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Additional Environmental Terms

Absorption (of light) A process by which light is taken-up by another material. Examples include soot consisting of tiny black particles, which absorb all visible light; and nitrogen dioxide, a pollutant mostly from diesel and gasoline engines, that absorbs blue light resulting in air with a brown tint.

Area A In accordance with Arizona Revised Statutes §49-541 , the part of the greater Phoenix Metropolitan area where specific pollution control programs are in place for ozone, carbon monoxide, and particulate matter. Includes parts of Yavapai and Pinal County.

Best available control technology An emission limitation, including a visible emissions standard, based on the maximum possible reduction of an air pollutant.

Billet A bar of steel or iron that is in an intermediate manufacturing stage.

Carbon monoxide A colorless, odorless gas formed by incomplete combustion of carbon or a material relating to, containing or composed of carbon material.

Electric arc shaft furnace A cylindrical furnace, which is lined with a material capable of enduring high temperatures, that produces molten steel by heating iron and steel scrap and other materials that are used as charge materials, using discharges of electricity from carbon-based conductors and direct-current electrical energy. This energy-efficient technology recovers the heat from the furnace off-gas by exhausting it through a shaft where the steel scrap is held prior to charging. The scrap is preheated to a temperature of more than 1,400 degrees Celsius before it is charged to the furnace.

Extinction (of light) The loss of light due to scattering and absorption as it passes through the atmosphere.

Inhalable particulate matter Any finely-divided airborne solid or liquid material with a diameter smaller than 10 micrometers while it is in the air.

Ladle metallurgical furnace A cylindrical furnace, which is lined with a material capable of enduring high temperatures, that is used for adjusting the chemical and mechanical properties of the molten steel produced in the electric arc shaft furnace.

Lead 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.

National ambient air quality standards Federal standards for the minimum ambient air quality needed to protect public health and welfare.

Nitrogen oxides All oxides of nitrogen except nitrous oxide.

Particulate matter Any finely-divided airborne solid or liquid material with a diameter smaller than 100 micrometers while it is in the air.

Prevention of significant deterioration A construction air pollution permitting program designed to ensure that air quality does not degrade beyond the national ambient air quality standard levels or beyond specified incremental amounts above a baseline level. It also ensures that the best available control technology is applied to major stationary sources and major modifications for regulated pollutants, and consideration of soils, vegetation and visibility affects in the permitting process.

Scattering (of light) An interaction of a light wave with an object like tiny particles of dust or soot, that cause the light to be redirected.

Sulfur dioxide A colorless, very irritating gas or liquid.

Transmissometer Currently ADEQ collects visibility data for Area A using a transmissometer with a path extending from the Phoenix Baptist Hospital at 2000 West Bethany Home Road, to the Quality Hotel and 3600 West 2nd Avenue.

A transmissometer is an instrument used to assess visibility by measuring the amount of light lost (or light extinction) between a light source and a light detector. The instrument consists of a laser and a computer-controlled receiver placed 1 to 2 miles away that measures the properties of the light it receives from the laser. The air along the path that the light from the laser travels, including the pollution scatters and absorbs the light. The reduction in the intensity of the light is measured as light extinction. Diagrams of the standard transmissometer components are provided below.

The transmitter emits a uniform light beam of constant intensity. Transmitter optics concentrate light into a narrow, well-defined uniform beam. Light intensity emitted from the transmitter is precisely controlled to keep the light output constant. The light source is frequently blocked (chopped), resulting in pulses of light, so the receiver can differentiate the amount of background light interfering with the constant light source. An eyepiece lets the operator precisely aim the light beam.

The receiver includes a telescope that gathers the transmitted light and converts it to an electrical signal. The receiver computer evaluates the pulses from the chopped light and separates the transmitter light from the natural (ambient) background light. The computer compares the measured transmitter light with the known transmitter light to calculate the transmission of light through the intervening atmosphere.

Visibility A measure of how far and how well an observer can see through the atmosphere.

Volatile organic compounds Any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, that participates in reactions of radiant energy, especially light, in the atmosphere.

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