Oxides of nitrogen are one of the main contributors to ozone.
Ozone contributes to respiratory diseases such as asthma, bronchitis and emphysema.
In addition, diesel vehicles contribute about 65 percent of the small particulate matter known as PM10, which also contributes to respiratory disease and is suspected of causing cancer and birth defects. An exact date for the start of inspections, which will be carried out at California Highway Patrol weigh stations and other locations that will not impede traffic flow, has not been selected. However, the program is expected to begin by mid-1998. When it is fully implemented, the inspection program will remove about 23 tons of pollutants a day from California's air. Inspections are done by using a measuring device to check the opacity or darkness of the smoke coming from the vehicle exhaust system.