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40 Absorption of Radiation: The uptake of radiation by a solid body, liquid, or gas. The absorbed energy may be transferred or re-emitted. Aerosol: Particulate matter, solid or liquid, larger than a mol- ecule but small enough to remain suspended in the atmo- sphere. Natural sources include salt particles from sea spray, dust and clay particles as a result of weathering of rocks, both of which are carried upward by the wind. Aerosols can also originate as a result of human activities and are often consid- ered pollutants. Aerosols are important in the atmosphere as nuclei for the condensation of water droplets and ice crystals, as participants in various chemical cycles, and as absorbers and scatterers of solar radiation, thereby influencing the radiation budget of the Earthâs climate system. Air Carrier: An operator (e.g., airline) in the commercial system of air transportation consisting of aircraft that hold certificates of Public Convenience and Necessity issued by the department of transportation to conduct scheduled or non- scheduled flights within the country or abroad. Air Pollution: One or more chemicals or substances in high enough concentrations in the air to harm humans, other animals, vegetation, or materials. Such chemicals or phys- ical conditions (such as excess heat or noise) are called air pollutants. Alternative Energy: Energy derived from nontraditional sources (e.g., compressed natural gas, solar, hydroelectric, wind). Anthropogenic: Human made. In the context of GHGs, anthropogenic emissions are produced as the result of human activities. Atmosphere: The mixture of gases surrounding the Earth. The Earthâs atmosphere consists of about 79.1% nitrogen (by volume), 20.9% oxygen, 0.036% carbon dioxide, and trace amounts of other gases. The atmosphere can be divided into a number of layers according to its mixing or chemical char- acteristics, generally determined by its thermal properties (temperature). The layer nearest the Earth is the troposphere, which reaches up to an altitude of about 8 km (about 5 mi) in the polar regions, and up to 17 km (nearly 11 mi) above the equator. The stratosphere, which reaches to an altitude of about 50 km (31 mi) lies atop the troposphere. The meso- sphere extends from 80 to 90 km (50 to 56 mi) atop the strato- sphere, and finally, the thermosphere, or ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is relatively little mixing of gases between layers. Aviation Gasoline: All special grades of gasoline for use in aviation reciprocating engines, as cited in ASTM Specifica- tion D 910. Includes all refinery products within the gasoline range that are to be marketed straight or in blends as aviation gasoline without further processing (any refinery operation except mechanical blending). Also included are finished com- ponents in the gasoline range, which will be used for blend- ing or compounding into aviation gasoline. Biodegradable: Material that can be broken down into sim- pler substances (elements and compounds) by bacteria or other decomposers. Paper and most organic wastes such as animal manure are biodegradable. Biofuel: Gas or liquid fuel made from plant material (biomass). Includes wood, wood waste, wood liquors, peat, railroad ties, wood sludge, spent sulfite liquors, agricultural waste, straw, tires, fish oils, tall oil, sludge waste, waste alcohol, municipal solid waste, landfill gases, other waste, and ethanol blended into motor gasoline. Biomass: Total dry weight of all living organisms that can be supported at each tropic level in a food chain. Also, materials that are biological in origin, including organic material (both living and dead) from above and below ground, for exam- ple, trees, crops, grasses, tree litter, roots, and animals and animal waste. Glossary
Biomass Energy: Energy produced by combusting biomass materials such as wood. The carbon dioxide emitted from burning biomass will not increase total atmospheric carbon dioxide if this consumption is done on a sustainable basis (i.e., if in a given period of time, re-growth of biomass takes up as much carbon dioxide as is released from biomass com- bustion). Biomass energy is often suggested as a replacement for fossil fuel combustion. British Thermal Unit (Btu): The quantity of heat required to raise the temperature of one pound of water one degree of Fahrenheit at or near 39.2 degrees Fahrenheit. Bunker Fuel: Fuel supplied to ships and aircraft for interna- tional transportation, irrespective of the flag of the carrier, consisting primarily of residual and distillate fuel oil for ships and jet fuel for aircraft. Carbon Black: An amorphous form of carbon, produced commercially by thermal or oxidative decomposition of hydro- carbons and used principally in rubber goods, pigments, and printerâs ink. Carbon Cycle: All carbon reservoirs and exchanges of car- bon from reservoir to reservoir by various chemical, phys- ical, geological, and biological processes. Usually thought of