Sulfur dioxide is a gas released by both human and natural sources. It is a colorless gas with a pungent, irritating odor and taste. Sulfur dioxide is used in many industrial processes such as chemical preparation, refining, pulp-making and solvent extraction. In addition, it is used in the preparation and preservation of food due to its ability to prevent bacterial growth and browning of fruit.

Burning of fossil fuels such as coal, oil and natural gas are the main source of sulfur dioxide emissions. Coal fired power stations, in particular, are major sources of sulfur dioxide, with coal burning accounting for 50 percent of annual emissions, as explained by the Tropospheric Emission Monitoring Internet Service (TEMIS). Moreover, oil burning accounts for a further 25-30 percent. Sulfur dioxide emissions are released primarily as a result of generated electricity through fossil fuel burning power stations. Additional smaller sources of sulfur dioxide are released from industrial processes. These include extracting metal from ore and the burning of fuels with a high sulfur content by locomotives, large ships and non-road equipment.

Volcanic eruptions release large quantities of sulfur dioxide into the air. The vast quantities of sulfur dioxide released during one eruption can be enough to alter the global climate. Similarly, hot springs release sulfur dioxide into the atmosphere. Sulfur dioxide can even be produced by the reaction of hydrogen sulfide with the oxygen in the air. Hydrogen sulfide is released from marshes and regions in which biological decay is taking place.

Air pollution in the form of sulfur dioxide can have detrimental effects on human health. Such effects include breathing problems, particularly in asthmatics, whereas short-term exposure can lead to chest tightness and coughing and wheezing. Continued exposure to sulfur dioxide has been linked with alterations of the lungs defenses and aggravation of existing cardiovascular disease.

The most common environmental impact of sulfur dioxide is the formation of acid rain. This occurs when the sulfur dioxide emissions combine with water vapor in the atmosphere, forming sulfuric acid, which falls to the ground as acid rain. Acid rain can acidify rivers and lakes, killing aquatic life in addition to damaging trees and plants. In addition, sulfur dioxide is a major precursor to particulate soot, which reduces air quality.