Editing Vehicle emissions control (section)

==Types of emissions==
Emissions of many [[Air pollution|air pollutants]] have been shown to have [[Environmental health|variety of negative effects]] on [[public health]] and the [[natural environment]]. Emissions that are principal pollutants of concern include:
* [[Hydrocarbon]]s (HC) – A class of burned or partially burned [[fuel]], hydrocarbons are [[toxin]]s. Hydrocarbons are a major contributor to [[smog]], which can be a major problem in [[urban area]]s. Prolonged exposure to hydrocarbons contributes to [[asthma]], [[liver disease]], [[lung disease]], and [[cancer]]. Regulations governing hydrocarbons vary according to type of [[engine]] and [[jurisdiction]]; in some cases, "non-[[methane]] hydrocarbons" are regulated, while in other cases, "total hydrocarbons" are regulated. Technology for one application (to meet a non-methane hydrocarbon standard) may not be suitable for use in an application that has to meet a total hydrocarbon standard. Methane is not directly toxic, but is more difficult to break down in fuel vent lines and a charcoal canister is meant to collect and contain fuel vapors and route them either back to the fuel tank or, after the engine is started and warmed up, into the air intake to be burned in the engine.
* [[Volatile organic compounds]] (VOCs) – Organic compounds which typically have a boiling point less than or equal to 250&nbsp;°C; for example [[chlorofluorocarbon]]s (CFCs) and [[formaldehyde]].
* [[Carbon monoxide]] (CO) – A product of incomplete combustion, inhaled carbon monoxide reduces the blood's ability to carry oxygen; overexposure ([[carbon monoxide poisoning]]) may be fatal.  (Carbon monoxide persistently binds to hemoglobin, the oxygen-carrying chemical in red blood cells, where oxygen (O<sub>2</sub>) would temporarily bind. The bonding of CO excludes O<sub>2</sub> and also reduces the ability of the hemoglobin to release already-bound oxygen, on both counts rendering the red blood cells ineffective.  Recovery is by the slow release of bound CO and the body's production of new hemoglobin{{snd}}a healing process{{snd}}so full recovery from moderate to severe [but nonfatal] CO poisoning takes hours or days.  Removing a person from a CO-poisoned atmosphere to fresh air stops the injury but does not yield prompt recovery, unlike the case where a person is removed from an asphyxiating atmosphere [i.e. one deficient in oxygen].  Toxic effects delayed by days are also common.)
* Nitrogen oxides ([[NOx|NO<sub>x</sub>]]) – Generated when [[nitrogen]] in the air reacts with oxygen at the high temperature and pressure inside the engine. NO<sub>x</sub> is a precursor to smog and [[acid rain]]. NO<sub>x</sub> includes NO and NO<sub>2</sub>.<ref>{{Cite web |url=http://www3.epa.gov/airquality/nitrogenoxides/health.html |title=EPA note on NO<sub>2</sub> and health |access-date=2015-09-21 |archive-date=2015-09-30 |archive-url=https://web.archive.org/web/20150930053842/http://www3.epa.gov/airquality/nitrogenoxides/health.html |url-status=live }}</ref> NO<sub>2</sub> is extremely reactive. NO<sub>x</sub> production is increased when an engine runs at its most efficient (i.e. hottest) operating point, so there tends to be a natural tradeoff between efficiency and control of NO<sub>x</sub> emissions. It is expected to be reduced drastically by use of [[Emulsified fuel|emulsion fuels]].<ref>{{cite journal |last1=Jhalani |first1=Amit |last2=Sharma |first2=Dilip |last3=Soni |first3=Shyamlal |title=Feasibility assessment of a newly prepared cow-urine emulsified diesel fuel for CI engine application |journal=Fuel |year=2021 |volume=288 |page=119713 |doi=10.1016/j.fuel.2020.119713|s2cid=229400709 }}</ref>
* [[Particulates|Particulate matter]] – [[Soot]] or smoke made up of particles in the [[micrometre]] size range: Particulate matter causes negative health effects, including but not limited to [[respiratory disease]] and [[cancer]].  Very fine particulate matter has been linked to cardiovascular disease.
* [[Sulfur oxide]] (SO<sub>x</sub>) – A general term for oxides of [[sulfur]], which are emitted from motor vehicles burning fuel containing sulfur. Reducing the level of fuel sulfur reduces the level of sulfur oxides emitted from the tailpipe.