Air Pollution and Management
History of Air Pollution
As the fastest moving fluid medium in the environment, the atmosphere has always been one of the most convenient places to dispose of unwanted materials. Ever since fire was first used by people, the atmosphere has been a sink of waste disposal.
People have long recognized the existence of atmospheric pollutants, both national and human induced. Leonardo da Vinci in 1550 observed that a blue haze formed from materials emitted into the atmosphere from trees. he had observed a natural photochemical smog resulting from hydrocarbons given off by living trees whose cause is still not completely understood. This haze gave rise to the name smoky mountains for the range in the southern United States.
The phenomenon of acid rain was first described in the 17th century and by the 18th century, it was known that smog and acid rain damaged plants in London. Beginning with industrial revolution in the 18th century, air pollution became more noticeable. The word smog was introduced by a physician at a public health conference in 1905 to denote poor air quality resulting from a mixture of smoke and fog.
A major event in Donors, Pennsylvania, in 1948 was responsible for increasing research on air pollution in the United States. The Donors event remains the worst industrial air pollution incident in U.S history causing twenty deaths and five thousand illnesses. What was called the "Donors fog" involved pollutants from the Donors zinc works metal smelting plant and other sources. Pollutants including sulfur dioxide, carbon monoxide and heavy metals were trapped by weather conditions in a narrow valley. The event lasted about three days until pollutants were washed out and dispersed by rain forms.
The Donors event was followed in 1952 by the London smog crisis following these events, regulators to control air quality began. Today, in the United States and other countries legislation to reduce emission of air pollutants has been successful, but more need to be done, chronic exposure to high levels of air pollutants continue to contribute to illnesses that kill people around the world.
Sources Of Air Pollution
There are two sources of air pollution and these are:
1. Stationary Sources
2. Mobile Sources
These are the sources of air pollution that have a relatively fixed location. These include point sources, fugitive sources and area sources.
1. Point Sources: These sources emit pollutants from one or more controllable sites such as smokestacks chimneys and exhausts of power plants.
2. Fugitive Sources: These sources generate air pollutants from open areas exposed to wind processes. Examples include burning for agricultural purpose as well as dirt roads, construction sites, farmlands, storage piles, surface mines and other exposed area from which particulates may be removed by wind.
3. Area Sources: These are well defined area within which are several sources of air pollutants, for example; small urban communities, areas of intense industrialization within urban complexes and agricultural areas sprayed with herbicides and pesticides.
These are sources of air pollutant that move from place to place while emitting pollutants. These include automobiles, trucks, buses, aircrafts, ships and trains.
CLASSIFICATION OF AIR POLLUTION
The major air pollutants occur either in gaseous forms or as particulate matter (PM)
1.Particulate matter pollutants (PM10) are particles of solid and liquid substances less than 10mn in diameter and may be organic or inorganic.
2. The gaseous pollutants include sulfur dioxide, nitrogen oxide carbon monoxide, ozone, volatile organic compounds such as hydrocarbons, hydrogen sulfide and hydrogen fluoride.
PRIMARY AND SECONDARY POLLUTANTS
Air pollutants can be classified as primary and secondary
1. Primary pollutants are those emitted directly from the air, they include particluates, sulfur dioxide, carbon monoxide, nitrogen oxide, and hydrocarbons.
2.Secondary pollutants are produced through reactions between primary pollutants and normal atmospheric compounds. For example, ozone forms over urban areas through reactions of primary pollutants, sunlight, and natural atmospheric gases. Thus ozone is a secondary pollutant.
Natural and Human Pollutants
The primary pollutants that account for nearly all air pollution problems are: carbon monixide (58%), volatile organic compounds (VOCs) (11%), nitrogen oxides (15%), sulfur oxides (13%), and particles (3%). In the United States today, about 140 million metric tons of these materials enter the atmosphere from human related processes. If these pollutants are uniformly distributed in the atmosphere; the concentration would be only a few parts per million by weight. Unfortunately pollutantsare not uniformly distributed but tend to be released, produced and concentrated locally or regionally as seen in large cities.
In addition to pollutants from human sources, our atmosphere contains many pollutants of natural origin. Examples of natural emissions of air pollutants include the following:
1.Release of sulfur-dioxide from volcanic eruptions. For example; volcanic activity on the island of Hawaii emits sulfur dioxide and other pollutants, which reacts in the atmosphere to produce volcanic smog called "Vog". The smog can present a healthy hazard to people and cause local acid rain.
2. Release of Ozone in the lower atmosphere as a result of unstable metro logical conditions such as violent thunder storms.
3. Emission of variety of particles from wild fires and windstorms.