Sulfur Oxides: Pollution Prevention and Control

Traditionally, measures designed to reduce localized ground-level concentrations of sulfur oxides (SOx) used high-level dispersion. Although these measures reduced localized health impacts, it is now realized that sulfur compounds travel long distances in the upper atmosphere and can cause damage far from the original source. Therefore the objective must be to reduce total emissions. The extent to which SOx emissions harm human health depends primarily on ground-level ambient concentrations, the number of people exposed, and the duration of exposure. Source location can affect these parameters; thus, plant siting is a critical factor in any SOx management strategy. The human health impacts of concern are short-term exposure to sulfur dioxide (SO2) concentrations above 1,000 micrograms per cubic meter, measured as a 10-minute average. Priority therefore must be given to limiting exposures to peak concentrations. Industrial sources of sulfur oxides should have emergency management plans that can be implemented when concentrations reach predetermined levels. Emergency management plans may include actions such as using alternative low-sulfur fuels. Traditionally, ground-level ambient concentrations of sulfur dioxide were reduced by emitting gases through tall stacks. Since this method does not address the problem of long-range transport and deposition of sulfur and merely disperses the pollutant, reliance on this strategy is no longer recommended. Stack height should be designed in accordance with good engineering practice (see, for example, United States, 40 CFR, Part 50, 100(ii).