Final answer:
Electric power plants are the largest source of sulfur dioxide (SO2) pollution, which is known to cause environmental issues such as acid rain and health problems like respiratory conditions. Coal-burning facilities contribute to a significant portion of SO2 emissions in the United States. The correct option is 3.
Step-by-step explanation:
The student asked what electric power plants are the largest source of. The correct answer is sulfur dioxide (SO2) pollution. Electric power plants, particularly those that burn high-sulfur coal, are a significant source of SO2. This emission is associated with numerous environmental and health issues such as acid rain and respiratory problems.
Furthermore, power plants that burn coal are responsible for a considerable part of the United States' sulfur dioxide emissions. These facilities produce not only around 64% of the country's SO2 emissions but they also contribute to other pollutants like mercury and nitrogen oxides.
The acid rain caused by SO2 can lead to damage to ecosystems, waterways, and built structures. In terms of adverse health effects, exposure to sulfur dioxide can exacerbate asthma and other respiratory conditions.
It is also important to note that coal power plants are substantial contributors to greenhouse gas emissions, such as carbon dioxide (CO2), which is a critical factor in climate change. However, when discussing the largest source of a specific pollutant from electric power plants, it is specifically SO2 pollution that they are most linked to.