Aftertreatment Devices: Devices that remove pollutants from exhaust gases after they are discharged from the combustion chamber e.g., catalytic converters, diesel particulate filters and diesel oxidation catalysts.  They are also known as emissions control devices or exhaust aftertreatment systems.  (Source:  Donaldson Company, Inc.)

Air pollution: is the contamination of air by the discharge of harmful substances. Air pollution can cause health problems, including burning eyes and nose, itchy irritated throat, and difficulty breathing. Some contaminants found in polluted air (e.g., benzene, carbon dioxide, carbon monoxide, lead, nitrogen oxide, particulate matter, and sulfur dioxide) can cause cancer, birth defects, brain and nerve damage, and long-term injury to the lungs and breathing passages. Above certain concentrations and durations, air pollutants can be extremely dangerous and can cause severe injury or death. (Source: National Safety Counsel)

Air Toxics: Chemicals in the air that are known or suspected to cause cancer or other serious health effects, such as reproductive problems or birth defects. Air toxics are also known as "hazardous air pollutants." Mobile sources emit a number of air toxics associated with both long-term and short-term health effects in people, including heart problems, asthma symptoms, eye and lung irritation, cancer, and premature death. Examples of substances classified as air toxics as toxics by the U.S. Clean Air Act include: acetaldehyde, benzene, 1,3-butadiene, formaldehyde, and polycyclic organic matter (POM).  California air toxics regulations also classify diesel exhaust particulates as a toxic air contaminant.(Source: USEPA, Donaldson Company, Inc.)

Alternative Fuel:  Fuel other than petroleum diesel or gasoline, i.e., biodiesel, compressed natural gas (CNG) or liquefied natural gas (LNG). (Source:  Donaldson Company, Inc.)

Benzene: A cancer-causing hydrocarbon (C6H6) derived from petroleum. Benzene is a component of gasoline. Benzene emissions occur in exhaust as a byproduct of fuel combustion and also occur when gasoline evaporates. (Source: USEPA)

Biodiesel Fuel: A renewable diesel fuel derived from various organic feedstocks including vegetable oils and animal fats, for use in compression ignition (diesel) engines. (Source:  Donaldson Company, Inc.)

Carbon Monoxide (CO): A colorless, odorless gas that forms when carbon in fuel is not burned completely. Carbon monoxide is a component of exhaust from motor vehicles and engines. Carbon monoxide emissions increase when conditions are poor for combustion; thus, the highest carbon monoxide levels tend to occur when the weather is very c old or at high elevations where there is less oxygen in the air to burn the fuel. (Source: USEPA)

Carbon Dioxide (CO2): A colorless, odorless, non-toxic gas that is a primary bi-product of fossil fuel combustion. Carbon dioxide is a greenhouse gas that is contributes to the potential for global warming. (Source:  Donaldson Company, Inc.)

Catalyst: A substance which influences the rate of a chemical reaction but is not consumed or altered in the reaction. Catalysts are used in many processes in the chemical and petroleum industries. Emissions control catalysts are used to promote reactions that change exhaust pollutants from internal combustion engine into less harmful substances. (Source:  Donaldson Company, Inc.)

Catalytic Converter: An anti-pollution device located between a vehicle's engine and tailpipe. Catalytic converters work by facilitating chemical reactions that convert exhaust pollutants such as carbon monoxide and nitrogen oxides to normal atmospheric gases such as nitrogen, carbon dioxide, and water. (Source: USEPA)

Combustion: The process of burning. Motor vehicles and equipment typically burn fuel in an engine to create power. Gasoline and diesel fuels are mixtures of hydrocarbons, which are compounds that contain hydrogen and carbon atoms. In "perfect" combustion, oxygen in the air would combine with all the hydrogen in the fuel to form water and with all the carbon in the fuel to form carbon dioxide. Nitrogen in the air would remain unaffected. In reality, the combustion process is not "perfect," and engines emit several types of pollutants as combustion byproducts. (Source: USEPA)

Critical Pollutants: The critical air pollutants established by the Untied States National Ambient Air Quality Standards include six air pollutants: ozone, lead, carbon monoxide, sulfur dioxide, nitrogen dioxide and respirable particulate matter. (Source:  Donaldson Company, Inc.)

