Health and Welfare Effects. Human Health Symptoms and Vegetation Injury Threshold. Physical Characteristics and Sources Sulfur dioxide is a colorless gas with a pungent odor detectable by the human nose at concentrations of about 0.5 to 0.8 ppm.
Sulfur dioxide is highly soluble in water, resulting in the formation of sulfurous acid.
On a worldwide basis, SO, is considered to be one of the major pollution problems. Wood, natural gas, propane, and other common fuels used for home heating do not contain significant quantities of sulfur and, therefore, are not considered to be a major source of sulfur dioxide. Diesel fuel, and to a lesser extent gasoline, contain sulfur and are considered a contributor to sulfur dioxide in the ambient air. Sulfur dioxide is also emitted in significant amounts from natural sources such as volcanic eruptions. However, natural sources rarely play an important role in the urban sulfur dioxide problem.