Environmental Monitoring, Evaluation, and Protection

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Abbreviations & Acronyms

A horizon: A dark-colored and biologically active mineral soil layer nearest the surface characterized by accumulation of humified organic materials and by loss of silicate clay, iron, and aluminum sesquioxides, with attendant development of granular or platy structure. The A horizon is generally known as the zone of leaching.

Abiotic: Non-living; usually applied to the physical characteristics of biological systems, such as moisture, nutrients, soils, solar radiation, etc.

Acetaldehyd: Acetaldehyde is mainly used as an intermediate in the synthesis of other chemicals. It is ubiquitous in the environment and may be formed in the body from the breakdown of ethanol. Acute (short-term) exposure to acetaldehyde results in effects including irritation of the eyes, skin, and respiratory tract. Symptoms of chronic (long-term) intoxication of acetaldehyde resemble those of alcoholism. Acetaldehyde is considered a probable human carcinogen (Group B2) based on inadequate human cancer studies and animal studies that have shown nasal tumors in rats and laryngeal tumors in hamsters.

Acid: Any of a class of substances whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals to form salts. A substance that yields hydrogen ions when dissolved in water. A substance that can act as a proton donor. A substance that can accept a pair of electrons to form a covalent bond. A substance that yields hydrogen ions when dissolved in water.

Acid deposition: A complex chemical and atmospheric phenomenon that occurs when emissions of sulfur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then deposited on earth in either wet or dry form. The wet forms, popularly called "acid rain," can fall to Earth as rain, snow, or fog and are usually collected in buckets. The dry forms are acidic gases or particles, and are usually collected on filters.

Acid neutralizing capacity (ANC): The ability of a body of water to buffer added acid. The acid-neutralizing capacity of a lake situated over limestone (which is alkaline and can therefore neutralize acids) is much greater than that of a lake over granite.

Acid rain: Air pollution produced when acid chemicals are incorporated into rain, snow, fog or mist. The "acid" in acid rain comes from sulfur oxides and nitrogen oxides, products of burning coal and other fuels and from certain industrial processes. The sulfur oxides and nitrogen oxides are related to two strong acids: sulfuric acid and nitric acid. When sulfur dioxide and nitrogen oxides are released from power plants and other sources, winds blow them far from their source. If the acid chemicals in the air are blown into areas where the weather is wet, the acids can fall to Earth in the rain, snow, fog or mist. In areas where the weather is dry, the acid chemicals may become incorporated into dust or smoke. Acid rain can damage the environment. human health and property.

Acid-gas compounds:

Acidification: The process of becoming acid or being converted into an acid.

Adhesion molecule: Receptors on blood cells and blood vessels that regulate inflammation.

Adsorption: Removal of a pollutant from air or water by collecting the pollutant on the surface of a solid material; e.g., an advanced method of treating waste in which activated carbon removes organic matter from waste-water.

Aerosol: 1. Small droplets or particles suspended in the atmosphere, typically containing sulfur. They are usually emitted naturally (e.g. in volcanic eruptions) and as the result of anthropogenic (human) activities such as burning fossil fuels. 2. The pressurized gas used to propel substances out of a container.

Agribusiness: Large-scale, organized production of food, farm machinery, and supplies as well as the storage, sale, and distribution of farm commodities, for profit.

Agrichemicals: In most cases, agrichemical refers to the broad range of insecticides, herbicides, and fungicides, but it may also include synthetic fertilizers, hormones and other chemical growth agents, and concentrated stores of raw animal manure.

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS): A unique optical sensor that delivers calibrated images of the spectral radiance in 224 contiguous spectral channels (bands) with wavelengths from 400 to 2500 nanometers. The main objective of using the AVIRIS data is to identify, measure, and monitor constituents of oil spills based on molecular absorption and particle scattering signatures.

Airflow: The motion of air relative to the surface of a body moving through the air. A streamlined vehicle design creates a smooth airstream as the vehicle moves, reducing drag and increasing fuel efficiency.

Airshed: The atmospheric equivalent of a watershed. The concept was developed for crude calculations of air pollution levels over large areas.

Airway inflammation: Recruitment of inflammatory blood cells to the lung

Air emissions: See emission.

Air pollutants (air pollution): unwanted chemicals or other materials found in the air. Pollutants can harm health, the environment and property. Many air pollutants occur as gases or vapors, but some are very tiny solid particles: dust, smoke or soot.

Albedo: A measure of reflectivity of a surface or body.

Aldehyde: A class of organic compounds produced by the oxidation of alcohols, which results in the formation of a -CHO (aldehyde) functional group. Aldehydes are very reactive.

Algae: Chiefly aquatic, eucaryotic one-celled or multicellular plants without true stems, roots and leaves, that are typically autotrophic, photosynthetic, and contain chlorophyll. Algae produces natural oils that can be used for biofuels.

Alternative fuels: Fuels that can replace ordinary gasoline. Alternative fuels may have particularly desirable energy efficiency and pollution reduction features. Alternative fuels include compressed natural gas, alcohols, liquefied petroleum gas (LPG), and electricity. The 1990 Clean Air Act encourages development and sale of alternative fuels.

Aluminum (Al): A very light, metallic element with atomic number 13 and atomic weight 26.98. Aluminum makes up about 7 percent of the earth's crust but occurs naturally only in combination with other elements. Aluminum is one of the most important variables for biological impacts due to its toxicity in the ionic form. Changes in concentrations and forms of aluminum are largely driven by changes in pH and DOC, with lower and less toxic aluminum concentrations resulting from high pH values and DOC concentrations. Dissolved aluminum can occur in a variety of forms: single-molecule and polymerized, and free and variously complexed. Because the different species of aluminum have different toxicities and buffering capacities, they are commonly distinguished in water chemistry research. Three principal types are of importance: particulate aluminum, inorganic monomeric aluminum, and organic monomeric aluminum.

Ambient: Surrounding, or present in the background, as in ambient noise levels, air temperature, or water temperature.

American Society for Testing and Materials: An international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services. The ASTM specification for biodiesel is located in section D 6751.

Ammonia: A colorless, alkaline gas with a pungent odor; its chemical formula is NH3. It is formed naturally when bacteria decompose nitrogen-containing compounds, such as proteins. It is used in the manufacture of plastics, explosives and fertilizers, applied as a gas.

Ammonia analyzer: An instrument used to obtain ambient-air ammonia measurements.

Ammonium (NH₄⁺): An ion with formula NH₄⁺ that does not exist in nature except in combination with other ions (as in ammonium chloride, NH₄Cl). Ammonium behaves like an ion of alkali metal when it combines with other substances; it forms many different ammonium salts, a number of which are used as fertilizers (ammonium sulfate, ammonium nitrate, ammonium phosphates).

Ammonium chloride (NH₄Cl): A slightly hygroscopic, white crystalline compound, NH₄Cl, used in dry cells, as a soldering flux, and as an expectorant. Also called sal ammoniac. A white salt.

Ammonium nitrate (NH₄N0₃): A salt consisting of the ammonium and nitrate ions. Ammonium nitrate is used extensively as a synthetic source of nitrogen in fertilizers; it is also used in the manufacture of some explosives. Runoff from fields recently fertilized with ammonium nitrate can contaminate surface water and ground water with nitrates.

Angina pectoris: A disease marked by brief paroxysmal attacks of chest pain precipitated by deficient oxygenation of the heart muscles. See unstable angina.

Anion: An atom or group of atoms with a negative charge. Examples of anions are the hydroxyl ion (OH^-), carboxylic acid functional groups (COO^-), and halide ions (Cl^-, F^-, Br^-, I^-).

Anode: The electrode of an electrochemical cell at which oxidation occurs.

Anthropogenic: Of, relating to, or resulting from the influence of human beings on nature.

Argon (Ar): A colorless, odorless, gaseous element that makes up about 1 percent of earth's atmosphere. Argon is inert (does not combine with other elements); it is the least reactive of its group in the periodic table, the largely inert noble gases. It has an atomic number of 18 and an atomic weight of 39.95. The gas is used in fluorescent light bulbs and was formerly used in radio tubes.

Aromatic Compounds: A type of hydrocarbon, such as benzene or toluene, with a specific type of ring structure. Aromatics are sometimes added to gasoline in order to increase octane. Some aromatics are toxic.

Asthma: A condition marked by labored breathing, constriction of the chest, coughing and gasping usually brought on by allergies.

Atmospheric deposition: The settling out of particulate matter (and also gases) onto the ground surface from the air. Includes wet and dry deposition.

Atmospheric emissions: Suspended pollutants -- solid particles, liquid aerosols, etc. -- or toxic gases released into the atmosphere from a polluting source, or type of source

Attainment area: A geographic area in which levels of a criteria air pollutant meet the health-based primary standard (national ambient air quality standard, or NAAQS) for the pollutant. An area may have on acceptable level for one criteria air pollutant, but may have unacceptable levels for others. Thus, an area could be both attainment and nonattainment at the same time. Attainment areas are defined using federal pollutant limits set by EPA.

Autonomic nervous system: A part of the vertebrate nervous system that innervates smooth and cardiac muscle and glandular tissues, and governs involuntary actions (as secretion, vasoconstriction, or peristalsis).

B100: Pure (100%) biodiesel

B horizon: A mineral soil layer characterized by the maximum accumulation of any combination of humified organic material, silicate clay, and iron or aluminum sesquioxides, with attendant development of blocky, prismatic, or columnar structure and usually redder or browner than overlying and underlying horizons; generally known as the zone of accumulation.

Barium (Ba): A soft metallic element with atomic number 56 and atomic weight 137.3. It has chemical properties similar to those of calcium.. Barium does not exist by itself but occurs in often-poisonous compounds; it is used as a pesticide in paint compounds. Barium sulfate is used medically in x-ray diagnostics.

Baseline Fuels: Fuels that contain no elements other than carbon, hydrogen, oxygen, nitrogen, and/or sulfur; contain less than 1.0% oxygen by weight; contain less than 0.05% sulfur by weight; possess the characteristics of diesel fuel as specified by ASTM standard D 975--93; and are derived only from conventional petroleum, heavy oil deposits, coal, tar sands, and/or oil sands.

Baseload: The minimum load on a power station over a standard period.

Base cations: Positively charged ions such as magnesium, sodium, potassium, and calcium that increase pH of water (make it less acidic) when released to solution through mineral weathering and exchange reactions.

Benthic community: The group of organisms inhabiting the region on the bottom of a body of water, such as a lake or ocean. The benthic community is the living portion of the benthic ecosystem.

Benzene: An aromatic component of gasoline, which is a known cancer-causing agent.

Benzofluoranthene (C₂₀H₁₂): A polycyclic aromatic hydrocarbon. Release of benzo(b)fluoranthene is most likely to result from the incomplete combustion of a variety of fuels including wood and fossil fuels.

