Why does low-sulfur subbituminous coal cause less sulfur pollution than some bituminous coal?

Low-sulfur subbituminous coal causes less sulfur pollution primarily because of its geological origin rather than its rank alone. Coal that formed in continental, freshwater basins—such as the Powder River Basin in the United States—typically contains much lower levels of sulfates compared to coal deposits that formed in environments adjacent to marine settings.1

While subbituminous coal is often favored by power plants to reduce emissions, it is important to note that its sulfur content is not inherently low due to its rank; rather, it is the specific depositional environment that dictates the sulfur concentration. Because subbituminous coal has a lower calorific value than bituminous coal, a greater quantity must be burned to generate the same amount of energy. Consequently, the environmental benefit of switching to subbituminous coal relies on selecting deposits that are naturally low in sulfur. In contrast, burning bituminous coal with high sulfur content releases significant amounts of sulfur oxides, which contribute to the formation of acid rain and other forms of air pollution.12