as a series of the four main reservoirs of carbon inter- connected by pathways of exchange. The four reservoirs, regions of the Earth in which carbon behaves in a system- atic manner, are the atmosphere, terrestrial biosphere (usu- ally includes freshwater systems), oceans, and sediments (includes fossil fuels). Each of these global reservoirs may be subdivided into smaller pools, ranging in size from indi- vidual communities or ecosystems to the total of all living organisms (biota). Carbon Dioxide: A colorless, odorless, nonpoisonous gas that is a normal part of the ambient air. Carbon dioxide is a prod- uct of fossil fuel combustion. Although carbon dioxide does not directly impair human health, it is a GHG that traps ter- restrial (i.e., infrared) radiation and contributes to the poten- tial for global warming. Carbon Equivalent (CE) or Carbon Dioxide Equivalent (CO2e): A metric measure used to compare the emissions of the different GHGs based upon their global warming potential (GWP). GHG emissions in the United States are most commonly expressed as âmillion metric tons of carbon equivalentsâ (MMTCE). Global warming potentials are used to convert GHGs to carbon dioxide equivalents. Carbon Sequestration: The uptake and storage of carbon. Trees and plants, for example, absorb carbon dioxide, release the oxygen and store the carbon. Fossil fuels were at one time biomass and continue to store the carbon until burned. Carbon Sinks: Carbon reservoirs and conditions that take in and store more carbon (i.e., carbon sequestration) than they release. Carbon sinks can serve to partially offset GHG emis- sions. Forests and oceans are large carbon sinks. Carbon Tetrachloride (CCl4): A compound consisting of one carbon atom and four chlorine atoms. It is an ozone-depleting substance. Carbon tetrachloride was widely used as a raw material in many industrial applications, including the pro- duction of chlorofluorocarbons, and as a solvent. Solvent use was ended in the United States when it was discovered to be carcinogenic. Chlorofluorocarbons (CFCs): Organic compounds made up of atoms of carbon, chlorine, and fluorine. An example is CFC-12 (CCl2F2), used as a refrigerant in refrigerators and air conditioners and as a foam-blowing agent. Gaseous CFCs can deplete the ozone layer when they slowly rise into the stratosphere, are broken down by strong ultraviolet ra- diation, release chlorine atoms, and then react with ozone molecules. Climate: The average weather, usually taken over a 30-year time period, for a particular region and time period. Climate is not the same as weather, but rather, it is the average pattern of weather for a particular region. Weather describes the short- term state of the atmosphere. Climatic elements include pre- cipitation, temperature, humidity, sunshine, wind velocity, phenomena such as fog, frost, and hailstorms, and other mea- sures of the weather. Climate Change: The term climate change is sometimes used to refer to all forms of climatic inconsistency, but because the Earthâs climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, climate change has been used synony- mously with the term global warming; scientists however, tend to use the term in the wider sense to also include natu- ral changes in climate. Climate Feedback: An atmospheric, oceanic, terrestrial, or other process that is activated by direct climate change induced by changes in radiative forcing. Climate feedbacks may increase (positive feedback) or diminish (negative feedback) the mag- nitude of the direct climate change. Climate System (or Earth System): The atmosphere, the oceans, the biosphere, the cryosphere, and the geosphere, together make up the climate system. Combustion: Chemical oxidation accompanied by the gen- eration of light and heat. Concentration: Amount of a chemical in a particular volume or weight of air, water, soil, or other medium. 41
Contrail: Contrails are line-shaped clouds or condensation trails, composed of ice particles that are visible behind jet aircraft engines, typically at cruise altitudes in the upper atmo- sphere. Aircraft engines emit water vapor, carbon dioxide (CO2), small amounts of nitrogen oxides (NOx), hydrocar- bons, carbon monoxide, sulfur gases, and soot and metal par- ticles formed by the high-temperature combustion of jet fuel during flight. Criteria Pollutant: A pollutant determined to be hazardous to human health and regulated under the USEPAâs National Ambient Air Quality Standards. The 1970 amendments to the Clean Air Act require USEPA to describe the health and welfare impacts of a pollutant as the âcriteriaâ for inclusion in the regulatory regime. In this report, emissions of the criteria pollutants are carbon monoxide (CO), nitrogen ox- ides (NOx), volatile organic compounds (VOCs), and sul- fur oxides (SOx). Distillate Fuel Oil: A general classification for the petroleum fractions produced in conventional distillation operations. Included are products known as No. 1, No. 2, and No. 4 fuel oils and No. 1, No. 