Exhaust gas#Particulate matter (PM10 and PM2.5)

The largest part of most combustion gas is nitrogen (N₂), water vapor (H₂O) (except with pure-carbon fuels), and carbon dioxide (CO₂) (except for fuels without carbon); these are not toxic or noxious (although water vapor and carbon dioxide are greenhouse gases that contribute to climate change). A relatively small part of combustion gas is undesirable, noxious, or toxic substances, such as carbon monoxide (CO) from incomplete combustion, hydrocarbons (properly indicated as C_xH_y, but typically shown simply as "HC" on emissions-test slips) from unburnt fuel, nitrogen oxides (NO_x) from excessive combustion temperatures, and particulate matter (mostly soot) from incomplete combustion.

Exhaust gas temperature (EGT) is important to the functioning of the catalytic converter of an internal combustion engine. It may be measured by an exhaust gas temperature gauge. EGT is also a measure of engine health in gas-turbine engines (see below).

File:Exhaust.jpg

During the first two minutes after starting the engine of a car that has not been operated for several hours, the amount of emissions can be very high. This occurs for two main reasons:

• Rich air-fuel ratio requirement in cold engines: When a cold engine is started, the fuel does not vaporize completely, creating higher emissions of hydrocarbons and carbon monoxide, which diminishes only as the engine reaches operating temperature. The duration of this start-up phase has been reduced by advances in materials and technology, including computer-controlled fuel injection, shorter intake lengths, and pre-heating of fuel and/or inducted air.
• Inefficient catalytic converter under cold conditions: Catalytic converters are very inefficient until warmed up to their operating temperature. This time has been much reduced by moving the converter closer to the exhaust manifold and even more so placing a small yet quick-to-heat-up converter directly at the exhaust manifold. The small converter handles the start-up emissions, which allows enough time for the larger main converter to heat up. Further improvements can be realised in many ways,Pulkrabek W.W. (2004) Engineering Fundamentals of the Internal Combustion Engine. Pearson Prentice Hall, new Jersey including electric heating, thermal battery, chemical reaction preheating, flame heating and superinsulation.

Comparable with the European emission standards EURO III as it was applied in October 2000

In 2000, the United States Environmental Protection Agency began to implement more stringent emissions standards for light duty vehicles. The requirements were phased in beginning with 2004 vehicles and all new cars and light trucks were required to meet the updated standards by the end of 2007.

Image:Automobile exhaust gas.jpg]]

{{see also|Automobile emissions control}}

In spark-ignition engines the gases resulting from combustion of the fuel and air mix are called exhaust gases. The composition varies from petrol to diesel engines, but is around these levels:

The 10% oxygen for "diesel" is likely if the engine was idling, e.g. in a test rig. It is much less if the engine is running under load, although diesel engines always operate with an excess of air over fuel. {{citation needed|date=July 2016}}

The CO content for petrol engines varies from ≈15 ppm for well tuned engine with fuel injection and a catalytic converter up to 100,000 ppm (10%) for a richly tuned carburetor engine, such as typically found on small generators and garden equipment.{{cite web|url=https://www.abe.iastate.edu/extension-and-outreach/carbon-monoxide-poisoning-operating-fossil-fuel-engines-inside-buildings-aen-206/|title=Carbon Monoxide Poisoning: Operating Fossil Fuel Engines Inside Buildings (AEN-206)|website=Department of Agricultural and Biosystems Engineering|accessdate=18 June 2023}}

Exhaust gas from an internal combustion engine whose fuel includes nitromethane will contain nitric acid vapour, which is corrosive, and when inhaled causes a muscular reaction making it impossible to breathe. People who are likely to be exposed to it should wear a gas mask.{{cite web |url=http://www.turbofast.com.au/racefuel6.html |title=Race Fuel - Nitromethane |website=www.turbofast.com.au |access-date=23 January 2008 |archive-date=13 March 2018 |archive-url=https://web.archive.org/web/20180313151211/http://www.turbofast.com.au/racefuel6.html |url-status=dead }}

