Emissions sources are activities which produce emissions, pollutants which enter the environment through the air. Many governments track levels of key pollutants such as particulates, carbon dioxide, nitrogen oxide, methane, lead, ozone, and sulfur oxide, for the purpose of monitoring air quality and making recommendations to reduce emissions. Some emissions sources are natural; volcanoes, for example, can produce a great deal of pollution when they are active. While such emissions are tracked, most government agencies are more interested in man made emissions, as these can be changed.
One of the most infamous emissions sources is the burning of fossil fuels. Fossil fuels are burned in engines of all sizes to power cars, boats, airplanes, and a variety of other machines. They are also burned to generate electricity, with coal-fired electricity production in particular being a concern, and to produce heat for cooking and heating. Fossil fuel emissions sources are a cause for concern because they produce a number of so-called greenhouse gases which have been linked with damage to the Earth's environment, and in urban areas, they can contribute to significant air quality problems.
Wood burning stoves and fires, including wildfires and controlled burns, are another emissions source. Activities such as using paints and solvents generate emissions, with these materials releasing gases as they are applied and as they cure. The manufacturing sector is another major area of interest among agencies which study emissions sources, as factories producing a wide variety of products generate an assortment of emissions, ranging from flue gases released through factory chimneys to pollutants released into waterways which evaporate into the air.
The agricultural industry houses several emissions sources, including livestock, which generate methane, agricultural equipment powered by fossil fuels, and fertilizer application. Other emissions sources include waste disposal, also linked with the production of methane, among other emissions, and service stations, which produce a number of inevitable emissions as fuel is transferred from tanker trunks to underground tanks and then to vehicles.
While many people think of carbon dioxide when they hear the word “emissions,” carbon dioxide is not the only chemical compound considered an emission of concern. A wide array of emissions sources contribute to problems like the development of smog, acid rain, declines in water quality, air quality issues, and a wide variety of other issues. Controlling emissions sources is the best way to address these problems: if the emissions aren't generated in the first place, it eliminates a large part of the problem.