Vehicle emissions control

Vehicle emissions inspection station in the US

Vehicle emissions control is the study and practice of reducing the motor vehicle emissions -- emissions produced by [motor vehicle]]s, especially internal combustion engines.

Emissions of many air pollutants have been shown to have variety of negative effects on public health and the natural environment. Emissions that are principal pollutants of concern include:

Hydrocarbons - A class of burned or partially burned fuel, hydrocarbons are toxins and are a major contributor to smog, which can be a major problem in urban areas. Prolonged exposure to hydrocarbons contributes to asthma, liver 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 toxic, but is more difficult to break down in a catalytic converter, so in effect a "non-methane hydrocarbon" standard can be considered to be looser. Since methane is a greenhouse gas, interest is rising in how to eliminate emissions of it.
Carbon monoxide (CO) - A product of incomplete combustion, carbon monoxide reduces the blood's ability to carry oxygen; overexposure (carbon monoxide poisoning) may be fatal.
Nitrogen oxides (NO_x) - Generated when nitrogen in the air reacts with oxygen at the high temperature and pressure inside the engine. NO_x is a precursor to smog and acid rain. NO_x is a mixture of NO and NO₂. NO₂ destroys resistance to respiratory infection. For dogs most of the nitrogen dioxide is removed in the nasal cavity. Jumbo vehicles and delivery trucks blow hot exhaust, containing life dangerous quantities of NO₂ into the atmosphere.
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.
Sulfur oxide (SO_x) - A general term for oxides of sulphur, which are emitted from motor vehicles burning fuel containing a high concentration of sulphur.
Volatile Organic Compounds (VOHs) - Organic compounds which typically have a boiling point less than or equal to 250 °C; for example Chlorofluorocarbons (CFCs) and Formaldehyde.

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Regulatory agencies

The agencies charged with regulating exhaust emissions vary from jurisdiction to jurisdiction, even in the same country. For example, in the United States, overall responsibility belongs to the EPA, but due to special requirements of the State of California, emissions in California are regulated by the Air Resources Board. In Texas, the Texas Railroad Commission is responsible for regulating emissions from LPG-fueled rich burn engines (but not gasoline-fueled rich burn engines).

North America

California Air Resources Board - California, United States (most sources)
Environment Canada - Canada (most sources)
Environmental Protection Agency - United States (most sources)
Texas Railroad Commission - Texas, United States (LPG-fueled engines only)
Transport Canada - Canada (trains and ships)

Europe

Ultimately, the European Union has control over regulation of emissions in EU member states; however, many member states have their own government bodies to enforce and implement these regulations in their respective countries. In short, the EU forms the policy (by setting limits such as the European emission standard) and the member states decide how to best implement it in their own country.

United Kingdom

In the United Kingdom, matters concerning environmental policy are what is known as "devolved powers" which means, each of the constituent countries deals with it separately through their own government bodies set up to deal with environmental issues in their respective country:

Environment Agency - England and Wales
Scottish Environment Protection Agency (SEPA) - Scotland
Department of the Environment - Northern Ireland

However, many UK-wide policies are handled by the Department of the Environment Food and Rural Affairs (DEFRA) and they are still subject to EU regulations.

Emissions control

Engine efficiency has been steadily improved with improved engine design, more precise ignition timing and electronic ignition, more precise fuel metering, and computerised engine management.

Advances in engine and vehicle technology continually reduce the toxicity of exhaust leaving the engine, but these alone have generally been proved insufficient to meet emissions goals. Therefore, technologies to detoxify the exhaust are an essential part of emissions control.

Air injection

One of the first-developed exhaust emission control systems is secondary air injection. Originally, this system was used to inject air into the engine's exhaust ports to provide oxygen so unburned and partially-burned hydrocarbons in the exhaust would finish burning. Air injection is now used to support the catalytic converter's oxidation reaction, and to reduce emissions when an engine is started from cold. After a cold start, an engine needs a fuel-air mixture richer than what it needs at operating temperature, and the catalytic converter does not function efficiently until it has reached its own operating temperature. The air injected upstream of the converter supports combustion in the exhaust headpipe, which speeds catalyst warmup and reduces the amount of unburned hydrocarbon emitted from the tailpipe.

Exhaust gas recirculation

In the United States and Canada, many engines in 1973 and newer vehicles (1972 and newer in California) have a system that routes a metered amount of exhaust into the intake tract under particular operating conditions. Exhaust neither burns nor supports combustion, so it dilutes the air/fuel charge to reduce peak combustion chamber temperatures. This, in turn, reduces the formation of NO_x.

Catalytic converter

The catalytic converter is a device placed in the exhaust pipe, which converts hydrocarbons, carbon monoxide, and NO_x into less harmful gases by using a combination of platinum, palladium and rhodium as catalysts.

Evaporative emissions control

Evaporative emissions are the result of gasoline vapors escaping from the vehicle's fuel system. Since 1971 (1970 in California), all U.S. vehicles have had fully sealed fuel systems that do not vent directly to the atmosphere; mandates for systems of this type appeared contemporaneously in other jurisdictions. In a typical system, vapors from the fuel tank and carburetor bowl vent (on carbureted vehicles) are ducted to canisters containing activated carbon. The vapors are adsorbed within the canister, and during certain engine operational modes fresh air is drawn through the canister, pulling the vapor into the engine, where it is burned.

Emission testing

In 1966, the first emission test cycle was enacted in the State of California measuring tailpipe emissions in PPM (parts per million).

Some cities are also using a technology developed by Dr. Donald Stedman of the University of Denver, which uses lasers to detect emissions while vehicles pass by on public roads, thus eliminating the need for owners to go to a test center. Stedman's laser detection of exhaust gases is commonly used in metropolitan areas.^[1]

Use of emission test data

Emission test results from individual vehicles are in many cases compiled to evaluate the emissions performance of various classes of vehicles, the efficacy of the testing program and of various other emission-related regulations (such as changes to fuel formulations) and to model the effects of auto emissions on public health and the environment. For example, the Environmental Working Group used California ASM emissions data to create an "Auto Asthma Index" that rates vehicle models according to emissions of hydrocarbons and nitrogen oxides, chemical precursors to photochemical smog.

External links

References

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