Glossary

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 dusts or smokes. Acid rain can damage the environment. human health and property.

After-treatment device

Engine pollutant emissions are generally reduced by engine modifications, fuel specifications or exhaust gas aftertreatment. An after-treatment device is a component used to reduce engine pollutant emissions downstream of the combustion chamber. Catalytic converters and particulate traps are examples of after-treatment devices.

Air toxics

Also known as toxic air pollutants or hazardous air pollutants are those pollutants known to or suspected of causing cancer or other serious health problems. Health concerns may be associated with both short and long term exposures to these pollutants. Many are known to have respiratory, neurological, immune or reproductive effects, particularly for more susceptible sensitive populations such as children.

Alternative fuels

An alternative fuel is any fuel other than gasoline and diesel fuels, such as methanol, ethanol, compressed natural gas, liquefied petroleum gas (LPG) and other gaseous fuels, and electricity. Alternative fuels may have particularly desirable energy efficiency and pollution reduction features. The 1990 Clean Air Act encourages development and sale of alternative fuels.

Ambient

Surrounding, as in the surrounding environment. In this assessment, ambient air refers to the air surrounding a person through which pollutants can be carried.

Area and other sources

Include sources that generally have smaller emissions on an individual basis than "major sources" and are often too small or ubiquitous in nature to be inventoried as individual sources. "Area sources" include facilities that have air toxics emissions below the major source threshold as defined in the air toxics sections of the Clean Air Act and thus emit less than 10 tons of a single toxic air pollutant or less than 25 tons of multiple toxic air pollutants in any one year. Area sources include smaller facilities, such as dry cleaners. "Other sources" include sources such as wildfires and prescribed burnings that may be more appropriately addressed by other programs rather than through regulations developed under certain air toxics provisions (section 112 or 129) in the Clean Air Act. For example, wildfires and prescribed burning are being addressed through the burning policy agreed to by the Interim Federal Wildland Policy.

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.

Automatic tire inflation system

Automatic tire inflation systems monitor and continually adjust the level of pressurized air to tires, maintaining proper tire pressure even when the truck is moving.

Auxiliary power unit (APU)

APU’s provide a larger array of comfort features for drivers looking to reduce idling. APU’s can provide heat, air conditioning, power for household electrical devices and engine heat. Most devices combine a small heater, a compressor for air conditioning and an alternator. APU’s may be powered by diesel fuel directly from the tractor fuel tank, or by a bank of rechargeable batteries. Diesel driven APU’s can operate for 5 hours or more on a single gallon of diesel fuel. Costs for these devices can range from $3500 to $9000, but are typically in the $6000 to $7000 range. For locomotives APUs automatically shut down the main locomotive engine idle while maintaining all vital main engine systems at greatly reduced fuel consumption.

Carbon dioxide

Burning fossil fuels releases carbon that has been stored underground for millions of years into the atmosphere. The carbon in these fossil fuels is transformed into carbon dioxide, the predominant gas contributing to the greenhouse effect, during the combustion process. While carbon dioxide is absorbed and released at nearly equal rates by natural processes on the earth, this equilibrium may be disrupted when large amounts of carbon dioxide are released to the atmosphere by human activities, such as the burning of fossil fuels.

Carbon monoxide

Carbon monoxide is colorless, odorless gas resulting from the incomplete combustion of hydrocarbon fuels including gasoline, oil and wood. The largest emissions contribution comes from highway motor vehicles. Thus, the focus of CO monitoring has been in urban areas where the main source of CO is motor vehicle exhaust. Other major CO sources are wood-burning stoves, incinerators and industrial sources.  Carbon monoxide interferes with blood's ability to carry oxygen to the body's tissues and results in numerous adverse health effects. 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.

Carcinogen

A chemical or physical agent capable of causing cancer.

