Chapter 19

Atmospheric Pressure
A measure of the mass per unit area of air.
Second layer of the atmosphere, extending about 17-48 kilometers (11-30 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 emitted by the sun. Compare troposphere
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
Air Pollution
One or more chemicals in high enough concentrations in the air to harm humans, other animals, vegetation, or materials. Excess heat and noise are also considered forms of air pollution. Such chemicals or physical conditions are called air pollutants. See primary pollutant, secondary pollutant
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.
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.
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 greenhouse gas that contributes heavily to global warming
Nitrogen Oxides
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 impairing the immune system. They can also suppress plant growth and reduce visibility when they are converted to nitric acid and nitrate salts
Sulfur Dioxide
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.
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).
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
Volatile Organic Compounds
Organic compounds that exist as gases in the air. Most are hydrocarbons
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.
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
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 industrial smog
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 inversion, subsidence temperature inversion.
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.
Substance that can react with hydrogen ions in a solution and thus hold the acidity or pH of a solution fairly constant. See pH.
Nitric acid
Formed when NO2 reacts with water vapor in the air. It is a component of acid deposition that returns to the earth and can damage trees, soils, and aquatic life in lakes
Originally a combination of smoke and fog but now used to describe other mixtures of pollutants in the atmosphere. See industrial smog, photochemical smog.
Sulfuric Acid
Formed in the atmosphere from sulfur dioxide. As microscopic suspended droplets, it is a component of acid deposition.