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Exhaust emission control systems employing air injection and exhaust manifold reactors in place of conventional exhaust manifolds have been developed to control vehicle emissions to 0·25 gram (20 p.p.m.) of hydrocarbons and 5·0 grams (0·22 per cent) of carbon monoxide per mile. These low emission levels have been achieved with good driveability, good vehicle performance and very little loss in fuel economy. Durability tests of a number of exhaust manifold reactor systems indicate that acceptable life in consumer service can be attained. Non-nickel alloy steels developed by specialty steel manufacturers, and based on the iron-chromium- aluminium system, appear to be useful materials of construction for reactors. These alloys coupled with the now demonstrated simplifications in reactor design offer one route to lower ultimate costs of these units. The commercial development and application of exhaust manifold reactor systems seems entirely feasible.

Relationships developed between automotive exhaust emissions and ambient air quality levels have been used to establish the degree of emission control needed to meet the ambient air quality standards in major urban areas. Interim emission standards already established for 1975 appear to be more than adequate for congested urban areas and the existing 1974 standards appear more than adequate for the remainder of the country. The very low levels mandated by the 1970 Amendments to the Clean Air Act do not appear necessary. Emission control systems based on engine modifications and thermal reactors have been shown to provide the degree of emission control needed to achieve the ambient air quality goals and are compatible with the continued use of leaded gasoline. Exhaust lead traps have been shown to be a practical means to reduce lead emissions to the environment should such control be needed. The lead tolerant control systems used with high compression ratio engines are shown to have the potential to improve fuel economy to a greater degree than proposed catalytic systems used with unleaded gasoline and low compression ratio engines. Both approaches are shown to impose severe fuel economy penalties at the very stringent emission standards mandated by the 1970 Amendments to the Clean Air Act.

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