Benzopyrene (also benzpyrene): A flammable, potent carcinogen found in polluted air, produced by automobile exhaust, burning tobacco, oil and coal furnaces, and manufacturing of asphalt. Benzpyrene also occurs in coal tar.

Beryllium (Be) A whitish metallic element with atomic number 4 and atomic weight 9.010. It has chemical properties similar to those of magnesium. Beryllium is used for windows in x-ray tubes, in alloys to make them stronger and lighter, and as a source of neutrons as well as a controller of neuron speed in atomic reactors. Beryllium and its compounds are toxic.

Bin 5 Emissions Standards: "Average" of new Tier 2 standards. NOx emissions levels of all vehicles sold by each automaker must average to the bin 5 NOx level or cleaner when standards are fully phased in later in the decade.

Binding: To combine with, form a chemical bond with, or be taken up by, as an enzyme with its substrate.

Bioaccumulants: Substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.

Bioaccumulation: Bioaccumulation refers to the absorption and concentration of a toxic chemical within the body of an organism. Heavy metals and pesticides, such as mercury and DDT, are stored in the fatty tissue and cannot be effectively excreted from the body. Because the chemical can accumulate over time, older and larger organisms (for example, swordfish) tend to have higher amounts in their bodies.

Biobutanol: Alcohol containing four carbon atoms per molecule, produced from the same feedstocks as ethanol, but with a modified fermentation and distillation process. Less water-soluble than ethanol, biobutanol has a higher energy density and can be transported by pipeline more easily.

Biochemical oxygen demand (BOD): An indication of the extent to which water is polluted by sewage or other organic waste. It is a measure of the dissolved oxygen consumed by microorganisms as they break down the organic matter in a sample of water; the greater the quantity of organic matter, the greater the oxygen required for its decomposition. It is expressed in parts per million of dissolved oxygen consumed. Also called biological oxygen demand.

Bioconcentration: Bioconcentration refers to the increasing concentration of toxic chemicals in living organisms within a food chain. Heavy metals and pesticides, such as mercury and DDT, are stored in the fatty tissues of animals and passed along to predators of those animals. The result is higher and higher concentrations of the chemical in fatty tissue, eventually reaching harmful levels in predators and those at the top of the food chain, such as eagles or humans. Also called biomagnification.

Biodiesel: A biodegradable transportation fuel for use in diesel engines that is produced through the transesterfication of organically- derived oils or fats. It may be used either as a replacement for or as a component of diesel fuel.

Biodiversity: The totality of genes, species, and ecosystems in a region or the world.

Bioenergy: Useful, renewable energy produced from organic matter - the conversion of the complex carbohydrates in organic matter to energy. Organic matter may either be used directly as a fuel, processed into liquids and gasses, or be a residual of processing and conversion.

Biofuel: Biomass converted to liquid or gaseous fuels such as ethanol, methanol, methane, and hydrogen.

Biogenic: Produced by natural processes. Usually used in the context of emissions that are produced by plants and animals.

Biogeochemical cycles: The cycling of chemicals such as carbon, oxygen, phosphorus, nitrogen, and water within (intrasystem nutrient cycles) or between (intersystem nutrient cycles) ecosystems and throughout the biosphere. These compounds are assimilated and broken down over and over again by living organisms. Also called nutrient cycles.

Biological indicator (bioindicator): See Biomarker and Indicator Species

Biomagnification: See Bioconcentration

Biomarker: A distinctive biological or biologically derived indicator (as a biochemical metabolite in the body) of a process, event, or condition (as aging, disease, or exposure to a toxic substance)

Biorefinery: A facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass.

Biotic: Concerning or produced by living organisms, such as environmental factors created by plants or microorganisms.

Black Carbon: A form of particulate air pollution most often produced from biomass burning, cooking with solid fuels and diesel exhaust. Black Carbon often settles as soot.

Blendstock: Blendstock is a sub-octane gasoline that is intended to be blended with an oxygenate.

British thermal unit: A British Thermal Unit (BTU) is the amount of heat energy needed to raise the temperature of one pound of water by one degree F. This is the standard measurement used to state the amount of energy that a fuel has as well as the amount of output of any heat generating device.

Brownout: When demand for electricity exceeds the available supply, a brownout occurs.

Buffer Strips: Strips of grass or other erosion-resisting vegetation between or below cultivated strips or fields.

Buffering Capacity: The resistance of water or soil to changes in pH.

Butanol: An alcohol with the chemical formula CH3(CH2)3OH. It is formed during anaerobic fermentation using bacteria to convert the sugars to butanol and carbon dioxide.

By-product heat: A secondary product; heat made incidentally during the production of something else.

Calcium (Ca): A soft, grayish, metallic element with an atomic number 20 and atomic weight 40.48. Calcium occurs commonly in limestone, marble, gypsum, and chalk. Because it is a major component of bones and teeth, it is an essential mineral in the human diet. It is used in plaster and as a reducing (or deoxidizing) agent in chemical reactions.

Calcium chloride (CaCl₂): A salt of calcium. It is used on walkways to melt ice; it is less toxic to plants than common table salt (sodium chloride). Calcium chloride is a strong deliquescent: It will absorb so much water from the air that the powder turns into a puddle. This property makes it useful as a chemical dehumidifier for damp closets, and effective industrially to remove water from gasses or air. Also called muriate of lime.

Cancer Unit Risk Estimate: The increased lifetime cancer risk caused by continuous lifetime exposure of a 1.0 microgram per cubic meter increase in the concentration of a given pollutant.

Cap and trade: A policy approach to controlling large amounts of emissions from a group of sources at costs that are lower than if sources were regulated individually. The approach first sets an overall cap, or maximum amount of emissions per compliance period, that will achieve the desired environmental effects. Authorizations to emit in the form of emission allowances are then allocated to affected sources, and the total number of allowances cannot exceed the cap. Individual control requirements are not specified for sources. The only requirements are that sources completely and accurately measure and report all emissions and then turn in the same number of allowances as emissions at the end of the compliance period.

Carbon (C): A nonmetallic element with an atomic weight of 12.01 and atomic number 6. It is found in all organic compounds, and is the only element whose compounds are considered an entire branch of chemistry. Pure carbon exists in two different crystalline forms, diamond and graphite, and in numerous noncrystalline forms such as charcoal and carbon black. Its ability to link into complex chains or rings of hydrocarbons and other organic compounds makes it the backbone of biochemistry.

Carbonaceous PM _2.5: Organic (carbon-based) component of PM _2.5

Carbon debt: Amount of initial GHG emissions due to land use change that would need to be repaid before gaining any net GHG benefits from a new land use practice, such as growing soybean for biodiesel production.

Carbon monoxide (CO): A colorless, odorless, poisonous gas, produced by incomplete burning of carbon-based fuels. including gasoline, oil and wood. Carbon monoxide is also produced from incomplete combustion of many natural and synthetic products. For instance, cigarette smoke contains carbon monoxide. When carbon monoxide gets into the body, the carbon monoxide combines with chemicals in the blood and prevents the blood from bringing oxygen to cells, tissues and organs. The body's parts need oxygen for energy, so high-level exposures to carbon monoxide can cause serious health effects, with death possible from massive exposures. Symptoms of exposure to carbon monoxide can include vision problems, reduced alertness, and general reduction in mental and physical functions. Carbon monoxide exposures are especially harmful to people with heart, lung and circulatory system diseases.

Carbon Sequestration: The provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the buildup of carbon dioxide (the principal greenhouse gas) concentration in the atmosphere will reduce or slow.

Carcinogenic: Causing or aggravating cancer.

Cardiac repolarization: Period of the heart beat when the heart muscle prepares for the next contraction

Cardiovascular system: The system of, relating to, or involving the heart and blood vessels

Catchment: The natural drainage area for precipitation, the collection area for water supplies, or a river system.

Cathode: The electrode of an electrochemical cell at which reduction occurs.

Cation: An atom or group of atoms with a positive charge. Examples of cations are the hydrogen ion (H⁺) and the ammonium ion (NH₄⁺).

Cation Exchange Capacity (CEC): The ability of a soil to retain cations (positively charged ions) in a form that is available to plants. A soil's CEC depends on the amount and kinds of colloids present. Although type of clay is important, in general, the more clay or organic matter present, the higher the CEC. The higher the CEC, the higher the potential yield of that soil before nutrients must be replenished.

Cellulosic Feedstock: Biomass feedstocks can be used to produce ethanol from cellulosic biomass. Materials considered include agricultural, industrial, and municipal wastes, as well as energy crops such as switchgrass.

centi- (c): A prefix used in the Systeme International d'Unites (SI) to denote one hundredth. A centimeter is one hundredth of a meter.

Chemical mass balance: The balance between the amount (mass) of a chemical entering or leaving a system

Chemiluminescence: Chemiluminescence is the process whereby energy from a chemical reaction is released directly as light without the involvement of heat or flame. Chemiluminescence is not similar to fluorescence (neon signs), phosphorescence (glow in the dark toys), or incandescence (light bulbs), but most similar to bioluminescence. The most common example of this process in nature is the bioluminescence of the firefly. In a state-of-the-art scientific application, environmental instruments can use chemiluminescence to measure oxides of nitrogen from sub parts per billion (ppb) to 5,000 parts per million (ppm).

Chlorine (Cl): An element that occurs as a toxic, irritating (and poisonous) greenish gas, with atomic weight 35.45 and atomic number 17. It exists as the diatomic molecule, Cl₂; it is also common as different salts in sea water (especially sodium chloride, table salt). It is one of the halogen elements.

Chlorofluorocarbons (CFCs): These chemicals and some related chemicals have been used in great quantities in industry, for refrigeration and air conditioning, and in consumer products. CFCs and their relatives, when released into the air, rise into the stratosphere, a layer of the atmosphere high above the Earth. In the stratosphere, CFCs and their relatives take part in chemical reactions that result in reduction of the stratospheric ozone layer, which protects the Earth's surface from harmful effects of radiation from the sun. The 1990 Clean Air Act includes provisions for reducing releases (emissions) and eliminating production and use of these ozone-destroying chemicals.

Clean Air Act: The original Clean Air Act was passed in 1963, but our national air pollution control program is actually based on the 1970 version of the law.

Clean Air Act Amendments (CAAA) of 1990: A reauthorization of the Clean Air Act passed by the U.S. Congress in 1990. The CAAA, which included provisions for the U.S. SO2 Allowance Trading Program, strengthened the ability of EPA to set and enforce pollution control programs aimed at protecting human health and the environment.

Clean Air Interstate Rule: See Interstate Air Quality Rule.

Clean Air Status and Trends Network (CASTNET): CASTNET is the nation's primary source for data on dry acidic deposition and rural, ground-level ozone. Operating since 1987, CASTNET is used in conjunction with other national monitoring networks to provide information for evaluating the effectiveness of national emission control strategies. CASTNET consists of over 80 sites accross the eastern and western United States. The US EPA cooperatively operates and funds CASTNET with the National Park Service.

