Reducing Polycyclic Aromatic Hydrocarbons (PAH) Content of Fuels: An Avenue to Reduce SOA Formation in Urban Centers?

ANTONIO H. MIGUEL (1), Arantza Eiguren-Fernandez (1)

(1) University of California, Los Angeles

     Abstract Number: 804
     Last modified: May 16, 2010

Abstract
Decades of research have established that several polycyclic aromatic hydrocarbons (PAHs) are toxic to living organisms, and that engine exhaust emissions constitute a major source in urban areas. Spark ignition (SI) and compression ignition (CI) engine exhaust emissions contain several classes of organic compounds, including polycyclic aromatic hydrocarbons (PAH), quinones, linear, branched, cyclic alkanes, alkenes and other aromatics. For over a decade, smog chamber experiments on SOA formation have focused on terpenes and other natural hydrocarbon precursors. More recent smog chamber work suggest that, under certain NOx conditions, low molecular weight PAHs such as naphthalene, methyl- and dimethylnaphthalene contribute with a significant fraction of the SOA yield, and represent a potentially large source of urban SOA (Chan et al., Atmos. Chem. Phys., 9, 3049-3060, 2009). Over the last decades, several studies have looked into the source of engine exhaust PAHs. For instance, Marr et al., (Environ. Sci. Technol. 33, 3091-3099, 1999) reported that, while no correlation was found between heavy-duty diesel truck PAH emission factors (emfs) and PAH concentrations in diesel fuel, light-duty vehicle PAH emission factors were correlated with PAH concentrations in gasoline. To update and extend the PAH emf database to all 16 priority PAHs in the particle- and the vapor-phase, we conducted a series of on-road measurements in summer and winter 2004 and 2005 at the Caldecott Tunnel (Berkeley). Size-resolved emission factors were estimated for light-duty (mainly gasoline) and heavy-duty diesel emissions down to 10nm particles (presented at the San Diego AAAR Specialty Conference, March 2010). We focus this report on our estimates of vapor-phase naphthalene (NAP) emfs from gasoline and diesel engine emissions. The average winter NAP emf estimated for CI engines (3,926 ug/kg of fuel) is three fold larger than for SI engines (1,310 ug/kg of fuel). However, taking into consideration that SI engines constitute 96% of the estimated 28 million California vehicle fleet, and that the NAP content in regular and premium gasoline ranges from 69 up to 2,600 ppm (Marr et al., ES&T, 1999), reductions of NAP from SI fuels may constitute an effective means of reducing the emissions of a major SOA-forming precursor to the atmosphere of large urban centers.