A Look at the Problem of Air Pollution and Its Sources in the United States


In the past with air pollution we included mainly the outdoor pollutants, although in recent years this is not the case. Today we separate pollutants in to two categories. Primary pollutants, because they come directly from various sources, and secondary which are byproducts of chemical interactions of the primary pollutants within the atmosphere.


Although air pollution might be thought of as unwanted gases in the atmosphere, two of five primary pollutants are really solid substances called particulates. Soot has always been a sure indicator of a polluted atmosphere, but other than soiling and a negative psychological effect, soot can't settle into the lungs and cause serious diseases. Thick, black smoke coming out of a stack is that what we think causes the pollution, but what really creates the damage is what we can't see. Particles like this are called suspended particles. They come from many incomplete burning and can consist a variety of substances. The most harmful type of particulate is so small that that it is microscopic. All the particulates are harmful for several reasons. When inhaled, they can damage the interior of the lung; they can also be poisonous. Sometimes gases will glue to their surfaces and in a process called adsorption they can reach the lungs. All these particles are mainly products of combustion. The major sources include industrial processes, power plants that are both coal and oil-fired, residential heating, and transportation. But coal burning is the greatest source.

Only 13% of the total is generated by transportation. Industrial sources account for nearly three times as much as 37%. Fires account for just about as much particulate emissions as transportation. That amount is matched by combustion from sources, which include the generation of all heat and electricity. http://environment.searchwho.com


When coal was the main source to generate energy, power plants and homes accounted for much greater contribution. The switch to oil and nuclear power has lowered those concentrations, but it hasn't been without its own problems. In addition to health-related problems, particles can damage materials through corrosion and erosion, as well as soiling. Particles can also impact the weather, through changes in visibility, and even in enhancing precipitation. Studies around major urban areas show an increase in precipitation and in thunderstorms with hail downwind from downtown areas. The weather modification is localizes but definite, and may be related to an increase in the large condensation nuclei that the particles provide.

Lead particulates are brutal primary pollutant. Their presence in the atmosphere has diminished sharply during the past 29 years. Since 1975, the concentration of lead has decreased by more than 90%, which can be directly linked to the elimination of lead from gasoline.


Another primary group of pollutants consists of the sulfur oxides(Sox), and the major contributor is SO2, a sulfur dioxide. This is generated whenever sulfur is burned, most often where fuel with a high sulfur content is used. Coal can have very high sulfur concentrations, as can some oil. Overall, coal and oil are the major sources for sulfur oxide pollution. The vast majority of this type of air pollution comes from generation of heat and electricity. These stationary sources account about 80% of all sulfur oxides. Transportation's contribution is minor, about 5%. The rest comes from industry.

Sulfur dioxides cause damage to vegetation and material.

Carbon monoxide (CO)

Carbon monoxide is colorless, odorless , tasteless,non-corrosive, highly poisonous gas of about the same density as that of air. It is very flammable, burns in air with bright blue flame.

Its melting point is at-205.0. Cand boiling point is at -191.5. C. There is no way to know if it is around, except we may no feel so well. When a fire burns in an enclosed space, oxygen is gradually depleted and carbon dioxide is increased. The changes in both of the these gases increasingly cause the combustion process to change from one of complete combustion to one of incomplete combustion, resulting in the release of increasing amounts of CO. Table two lists some of the effects of CO to humans. (TABLE 2CO concentration in Parts Per Million or as as percentage of air % of CO in air 

Change of Fuels

The most direct method of pollution control involves changing the fuel. High sulfur coal was responsible for the greatest smog outbreaks of the early twentieth century. Sulfur oxides and particulates reached dangerous levels in many areas, especially in industrial areas. During the 1960s and 1970s a switch to low sulfur oil, natural gas and nuclear power brought the levels of that kind of smog down to relatively low concentrations. Although complex control devices are available, the fuel switch in power plants accounts for most of the improvement.

Smokestack emissions control

Particles come in assorted sizes and shapes, and a number of control systems have been designed for removing them from the stream of gases that go up the smokestack. The type of device depends on the type of particle and size. Soluble particles can be drained out of an effluent by washing with scrubbers. Sometimes, the particles will simply settle out before being emitted, in what are called settling chambers. Sometimes the gas is pushed through filters of cloth collectors.

Internal Combustion Engine

One of the greatest polluters on Earth is the automobile. Volatile organic compounds, nitrogen oxides and carbon monoxides are the major pollutants that come out of a car's exhaust. If the air-fuel mix is lean, there is a good deal of air and less fuel. The combustion temperature will be relatively high, which will favor the complete burning of the gases, and hydrocarbons will convert to water vapor and carbon dioxides. It raises the temperature of gases that will be exhausted, so there will be further burning of the hydrocarbons. As a result we end with more water vapor and carbon monoxide


Once exposure levels have been set, steps can be undertaken to reduce exposure to air pollution. These can be accomplished by regulation of man-made pollution through legislation. Many countries have set controls on pollution emissions for transportation vehicles and industry. This is usually done to through a variety of coordinating agencies which monitor the air and the environment.

A significant problem that has to deal with all the changes is the cost. A company that has to install million dollar electrostatic precipitators may have a serious economic problem with pollution control But in general, the overall costs of not controlling air pollution are far greater that the collective costs of pollution control. The problem of course is the concentration of costs within specific industries. Creative techniques of distributing that cost could go a very long way in maintaining our standard of living while having good and healthy air to breath.


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