Final answer:
Most sulfur in coal primarily comes from sulfur left behind by evaporating sea water that once covered swampy areas during coal formation, particularly in regions like the eastern United States with coal deposits having high sulfur content.
Step-by-step explanation:
The majority of the sulfur in coal originates from seawater that covered swamps during the formation of coal. As these seas dried up, the sulfur was left behind and became part of the coal deposits. This is particularly true for areas like the eastern United States where coal was formed from swamps overlaid by seawater. Additionally, bituminous coal, the most abundant form of coal in the United States, is known to have a high sulfur content due to the presence of pyrite, which releases sulfur dioxide during combustion contributing to acid rain. However, not all coal deposits have high sulfur content; for example, those formed from freshwater swamps typically have less sulfur. When plants and other vegetation from these areas die and decompose, sulfur can be released back into the atmosphere as hydrogen sulfide gas.