e., carbon sequestration) than they
burning biomass will not increase total atmospheric carbon release. Carbon sinks can serve to partially offset GHG emis-
dioxide if this consumption is done on a sustainable basis sions. Forests and oceans are large carbon sinks.
(i.e., if in a given period of time, re-growth of biomass takes
Carbon Tetrachloride (CCl4): A compound consisting of one
up as much carbon dioxide as is released from biomass com-
carbon atom and four chlorine atoms. It is an ozone-depleting
bustion). Biomass energy is often suggested as a replacement
substance. Carbon tetrachloride was widely used as a raw
for fossil fuel combustion.
material in many industrial applications, including the pro-
British Thermal Unit (Btu): The quantity of heat required duction of chlorofluorocarbons, and as a solvent. Solvent use
to raise the temperature of one pound of water one degree of was ended in the United States when it was discovered to be
Fahrenheit at or near 39.2 degrees Fahrenheit. carcinogenic.
Bunker Fuel: Fuel supplied to ships and aircraft for interna- Chlorofluorocarbons (CFCs): Organic compounds made
tional transportation, irrespective of the flag of the carrier, up of atoms of carbon, chlorine, and fluorine. An example
consisting primarily of residual and distillate fuel oil for ships is CFC-12 (CCl2F2), used as a refrigerant in refrigerators
and jet fuel for aircraft. and air conditioners and as a foam-blowing agent. Gaseous
Carbon Black: An amorphous form of carbon, produced CFCs can deplete the ozone layer when they slowly rise into
commercially by thermal or oxidative decomposition of hydro- the stratosphere, are broken down by strong ultraviolet ra-
carbons and used principally in rubber goods, pigments, and diation, release chlorine atoms, and then react with ozone
printer's ink. molecules.
Carbon Cycle: All carbon reservoirs and exchanges of car- Climate: The average weather, usually taken over a 30-year
bon from reservoir to reservoir by various chemical, phys- time period, for a particular region and time period. Climate
ical, geological, and biological processes. Usually thought is not the same as weather, but rather, it is the average pattern
of as a series of the four main reservoirs of carbon inter- of weather for a particular region. Weather describes the short-
connected by pathways of exchange. The four reservoirs, term state of the atmosphere. Climatic elements include pre-
regions of the Earth in which carbon behaves in a system- cipitation, temperature, humidity, sunshine, wind velocity,
atic manner, are the atmosphere, terrestrial biosphere (usu- phenomena such as fog, frost, and hailstorms, and other mea-
ally includes freshwater systems), oceans, and sediments sures of the weather.
(includes fossil fuels). Each of these global reservoirs may Climate Change: The term climate change is sometimes used
be subdivided into smaller pools, ranging in size from indi- to refer to all forms of climatic inconsistency, but because the
vidual communities or ecosystems to the total of all living Earth's climate is never static, the term is more properly used
organisms (biota). to imply a significant change from one climatic condition to
Carbon Dioxide: A colorless, odorless, nonpoisonous gas that another. In some cases, climate change has been used synony-
is a normal part of the ambient air. Carbon dioxide is a prod- mously with the term global warming; scientists however,
uct of fossil fuel combustion. Although carbon dioxide does tend to use the term in the wider sense to also include natu-
not directly impair human health, it is a GHG that traps ter- ral changes in climate.
restrial (i.e., infrared) radiation and contributes to the poten- Climate Feedback: An atmospheric, oceanic, terrestrial, or
tial for global warming. other process that is activated by direct climate change induced
Carbon Equivalent (CE) or Carbon Dioxide Equivalent by changes in radiative forcing. Climate feedbacks may increase
(CO2e): A metric measure used to compare the emissions (positive feedback) or diminish (negative feedback) the mag-
of the different GHGs based upon their global warming nitude of the direct climate change.
potential (GWP). GHG emissions in the United States are Climate System (or Earth System): The atmosphere, the
most commonly expressed as "million metric tons of carbon
oceans, the biosphere, the cryosphere, and the geosphere,
equivalents" (MMTCE). Global warming potentials are used
together make up the climate system.
to convert GHGs to carbon dioxide equivalents.
Combustion: Chemical oxidation accompanied by the gen-
Carbon Sequestration: The uptake and storage of carbon.
eration of light and heat.