2, and No. 4 diesel fuels. Used primarily for space heating, on- and off-highway diesel engine fuel (includ- ing railroad engine fuel and fuel for agricultural machinery), and electric power generation. Emission Factor: The rate at which pollutants are emitted into the atmosphere by one source or a combination of sources. Emission Inventory: A list of air pollutants emitted into the atmosphere of a community, state, nation, or the Earth, in amounts per some unit time (e.g., day or year) by type of source. An emission inventory has both political and scientific applications. Emissions Coefficient/Factor: A unique value for scaling emissions to activity data in terms of a standard rate of emis- sions per unit of activity (e.g., grams of carbon dioxide emit- ted per barrel of fossil fuel consumed). Emissions: Releases of gases to the atmosphere (e.g., the re- lease of carbon dioxide during fuel combustion). Emissions can be either intended or unintended releases. Energy Conservation: Reduction or elimination of unneces- sary energy use and waste. Energy Intensity: Ratio between the consumption of energy to a given quantity of output; usually refers to the amount of primary or final energy consumed per unit of gross domestic product. Energy Quality: Ability of a form of energy to do useful work. High-temperature heat and the chemical energy in fossil fuels and nuclear fuels are concentrated high-quality energy. Low- quality energy such as low-temperature heat is dispersed or diluted and cannot do much useful work. Energy: The capacity for doing work as measured by the ca- pability of doing work (potential energy) or the conversion of this capability to motion (kinetic energy). Energy has several forms, some of which are easily convertible and can be changed to another form useful for work. Most of the worldâs convertible energy comes from fossil fuels that are burned to produce heat that is then used as a transfer medium to mechanical or other means in order to accomplish tasks. In the United States, electrical energy is often measured in kilowatt hours (kWh), while heat energy is often measured in British thermal units (Btu). Energy-Efficiency: The ratio of the useful output of services from an article of industrial equipment to the energy use by such an article; for example, vehicle miles traveled per gallon of fuel (mpg). Enhanced Greenhouse Effect: The concept that the natural greenhouse effect has been enhanced by anthropogenic emis- sions of GHGs. Increased concentrations of carbon dioxide, methane, and nitrous oxide, CFCs, HFCs, PFCs, SF6, NF3, and other photochemically important gases caused by human activities such as fossil fuel consumption, trap more in- frared radiation, thereby exerting a warming influence on the climate. Enplanements: The number of passengers on a departing aircraft. Ethanol (C2H5OH): Otherwise known as ethyl alcohol, alco- hol, or grain spirit. A clear, colorless, flammable oxygenated hydrocarbon with a boiling point of 78.5 degrees Celsius in the anhydrous state. In transportation, ethanol is used as a vehi- cle fuel by itself (E100), blended with gasoline (E85), or as a gasoline octane enhancer and oxygenate (10% concentration). FAA ASDi (Aircraft Situation Display to Industry): This represents data collected by the FAA that tracks the minute- by-minute progress of their aircraft in real-time. The ASDI information includes the location, altitude, airspeed, destina- tion, estimated time of arrival, and tail number or designated identifier of air carrier and general aviation aircraft operating on IFR flight plans within U.S. airspace. FAA T-1 Data: This database refers to information collected by the FAA and reported by the Bureau of Transportation Statistics concerning on-time arrival data for non-stop domes- tic flights by major air carriers, and provides such additional items as departure and arrival delays, origin and destination airports, flight numbers, scheduled and actual departure and arrival times, cancelled or diverted flights, taxi-out and taxi-in times, air time, and non-stop distance. 42
Fixed-Based Operator (FBO): A private operator that may conduct refueling, aircraft, or ground support equipment services for others at the airport. Fluorocarbons: Carbon-fluorine compounds that often con- tain other elements such as hydrogen, chlorine, or bromine. Common fluorocarbons include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs). Forcing Mechanism: A process that alters the energy balance of the climate system (i.e., changes the relative balance between incoming solar radiation and outgoing infrared radiation from Earth). Such mechanisms include changes in solar irra- diance, volcanic eruptions, and enhancement of the natural greenhouse effect by emission of carbon dioxide. Forest: Terrestrial ecosystem (biome) with enough average annual precipitation (at least 76 cm or 30 in.) to support growth of various species of trees and smaller forms of vegetation. Fossil Fuel: A general term for buried combustible geologic