acid precipitation
	Acidic rain, snow, or dry particles deposited from the air due to increased acids released by anthropogenic or natural resources.
aerosols
	Minute particles or liquid droplets suspended in the air.
aesthetic degradation
	Changes in envionmental quality that offend our aesthetic senses.
ambient air
	The air immediately around us.
bronchitis
	An inflammation of bronchial linings that causes persistent cough, copious production of sputum, and involuntary muscle spasms that constrict airways.
carbon monoxide (CO)
	Colorless, odorless, nonirritating but highly toxic gas produced by incomplete combustion of fuel, incineration of biomass or solid waste, or partially anaerobic decomposition of organic material.
chlorofluorocarbons
	Chemical compounds with a carbon skeleton and one or more attached chlorine and fluorine atoms. Commonly used as refrigerants, solvents, fire retardants, and blowing agents.
conventional pollutants
	The seven substances (sulfur dioxide, carbon monoxide, particulates, hydrocarbons, nitrogen oxides, photochemical oxidants, and lead) that make up the largest volume of air quality degradation; identified by the Clean Air Act as the most serious threat of all pollutants to human health and welfare; also called criteria pollutants.
dry alkali injection
	Spraying dry sodium bicarbonate into flue gas to absorb and neutralize acidic sulfur compounds.
electrostatic precipitators
	The most common particulate controls in power plants; fly ash particles pick up an electrostatic surface charge as they pass between large electrodes in the effluent stream, causing particles to migrate to the oppositely charged plate.
emission standards
	Regulations for restricting the amounts of air pollutants that can be released from specific point sources.
emphysema
	An irreversible, obstructive lung disease in which airways become permanently constricted and alveoli are damaged or destroyed.
filters
	A porous mesh of cotton cloth, spun glass fibers, or asbestos-cellulose that allows air or liquid to pass through but holds back solid particles.
fugitive emissions
	Substances that enter the air without going through a smokestack, such as dust from soil erosion, strip mining, rock crushing, construction, and building demolition.
nitrogen oxides
	Highly reactive gases formed when nitrogen in fuel or combustion air is heated to over 650° C (1200° F) in the presence of oxygen or when bacteria in soil or water oxidize nitrogen-containing compounds.
ozone
	A highly reactive molecule containing three oxygen atoms; a dangerous pollutant in ambient air. In the stratosphere, however, ozone forms an ultraviolet absorbing shield that protects us from mutagenic radiation.
particulate material
	Atmospheric aerosols, such as dust, ash, soot, lint, smoke, pollen, spores, algal cells, and other suspended materials; originally applied only to solid particles but now extended to droplets of liquid.
photochemical oxidants
	Products of secondary atmospheric reactions. See smog.
primary pollutants
	Chemicals released directly into the air in a harmful form.
primary standards
	Regulations of the 1970 Clean Air Act; intended to protect human health.
radon
	An odorless, colorless, radioactive gas produced by the radioactive decay of natural radium.
secondary pollutants
	Chemicals modified to a hazardous form after entering the air or that are formed by chemical reactions as components of the air mix and interact.
secondary standards
	Regulations of the 1970 Clean Air Act intended to protect materials, crops, visibility, climate, and personal comfort.
sulfur dioxide
	A colorless, corrosive gas directly damaging to both plants and animals.
synergistic effects
	When an injury caused by exposure to two environmental factors together is greater than the sum of exposure to each factor individually.
volatile organic compounds
	Organic chemicals that evaporate readily and exist as gases in the air.

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