Motor vehicle emissions

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Typical appearance of car exhaust on a correctly maintained and warmed car. 99.4% of pollutant gases are invisible1

Motor vehicle emissions are composed of the by-products that comes out of the exhaust systems or other emissions such as gasoline evaporation. These emissions contribute to air pollution and are a major ingredient in the creation of smog in some large cities.2345 A 2013 study by MIT indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions.6

Cold engines

Steam from tailpipe of cold car

During the first couple of 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: Upon starting a cold engine, the fuel does not vaporise completely, creating higher emissions of Hydrocarbons, Nitrogen Oxides 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 up to their operating temperature. This time has been much reduced by moving the converter closer to the exhaust manifold and even moreso 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,7 including electric heating, thermal battery, chemical reaction preheating, flame heating and superinsulation.

Main motor vehicle emissions


Smog in New York City as viewed from the World Trade Center in 1988. A 2009 report indicates that, despite the City's air being close to the EPA's short-term ozone standard, that New Yorkers still face a 25 per-cent increased risk of dying from lung disease.8

Mono-nitrogen oxides NO and NO2 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 such particles may cause or worsen respiratory diseases such as emphysema and bronchitis. It may also aggravate existing heart disease.91011 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.11

Volatile organic compounds

Non road equipment is mostly gasoline and diesel stations.12

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.12 27% of VOC emissions are from solvents which are used in the manufacturer of paints and paint thinners and other uses.13


Ozone is beneficial in the upper atmosphere,14 but at ground level, ozone irritates the respiratory system, causing coughing, choking, and reduced lung capacity.15 and has many bad effects throughout the ecosystem.16

Carbon monoxide (CO)

MOPITT satellite computer image of carbon monoxide March 2010.

Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries.17 Carbon monoxide is colorless, odorless and tasteless, but highly toxic. It combines with hemoglobin to produce carboxyhemoglobin, which is ineffective for delivering oxygen to bodily tissues. In the U.S. 60% of carbon monoxide is caused by on road vehicles.18

Hazardous air pollutants (toxics)

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.1920

Particulate matter (PM10 and PM2.5)

The health effects of inhaling airborne particulate matter have been widely studied in humans and animals and include asthma, lung cancer, cardiovascular issues, and premature death. Because of the size of the particles, they can penetrate the deepest part of the lungs.21 A 2011 UK study estimates 90 deaths per year due to passenger vehicle PM.22 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 PM2.5 emissions came from the exhaust of on-road motor vehicles (mostly from diesel engines).23

Carbon dioxide (CO2)

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 is believed by a majority of scientists to play a significant part in climate changecitation needed. Motor vehicles are calculated to generate about 20% of the European Union's man-made CO2 emissions, with passenger cars contributing about 12%.24 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.25

Passenger car emissions summary

U.S. Environmental Protection Agency estimates of average passenger car emissions in the United States for July 200026
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 - Green house gas 0.916 pounds per mile (258 g/km) 11,450 pounds (5,190 kg)

Comparable with the european emission standards EURO III as it was applied on 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.

United States Light-Duty Vehicle, Light-Duty Truck, and Medium-Duty Passenger Vehicle—Tier 2 Exhaust Emission Standards (for Bin 5)27
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)

Health Studies

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.28 A World Health Organization study found that diesel fumes cause an increase in lung cancer.29

Localised effects

The California Air Resources Board (C.A.R.B.) found in studies that 50% or more of the air pollution (smog) in Southern California is due to car emissions.citation needed30

