???? ????? - Glossary of Terms

This glossary provides definitions of important terms associated with air pollution and their environmental and health impacts. More information is provided in the hyperlinks detailed below. For your convenience, the glossary was divided according to associative topics. You may also use the "Find" option (Ctrl F).

Black carbon particles: Black carbon (BC) (sometimes termed “elemental carbon”, “light-absorbing carbon”, or “soot”) is the dominant visible light-absorbing particulate species in the troposphere and mostly results from anthropogenic combustion sources; are seldom found in emissions from efficient combustion sources, although they are abundant in motor vehicle exhaust, fires, and residential heating emissions.

Carbon Dioxide (CO2): A naturally occurring gas, and also a by-product of burning fossil fuels and biomass, as well as land-use changes and other industrial processes. It is the principal anthropogenic greenhouse gas that affects the earth's radiative balance. It is the reference gas against which other greenhouse gases are measured and therefore has a Global Warming Potential (GWP) of 1.

Carbon Monoxide (CO): Carbon monoxide is an odorless, colorless and toxic gas. Because it is impossible to see, taste or smell the toxic fumes, CO can kill you before you are aware it is in your home. At lower levels of exposure, CO causes mild effects that are often mistaken for the flu. These symptoms include headaches, dizziness, disorientation, nausea and fatigue. The effects of CO exposure can vary greatly from person to person depending on age, overall health and the concentration and length of exposure.

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.

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.

Learn more: http://www.epa.gov/iaq/co.html

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.

Heavy metal: Metallic elements with high atomic weights, e.g., mercury, chromium, cadmium, arsenic, and lead; can damage living things at low concentrations and tend to accumulate in the food chain.

Lead (Pb): A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

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 (CH₄): A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at 23 times that of carbon dioxide (CO₂). Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and petroleum, coal production, and incomplete fossil fuel combustion. The global warming potential (GWP) is from the Intergovernmental Panel on Climate Change’s (IPCC's) Third Assessment Report (TAR).

Natural Gas: Underground deposits of gases consisting of 50 to 90 percent methane (CH4) and small amounts of heavier gaseous hydrocarbon compounds such as propane (C₃H₈) and butane (C₄H₁₀).

Nitrogen oxides (NO_x): Compounds of nitrogen (N) and oxygen (O) in ambient air; i.e., nitric oxide (NO) and others with a higher oxidation state of N, of which NO₂ is the most important toxicologically.

Organic solvent: These are chemical compounds, generally liquids, that contain carbon and are used to dissolve another substance.

Oxidant: A chemical compound that has the ability to remove, accept, or share electrons from another chemical species, thereby oxidizing it.

Ozone (O3): is a photochemical oxidant and the major component of smog. While O3 in the upper atmosphere shields the earth from harmful ultraviolet radiation that comes from the sun, high concentrations of O3 at ground level are a major health and environmental concern. O3 is not emitted directly into the air but is formed through complex chemical reactions between emissions of volatile organic compounds (VOC) and oxides of nitrogen (NOx) in the presence of sunlight. These reactions are stimulated by sunlight and temperature so that peak O3 levels occur typically during the warmer times of the year. Both VOCs and NOx are emitted by transportation and industrial sources such as autos, chemical manufacturing, dry cleaners and paint shops.

Particles: Fine solids such as dust, smoke, fumes, or smog, found in the air or in emissions.

Particulate Matter (PM): The term "particulate matter" (PM) includes both solid particles and liquid droplets found in air. Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes.

Particles less than 10 micrometers in diameter (PM₁₀) pose a health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter (PM_2.5) are referred to as "fine” particles and are believed to pose the largest health risks. Because of their small size (less than one-seventh the average width of a human hair), fine particles can lodge deeply into the lungs.

Health studies have shown a significant association between exposure to fine particles and premature mortality. Other important effects include aggravation of respiratory and cardiovascular disease (as indicated by increased hospital admissions, emergency room visits, absences from school or work, and restricted activity days), lung disease, decreased lung function, asthma attacks, and certain cardiovascular problems such as heart attacks and cardiac arrhythmia. Individuals particularly sensitive to fine particle exposure include older adults, people with heart and lung disease, and children.

