Sulfur dioxide
Nature of the Pollutant
Worldwide, sulfur oxides and in particular, sulfur dioxide (SO2) are emitted by both manmade and natural sources of combustion. Erupting volcanoes and decaying organic matter are two examples of natural sources which release sulfur oxides. Commercial combustion in industrialized regions of the United States is the largest single source of sulfur oxides pollution locally. Solid and liquid fossil fuels, such as coal and oil, contain sulfur which is oxidized during the combustion process.
More than 90 percent of the sulfur emitted by industrial sources is released in the form of SO2, the criteria pollutant regulated by EPA. The breakdown of major SO2 emitting sources is as follows: utilities 69.5%; industrial manufacturing processes 12.7%; industrial combustion 11.6%; transportation 3.7%, and other 2.5%.
Acidic deposition, or acid rain as it is commonly known, occurs when chemically laden emissions react in the atmosphere with water, oxygen and oxidants to form various acidic compounds. These compounds then fall to the earth in either a dry form (as gas and particles) or wet form (as rain, fog, or snow).
The acid rain causes surface water acidification and damages trees at high elevations. Air concentrations degrade visibility and pose a risk to public health. In addition, acid rain accelerates the decay of building materials and paints. High levels of SO2 have been proven to cause or aggravate various types of lung disorders. These problems, which affect a person's ability to breathe, have led to both increase sickness and deaths. Based on these concerns, SO2 has been regulated under the Clean Air Act. RAPCA has not observed ambient concentrations sufficient to induce these effects in it's six-county area.
Title IV of the 1990 Clean Air Act Amendments was implemented to achieve significant reductions in annual SO2 emissions. The primary goal was to reduce SO2 emissions by 10 million tons below 1980 levels using a two-phase approach. Phase I, which began in 1996, affects 110 coal burning electric utility plants located in 21 eastern and midwestern states. Phase II, which began in 2000, tightened the emissions on these large plants and put into play restrictions on smaller plants fired by coal, oil, and gas.
The Monitoring Technique
A mixture of ambient gases enters the analyzer where the SO2 gas is identified and its concentration measured. RAPCA's two continuous analyzers utilize a fluorescent light principle of detection. This method exposes the SO2 molecules which then give off a characteristic radiation as they return to their normal state. The intensity of this radiation provides a continuous direct measure of the concentration of SO2 in the sample.