Manufacturing Standards

Federal and state governments have established air quality standard during the past 20 years. Automobile manufacturers design their vehicles to conform to standards where the vehicle will be sold and operated. These standards cover carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx).

Federal and California Standards which must be met by manufacturers are specified in units easily measured in a testing laboratory. Since 1970, these standards have been in "grams per mile". This means no vehicle, whether 2-cylinder or V8, may emit more than a set weight (in grams) of pollutants for each mile travelled. Since large engines burn more fuel per mile than do small engines, they must be "cleaner" per gallon burned if they are to meet these standards.

When manufacturers certify vehicle models prior to sale, the vehicles are placed on a dynamometer and the exhaust gases are collected in a bag. After the vehicle runs for a specified time, the gases are analyzed and weighed. Engines and emission systems are designed so the weight of emissions will be less than the specified grams per mile standard.

Infrared exhaust analyzers are commonly used in vehicle test stations. The analyzer uses a test probe placed in the exhaust stream to sample the exhaust gases, and measure the percentage of CO and the parts per million of HC. These are not the same units used by the manufacturer when the vehicle is certified. The NOx emissions cannot be measured by an infrared exhaust analyzer. Laboratory equipment must be used to determine NOx emissions.