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

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 what pollutants are released because the fuel’s composition and the way it burns determine which emissions form and how much. Natural gas contains very little sulfur and fine particulates, so burning it instead of coal generally lowers sulfur dioxide and particulate matter emissions. The amount of nitrogen oxides (NOx) that form depends strongly on flame temperature and combustion conditions, so NOx can decrease with the cooler, cleaner combustion of natural gas, but under certain high-temperature conditions it can still rise. Carbon dioxide is also lower per unit of energy produced when using natural gas compared with coal, so CO2 is typically reduced too, even though that isn't emphasized in this option. The statement that best fits how emissions behave overall is that sulfur dioxide and particulate matter decrease, while NOx can go either way depending on temperature, reflecting the variable nature of NOx formation. The other options either misstate the typical pollutant changes or ignore the CO2 result.

Switching fuels changes what pollutants are released because the fuel’s composition and the way it burns determine which emissions form and how much. Natural gas contains very little sulfur and fine particulates, so burning it instead of coal generally lowers sulfur dioxide and particulate matter emissions. The amount of nitrogen oxides (NOx) that form depends strongly on flame temperature and combustion conditions, so NOx can decrease with the cooler, cleaner combustion of natural gas, but under certain high-temperature conditions it can still rise. Carbon dioxide is also lower per unit of energy produced when using natural gas compared with coal, so CO2 is typically reduced too, even though that isn't emphasized in this option. The statement that best fits how emissions behave overall is that sulfur dioxide and particulate matter decrease, while NOx can go either way depending on temperature, reflecting the variable nature of NOx formation. The other options either misstate the typical pollutant changes or ignore the CO2 result.