Clean fuels: Low-pollution fuels that can replace ordinary gasoline. These are alternative fuels, including gasohol (gasoline-alcohol mixtures), natural gas and LPG (liquefied petroleum gas).

Climate change: Often refers to significant change from one climatic condition to another. In some cases, climate change has been used synonymously with the term "global warming"; in its broader sense, it also refers to natural changes in climate.

Coagulation: The solidification into a gelatinous mass, an alteration of a disperse phase or of a dissolved solid, which causes the separation of the system into a liquid phase and an insoluble mass called the clot or curd. Coagulation is usually irreversible.

Coal-fired power plant: Electricity-generating facility that is fueled with coal.

Coal gasification: The conversion of coal to flammable methane gas by a chemical reaction with air and steam.

Cobalt (Co): A hard, gray, metallic element with atomic number 27 and atomic weight 58.93. It is used in many alloys for its strength. Cobalt is used as a blue pigment in glass and pottery; a radioactive isotope (cobalt 60) is used in medicine.

Combined cycle: A high-efficiency power production process. In a typical combined cycle power plant, combustion turbines burn natural gas or oil to generate electricity in the first cycle. In the second cycle, the exhaust heat is captured and used to generate steam, which drives steam turbines to supply additional electric power.

Combined Heat and Power (CHP): CHP, or cogeneration, is the sequential production of power (electricity or shaft work) and thermal energy from a single fuel source. CHP is a more efficient, cleaner, and reliable alternative to conventional generation.

Combustion: Burning. A chemical change, especially through the rapid combination of a substance with oxygen, producing heat and, usually, light. Many important pollutants, such as sulfur dioxide, nitrogen oxides, and particulates (PM-10) are combustion products, often products of the burning of fuels such as coal, oil, gas and wood.

Command-and-control: A policy tool in which the regulating authority establishes the necessary emission reduction or applicable emission limit for specific sources, typically by setting a source-specific emission rate standard or mandating the installation of specific emission reduction technology.

Common loon (Gavia immer): An indicator species that is being used to assess the mercury exposure and risk in aquatic ecosystems in the Adirondack Park of New York State.

Composite samples: Often prepared as a mixture of several different (usually bulk) samples, and from which the laboratory sample is taken.

Compressed natural gas (CNG): An alternative fuel for motor vehicles; considered one of the cleanest because of low hydrocarbon emissions and its vapors are relatively non-ozone producing. However, vehicles fueled with CNG do emit a significant quantity of nitrogen oxides.

Condensation nuclei: Minute particles that catalyze the condensation of water vapor into a droplet by providing a surface for deposition. The particles are often salt near a seacoast, microscopic pieces of dust, or smoke particles.

Continuous emission monitoring systems (CEMS): Machines that measure, on a continuous basis, pollutants released by a source. The 1990 Clean Air Act requires continuous emission monitoring systems for certain large sources.

Continuous Regenerating Technology (CRT): Contains a platinum-coated catalyst and a particulate filter for diesel vehicles that run on reduced sulfur diesel fuel. It mounts on a vehicle in place of the original equipment manufacturer (OEM) muffler.

Control technology; control measures: equipment, processes or actions used to reduce air pollution. The extent of pollution reduction varies among technologies and measures. In general, control technologies and measures that do the best job of reducing pollution will be required in the areas with the worst pollution. For example, the best available control technology/best available control measures (BACT,BACM) will be required in serious nonattainment areas for particulates, a criteria air pollutant. A similar high level of pollution reduction will be achieved with maximum achievable control technology (MACT) which will be required for sources releasing hazardous air pollutants.

Conventional Gasoline: Finished motor gasoline not included in the oxygenated or reformulated gasoline categories.

Co-pollutant: Other gases or particles that may be present in the atmosphere, which is a heterogeneous mix. For example, while we may be interested in PM, there are also VOCs, NO_x, or SO₂ that may be present

Copper (Cu): A reddish metallic element with atomic weight 63.54 and atomic number 29. Copper has many uses because it is easily shaped, resistant to corrosion, and is an excellent conductor of electricity and heat. It is an essential mineral in plant and animal metabolisms.

Coproducts: The resulting substances and materials that accompany the production of ethanol by fermentation process.

Corn Stover: The dried stalks and leaves of a corn crop remaining after the corn has been harvested.

Corn-Ethanol: Biofuel produced from corn crop. 13% of U.S. corn crop is turned into ethanol, producing 12 billion liters of corn-ethanol in 2004.

Coronary stent: A short narrow metal or plastic tube often in the form of a mesh that is inserted into the lumen of an anatomical vessel (as an artery or bile duct) especially to keep a previously blocked passageway open.

Cover Crop: A crop that provides temporary protection for delicate seedlings and/or provides a cover canopy for seasonal soil protection and improvement between normal crop production periods.

Criteria air pollutants: a group of very common air pollutants regulated by EPA on the basis of criteria (information on health and/or environmental effects of pollution). Criteria air pollutants are widely distributed all over the United States.

Critical load: The maximum load of deposition required to protect against further acidification or to allow resource recovery

Crop rotation: A soil conservation technique involving changing crops grown on a given parcel of land from year to year. Crop rotations may include fallow periods.

Curtailment programs: restrictions on operation of fireplaces and woodstoves in areas where these home heat sources make major contributions to pollution.

Cyanide (CN^-): An ion, or any of a number of inorganic salts containing the CN^- anion. Often used to refer to the poison potassium cyanide. Cyanide is used in the manufacture of plastics and in the mining of gold.

deca- (da): A prefix used in the Systeme International d'Unites (SI) to denote 10. A decagram is 10 grams.

deci- (d): A prefix used in the System International d'Unites (SI) to denote one-tenth. A decimeter is 0.1 meter.

Demineralization: 1) The act or process of removing minerals or mineral salts from a liquid, such as water. 2) The loss, deprivation, or removal of minerals or mineral salts from the body, especially through disease, as the loss of calcium from bones or teeth.

Denitrification: The reduction of nitrates and nitrites, especially when accomplished by denitrifying bacteria, which require organic matter as an energy source. Denitrification reduces the amount of nitrogen present in the soil; it occurs most rapidly under warm, anaerobic conditions.

Deposition: The processes by which chemical constituents move from the atmosphere to the earth's surface. These processes include precipitation (wet deposition, such as rain or cloud fog), as well as particle and gas deposition (dry deposition).

Desorption: The opposite of adsorption; the release of materials from being adsorbed onto a surface. Outgassing is a form of desorption.

Detritus: Detritus is usually organic material, such as dead or partially decayed plants and animals, or excrement.

Detritivore: A decomposer or saprobe; an organism that feeds on dead organic matter, including scavengers.

Diatom: Diatoms are unicellular algae generally placed in the family Bacillariophyceae. The cell walls of these organisms are made of silica, and the varied shapes and beautiful ornamentation of these walls made the study of the diatoms and related siliceous organisms a favored pursuit of the microscopical pioneers. The cell wall is also one of the major reasons why these algae are today a favorite tool of modern ecological and evolutionary researchers, because the fossils are often well preserved in lake and marine systems.

Dieback: 1) A sudden decline in an animal population; a population crash. 2) a condition in plants in which the shoots wither and die, sometimes progressing to other parts of the plant. 3) A gradual and progressive death of trees occurring over a wide area, often progressing from the tops and periphery of the crown toward the base of the tree. It is believed to be caused by air pollution, acid rain, or some cause other than a known disease organism.

Differential TEOM (Differential TEOM Mass Monitoring System): The differential TEOM monitor concept is based on the direct mass reading and real-time capability of the TEOM mass monitor. An electrostatic precipitator (ESP) is added upstream of the mass monitor so that measurements can be made with the ESP switched on and off for known periods of time. When the ESP is off, the TEOM mass sensor samples PM much like a conventional TEOM monitor. When the ESP is on, PM is removed from the sample stream and captured by the ESP. During this ESP-on period, evaporation of collected PM or filter artifacts, such as gas adsorption, desorption, or chemical reactions, may occur. The system is self-referencing, or self-correcting, and removes from the final reported value the artifacts that are problematic with the FRM.

Dilution tunnel sampler: System used to measure particulate matter emissions from mobile and stationary sources by which sampled gas is cooled to ambient temperatures through dilution with ambient air, resulting in conditions similar to those in the actual plume, where exhaust gases leaving the stack mix with the atmosphere.

Dimethyl phenanthrene: One of a family of phenanthrenes (a semi-volatile organic compound -SVOC). Release of phenanthrene (PHEN) most likely results from the incomplete combustion of a variety of organic compounds including wood and fossil fuels. Phenanthrene released to the atmosphere is expected to rapidly adsorb to particulate matter. Phenanthrene adsorbed on fly ash has been shown to photolyze rapidly (half-life 49 hr) and Phenanthrene adsorbed on particulate matter will be subject to wet and dry deposition. PHEN is a contaminant in air, water, sediment, soil, fish and other aquatic organisms and food.

Displacement Index: Percent reduction in emissions or energy compared to the fuel that it replaces. Thus, a displacement index value represents the impact of replacing a Btu of gasoline or diesel with a Btu of the renewable fuel under consideration. Displacement indices are calculated for fossil fuel, for petroleum, for GHG, and for CO2 alone. In each case, the value, a percent change, is based upon replacing a Btu of gasoline or diesel with a Btu of a specific biofuel, given its lifecycle.

Dissolved inorganic carbon (DIC): Along with dissolved organic carbon (DOC) and particulate organic carbon (POC), DIC is part of the most important pools of carbon in aquatic systems. DIC consists of carbon dioxide, bicarbonate, and carbonate. The largest input of DIC is from atmospheric CO₂, and the dominant abiotic outputs are evolution of dissolved CO₂ into the atmosphere and precipitation of calcite. Respiration is the biological input, and photosynthesis and chemosynthesis are the biological outputs.

Dissolved organic carbon (DOC): The fraction of carbon bound into organic compounds in wastewater or other water that is made up of the smallest molecules. DOC is one indication of water quality, measured as particles smaller than 0.45 micrometers; it is separated out from total organic carbon by passing it through a filter with pores measuring 0.45 micrometers in diameter. Dissolved organic carbon includes many polar organic molecules such as humic and fulvic acids as well as those synthetic organic compounds that are water soluble.

Dissolved organic nitrogen (DON): DON comes from the excretion from organisms and the decomposition of detritus. It consists mainly of polypeptides and other complex amino groups.

Distiller's Dried Grains and Solubles: Byproduct of dry mill ethanol production that can be used to feed livestock.

Distillate Fuels: Any distilled fuel product. Distillate fuels are light petroleum products used for home heating and most machinery.

