A method of introducing additives to an air intake system of an engine in order to overcome one or more of the various problems created by formulation of additives in fuels. The method controls at least one of the amount, aerosol particle size and timing of introduction of additives based on information relevant to operation of the engine. The introduced additives form an air-additive mixture and are carried by the airflow in the air-intake system to the combustion chamber of the engine. Another aspect of the invention is an additive introduction system that includes one or more containers for additives, a control system for determining at least one of the amount, aerosol particle size and timing of introduction of the additives, and a device to introduce the additives into the air intake system under the control of the control system.