Diesel Oxidation Catalyst (DOC): A catalyst for diesel engines that promotes the oxidation of diesel exhaust gases. DOC's achieve average reduction efficiencies of 15% - 30%. DOC's are only capable of reducing soluble organic fraction emissions (gas-phase hydrocarbons and carbon monoxide). DOC's are not capable of oxidizing solid inorganic fraction emissions.

Diesel Particulate Filter (DPF): A devise which physically captures diesel particulates and prevents their discharge from the tailpipe. DPF's are normally coated with precious metal catalysts such as platinum or palladium. These catalysts enable the DPF to burn the particulates it has collected. The devices reoccurring process of burring captured material is called "regeneration". DPF's can achieve high levels of Particulate Material reduction, however, DPF's are expensive and they do not work well in fuel environments in which fuel sulfur levels exceed 150 PPM.

Dioxins are among the most toxic substances known to man.  “Dioxins” refers to a group of chemical compounds (halogenated organic compounds) that share certain chemical structures and biological characteristics. Several hundred of these compounds exist and they are members of three closely related families: the chlorinated dibenzo-p-dioxins (CDDs), chlorinated dibenzofurans (CDFs) and certain polychlorinated biphenyls (PCBs).  According to the USEPA, common sources of dioxins include: coal fired utilities, metal smelting, diesel trucks, land application of sewage sludge, burning treated wood, trash burn barrels.  One of the most comprehensive reviews on dioxins is the USEPA’s Draft Dioxin Reassessment of 2003. For information regarding the human health impacts of dioxins, refer to The World Health Organization's fact sheet entitled Dioxins and Their Effects on Human Health (Source: United States Environmental Protection Agency)

Elemental Carbon: Inorganic carbon, as opposed to organic compounds, sometimes used as a surrogate measure for diesel particulate matter, especially in occupational health environments. Elemental carbon usually accounts for 40% - 60% of the total diesel PM mass. (Source:  Donaldson Company, Inc.)

Emissions: Releases of pollutants into the air from a source, such as a motor vehicle or a factory. (Source: USEPA)

Emission Standards: Rules and regulations that set limits on how much pollution can be emitted from a given source. Vehicle and equipment manufacturers have responded to many mobile source emission standards by redesigning vehicles and engines to reduce pollution. (Source: USEPA)

Evaporation: The process by which a substance is converted from a liquid into a vapor. "Evaporative emissions" occur when a liquid fuel evaporates and fuel molecules escape into the atmosphere. A considerable amount of hydrocarbon pollution results from evaporative emissions that occur when gasoline leaks or spills, or when gasoline gets hot and evaporates from the fuel tank or engine. (Source: USEPA)

Federal Test Procedure: A prescriptive test cycle used in the U.S. for emissions testing and certification of engines and vehicles. The chassis dynamometer cycle for light duty vehicle testing is commonly referred to as FTP-75. The engine dynamometer cycle for testing of heavy-duty (HD) engines is known as HD FTP, or FTP Transient cycle. (Source:  Donaldson Company, Inc.)

Fossil Fuels: Fuels—such as coal, natural gas, and crude oil— that come from the compressed remains of ancient plants and animals. Gasoline and diesel are fossil fuels that can be burned in internal combustion engines to power everything from jet planes to automobiles to railroad locomotives. (Source: USEPA)

Gas chromatography-mass spectrometry (GC-MS) is a method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC-MS include drug detection, fire investigation, environmental analysis, and explosives investigation. Additionally, it can identify trace elements in materials that were previously thought to have disintegrated beyond identification. GC-MS is becoming the tool of choice tool of choice for tracking organic pollutants in the environment. (Source: Wikipedia)

Haze: Atmospheric particulate matter and gases that diminish visibility. Visibility is reduced when light encounters tiny pollution particles, such as soot and dust, and some gases (such as nitrogen dioxide) in the air. Some light is absorbed by the particles and gases and other light is scattered away before it reaches your eye. More pollutants mean more absorption and scattering of light, resulting in more haze. Some haze-causing pollutants are directly emitted to the atmosphere from vehicle emissions; others are formed indirectly when pollutants from mobile sources react with other elements and materials in the atmosphere. (Source: USEPA)