{{See also|Soot}}

{{Excerpt|Diesel exhaust|only=paragraphs}}

In aircraft gas turbine engines, "exhaust gas temperature" (EGT) is a primary measure of engine health. Typically the EGT is compared with a primary engine power indication called "engine pressure ratio" (EPR). For example: at full power EPR there will be a maximum permitted EGT limit. Once an engine reaches a stage in its life where it reaches this EGT limit, the engine will require specific maintenance in order to rectify the problem. The amount the EGT is below the EGT limit is called EGT margin. The EGT margin of an engine will be greatest when the engine is new, or has been overhauled. For most airlines, this information is also monitored remotely by the airline maintenance department by means of ACARS.

Image:Jet exhaust by David Shankbone.jpgs.]]

In jet engines and rocket engines, exhaust from propelling nozzles which in some applications shows shock diamonds.{{Citation needed|date=April 2009}}

Flue gas is that emitted from ovens, furnaces and boilers.

In steam engine terminology the exhaust is steam that is now so low in pressure that it can no longer do useful work.

Image:SmogNY.jpg as viewed from the World Trade Center in 1988]]

Mono-nitrogen oxides NO and NO₂ (NOx) (whether produced this way or naturally by lightning) react with ammonia, moisture, and other compounds to form nitric acid vapor and related particles. Small particles can penetrate deeply into sensitive lung tissue and damage it, causing premature death in extreme cases. Inhalation of NO species increases the risk of lung cancer{{cite journal|last1=Hamra|first1=GB|last2=Laden|first2=F|last3=Cohen|first3=AJ|last4=Raaschou-Nielsen|first4=O|last5=Brauer|first5=M|last6=Loomis|first6=D|title=Lung Cancer and Exposure to Nitrogen Dioxide and Traffic: A Systematic Review and Meta-Analysis.|journal=Environmental Health Perspectives|date=November 2015|volume=123|issue=11|pages=1107–12|doi=10.1289/ehp.1408882|pmid=25870974|pmc=4629738}} and colorectal cancer.{{cite journal|last1=Turner|first1=MC|last2=Krewski|first2=D|last3=Diver|first3=WR|last4=Pope CA|first4=3rd|last5=Burnett|first5=RT|last6=Jerrett|first6=M|last7=Marshall|first7=JD|last8=Gapstur|first8=SM|title=Ambient Air Pollution and Cancer Mortality in the Cancer Prevention Study II.|journal=Environmental Health Perspectives|date=21 August 2017|volume=125|issue=8|page=087013|doi=10.1289/EHP1249|pmid=28886601|pmc=5783657}} {{open access}} and inhalation of such particles may cause or worsen respiratory diseases such as emphysema and bronchitis and heart disease.{{cite web | url = http://www.epa.gov/air/nitrogenoxides/health.html | work = Nitrogen Dioxide | title = Health | publisher = United States Environmental Protection Agency | date = 14 February 2013}}{{cite web | url = http://www.epa.gov/air/noxfacts.pdf | title = The Regional Transport of Ozone: New EPA Rulemaking on Nitrogen Oxide Emissions (EPA-456/F-98-006) | publisher = United States Environmental Protection Agency | date = September 1998}}{{cite web | url = http://www.epa.gov/cgi-bin/broker?_service=data&_debug=0&_program=dataprog.national_1.sas&polchoice=NOX | title = State and County Emission Summaries: Nitrogen Oxides | work = Air emission sources | publisher = United States Environmental Protection Agency | date = 25 October 2013}}

In a 2005 U.S. EPA study the largest emissions of {{NOx}} came from on road motor vehicles, with the second largest contributor being non-road equipment which is mostly gasoline and diesel stations.

The resulting nitric acid may be washed into soil, where it becomes nitrate, which is useful to growing plants.