deposits of organic materials, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the Earthâs crust over hundreds of millions of years. Fossil Fuel Combustion: Burning of coal, oil (including gaso- line), or natural gas. The burning needed to generate energy releases carbon dioxide by-products that can include unburned hydrocarbons, methane, and carbon monoxide. Carbon monoxide, methane, and many of the unburned hydrocar- bons slowly oxidize into carbon dioxide in the atmosphere. Common sources of fossil fuel combustion include cars and electric utilities. Freon: See chlorofluorocarbons. Fugitive Emissions: Unintended gas leaks from the pro- cessing, transmission, and/or transportation of fossil fuels, CFCs from refrigeration leaks, SF6 from electrical power distributor, etc. General Aviation: The portion of civil aviation that encom- passes all facets of aviation except air carriers. It includes any air taxis, commuter air carriers, and air travel clubs that do not hold Certificates of Public Convenience and Necessity. Global Warming Potential (GWP): The index used to trans- late the level of emissions of various gases into a common measure in order to compare the relative radiative forcing of different gases without directly calculating the changes in atmospheric concentrations. GWPs are calculated as the ratio of the radiative forcing that would result from the emis- sions of 1 kg of a GHG to that from the emission of 1 kg of carbon dioxide over a period of time (usually 100 years). Gases involved in complex atmospheric chemical processes have not been assigned GWPs. Global Warming: The progressive gradual rise of the Earthâs surface temperature thought to be caused by the green- house effect and responsible for changes in global climate patterns. Greenhouse Effect: Trapping and build-up of heat in the atmosphere (troposphere) near the Earthâs surface. Some of the heat flowing back toward space from the Earthâs sur- face is absorbed by water vapor, carbon dioxide, ozone, and several other gases in the atmosphere and then reradiated back toward the Earthâs surface. If the atmospheric concen- trations of these GHGs rise, the average temperature of the lower atmosphere will gradually increase. Greenhouse Gas (GHG): Any gas that absorbs infrared radi- ation in the atmosphere. GHGs include, but are not limited to, water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrochlorofluorocarbons (HCFCs), ozone (O3), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Halocarbons: Chemicals consisting of carbon, sometimes hydrogen, and either chlorine, fluorine, bromine, or iodine. Hydrocarbons: Substances containing only hydrogen and carbon. Fossil fuels are made up of hydrocarbons. Hydrochlorofluorocarbons (HCFCs): Compounds contain- ing hydrogen, fluorine, chlorine, and carbon atoms. Although ozone-depleting substances, they are less potent at destroying stratospheric ozone than chlorofluorocarbons (CFCs). They have been introduced as temporary replacements for CFCs and are also GHGs. Hydrofluorocarbons (HFCS): Compounds containing only hydrogen, fluorine, and carbon atoms. They were introduced as alternatives to ozone-depleting substances in serving many industrial, commercial, and personal needs. HFCs are emit- ted as by-products of industrial processes and are also used in manufacturing. They do not significantly deplete the strato- spheric ozone layer, but they are powerful GHGs with global warming potentials ranging from 140 (HFC-152a) to 11,700 (HFC-23). Hydrosphere: All of the Earthâs liquid water (oceans, smaller bodies of fresh water, and underground aquifers), frozen water (polar ice caps, floating ice, and frozen upper layer of soil known as permafrost), and small amounts of water vapor in the atmosphere. Infrared Radiation: The heat energy that is emitted from all solids, liquids, and gases. In the context of the greenhouse 43
issue, the term refers to the heat energy emitted by the Earthâs surface and its atmosphere. GHGs strongly absorb this radi- ation in the Earthâs atmosphere, and re-radiate some of it back toward the surface, creating the greenhouse effect. Inorganic Compound: Combination of two or more elements other than those used to form organic compounds. Intergovernmental Panel on Climate Change (IPCC): The IPCC was established jointly by the United Nations Environ- ment Programme and the World Meteorological Organization in 1988. The purpose of the IPCC is to assess information in the scientific and technical literature related to all significant components of the issue of climate change. The IPCC draws upon hundreds of the worldâs expert scientists as authors and thousands as expert reviewers. Leading experts on climate change and environmental, social, and economic sciences from some 60 nations have helped the IPCC prepare periodic assessments of the scientific underpinnings for understand- ing global climate change and its consequences. With its ca- pacity for reporting on climate change, its consequences, and the viability