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Is Your Bus Exhausting? Stevens Institute of Technology


Technology Transfer Network National Air Toxins Glossary

Acetaldehyde - Acetaldehyde is ubiquitous, it is an intermediate product of higher plant respiration and is formed as a product of incomplete wood combustion in fireplaces and stoves, coffee roasting, burning of tobacco, vehicle exhaust fumes, and coal refining and waste processing.  Acetaldehyde is found in vehicle exhaust and is formed as a result of incomplete combustion of both gasoline and diesel fuel.   The primary acute effects associated with exposure to acetaldehyde include irritation of the eyes, skin, and respiratory tract, and is classified as a probable human carcinogen.

Acrolein - Acrolein is found in vehicle exhaust and is formed as a result of incomplete combustion of both gasoline and diesel fuel.  Acute exposure results in upper respiratory tract irritation and congestion, where as chronic exposures in animals indicated an increase in cell proliferation and in the number of white blood cells in the tissues lining the nasal passages.  Acrolein has been classified as a possible carcinogen.

Acrylonitrile - Acrylonitrile is primarily used in the manufacture of acrylic and modacrylic fibers. It is also used as a raw material in the manufacture of plastics.  Acrylonitrile may be released to the ambient air during its manufacture and use, from landfills, and through incineration of sewage sludge.

Arsenic Compounds - Arsenic is a naturally occurring element, found throughout the environment.  It is released into the air by volcanoes, the weathering of arsenic-containing minerals and ores, and by commercial or industrial processes.  For most people, food is the largest source of arsenic exposure, with lower amounts coming from drinking water and air.  Inhalation exposure to inorganic arsenic has been shown to be strongly associated with lung cancer in humans, therefore it has been classified as a human carcinogen.  Acute, high-level inhalation exposure to arsenic dust or fumes has resulted in gastrointestinal  effects, central and peripheral nervous system disorders.

Benzene - Benzene is present in both exhaust and evaporative emissions from motor vehicles as well as from the burning of coal and oil.  Benzene is also used as a solvent for fats, waxes, resins, oils, inks, paints, plastics, and rubber.  Benzene is also used in the manufacture of detergents, explosives, and pharmaceuticals.  Tobacco smoke contains benzene and accounts for nearly half the national exposure to benzene.  Benzene is classified as a human carcinogen.  There are a number of non-cancerous harmful effects caused by exposure, both acute and chronic. Respiration is the major source of human exposure and at least half of the respiratory exposure is by way of gasoline vapors and automotive emissions.

Beryllium Compounds -  Beryllium emissions are predominantly a result of the burning of coal or fuel oil.

1,3 Butadiene - 1,3-Butadiene is a gas used commercially in the production of styrene-butadiene rubber, plastics, and thermoplastic resins. The major environmental source of 1,3-butadiene is the incomplete combustion of fuels from mobile sources (e.g., automobile exhaust). Tobacco smoke can be a significant source of 1,3-butadiene in indoor air.

Cadmium Compounds - Cadmium emissions are mainly from the burning of fossil fuels such as coal or oil, and the incineration of municipal waste. Cadmium may also be emitted into the air from zinc, lead, or copper smelters. For nonsmokers, food is generally the largest source of cadmium exposure. Cadmium levels in some foods can be increased by the application of phosphate fertilizers or sewage sludge to farm fields.

Carbon tetrachloride - Carbon tetrachloride was produced in large quantities to make refrigerants and propellants for aerosol cans, as a solvent for oils, fats, lacquers, varnishes, rubber waxes, and resins, and as a grain fumigant and a dry cleaning agent. Consumer and fumigant uses have been discontinued and only industrial uses remain. Individuals may be exposed to carbon tetrachloride in the air from accidental releases from production and uses, its disposal in landfills, and wastewater processing.

Chloroform - Chloroform may be released to the air from a large number of sources related to its manufacture and use, as well as its formation in the chlorination of drinking water, wastewater, and swimming pools. Pulp and paper mills, hazardous waste sites, and sanitary landfills are also sources of air emissions. Chloroform was used in the past as an extraction solvent for fats, oils, greases, and other products; as a dry cleaning spot remover; in fire extinguishers; as a fumigant; and as an anesthetic. However, chloroform is no longer used in these products.

