Editing Engine (section)

==== Air quality ====
[[Exhaust gas]] from a spark ignition engine consists of the following: [[nitrogen]] 70 to 75% (by volume), [[water vapor]] 10 to 12%, [[carbon dioxide]] 10 to 13.5%, [[hydrogen]] 0.5 to 2%, [[oxygen]] 0.2 to 2%, [[carbon monoxide]]: 0.1 to 6%, unburnt [[hydrocarbons]] and partial [[oxidation]] products (e.g. [[aldehyde]]s) 0.5 to 1%, [[nitrogen monoxide]] 0.01 to 0.4%, [[nitrous oxide]] <100 ppm, [[sulfur dioxide]] 15 to 60 ppm, traces of other compounds such as fuel additives and lubricants, also halogen and metallic compounds, and other particles.<ref>Paul Degobert, Society of Automotive Engineers (1995), ''Automobiles and Pollution''</ref> Carbon monoxide is highly toxic, and can cause [[carbon monoxide poisoning]], so it is important to avoid any build-up of the gas in a confined space. [[Catalytic converter]]s can reduce toxic emissions, but not eliminate them. Also, resulting greenhouse gas emissions, chiefly [[carbon dioxide]], from the widespread use of engines in the modern industrialized world is contributing to the global [[greenhouse effect]] – a primary concern regarding [[global warming]].