File:Sources of Volatile Organic Compounds.PNG

When oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight, ground level ozone is formed, a primary ingredient in smog. A 2005 U.S. EPA report gives road vehicles as the second largest source of VOCs in the U.S. at 26% and 19% are from non road equipment which is mostly gasoline and diesel stations. 27% of VOC emissions are from solvents which are used in the manufacturer of paints and paint thinners and other uses.{{cite web | url = http://toxics.usgs.gov/definitions/vocs.html | title = Volatile Organic Compounds (VOCs) | publisher = United States Geological Survey (USGS) | work = Toxic Substances Hydrology Program | date = 12 April 2013 | access-date = 2 June 2014 | archive-date = 5 September 2015 | archive-url = https://web.archive.org/web/20150905205650/http://toxics.usgs.gov/definitions/vocs.html | url-status = dead }}

Ozone is beneficial in the upper atmosphere,{{cite web|url=http://www.epa.gov/ozone/basicinfo.html|title=Ozone Layer Protection - US EPA|first=US|last=EPA, OAR, OAP, SPD|website=US EPA}} but at ground level ozone irritates the respiratory system, causing coughing, choking, and reduced lung capacity.{{cite web|url=http://www.epa.gov/airquality/ozonepollution/health.html|title = Air Quality Planning and Standards}} It also has many negative effects throughout the ecosystem.{{cite web |url=http://www.epa.gov/groundlevelozone/ecosystem.html |title=Ecosystem Effects {{!}} Ground-level Ozone {{!}} US EPA |website=www.epa.gov |url-status=dead |archive-url=https://web.archive.org/web/20120518004831/http://www.epa.gov/groundlevelozone/ecosystem.html |archive-date=2012-05-18}}

File:MOPITT www.acd.ucar.edu.Web-201003-mixing ratio at surface.png satellite computer image of carbon monoxide March 2010]]

Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries.{{cite journal|author=Omaye ST.| title=Metabolic modulation of carbon monoxide toxicity|journal=Toxicology|year=2002|pages=139–150|volume=180|issue=2|doi=10.1016/S0300-483X(02)00387-6|pmid=12324190}} Carbon monoxide is colorless, odorless and tasteless, but highly toxic. It combines with hemoglobin to produce carboxyhemoglobin, which blocks the transport of oxygen. At concentrations above 1000ppm it is considered immediately dangerous and is the most immediate health hazard from running engines in a poorly ventilated space. In 2011, 52% of carbon monoxide emissions were created by mobile vehicles in the U.S.{{cite web | url = http://www.epa.gov/cgi-bin/broker?_service=data&_debug=0&_program=dataprog.national_1.sas&polchoice=CO | work = Air Emission Sources | title = State and County Emission Summaries: Carbon Monoxide | date = 25 October 2013 | publisher = United States Environmental Protection Agency}}

Chronic (long-term) exposure to benzene (C₆H₆) damages bone marrow. It can also cause excessive bleeding and depress the immune system, increasing the chance of infection. Benzene causes leukemia and is associated with other blood cancers and pre-cancers of the blood.{{cite web | url = http://www.theaa.com/motoring_advice/car-buyers-guide/cbg_toxics.html | title = Exhaust emissions: What comes out of your car's exhaust? | date = 23 February 2012 | publisher = Automobile Association Developments Limited}}{{Cite journal | url = http://www.browardcountymufflers.com/wp-content/uploads/2014/07/f02004.pdf | title = Air Toxics from Motor Vehicles | journal = Transportation and Air Quality | publisher = United States Environmental Protection Agency}}

