Air pollution is a broad term that is applied to particulate matter and chemical compounds that are released by humans into the atmosphere and modify its composition. It was first perceived as a local problem in urban industrialized areas, so factories and power plants started building taller smoke-stacks. However, taller stacks merely transported the problem elsewhere and soon regional problems such as acid rain were recognized. In Scandinavia, for example, the acidification of lakes was found to be the result of sulfur dioxide emissions from tall stacks located in central European countries such as Germany and even in places as far off as Great Britain. More recently, global problems such as climate change and stratospheric ozone depletion have been widely publicized.
Natural sources that affect atmospheric chemistry include sulfur and nitrogen compounds from volcanoes and biological decay and particulate matter from dust storms and volcanoes. Plants, trees, and even grasses release volatile organic compounds (VOCs), such as methane, into the air. Of more concern, since we have the ability to control them, are anthropogenic (human-made) air pollutants, such as carbon monoxide, sulfur dioxide, some fraction of VOCs and nitrogen oxides. The largest source of anthropogenic pollution is the burning of fossil fuels, including coal, oil, and gas, in our homes, factories, and vehicles.
There are many forms of air pollution that are human-made. Industrial plants, combustion-fired power plants and vehicles with internal combustion engines generate nitrogen oxides, VOCs, carbon monoxide, carbon dioxide, sulfur dioxide and particulates. In many cities cars are the primary source of air pollutants. Stoves and incinerators, especially ones that are coal or wood-fired, and farmers burning their crop waste produce carbon monoxide, carbon dioxide, as well as particulates. Other human-made sources include aerosol sprays and gases leaking from refrigeration systems, as well as fumes from paint, varnish, and other solvents. Additional pollutants, like ozone and acids, are made in the atmosphere when human-made gases combine chemically.
Air pollution doesn’t stay in one place. Winds and weather play an important part in transport of pollution locally, regionally, and even around the world.