of adaptation and mitigation measures, the IPCC is also looked to as the official advisory body to the worldâs governments on the state of the science of the climate change issue. For example, the IPCC organized the development of internationally accepted methods for conducting national GHG emission inventories. International Council for Local Environmental Initiatives (ICLEI): http://rds.yahoo.com/_ylt=A0oGklceR8tGshwA61 NXNyoA;_ylu=X3oDMTE5NmF1MzA3BHNlYwNzcgRwb3 MDMQRjb2xvA3NrMQR2dGlkA0Y4NjJfMTI1BGwDV1Mx/ SIG=119u5jimp/EXP=1187813534/**http%3a/www.iclei.org/ is an international association of local governments and na- tional and regional local government organizations that have made a commitment to sustainable development. More than 630 cities, towns, counties, and their associations world- wide comprise ICLEIâs growing membership. ICLEI works with these and hundreds of other local governments through international performance-based, results-oriented cam- paigns and programs. The ICLEI Cities for Climate Protec- tion (CCP) Campaign assists cities in adopting policies and implementing quantifiable measures to reduce local GHG emissions, improve air quality, and enhance urban livability and sustainability. More than 800 local governments partic- ipate in the CCP, integrating climate change mitigation into their decision-making processes. See http://www.iclei.org/ index.php?id=800 Jet Fuel: Includes both naphtha-type and kerosene-type fuels meeting standards for use in aircraft turbine engines. Although most jet fuel is used in aircraft, some is used for other purposes such as generating electricity. Joule: The energy required to push with a force of one Newton for one meter. Kerosene: A petroleum distillate that has a maximum dis- tillation temperature of 401 degrees Fahrenheit at the 10% recovery point, a final boiling point of 572 degrees Fahrenheit, and a minimum flash point of 100 degrees Fahrenheit. Used in space heaters, cookstoves, and water heaters, and suitable for use as an illuminant when burned in wick lamps. Kyoto Protocol: An international agreement struck by na- tions attending the Third Conference of Parties (COP) to the United Nations Framework Convention on Climate Change (held in December of 1997 in Kyoto, Japan) to reduce world- wide emissions of GHGs. If ratified and put into force, indi- vidual countries have committed to reduce their GHG emis- sions by a specified amount. Landing and Takeoff Cycle (LTO): One aircraft LTO is equivalent to two aircraft operations (one landing and one takeoff). The standard LTO cycle begins when the aircraft crosses into the mixing zone as it approaches the airport on its descent from cruising altitude, lands, and taxis to the gate. The cycle continues as the aircraft taxis back out to the runway for takeoff and climbout as it heads out of the mix- ing zone and back up to cruising altitude. The five specific operating modes in a standard LTO are: approach, taxi/ idle-in, taxi/idle-out, takeoff, and climbout. Most aircraft go through this sequence during a complete standard oper- ating cycle. Lifetime (Atmospheric): The lifetime of a GHG refers to the approximate amount of time it would take for the anthro- pogenic increment to an atmospheric pollutant concentra- tion to return to its natural level (assuming emissions cease) as a result of either being converted to another chemical com- pound or being taken out of the atmosphere via a sink. This time depends on the pollutantâs sources and sinks as well as its reactivity. The lifetime of a pollutant is often considered in conjunction with the mixing of pollutants in the atmosphere; a long lifetime will allow the pollutant to mix throughout the atmosphere. Average lifetimes can vary from about a week (e.g., sulfate aerosols) to more than a century (e.g., CFCs, car- bon dioxide). Light-Duty Vehicles: Automobiles and light trucks combined. Liquefied Natural Gas (LNG): Natural gas converted to liq- uid form by cooling to a very low temperature. Liquefied Petroleum Gas (LPG): Ethane, ethylene, propane, propylene, normal butane, butylene, and isobutane pro- duced at refineries or natural gas processing plants, includ- ing plants that fractionate new natural gas plant liquids. 44
Longwave Radiation: The radiation emitted in the spectral wavelength greater than 4 µm corresponding to the radia- tion emitted from the Earth and atmosphere. It is sometimes, although somewhat imprecisely, referred to as terrestrial radi- ation or infrared radiation. Low-Emission Vehicle (LEV): A vehicle meeting the low- emission vehicle standards. Methane (CH4): A hydrocarbon that is a GHG with a global warming potential most recently estimated at 21. Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and petroleum, coal production, and incomplete fossil fuel combustion. The atmospheric concentration of methane has been shown to be increasing at a rate of about 0.6% per year and the concentration of about 1.7 per million by volume (ppmv) is more than twice its pre-industrial value. However, the rate of increase of methane in the atmosphere may be stabilizing. Methanol (CH3OH): A colorless, poisonous liquid with es- sentially no odor and little taste. It is the simplest alcohol with a boiling point of 64.7 degrees Celsius. In transportation, methanol is used as a vehicle fuel by itself (M100) or blended with gasoline (M85). Metric Ton: Common international measurement for the quantity of GHG emissions. A metric ton is equal to 1,000 kg, 2,204.6 lbs, or 1.1023 short tons. Mixing Height: The height of the completely mixed portion of atmosphere that begins at the earthâs surface and extends to a few thousand feet overhead where the atmosphere be- comes fairly stable. Mobile Source: A moving vehicle that emits pollutants. Such sources include airplanes, cars, trucks, and ground support equipment. Montreal Protocol on Substances that Deplete the Ozone Layer: The Montreal Protocol and its amendments control the phase-out of ozone-depleting substances production and use. Under the Protocol, several international organizations report on the science of ozone-depletion, implement proj- ects to help move away from ozone-depleting substances, and provide a forum for policy discussions. In the United States, the Protocol is implemented under the rubric of the Clean Air Act Amendments of 1990. Natural Gas: Underground deposits of gases consisting of 50% to 90% methane (CH4) and small amounts of heavier gaseous hydrocarbon compounds such as propane (C3H4) and butane (C4H10). Nitrogen Cycle: Cyclic movement of nitrogen in different chemical forms from the environment to organisms, and then back to the environment. Nitrogen Oxides (NOx): Gases consisting of one molecule of nitrogen and varying numbers of oxygen molecules. Nitrogen oxides are produced, for example, by the combustion of fossil fuels in vehicles and electric power plants. In the atmosphere, nitrogen oxides can contribute to formation of photochemical ozone (smog), impair visibility, and have health consequences; they are considered pollutants. Nitrous Oxide (N2O): A powerful GHG with a global warm- ing potential most recently evaluated at 310. Major sources of nitrous oxide include soil cultivation practices, especially the use of commercial and organic fertilizers, fossil fuel combus- tion, nitric acid production, and biomass burning. Nonbiodegradable: Substance that cannot be broken down in the environment by natural processes. Non-Methane Volatile Organic Compounds (NMVOCs): Organic compounds, other than methane, that participate in atmospheric photochemical reactions. Non-Point Source: Large land area such as crop fields and urban areas that discharge pollutant into surface and under- ground water over a large area. Nuclear Electric Power: Electricity generated by an electric power plant whose turbines are driven by steam generated in a reactor by heat from the fissioning of nuclear fuel. Nuclear Energy: Energy released when atomic nuclei undergo a nuclear reaction such as the spontaneous emission of radio- activity, nuclear fission, or nuclear fusion. Organic Compound: Molecule that contains atoms of the element carbon, usually combined with itself and with atoms of one or more other element such as hydrogen, oxygen, nitro- gen, sulfur, phosphorus, chlorine, or fluorine. Oxidize: To chemically transform a substance by combining it with oxygen. Oxygen Cycle: Cyclic movement of oxygen in different chem- ical forms from the environment to organisms, and then back to the environment. Ozone: A colorless gas with a pungent odor, having the mo- lecular form of O3, found in two layers of the atmosphere, the stratosphere and the troposphere. Ozone is a form of oxygen found naturally in the stratosphere that provides a protective layer shielding the Earth from ultraviolet radia- tionâs harmful health effects on humans and the environ- ment. In the troposphere, ozone is a chemical oxidant and 45
major component of photochemical smog. Ozone can seri- ously affect the human respiratory system. Ozone-Depleting Substance (ODS): A family of man-made compounds that includes, but is not limited to, chlorofluo- rocarbons (CFCs), bromofluorocarbons (halons), methyl chloroform, carbon tetrachloride, methyl bromide, and hydro- chlorofluorocarbons (HCFCs). These compounds have been shown to deplete stratospheric ozone, and therefore are typi- cally referred to as ODSs. Ozone Layer: Layer of gaseous ozone (O3) in the stratosphere that protects life on Earth by filtering out harmful ultraviolet radiation from the sun. Ozone Precursors: Chemical compounds, such as carbon monoxide, methane, non-methane hydrocarbons, and nitro- gen oxides that, in the presence of solar radiation, react with other chemical compounds to form ozone, mainly in the troposphere. Particulate Matter (PM): Solid particles or liquid droplets suspended or carried in the air. Parts Per Billion (ppb): Number of parts of a chemical found in one billion parts of a particular gas, liquid, or solid mixture. Parts Per Million (ppm): Number