Programs to control motor vehicle emissions originated in California as a result of Professor A.J. Haagen-Smit of the California Institute of Technology discovering that two invisible automobile emissions, hydrocarbons and oxides of nitrogen, react together in the presence of sunlight to form oxidants such as ozone, a principal ingredient of the infamous Los Angeles area “smog”. The State of California became the first government to regulate the emissions of new automobiles when it adopted requirements for the use of positive crankcase ventilation (PCV) valves beginning with the 1963 model year. The program has now progressed to the point where 1980 model year California passenger cars are certified to standards which represent 95 percent less hydrocarbons, 89 percent less carbon monoxide and 72 percent less oxides of nitrogen in their exhaust than the uncontrolled cars in the early 1960’s, In actual customer service these vehicles are expected to achieve reductions of 82 percent, 88 percent and 65 percent for the respective pollutants. This level of control will occur despite the fact that cars in customer service are often improperly maintained.Although the degree of vehicle and industrial pollution control which has already been achieved might have been sufficient to solve the air pollution problems that existed when the program began, further controls of both motor vehicle and industrial sources are still needed. The tremendous growth that has occurred in motor vehicle traffic and industrial sources has substantially reduced the rate of progress toward the achievement of clean air for California. Motor vehicles are projected to remain a very significant contributor to California’s air problems unless further control is achieved.