INTRODUCTION This report covers the fourth and final year of research conducted on the exhaust emissions of polynuclear aromatic hydrocarbons (PNA) under CRC-APRAC Project CAPE-6-68. Previous findings have been published in three Annual Reports (1@ 2@ 3) and in two SAE papers (4@ 5). The fourth year of CAPE-6-68 differed administratively from prior years In that the U. S. Environmental Protection Agency@ which previously had provided one-third of the financial support of the project@ no longer provided financial support. The main features of the fourth year technical program were as follows: ? The same 1966@ 1968@ and 1970 test vehicles were used. ? Deposit accumulation mileage between emission tests was increased. ? Deposit - accumulation fuels with field average PNA contents were used to supplement earlier data obtained with fuels of near zero and field maximum PNA contents. ? Used engine oils were used In most emission tests in contrast to the earlier practice of using fresh oil. ? PNA emissions were measured under artificially-induced high oil consumption conditions. ? Phenol emissions were measured only under artlficially-induced high oil consumption conditions. ? The PNA content of engine combustion chamber deposits was related to fuel PNA content and to PNA emissions. ? The GC/UV analysis technique developed by CAPE-12-68 (6) for PNA in emission samples@ fuels@ deposits and oils was expanded from the determination of 11 PNA species to 18 species and was applied to a large number of samples retained from previous years. Many of these samples were also analyzed by low voltage mass spectroscopy (6) and the results correlated and compared with GC/UV results. ? Selected samples of retained exhaust gas aqueous condensate@ previously analyzed for total phenol content@ were analyzed by a GC method (6) for individual phenols. ? The demonstration of sampling losses for certain reactive PNA species@ reported in the Third Annual Report (3)@ was placed on a more quantitative basis@ and was extended to the seven additional PNA species for which GC/UV analytical results became available. The third year of Project CAFE-6-68 ended with emission tests which indicated the following. ? PNA emissions were substantially higher in the presence of deposits formed from fuels with the field maximum PNA content (3 ppm BaP) than in the presence of deposits formed from near zero PNA fuels. ? In a low-PNA fuel@ the addition of 2-ring and 3-ring aromatics@ from either heavy catalytic reformate or heavy catalytic naphtha@ caused a small increase in PNA emissions. ? PNA in fuel was apparently stored in engine deposits that were accumulated during light-duty operation and were then emitted under the heavier-load operation occurring during emission testing. PNA emissions were greatest with fresh high-PNA deposits and decreased in successive testing as the deposits became stabilized@ but deposits from a near-zero PNA fuel gave low PNA emissions under all deposit conditions. ? The PNA contents of 2000 mile used oil samples correlated with the PNA contents of the fuels used for mileage accumulation. We have now extended our knowledge in several of these areas. Additional deposit miles were accumulated with fuels containing added heavy catalytic reformate or heavy catalytic naphtha. During the emission tests for these series both new oil and used oils of different PNA contents were used. In tests with fuels of field average PNA content@ the build-up of oil PNA with mileage was monitored out to 8@000 miles. Periodic PNA emission tests were made during these mileage accumulations. Deposits formed in these 8@000 mile runs were analyzed for PNA content. Similar emission tests and deposit analyses were carried out for extended mileage operation with the same fuels after the removal of (a) oil-control piston rings or (b) Intake valve-guide oil seals to create high oil consumption conditions. All of the emission tests for the fourth-year program were done with fresh engine deposits present. This procedure maximized the effects of fuel PNA. PNA emission data for various PNA species were shown to be linearly correlated with the PNA contents of the deposit-formation fuels@ using data from fuels of near-zero@ fieId-average@ and field-maximum PNA contents.