The Effect of Unleaded Fuel Composition on Polynuclear Aromatic Hydrocarbon Emissions

Three cars have been operated for approximately 8000 miles on each of four unleaded gasolines. These gasolines encompassed varied levels of C₆-C₈ aromatics and varied polynuclear aromatic (PNA) content. Exhaust PNA emissions and lube oil PNA content were measured periodically during the course of mileage accumulation.

Results of this study show that increases in both light C₆-C₈ fuel aromatics and fuel-contained PNAs can result in significantly increased exhaust PNAs. Vehicles meeting increasingly stringent hydrocarbon (HC) and carbon monoxide (CO) emissions standards emit greatly reduced quantities of exhaust PNAs, though the rate of lube oil PNA accumulation appears to be unaffected by emissions control systems. Accumulated lubricating oil mileage was found to correlate with increased PNA emissions with a high level of statistical significance. This may be the result of an observed increase in lube oil PNA content with mileage accumulation. Oil change was found to result in an immediate reduction in PNA emissions.