Distributed generation (DG): The use of small-scale power generation technologies located close to the load being served. For some customers DG can lower costs, improve reliability, reduce emissions, or expand their energy options. DG may add redundancy that increases grid security even while powering emergency lighting or other critical systems. Technologies include photovoltaics, fuel cells, wind turbines, reciprocating engines, microturbines, and combustion gas turbines.

Diurnal: 1.) Occurring daily, as in a 24-hour cycle. 2.) Active during daylight; describing animals that are not nocturnal or plants whose leaves or flowers open during the day and close at nightfall.

Diurnal patterns: See Diurnal.

Divalent mercury (Hg[II]): The majority of mercury in the atmosphere is in the form of gaseous elemental mercury, Hg(0). This form of mercury can travel long distances in the atmosphere for many months. Some Hg(0) is converted into two other forms of mercury: a more water soluble form of mercury, divalent or oxidized mercury, Hg (II), which can bind with particulate matter or aerosols to form particulate mercury, Hg(p). These two forms of mercury are rapidly removed from the atmosphere in precipitation and fall onto land and into water bodies, including the ocean.

Downstream: Commercial operations that occur from the pipeline that connects to the wellhead or lease site to the market hubs.

Drainage lakes: Drainage lakes, along with seepage lakes, make up the two dominant lake types in the Adirondacks. Drainage lakes have an outlet and receive a higher proportion of water from surface runoff than direct precipitation or groundwater.

Dry deposition: Fallout of particulate air pollutants from the atmosphere, other than what is carried to the earth's surface by some form of precipitation.

Dry-grind Ethanol Process: A process used by most farmer-owned ethanol facilities. The two primary products from this process are ethanol and distillers dried grains and solubles.

E10: Blend of 10% ethanol and 90% gasoline

E20: Blend of 20% ethanol and 80% gasoline

E85: Blend of 85% ethanol and 15% gasoline

Effluent outflow: from a particular source, such as a stream that flows from a lake or liquid waste that flows from a factory or sewage-treatment plant.

Electricity demand reduction: The reduction of demand for electric power from the power grid, with particular attention to system peak; sometimes refers to demand reduction on a city or regional level.

Electrolyte: Any of the various ions that regulate the electric charge on cells and the flow of water across their membranes.

Electrophysiology: The study of electrical phenomena associated with the function of the heart.

Element: A substance composed of atoms having an identical number of protons in each nucleus. Elements cannot be reduced to simpler substances by normal chemical means.

Elemental carbon (EC): The light-absorbing cabonaceous material in atmospheric particles. Usually produced from the combustion of gaseous and liquid hydrocarbons with restricted air supply.Since it is not easy to remove the last traces of the product from gases leaving the stack, its production is often a source of intense air pollution. EC is sometimes used interchangeably with black carbon.

Elemental mercury (Hg[0]): The majority of mercury in the atmosphere is in the form of gaseous elemental mercury, Hg(0). This form of mercury can travel long distances in the atmosphere for many months. Some Hg(0) is converted into two other forms of mercury: a more water soluble form of mercury, divalent or oxidized mercury, Hg (II), which can bind with particulate matter or aerosols to form particulate mercury, Hg(p). These two forms of mercury are rapidly removed from the atmosphere in precipitation and fall onto land and into waterbodies, including the ocean.

Emergency room (ER): The section of a health care facility for providing rapid treatment to victims of sudden illness or trauma.

Emission: 1) Waste discharged into the environment by industrial or other human processes. Usually used to refer to gaseous discharges, but can also refer to liquid discharge or radioactivity. 2) The giving off of electrons, electromagnetic energy, or radioactivity.

Emission allowance: An authorization to emit a fixed amount of a pollutant.

Emissions caps: A limit on the total amount of pollution that can be emitted (released) from all regulated sources (e.g., power plants); the cap is set lower than historical emissions to cause reductions in emissions.

Emission controls: The term for administrative mechanisms of control and the various technical processes and devices available for reducing emissions, such as filtration, scrubbing, or neutralization.

Emission factor: The relationship between the amount of pollution produced and the amount of raw material processed. For example, an emission factor for a blast furnace making iron would be the number of pounds of particulates per ton of raw material.

Emission inventory: A listing, by source, of the amount of air pollutants discharged into the atmosphere of a community; used to establish emission standards.

Emission reduction credits (ERCs): ERCs are issued when an air pollution source, such as an end-user's boiler, makes real, quantifiable, surplus, and verifiable reductions in its emissions of nonattainment pollutants. ERCs are bankable for current or future use and can be bought and sold in established emission trading markets.

Emission scenarios: Modeling scenarios indicating levels of emissions under different future policy regimes.

Emission sources: Sources or source categories from which emissions originate.

Emission standard: Legal acceptable limit of output of specific chemicals. National emission standards were established by the three Clean Air Acts of 1970, 1977, and 1990.

Endothelium cells: cells that line the blood vessels.

End user: The final consumer of a product; the intended recipient or user.

Energy efficiency: The extent to which energy produced in a process is used and not wasted.

Energy return on investment: See net energy ratio.

Engine-generated emissions: See emission.

Enforcement: the legal methods used to make polluters obey the Clean Air Act. Enforcement methods include citations of polluters for violations of the law (citations are much like traffic tickets), fines and even jail terms. EPA and the state and local governments are responsible for enforcement of the Clean Air Act, but if they don't enforce the law, members of the public can sue EPA or the states to get action. Citizens can also sue violating sources, apart from any action EPA or state or local governments have taken. Before the 1990 Clean Air Act, all enforcement actions had to be handled through the courts. The 1990 Clean Air Act gave EPA authority so that, in some cases, EPA can fine violators without going to court first. The purpose of this new authority is to speed up violating sources' compliance with the law and reduce court time and cost.

Epidemiology: The empirical, statistics-based study of the relationships between exposure to a human stress and the human physiological or disease-based response.

Episode (pollution): An air pollution incident in a given area caused by a concentration of atmospheric pollutants under meteorological conditions that may result in a significant increase in illnesses, deaths or adverse impacts to the environment. For example, episodic acidification. May also describe water pollution events or hazardous material spills.

Episodic: Occurring or appearing at usually irregular intervals.

Episodic acidification: See episodic, see acidification.

ERG Biofuel Analysis Meta-Model: EBAMM considers the energy and GHG impacts of the production of corn ethanol. In order to compare across studies, this model was designed to account for coproduct credits where appropriate, apply consistent system boundaries to the studies surveyed, account for multiple process energy types, and calculate metrics that are relevant for policy makers. EBAMM considers only the production of E100.

Esterification: The general name for a chemical reaction in which two reactants (typically an alcohol and an acid) form an ester as the reaction product.

Estuary: Region of interaction between rivers and near-shore ocean waters, where tidal action and river flow mix fresh and salt water. Such areas include bays, mouths of rivers, salt marshes, and lagoons. These brackish water ecosystems shelter and feed marine life, birds, and wildlife.

Ethanol: An alternative automotive fuel derived from grain and corn; usually blended with gasoline to form gasohol.

Eutrophication: The slow aging process during which a lake, estuary, or bay evolves into a bog or marsh and eventually disappears. During the later stages of eutrophication the water body is choked by abundant plant life due to higher levels of nutritive compounds such as nitrogen and phosphorus. Human activities can accelerate the process.

Evapotranspiration: The combined water loss from a biotic community or ecosystem into the atmosphere caused by evaporation of water from the soil plus the transpiration of plants.

Exchangeable Acidity: The quantity of hydrogen plus aluminum ions held on exchange sites in soils. It is measured as the ions displaced from exchange sites by the cation in an added solution. In mineral soils, aluminum is the dominant form of exchangeable acidity.

Exposure pathway: An exposure pathway refers to the way in which a person may come into contact with a hazardous substance, whether it is a chemical, biological, or some other harmful substance.

Factor analysis: A mathematical tool which can be used to examine a wide range of data sets. The purpose of factor analysis is to discover simple patterns in the pattern of relationships among the variables. In particular, it seeks to discover if the observed variables can be explained largely or entirely in terms of a much smaller number of variables called factors. Factor analysis is a statistical technique used to reduce a set of variables to a smaller number of variables or factors. It examines the pattern of intercorrelations between the variables, and determines whether there are subsets of variables (or factors) that correlate highly with each other but that show low correlations with other subsets (or factors).

Federal Reference Method (FRM): A method of sampling and analyzing the ambient air for an air pollutant that is specified in Federal Regulations promulgated by the Environmental Protection Agency (EPA).

Feedstocks: Any material that is converted to another form or product through a manufacturing process. For example, corn kernels can be the feedstock for ethanol, while natural gas is a primary feedstock for ammonia used in nitrogen fertilizer.

Field-to-Wheel: Accounting of the energy inputs required to produce biofuel, including land use, pesticide use, etc.

Filter Dynamics Measurement System (FDMS^TM): The FDMS^TM was developed to account for both the volatile and non-volatile components of particulate matter (PM), and report the combination as a mass concentration result. This is done by measuring the volatile portion of the sample independently from the total incoming sample, and using this fraction in calculating the PM mass concentration. Conventional PM monitoring approaches do not account for the rapid mass loss that occurs due to volatilization.

Fine particles (PM_2.5): PM_2.5 describes the "fine" particles that are less than or equal to 2.5 µm in diameter.

Fischer-Tropsch Process: Method of producing liquid fuels, usually diesel fuel, from natural gas or synthetic gas from gasified coal or biomass.

Fish consumption advisory: Some fish may contain chemicals that could pose health risks. When contaminant levels are unsafe, consumption advisories may recommend that people limit or avoid eating certain species of fish caught in certain places. In New York State the NYS Department of Health issues fish consumption advisories annually.

Fish species richness: The number or diversity of species present in an environment.

Fixing: 1) To place securely; make stable or firm. To secure to another; attach. 2) To put into a stable or unalterable form. To make (a chemical substance) nonvolatile or solid. To convert (nitrogen) into stable, biologically assimilable compounds.

Flexible Fuel Vehicle: Automobile capable of running on gasoline and high-ethanol blends interchangeably

Floodplain: The relatively flat land adjacent to a river channel that is constructed of unconsolidated sediment deposited by periodic flooding and lateral migration of the river channel.

Fluoranthene (C₁₅H₁₀): A white crystalline hydrocarbon C₁₅H₁₀, of a complex structure, found as one ingredient of the higher boiling portion of coal tar.

Fluorine (F): A gaseous, poisonous, halogen element existing as the diatomic molecule F₂; it has an atomic number of 9 and atomic weight 19.00. It is the most chemically reactive of all the elements; as a result, it is never found alone in nature and is very dangerous to work with (explosive and extremely corrosive) in pure form. It is used to form uranium hexafluoride (UF6) in the separation of uranium isotopes for nuclear fuel and in the manufacture of the many organic compounds containing fluorine (including CFCs).

Flux: 1) A continuous flow, as in a stream, or succession of changes, as in a state of flux. 2) Rate of flow, as of a liquid or other fluid or radiation, across a given area.