Catalytic converter

A catalytic converter consists of a metal housing filled with a hard material which is covered with a catalytic compound. The presence of the catalytic converter in the engine exhaust system breaks down the chemicals in the exhaust and reduces harmful pollutant emissions.

CFCs (chlorofluorocarbons)

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 which 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 federal Clean Air Act was passed in 1963, but our national air pollution control program is actually based on the 1970 version of the law. The 1990 Clean Air Act Amendments are the most far-reaching revisions of the 1970 law. We refer to the 1990 amendments as the 1990 Clean Air Act.

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).

Combustion

Burning. 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.

Conformity (Rule)

The conformity rule requires that transportation plans, programs, and projects conform to state air quality implementation plans (SIPs) and establishes the criteria and procedures to determine if plans comply. Conformity to a SIP means that transportation activities will not produce new air quality violations, worsen existing violations, or delay timely attainment of the national ambient air quality standards.

CMAQ

Congestive Mitigation and Air Quality Improvement Program.  CMAQ was introduced in the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA). It is set up to provide Federal funding to help fulfill Clean Air Act mandates in areas that do not meet ambient air quality standards or may have trouble meeting those standards (nonattainment or maintenance areas).

Continuous emission monitoring systems (CEMS)

Machines which measure, on a continuous basis, pollutants released by a source. The 1990 Clean Air Act requires continuous emission monitoring systems for certain large sources.

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.

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 country.

Curtailment programs

Restrictions on operation of fireplaces and woodstoves in areas where these home heat sources make major contributions to pollution.

Diesel oxidation catalyst (DOC)

A diesel oxidation catalyst (DOC) is a device added to the exhaust system of a tractor that reduces the amount of particulate matter (PM) emitted. The device is generally a large honeycomb structure with an active catalyst made up of a layer of precious metal. Emission reductions are approximately 20 percent for PM, 40 percent for hydrocarbons and 50 percent for carbon monoxide.

Diesel particulate filter (DPF)

A diesel particulate filter (DPF) is similar to a diesel oxidation catalyst and is one of the two major technologies being employed to meet the 2007 emissions regulations. A DPF is considered a "flow-through" device whereby the exhaust is forced through a honeycomb shaped, ceramic filter that is blocked at one end. One major difference between the DOC and DPF is that the DPF requires the use of ultra low sulfur diesel (ULSD) fuel with sulfur content at or below 15 parts per million. Emission reductions are approximately 50 - 90 percent for PM, 90 percent for hydrocarbons and 90 percent for carbon monoxide.

Direct fired heater (DFH)

Direct fired heaters, or bunk heaters, are devices that can reduce idling by providing in-cabin heat for drivers in cold temperatures. Some product models offer an engine heating option that will also keep the engine warm overnight. Most DFHs operate by using fuel directly from the main tractor fuel tank. These devices can generally provide 10 to 20 hours of heat on a single gallon of diesel fuel, depending on the settings and options.

Dioxins

Dioxins are man-made chemical compounds that enter the air through fuel and waste emissions, including motor vehicle exhaust fumes and garbage incineration. Skin rashes, liver damage, weight loss, and a reduction in the effectiveness of the immune system have all been attributed to human exposure to dioxins.

Emission

Release of pollutants into the air from a source. We say sources emit pollutants. Continuous emission monitoring systems (CEMS) are machines which some large sources are required to install, to make continuous measurements of pollutant release.

Energy efficiency

Energy efficiency refers to products or systems using less energy to do the same or better job than conventional products or systems. Energy efficiency saves energy, saves money on utility bills, and helps protect the environment by reducing the amount of electricity that needs to be generated. When buying or replacing products or appliances for your home, look for the ENERGY STAR® label — the national symbol for energy efficiency.

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.

Engine shutdown

Engine shutdown is the automatic or voluntary shutoff of the tractor engine after a certain amount of time. Engine shutdown can be as simple as a corporate “shut down” or “no idle” policy or it can be more complex with the use of electronic devices or software encoded onto the engine control chip that automatically shuts the engine down. Engine shutdown works most effectively when combined with a comprehensive driver training program and driver incentive program.