Sources of fine particles include all types of combustion activities (motor vehicles, power plants, wood burning, etc.) and certain industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse." Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads.

Sulfur Dioxide: 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.

Volatile organic compound (VOC): Any organic compound that participates in atmospheric photochemical reactions except those designated by EPA as having negligible photochemical reactivity.

Acid Aerosol: Acidic liquid or solid particles that are small enough to become airborne. High concentrations of acid aerosols can be irritating to the lungs and have been associated with some respiratory diseases, such as asthma.

Climate Change: Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer). Climate change may result from:

Natural factors, such as changes in the sun's intensity or slow changes in the earth's orbit around the sun
Natural processes within the climate system (e.g. changes in ocean circulation)
Human activities that change the atmosphere's composition (e.g., through burning fossil fuels) and the land surface (e.g., deforestation, reforestation, urbanization, desertification, etc.)

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. For more information on the science and impacts of global climate change

Stratosphere: The portion of the atmosphere approximately 6 to 30 miles above the earth's surface.

Air quality standards: The level of pollutants prescribed by regulations that may not be exceeded during a given time in a defined area.

Air Monitoring: Sampling for and measuring of pollutants present in the atmosphere.

Best Available Technology Economically Achievable (BAT): technology-based standard established by the Clean Water Act (CWA) as the most appropriate means available on a national basis for controlling the direct discharge of toxic and non-conventional pollutants to navigable environment. BAT effluent limitations guidelines, in general, represent the best existing performance of treatment technologies that are economically achievable within an industrial point source category or subcategory.

Criteria Pollutants: The 1970 amendments to the Clean Air Act required EPA to set National Ambient Air Quality Standards for certain pollutants known to be hazardous to human health. EPA has identified and set standards to protect human health and welfare for six pollutants: ozone, carbon monoxide, total suspended particulates, sulfur dioxide, lead, and nitrogen oxide. The term, “criteria pollutants” derives from the requirement that EPA must describe the characteristics and potential health and welfare effects of these pollutants. It is on the basis of these criteria that standards are set or revised.

Emissions: is the term used to describe the gases and particles put into the air by a variety of sources, including factories, power plants, motor vehicles, airplanes and natural sources such as trees and vegetation. These emissions can pose health risks and contribute to air pollution, global warming and the destruction of the ozone layer. Under the auspices of the Clean Air Act and its amendments, the EPA measures, evaluates and reports emissions data with the goal of improving air quality. The EPA also plays an important role in researching new methods of assessing the impact of air pollution emissions on the environment and developing new ways to curb these emissions.

Emission cap: A limit designed to prevent projected growth in emissions from existing and future stationary sources from eroding any mandated reduction. Generally, such provisions require any emission growth from facilities under the restrictions be offset by equivalent reductions at other facilities under the same cap.

Emission factors: Emission factors and emission inventories have long been fundamental tools for air quality management. Emission estimates are important for developing emission control strategies, determining applicability of permitting and control programs, ascertaining the effects of sources and appropriate mitigation strategies, and a number of other related applications by an array of users, including federal, state, and local agencies, consultants, and industry. Data from source-specific emission tests or continuous emission monitors are usually preferred for estimating a source's emissions because those data provide the best representation of the tested source's emissions. However, test data from individual sources are not always available and, even then, they may not reflect the variability of actual emissions over time. Thus, emission factors are frequently the best or only method available for estimating emissions, in spite of their limitations.

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.

Dilution/attenuation factor (DAF): DAFs are used to measure the difference in the concentration of waste constituents found in the leachate released from a waste management unit at the source and the same leachate subsequently arriving at a receptor well. DAF is defined as the ratio of the leachate concentration at the source to the receptor well concentration.

Hazardous material: A chemical for which there is statistically significant evidence based on at least one study conducted in accordance with established scientific principles that acute or chronic health effects may occur in exposed employees (or people). OSHA defines it as a chemical that has a physical hazard or a health hazard.

