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Exhaust gas orflue gas is emitted as a result of thecombustion of fuels such asnatural gas,gasoline (petrol),diesel fuel,fuel oil, biodiesel blends,[1] orcoal. According to the type of engine, it is discharged into the atmosphere through anexhaust pipe,flue gas stack, orpropelling nozzle. It often disperses downwind in a pattern called anexhaust plume.
It is a major component ofmotor vehicle emissions (and from stationaryinternal combustion engines), which can also includecrankcase blow-by and evaporation of unused gasoline.
Air pollution from burningfossil fuels is estimated to kill over 5 million people each year. Motor vehicle emissions are a common source of air pollution and are a major ingredient in the creation ofsmog in some large cities.
The largest part of most combustion gas isnitrogen (N2), water vapor (H2O) (except with pure-carbon fuels), andcarbon dioxide (CO2) (except for fuels without carbon); these are not toxic or noxious (although water vapor and carbon dioxide aregreenhouse gases that contribute toclimate change). A relatively small part of combustion gas is undesirable, noxious, or toxic substances, such ascarbon monoxide (CO) from incomplete combustion,hydrocarbons (properly indicated as CxHy, but typically shown simply as "HC" on emissions-test slips) from unburnt fuel,nitrogen oxides (NOx) from excessive combustion temperatures, andparticulate matter (mostlysoot) from incomplete combustion.
Exhaust gas temperature (EGT) is important to the functioning of thecatalytic converter of aninternal combustion engine. It may be measured by anexhaust gas temperature gauge. EGT is also a measure of engine health in gas-turbine engines (see below).
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:
| Component | Emission Rate | Annual pollution emitted |
|---|---|---|
| Hydrocarbons | 2.80 grams/mile (1.75 g/km) | 77.1 pounds (35.0 kg) |
| Carbon monoxide | 20.9 grams/mile (13.06 g/km) | 575 pounds (261 kg) |
| NOx | 1.39 grams/mile (0.87 g/km) | 38.2 pounds (17.3 kg) |
| Carbon dioxide - greenhouse gas | 415 grams/mile (258 g/km) | 11,450 pounds (5,190 kg) |
Comparable with theEuropean emission standards EURO III as it was applied in October 2000
In 2000, the United StatesEnvironmental Protection Agency began to implement more stringentemissions 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.
| Component | Emission Rate | Annual pollution emitted |
|---|---|---|
| NMOG (Volatile organic compounds) | 0.075 grams/mile (0.046 g/km) | 2.1 pounds (0.95 kg) |
| Carbon Monoxide | 3.4 grams/mile (2.1 g/km) | 94 pounds (43 kg) |
| NOX | 0.05 grams/mile (0.0305 g/km) | 1.4 pounds (0.64 kg) |
| Formaldehyde | 0.015 grams/mile (0.0092 g/km) | 0.41 pounds (0.19 kg) |
Inspark-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:
| Compound | % of total | |
|---|---|---|
| Petrol | Diesel | |
| Nitrogen | 71 | 67 |
| Carbon dioxide | 14 | 12 |
| Water vapor | 13 | 11 |
| Oxygen | 10 | |
| Trace elements[citation needed] | < 0.6 | ~ 0.3 |
| Nitrogen oxides | < 0.25 | < 0.15 |
| Carbon monoxide | 1 - 2 | < 0.045 |
| Particulate matter | < 0.045 | |
| Hydrocarbons | < 0.25 | < 0.03 |
| Sulfur dioxide | Possible traces | < 0.03 |
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]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.[6]
Exhaust gas from an internal combustion engine whose fuel includesnitromethane will containnitric 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 agas mask.[7]
Diesel exhaust is the exhaust gas produced by adiesel engine, plus any containedparticulates. Its composition may vary with the fuel type, rate of consumption or speed of engine operation (e.g., idling or at speed or under load), and whether the engine is in an on-road vehicle, farm vehicle, locomotive, marine vessel, or stationary generator or other application.[8]
Diesel exhaust causeslung cancer and other diseases such asasthma, and many premature deaths.[9][10][11] Methods exist to reduce nitrogen oxides (NOx) and particulate matter (PM) in the exhaust.