Environmental Justice

The goal of environmental justice is to ensure that all people, regardless of race, national origin or income, are protected from the adverse impacts of environmental hazards and to ensure that one group is not disproportionately affected. To be classified as an environmental justice community, residents must be a minority and/or low income group; excluded from the environmental policy setting and/or decision-making process; subject to a disproportionate impact from one or more environmental hazards; and experience a disparate implementation of environmental regulations, requirements, practices and activities in their communities. Environmental justice is about real people facing real problems and designing practical solutions to address challenging environmental issues. The environmental justice movement advocates programs that promote environmental protection within the context of sustainable development. Utilizing various methods, including traditional knowledge about the eco-system and community mobilization, the environmental justice community has become a formidable force in protection of both the urban and rural environments.

Friable, Asbestos-Containing Material

Means asbestos-containing material that when dry, can be crumbled, pulverized, or reduced to powder by hand pressure or by the forces expected to act upon the material in the course of the demolition, renovation, or disposal. Such materials include, but are not limited to thermal system insulation, surfacing material, sheet-vinyl flooring with asbestos backing, and cement asbestos products.

Fossil fuels

Fossil fuels are the nation’s principal source of electricity. The popularity of these fuels is largely due to their low costs. Fossil fuels come in three major forms-coal, oil, and natural gas. Because fossil fuels are a finite resource and cannot be replenished once they are extracted and burned, they are not considered renewable.

Global climate change

Global climate change could result in sea level rises, changes to patterns of precipitation, increased variability in the weather, and a variety of other consequences. These changes threaten our health, agriculture, water resources, forests, wildlife, and coastal areas.

Green power

Electricity that is generated from renewable energy sources is often referred to as “green power.” Green power products can include electricity generated exclusively from renewable resources or, more frequently, electricity produced from a combination of fossil and renewable resources. Also known as “blended” products, these products typically have lower prices than 100 percent renewable products. Customers who take advantage of these options usually pay a premium for having some or all of their electricity produced from renewable resources.

Ground-level ozone

Ground-level ozone is formed by a chemical reaction between volatile organic compounds and oxides of nitrogen in the presence of sunlight. Ozone concentrations can reach unhealthful levels when the weather is hot and sunny with little or no wind. High concentrations of ozone near ground level are harmful to people, animals, crops, and other materials.

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.)

Haze

Haze consists of sufficient smoke, dust, moisture, and vapor suspended in air to impair visibility. The term regional haze means haze that impairs visibility in all directions over a large area.

HC

An exhaust and evaporative pollutant of hydrogen and carbon atoms resulting from unburned fuel. HC contributes to the formation of ozone which is responsible for the choking, coughing, and stinging eyes associated with smog. Ozone damages lung tissue, aggravates respiratory disease, and makes people more susceptible to respiratory infections. Children are especially vulnerable to ozone's harmful effects, as are adults with existing disease.

Highway engine

Any engine which is designed to transport people or property on a street or highway.

Industrial air pollution

This term refers to the emissions of the following pollutants: sulfur oxides, nitrogen oxides, mercury, and carbon dioxide. These air emissions contribute to such environmental concerns as urban smog; acid deposition; excessive nutrient loads to important bodies of wate; haze in national parks and wilderness areas; and global climate change.

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 which 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.

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.

Marine engine

An engine that is installed or intended to be installed on a marine vessel. This definition does not include portable auxiliary engines for which the fueling, cooling and exhaust systems are not integral parts of the vessel.

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.

Mercury/Mercury compounds

Mercury is a toxic heavy metal that is a byproduct of the combustion of fossil fuels, especially coal. Mercury and compounds containing mercury can accumulate in the environment and are highly toxic to humans and animals if inhaled or swallowed. Exposure can permanently damage the brain, kidneys, and fetuses.