Trees and plants, for example, absorb carbon dioxide, release
the oxygen and store the carbon. Fossil fuels were at one time Concentration: Amount of a chemical in a particular volume
biomass and continue to store the carbon until burned. or weight of air, water, soil, or other medium.
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Contrail: Contrails are line-shaped clouds or condensation quality energy such as low-temperature heat is dispersed or
trails, composed of ice particles that are visible behind jet diluted and cannot do much useful work.
aircraft engines, typically at cruise altitudes in the upper atmo-
Energy: The capacity for doing work as measured by the ca-
sphere. Aircraft engines emit water vapor, carbon dioxide
pability of doing work (potential energy) or the conversion of
(CO2), small amounts of nitrogen oxides (NOx), hydrocar-
this capability to motion (kinetic energy). Energy has several
bons, carbon monoxide, sulfur gases, and soot and metal par-
forms, some of which are easily convertible and can be
ticles formed by the high-temperature combustion of jet fuel
changed to another form useful for work. Most of the world's
during flight.
convertible energy comes from fossil fuels that are burned
Criteria Pollutant: A pollutant determined to be hazardous to produce heat that is then used as a transfer medium to
to human health and regulated under the USEPA's National mechanical or other means in order to accomplish tasks. In the
Ambient Air Quality Standards. The 1970 amendments to United States, electrical energy is often measured in kilowatt
the Clean Air Act require USEPA to describe the health and hours (kWh), while heat energy is often measured in British
welfare impacts of a pollutant as the "criteria" for inclusion thermal units (Btu).
in the regulatory regime. In this report, emissions of the
Energy-Efficiency: The ratio of the useful output of services
criteria pollutants are carbon monoxide (CO), nitrogen ox-
from an article of industrial equipment to the energy use by
ides (NOx), volatile organic compounds (VOCs), and sul-
such an article; for example, vehicle miles traveled per gallon
fur oxides (SOx).
of fuel (mpg).
Distillate Fuel Oil: A general classification for the petroleum
Enhanced Greenhouse Effect: The concept that the natural
fractions produced in conventional distillation operations.
greenhouse effect has been enhanced by anthropogenic emis-
Included are products known as No. 1, No. 2, and No. 4 fuel
sions of GHGs. Increased concentrations of carbon dioxide,
oils and No. 1, No. 2, and No. 4 diesel fuels. Used primarily for
methane, and nitrous oxide, CFCs, HFCs, PFCs, SF6, NF3,
space heating, on- and off-highway diesel engine fuel (includ-
and other photochemically important gases caused by human
ing railroad engine fuel and fuel for agricultural machinery),
activities such as fossil fuel consumption, trap more in-
and electric power generation.
frared radiation, thereby exerting a warming influence on
Emission Factor: The rate at which pollutants are emitted into the climate.
the atmosphere by one source or a combination of sources.
Enplanements: The number of passengers on a departing
Emission Inventory: A list of air pollutants emitted into aircraft.
the atmosphere of a community, state, nation, or the Earth, Ethanol (C2H5OH): Otherwise known as ethyl alcohol, alco-
in amounts per some unit time (e.g., day or year) by type of hol, or grain spirit. A clear, colorless, flammable oxygenated
source. An emission inventory has both political and scientific hydrocarbon with a boiling point of 78.5 degrees Celsius in the
applications. anhydrous state. In transportation, ethanol is used as a vehi-
Emissions Coefficient/Factor: A unique value for scaling cle fuel by itself (E100), blended with gasoline (E85), or as a
emissions to activity data in terms of a standard rate of emis- gasoline octane enhancer and oxygenate (10% concentration).
sions per unit of activity (e.g., grams of carbon dioxide emit- FAA ASDi (Aircraft Situation Display to Industry): This
ted per barrel of fossil fuel consumed). represents data collected by the FAA that tracks the minute-
Emissions: Releases of gases to the atmosphere (e.g., the re- by-minute progress of their aircraft in real-time. The ASDI
lease of carbon dioxide during fuel combustion). Emissions information includes the location, altitude, airspeed, destina-
can be either intended or unintended releases. tion, estimated time of arrival, and tail number or designated
identifier of air carrier and general aviation aircraft operating
Energy Conservation: Reduction or elimination of unneces-
on IFR flight plans within U.S. airspace.
sary energy use and waste.
