Pollution is defined as the release of substances into the environment that change it for the worse.Most pollution is the result of human activity. In particular, the technology that we depend on to create material goods and increase our quality of life often releases pollutants simultaneously. Pollution is typically classified into three categories based upon the medium that is impacted: air, land and water. Each of these types of pollution is related to the other. For instance, chemicals released as a gas from a coal-burning electric generator is a form of air pollution. However, as rain traps these chemicals and falls to the ground, the impact is to make the water more acidic. Acid rain collects in bodies of water (water pollution) and harms plant and animal life. Acid rain can also change the chemistry of the soil. Though these changes are often not dramatic enough to be considered land pollution, the change can hurt plants that depend upon a stable pH.

Air Pollution
The air we breathe is made up of gaseous nitrogen (78%) and oxygen (21%) with trace amounts of other gases, vaporized liquids, and tiny particles of solids. Only 0.035% of the air is carbon dioxide. Studies have detected over 2500 additional chemicals in urban air. Most of the materials that are considered air pollutants come from cars, trucks, factories, cigarettes, cleaning materials, fumes and fibers from synthetic materials, and other products of human activity. Repeated exposure to air pollutants can cause damage to the lungs, green plants, buildings, metals, and other materials.

Air pollutants can exist both outside and inside the home. There are five categories of air pollutants: chemical pollutants (such as carbon oxides, sulfur oxides, nitrogen oxides, volatile organic compounds, and photochemical oxidants), suspended particulate material (such as dust, heavy metals, and pollen), radioactive substances, heat, and noise.

Though Utah is impacted by all types of air pollution, the most obvious form of air pollution occurs as smog (or haze) in the Greater Salt Lake Valley. The pollution in the valley is primarily from suspended particulate material and carbon monoxide. As air heats, it rises. Because the mountains on either side of the valley restrict air flow, cool dense air is sometimes trapped in the valley by warm air above. This is called a temperature inversion.The result of such an inversion is to trap all the pollutants that we produce in the air that we breathe. Most of the air pollution in the Salt Lake valley is caused by cars and trucks.

Acid rain, the deletion of the ozone layer, and the greenhouse effect are three of the more familiar issues related to air pollution. Acid rain occurs when waste products such as sulfur dioxide and nitric oxide are released from smokestacks of factories; often from burning coal. When exposed to the air, the pollutants combine with other materials to make sulfuric and nitric acids. Acid rain, the combination of the acids in the air and rain water, return to the earth's surface causing harm to plants, animals, and human-made structures. One of the greatest problems with acid rain is that the gases initially formed can travel great distances from their original source. Therefore, the damage caused by acid rain can occur hundreds of miles away from the source of the pollution. For this reason, the control of acid rain has become an international issue.

The earth is surrounded by only a thin layer of gas, known as our atmosphere. One of the outer layers, the ozone layer, helps filter out the sun's most harmful ultraviolet rays. Use of chemicals called chlorofluorocarbons (CFCs), have been attributed to depleting the ozone. CFCs are found in coolants such as those used in refrigerators and air conditioners, and in propellants like those found in aerosol cans. International attempts to ban or limit the use of CFCs have not been effective enough to prevent ozone depletion.

The greenhouse effect is caused by increased levels of carbon dioxide and other greenhouse gases in the atmosphere. Such changes in the atmosphere are predicted to cause the gradual warming of the earth, eventually impacting plant growth and the melting of the ice caps. Factors contributing to the greenhouse effect include the burning of fossil fuels and deforestation. Solutions include improving energy efficiency, reducing deforestation, and planting trees.

Water Pollution
Though water is a renewable resource, we can contaminate water to such an extent that it is harmful to the plants and animal life that depend on it. Water pollution is related to air and land pollution. Air pollutants fall back to earth in the form of rain. Fertilizers and pesticides are washed off farm lands into the water supply.
As with air pollution, polluted water supplies do not recognize national boundaries.

Water pollution can be caused by disease-carrying agents (such as bacteria, viruses, and protozoa like Giardia), chemicals (such as fertilizers, heavy metals, oil and gasoline), sediment or suspended matter such as silt, radioactive substances, and heat.There are two categories of water pollution used for control and regulation. Point sources discharge pollutants at a specific location through pipes, ditches, or sewers. Point sources include factories, mining facilities, and sewer treatment plants. Nonpoint sources are big land areas that discharge pollutants from across their surface with water runoff. Examples include croplands, livestock feedlots, roads, urban areas, logged forests, and parking lots. Approximately 60% of all water pollution comes from nonpoint sources. Nonpoint water pollution is much more difficult to control since it is difficult to identify and control pollution sources over such a widespread area.