Methane

Methane is one of many greenhouse gases that trap heat in the atmosphere, resulting in a “greenhouse effect.” It is the second-most prevalent greenhouse gas emitted by U.S. sources. Methane's overall contribution to global warming is significant because it is estimated to be 21 times more effective at trapping heat in the atmosphere than carbon dioxide. Currently, methane represents approximately 10 percent of the greenhouse gas emissions from U.S. activities that contribute to global warming. Over the last two centuries, methane's concentration in the atmosphere has more than doubled due to increasing methane emissions from several human activities, including placing municipal solid waste (MSW) in landfills, producing natural gas and petroleum, mining coal, and burning fossil fuels. Methane emissions from the production and processing of fossil fuels contribute to almost one-third of the total methane emitted in the U.S.

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.

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.

National Ambient Air Quality Standards (NAAQS)

The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards for pollutants considered harmful to public health and the environment. The Clean Air Act established two types of national air quality standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.  The EPA Office of Air Quality Planning and Standards (OAQPS) has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" pollutants.

Natural gas

Natural gas is a fossil fuel formed when layers of buried plants and animals decompose over a long period of time. The energy that the plants and animals originally obtained from the sun is stored in the natural gas. The primary component of natural gas is methane, a potent greenhouse gas. Natural gas is a nonrenewable resource because it cannot be replenished on a human time frame. Natural gas power plants provide about 14 percent of the electricity produced in the United States, ranking third behind coal and nuclear power. Natural gas is available in most areas of the U.S. However, natural gas is not as plentiful as coal, and it is estimated that United States' supply of natural gas will last only 60 more years.

Nitrogen oxides (NOx)

A criteria air pollutant, oxides of nitrogen (NOx) are a family of reactive gaseous compounds that contribute to air pollution in both urban and rural environments. NOx emissions are produced during the combustion of fuels at high temperatures. The primary sources of atmospheric NOx include highway sources (such as light-duty and heavy-duty vehicles), nonroad sources (such as construction and agricultural equipment, and locomotives) and stationary sources (such as power plants and industrial boilers). NOx can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections. Nitrogen oxides are an important precursor both to ozone and acid rain, and may affect both terrestrial and aquatic ecosystems.

Nonattainment area

A geographic area in which the level of a criteria air pollutant persistently exceed National Ambient Air Quality Standards. Designating an area as nonattainment is a formal rulemaking process and EPA normally takes this action only after air quality standards have been exceeded for several consecutive years. A single geographic area may have acceptable levels of one criteria air pollutant but unacceptable levels of one or more other criteria air pollutants; thus, an area can be both attainment and nonattainment at the same time. It has been estimated that 60% of Americans live in nonattainment areas.

Nonfriable, Asbestos-Containing Material

Means asbestos containing material that, when dry, cannot be crumbled, pulverized, or reduced to powder by hand pressure or by the forces expected to act on the material in the course of demolition, renovation, or disposal. This includes asbestos roofing, vinyl asbestos tile, mastic, and caulking.

Nonroad mobile sources

Mobile sources not found on roads and highways (e.g., airplanes, trains, lawn mowers, construction vehicles, farm machinery).

Offset

A method used in the 1990 Clean Air Act to give companies which 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.

Onroad mobile sources

Vehicles found on roads and highways (e.g., cars, trucks, buses).

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.

Ozone

A gas which is a variety of oxygen. The oxygen gas found in the air consists of two oxygen atoms stuck together; this is molecular oxygen. Ozone consists of three oxygen atoms stuck together into an ozone molecule. Ozone occurs in nature; it produces the sharp smell you notice near a lightning strike. High concentrations of ozone gas are found in a layer of the atmosphere -- the stratosphere -- high above the Earth. Stratospheric ozone shields the Earth against harmful rays from the sun, particularly ultraviolet B. Smog's main component is ozone; this ground-level ozone is a product of reactions among chemicals produced by burning coal, gasoline and other fuels, and chemicals found in products including solvents, paints, hairsprays, etc.