FAA T-1 Data: This database refers to information collected
Energy Intensity: Ratio between the consumption of energy
by the FAA and reported by the Bureau of Transportation
to a given quantity of output; usually refers to the amount of
Statistics concerning on-time arrival data for non-stop domes-
primary or final energy consumed per unit of gross domestic
tic flights by major air carriers, and provides such additional
product.
items as departure and arrival delays, origin and destination
Energy Quality: Ability of a form of energy to do useful work. airports, flight numbers, scheduled and actual departure and
High-temperature heat and the chemical energy in fossil fuels arrival times, cancelled or diverted flights, taxi-out and taxi-in
and nuclear fuels are concentrated high-quality energy. Low- times, air time, and non-stop distance.
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Fixed-Based Operator (FBO): A private operator that may carbon dioxide over a period of time (usually 100 years). Gases
conduct refueling, aircraft, or ground support equipment involved in complex atmospheric chemical processes have
services for others at the airport. not been assigned GWPs.
Fluorocarbons: Carbon-fluorine compounds that often con- Global Warming: The progressive gradual rise of the Earth's
tain other elements such as hydrogen, chlorine, or bromine. surface temperature thought to be caused by the green-
Common fluorocarbons include chlorofluorocarbons (CFCs), house effect and responsible for changes in global climate
hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons patterns.
(HFCs), and perfluorocarbons (PFCs).
Greenhouse Effect: Trapping and build-up of heat in the
Forcing Mechanism: A process that alters the energy balance atmosphere (troposphere) near the Earth's surface. Some
of the climate system (i.e., changes the relative balance between of the heat flowing back toward space from the Earth's sur-
incoming solar radiation and outgoing infrared radiation face is absorbed by water vapor, carbon dioxide, ozone, and
from Earth). Such mechanisms include changes in solar irra- several other gases in the atmosphere and then reradiated
diance, volcanic eruptions, and enhancement of the natural back toward the Earth's surface. If the atmospheric concen-
greenhouse effect by emission of carbon dioxide. trations of these GHGs rise, the average temperature of the
lower atmosphere will gradually increase.
Forest: Terrestrial ecosystem (biome) with enough average
annual precipitation (at least 76 cm or 30 in.) to support growth Greenhouse Gas (GHG): Any gas that absorbs infrared radi-
of various species of trees and smaller forms of vegetation. ation in the atmosphere. GHGs include, but are not limited
to, water vapor, carbon dioxide (CO2), methane (CH4), nitrous
Fossil Fuel: A general term for buried combustible geologic
oxide (N2O), hydrochlorofluorocarbons (HCFCs), ozone
deposits of organic materials, formed from decayed plants and
(O3), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs),
animals that have been converted to crude oil, coal, natural
and sulfur hexafluoride (SF6).
gas, or heavy oils by exposure to heat and pressure in the
Earth's crust over hundreds of millions of years. Halocarbons: Chemicals consisting of carbon, sometimes
hydrogen, and either chlorine, fluorine, bromine, or iodine.
Fossil Fuel Combustion: Burning of coal, oil (including gaso-
line), or natural gas. The burning needed to generate energy Hydrocarbons: Substances containing only hydrogen and
releases carbon dioxide by-products that can include unburned carbon. Fossil fuels are made up of hydrocarbons.
hydrocarbons, methane, and carbon monoxide. Carbon
Hydrochlorofluorocarbons (HCFCs): Compounds contain-
monoxide, methane, and many of the unburned hydrocar-
ing hydrogen, fluorine, chlorine, and carbon atoms. Although
bons slowly oxidize into carbon dioxide in the atmosphere.
ozone-depleting substances, they are less potent at destroying
Common sources of fossil fuel combustion include cars and
stratospheric ozone than chlorofluorocarbons (CFCs). They
electric utilities.
have been introduced as temporary replacements for CFCs
Freon: See chlorofluorocarbons. and are also GHGs.
