Air pollution is one of the most visible forms of pollution. Anyone who's seen the brownish-yellow sky over a city, or dark smoke belching from the tail pipe of a bus or industrial smoke stack knows what it looks like. It's effects are not always so obvious, and range from contaminated rain to ozone levels to global warming. There are also health concerns, making air pollution a serious environmental concern.
Air pollution is essentially the introduction of particles into the atmosphere that does not belong there. Particulate matter, tiny pieces of contaminants, which because they are lighter than air become airborne. They might then rise high into the air to travel on the winds, or float near ground level. This is a result of both the kind of pollutant and where it is released. Car exhaust, for example, starts much lower than industrial smoke. Air pollution does not have to be man made chemicals. The desertification of wilderness areas releases extra dust and sand into the air that also causes many of the problems associated with chemical air pollution.
One of the most visible effects of air pollution is smog. A fog-like smoke (hence the term, "smog") that blankets many cities, it can be seen as a discolored haze that obscures the view of skylines around the world. It comes from car exhausts and other emissions put out by a modern city such as furnaces, incinerators, and surrounding industries. This effects not only the people who breathe it but also all systems that rely on circulating air. When it is particularly heavy, the dust and grime can adversely impact machinery by clogging filters, and gears.
Acid rain is caused when chemicals from pollutants enter the atmosphere and become bound to rain droplets. The chemical composition of the water then changes and becomes acidic. When it falls to earth it has numerous consequences. Aside from polluting the existing water table, the acid also affects plants and trees. Acid rain can kill a forest by affecting not only the leaves and bark, but also by raising the acidity of the soil. Acid rain affects human constructions as well, especially any item made of stone. This includes monuments and statures, but also building structures which are eaten away by the acid.
Air pollution causes numerous health consequences for people. Like the filters in machinery and buildings, a person's lungs can become coated with the particulate matter in the pollution. This can lead to any number of respiratory problems, depending on the levels of exposure. At the very minimum, people who suffer from asthma or respiratory issues may have more difficulty. Long term exposure can lead to health concerns similar to long term smoking, such as cancer and emphysema. This is in addition to any contamination caused by toxic chemicals that may be in the pollution, which themselves carry numerous health risks.
One of the biggest effects of air pollution is it's global reach. Even areas that don't have vehicles or industry, such as the arctic, are still affected by air pollution as global currents carry chemicals and particles around the world. Another aspect of air pollution is also global warming, which is caused by excess carbon dioxide. Although CO2 is a gas, and not a particle, because more of it is being put into the atmosphere through human activities, it counts as a pollutant. So does changes to the ozone levels, both the higher atmospheric ozone layer (affected by CFC's) and also ground level ozone which is similar to smog.