Air is a very important component of the natural environment. Indeed it can be described as the most important life support component; hence man can survive for weeks without food and days without water but can hardly survive minutes without air.
As important as air is to man, it is a medium through which pollutants can get to human body and cause ill-health. When pollutants get into the air media in such a state as to call for concern, air pollution has taken place. The study of air as a media of pollution is very important to environmental health.
Air is a colorless, odorless, tasteless, gaseous mixture, mainly Nitrogen (approximately 78%) and oxygen (approximately 21%) with other lesser gases that surround the earth. Air as a medium is a composition of thick envelop of gases surrounding the surface of the earth.
It is also called the atmosphere. There are five layers that make up the atmosphere thus; the troposphere, stratosphere, mesosphere, thermosphere and the exosphere.
The most important layers that are affected by pollution are the troposphere and to a certain extent stratosphere.
The troposphere is the layer nearest the earth crust. It extends from the ground level to about 17km above the sea level (Oreyomi, 2005). It is the densest of all the layers, containing about 75% of the total gaseous mass of the atmosphere.
The gases present in the troposphere are oxygen, nitrogen, carbon dioxide, noble gases, water vapor, dust particles and some other substances.
The troposphere is the most important layer of the atmosphere because of its paramount biotic activities. It is characterized by the following:
– Weather phenomena such as cloud formation
– Irregular and violent movements of the air known as turbulences
– Temperature decrease with increase in altitude at an average rate of 6.50C per kilometre (Lapse rate). That is, ‘the higher you go, the cooler it becomes‘‘
– Pressure decrease with increase in altitude.
The tropopause demarcates the troposphere from the stratosphere and prevents the mixing of air between them.
The stratosphere is described as the earth‘s global sunscreen. Within it is the well acknowledged ozone layer known for its protective shield against the sun‘s ultra-violet radiation where it prevents it from reaching the earth‘s surface. According to Corson (1990), the stratosphere extends from above the upper limit of the troposphere to about 50km above the earth‘s surface.
Air, in its natural, unfouled composition is a supporter of life and very essential for the survival of all higher forms of life on the planet. Although slight variations may exist, depending on the location, air (as well as other environmental media), through a process of self-cleansing maintains a degree of consistency in the constitution of its natural components.
However, owing to certain natural processes and events, coupled with human activities, extraneous materials are often released into the atmosphere, thereby altering the natural quality of the air beyond its self-cleansing capacity at a particular time or period. It is this undesirable change in the characteristics of air that is termed air pollution.
The United Nations Environment Programme (UNEP, 1986) defined air pollution as the presence in the out-door atmosphere of one or more contaminants, such as dust, fumes, gas, mist, odor, smoke or vapor, in quantities or characteristics, and of duration such as to be injurious to human, plant or animal life or to property or which unreasonably interfere with the comfortable enjoyment of life and property.
Another more encompassing definition is offered by Masters (2005) who states that air pollution is the introduction of materials or energy into the air which alter it in composition or condition, directly or indirectly, and in high enough concentrations or levels as to harm humans, animals, vegetation or materials.
Types of Air Pollution
Air pollution is classified in two ways: based on origin and location (Agbi, 2003).
1. Based on Origin
Natural: This emanates from natural phenomena such as volcanic eruptions, Landslides, Windstorms, Earthquakes, Forest- fires, Putrefaction of plants and animals.
Most pollutants entering the atmosphere come from the above sources. However, natural air pollution sources, according to Chiras (1998), do not raise the ambient concentrations of a given pollutant very much, because they are usually widely dispersed or infrequent events.
For example, diffuse organic processes such as bacterial decay of organic matter produce insignificant amounts of pollution over large areas.
Man-made or Anthropogenic: This is caused by human activities. They could be many and varied, stationary (e.g. Industrial and domestic sources) or mobile (e.g. Vehicular sources). The following human activities as major sources of air pollution: Transportation, industrial processes, municipal solid waste disposal, incineration, cooking, bush-burning, power generators etc.
2. Based on Location
This can be out-door or in-door. Out-door pollutants may be primary pollutants released directly in a harmful form. They require no further modification in order to render them harmful, examples include – particulate matter, Carbon monoxide, sulphur dioxide etc.
They may also be secondary pollutants, by contrast, modified to hazardous forms after they enter the atmosphere or are formed by chemical reactions as components of the air mix and interact. Examples include carbon dioxide which reacts with water vapor in the atmosphere to form carbonic acid.
In conclusion, Air pollution in whatever form it presents can be very inimical to human health especially at this era of massive natural resources exploitation, industrialization and the preponderance of motor vehicles and the release of exhaust of petroleum products used as fuel for energy. Next unit we are going to examine another environmental media of pollution – Water.
Air is a medium for pollutants and pollution. It is made up of five important layers thus; troposphere, stratosphere, mesosphere, thermosphere and exosphere. The most important of these layers that affect pollution are the troposphere and the stratosphere.
Air pollution is the introduction of materials or energy into the atmosphere which has the potential to cause harm to health and the environment. There are different types of air pollution which can be classified either based on origin or based on location.