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.

Particulate matter (PM)

Considered a criteria air pollutant, is a mixture of particles that can adversely affect human health, damage materials, and form atmospheric haze that degrades visibility. Particulate matter includes dust, soot and other tiny bits of solid materials that are released into and move around in the air. Particulates are produced by many sources, including burning of diesel fuels by trucks and buses, incineration of garbage, mixing and application of fertilizers and pesticides, road construction, industrial processes such as steel making, mining operations, agricultural burning (field and slash burning), and operation of fireplaces and woodstoves. PM is usually divided into different classes based on size, ranging from total suspended matter (TSP) to PM-2.5 (particles less than 2.5 microns in aerodynamic diameter). In general, the smallest particles pose the highest human health risks. PM exposure can affect breathing, aggravate existing respiratory and cardiovascular disease, alter the body's defense systems against foreign materials, and damage lung tissue, contributing to cancer and premature death. Individuals with chronic obstructive pulmonary or cardiovascular disease, asthmatics, the elderly, and children are most sensitive to the effects of PM.

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.

Pollutants (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.

Primary standard

A pollution limit based on health effects. Primary standards are set for criteria air pollutants.

Reformulated gasoline

Specially refined gasoline with low levels of smog-forming volatile organic compounds (VOCs) and low levels of hazardous air pollutants. The 1990 Clean Air Act requires sale of reformulated gasoline in the nine smoggiest areas. Reformulated gasolines were sold in several smoggy areas even before the 1990 Clean Air Act was passed.

Renewable energy

The term renewable energy generally refers to electricity supplied from renewable energy sources, such as wind and solar power, geothermal, hydropower, and various forms of biomass. These energy sources are considered renewable sources because they are continuously replenished on the Earth.

Retrofit

An engine "retrofit" includes (but is not limited to) any of these activities:

• addition of new/better pollution control after-treatment equipment to certified engines
• upgrading a certified engine to a cleaner certified configuration
• upgrading an uncertified engine to a cleaner "certified-like" configuration
• conversion of any engine to a cleaner fuel
• early replacement of older engines with newer (presumably cleaner) engines (in lieu of regular expected rebuilding)
• use of cleaner fuel and/or emission reducing fuel additive (without engine conversion).

Risk

The probability that damage to life, health, and/or the environment will occur as a result of a given hazard (such as exposure to a toxic chemical). Some risks can be measured or estimated in numerical terms (e.g., one chance in a hundred).

Secondary standard

A pollution limit based on environmental effects such as damage to property, plants, visibility, etc. Secondary standards are set for criteria air pollutants.

Smog

A mixture of pollutants, principally ground-level ozone, produced by chemical reactions in the air involving smog-forming chemicals. A major portion of smog-formers come from burning of petroleum-based fuels such as gasoline. Other smog-formers, volatile organic compounds, are found in products such as paints and solvents. Smog can harm health, damage the environment and cause poor visibility. Major smog occurrences are often linked to heavy motor vehicle traffic, sunshine, high temperatures and calm winds or temperature inversion (weather condition in which warm air is trapped close to the ground instead of rising). Smog is often worse away from the source of the smog-forming chemicals, since the chemical reactions that result in smog occur in the sky while the reacting chemicals are being blown away from their sources by winds.

Source

Any place or object from which pollutants are released. A source can be a power plant, factory, dry cleaning business, gas station or farm. Cars, trucks and other motor vehicles are sources, and consumer products and machines used ir industry can be sources too. Sources that stay in one place are referred to as stationary sources; sources that move around, such as cars or planes, are called mobile sources.

State implementation plan (SIP)

State implementation plans are collections of the regulations used by a state to reduce air pollution. The Clean Air Act requires that EPA approve each state implementation plan. Section 110 of the Clean Air Act requires that states develop air quality plans for areas that do not meet national air standards outlining how they will reduce pollution. Members of the public are given opportunities to participate in review and approval of state implementation plans.