O3 causes health problems because it damages lung tissue, reduces lung function and sensitizes the lungs to other irritants. Scientific evidence indicates that ambient levels of O3 not only affect people with impaired respiratory systems, such as asthmatics, but healthy adults and children as well. Exposure to O3 for several hours at relatively low concentrations has been found to significantly reduce lung function and induce respiratory inflammation in normal, healthy people during exercise. This decrease in lung function generally is accompanied by symptoms including chest pain, coughing, sneezing and pulmonary congestion.

IDLH (Immediately Dangerous to Life and Health): This is a regulatory value defined as the maximum exposure concentration in the workplace from which one could escape within 30 minutes without any escape-impairing symptoms or any irreversible health effects. This value should be referred to in respirator selection.

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 water, such as the Chesapeake Bay; haze in national parks and wilderness areas; and global climate change.

Nuclear Energy: Nuclear energy originates from the splitting of uranium atoms in a process called fission. At the power plant, the fission process is used to generate heat for producing steam, which is used by a turbine to generate electricity. Because nuclear power plants do not burn fuel, they do not emit air pollutant emissions. All of the nuclear power plants in the United States collectively produce about 2,000 metric tons per year of radioactive waste. Abandoned uranium mines contaminated with high-level radioactive waste can continue to pose radioactive risks for as long as 250,000 years after closure. There are more than 60 nuclear power plants currently in operation in the U.S., which accounts for approximately 20 percent of the country’s electricity production. No nuclear power plants have been built since 1996, mostly due to economic factors and environmental concerns.

Source reduction: Source reduction involves reducing the amount of waste from the beginning of a process with the goal of limiting the amount of waste at the conclusion of a project and eliminating the amount of waste going to a landfill.

Particulate Trap/Filter: An after-treatment device which filters or traps diesel particulate matter from engine exhaust until the trap becomes loaded to the point that a regeneration cycle is implemented to burn off the trapped particulate matter.

Plume: an elongated and mobile column or band of a contaminant moving through the subsurface.

Radiation: Transmission of energy through space or any medium. Also known as radiant energy.

Smog: Smog is the brownish haze that pollutes our air, particularly over cities in the summertime. Smog can make it difficult for some people to breathe and it greatly reduces how far we can see through the air. The primary component of smog is ozone, a gas that is created when nitrogen oxides react with other chemicals in the atmosphere, especially in strong sunlight.

TLV (Threshold Limit Value): Recommended guidelines for occupational exposure to airborne contaminants published by the American Conference of Governmental Industrial Hygienists (ACGIH). TLVs represent the average concentration in mg/m3 for an 8-hour workday and a 40-hour workweek to which nearly all workers may be repeatedly exposed, day after day, without adverse effect

Toxic material: A toxic material is capable of causing injury, health problems, or death, usually through exposure to chemicals or poisons.

Zero emission management: Achieving the condition of generating no emission, incorporating any potential emission in other uses, or preventing emission in all steps of a process produces zero emission management.

Criteria: The numeric values and the narrative standards that represent contaminant concentrations that are not to be exceeded in the receiving environmental media (air shed, sediment) to protect beneficial uses.

Dose Response: Shifts in toxicological responses of an individual (such as alterations in severity) or populations (such as alterations in incidence) that are related to changes in the dose of any given substance.

Parts per billion (ppb): A unit commonly used to express a concentration ratio (proportion) equal to 10^-9.

Parts per million (ppm): A unit commonly used to express a concentration ratio (proportion) equal to 10^-6.

Acute: Acute generally refers to a short-term exposure of fairly high concentrations, which leads to some adverse health conditions.

Allergen: A material that, as a result of coming into contact with appropriate tissues of an animal body, induces a state of allergy or hypersensitivity; generally associated with idiosyncratic hypersensitivities.

Asthma: A disease characterized by an increased responsiveness of the airways to various stimuli and manifested by slowing of forced expiration which changes in severity either spontaneously or as a result of therapy. The term asthma may be modified by words or phrases indicating its etiology, factors provoking attacks, or its duration.

