15. Carbonyl Profiles in Vehicular Exhaust Emission Prior to the Mandated MTBE Ban in California: A Sepulveda Tunnel Experiment

Carbonyls are known air toxics, mutagenic and/or carcinogenic (U.S. CAAA, 1990). These compounds also play an important role in the chemistry of ozone production due to their capacity to generate free radicals (Veyret et al., 1989). Carbonyls are mostly found in the atmosphere in the vapor-phase. They are formed as a result of photochemical reactions involving hydrocarbons, and are also emitted directly from vehicular exhaust and other anthropogenic sources. Specific chemical species of gasoline can affect the emission rates of carbonyls and the additions of oxygenated compounds, such as methyl tert-butyl ether (MTBE) or ethanol, has been shown to lead to changes in the profile of the exhaust components. Elimination of the use of MTBE in gasoline was mandated in California on 31 December, 2003, thus affected to the carbonyl composition of vehicular exhaust since then. In this study, carbonyl samples were collected in the Sepulveda Tunnel, south exit, (LAX airport, Los Angeles, CA) during December 11 and 12, 2003. One hr samples were collected to measure the carbonyl profile of vehicular exhaust emissions before MTBE was complete banned. Formaldehyde (a well know irritant) presented the highest concentrations, followed by acetaldehyde and acetone. Acrolein (among the most toxic carbonyls) and methacrolein concentrations as high as 0.23 and 0.27 ug/m3, respectively, were observed. Increase carbonyl concentration were observed with increasing traffic volume in the tunnel. The results obtained in this study will be compared with previous carbonyl concentrations measured before the MTBE was banned.

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