Emission rates and physico-chemical characteristics of Mn particles emitted by vehicles using methylcyclopentadienyl manganese tricarbonyl (MMT) as an octane improver

Since 1990, methylcyclopentadienyl manganese tricarbonyl (MMT) has been added to all gasoline in Canada as an antiknock agent. The objective of this study is to determine the percentage of manganese emitted by different types of automobiles and to evaluate the size and chemical characteristics of the Mn-containing particles. Nine vehicles with different mileage and engine capacity were tested using standard procedures for urban and highway driving cycles. One ran on gasoline without MMT and served as a control. The particles were collected using two separate systems: a trapping device consisting of a water tank connected to the tailpipe and a pumping device linked to a cassette containing Teflon filters. Water samples were analyzed by neutron activation to determine the amount of Mn emitted at the tailpipe for each test. Teflon filters were analyzed by electron microscopy to determine the size and the chemical characteristics of the particles. The amount of manganese emitted from the tailpipe varied from 4 to 41% of the manganese consumed, depending on the driving cycle and the vehicle. For the urban cycle, the emission rate was positively correlated with previous mileage. Almost all particles found on teflon filters had a size less than 5 mu m. They appeared to be mainly Mn oxides but other elements could be masked by the gold and paladium peaks.