Bronchitis: A non-neoplastic disorder of structure or function of the bronchi resulting from infectious or noninfectious irritation. The term bronchitis should be modified by appropriate words or phrases to indicate its etiology, its chronicity, the presence of associated airways dysfunction, or type of anatomic change. The term chronic bronchitis, when unqualified, refers to a condition associated with prolonged exposure to nonspecific bronchial irritants and accompanied by mucous hypersecretion and certain structural alterations in the bronchi. Anatomic changes may include hypertrophy of the mucous-secreting apparatus and epithelial metaplasia, as well as more classic evidences of inflammation. In epidemiologic studies, the presence of cough or sputum production on most days for at least three months of the year has sometimes been accepted as a criterion for the diagnosis.

Chronic: In the context of this topic hub, chronic refers to a long-term exposure of fairly low concentrations, which can lead to some adverse health effects.

Chronic obstructive pulmonary disease (COPD): This term refers to chronic lung disorders that result in blocked air flow in the lungs. The two main COPD disorders are emphysema and chronic bronchitis, the most common causes of respiratory failure. Emphysema occurs when the walls between the lung's air sacs become weakened and collapse. Damage from COPD is usually permanent and irreversible.

Decrements in lung function: Decreases in lung function that can be measured by spirometry.

Epidemiology: A branch of medical science that deals with the incidence, distribution, and control of disease in a population.

House dust mite (HDM): Either of two widely distributed mites of the genus Dermatophagoides (D. farinae and D. pteronyssinus) that commonly occur in house dust and often induce allergic responses, especially in children.

Immunoglobulin: A class of proteins produced in lymph tissue in vertebrates that function as antibodies in the immune response.

Induction of asthma: The process of lung sensitization and respiratory inflammation resulting in increased difficulty with breathing; it can be caused by a variety of external stimuli (e.g., pollens, air pollutants, viruses, animal hair, mites, and roach feces).

Lymphocyte: A variety of white blood cell produced in lymphoid tissues and lymphatic glands of the body. Lymphocytes have a number of very important roles in the immune system including the production of antibodies and other substances that fight infection and disease.

Mucociliary transport: The process by which mucus is transported, by ciliary action, from the lungs.

An EPA webpage contains glossary of terms and acronyms relating to health effects of air pollutants:

Learn more: http://www.epa.gov/iaq/co.html

Heavy metal: Metallic elements with high atomic weights, e.g., mercury, chromium, cadmium, arsenic, and lead; can damage living things at low concentrations and tend to accumulate in the food chain.

Lead (Pb): A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

Natural Gas: Underground deposits of gases consisting of 50 to 90 percent methane (CH4) and small amounts of heavier gaseous hydrocarbon compounds such as propane (C₃H₈) and butane (C₄H₁₀).

Climate Change: Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer). Climate change may result from:

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.

Particulate Trap/Filter: An after-treatment device which filters or traps diesel particulate matter from engine exhaust until the trap becomes loaded to the point that a regeneration cycle is implemented to burn off the trapped particulate matter.

Radiation: Transmission of energy through space or any medium. Also known as radiant energy.

Learn more: http://www.epa.gov/iaq/co.html

Heavy metal: Metallic elements with high atomic weights, e.g., mercury, chromium, cadmium, arsenic, and lead; can damage living things at low concentrations and tend to accumulate in the food chain.

Lead (Pb): A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

Natural Gas: Underground deposits of gases consisting of 50 to 90 percent methane (CH4) and small amounts of heavier gaseous hydrocarbon compounds such as propane (C3H8) and butane (C4H10).

Climate Change: Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer). Climate change may result from:

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.

Particulate Trap/Filter: An after-treatment device which filters or traps diesel particulate matter from engine exhaust until the trap becomes loaded to the point that a regeneration cycle is implemented to burn off the trapped particulate matter.

Radiation: Transmission of energy through space or any medium. Also known as radiant energy.

Natural Gas: Underground deposits of gases consisting of 50 to 90 percent methane (CH4) and small amounts of heavier gaseous hydrocarbon compounds such as propane (C₃H₈) and butane (C₄H₁₀).