Water pollution impacts multiple bodies of water. Rivers can become contaminated with sediments and excess heat from industry, causing harm to the plants and animals that live there. Lakes and ponds can become collection points for non- point pollutants. Since pure water evaporates but pollutants in water do not, pollutants will accumulate. After many years, the water quality of these bodies of water may steadily deteriorate if the source of pollution is not controlled. Aquifers, or water that travels underground and through rocks, often supply us with our drinking water. Burying heavy metals and radioactive materials deep in the ground can accidentally poison our water supplies. Finally, all water eventually returns to the oceans. Though ocean dumping of wastes have been greatly reduced, pollutants from rivers and streams all find their way back to the ocean. Coastal areas are the most severely threatened by water pollution. This causes two concerns. First, humans enjoy coastal areas. Pollution can cause the closing of beaches and may limit the recreational and aesthetic value of an area. Second, most of the food that we harvest from the ocean comes from areas near the shore. As estuaries and coastal areas become more polluted, the harvest of fish and shellfish decreases. Other problems may be caused by bio-magnification.Bio- magnification occurs when plants or animals absorb pollutants that are not at levels sufficient to harm them. For instance, a fish may be exposed to a low level of mercury, causing it no harm. However, if a human eats many of these fish over many years, there may be a sufficient buildup of mercury to cause cancer or birth defects in children.

Land Pollution
Land pollution comes in many forms. Solid waste, such as trash from human activities, is one obvious form. Pesticides and the residues that remain in the soil are another. Radioactive materials and other forms of hazardous wastes make up a third. All of these forms of pollution are a direct result of more people using more resources. The increased production of material goods, the need for more and more raw materials, and increased food demands have all helped contribute to the problem of land pollution.

Every living thing produces waste. Trees drop leaves and fruit, insects shed their exoskeletons, and animals produce waste and eventually die. These waste materials are said to be biodegradable since they can be broken down by living things such as earthworms, bacteria, insects, and molds. There was a time when the earth was able to keep up with the breakdown of natural wastes. However, as more people live in smaller areas, natural processes are not sufficient to keep up with waste production. In addition, humans have manufactured new types of waste materials such as plastics, glass, and waste materials from the production of energy and mineral resources. Many of these materials cannot be broken down by natural processes. For instance, plastics and glass have no natural processes by which they return to the soil. Scientists are currently working on newer forms of plastic that may break down more quickly, but the ultimate consequences of these developments are unknown.

The United States is the world's trashiest country, leading in the production of hazardous and nonhazardous waste. Currently the U.S. produces 11 billion tons of waste--an average of 44 tons per American. Most of this solid waste, 98.5%, comes from mining, oil and natural gas production, and industrial activities. Municipal waste from homes and businesses makes up the remaining 1.5% of waste produced. Much of this waste is stored in landfills. Sanitary landfills are designed to reduce both pollution and pest problems. In a landfill, waste is compacted and capped off with soil and clay. Fences are used to prevent windblown trash from escaping the area. Though landfills are very effective methods of removing waste materials, we will eventually run out of spaces to fill.

Conservation Practices
When the human population was small and scattered across the earth, pollution was rarely a concern. Waste materials that were produced, whether solid, liquid, or gas, could easily be disposed of through natural processes. Most of the wastes produced were organic, and the ability of nature to dilute the waste materials that could not be quickly broken down was simple. However, as the population of the earth has increased and more and more people are living in more concentrated areas, the ability of natural processes to keep up with waste removal has been diminished. We now recognize that there is no "away." Materials that we dispose of in a river or an air current shows up at someone else's backdoor. We can no long dilute or disperse waste materials - someone is always downwind or downstream.

The most obvious form of pollution control is to stop pollution at its source. Technological advances are being made to control emissions from cars and factories. Pesticides, fertilizers, and plastics are all being designed to break down more quickly in the environment. However, there are more concrete actions that we can take as individuals. The most common suggestion is to reduce, reuse, recycle.This statement reminds us to reduce that amount of materials goods we buy that may become waste (such as excess packaging), reuse materials many times before we relegate them to the trash, and to recycle materials that we can. Unfortunately, recycling is not a perfect solution since the process takes energy and produce its own pollutants.