Sulfur dioxide (SO2) is a gaseous air pollutant composed of sulfur and oxygen. It is one of a group of highly reactive gases known as "oxides of sulfur" and is emitted into the air as a result of various activities, including the burning of fossil fuels by power plants and other industrial facilities, industrial processes, natural sources such as volcanoes, and vehicles and heavy equipment that burn fuel with a high sulfur content
. SO2 can affect both health and the environment. Short-term exposures to SO2 can harm the human respiratory system and make breathing difficult, particularly for people with asthma, while long-term exposure at high levels can increase respiratory symptoms and reduce lung function
. SO2 can also harm trees and plants by damaging foliage and decreasing growth, and contribute to the formation of thick haze, smog, and acid rain
. It is a major air pollutant and is subject to primary and secondary National Ambient Air Quality Standards under the federal Clean Air Act
