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Exhaust manifold thermal reactors, exhaust gas recirculation, exhaust particulate trapping systems, and appropriate engine adjustments have been combined to produce total emission control systems which reduce all gaseous and exhaust particulate emissions from passenger vehicles. The first generation system was developed to meet the former United States and State of California emission standards for 1975. Field service tests demonstrated that the emission standards were met, but unexpected operational problems were encountered. Solutions to these problems have been found. Second generation total emission control systems are being developed in an attempt to meet the current United States emission standards for 1975 - 1976. These systems in their present state of development produce very low exhaust emission levels; the hydrocarbons are well below the standards and the carbon monoxide and nitrogen oxide levels are quite close to the 1975 - 1976 standards.

Laboratory and field tests were conducted to determine how changes in some gasoline compositional factors might affect atmospheric visibility and soiling caused by exhaust particulate matter emitted from late model automobiles. In the laboratory tests, measurements of light scattering, soiling index, and mass emission rates of air-suspendible particles were made on diluted exhaust from cars driven on a programmed chassis dynamometer. These tests showed that light scattering, and also soiling, were increased by increasing the aromatic content, removing lead antiknocks, or increasing the combined amounts of sulfur and phosphorus in gasoline. Field tests in a turnpike tunnel used two 4-car fleets operating on leaded and unleaded premium gasoline of high and average aromatic content. The air in the tunnel sampled during the tests with the cars using the unleaded gasolines soiled the filters 57% more than the air sampled during the tests with the cars using the leaded gasolines.

The role of lead antiknocks in modern gasolines is discussed in terms of engine-fuel relationships. Exhaust emission characteristics of leaded and unleaded gasolines are compared in terms of both gaseous and particulate constituents. The effect of removing lead from gasoline on engine cleanliness, exhaust valve seat recession, octane requirements, and octane requirement increase is assessed. Extensive use is made of published information and some new information is presented. It is apparent that the use of lead antiknocks in gasoline produces effects on engine performance and exhaust emission characteristics which are both positive and negative in nature. Much more information is needed, particularly in terms of future vehicles equipped with advanced control systems, to determine the optimum fuel composition.