What is air pollution?

Air pollution is caused by many sources. There are natural pollutants that have been around as long as the Earth, such as dust, smoke, volcanic ash, and pollens.

Humans have added to air pollution with chemicals and particulates due to combustion and industrial activity (anthropogenic sources).

What is smog?

The word "smog" is a combination of two other words: smoke and fog. Harold Des Voeux, a British physician who was concerned about air quality, is credited with coming up with coining the term in 1911. However, what we refer to as smog has nothing to do with either fog or smoke, usually. Smog is simply another name for air pollution. Scientists refer to it, more precisely, as photochemical smog because it is the result of chemical reactions in the presence of sunlight. The brownish haze associated with smog is the result of nitrogen dioxide in the air, but smog also includes a soup of nitrogen oxides, hydrocarbons, aldehydes, ozone, peroxyethanoyl nitrates (PANs), and suspended particulate matter. Yuck.

What is a photochemical grid model?

A photochemical grid model is a computer model used by meteorologists and environmental scientists to simulate what might happen during air pollution episodes under various weather conditions. A grid system is employed in which the area of study—for instance, a city—is cut up into thousands of cells, each usually a couple miles or kilometers wide and long; the cells also have a third dimension (height), varying in depth according to the altitude that scientists wish to study. These models simulate vertical and horizontal air movements, increases in various gases and particles from sources ranging from buildings and cars to plants and animals, and chemical reactions occurring in the atmosphere; they are very useful in predicting effects on ozone levels. A photochemical grid model is thus not the same as a meteorological model, but it does use this meteorological tool to study how pollution increases, dissipates, and affects certain areas. Photochemical grid models can be used to simulate how making different decisions affecting pollutant outputs would affect air quality. For example, if city officials decided to limit commuter traffic into the downtown area by ten percent, they could simulate how levels of carbon monoxide would be reduced.

How much carbon monoxide is produced in the United States by cars?

As of 2002, automobile traffic in the United States was producing 346 tons (314 metric tons) of carbon monoxide per day.

Is carbon dioxide pollution a problem?

While carbon dioxide occurs naturally in the environment, and, indeed, is essential to plant life, too much of even a good thing can be bad. Increased carbon dioxide levels, of course, are now infamous for leading to global warming (see the chapter on climate change for more on this), but near ground level this gas can also be poisonous to plants and animals. This became readily apparent during a 1990 incident in which carbon dioxide emissions from volcanic faults in California's Inyo Nation-

What U.S. city is particularly noted for its problems with smog?

Los Angeles has a rough time with smog. The brown haze that often lingers over the city is a result of several factors. Of course, the urban area is filled with cars and other sources of pollutants, but the natural environment conspires to make matters worse. First of all, very little rain falls in L.A., which might attract tourists and new residents but does nothing to wash away pollutants; and secondly, the city is in a basin surrounded by mountains. Ocean breezes blowing in from the west keep air pollution from escaping in that direction, but then the smog finds another barrier in the mountains that lie east, north, and south of the city. Even before Spanish and other European settlers came to the area, the Native American Chumash tribe called what is now Los Angeles the "valley of smoke," because haze from brush fires and dust would be trapped there for long periods.

al Forest killed trees and caused tourists to become dizzy and lightheaded. The tourists became ill while inside cabins, where the levels of carbon dioxide had increased to 25 percent of the air content.

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