Chromium Compounds - Chromium is a naturally occurring element in rocks, animals, plants, soil, and volcanic dust and gases.  Air emissions of chromium are in the form of small particles or aerosols.  Ore refining, chemical and refractory processing, cement-producing plants, automobile brake lining and catalytic converters for automobiles, leather tanneries, and chrome pigments also contribute to the atmospheric burden of chromium.  The respiratory tracts is the major target organ for acute and chronic inhalation.  Shortness of breath, coughing, and wheezing were reported from acute exposure, while perforations and ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia, and other respiratory effects have been noted from chronic exposure.  Chromium is classified as a human carcinogen.

Coke Oven Emissions - Coke oven emissions are a mixture of coal tar, coal tar pitch, and creosote and contain chemicals such as benzo(a)pyrene, benzanthracene, chrysene, and phenanthrene. Coke oven emissions may occur from coke ovens and facilities associated with the manufacture of aluminum, steel, and graphite as well as electrical and construction industries.

1,3 - Dichloropropane - 1,3-Dichloropropene is used as a component in formulations for soil fumigants. Emissions are associated with its manufacture or application as a soil fumigant.

Diesel Particulate Matter - Diesel particulate matter is part of a complex mixture that makes up diesel exhaust.  Diesel exhaust is emitted from a broad range of diesel engines; on road diesel engines of trucks, buses and cars and off road diesel engines including locomotives, marine vessels and heavy duty equipment. School buses are a significant contributor to the overall emissions.  There are several exposure related, non-cancerous effects of diesel exhaust emissions.  Overall diesel exhaust is recognized as a human carcinogen.

Ethylene dibromide - Ethylene dibromide was used in the past as an additive to leaded gasoline and as a fumigant. Ethylene dibromide is currently used in the treatment of felled logs for bark beetles and termites, and control of wax moths in beehives. Ethylene dibromide is also used as an intermediate for dyes, resins, waxes, and gums.

Ethylene dichloride - Ethylene dichloride is primarily used in the production of vinyl chloride as well as other chemicals. It is used in solvents in closed systems for various extraction and cleaning purposes in organic synthesis.

Ethylene oxide - Ethylene oxide is used mainly as a chemical intermediate in the manufacture of textiles, detergents, polyurethane foam, antifreeze, solvents, medicinals, adhesives, and other products. The major sources of emissions are commercial and hospital sterilizers.

Formaldehyde - Formaldehyde is used mainly to produce resins used in particle board products.  It also has minor uses in agriculture, in concrete and plaster additives, cosmetics, disinfectants, fumigants, photography and wood preservation.  The highest level of airborne formaldehyde have been detected in indoor air, where it is released from various consumer products, such as building materials and home furnishings.  Formaldehyde is present in vehicle exhaust, formed from the incomplete combustion of both gasoline and diesel fuels.  Formaldehyde has been classified as a probable human carcinogen, and exposure to formaldehyde also causes a range of non-cancer health effects.

Hexachlorobenzene - Hexachlorobenzene is formed as a byproduct during the manufacture of other chemicals (mainly solvents) and pesticides. It was widely used as a pesticide until 1965. There are currently no commercial uses of hexachlorobenzene in the United States.

Hydrazine - Hydrazine is used in agricultural chemicals (pesticides), chemical blowing agents, pharmaceutical intermediates, photography chemicals, boiler water treatment for corrosion protection, textile dyes, and as fuel for rockets and spacecraft.

Lead Compounds - Lead is a metal found naturally in the environment as well as in manufactured products.  Lead is a very toxic element, causing a variety of effects at low dose levels.  Brain damage, kidney damage, and gastrointestinal distress are seen in humans receiving acute exposure, while chronic exposure affects the blood, central nervous system, blood pressure, and kidneys.  Children are particularly sensitive to the chronic effects of lead.

Manganese Compounds - Manganese is a naturally occurring substance found in many types of rock and soil, it is ubiquitous in the the environment and found in low levels in water, air, and soil.  Manganese can also be released into the air by iron and steel production plants, and coke ovens.  Manganese compounds from mobile sources comprise less than 2 percent of the 1996 National Air Toxics Inventory.  Key health concerns in humans have been associated with neurotoxic and perhaps developmental effects.

