Introduction to Sulfur Dioxides

Sulfur Dioxide (SO2) is a gas that accounts for approximately 95% of sulfur emissions in the United States. SO2 can be found in the troposphere at appreciable levels, its concentration can be as low as one part per billion (ppb), and in urban areas can be as high as 1.5 to 2.3 parts per million (ppm). Upon entering the atmosphere is typically oxidized to SO3, which is then rapidly converted to H2SO4 and precipitated back to the earth as acid rain.

Sources of SO2

Sulfur compounds are emitted into the atmosphere by both natural and anthropogenic sources. The majority of these are stationary sources that use sulfur-containing fossil fuels (coal and oil). The following chart identifies the major sources of sulfur dioxide (chart adapted from http://www.pca.state.mn.us/air/emissions/so2.html):

Health Effects of SO2

High concentrations of SO2 can cause breathing problems, respiratory illness, and can aggravate respiratory and cardiovascular diseases. Although SO2 is almost completely removed from the mouth, throat, and nose through breathing due to its solubility, it can still disturb the function of the upper respiratory system. Low level exposure (0.25 - 0.5 ppm) can cause bronchitus, concentrations up to six ppm irritate the lungs and throat, and concentrations above six ppm impair respiratory immune function. The people who are most susceptible to the deleterious effects of SO2 are children, the elderly, asthmatics, and persons with chronic lung disease.

Ecological Effects

SO2 acts as a corrosive agent on many parts of the environment-- both the manmade environment and the human-made environment. It can damage metals, stone, paint, leather, paper, fibers, and electrical equipment. When SO2 reacts to become H2SO4, acid rain occurs, which can lower the pH in soils and lakes, causing damage to plants and aquatic life.

SO2 can also injure plants, visibly changing the structure of the leaf. Some of these changes include chlorosis (chlorophyll destruction) and necrosis (plant tissue death). These can come about due to long-term exposure, or short-term exposure to high levels.

(Thanks to State of Minnesota for use of their materials for this page)
Quick Quiz: What is the main source of SO2 emmissions?
Manufacturing Industry
Electric Utility fuel combustion
transportation
industrial fuel combustion

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