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The several principal experimental matrices of the Auto/Oil Air Quality Improvement Research Program (AQIRP) were statistically designed as regards vehicle fleet size and fuel property combinations. The test results were analyzed using powerful standard statistical methods to extract the maximum amount of information from the data. The analysis included the use of appropriate data transformations and also graphical methods to display the results. The test fleets were sized to control the risk of failing to detect an important effect while providing assurance that unimportant, small effects have little chance to be found highly significant. To do this required estimation of the pertinent error term from other test programs which did not completely correspond to the type of testing contemplated in the AQIRP. These estimates turned out to be quite good. The compositional fuel matrices were blocked into two fuel groups.

The analysis of data from the Auto/Oil Air Quality Improvement Research Program (AQIRP) study of the effect of aromatics, MTBE, olefins, and T90 on mass exhaust emissions from current (1989) vehicles was extended to include individual vehicles during individual operating modes. The results of the modal data analysis agree with and complement results which have been reported previously by AQIRP. Beyond this, attention is focused on three fuel compositional changes where the effect on emissions shows a reversal in sign depending on the vehicle operating mode chosen.