Which pollutant is primarily emitted by coal-fired power plants and oil refineries?

• A. Nitrogen dioxide
• B. Lead
• C. Sulfur dioxide
• D. Ozone

Answer: (C)

When fossil fuels that contain sulfur are burned, the sulfur is oxidized to sulfur dioxide (SO2) and emitted directly from the combustion source. Coal often has significant sulfur content, and oil refineries process and burn sulfur-containing fuels, so SO2 becomes the primary pollutant released by these facilities. Ozone is not directly emitted but forms in the atmosphere from NOx and VOCs; lead comes from a different set of processes and has declined in many areas; nitrogen dioxide is important from combustion but does not dominate emissions from these two sources as SO2 does. Sulfur dioxide is also a major precursor to acid rain, making it a characteristic pollutant of coal-fired power plants and oil refineries.