Fugitive Emissions: Unintended gas leaks from the pro- Hydrofluorocarbons (HFCS): Compounds containing only
cessing, transmission, and/or transportation of fossil fuels, hydrogen, fluorine, and carbon atoms. They were introduced
CFCs from refrigeration leaks, SF6 from electrical power as alternatives to ozone-depleting substances in serving many
distributor, etc. industrial, commercial, and personal needs. HFCs are emit-
ted as by-products of industrial processes and are also used
General Aviation: The portion of civil aviation that encom-
in manufacturing. They do not significantly deplete the strato-
passes all facets of aviation except air carriers. It includes
spheric ozone layer, but they are powerful GHGs with global
any air taxis, commuter air carriers, and air travel clubs
warming potentials ranging from 140 (HFC-152a) to 11,700
that do not hold Certificates of Public Convenience and
(HFC-23).
Necessity.
Hydrosphere: All of the Earth's liquid water (oceans, smaller
Global Warming Potential (GWP): The index used to trans-
bodies of fresh water, and underground aquifers), frozen
late the level of emissions of various gases into a common
water (polar ice caps, floating ice, and frozen upper layer of
measure in order to compare the relative radiative forcing
soil known as permafrost), and small amounts of water vapor
of different gases without directly calculating the changes
in the atmosphere.
in atmospheric concentrations. GWPs are calculated as the
ratio of the radiative forcing that would result from the emis- Infrared Radiation: The heat energy that is emitted from
sions of 1 kg of a GHG to that from the emission of 1 kg of all solids, liquids, and gases. In the context of the greenhouse
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issue, the term refers to the heat energy emitted by the Earth's Joule: The energy required to push with a force of one Newton
surface and its atmosphere. GHGs strongly absorb this radi- for one meter.
ation in the Earth's atmosphere, and re-radiate some of it
Kerosene: A petroleum distillate that has a maximum dis-
back toward the surface, creating the greenhouse effect.
tillation temperature of 401 degrees Fahrenheit at the 10%
Inorganic Compound: Combination of two or more elements recovery point, a final boiling point of 572 degrees Fahrenheit,
other than those used to form organic compounds. and a minimum flash point of 100 degrees Fahrenheit. Used
in space heaters, cookstoves, and water heaters, and suitable
Intergovernmental Panel on Climate Change (IPCC): The
for use as an illuminant when burned in wick lamps.
IPCC was established jointly by the United Nations Environ-
ment Programme and the World Meteorological Organization Kyoto Protocol: An international agreement struck by na-
in 1988. The purpose of the IPCC is to assess information in tions attending the Third Conference of Parties (COP) to the
the scientific and technical literature related to all significant United Nations Framework Convention on Climate Change
components of the issue of climate change. The IPCC draws (held in December of 1997 in Kyoto, Japan) to reduce world-
upon hundreds of the world's expert scientists as authors and wide emissions of GHGs. If ratified and put into force, indi-
thousands as expert reviewers. Leading experts on climate vidual countries have committed to reduce their GHG emis-
change and environmental, social, and economic sciences sions by a specified amount.
from some 60 nations have helped the IPCC prepare periodic
assessments of the scientific underpinnings for understand- Landing and Takeoff Cycle (LTO): One aircraft LTO is
ing global climate change and its consequences. With its ca- equivalent to two aircraft operations (one landing and one
pacity for reporting on climate change, its consequences, and takeoff). The standard LTO cycle begins when the aircraft
the viability of adaptation and mitigation measures, the IPCC crosses into the mixing zone as it approaches the airport on
is also looked to as the official advisory body to the world's its descent from cruising altitude, lands, and taxis to the
governments on the state of the science of the climate change gate. The cycle continues as the aircraft taxis back out to the
issue. For example, the IPCC organized the development of runway for takeoff and climbout as it heads out of the mix-
internationally accepted methods for conducting national ing zone and back up to cruising altitude. The five specific
GHG emission inventories. operating modes in a standard LTO are: approach, taxi/
idle-in, taxi/idle-out, takeoff, and climbout. Most aircraft
International Council for Local Environmental Initiatives go through this sequence during a complete standard oper-
(ICLEI): http://rds.yahoo.com/_ylt=A0oGklceR8tGshwA61 ating cycle.