Hydrocarbons (HC): Chemical compounds that contain hydrogen and carbon. Most motor vehicles and engines are powered by hydrocarbon-based fuels such as gasoline and diesel. Hydrocarbon pollution results when unburned or partially burned fuel is emitted from the engine as exhaust, and also when fuel evaporates directly into the atmosphere. Hydrocarbons include many toxic compounds that cause cancer and other adverse health effects. Hydrocarbons also react with nitrogen oxides in the presence of sunlight to form ozone. Hydrocarbons, which may take the form of gases, tiny particles, or droplets, come from a great variety of industrial and natural processes. In typical urban areas, a very significant fraction comes from cars, buses, trucks, and non-road mobile sources such as construction vehicles and boats. (Source: USEPA)

Lean NOx Catalyst (LNC): Catalyst designed to reduce nitrogen oxides from diesel or spark-ignited engine exhaust gas conditions, i.e. in the presence of excessive amounts of oxygen. (Source:  Donaldson Company, Inc.)

Micormeter (µm): is a length equal to one millionth a a meter (1m/1,000,000), or about one tenth the diameter of a droplet of mist or fog. This same unit of measurement is also commonly refered to as a "micron". (Source: Wikipedia)

Mobile Sources: Motor vehicles, engines, and equipment that move, or can be moved, from place to place. Mobile sources include vehicles that operate on roads and highways ("on-road" or "highway" vehicles), as well as non-road vehicles, engines, and equipment. Examples of mobile sources are cars, trucks, buses, earth-moving equipment, lawn and garden power tools, ships, railroad locomotives, and airplanes. (Source: USEPA)

Nanometer (nm): is a length of measure equal to one billionth of a meter (1m/(1,000,000,000). (Source: Wikipedia)

National Ambient Air Quality Standard (NAAQS): The EPA's 1990 amendment to the Clean Air Act requires the EPA to set National Standards for wide-spread pollutants which are considered harmful to human health and the physical environment. The Clean Air Act established two types of national air quality standards: 1) Primary standards which established limits to protect public health, including the health of "sensitive" populations, such as asthmatics, children and the elderly; 2) Secondary standards which establish limits to protect public welfare, including protection against visibility impairment, damage to animals, crops vegetation, and buildings. (Source: USEPA)

Nitrogen Oxides (NOx): A group of highly reactive gases that contain nitrogen and oxygen in varying amounts. Many of the nitrogen oxides are colorless and odorless. The common pollutant nitrogen dioxide (NO2) can often be seen combined with particles in the air as a reddish-brown layer over many urban areas. Nitrogen oxides are formed when the oxygen and nitrogen in the air react with each other during combustion. The formation of nitrogen oxides is favored by high temperatures and excess oxygen (more than is needed to burn the fuel). The primary sources of nitrogen oxides are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. (Source: USEPA)

Nonattainment Area: A region that exceeds the U.S. National Ambient Air Quality Standards (NAAQS) for one or more criteria pollutants. Nonattainment regions, or areas, are required to develop State Implementations Plans (SIP's), setting forth a reasonable timetable using means that are approved by the U.S. Environmental Protection Agency, including retrofits, to achieve compliance. Under the U.S. Clean Air Act, if a nonattainment area fails to implement NAAQS, the EPA may superimpose a Federal Implementation Plan (FIP) with stricter requirements, impose fines, construction bans, or cut-offs in Federal grant revenues until the area achieves applicable NAAQS compliance. (Source:  Donaldson Company, Inc.)

Ozone: A gaseous molecule that contains three oxygen atoms (O3). Ozone can exist either high in the atmosphere, where it shields the Earth against harmful ultraviolet rays from the sun, or close to the ground, where it is the main component of smog. Ground-level ozone is a product of reactions involving hydrocarbons and nitrogen oxides in the presence of sunlight. Ozone is a potent irritant that causes lung damage and a variety of respiratory problems. (Source: USEPA)

Particulate Matter (PM): Tiny particles or liquid droplets suspended in the air that can contain a variety of chemical components. Larger particles are visible as smoke or dust and settle out relatively rapidly. The tiniest particles can be suspended in the air for long periods of time and are the most harmful to human health because they can penetrate deep into the lungs. Some particles are directly emitted into the air. They come from a variety of sources such as cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, stone crushing, and wood burning. Other particles are formed in the atmosphere by chemical reactions. (Source: USEPA)

