How does switching from coal to natural gas affect air pollutant emissions and why?

• A. Only reduces CO2 emissions.
• B. Reduces SO2 and PM; NOx may decrease or increase depending on temperature.
• C. Increases SO2 and PM emissions.
• D. Reduces NOx emissions but increases CO2.

Answer: (D)

Switching fuels changes emissions mainly because natural gas is much cleaner in composition and burns more cleanly than coal. Coal contains sulfur and impurities that form sulfur dioxide and particulate matter when burned, so moving to natural gas dramatically lowers both SO2 and PM emissions. The amount of nitrogen oxides (NOx) depends on the flame temperature and the way the burner is designed. Natural gas fuel has little nitrogen to contribute, and its combustion can be run in ways that minimize NOx, so NOx emissions often go down, though at very high flame temperatures NOx can still rise. Carbon dioxide (CO2) emissions generally decrease with natural gas because it contains less carbon per unit of energy and because plants using natural gas are typically more efficient, producing less CO2 per unit electricity generated.

So the overall pattern is fewer SO2 and PM, NOx that can either decrease or increase based on temperature and design, and lower CO2 emissions—not higher.