Possibilities for the reduction of automobile emissions by changes in gasoline composition have been reviewed. Small benefits are achievable by limiting front end volatility and light olefin content. California has already passed legislation which places limits on these fuel properties.
Fuel hydrocarbon type, octane number, and lead antiknock content are interrelated. Maintenance of octane number while removing lead can be achieved by increasing the fuels aromatic content with a resulting increase in some aspects of the exhaust's reactivity. Alternatively, lead may be removed without changing hydrocarbon composition if the engines octane number requirement is reduced. These changes may result in lower exhaust hydrocarbon content. They will result in lower engine efficiency and hence higher exhaust flow rates. The net effect on pollutant emissions is in doubt.
Gasoline additives, other than lead, make little direct contribution to the pollutant content of exhaust. They do perform functions which minimize the deterioration of an engine's emission characteristics.