SIP credit

The permanent, measurable emission benefits that are accounted for in a State Implementation Plan.

Stationary source

A place or object from which pollutants are released and which does not move around. Stationary sources include power plants, gas stations, incinerators, houses etc.

Stratosphere

Part of the atmosphere, the gases that encircle the Earth. The stratosphere is a layer of the atmosphere 9-31 miles above the Earth. Ozone in the stratosphere filters out harmful sun rays, including a type of sunlight called ultraviolet B, which has been linked to health and environmental damage.

Sulfur dioxide

A criteria air pollutant. High concentrations of sulfur dioxide affect breathing and may aggravate existing respiratory and cardiovascular disease. Sensitive populations include asthmatics, individuals with bronchitis or emphysema, children, and the elderly. Sulfur dioxide is also a primary contributor to acid rain, which causes acidification of lakes and streams and can damage trees, crops, historic buildings, and statues. In addition, sulfur compounds in the air contribute to visibility impairment in large parts of the country. This is especially noticeable in national parks. Sulfur dioxide is released primarily from burning fuels that contain sulfur (such as coal, oil, and diesel fuel). Stationary sources such as coal- and oil-fired power plants, steel mills, refineries, pulp and paper mills, and nonferrous smelters are the largest releasers.

Temperature inversion

One of the weather conditions that are often associated with serious smog episodes in some portions of the country . In a temperature inversion, air doesn't rise because it is trapped near the ground by a layer of warmer air above it. Pollutants, especially smog and smog-forming chemicals, including volatile organic compounds, are trapped close to the ground. As people continue driving, and sources other than motor vehicles continue to release smog-forming pollutants into the air, the smog level keeps getting worse.

Truck stop electrification (TSE)

Truck plazas equipped with truck stop electrification systems allow drivers to draw electrical power and in some cases, heating, cooling, telecommunication, and Internet hookups from a ground source. Different systems may or may not require the purchase of an adaptor to connect to the tractor.

Ultraviolet B (UVB)

A type of sunlight. The ozone in the stratosphere, high above the Earth, filters out ultraviolet B rays and keeps them from reaching the Earth. Ultraviolet B exposure has been associated with skin cancer, eye cataracts and damage to the environment. Thinning of the ozone layer in the stratosphere results in increased amounts of ultraviolet B reaching the Earth.

Vapor recovery nozzles

Special gas pump nozzles that will reduce release of gasoline vapor into the air when people put gas in their cars. There are several types of vapor recovery nozzles, so nozzles may look different at different gas stations. The 1990 Clean Air Act requires installation of vapor recovery nozzles at gas stations in smoggy areas.

Volatile organic compounds (VOCs)

Organic chemicals all contain the element carbon (C); organic chemicals are the basic chemicals found in living things and in products derived from living things, such as coal, petroleum and refined petroleum products. Many of the organic chemicals we use do not occur in Nature, but were synthesized by chemists in laboratories. Volatile chemicals produce vapors readily; at room temperature and normal atmospheric pressure, vapors escape easily from volatile liquid chemicals. Volatile organic chemicals include gasoline, industrial chemicals such as benzene, solvents such as toluene and xylene, and tetrachloroethylene (perchloroethylene, the principal dry cleaning solvent). Many volatile organic chemicals are also hazardous air pollutants; for example, benzene causes cancer.

Voluntary Mobile Source Emission Reduction Policy (VMEP)

VMEP is a policy that allows states to obtain SIP credits for voluntary emission reduction activities. The policy also encourages investment in innovative emission reduction programs and actions.

¹Sources:

• Clean Air Act glossary

• Voluntary Diesel Retrofit Program glossary

• Terms Relating to the SmartWay Transport Partnership

• Clean Energy glossary

• National Air Toxics Assessment glossary