of parts of a chemical found in one million parts of a particular gas, liquid, or solid. Perfluorocarbons (PFCs): A group of human-made chemi- cals composed of carbon and fluorine only. These chemicals (predominantly CF4 and C2F6) were introduced as alterna- tives, along with hydrofluorocarbons, to ozone-depleting substances. In addition, PFCs are emitted as by-products of industrial processes and are also used in manufacturing. PFCs do not harm the stratospheric ozone layer, but they are powerful GHGs: CF4 has a global warming potential (GWP) of 6,500 and C2F6 has a GWP of 9,200. Petroleum: A generic term applied to oil and oil products in all forms, such as crude oil, lease condensate, unfinished oils, petroleum products, natural gas plant liquids, and non- hydrocarbon compounds blended into finished petroleum products. Point Source: A single identifiable source that discharges pollutants into the environment. Examples are a smokestack, sewer, ditch, or pipe. Pollution: A change in the physical, chemical, or biological characteristics of the air, water, or soil that can affect the health, survival, or activities of humans in an unwanted way. Some expand the term to include harmful effects on all forms of life. Polyvinyl Chloride (PVC): A polymer of vinyl chloride. It is tasteless, odorless, and insoluble in most organic solvents. A member of the family vinyl resin, used in soft flexible films for food packaging and in molded rigid products, such as pipes, fibers, upholstery, and bristles. Radiation: Energy emitted in the form of electromagnetic waves. Radiation has differing characteristics depending upon the wavelength. Because the radiation from the Sun is rela- tively energetic, it has a short wavelength (e.g., ultraviolet, visible, and near infrared) while energy re-radiated from the Earthâs surface and the atmosphere has a longer wavelength (e.g., infrared radiation) because the Earth is cooler than the Sun. Radiative Forcing: A change in the balance between incoming solar radiation and outgoing infrared (i.e., thermal) radiation. Without any radiative forcing, solar radiation coming to the Earth would continue to be approximately equal to the infrared radiation emitted from the Earth. The addition of GHGs to the atmosphere traps an increased fraction of the infrared radiation, reradiating it back toward the surface of the Earth and thereby creates a warming influence. Recycling: Collecting and reprocessing a resource so it can be used again. An example is collecting aluminum cans, melting them down, and using the aluminum to make new cans or other aluminum products. Reforestation: Replanting of forests on lands that have been harvested recently. Renewable Energy: Energy obtained from sources that are essentially inexhaustible, unlike, for example, fossil fuels, of which there is a finite supply. Renewable sources of energy include wood, waste, geothermal, wind, photovoltaic, and solar thermal energy. Residence Time: Average time spent in a reservoir by an in- dividual atom or molecule. Also, this term is used to define the age of a molecule when it leaves the reservoir. With respect to GHGs, residence time usually refers to how long a partic- ular molecule remains in the atmosphere. Sector: Division, most commonly used to denote type of en- ergy consumer (e.g., residential) or according to the Intergov- ernmental Panel on Climate Change, the type of GHG emitter (e.g., industrial process). 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. Sink: A reservoir that uptakes a pollutant from another part of its cycle. Soil and trees tend to act as natural sinks for carbon. Solar Energy: Direct radiant energy from the Sun. It also in- cludes indirect forms of energy such as wind, falling or 46
flowing water (hydropower), ocean thermal gradients, and biomass, which are produced when direct solar energy inter- acts with the Earth. Solar Radiation: Energy from the Sun. Also referred to as short-wave radiation. Of importance to the climate system, solar radiation includes ultraviolet radiation, visible radiation, and infrared radiation. Source: Any process or activity that releases a GHG, an aerosol, or a precursor of a GHG into the atmosphere. Special Naphtha: All finished products within the naphtha boiling range that are used as paint thinners, cleaners, or sol- vents. Those products are refined to a specified flash point. Still Gas: Any form or mixture of gases produced in refiner- ies by distillation, cracking, reforming, and other processes. Principal constituents are methane, ethane, ethylene, normal butane, butylene, propane, propylene, etc. Used as a refinery fuel and as a petrochemical feedstock. Stratosphere: Second layer of the atmosphere, extending from about 19 to 48 km (12 to 30 mi) above the Earthâs surface. It contains small amounts of gaseous ozone (O3), which filters out about 99% of the incoming harmful ultraviolet (UV) radiation. Most commercial airline flights operate at a cruising altitude in the lower stratosphere. Stratospheric Ozone: See ozone layer. Sulfur Cycle: Cyclic movement of sulfur in different chem- ical forms from the environment to organisms, and then back to the environment. Sulfur Dioxide (SO2): A compound composed of one sulfur and two oxygen molecules. Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes is changed in a complex series of chemical reactions in the atmosphere to sulfate aerosols. These aerosols are believed to result in negative radiative forcing (i.e., tending to cool the Earthâs surface) and do result in acid deposition (e.g., acid rain). Sulfur Hexafluoride (SF6): A colorless gas soluble in alcohol and ether, slightly soluble in water. A very powerful GHG used primarily in electrical transmission and distribution sys- tems and as a dielectric in electronics. The global warming potential of SF6 is 23,900. Synthetic Natural Gas (SNG): A manufactured product chemically similar in most respects to natural gas, resulting from the conversion or reforming of petroleum hydrocar- bons. It may be substituted easily for, or interchanged with, pipeline quality natural gas. Temperature: Measure of the average speed of motion of the atoms or molecules in a substance or combination of sub- stances at a given moment. Terrestrial: Pertaining to land. Terrestrial Radiation: The total infrared radiation emitted by the Earth and its atmosphere in the temperature range of approximately 200 to 300 degrees K. Terrestrial radiation provides a major part of the potential energy changes neces- sary to drive the atmospheric wind system and is responsible for maintaining the surface air temperature within limits of livability. Transportation Sector: Consists of private and public passen- ger and freight transportation, as well as government trans- portation, including military operations. Troposphere: The lowest layer of the atmosphere, which contains about 95% of the mass of air in the Earthâs atmosphere. The troposphere extends from the Earthâs surface up to about 10 to 15 km (6 to 12 mi). All weather processes take place in the troposphere. Ozone that is formed in the troposphere plays a significant role in both the GHG effect and urban smog. Ultraviolet Radiation (UV): A portion of the electromagnetic spectrum with wavelengths shorter than visible light. The sun produces UV, which is commonly split into three bands of decreasing wavelength. Shorter wavelength radiation has a greater potential to cause biological damage on living organ- isms. The longer wavelength ultraviolet band, UVA, is not absorbed by ozone in the atmosphere. UVB is mostly ab- sorbed by ozone, although some reaches the Earth. The short- est wavelength band, UVC, is completely absorbed by ozone and normal oxygen in the atmosphere. United Nations Framework Convention on Climate Change (UNFCCC): The international treaty unveiled at the United Nations Conference on Environment and Development (UNCED) in June 1992. The UNFCCC commits signatory countries to stabilize anthropogenic (i.e., human-induced) GHG emissions to âlevels that would prevent dangerous anthropogenic interference with the climate system.â The UNFCCC also requires that all signatory parties develop and update national inventories of anthropogenic emissions of all GHGs not otherwise controlled by the Montreal Protocol. See http://www.ipcc.ch/ Vehicle Miles Traveled (VMT): One vehicle traveling the distance of 1 mi. Thus, total vehicle miles is the total mileage traveled by all vehicles. Volatile Organic Compounds (VOCs): Organic compounds that evaporate readily into the atmosphere at normal tem- peratures. VOCs contribute significantly to photochemical smog production and certain health problems. Water Vapor: The most abundant GHG; it is the water pres- ent in the atmosphere in gaseous form. Water vapor is an important part of the natural greenhouse effect. Although 47
humans are not significantly increasing its concentration, it contributes to the enhanced greenhouse effect because the warming influence of GHGs leads to a positive water vapor feedback. In addition to its role as a natural GHG, water vapor plays an important role in regulating the temperature of the planet because clouds form when excess water vapor in the atmosphere condenses to form ice and water droplets and precipitation. Weather: Weather is the specific condition of the atmosphere at a particular place and time. It is measured in terms of such things as wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most places, weather can change from hour to hour, day to day, and season to season. Climate is the average of weather over time and space. A sim- ple way of remembering the difference is that climate is what you expect (e.g., cold winters) and weather is what you get (e.g., a blizzard). World Resource Institute (WRI): The World Resources Institute (WRI) is an environmental think tank. WRI, in com- bination with the World Business Council for Sustainable Development published guidance in 2005 concerning the development of GHG inventories. See www.wri.org 48
