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Oxidizing Smog

To a large degree, oxidizing or Los Angeles-type smogs have supplanted reducing smog in importance in most industrialized countries. Oxidizing smogs are common in sunny places where there are large emissions to the atmosphere of nitric oxide and hydrocarbons, and where the atmospheric conditions are frequently stable. Oxidizing smogs form when those emitted (or primary) pollutants are transformed through photochemical reactions into secondary pollutants, the most important of which are the strong oxidant gases, ozone and peroxyacetyl nitrate. These secondary gases are the major components of oxidizing smog that are harmful to people and vegetation.

Typically, the concentrations of these various chemicals vary predictably during the day, depending on their rates of emission, the intensity of sunlight, and atmospheric stability. In the vicinity of Los Angeles, for example, ozone concentrations are largest in the early-tomid afternoon, after which these gases are diluted by fresh air blowing inland from the Pacific Ocean. These winds blow the polluted smog further inland, where pine forests are affected on the windward slopes of nearby mountains. The photochemical reactions also cease at night, because sunlight is not available then. This sort of daily cycle is typical of places that experience oxidizing smog.

Humans are sensitive to ozone, which causes irritation and damage to membranes of the respiratory system and eyes, and induces asthma. People vary greatly in their sensitivity to ozone, but hypersensitive individuals can suffer considerable discomfort from exposure to oxidizing smog. However, in contrast to some of the events of reducing smog, ozone and oxidizing smog more generally do not appear to cause the death of many large people. Ozone is also by far the most important gaseous pollutant in North America, in terms of causing damage to agricultural and wild plants.



Freedman, B. Environmental Ecology. 2nd ed. San Diego: Academic Press, 1995.

Harrison, R.M., and R.E. Hester, eds. Air Pollution and Health. Royal Society of Chemistry, 1998.

Hemond, H.F., and E.J. Fechner. Chemical Fate and Transport in the Environment. San Diego: Academic Press, 1994.

Warner, C.F., W.T. Davis, and K. Wark. Air Pollution: Its Origin and Control. Addison-Wesley Pub., 1997

Bill Freedman


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Olfactory bulb

—The primitive part of the brain that first processes olfactory information; in insects, its function is served by nerve-cell bundles called olfactory ganglia

Olfactory cortex

—The parts of the cerebral cortex that make use of information from the olfactory bulb.

Olfactory epithelium

—The patch of mucus membrane at the top of the nasal cavity that is sensitive to odor.

Olfactory nerve cell

—The cell in the olfactory epithelium that detects odor and transmits the information to the olfactory bulb of the brain.


—Scent molecules made by the body that attract a mate and help initiate mating behaviors.

Receptor protein

—A protein in a cell that sticks to a specific odorant or other signal molecule.

Stereospecific theory

—The theory that the nose recognizes odorants when they bind to receptor proteins that recognize the odorants' molecular shape.


—Readily able to form a vapor at a relatively low temperature.

Vomeronasal organ

—A pit on the roof of the mouth in most vertebrates that serves to detect odor molecules that are not as volatile as those detected by the nose.

Additional topics

Science EncyclopediaScience & Philosophy: Adam Smith Biography to Spectroscopic binarySmog - Reducing Smog, Oxidizing Smog