The health effects of inhaling airborne particulate matter have been widely studied in humans and animals and include asthma, lung cancer, cardiovascular issues, premature death.{{cite journal|last1=Kurt|first1=OK|last2=Zhang|first2=J|last3=Pinkerton|first3=KE|title=Pulmonary health effects of air pollution.|journal=Current Opinion in Pulmonary Medicine|date=March 2016|volume=22|issue=2|pages=138–43|doi=10.1097/MCP.0000000000000248|pmid=26761628|pmc=4776742}}{{cite journal|last1=Bourdrel|first1=T|last2=Bind|first2=MA|last3=Béjot|first3=Y|last4=Morel|first4=O|last5=Argacha|first5=JF|title=Cardiovascular effects of air pollution.|journal=Archives of Cardiovascular Diseases|date=November 2017|volume=110|issue=11|pages=634–642|doi=10.1016/j.acvd.2017.05.003|pmid=28735838|pmc=5963518}}{{cite journal|last1=Babadjouni|first1=RM|last2=Hodis|first2=DM|last3=Radwanski|first3=R|last4=Durazo|first4=R|last5=Patel|first5=A|last6=Liu|first6=Q|last7=Mack|first7=WJ|title=Clinical effects of air pollution on the central nervous system; a review.|journal=Journal of Clinical Neuroscience|date=September 2017|volume=43|pages=16–24|doi=10.1016/j.jocn.2017.04.028|pmid=28528896|pmc=5544553}} Because of the size of the particles, they can penetrate the deepest part of the lungs.Region 4: Laboratory and Field Operations — PM 2.5 (2008).PM 2.5 Objectives and History. U.S. Environmental Protection Agency. A 2011 UK study estimates 90 deaths per year due to passenger vehicle PM.{{cite journal| doi=10.1021/es060517w| title=Air Quality Impacts of Climate Mitigation: UK Policy and Passenger Vehicle Choice| year=2007| last1=Mazzi| first1=Eric A.| last2=Dowlatabadi| first2=Hadi| journal=Environmental Science & Technology| volume=41| pages=387–92| issue=2| pmid=17310696| bibcode=2007EnST...41..387M| doi-access=free}} In a 2006 publication, the U.S. Federal Highway Administration (FHWA) state that in 2002 about 1 per-cent of all PM₁₀ and 2 per-cent of all PM_2.5 emissions came from the exhaust of on-road motor vehicles (mostly from diesel engines).{{cite web |url=http://www.fhwa.dot.gov/environment/aqfactbk/page10.htm |archive-url=https://web.archive.org/web/20060616142403/http://www.fhwa.dot.gov/environment/aqfactbk/page10.htm |url-status=dead |archive-date=16 June 2006 |title=Transportation Air Quality: Selected Facts and Figures |year=2006 |publisher=U.S. Department of Transportation Federal Highway Commission |access-date=2010-04-14}} In Chinese, European, and Indian markets, both diesel and gasoline vehicles are required to have a tailpipe filter installed, while the United States has mandated it for diesel only. In 2022, British testing specialist Emissions Analytics estimated that the 300 million or so gasoline vehicles in the US over the subsequent decade would emit around 1.6 septillion harmful particles.{{cite news |last1=Lewis |first1=Barbara |last2=Carey |first2=Nick |title=Lacking filters, U.S. cars set to emit a septillion more particles - research |url=https://www.reuters.com/business/autos-transportation/lacking-filters-us-cars-set-emit-septillion-more-particles-research-2022-04-27/ |work=Reuters |date=27 April 2022 |language=en}}

Carbon dioxide is a greenhouse gas. Motor vehicle CO₂ emissions are part of the anthropogenic contribution to the growth of CO₂ concentrations in the atmosphere which according to the vast majority of the scientific community is causing climate change.[http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_FINAL.pdf IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Motor vehicles are calculated to generate about 20% of the European Union's man-made CO₂ emissions, with passenger cars contributing about 12%.{{cite web

|url=http://europa.eu/rapid/pressReleasesAction.do?reference=IP/07/155&format=HTML&aged=0&language=EN&guiLanguage=en

|title=Commission plans legislative framework to ensure the EU meets its target for cutting CO2 emissions from cars

|date=2007-02-07

|publisher=European Commission}} European emission standards limit the CO₂ emissions of new passenger cars and light vehicles. The European Union average new car CO₂ emissions figure dropped by 5.4% in the year to the first quarter of 2010, down to 145.6 g/km.{{cite web

|url=http://www.autoevolution.com/news/eu-average-new-car-co2-emissions-down-54-percent-in-q1-19385.html

|title=EU Average New Car CO2 Emissions Down 5.4 Percent in Q1

|date=2010-04-19

|publisher=SoftNews NET

|work=autoevolution}}

Vehicle exhaust contains much water vapour.