Particulate Matter 2.5 (PM2.5): Particles that are less than 2.5 microns in diameter. These particles are often referred to as "PM fine." PM fine particles are so small that they are not typically visible to the naked eye. In the atmosphere, however, they are significant contributors to haze. Smaller particles are generally more harmful to human health because they can penetrate more deeply into the lungs than larger particles. Virtually all particulate matter from mobile sources is PM2.5. (Source: USEPA)

Particulate Filter: An anti-pollution device designed to trap particles in diesel exhaust before they can escape into the atmosphere. (Source: USEPA)

Persistent Organic Pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potential significant impacts on human health and the environment. In May 1995, the UNEP Governing Council (GC) begin investigating POPs. As a result, the UNEP established a list--often referred to as the "dirty dozen"--of 12 POPs which are considered particularly toxic. These include: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and toxaphene. (Sources: Wikipedia, UNEP)

Pollutants (Pollution): Unwanted chemicals or other materials found in the environment. Pollutants can harm human health, the environment, and property. Air pollutants occur as gases, liquid droplets, and solids. Once released into the environment, many pollutants can persist, travel long distances, and move from one environmental medium (e.g., air, water, land) to another. (Source: USEPA)

Polynuclear aromatic hydrocarbons (PAHs) are hydrocarbon compounds with multiple benzene rings. PAHs are typical components of asphalts, fuels, oils, and greases. They are also called Polycyclic Aromatic Hydrocarbons. (Source: United States Geological Survey, Wikipedia)

Smog: A commonly used term for pollution caused by complex chemical reactions involving nitrogen oxides and hydrocarbons in the presence of sunlight. Ozone is a key component of smog. Smog-forming chemicals come from a wide variety of combustion sources and are also found in products such as paints and solvents. Smog can harm human health, damage the environment, and cause poor visibility. Major smog occurrences are often linked to heavy motor vehicle traffic. (Source: USEPA)

Soluble Organic Fraction (SOL): The organic fraction of diesel particulates, including heavy hydrocarbons from both the fuel and engine lubricating oil. The term soluble" originates from the analytical method used to measure SOF which is based on extraction of particulate matter samples using organic solvents. The SOL is often referred to as the "wet" fraction of PM.

Source: Any place or object from which pollutants are released, such as a power plant, factory, tractor, car, or other machines. Mobile sources move (e.g., cars and buses), while stationary sources do not (e.g., factories). (Source: USEPA)

Total Carbon: The sum of elemental carbon and organic carbon associated with diesel particulates. Total carbon typically amounts to 80 - 85% of the total diesel PM mass. (Source:  Donaldson Company, Inc.)

Total Particulate Matter (TPM): TPM emissions including all fractions of diesel particulates, i.e. the soluble organic fraction, the solid inorganic fraction and sulfate particulates.

Ultra Low Sulfur Diesel (ULSD): Classified by the U.S. EPA as diesel fuel comprised of ≤ 15 PPM sulfur.

Vapor Recovery System: An anti-pollution system designed to capture gasoline vapors that would otherwise escape into the atmosphere from hot vehicle engines and fuel tanks. (Source: USEPA)

Vehicle Miles Traveled (VMT): The total number of miles traveled in a given period of time (e.g., day, year) by a given vehicle or fleet of vehicles. VMT, combined with pollution rates per mile traveled, provide an estimate of the total amount of vehicle pollution in a given period of time. (Source: USEPA)

Verification: The process of approval for the aftertreatment devices. These processes are outlined by the US EPA and the California Air Resources Board.

Volatile Organic Compounds (VOC's):VOC's, in combination with nitrogen oxides, are responsible for ground level ozone and smog. Volatile Organic Compounds, or VOC's, are organic chemicals that form gases at room temperature. They are called organic because they contain elemental carbon. There are many types of VOC's. Hydrocarbons have both hydrogen and carbon atoms and include benzene and toluene. Oxygenates contain carbon, hydrogen and oxygen and originate in automobile exhaust. In addition to the health problems caused by VOC's, VOC's in the air react with ultraviolet light and nitrogen oxides to form ground level ozone. The Ontario Ministry of the Environment publishes a List of Volatile Organic Compounds that provides a comprehensive inventory of VOC’s.