Foliage: All the leaves on a plant or in a plant community.

Foliar: Of or relating to a leaf or leaves.

Foliar chemistry: The study of the inorganic and organic components of plant tissue/leaves.

Food chain: The system of feeding (trophic) levels in any biotic community. Members of one level feed upon members of the level below and are in turn eaten by organisms in the next level above. The lowest trophic level in any food chain ultimately contains plants, which fix inorganic compounds into plant tissues that can be digested by animals. Food chains may also be fueled by dead organic matter originating from photosynthesis outside the community; organisms dying within the community serve as a source of energy for decomposing or reducing organisms.

Food web: A complex feeding system comprised of linked food chains in a particular ecosystem.

Forest canopy: The top layer of a forest or wooded ecosystem consisting of overlapping leaves and branches of trees, shrubs, or both.

Forest floor: 1) The ground level in a forest community. 2) The surface of the soil, including its organic matter, in a forest ecosystem.

Forest health: Forest health is a relative condition of a forest based on selected ecological indicators and the collective value judgments of stakeholders of that forest.

Forest nitrogen cycle: See Nitrogen cycle.

Forest sensitivity maps: Environmental sensitivity mapping is based on the number of environmental assets at a given location. It is analogous to a density map, whereby the higher the number of environmental assets in an area, the darker the color on the map. Within a GIS, it is possible to weight or score different assets depending on their importance or significance. The environmental sensitivity map can then be based on the total score, rather than the total number of assets. You can get a list of all the environmental assets at a particular location by simply clicking on the area of the map that interests you.

Formaldehyde (H₂CO or CH₂0): A strong smelling gas that irritates the eyes and the upper respiratory track and is a probable carcinogen. Formaldehyde is used as a disinfectant and preservative and in the formation of many plastics and adhesives. It is used extensively in plywood, fiber board, and particle board. As buildings have become more airtight, formaldehyde has become recognized as an indoor air pollutant. In addition to being given off by construction materials, it is produced by incomplete combustion, and so is found in cigarette smoke, automobile exhaust, wood smoke, and emissions from power plants and incinerators. Also known as methyl aldehyde and methanal.

Frass (frassfall): Insect droppings.

Fuel Displacement: See Displacement index

Gas: The state of matter distinguished from the solid and liquid states by relatively low density and viscosity, relatively great expansion and contraction with changes in pressure and temperature, the ability to diffuse readily, and the spontaneous tendency to become distributed uniformly throughout any container.

Gaseous divalent mercury (Hg [II]): See Divalent mercury.

Gaseous elemental mercury (Hg [0]): See Elemental mercury.

Gas Turbine Combined-Cycle: A system in which a gas turbine generator generates electricity and the waste heat is used to make steam to generate additional electricity via a steam turbine; this last step enhances the efficiency of electricity generation.

Generator: An apparatus, equipment, etc, to convert or change energy from one form to another. An apparatus in which vapor or gas is formed from a liquid or solid by means of heat or chemical process, as a steam boiler, gas retort etc.

Geographic Information System (GIS): A system, usually computer-based, for the input, storage, retrieval, analysis and display of interpreted geographic data. The data base is typically composed of map-like spatial representations, often called coverages or layers. These layers may involve a three-dimensional matrix of time, location, and attribute or activity. A GIS may include digital line graph (DLG) data, digital elevation models (DEM), geographic names, land-use characterizations, land ownership, land cover, registered satellite and/or aerial photography along with any other associated or derived geographic data.

GHGenius: A spreadsheet model that calculates the amount of greenhouse gases generated from the time a fuel is extracted or grown to the time that it is converted in a motive energy vehicle to produce power. Whether the fuel is burned in an internal combustion engine or transformed in a fuel cell, GHGenius identifies the amount of greenhouse gases generated by a wide variety of fuels and technologies, the amount of energy used and provided, and the cost effectiveness of the entire life cycle.

Giga: one billion; 10⁹

Global Warming Potential: A measure of the potential of substances (normally gases or volatile liquids) to heat up the atmosphere. All measures of GWP are given relative to Carbon dioxide, the most well-known gas with global warming potential, which has a GWP of 1.

Greenhouse Gas: A gas, such as water vapor, carbon dioxide, tropospheric ozone, methane, and low level ozone, which contributes to the greenhouse effect.

Greenhouse gases, Regulated Emissions, and Energy use in Transportation: This model analyses the entire life cycle of corn ethanol as well as cellulosic ethanol, from production of agricultural chemicals through to vehicle use. GREET 1.7 calculates energy use in Btu per mile, and emissions in grams per mile throughout the entire "well to wheel" lifecycle (in the case of biofuels, this is sometimes referred to as the "field to wheel" lifecycle). The model calculates the total energy use from all energy sources, the fossil energy use, and the petroleum use.

Ground-level ozone: Ozone is not emitted directly into the air, but is formed by gases called nitrogen oxides (NO_x) and volatile organic compounds (VOCs) that in the presence of heat and sunlight react to form ozone. Ground-level ozone forms readily in the atmosphere, usually during hot weather. It is the prime ingredient of smog in our cities and other areas of the country. When inhaled, even at very low levels, ozone can cause acute respiratory problems; aggravate asthma; cause significant temporary decreases in lung capacity; cause inflammation of lung tissue; lead to hospital admissions and emergency room visits; and impair the body's immune system defenses, making people more susceptible to respiratory illnesses, including bronchitis and pneumonia. Also tropospheric ozone.

Habitat: The dwelling place of a species or community, providing a particular set of environmental conditions (e.g., forest floor, sea shore, etc.). A particular habitat is usually characterized either by physical features or by dominant plants, such as deserts, lakes or forests.

Haiku Model: The RFF Haiku Electricity Market Model is a simulation model of regional electricity markets and interregional electricity trade in the continental United States. The model can be used to simulate changes in electricity markets stemming from public policy associated with regulation of the industry to promote competition and environmental benefits.

Hazardous air pollutants (HAPs): chemicals that cause serious health and environmental effects. Health effects include cancer, birth defects, nervous system problems and death due to massive accidental releases such as occurred at the pesticide plant in Bhopal, India. Hazardous air pollutants are released by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles (cars, trucks, buses, etc.)

Headwater: The highest reaches of a stream in a drainage basin.

Headwater wetland: Headwater wetlands are temporarily to seasonally flooded wetlands located at the origins of streams.

Health effect: Health effects, health impacts or health risks are an important consideration in many areas, such as hygiene, pollution studies, workplace safety, nutrition and health sciences in general. A non-stochastic or deterministic health effect has a severity that is dependent on dose and is believed to have a threshold level for which no effect is seen. Stochastic health effects occur by chance, generally occurring without a threshold level of dose, whose probability is proportional to the dose and whose severity is independent of the dose, such as cancer and genetic effects.

Heat recovery steam generation: Boilers that capture or recover the exhaust of a prime mover such as a combustion turbine, natural gas or diesel engine to create steam.

Heavy oils: Any type of crude oil which does not flow easily. It is referred to as "heavy" because its density or specific gravity is higher than of light crude oil.

Hectare (ha): Unit of measurement of area. 1 ha = 2.47 acres = 10,000 m²; 100 ha = 1 km².

Higher heating value: The maximum potential energy released during complete oxidation of a unit of fuel. Includes the thermal energy recaptured by condensing and cooling all products of combustion. As HHV varies with moisture content, HHV should only be presented in conjunction with moisture content.

Horizon: 1) An identifiable layer of a soil. 2) A body of rock strata with identifiable upper and lower boundaries.

Hydrocarbons: Chemical compounds that consist entirely of carbon and hydrogen.

Hydrochloric acid (HCl): A solution of hydrochloride in water. It is a strong acid with an acrid odor and is highly corrosive. It dissolves many metals to form chloride salts, giving off hydrogen gas. It is secreted by the body for digestion in the stomach; it also has many industrial uses. Also known as muriatic acid.

Hydrogen (H): The lightest of all the elements, hydrogen is gaseous and has an atomic number of 1 and at atomic weight of 1.008. Its elemental form is a diatomic molecule, H₂. Hydrogen is much more abundant throughout the universe than any other element. It is found in water and in most organic compounds. Deuterium and tritium are two isotopes of hydrogen.

Hydrologic cycle: A natural solar-driven cycle of evapotranspiration, condensation, precipitation, and runoff. The hydrologic cycle controls the water movement between the atmosphere, oceans, aquatic, and terrestrial environments.

Hydrology: The science of water in the hydrologic cycle.

Hydroxide (OH^-): 1) OH^-, the anion resulting from loss of a proton (H⁺) from a water molecule or from addition of a proton to the oxide anion (O^-2). The hydroxide ion is responsible for the properties of solutions associated with bases. It is also called the hydroxyl ion. 2) A class of compounds containing the hydroxide anion. Examples are calcium hydroxide - Ca(OH)₂, lime and sodium hydroxide - NaOH. Hydroxides dissolve in water to give hydroxide ions (OH^-), which produce a basic solution.

Hygroscopic: Readily absorbing moisture, as from the atmosphere.

Hyperspectral remote-sensing imagery: The collection of reflected, emitted, or backscattered energy from an object or area of interest in hundreds of bands (regions) of the electromagnetic spectrum.

Hypoxia: Waters with dissolved oxygen concentrations of less than 2 ppm, the level generally accepted as the minimum required for most marine life to survive and reproduce.

IMPLAN Modeling System: The IMPLAN modeling system combines the U.S. Bureau of Economic Analysis' Input-Output Benchmarks with other data to construct quantitative models of trade flow relationships between businesses and between businesses and final consumers.

Indeno(1,2,3-cd)pyrene: Indeno(1,2,3-cd)pyrene (IP) is formed in most combustion or elevated temperature processes that involve compounds containing carbon and hydrogen. Known IP sources include coal, wood, and gasoline combustion, municipal waste incineration, coke ovens and cigarette smoke. IP has also been found in gasoline, fresh and used motor oil, and road runoff. IP released to water will sorb strongly to suspended particulate matter, biota and sediments. IP will probably be persistent in the aquatic environment and concentrate in sediments. Almost all IP released to the atmosphere will be sorbed to particulate matter; thus its atmospheric fate will primarily depend on physical processes such as dry and wet deposition.

Indicator Species: An organism whose presence (or state of health) is used to identify a specific type of biotic community, or as a measure of ecological conditions or changes occurring in the environment. A number of different plants have been used in the western United States to appraise water and soil conditions. Also called a biological indicator or index species.

Inflammation: A localized protective reaction of tissue to irritation, injury, or infection, characterized by pain, redness, swelling, and sometimes loss of function.

Influence function analysis: A diagnostic mathematical tool used to determine how different factors may have influenced a particular result. For example, influence function analysis can be used to determine the transport history of air masses arriving at a specific location and therefore the relative influences of local vs. long-distance sources or source areas on the deposition measured at a particular site.

