6.6 Fossil Fuel Combustion

Burning Fossil Fuels Releases Energy and Pollutants

Fossil fuel combustion occurs when coal, oil, or natural gas react with oxygen, releasing stored chemical energy as heat. This heat powers turbines to generate electricity or drives engines. Combustion also releases byproducts including carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides (NOx), particulates, and sometimes carbon monoxide (CO) and mercury, depending on fuel type and combustion completeness.

Coal vs. Oil vs. Natural Gas

Coal produces the most CO2, SO2, and particulates per unit energy due to impurities like sulfur and ash content. Oil combustion (in vehicles/power plants) releases CO2, NOx, and particulates. Natural gas (mostly methane) burns cleanest, producing less CO2, SO2, and particulates per unit energy, though methane leaks during extraction contribute to greenhouse gas emissions.

Environmental Consequences

Combustion pollutants cause acid rain (from SO2 and NOx forming acids), smog and respiratory illness (from particulates and NOx), and contribute to global climate change (from CO2, a greenhouse gas). Incomplete combustion produces toxic carbon monoxide. These impacts drive interest in cleaner alternatives and technologies like scrubbers and catalytic converters to reduce emissions.

Key terms

Fossil fuel combustion

The burning of coal, oil, or natural gas with oxygen to release stored energy as heat, along with pollutant byproducts.

Why does coal produce more pollution than natural gas?

Coal contains more sulfur and impurities, producing more SO2, particulates, and CO2 per unit of energy released.

Carbon monoxide (CO)

A toxic gas produced by incomplete combustion when there isn't enough oxygen to fully oxidize carbon to CO2.

Acid rain

Precipitation with lowered pH caused by SO2 and NOx emissions reacting with atmospheric water vapor to form acids.

Main greenhouse gas from fossil fuel combustion

Carbon dioxide (CO2), which traps heat in the atmosphere and drives global climate change.

Try an AP-style question

What are the main products of complete fossil fuel combustion?

1. CO₂ and water
2. O₂ and nitrogen
3. Ozone and CFCs
4. Uranium and lead