Automobile emissions control is the study and practice of reducing the polluting emissions produced by automobiles.
Motor vehicles produce many different pollutants. The principle pollutants of concern — those that have been demonstrated to have significant effects on human, animal, plant, and environmental health and welfare — include:
- Hydrocarbons: this class is made up of unburned or partially burned fuel, and is a major contributor to urban smog, as well as being toxic. They can cause liver damage and even cancer. The regulations regarding hydrocarbons vary according to the engine regulated, as well as the 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 and is dangerous to people with heart disease.
- Nitrogen oxides (NOx): These are generated when nitrogen in the air reacts with oxygen at the high temperature and pressure inside the engine. NOx is a precursor to smog and acid rain.
- Carbon dioxide (CO2): CO2 is not a pollutant per se, but is a greenhouse gas and so plays a role in global warming. The only way to reduce CO2 emission is to burn less fuel.
- Particulates — soot or smoke made up of particles in the micrometre size range. Particulate matter causes respiratory health effects in humans and animals.
- Sulphur oxide (SOx) General term for oxides of sulphur, which are emitted from motor vehicles burning fuel containing a high concentration of sulphur.
Throughout the 1950s and 1960s, various federal, state and local governments in the United States conducted studies into the numerous sources of air pollution. These studies ultimately attributed a significant portion of air pollution to the automobile, and concluded air pollution is not bounded by local political boundaries. At that time, such minimal emission control regulations as existed in the U.S. were promulgated at the municipal or, occasionally, the state level. The ineffective local regulations were gradually supplanted by more comprehensive state and federal regulations. By 1967 the state of California created the California Air Resources Board, and in 1970, the U.S. Environmental Protection Agency was formed. Both agencies now create and enforce emission regulations for automobiles, as well as for many other sources. Similar agencies and regulations were contemporaneously developed and implemented in Western Europe, Australia, and Japan.
The first effort at controlling pollution from automobiles was the PCV (positive crankcase ventilation) system. This draws crankcase fumes heavy in unburned hydrocarbons — a precursor to photochemical smog — into the engine's intake tract so they are burned rather than released unburned from the crankcase into the atmosphere. Positive crankcase ventilation was first installed on a widespread basis by law on all new 1961-model cars first sold in California. The following year, New York required it. By 1964, most new cars sold in the U.S. were so equipped, and PCV quickly became standard equipment on all vehicles worldwide.
The first legislated exhaust (tailpipe) emission standards were promulgated by the State of California for 1966 model year for cars sold in that state, followed by the United States as a whole in model year 1968. The standards were progressively tightened year by year, as legislated by the U.S. EPA.
By the 1974 model year, the emission standards had tightened such that the de-tuning techniques used to meet them were seriously reducing engine efficiency and thus increasing fuel usage. The new emission standards for 1975 model year, as well as the increase in fuel usage, forced the invention of the catalytic converter for after-treatment of the exhaust gas. This was not possible with existing leaded gasoline, because the lead residue contaminated the platinum catalyst. In 1972, General Motors proposed to the American Petroleum Institute the elimination of leaded fuels for 1975 and later model year cars. The production and distribution of unleaded fuel was a major challenge, but it was completed successfully in time for the 1975 model year cars. All modern cars are now equipped with catalytic converters and unleaded fuel can now be found almost everywhere.
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.
One of the first exhaust emission control systems is secondary air injection. Originally, this system was used to inject air into the engine's exhaust ports, providing oxygen to burn unburned hydrocarbons in the engine exhaust.
Many engines produced after the 1973 model year have an exhaust gas recirculation (EGR) valve between the exhaust and intake manifolds. The valve opens under certain conditions to admit exhaust into the intake tract. Exhaust is largely inert — it 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 NOx
The catalytic converter is a device placed in the exhaust pipe, which converts hydrocarbons, carbon monoxide, and NOx into less harmful gases by using a combination of platinum, palladium and rhodium as catalysts.
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.
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.
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.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)