The Science of the Total Environment 305 (2003) 129–141 0048-9697/03/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII:S0048-9697 Ž 02 . 00476-X Effect on exhaust emissions by the use of methylcyclopentadienyl manganese tricarbonyl (MMT) fuel additive and other lead replacement gasolines Savas Geivanidis, Panayotis Pistikopoulos, Zissis Samaras* Laboratory of Applied Thermodynamics, Department of Mechanical Engineering, Aristotle University, 54124 Thessaloniki, Greece Received 9 May 2002; received in revised form 26 September 2002; accepted 29 September 2002 Abstract This paper examines the potential effects on car exhaust emissions of a range of alternative lead replacement gasolines in the context of south European countries such as Greece. The main objective of this study was to assess the effects on emissions from non-catalyst passenger vehicles by the substitution of leaded (‘super’) gasoline with Euro95 unleaded enriched with the additive MMT or other alternative to leaded gasoline fuels. Regulated emissions, two non-regulated pollutants and vehicle performance were measured on two catalyst-equipped and two conventional, non-catalyst vehicles. It was found that there was no measurable effect on regulated emissions (CO, HC and NO ) x and on fuel consumption by the introduction of the lead replacement fuels for both catalyst and non-catalyst cars. In the case of the non-catalyst car, the shift from leaded to unleaded gasoline was associated with an increase in benzene and formaldehyde emissions, a trend probably attributable to the increased aromatics content of the lead replacement fuels.  2002 Elsevier Science B.V. All rights reserved. Keywords: Lead replacement gasoline; MMT; Manganese; MTBE; Passenger cars 1. Introduction The European Union, based on the findings and suggestions of the Auto Oil Programme (European Commission, 1996; European Parliament, 1998), decided to completely phase-out the use of leaded gasoline from January 2000. This decision aimed primarily to address the known health concerns associated with lead in gasoline identified through epidemiological and toxicological studies. *Corresponding author. Tel.: q30-310-996-014; fax: q30- 310-996-019. E-mail address: zisis@eng.auth.gr (Z. Samaras). However, replacing leaded gasoline with unlead- ed gasoline raises a number of questions: ● In the absence of lead, which acts as a valve seat lubricant, valve seat recession may appear on older vehicle engines that were designed to run on leaded fuel (Hutcheson, 2000). This can lead to increased emissions, poor idling, loss of power, and eventually in valve burning and engine failure. ● Leaded gasoline was generally characterised by higher octane number, of the order of 96–98 RON. On the other hand, the so-called Euro 95 gasoline has an octane number of 95 RON