There has been research into ways that troops in deserts can recover drinkable water from their vehicles' exhaust gases.{{cite web|url=https://www.google.co.uk/search?q=recovering+water+from+diesel+exhaust&ie=utf-8&oe=utf-8&gws_rd=cr&ei=qI7hVsOSHYr3UKvnruAE#q=recovering+water+from+exhaust|title=recovering water from diesel exhaust - Google Search|website=www.google.co.uk}}

{{see also | Air suction valve | Vehicle-specific power}}

Emission standards focus on reducing pollutants contained in the exhaust gases from vehicles as well as from industrial flue gas stacks and other air pollution exhaust sources in various large-scale industrial facilities such as petroleum refineries, natural gas processing plants, petrochemical plants and chemical production plants.{{cite web|url=http://www.epa.gov/oar/oaqps/peg_caa/pegcaain.html|title=EPA Plain English Guide to the Clean Air Act|accessdate=18 June 2023}}[http://www.epa.gov/ttn/chief/ap42/index.html US EPA Publication] AP 42, Fifth Edition, Compilation of Air Pollutant Emission Factors However, these are often referred to as flue gases. Catalytic converters in cars intend to break down the pollution of exhaust gases using a catalyst. Scrubbers in ships intend to remove the sulfur dioxide (SO₂) of marine exhaust gases. The regulations on marine sulfur dioxide emissions are tightening, however only a small number of special areas worldwide have been designated for low sulfur diesel fuel use only.

Air pollution from fossil fuel use by industry, power generation, and transportation is estimated to kill over 5 million people each year.{{Cite journal |last=Lelieveld |first=Jos |last2=Haines |first2=Andy |last3=Burnett |first3=Richard |last4=Tonne |first4=Cathryn |last5=Klingmüller |first5=Klaus |last6=Münzel |first6=Thomas |last7=Pozzer |first7=Andrea |date=2023-11-29 |title=Air pollution deaths attributable to fossil fuels: observational and modelling study |url=https://www.bmj.com/content/383/bmj-2023-077784 |journal=BMJ |language=en |volume=383 |pages=e077784 |doi=10.1136/bmj-2023-077784 |issn=1756-1833 |pmid=38030155|hdl=10230/60465 |hdl-access=free }} A 2013 study by the Massachusetts Institute of Technology (MIT) indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions.{{cite journal |last1=Caiazzo |first1=Fabio |last2=Ashok |first2=Akshay |last3=Waitz |first3=Ian A. |last4=Yim |first4=Steve H.L. |last5=Barrett |first5=Steven R.H. |date=November 2013 |title=Air pollution and early deaths in the United States. Part I: Quantifying the impact of major sectors in 2005 |journal=Atmospheric Environment |volume=79 |pages=198–208 |bibcode=2013AtmEn..79..198C |doi=10.1016/j.atmosenv.2013.05.081}} According to another study from the same university, traffic fumes alone cause the death of 5,000 people every year just in the United Kingdom.{{cite news |author=Roland Pease |title=Traffic pollution kills 5,000 a year in UK, says study |url=https://www.bbc.com/news/science-environment-17704116 |work=BBC News}}