Mercury Compounds - Mercury exists in three forms, elemental mercury (used in thermometers), inorganic mercury (in the past used in creams, soaps and latex paint), and organic (no uses in industry) mercury compounds.  All forms of mercury are quite toxic.  The most recent data shows negligible emissions from gasoline vehicles.  The major source of exposure to mercury is in occupational settings.

Methylene chloride - Methylene chloride is predominantly used as a solvent in paint strippers and removers; as a process solvent in the manufacture of drugs, pharmaceuticals, and film coatings; as a metal cleaning and finishing solvent in electronics manufacturing; and as an agent in urethane foam blowing.  Other sources of emissions are landfills and wastewater processing.

Nickel Compounds - Nickel is a natural element of the earth's crust, as a result, small amounts are found in food, water, soil and air.  Food is the major source of nickel exposure.  Individuals also may be exposed to nickel in occupations involved in its production, and use, or through everyday contact with items such as nickel-containing jewelry and stainless steel cooking and eating utensils, and by smoking tobacco.  Nickel dermatitis, causing itching of the fingers, hands, and forearms, is the most common effect in humans from chronic skin contact with nickel.

Perchloroethylene - Perchloroethylene is widely used for dry-cleaning fabrics and metal degreasing operations.

Polychlorinated biphenyls (PCB's) - Polychlorinated biphenyls (PCBs) are a group of chemicals that contain 209 individual compounds. PCBs are no longer produced or used in the United States today; the major source of exposure to PCBs today is the redistribution of PCBs already present in soil and water. PCBs were used in capacitors, transformers, plasticizers, surface coatings, inks, adhesives, pesticide extenders, carbonless duplicating paper. Smaller amounts of PCBs may be released to the air from disposal sites and combustion. PCBs have been detected in food; they bioaccumulate through the food chain, with some of the highest concentrations found in fish.

Polycyclic Organic Matter (POM) - Polycyclic organic matter defines a broad class of compounds that includes the polycyclic aromatic hydrocarbon compounds (PAHs).  The primary source of POM is formation during combustion.  Polycyclic organic compounds have been detected in ambient air from sources including cigarette smoke, gasoline and diesel engine exhausts, asphalt road paving, coal burning, application of coal tar, agricultural burning, residential wood burning and hazardous waste sites.  Cancer is the major concern from exposure to POM.

7 - PAH - (Polycyclic Aromatic Hydrocarbons) The 7-PAH are a subset of 16-PAH (16-PAH is referred to as Polycyclic Organic matter or "POM", see above). The 7 groups that make up 7-PAH are probable human carcinogens.

Propylene dichloride - Propylene dichloride is used as a chemical intermediate in the production of chlorinated organic chemicals, as an industrial solvent, in ion exchange manufacture, in toluene diisocyanate production, in photographic film manufacture, for paper coating, and for petroleum catalyst regeneration.  Propylene dichloride is also emitted from landfills.

Quinoline - Quinoline is used mainly as an intermediate in the manufacture of other products. Quinoline is also used as a catalyst, a corrosion inhibitor, in metallurgical processes, in the manufacture of dyes, as a preservative for anatomical specimens, in polymers and agricultural chemicals, and as a solvent for resins and terpenes. It is also used as an antimalarial medicine. A potential source of very low exposure to quinoline includes the inhalation of ambient air contaminated by emissions from petroleum refining, quenching and coking, and wastewater processing.

1,1,2,2 - tetrachloroethane - 1,1,2,2-tetrachloroethane is no longer used much in the United States, current air emissions predominantly result from its use as a chemical intermediate during the manufacture of other chemicals. One of the sources of emissions is landfills.

Trichloroethane - Trichloroethylene used in the United States is mainly associated with industrial degreasing operations and is also emitted from landfills.

Vinyl chloride - Vinyl chloride is used to make polyvinyl chloride (PVC) plastic and vinyl products. Sources of emissions include the discharge of exhaust gases from factories that manufacture or process vinyl chloride, landfills, or evaporation from areas where chemical wastes are stored.


All definitions and information on this page were compiled from several USEPA resources.


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