AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
On-Road Gasoline and Diesel Engine Exhaust Naphthalene Emissions: Contributions to Regional SOA Formation in Southern California
Alexander Cohan, Donald Dabdub, Arantzazu Eiguren-Fernandez, ANTONIO H. MIGUEL, University of California, Irvine
Abstract Number: 377 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Naphthalene is the simplest and most abundant polycyclic aromatic hydrocarbon (PAH) in the polluted urban atmosphere (Arey et al., 1998; Atkinson et al., 1988). Naphthalene is the predominant PAH in California fuels, with concentrations of up to 2600 mg L-1 in gasoline and 1600 mg L-1 in diesel fuel (Marr et al., 1999). Present primarily in the vapor-phase, naphthalene is defined as a hazardous air pollutant by the U.S. Environmental Protection Agency (EPA), and classified as possibly carcinogenic to humans (International Agency for Research on Cancer (IARC, 2002). Naphthalene may constitute an important contributor to secondary aerosol formation (SOA) (Chan et al., 2009; Kautzman et al., 2010; Odum et al., 1997). Naphthalene emission factors for gasoline and diesel vehicles measured in summer 2004 and winter 2005 in the Caldecott Tunnel in Berkeley, California (Miguel & Eiguren-Fernandez, AAAR 29th Annual Conference, Portland, OR) are combined in this work with an activity-based automobile inventory to characterize anthropogenic naphthalene emissions in the South Coast Air Basin of California (SoCAB). A 3-dimensional air quality grid model is used to examine transport and chemical reaction losses of naphthalene in the SoCAB. Only naphthalene emissions from gasoline and diesel vehicles, which account for ca. 40% of the total naphthalene emissions to the SoCAB, were included in the model. SOA formation from naphthalene engine exhaust emissions is predicted using a two product semi-empirical partitioning model. Gas- and particle-phase modeled predictions are evaluated against measurements obtained in the spring of 2005 in the SoCAB. The inclusion of roadway driven gas-phase naphthalene in the emissions inventory was found to increase SOA growth by up to 10%, and to correlate better inland than on the coast. Gasoline vehicles make up 96% of the estimated 28 million California vehicle fleet. Hence, reductions of naphthalene from gasoline fuels may be an effective means of reducing the emissions of an important SOA-forming precursor to the atmosphere of large urban centers.