SCOPE OF STUDY Prior to initiating the experimental program@ the literature on the formation of aerosols in photochemical smog@ the effects of such aerosols on visibility@ and the techniques available for measuring visibility reduction was reviewed.(1)* The most striking observation was the extensive lack of agreement among workers in the field. There was disagreement not only in regard to the relative reactivity of different compounds but even in regard to which classes of hydrocarbons cause aerosol formation in photochemical smog. There was also little agreement on the mechanism of aerosol formation@ the composition of the aerosol@ the role of sulfur dioxide@ and the influence of other parameters such as relative humidity and the hydrocarbon itrogen oxides ratio. The literature survey proved to be very useful for identifying key problem areas and for planning the experimental program. The disagreements found in the literature made it clear that@ before technically acceptable aerosol data could be obtained@ it would be necessary to ascertain the factors most responsible for the wide variety of results in the literature. Therefore@ the experimental program was devoted first to characterizing the effect of various parameters in photochemical aerosol formation. In that work a number of smog-chamber operating conditions were identified which have an important@ but previously unappreciated@ influence on aerosol formation. Those experimental findings are given later in this report. Another sizable effort leading up to the smog-chamber studies with auto exhaust involved the development of operational and analytical procedures that would insure that meaningful data would be obtained during the fuel study. The methodology finally adopted is presented in Appendix A. The major effort of the program consisted of 44 smog-chamber experiments in which the auto exhaust of seven different fuel types was examined for their potential to form secondary aerosol. In the course of the investigation it became apparent that information on primary aerosol was needed to aid in interpreting the photochemical smog observations. Therefore@ the relationship between fuel type and yield of primary aerosol was sought in addition to that between fuel type and yield of secondary aerosol. Some caution is required in the interpretation of the primary aerosol data. It is well recognized that primary aerosol emissions vary dramatically with variations in such factors as the make@ model@ and year of the car@ its mileage@ the engine tune@ and the relative humidity and temperature of both the intake air and exhaust-dilutant air@ to name only a few. In this study it became evident that even very subtle changes in otherwise identical cycle-to-cycle operation of a car on the same fuel can result in significant variation in primary-aerosol emission. Thus primary-aerosol emissions are extremely sensitive to the many parameters involved in their formation. For this reason@ the interpretation of the primary-aerosol data should be restricted to vehicles similar to the project car. *References are given on page 39.
API 4147-1972 history
1972API 4147-1972 A STUDY OF MOTOR FUEL COMPOSITION EFFECTS ON AEROSOL FORMATION Part III Visibility Reduction from Automobile Exhaust