Some countries have set a date tostop selling diesel vehicles, and some city centres will ban diesel cars.[12]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 ofACARS.
Injet engines androcket engines, exhaust frompropelling nozzles which in some applications showsshock diamonds.[citation needed]
Flue gas is that emitted from ovens, furnaces and boilers.
Insteam engine terminology the exhaust is steam that is now so low in pressure that it can no longer do useful work.
Mono-nitrogen oxides NO and NO2 (NOx) (whether produced this way or naturally bylightning) react withammonia, moisture, and other compounds to formnitric 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 oflung cancer[13] and colorectal cancer.[14] and inhalation of such particles may cause or worsen respiratory diseases such asemphysema andbronchitis and heart disease.[15][16][17]
In a 2005U.S. EPA study the largest emissions ofNOx came from on road motor vehicles, with the second largest contributor beingnon-road equipment which is mostly gasoline and diesel stations.[17]
The resulting nitric acid may be washed into soil, where it becomesnitrate, which is useful to growing plants.
When oxides of nitrogen (NOx) andvolatile organic compounds (VOCs) react in the presence of sunlight, ground levelozone is formed, a primary ingredient insmog. 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.[18] 27% of VOC emissions are from solvents which are used in the manufacturer of paints and paint thinners and other uses.[19]
Ozone is beneficial in the upper atmosphere,[20] but at ground level ozone irritates therespiratory system, causing coughing, choking, and reduced lung capacity.[21] It also has many negative effects throughout the ecosystem.[22]
Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries.[23]Carbon monoxide is colorless, odorless and tasteless, but highly toxic. It combines withhemoglobin to producecarboxyhemoglobin, 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.[24]
Chronic (long-term) exposure tobenzene (C6H6) damagesbone marrow. It can also cause excessive bleeding and depress theimmune system, increasing the chance ofinfection. Benzene causes leukemia and is associated with other blood cancers and pre-cancers of the blood.[25][26]
Thehealth effects of inhalingairborne particulate matter have been widely studied in humans and animals and includeasthma,lung cancer, cardiovascular issues, prematuredeath.[27][28][29] Because of the size of the particles, they can penetrate the deepest part of the lungs.[30] A 2011 UK study estimates 90 deaths per year due to passenger vehicle PM.[31] In a 2006 publication, theU.S. Federal Highway Administration (FHWA) state that in 2002 about 1 per-cent of all PM10 and 2 per-cent of all PM2.5 emissions came from the exhaust of on-road motor vehicles (mostly fromdiesel engines).[32] In Chinese, European, and Indian markets, both diesel and gasoline vehicles are required to have atailpipe 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.[33]
Carbon dioxide is agreenhouse 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 causingclimate change.[34] Motor vehicles are calculated to generate about 20% of the European Union's man-made CO2 emissions, with passenger cars contributing about 12%.[35]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 145.6g/km.[36]
Vehicle exhaust contains muchwater vapour.
There has been research into ways that troops in deserts can recover drinkable water from their vehicles' exhaust gases.[37]
Emission standards focus on reducingpollutants contained in the exhaust gases from vehicles as well as from industrial flue gas stacks and otherair pollution exhaust sources in various large-scale industrial facilities such aspetroleum refineries,natural gas processing plants,petrochemical plants andchemical production plants.[38][39] However, these are often referred to asflue 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.[40] A 2013 study by theMassachusetts Institute of Technology (MIT) indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions.[41] 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.[42]
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.[43] AWorld Health Organization study found that diesel fumes cause an increase in lung cancer.[44]
TheCalifornia Air Resources Board found in studies that 50% or more of theair pollution (smog) inSouthern California is due to car emissions.[citation needed] 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.[45]
composition can vary markedly with fuel composition, engine type, operating conditions ... combustion of petroleum fuel produces primarily carbon dioxide, water, and nitrogen ... The health risks lie in the small, invisible or poorly visible particles ... carbon (EC) core of diesel soot ... serves as a nucleus for condensation of organic compounds from unburned or incompletely burned fuel ... it still appears that nitrated PAHs are the most predominant bacterial mutagens
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