NXNyoA;_ylu=X3oDMTE5NmF1MzA3BHNlYwNzcgRwb3
MDMQRjb2xvA3NrMQR2dGlkA0Y4NjJfMTI1BGwDV1Mx/ Lifetime (Atmospheric): The lifetime of a GHG refers to the
SIG=119u5jimp/EXP=1187813534/**http%3a/www.iclei.org/ approximate amount of time it would take for the anthro-
is an international association of local governments and na- pogenic increment to an atmospheric pollutant concentra-
tional and regional local government organizations that have tion to return to its natural level (assuming emissions cease)
made a commitment to sustainable development. More than as a result of either being converted to another chemical com-
630 cities, towns, counties, and their associations world- pound or being taken out of the atmosphere via a sink. This
wide comprise ICLEI's growing membership. ICLEI works time depends on the pollutant's sources and sinks as well as
with these and hundreds of other local governments through its reactivity. The lifetime of a pollutant is often considered in
international performance-based, results-oriented cam- conjunction with the mixing of pollutants in the atmosphere;
paigns and programs. The ICLEI Cities for Climate Protec- a long lifetime will allow the pollutant to mix throughout
tion (CCP) Campaign assists cities in adopting policies and the atmosphere. Average lifetimes can vary from about a week
implementing quantifiable measures to reduce local GHG (e.g., sulfate aerosols) to more than a century (e.g., CFCs, car-
emissions, improve air quality, and enhance urban livability bon dioxide).
and sustainability. More than 800 local governments partic- Light-Duty Vehicles: Automobiles and light trucks combined.
ipate in the CCP, integrating climate change mitigation into
their decision-making processes. See http://www.iclei.org/ Liquefied Natural Gas (LNG): Natural gas converted to liq-
index.php?id=800 uid form by cooling to a very low temperature.
Jet Fuel: Includes both naphtha-type and kerosene-type fuels Liquefied Petroleum Gas (LPG): Ethane, ethylene, propane,
meeting standards for use in aircraft turbine engines. Although propylene, normal butane, butylene, and isobutane pro-
most jet fuel is used in aircraft, some is used for other purposes duced at refineries or natural gas processing plants, includ-
such as generating electricity. ing plants that fractionate new natural gas plant liquids.
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Longwave Radiation: The radiation emitted in the spectral Nitrogen Cycle: Cyclic movement of nitrogen in different
wavelength greater than 4 µm corresponding to the radia- chemical forms from the environment to organisms, and
tion emitted from the Earth and atmosphere. It is sometimes, then back to the environment.
although somewhat imprecisely, referred to as terrestrial radi-
Nitrogen Oxides (NOx): Gases consisting of one molecule of
ation or infrared radiation.
nitrogen and varying numbers of oxygen molecules. Nitrogen
Low-Emission Vehicle (LEV): A vehicle meeting the low- oxides are produced, for example, by the combustion of fossil
emission vehicle standards. fuels in vehicles and electric power plants. In the atmosphere,
nitrogen oxides can contribute to formation of photochemical
Methane (CH4): A hydrocarbon that is a GHG with a global
ozone (smog), impair visibility, and have health consequences;
warming potential most recently estimated at 21. Methane is
they are considered pollutants.
produced through anaerobic (without oxygen) decomposition
of waste in landfills, animal digestion, decomposition of Nitrous Oxide (N2O): A powerful GHG with a global warm-
animal wastes, production and distribution of natural gas ing potential most recently evaluated at 310. Major sources of
and petroleum, coal production, and incomplete fossil fuel nitrous oxide include soil cultivation practices, especially the
combustion. The atmospheric concentration of methane has use of commercial and organic fertilizers, fossil fuel combus-
been shown to be increasing at a rate of about 0.6% per year tion, nitric acid production, and biomass burning.
and the concentration of about 1.7 per million by volume
(ppmv) is more than twice its pre-industrial value. However, Nonbiodegradable: Substance that cannot be broken down
the rate of increase of methane in the atmosphere may be in the environment by natural processes.
stabilizing. Non-Methane Volatile Organic Compounds (NMVOCs):
Methanol (CH3OH): A colorless, poisonous liquid with es- Organic compounds, other than methane, that participate in
sentially no odor and little taste. It is the simplest alcohol with atmospheric photochemical reactions.
a boiling point of 64.7 degrees Celsius. In transportation, Non-Point Source: Large land area such as crop fields and
methanol is used as a vehicle fuel by itself (M100) or blended urban areas that discharge pollutant into surface and under-
with gasoline (M85). ground water over a large area.