See also


  1. ^ "Motor vehicle pollution". Queensland Government. 4 April 2013. 
  2. ^ "EPA Tools Available as Summer Smog Season Starts" (Press release). Boston, Massachusetts: United States Environmental Protection Agency. 30 April 2008. 
  3. ^ "Sprawl Report 2001: Measuring Vehicle Contribution to Smog". Sierra Club. 2001. 
  4. ^ "Smog - Causes". The Environment: A Global Challenge. Retrieved 25 October 2013. 
  5. ^ Smog — Who Does It Hurt? What You Need to Know About Ozone and Your Health (EPA-452/K-99-001) (PDF). United States Environmental Protection Agency. July 1999 
  6. ^ Caiazzo, Fabio; Ashok, Akshay; Waitz, Ian A.; Yim, Steve H.L.; Barrett, Steven R.H. (November 2013). "Air pollution and early deaths in the United States. Part I: Quantifying the impact of major sectors in 2005". Atmospheric Environment (Elsevier) 79: 198–208. Bibcode:2013AtmEn..79..198C. doi:10.1016/j.atmosenv.2013.05.081. Retrieved 25 October 2013. 
  7. ^ Pulkrabek W.W. (2004) Engineering Fundamentals of the Internal Combustion Engine. Pearson Prentice Hall, new Jersey
  8. ^ Bravender, Robin (2009-03-12). "Study links smog exposure to premature death". The New York Times. 
  9. ^ "Health". Nitrogen Dioxide. United States Environmental Protection Agency. 14 February 2013. 
  10. ^ "The Regional Transport of Ozone: New EPA Rulemaking on Nitrogen Oxide Emissions (EPA-456/F-98-006)" (PDF). United States Environmental Protection Agency. September 1998. 
  11. ^ a b "State and County Emission Summaries: Nitrogen Oxides". Air emission sources. United States Environmental Protection Agency. 25 October 2013. 
  12. ^ a b "State and County Emission Summaries: Volatile Organic Compounds". Air emission sources. United States Environmental Protection Agency. 25 October 2013. 
  13. ^ "Volatile Organic Compounds (VOCs)". Toxic Substances Hydrology Program. United States Geological Survey (USGS). 12 April 2013. 
  14. ^
  15. ^
  16. ^
  17. ^ Omaye ST. (2002). "Metabolic modulation of carbon monoxide toxicity". Toxicology 180 (2): 139–150. doi:10.1016/S0300-483X(02)00387-6. PMID 12324190. 
  18. ^ "State and County Emission Summaries: Carbon Monoxide". Air Emission Sources. United States Environmental Protection Agency. 25 October 2013. 
  19. ^ "Exhaust emissions: What comes out of your car's exhaust?". Automobile Association Developments Limited. 23 February 2012. 
  20. ^ Transportation and Air Quality (United States Environmental Protection Agency) |url= missing title (help) dead link
  21. ^ Region 4: Laboratory and Field Operations — PM 2.5 (2008).PM 2.5 Objectives and History. U.S. Environmental Protection Agency.
  22. ^ Mazzi, Eric A.; Dowlatabadi, Hadi (2007). "Air Quality Impacts of Climate Mitigation: UK Policy and Passenger Vehicle Choice". Environmental Science & Technology 41 (2): 387. doi:10.1021/es060517w. 
  23. ^ "Transportation Air Quality: Selected Facts and Figures". U.S. Department of Transportation Federal Highway Commission. 2006. Retrieved 2010-04-14. 
  24. ^ "Commission plans legislative framework to ensure the EU meets its target for cutting CO2 emissions from cars". European Commission. 2007-02-07. 
  25. ^ "EU Average New Car CO2 Emissions Down 5.4 Percent in Q1". autoevolution. SoftNews NET. 2010-04-19. 
  26. ^ Transportation and Air Quality. United States Environmental Protection Agency |url= missing title (help). dead link
  27. ^ "Light-Duty Vehicle, Light-Duty Truck, and Medium-Duty Passenger Vehicle -- Tier 2 Exhaust Emission Standards". Emission Standards Reference Guide. United States Environmental Protection Agency. 14 November 2012. 
  28. ^ Reinberg, Steven (9 April 2013). "Smog Exposure During Pregnancy Might Raise Child's Cancer Risk: Study". USNews. 
  29. ^
  30. ^ Note: this Wikipedia page also needs the same reference: Los Angeles smog#The Cause of Smog in Los Angeles

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