acid deposition
The falling of acids and acid-forming compounds from the atmosphere to the earth's surface. Acid deposition is commonly known as acid rain, a term that refers only to wet deposition of droplets of acids and acid-forming compounds.
air pollution
atmospheric pressure
buffer
Substance that can react with hydrogen ions in a solution and thus hold the acidity or pH of a solution fairly constant. See pH.
carbon oxides
Carbon and oxygen compounds: carbon monoxide (CO) and carbon dioxide (CO2). Carbon monoxide is a colorless, odorless, highly toxic gas that forms during the incomplete combustion of carbon-containing materials. Carbon dioxide is a colorless, odorless gree
industrial smog
Type of air pollution consisting mostly of a mixture of sulfur dioxide, suspended droplets of sulfuric acid formed from some of the sulfur dioxide, and a variety of suspended solid particles. Compare photochemical smog.
nitric acid (HNO3)
nitrogen oxides (NOx)
Nitrogen oxide (NO) and nitrogen dioxide (NO2) collectively. These gases play a role in photochemical smog and can irritate the eyes, nose, throat, and lungs; aggravate asthma and bronchitis; and increase susceptibility to respiratory infections by impair
ozone (O3)
Colorless and highly reactive gas; a major component of photochemical smog and also found in the stratosphere where it protects life by filtering out most harmful UV radiation from the sun.
ozone depletion
Decrease in concentration of ozone (O3) in the stratosphere. See ozone layer.
ozone layer
Layer of gaseous ozone (O3) in the stratosphere that protects life on earth by filtering out most harmful ultraviolet radiation from the sun.
PANs
Peroxyacyl nitrates. Group of chemicals found in photochemical smog.
particulates
Solid particles and liquid droplets small and light enough to remain suspended in the air for short to long periods. Also referred to as suspended particulate matter (SPM).
photochemical smog
Complex mixture of air pollutants produced in the lower atmosphere by the reaction of hydrocarbons and nitrogen oxides under the influence of sunlight. Especially harmful components include ozone, peroxyacyl nitrates (PANs), and various aldehydes. Compare
primary pollutant
Chemical that has been added directly to the air by natural events or human activities and occurs in a harmful concentration. Compare secondary pollutant.
radon (Rn)
Naturally occurring colorless and odorless radioactive gas found in some types of soil and rock. It can seep into homes and buildings sitting above such deposits. Long-term exposure can cause lung cancer, especially among smokers.
secondary pollutant
Harmful chemical formed in the atmosphere when a primary air pollutant reacts with normal air components or other air pollutants. Compare primary pollutant.
smog
Originally a combination of smoke and fog but now used to describe other mixtures of pollutants in the atmosphere. See industrial smog, photochemical smog.
stratosphere
Second layer of the atmosphere, extending about 17[[endash]]48 kilometers (11[[endash]]30 miles) above the earth's surface. It contains small amounts of gaseous ozone (O3), which filters out about 95% of the incoming harmful ultraviolet (UV) radiation emi
sulfur dioxide (SO2)
Colorless gas with an irritating odor. About two-thirds (and as high as 90% in urban areas) comes from human sources, mostly combustion of sulfur-containing coal in electric power and industrial plants and from oil refining and smelting of sulfide ores.
sulfuric acid (H2SO4)
Formed in the atmosphere from sulfur dioxide. As microscopic suspended droplets, it is a component of acid deposition.
temperature inversion
Layer of dense, cool air trapped under a layer of less dense, warm air. This prevents upward-flowing air currents from developing. In a prolonged inversion, air pollution in the trapped layer may build up to harmful levels. See radiation temperature inver
volatile organic compounds (VOCs)
Organic compounds that exist as gases in the air. Most are hydrocarbons.
chlorofluorocarbons (CFCs)
Organic compounds made up of atoms of carbon, chlorine, and fluorine. An example is Freon-12 (CCl2F2), used as a refrigerant in refrigerators and air conditioners and in making plastics such as Styrofoam. Gaseous CFCs can deplete the ozone layer when they
global climate change
global warming
Warming of the earth's atmosphere because of increases in the concentrations of one or more greenhouse gases primarily as a result of human activities. See greenhouse effect, greenhouse gases.