Metric Ton: Common international measurement for the Nuclear Electric Power: Electricity generated by an electric
quantity of GHG emissions. A metric ton is equal to 1,000 kg, power plant whose turbines are driven by steam generated in
2,204.6 lbs, or 1.1023 short tons. a reactor by heat from the fissioning of nuclear fuel.
Mixing Height: The height of the completely mixed portion Nuclear Energy: Energy released when atomic nuclei undergo
of atmosphere that begins at the earth's surface and extends a nuclear reaction such as the spontaneous emission of radio-
to a few thousand feet overhead where the atmosphere be- activity, nuclear fission, or nuclear fusion.
comes fairly stable.
Organic Compound: Molecule that contains atoms of the
Mobile Source: A moving vehicle that emits pollutants. Such element carbon, usually combined with itself and with atoms
sources include airplanes, cars, trucks, and ground support of one or more other element such as hydrogen, oxygen, nitro-
equipment. gen, sulfur, phosphorus, chlorine, or fluorine.
Montreal Protocol on Substances that Deplete the Ozone
Oxidize: To chemically transform a substance by combining
Layer: The Montreal Protocol and its amendments control
it with oxygen.
the phase-out of ozone-depleting substances production and
use. Under the Protocol, several international organizations Oxygen Cycle: Cyclic movement of oxygen in different chem-
report on the science of ozone-depletion, implement proj- ical forms from the environment to organisms, and then back
ects to help move away from ozone-depleting substances, and to the environment.
provide a forum for policy discussions. In the United States,
Ozone: A colorless gas with a pungent odor, having the mo-
the Protocol is implemented under the rubric of the Clean Air
lecular form of O3, found in two layers of the atmosphere,
Act Amendments of 1990.
the stratosphere and the troposphere. Ozone is a form of
Natural Gas: Underground deposits of gases consisting of oxygen found naturally in the stratosphere that provides a
50% to 90% methane (CH4) and small amounts of heavier protective layer shielding the Earth from ultraviolet radia-
gaseous hydrocarbon compounds such as propane (C3H4) and tion's harmful health effects on humans and the environ-
butane (C4H10). ment. In the troposphere, ozone is a chemical oxidant and
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major component of photochemical smog. Ozone can seri- Polyvinyl Chloride (PVC): A polymer of vinyl chloride. It is
ously affect the human respiratory system. tasteless, odorless, and insoluble in most organic solvents. A
member of the family vinyl resin, used in soft flexible films for
Ozone-Depleting Substance (ODS): A family of man-made
food packaging and in molded rigid products, such as pipes,
compounds that includes, but is not limited to, chlorofluo-
fibers, upholstery, and bristles.
rocarbons (CFCs), bromofluorocarbons (halons), methyl
chloroform, carbon tetrachloride, methyl bromide, and hydro- Radiation: Energy emitted in the form of electromagnetic
chlorofluorocarbons (HCFCs). These compounds have been waves. Radiation has differing characteristics depending upon
shown to deplete stratospheric ozone, and therefore are typi- the wavelength. Because the radiation from the Sun is rela-
cally referred to as ODSs. tively energetic, it has a short wavelength (e.g., ultraviolet,
visible, and near infrared) while energy re-radiated from the
Ozone Layer: Layer of gaseous ozone (O3) in the stratosphere Earth's surface and the atmosphere has a longer wavelength
that protects life on Earth by filtering out harmful ultraviolet (e.g., infrared radiation) because the Earth is cooler than
radiation from the sun. the Sun.
Ozone Precursors: Chemical compounds, such as carbon Radiative Forcing: A change in the balance between incoming
monoxide, methane, non-methane hydrocarbons, and nitro- solar radiation and outgoing infrared (i.e., thermal) radiation.
gen oxides that, in the presence of solar radiation, react with Without any radiative forcing, solar radiation coming to
other chemical compounds to form ozone, mainly in the the Earth would continue to be approximately equal to the
troposphere. infrared radiation emitted from the Earth. The addition of
Particulate Matter (PM): Solid particles or liquid droplets GHGs to the atmosphere traps an increased fraction of the
suspended or carried in the air. infrared radiation, reradiating it back toward the surface of
the Earth and thereby creates a warming influence.
