Smog - California Smog Check
 State Certified Emission Testing, Inspections, Stations, Gross Polluters
Napa Valley, San Francisco North Bay, Ca. USA

Smog Check Automobile emissions control

 covers all the technologies that are employed to reduce the air pollution-causing emissions produced by automobiles. Exhaust emissions control  systems were first required on 1966 model year vehicles produced for sale in the state of California, followed by the United States as a whole in model year 1968. Their use became widespread in the following decades and now they are ubiquitous in industrialized nations and common in most others.