Manufacturing Standards

Federal and state governments have established air quality standards during the past 20 years. Automobile manufacturers design their vehicles to conform to standards where the vehicle will be sold. 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 it travels. Since large engines burn more fuel than smaller ones, they must be "cleaner" per gallon burned if they are to meet these standards.

When manufacturers certify vehicles, the cars 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.

Infra-red exhaust analyzers are commonly used in automotive test stations. They use a test probe placed in the exhaust stream, and measure the percentage of CO in the exhaust gas, or parts per million of HC. These are not the same units used by the manufacturer when the car is certified. (NOx emissions can be measured only in a laboratory).