Parts Per Billion (ppb): Number of parts of a chemical
Recycling: Collecting and reprocessing a resource so it can be
found in one billion parts of a particular gas, liquid, or solid
used again. An example is collecting aluminum cans, melting
mixture.
them down, and using the aluminum to make new cans or
Parts Per Million (ppm): Number of parts of a chemical other aluminum products.
found in one million parts of a particular gas, liquid, or solid.
Reforestation: Replanting of forests on lands that have been
Perfluorocarbons (PFCs): A group of human-made chemi- harvested recently.
cals composed of carbon and fluorine only. These chemicals
Renewable Energy: Energy obtained from sources that are
(predominantly CF4 and C2F6) were introduced as alterna-
essentially inexhaustible, unlike, for example, fossil fuels, of
tives, along with hydrofluorocarbons, to ozone-depleting
which there is a finite supply. Renewable sources of energy
substances. In addition, PFCs are emitted as by-products include wood, waste, geothermal, wind, photovoltaic, and
of industrial processes and are also used in manufacturing. solar thermal energy.
PFCs do not harm the stratospheric ozone layer, but they are
powerful GHGs: CF4 has a global warming potential (GWP) Residence Time: Average time spent in a reservoir by an in-
of 6,500 and C2F6 has a GWP of 9,200. dividual atom or molecule. Also, this term is used to define
the age of a molecule when it leaves the reservoir. With respect
Petroleum: A generic term applied to oil and oil products to GHGs, residence time usually refers to how long a partic-
in all forms, such as crude oil, lease condensate, unfinished ular molecule remains in the atmosphere.
oils, petroleum products, natural gas plant liquids, and non-
hydrocarbon compounds blended into finished petroleum Sector: Division, most commonly used to denote type of en-
products. ergy consumer (e.g., residential) or according to the Intergov-
ernmental Panel on Climate Change, the type of GHG emitter
Point Source: A single identifiable source that discharges (e.g., industrial process).
pollutants into the environment. Examples are a smokestack,
sewer, ditch, or pipe. Short Ton: Common measurement for a ton in the United
States. A short ton is equal to 2,000 lbs. or 0.907 metric tons.
Pollution: A change in the physical, chemical, or biological
characteristics of the air, water, or soil that can affect the Sink: A reservoir that uptakes a pollutant from another part of
its cycle. Soil and trees tend to act as natural sinks for carbon.
health, survival, or activities of humans in an unwanted way.
Some expand the term to include harmful effects on all forms Solar Energy: Direct radiant energy from the Sun. It also in-
of life. cludes indirect forms of energy such as wind, falling or
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flowing water (hydropower), ocean thermal gradients, and Terrestrial: Pertaining to land.
biomass, which are produced when direct solar energy inter-
Terrestrial Radiation: The total infrared radiation emitted
acts with the Earth.
by the Earth and its atmosphere in the temperature range of
Solar Radiation: Energy from the Sun. Also referred to as approximately 200 to 300 degrees K. Terrestrial radiation
short-wave radiation. Of importance to the climate system, provides a major part of the potential energy changes neces-
solar radiation includes ultraviolet radiation, visible radiation, sary to drive the atmospheric wind system and is responsible
and infrared radiation. for maintaining the surface air temperature within limits of
livability.
Source: Any process or activity that releases a GHG, an
aerosol, or a precursor of a GHG into the atmosphere. Transportation Sector: Consists of private and public passen-
Special Naphtha: All finished products within the naphtha ger and freight transportation, as well as government trans-
boiling range that are used as paint thinners, cleaners, or sol- portation, including military operations.
vents. Those products are refined to a specified flash point. Troposphere: The lowest layer of the atmosphere, which
Still Gas: Any form or mixture of gases produced in refiner- contains about 95% of the mass of air in the Earth's atmosphere.
ies by distillation, cracking, reforming, and other processes. The troposphere extends from the Earth's surface up to about
Principal constituents are methane, ethane, ethylene, normal 10 to 15 km (6 to 12 mi). All weather processes take place in
butane, butylene, propane, propylene, etc. Used as a refinery the troposphere. Ozone that is formed in the troposphere
fuel and as a petrochemical feedstock. plays a significant role in both the GHG effect and urban smog.