Inorganic: 1) Not coming from animal or vegetable sources, as in inorganic fertilizers. 2) Describing compounds that either contain no carbon or contain only carbon bound to elements other than hydrogen.

Inorganic monomeric aluminum: Single aluminum molecules, free or complexed with inorganic cations like hydroxide and flouride. This is highly toxic to many aquatic animals.

Inspection and maintenance program (I/M program): Auto inspection programs are required for some polluted areas. These periodic inspections, usually done once a year or once every two years, check whether a car is being maintained to keep pollution down and whether emission control systems are working properly. Vehicles that do not pass inspection must be repaired. As of 1992, 111 urban areas in 35 states already had I/M programs. Under the 1990 Clean Air Act, some especially polluted areas will have to have enhanced inspection and maintenance programs, using special machines that can check for such things as how much pollution a car produces during actual driving conditions.

Interannual: Between years.

Interfacial Tension: The strength of the film separating two immiscible fluids (e.g. oil and water) measured in dynes per, or millidynes per centimeter.

International air pollution: Canada and Mexico, the United States' neighbors, share the air at our borders. Pollution moves across the national borders; this international pollution can be serious. The 1990 Clean Air Act includes provisions for cooperative efforts to reduce pollution that originates in one country and affects another.

Interstate air pollution: In many areas, two or more states share the same air. We say these states are in the same air basin defined by geography and wind patterns. Often, air pollution moves out of the state in which it is produced into another state. Some pollutants, such as the power plant combustion products that cause acid rain, may travel over several states before affecting health, the environment and property. The 1990 Clean Air Act includes many provisions, such as interstate compacts, to help states work together to protect the air they share. Reducing interstate air pollution is very important since many Americans live and work in areas where more than one state is part of a single metropolitan area.

Interstate Air Quality Rule: In January 2004 the U.S. EPA proposed new rules for reducing emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and mercury. The Interstate Air Quality Rule focuses on states with SO2 and NOx emissions that contribute significantly to fine particle and ozone pollution problems in other downwind states. It would cover 29 states in the Eastern United States and the District of Columbia. In a separate but closely related action, the U.S. EPA proposed the Utility Mercury Reductions Rule for controlling mercury emissions from power plants. Together, the two proposals constitute a multi-pollutant strategy to improve air quality throughout the country.

Invertebrate: An animal without a backbone or internal bony skeleton. Also used as an adjective to describe such organisms.

Iron (Fe): A magnetic, metallic element with atomic weight 55.85 and atomic number 26. It is the most common and most used of all the metallic elements, incorporated into many commercial metals. Iron is found at the center of the hemoglobin molecule that transports oxygen throughout the human body.

Isotope: Isotopes are atoms of a particular element that have a different mass number, specifically, a different number of neutrons in their nuclei. The significance of recent advances in isotopic techniques is that researchers can, for example, quantify sources of nitrogen more accurately.

Jatropha: Jatropha is a non-edible evergreen shrub found in Asia, Africa and the West Indies. Its seeds contain a high proportion of oil which can be used for making biodiesel.

Joules: Metric unit of energy, equivalent to the work done by a force of one Newton applied over a distance of one meter.

kilo- (k): Prefix used in the Systeme International d'Unites (SI) to denote one thousand, 1x10³. A kilowatt is 10³ watts.

Leachate: The chemical solution obtained by the process of leaching.

Leaching: The process by which soluble constituents are dissolved and filtered through the soil by a percolating fluid.

Lead (Pb): A soft, heavy, metallic element with atomic weight 207.2 and atomic number 82. It is found in several different ores (primarily galena, but also anglesite and cerussite) and used in a wide variety of alloys. Lead makes an excellent shield for radioactive materials. Lead compounds are toxic and will accumulate in the body and cause poisoning if levels as low as 0.5 mg are absorbed daily. Low-level or chronic lead poisoning is common; symptoms include muscle cramps, abdominal pain ("lead colic"), and eventual nervous system and brain damage. Lead was formerly widely used in house paint (especially white paint) and as plumbing solder; both uses are now banned because they resulted in dust, paint chips, and drinking water with significant lead levels.

Leukocyte: A pale, nucleated cell that acts as a part of the immune system by destroying invading cells and removing debris.

Life-Cycle Analysis: A total valuation of a process, in which all the inputs and outcomes of a reaction are fully considered.

Lifecycle Emissions Model: Estimates energy use, criteria pollutant emissions, and CO2-equivalent greenhouse-gas emissions from a variety of transportation and energy lifecycles.

Light duty vehicle: A passenger car or passenger car derivative capable of seating 12 passengers or less.

Light surfaces: Urban surfaces with high reflectivity (albedo), designed to reflect rather than absorb solar radiation.

Lignin: A complex organic polymer that increases the rigidity of plant cell walls. Cellulose and lignin, often combined, make up a large percentage of woody tissue, and therefore of harvested wood.

Liming: The addition of calcium carbonate to a water body to reduce its acidity and help preserve fish stocks.

Litter: Dead and partially decomposed leaves and other recognizable plant residues on the soil surface of the forest floor, also called the litter layer.

Litterfall: The amount of dead plant matter added to the forest floor in a given community over a given time period, usually a year. Annual litterfall, when coupled with measures of the humus layers, can be used to estimate rates of soil metabolism (respiration) and activity of detritivores.

Load: 1) The amount of a substance carried by a system, as in the sediment load of a stream. 2) Total demand for electric power from a given supply such as an electrical generator. 3) Mechanical force applied to an object.

Long-range transport: The transport of pollutants over a great distance, for example between regions or continents. Means whereby nonlocal emissions arrive at a particular site.

Loss on ignition (LOI): A common method used to estimate the organic and carbonate content of sediments. Organic matter content in a sediment sample is determined by measuring weight loss in subsamples after burning at selected temperatures.

Lower heating value: The net energy released during oxidation of a unit of fuel excluding the heat required for vaporisation of the water in the fuel and the water produced from combustion of the fuel hydrogen. LHV= HHV- 21.998 (H) - 2.444 (W).

Lysimeter: 1) A device for measuring evapotranspiration in vegetated soils. 2) A device for collection of soil water in the vadose zone.

Macroinvertebrate: An invertebrate animal (animal without a backbone) large enough to be seen without magnification.

Magnesium (Mg): White, metallic element with atomic weight 24.31 and atomic number 12, found in nature only in compounds with other elements. It is used in many alloys and in magnesium flares and fireworks. It is an essential nutrient for both plants and animals and is an essential part of the chlorophyll molecule.

Manganese (Mn): A brittle, metallic element with atomic weight 54.94 and atomic number 25. It is used in the manufacture of steel and industrial chemicals. It is also an essential trace nutrient for animal and plant life and so is included in some fertilizers.

Market penetration: The extent to which a product is recognized and bought by customers in a particular market.

Material safety data sheets (MSDS): product safety information sheets prepared by manufacturers and marketers of products containing toxic chemicals. These sheets can be obtained by requesting them from the manufacturer or marketer. Some stores, such as hardware stores, may have material safety data sheets on hand for products they sell.

Mega: one million; 10⁶

Mercury (Hg): A heavy, poisonous liquid metallic element with atomic weight 200.59 and atomic number 80. Mercury is a solvent for most metals, producing amalgams. It is used in thermometers, barometers, light switches, paints, and batteries. Once in the environment, mercury persists and concentrates as it moves up the food chain, reaching particularly high levels in fish and shellfish. Prolonged exposure to mercury, either through inhaling or swallowing, can damage the central nervous system. Major emission sources are coal burning, the paper industry and chemical plants.

Mercury cycling: The processes mercury undergoes in the environment that affect its fate, transformations, and the forms in which it appears. Once in the atmosphere, mercury is widely disseminated and can circulate for years, accounting for its wide-spread distribution. Mercury is found in the atmosphere as a gas which consists primarily of elemental mercury but also of other small amounts of other mercury-containing compounds (e.g., mercuric chloride). Mercury also exists in the atmosphere in the liquid phase as water droplets (e.g., cloud water) and in precipitation (rain and snow). In addition to these forms, mercury is also exchanged between the atmosphere and the earth's surface.

Mercury Deposition Network (MDN): A program of the National Atmospheric Deposition Program (NADP). The objective of the MDN is to develop a national database of weekly concentrations of total mercury in precipitation and the seasonal and annual flux of total mercury in wet deposition. The data will be used to develop information on spatial and seasonal trends in mercury deposited to surface waters, forested watersheds, and other sensitive receptors.

Mercury speciation: See speciation.

Mercury transport: Certain forms of mercury can exist for a very long time in the atmosphere and can therefore be transported over great distances. As a result, mercury emissions are a global problem.

Mesoclimate: The climate of a natural region of small extent, for example, valley, forest, plantation, and park. Because of subtle differences in elevation and exposure, the climate may not be representative of the general climate of the region.

Metal: A class of elements characterized by being good conductors of heat and electricity, typically existing as lustrous solids, and easily shaped by casting, hammering, or drawing out into wires. Metallic elements readily give up electrons to form positive ions.

Methyl tertiary butyl ether: Ether created from methanol that can increase octane and decrease the volatility of gasoline, decreasing evaporation and smog formation.

Methylation: The process whereby a compound is modified chemically, often through bacterial action, by the replacement of a hydrogen atom by a methyl group, -CH3. In this process, inorganic mercury is converted to the organic form, methylmercury, which is the bioavailable toxic form of mercury.

Methylmercury: In a water body and its sediments mercury may be converted by bacterial action into an organic form, methylmercury, CH₃Hg. Acidic conditions and elevated ozone levels are believed to promote this conversion. Methylmercury can bioaccumulate up the food chain as a result of the ingestion of contaminated aquatic organisms. Large fish and aquatic mammals at the top of the food chain may contain dangerously high levels of methylmercury. Contaminated fish become a human health hazard when they are consumed.

micro- (µ): 1) Prefix meaning small. 2) Prefix in the Systeme International d'Unites (SI) indicating one millionth, 1x10-⁶. One microgram equals one millionth of a gram, or 10-⁶g.

Microbes: Microorganisms such as yeast that are used in the ethanol fermentation process.

Mill Residues: Wood and bark residues produced in processing logs into lumber, plywood, and paper.

milli- (m): Prefix in the Systeme International d'Unites (SI) indicating one thousandth, 1 x 10^-3. One millimeter equals one thousandth of a meter, or 10^-3m.

Mineral: A naturally occurring inorganic substance with relatively consistent chemical formula and physical properties, including a characteristic atomic structure that is usually crystalline. The term is also used more loosely for ores, rocks, and similar substances extracted by mining or quarrying.

Mineralization: The breakdown of organic matter into its inorganic chemical components (minerals), such as nitrogen, phosphorous, potassium, and sulfur. Mineralization is a stage in the biogeochemical cycles of most minerals during which they are released back into the environment.

