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Understanding car emissions and controls

Understanding car emissions and controls

In the 1950s and 60’s there were numerous federal, state and local government studies about the effects of air pollution. The result of these studies was not good, and the local regulations were not really very effective in controlling emissions.

California had always been a leader in emissions and so, in 1967, created the California Air Resources Board to oversee emissions and the like. In 1970, the federal United States Environmental Protection Agency (EPA) was established.

Both of these governmental agencies now create and enforce emission regulations for automobiles in the United States.

The first effort at controlling air pollution was the PCV (positive crankcase ventilation) system. The PCV system draws unburned hydrocarbon fumes, a precursor of photochemical smog, from the crankcase and then directs the fumes into the intake tract where they are burned. 

Positive crankcase ventilation was first installed on a widespread basis on all new 1961-model cars first sold in California. By 1962, New York required it as well.

By 1964, most new cars sold in the U.S. were so equipped, and PCV quickly became standard equipment on all vehicles worldwide. It was a rather plain system that required a few hoses and a valve.

In 1966, California set another piece of anti-pollution legislation- this was the emission exhaust tailpipe standards for cars sold in that state.  Also in 1966, the first emission test cycle was enacted in the State of California measuring tailpipe emissions in PPM (parts per million).

These standards were progressively tightened year by year, as mandated by the EPA making it more and more difficult for cars to pass. By the late 1970s, open the hood of a car and you would be greeted by a mass of hoses.

By 1974, it was obvious that detuning automobile engines so they would pass the fuel standards was no longer viable; not only did the vehicles use too much gasoline, they were also down on power.

By 1975, the use of unleaded gasoline was finally supplanted the leaded gasoline previously used; catalytic converters were also used in the treatment of exhaust gas.

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The problem with emissions

The emissions given off by the burning of gasoline have shown to be toxic. Here are the major pollutants:

Hydrocarbons (HC)
Hydrocarbons are toxins and a major contributor to smog. Prolonged exposure to hydrocarbons contribute to asthma, liver disease, lung disease, and cancer. Methane, which is an HC, is not directly toxic, but is more difficult to break down in a catalytic converter. 

HC emissions can come not only from a vehicle's engine but also directly from the fuel tank and lines 24 hours a day- even when the engine is turned off. 

Carbon monoxide (CO) 
A product of incomplete combustion, inhaled carbon monoxide reduces the blood's ability to carry oxygen; overexposure may be fatal.

NOx
Generated when nitrogen in the air reacts with oxygen, and this is when the high temperature and pressure occurs inside the engine. NOx is a precursor to smog and acid rain. 

Particulate matter
Soot, or smoke is made up of particles in the micrometer size range: it has negative health effects, including respiratory disease and cancer. Very fine particulate matter has been linked to cardiovascular disease.

Sulfur oxide (Sox)
A general term for oxides of sulfur, which are emitted from automobiles burning fuel containing sulfur. Reducing the level of fuel sulfur reduces the level of Sulfur oxide emitted from the tailpipe.

Volatile organic compounds (VOCs) 
Organic compounds which typically have a boiling point less than or equal to 250 °C, such as chlorofluorocarbons(CFCs) and formaldehyde.  

Emissions controls explained

In spite of catalytic converters, unleaded gasoline, electronic ignition, more precise fuel metering and computerized engine management, still more is needed to make emission systems work.

Air Injection
Air injection was one of the first emission control systems. This system would inject more oxygen into the exhaust system. Air injection is now used to support the catalytic converter's oxidation reaction as the air injection system speeds up catalytic warm-up. 

Exhaust Gas Recirculation
This system originated in 1972, routes a metered amount of exhaust gas into the intake tract. As the exhaust gas doesn’t burn, it dilutes the air/fuel charge and so reduces peak combustion temperatures, and thus reduces formation of  NOx.

Catalytic Converter
The catalytic converter is a unit placed in the exhaust system which converts hydrocarbons, carbon monoxide, and NOx into less harmful gases by using a combination of platinum, palladium and rhodium as catalysts.