Stratosphere: Second layer of the atmosphere, extending from Ultraviolet Radiation (UV): A portion of the electromagnetic
about 19 to 48 km (12 to 30 mi) above the Earth's surface. It spectrum with wavelengths shorter than visible light. The sun
contains small amounts of gaseous ozone (O3), which filters produces UV, which is commonly split into three bands of
out about 99% of the incoming harmful ultraviolet (UV) decreasing wavelength. Shorter wavelength radiation has a
radiation. Most commercial airline flights operate at a cruising greater potential to cause biological damage on living organ-
altitude in the lower stratosphere. isms. The longer wavelength ultraviolet band, UVA, is not
absorbed by ozone in the atmosphere. UVB is mostly ab-
Stratospheric Ozone: See ozone layer. sorbed by ozone, although some reaches the Earth. The short-
Sulfur Cycle: Cyclic movement of sulfur in different chem- est wavelength band, UVC, is completely absorbed by ozone
ical forms from the environment to organisms, and then back and normal oxygen in the atmosphere.
to the environment. United Nations Framework Convention on Climate Change
Sulfur Dioxide (SO2): A compound composed of one sulfur (UNFCCC): The international treaty unveiled at the United
and two oxygen molecules. Sulfur dioxide emitted into the Nations Conference on Environment and Development
atmosphere through natural and anthropogenic processes (UNCED) in June 1992. The UNFCCC commits signatory
is changed in a complex series of chemical reactions in the countries to stabilize anthropogenic (i.e., human-induced)
atmosphere to sulfate aerosols. These aerosols are believed to GHG emissions to "levels that would prevent dangerous
result in negative radiative forcing (i.e., tending to cool the anthropogenic interference with the climate system." The
Earth's surface) and do result in acid deposition (e.g., acid rain). UNFCCC also requires that all signatory parties develop and
update national inventories of anthropogenic emissions of
Sulfur Hexafluoride (SF6): A colorless gas soluble in alcohol all GHGs not otherwise controlled by the Montreal Protocol.
and ether, slightly soluble in water. A very powerful GHG See http://www.ipcc.ch/
used primarily in electrical transmission and distribution sys-
tems and as a dielectric in electronics. The global warming Vehicle Miles Traveled (VMT): One vehicle traveling the
potential of SF6 is 23,900. distance of 1 mi. Thus, total vehicle miles is the total mileage
traveled by all vehicles.
Synthetic Natural Gas (SNG): A manufactured product
chemically similar in most respects to natural gas, resulting Volatile Organic Compounds (VOCs): Organic compounds
from the conversion or reforming of petroleum hydrocar- that evaporate readily into the atmosphere at normal tem-
bons. It may be substituted easily for, or interchanged with, peratures. VOCs contribute significantly to photochemical
pipeline quality natural gas. smog production and certain health problems.
Temperature: Measure of the average speed of motion of the Water Vapor: The most abundant GHG; it is the water pres-
atoms or molecules in a substance or combination of sub- ent in the atmosphere in gaseous form. Water vapor is an
stances at a given moment. important part of the natural greenhouse effect. Although
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humans are not significantly increasing its concentration, it cloudiness, and precipitation. In most places, weather can
contributes to the enhanced greenhouse effect because the change from hour to hour, day to day, and season to season.
warming influence of GHGs leads to a positive water vapor Climate is the average of weather over time and space. A sim-
feedback. In addition to its role as a natural GHG, water ple way of remembering the difference is that climate is what
vapor plays an important role in regulating the temperature you expect (e.g., cold winters) and weather is what you get
of the planet because clouds form when excess water vapor in (e.g., a blizzard).
the atmosphere condenses to form ice and water droplets and
World Resource Institute (WRI): The World Resources
precipitation.
Institute (WRI) is an environmental think tank. WRI, in com-
Weather: Weather is the specific condition of the atmosphere bination with the World Business Council for Sustainable
at a particular place and time. It is measured in terms of such Development published guidance in 2005 concerning the
things as wind, temperature, humidity, atmospheric pressure, development of GHG inventories. See www.wri.org