Mineral weathering: The physical and chemical breakdown of rocks that releases ions such as calcium and aluminum.

Mitigate/mitigation: To moderate (a quality or condition) in force or intensity; alleviate.

Mobile sources: moving objects that release pollution; mobile sources include cars, trucks, buses, planes, trains, motorcycles and gasoline-powered lawn mowers. Mobile sources are divided into two groups: road vehicles, which includes cars, trucks and buses, and non-road vehicles, which includes trains, planes and lawn mowers.

Modeling: Modeling is a vital mathematical tool in trying to understand the behavior of complex systems under variable conditions, given available information. For example, modeling can be used to gauge the efficacy of future policy scenarios, and to study the fate, transport, and behavior of pollutants in the environment.

Model of Acidification in Groundwater in Catchments (MAGIC): This model is calibrated to the watershed of an individual lake or stream and used to simulate the response of that system to changes in atmospheric deposition.

Mold: 1) A fungal growth on a surface, often velvety or powdery and usually growing on damp and decaying organic matter or living organisms. 2) Soil very rich in humus, as in leaf mold.

Molecular marker: An individual molecule that comprises the chemical profile of an emission source.

Monitoring (monitor) Measurement of air pollution is referred to as monitoring. EPA, state and local agencies measure the types and amounts of pollutants in community air. The 1990 Clean Air Act requires certain large polluters to perform enhanced monitoring to provide an accurate picture of their pollutant releases. Enhanced monitoring programs may include keeping records on materials used by the source, periodic inspections, and installation of continuous emission monitoring systems (CEMS). Continuous emission monitoring systems will measure, on a continuous basis, how much pollution is being released into the air. The 1990 Clean Air Act requires states to monitor community air in polluted areas to check on whether the areas are being cleaned up according to schedules set out in the law.

Monomer/Monomeric: A molecule that can combine with others to form a polymer.

Monomeric aluminum (Al_m): Aluminum that occurs as a free ion (Al³⁺), simple inorganic complexes, or simple organic complexes, but not in polymeric forms. Reactive.

Morbidity: 1. A diseased state or symptom. 2.The incidence of disease : the rate of sickness (as in a specified community or group).

Mortality: The number of deaths in a given time or place; the proportion of deaths to population

Multi-Area Production Simulation (MAPS): MAPS is a model of the economic operation of the power system. MAPS captures the complex interactions between electricity generation and transmission systems, integrating highly detailed representations of a system's load, generation, and transmission into a single simulation. As a result, hourly production costs can be calculated in light of the constraints imposed by the transmission system on the economic dispatch of generation.

Multi-pollutant policy: A policy that addresses emissions from the electricity sector of three or more of the following pollutants: NOX, SO2, CO2, and mercury. A number of such policies are currently under debate at the state and federal levels.

Mycorrhizae: The symbiotic relationship between the mycelia of some species of fungi and the roots or other structures of some flowering plants. The fungal mycelia help the plant absorb minerals and in return absorb energy compounds produced by the plant.

Myocardial infarction: Heart attack

nano- (n): Prefix in the Systeme International d'Unites (SI) indicating one billionth, 1x10^-9. One nanosecond equals one billionth of a second, or 10^-9 sec.

Nanoparticle: A microscopic particle that is generally less than 50 nm (0.05 microns) in diameter. These particles may play a critical role in the deleterious health effects of particulate matter (PM).

National Ambient Air Quality Standard (NAAQS): Standards established by EPA that apply for outdoor air throughout the country.

National Agriculture Statistic Service: Conducts hundreds of surveys every year and prepares reports covering virtually every aspect of U.S. agriculture.

National Atmospheric Deposition Program (NADP): The National Atmospheric Deposition Program/National Trends Network (NADP/NTN) is a nationwide network of precipitation monitoring sites. The network is a cooperative effort between many different groups, including the State Agricultural Experiment Stations, U.S. Geological Survey, U.S. Department of Agriculture, and numerous other governmental and private entities.

Net energy balance: The sum of the energy value of the biofuel and its coproducts (outputs) minus the sum of direct and indirect energy to produce the fuel (inputs). The NEB ratio is also defined as the outputs/inputs.

Net energy ratio: Also known as the enegy return on investment (EROI). The ratio of the energy content of a fuel divided by the non-renewable energy required to produce and deliver the fuel. An EROI greater than one means that the ethanol has at least captured some surplus renewable energy, and an EROI greater than 0.76 (the EROI of gasoline) means that the ethanol requires less non-renewable energy than gasoline to produce.

Net energy value: The energy content of ethanol, minus the fossil energy used to produce the ethanol. Coproduct credits are included in the calculation of NEV.

Nickel (Ni): A hard, metallic element with atomic weight 58.71 and atomic number 28. Nickel is easily shaped and used in numerous alloys (including some coins) and for electroplating. It is also used as a catalyst by the chemical industry, as in the production of adipic acid, a starting material for the production of nylon.

Nitrate (NO₃^-): 1) The ion NO₃^-. 2) A salt or ester of nitric acid, which contains the nitrate ion. Nitrates are important as concentrated sources of nitrogen in fertilizers (potassium nitrate and sodium nitrite); they are also used in explosives. Nitrates are very water soluble and easily leached from soils, resulting in contamination of drinking water supplies. An excess of nitrate in drinking water (more than 10 milligrams per liter) can cause a condition known as methemoglobinemia in infants.

Nitric oxide (NO): A gas formed in internal combustion engines and similar forms of combustion under heat and pressure. Although not problematic itself, when released into the atmosphere, nitric oxide reacts with oxygen (O₂) to form the hazardous pollutant, nitrogen dioxide (NO₂). Nitric oxide also destroys ozone and is thus harmful to the earth's ozone shield. Nitric oxide is also known as nitrogen monoxide.

Nitrification: Conversion of relatively immobile ammonium to nitrite and mobile nitrate by bacteria.

Nitrite (NO₂-): 1) The ion NO₂-. 2) A salt or ester of nitrous acid, which contains the nitrite ion. Unlike the nitrate used in fertilizers, nitrite is toxic to plants in large concentrations. Solid bacteria form nitrites as a stage in converting nitrogen (ammonia) to usable nitrates.

Nitrogen (N): Gaseous element with atomic weight 14.02 and atomic number 7. In its elemental form it exists as a diatomic molecule, N₂. It makes up about 80% of the volume of earth's atmosphere and is found in all plant and animal tissues. It is used commercially as a coolant, an aerosol propellant, and to create an inert atmosphere in food packaging.

Nitrogen cascade: The sequential transfer of reactive nitrogen through environmental systems that results in environmental changes as it moves through or is temporarily stored within each system.

Nitrogen cycle: The process by which nitrogen moves within and between ecosystems throughout the biosphere. The nitrogen cycle is not a simple circuit; it involves many interconnected processes that are often mediated by bacterial activity. Nitrogen generally enters ecosystems from the atmosphere in the form of nitrate or ammonia through electrical discharge (lightning), biological fixation, or precipitation. These nitrogen compounds are taken up by plants, which in turn are consumed by animals, which release nitrogen back into the environment, largely in the form of urea. The bodies of all organisms release nitrogen from proteins and amino acids into the environment as they decompose; these nitrogen compounds are converted to ammonia through ammonification. Ammonia is then converted to nitrite and then nitrate through nitrification. Nitrate may be reduced to molecular N₂ through denitrification.

Nitrogen cycling: see Nitrogen cycle.

Nitrogen Dioxide: The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog.

Nitrogen fixation: The process of converting inorganic, atmospheric nitrogen into an organic form of nitrogen, ammonia. The conversion is carried out by various microorganisms, especially certain bacteria and cyanobacteria present in nodules on the roots of leguminous plants (such as alfalfa, clover, lupine, peas and beans). The ammonia formed can be used directly by plants or may undergo nitrification.

Nitrogen fixing plants: Plants that convert inorganic, atmospheric nitrogen into an organic form of nitrogen, ammonia. The conversion is carried out by various microorganisms, especially certain bacteria and cyanobacteria present in nodules on the roots of leguminous plants (such as alfalfa, clover, lupine, peas and beans). The ammonia formed can be used directly by plants or may undergo nitrification.

Nitrogen loading: Excessive nitrogen inputs to the environment. Major sources of nitrogen include fertilizers, animal manure, atmospheric deposition, and other point sources. Nitrogen tends to regulate the growth of aquatic plants and can therefore lead to eutrophication of inland waters. Excess nitrogen can also cause health hazards to humans and animals, including methaemoglobinaemia (blue baby syndrome) in infants.

Nitrogen mineralization: See mineralization.

Nitrogen oxide (NO_x): Compounds formed by the oxidation of nitrogen, including nitrogen dioxide and nitric oxide. These compounds are air pollutants because they undergo photochemical reactions to form smog and ozone; they are also believed to contribute to the depletion of the earth's protective ozone layer.

Nitrogen sink: A subsystem with more nitrogen input than output, as opposed to a source.

Nitrous acid (HNO₂ or HONO): A weak inorganic acid, HNO₂, existing only in solution or in the form of its salts.

Nitrous oxide (N₂O): Also called laughing gas and dinitrogen oxide, it is a gaseous compound used for anesthesia and as an aerosol propellant.

Nonattainment area: Area that does not meet one or more of the National Ambient Air Quality Standards for the criteria pollutants designated in the Clean Air Act.

Nonpoint sources: Pollution-producing entities that are not tied to a specific origin such as an individual smokestack. Nonpoint sources of water pollution include runoff washing pollutants from roads into storm sewers and water bodies; runoff carrying agricultural chemicals from lawns, fields, and golf courses; and automobiles, which constitute multiple small, mobile sources of air pollution.

Non-point sources: Diffuse pollution sources (i.e. without a single point of origin or not introduced into a receiving stream from a specific outlet). The pollutants are generally carried off the land by storm water. Common non-point sources are agriculture, forestry, urban, mining, construction, dams, channels, land disposal, saltwater intrusion, and city streets.

NO_X allowance set-asides: A provision included in rules that would reserve part of the total allowance cap (e.g., 3%) as economic incentives awarded to qualifying renewable-energy and energy-efficiency (EE/RE) projects. Upon receipt of set-aside allowances, EE/RE projects would be able to sell them in established emission markets and thereby realize additional value.

No_y: Sum of all reactive, oxygen-containing nitrogen species: (NO+NO2 +PAN+HNO3+NO3+N2O5+NO3-+organic nitrates+...)

Nucleation: Process by which a gas interacts and combines with droplets

Nucleation event: The process in which gases are converted to particles. This may occur due to a reaction of gaseous precursors into a product that becomes a particle.

Nucleation-mode particles: Most nucleation-mode particles are smaller than 50 nm and thus are always nanoparticles. N-mode particles, produced in the conversion of gases to particulate matter, are formed in an engine's exhaust, for example.

