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Carbon Monoxide Emissions

In the complete combustion of hydrocarbons the products are carbon dioxide, water and unaffected nitrogen. However with the incomplete combustion of hydrocarbons in automobiles the products include unburned hydrocarbons, nitrogen oxides, carbon monoxide, carbon dioxide and water. These types of auto emissions are responsible carbon monoxide poisoning and affect global environmental trends. In 1970 Congress established the Environmental Protection Agency with the responsibility for regulating motor vehicle pollution. Congress enacted the Clean Air Act in 1990 to investigate and reduce auto emissions by establishment of emission standards. Two-thirds of the carbon monoxide emissions were found to come from transportation sources. In urban areas the percentage exceeded 90%. New Jersey has more motor vehicles per square mile than any other state in the nation and ranks 41st in pollution generated.

 

Auto emission systems:

 

 

What has been done to decrease carbon monoxide emissions? In 1975 most new cars were equipped with catalytic converters designed to convert carbon monoxide to carbon dioxide while using unleaded fuel. The catalytic converter is installed in the exhaust line between the exhaust manifold and the muffler.

 

The converter’s action involves two oxidation and one reduction reaction. The converter is lined with aluminum oxide, platinum, and palladium. These chemicals acting as catalysts cause the carbon monoxide and hydrocarbons to form water vapor and carbon monoxide. (Some converters have a third lining of platinum and rhodium, which reduce nitrogen oxides.) The reason lead gasoline can’t be used with the converter is that the lead coats the chemicals in the converter rendering them ineffective.

 

In the 1980’s on-board computers were added to help optimize the efficiency of the catalytic converter. Their oxygen sensor positioned in the exhaust pipe helps to maintain the 14.7:1 mixture of air to fuel for optimum combustion. A zirconia-type oxygen sensor will produce a 0.5 volt signal to the engine computer when a 14.7:1 ratio is present. Higher ratios will decrease the voltage signal to 0.2 volts while lower ratios will increase the voltage to one volt. Catalysts typically reduce CO emissions by 80 percent.

 

Inspection and Maintenance programs were established in 1983 in 64 cities nationwide to enforce emission standards and maintain an owner’s automobile for maximum combustion efficiency. During inspection carbon monoxide emissions are analyzed with infra red detectors. Current sensors include the Non-Dispersive Infrared (NDIR) Analyzer, which is able to identify gross polluters, and laser diode sensors, operating at other wavelengths, which are limited to a quarter of a percent accuracy by weak line-strengths and interference from other transitions from water vapor and carbon dioxide.