Department of Earth System Science

The combustion of a hydrocarbon fuel removes molecular oxygen (O₂) from the atmosphere and releasesequivalent amounts of water (H₂O) and carbon dioxide (CO₂), almost always with trace amounts of numerous other compounds including hydrocarbons (CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₈, C₆H₆, CH₃CHO, etc.), carbon monoxide (CO), nitrogen oxides (NO, N₂O) and reduced nitrogen (NH₃ and HCN), sulfur gases (SO₂, OCS, CS₂) halocarbons (CH₃Cl and CH₃Br), and particles. A review of the atmospheric budgets of these gases shows that burning of fossil fuels and recent biomass has led to global alterations in the composition of our atmosphere. Combustion is clearly responsible for most of the enhanced greenhouse forcing to data (through CO₂, tropospheric O₃, soot) and also some counteracting effects (through SO₂). it has had minimal impact on stratospheric O₃ (through CH₃Cl, CH₃Br, CH₄), but has likely changed the tropospheric oxidant levels (through CO, NO_x, NMHC), at least over the northern hemisphere. Most of the important greenhouse gases and tropospheric oxidant gases have significant natural sources, which are not well defined today and may be changing; and thus, quantifying the role of combustion is difficult.