Nutrient: Element or compound essential for animal and plant growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium.

Nutrient cycles: See biogeochemical cycles.

Nutrient cycling: See Nutrient cycles or Biogeochemical cycles.

Nutrient Leaching: 1) An intrasystem nutrient transfer in terrestrial ecosystems that occurs when precipitation is channeled down plant surfaces and stems (stem flow) as well as washing through the canopy directly to the soil surface (throughfall). 2) The movement of dissolved nutrients from surface soil horizons to deep soil horizons by groundwater infiltration.

Offset: a method used in the 1990 Clean Air Act to give companies that own or operate large (major) sources in nonattainment areas flexibility in meeting overall pollution reduction requirements when changing production processes. If the owner or operator of the source wishes to increase release of a criteria air pollutant, an offset (reduction of a somewhat greater amount of the same pollutant) must be obtained either at the same plant or by purchasing offsets from another company.

Oil Palm: Palms that produce palm oil, which is the 2nd most produced vegetable oil in the world and can be used as an ingredient in biodiesel.

Oilseed: Crops such as soybeans and canola that are used to produce vegetable oils and oilseed meal, which in turn are used to produce oil that can be used in biofuels.

Oleochemical: Chemicals derived from biological oils or fats.

O horizon: The O horizon is primarily composed of organic matter. Fresh litter is found at the surface, while at depth all signs of vegetation structure has been destroyed by decomposition. The decomposed organic matter, or humus, enriches the soil with nutrients (nitrogen, potassium, etc.), aids soil structure (acts to bind particles), and enhances soil moisture retention.

Organic carbon (OC): Includes both primary emissions and secondary organic aerosols (SOA) produced in the atmosphere by chemical transformations of volatile organic compounds (VOCs). Primary OC emissions include directly emitted particles as well as those formed by nucleation or condensation of high molecular weight organic vapors in the immediate vicinity of the source.

Organic compounds: Compounds or molecules containing carbon bound to hydrogen; these are far more prevalent than inorganic compounds and make up all living matter. The behaviour of organic compounds is dependent upon their molecular structure, size and shape, and the presence of functional groups that are important determinants of toxicity. The organic compounds that are dangerous to the environment are all man-made and have only existed during the last century.

Organic aluminum (Al₀): Single aluminum molecules complexed with polymeric or monomeric organic compounds. This is relatively non-toxic.

Organic particulate matter: Particulate matter containing carbon-based molecules.

Original equipment manufaturer (OEM): A producer that provides a product to its customers, who proceed to modify or bundle it before distributing it to their customers.

Oxidant: An oxidizing agent; substance that causes oxidation. Oxidants undergo reduction in the process of causing oxidation of another substance.

Oxygen (O): Gaseous element essential for all aerobic respiration; it has atomic weight 16.00 and atomic number 8. In its elemental form, it exists as the diatomic molecule O₂. On Earth, oxygen is the most abundant of the elements, comprising a fifth of the atmosphere as O₂, almost 90 percent of the oceans as H₂O, and almost 50 percent of the earth's crust as metal oxides and silicates.

Oxygenates: Substances which, when added to gasoline, increase the amount of oxygen in that gasoline blend. Ethanol, methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), and methanol are common oxygenates.

Oxygenated fuel (oxyfuel): special type of gasoline, which burns more completely than regular gasoline in cold start conditions; more complete burning results in reduced production of carbon monoxide, a criteria air pollutant. In some parts of the country, carbon monoxide release from cars starting up in cold weather makes a major contribution to pollution. In these areas, gasoline refiners must market oxygenated fuels, which contain a higher oxygen content than regular gasoline. Some gasoline companies started selling oxyfuels in cities with carbon monoxide problems before the 1990 Clean Air Act was passed.

Oxygenated gasoline: Finished motor gasoline, other than reformulated gasoline, having an oxygen content of 2.7 percent or higher by weight and required by the U.S. Environmental Protection Agency (EPA) to be sold in areas designated by EPA as carbon monoxide (CO) nonattainment areas.

Ozone (O₃): A compound that is formed when oxygen gas is exposed to ultraviolet radiation. In the outer atmosphere (stratosphere) ozone acts to shield the earth from excessive radiation. In the lower atmosphere (troposphere), however, it forms from combustion gases and is a major air pollutant contributing to photochemical smog. Ozone has commercial uses as a bleaching agent and water purifier.

Ozone hole: thin place in the ozone layer located in the stratosphere high above the Earth. Stratospheric ozone thinning has been linked to destruction of stratospheric ozone by CFCs and related chemicals. The 1990 Clean Air Act has provisions to reduce and eliminate ozone destroying chemicals' production and use. Ozone holes have been found above Antarctica and above Canada and northern parts of the United States, as well as above northern Europe.

Particle: Extremely small bit of matter with finite mass but no appreciable volume. Used under different circumstances for the particles constituting particulate matter, molecules and atoms, and elementary of subatomic particles.

Particulate aluminum: Aluminum in clay or suspended particles. This is fairly inactive and usually not of great interest.

Particulate divalent mercury (Hg[p]): The majority of mercury in the atmosphere is in the form of gaseous elemental mercury, Hg(0). This form of mercury can travel long distances in the atmosphere for many months. Some Hg(0) is converted into two other forms of mercury: a more water soluble form of mercury, divalent or oxidized mercury, Hg (II), which can bind with particulate matter or aerosols to form particulate mercury, Hg(p). These two forms of mercury are rapidly removed from the atmosphere in precipitation and fall onto land and into water bodies, including the ocean.

Particulate mass monitoring: The measurement of the mass of particles. A variety of instruments have been developed to more precisely measure (and monitor over time) particle mass.

Particulate matter: A category of air pollutants that refers to small, solid particles or liquid droplets, suspended in air. Such particulates include soot, fumes, dust, pollen and spores, smoke, spray, and even fog.

Particulates: Having the qualities of a particle. When plural, particulates is short for particulate matter.

Parts per billion (ppb): Amount of a substance, often a pollutant, in every billion (10⁹) parts of another substance such as air, water, or soil.

Parts per million (ppm): Amount of a substance, often a pollutant, in every million (10⁶) parts of another substance such as air, water, or soil.

Parts per trillion (ppt): Amount of a substance, often a pollutant, in every trillion (10¹²) parts of another substance such as air, water, or soil.

Pathway: The physical course a chemical or pollutant takes from its source to the exposed organism.

Peak demand period: The greatest amount of energy that must be supplied to customers at any given time.

Peatlands: A dense layer (or layers) of water-saturated, dead, and partially decomposed organic matter that forms in acidic bogs. Same as peat.

Pedon: The smallest unit of soil classsification that represents all of the typical horizons and structures of a soil profile.

Perennial: Plant that doesn't have to be planted every year like traditional row crops

Periphytic diatoms: Single-celled microalgae that grow on all moist or submerged surfaces (e.g., rocks, sediment, or plants).

Periphyton: Benthic algae that grow attached to surfaces such as rocks or larger plants. Periphyton are primary producers and sensitive indicators of environmental change due to a naturally high number of species, a rapid response time to both exposure and recovery, identification to a species level by experienced biologists and ease of sampling requiring few people. Tolerance or sensitivity to specific changes in environmental conditions is known for many species.

Permeability: The rate at which liquids pass through soil or other materials in a specified direction.

Permit: a document that resembles a license, required by the Clean Air Act for big (major) sources of air pollution, such as power plants, chemical factories and, in some cases, smaller polluters. Usually permits will be given out by states, but if EPA has disapproved part or all of a state permit program, EPA will give out the permits in that state. The 1990 Clean Air Act includes requirements for permit applications, including provisions for members of the public to participate in state and EPA reviews of permit applications. Permits will have, in one place, information on all the regulated pollutants at a source. Permits include information on which pollutants are being released, how much the source is allowed to release, and the program that will be used to meet pollutant release requirements. Permits are required both for the operation of plants (operating permits) and for the construction of new plants. The 1990 Clean Air Act introduced a nationwide permit system for air pollution control.

Permit fees: fees paid by businesses required to have a permit. Permit fees are like the fees drivers pay to register their cars. The money from permit fees will help pay for state air pollution control activities.

Peroxyacetyl Nitrate: Organic compound formed in the atmosphere from the addition of nitrogen dioxide, NO2, to the peroxyacyl radical formed in the oxidation of acetaldehyde. PAN and its larger homologs are irritants to the eyes and breathing system.

pH: A measure of the relative concentration of hydrogen ions in a solution; this value indicates the acidity or alkalinity of the solution. It is calculated as the negative logarithm to the base ten of the hydrogen ion concentration in moles per liter. A pH value of 7 indicates a neutral solution; pH values greater than 7 are basic, and those below 7 are acidic. Vinegar has a pH of 3; ocean water has a pH value of approximately 8.

Phosphate (PO₄^-3) 1): The phosphate ion, PO₄^-3. 2) A salt (or ester) of phosphoric acid (H₃PO₄). Phosphates are essential nutrients for plant and animal metabolism; some forms of rock and decaying organic matter provide sources. Because phosphorous is often the limiting nutrient in an ecosystem, when large quantities of phosphates are released into water bodies, they cause a boom in algae populations that deplete the available oxygen supply and contribute to eutrophication.

Photoactive: Capable of responding to sunlight or ultraviolet radiation by chemical reaction.

Photochemical reactions: Chemical reactions in which the necessary energy comes from light, usually sunlight. Photo-oxidation and photosynthesis are examples of reactions that use light as their energy source.

Photochemical Smog: Air pollution caused by chemical reactions of various pollutants emitted from different sources.

pico- (p): Prefix in the Systeme International d'Unites (SI) indicating one trillionth, 1x10^-12. One picofarad equals one trillionth of a farad, or 10^-12 F.

PM _2.5: Technology Assessment and Characterization Study - New York (PMTACS-NY) One of several U.S. EPA "Supersites" intended to provide enhanced measurement data on chemical and physical composition of PM and its associated precursors.

PM_2.5/co-pollutant complex: See co-pollutant.

PM₁₀/PM_2.5: PM₁₀ is measure of particles in the atmosphere with a diameter of less than ten or equal to a nominal 10 micrometers (microns). PM_2.5 is a measure of smaller particles (less than 2.5 microns in diameter) in the air. PM₁₀ has been the pollutant particulate level standard against which EPA has been measuring Clean Air Act compliance. On the basis of newer scientific findings, the Agency is considering regulations that will make PM_2.5 the new standard.

PM_2.5/co-pollutant complex:

PnET-BGC Model: Model developed at Syracuse University describing the interactive cycles of carbon, water, nitrogen and additional elements in forest ecosystems. PnET-BGC was designed to capture the important features of forest ecosystem function while requiring as few input parameters as possible. Input parameters describing physical, chemical or biological processes (e.g., foliar N concentration, solar radiation) are derived directly from field measurements and are not modified to increase