Researchers from the University of California, Los Angeles School of Public Health say preliminary results of their statistical study of children listed in the California Cancer Registry born between 1998 and 2007 found that traffic pollution may be associated with a 5% to 15% increase in the likelihood of some cancers.{{cite news | url = http://health.usnews.com/health-news/news/articles/2013/04/09/smog-exposure-during-pregnancy-might-raise-childs-cancer-risk-study | title = Smog Exposure During Pregnancy Might Raise Child's Cancer Risk: Study | date = 9 April 2013 | first = Steven | last = Reinberg | newspaper = USNews}} A World Health Organization study found that diesel fumes cause an increase in lung cancer.{{cite web|url=https://www.iarc.who.int/news-events/iarc-diesel-engine-exhaust-carcinogenic/|title=IARC Diesel engine exhaust carcinogenic |website=iarc.fr|access-date=18 June 2023}}

The California Air Resources Board found in studies that 50% or more of the air pollution (smog) in Southern California is due to car emissions.{{Citation needed|date=April 2010}} Concentrations of pollutants emitted from combustion engines may be particularly high around signalized intersections because of idling and accelerations. Computer models often miss this kind of detail.{{cite journal

| last = Int Panis L| title = Modelling instantaneous traffic emission and the influence of traffic speed limits

| journal = Science of the Total Environment | volume = 371 | issue = 1–3 | pages = 270–285 | year = 2006 | doi =10.1016/j.scitotenv.2006.08.017 | pmid = 17049967

|display-authors=etal| bibcode =2006ScTEn.371..270I}}

{{Div col|small=no}}

• Air pollution#Most polluted cities
• Alternative propulsion
• Atmospheric dispersion modeling
• Automobile#Environmental impact
• Clean Air Act
• Congestion pricing
• Emission standard
• Environmental effects of transport
• European emission standards
• Flue gas
• Kyoto Protocol
• Landfill gas
• Low-emission zone
• Mobile source air pollution
• Motor vehicle emissions and pregnancy
• Rolling coal
• Space jellyfish
• United States emission standards
• Vehicle emissions control

{{Div col end}}

{{reflist}}

• [http://www.arb.ca.gov/research/health/health.htm Health and Air Pollution] Publication of the California Air Resources Board
• {{cite news | url = http://www.huffingtonpost.com/2008/11/13/california-air-pollution-_n_143521.html | title = California Air Pollution Kills More People Than Car Crashes, Study Shows | first = Tracie | last = Cone | date = 13 November 2008 | newspaper = Huffington Post}}
• {{cite web | url = http://www.nutramed.com/environment/carschemicals.htm | title = Automotive Exhaust Chemicals: disease causing effects | work = Alpha Online | publisher = Environmed Research Inc. | url-status = dead | archive-url = https://web.archive.org/web/20140705211720/http://nutramed.com/environment/carschemicals.htm | archive-date = 2014-07-05 }}
• {{cite web | url = http://www.ucsusa.org/clean_vehicles/vehicle_impacts/cars_pickups_and_suvs/cars-trucks-air-pollution.html | publisher = Union of Concerned Scientists | title = Cars, Trucks, and Air Pollution | date = 3 September 2013 | work = Clean Vehicles}}
• About diesel exhaust:
• [https://www.osha.gov/SLTC/dieselexhaust/ U.S. Department of Labor Occupational Safety & Health Administration: Safety and Health Topics: Diesel Exhaust]
• [https://www.osha.gov/SLTC/dieselexhaust/chemical.html Partial List of Chemicals Associated with Diesel Exhaust]
• [https://web.archive.org/web/20051031101139/http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s069dies.pdf Diesel Exhaust Particulates: Reasonably Anticipated to Be A Human Carcinogen]
• [http://ajrccm.atsjournals.org/cgi/content/full/159/3/702 Scientific Study of Harmful Effects of Diesel Exhaust: Acute Inflammatory Responses in the Airways and Peripheral Blood After Short-Term Exposure to Diesel Exhaust in Healthy Human Volunteers]
• [https://web.archive.org/web/20080414094408/http://www.losh.ucla.edu/catalog/factsheets/diesel_english.pdf Diesel exhaust: what you need to know]

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