The control of SO2 is largely based on chemical means. The sulfur present in organic compounds can be converted to various forms by oxidation or reduction. Sulfur oxidizes to Sulfur Dioxide (SO2) and then Sulfur Trioxide (SO3). In the atmosphere SO3 reacts with water to form sulfuric acid, which then reacts with ammonia or other cat-ions to form particles of ammonia sulfate or some other sulfate. These small particles are responsible for urban particulate and visibility problems. Reduction means the removal of oxygen or the addition of hydrogen.
The major source of SO2in the US are coal burning electric power plants. The typical SO2 content of the emissions is about 0.1% SO2 or 1000 ppm. Low concentration of SO2 in gas stream makes it unprofitable for recovery as H2SO4. The most widely used method is scrubbing. The installation and operation of these air pollution control device is expensive and require large capital expenditure.