Characterization of the Single Particle Mixing State of Individual Ship Plume Events Measured at the Port of Los Angeles ANDREW P. AULT, † CASSANDRA J. GASTON, ‡ YING WANG, †,§ GERARDO DOMINGUEZ, † MARK H. THIEMENS, † AND KIMBERLY A. PRATHER* ,†,‡ Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, and Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093 Received September 30, 2009. Revised manuscript received January 5, 2010. Accepted January 21, 2010. Ship emissions contribute significantly to gaseous and particulate pollution worldwide. To better understand the impact of ship emissions on air quality, measurements of the size- resolved chemistry of individual particles in ship emissions were made at the Port of Los Angeles using real-time, single- particle mass spectrometry. Ship plumes were identified through a combination of ship position information and measurements of gases and aerosol particles at a site 500 m from the center of the main shipping channel at the Port of Los Angeles. Single particles containing mixtures of organic carbon, vanadium, and sulfate (OC-V-sulfate) resulted from residual fuel combustion (i.e., bunker fuel), whereas high quantities of fresh soot particles (when OC-V-sulfate particles were not present) represented distinct markers for plumes from distillate fuel combustion (i.e., diesel fuel) from ships as well as trucks in the port area. OC-V-sulfate particles from residual fuel combustion contained significantly higher levels of sulfate and sulfuric acid than plume particles containing no vanadium. These associations may be due to vanadium (or other metals such as iron) in the fuel catalyzing the oxidation of SO 2 to produce sulfate and sulfuric acid on these particles. Enhanced sulfate production on OC-V-sulfate ship emission particles would help explain some of the higher than expected sulfate levels measured in California compared to models based on emissions inventories and typical sulfate production pathways. Understanding the overall impact of ships emissions is critical for controlling regional air quality in the many populated coastal regions of the world. Introduction Ship emissions represent one of the least regulated forms of anthropogenic pollution due in large part to the challenges involved in establishing international policies. Ship emissions impact climate by initiating cloud formation and altering the Earth’s radiation budget (1, 2). Ships emit high concen- trations of soot and heavy metals (i.e., vanadium and nickel) (3, 4), in addition to an estimated 2.4 tons of SO 2 globally, producing up to 10% of sulfate mass globally through atmospheric reactions (5). Over the next century, SO 2 levels are predicted to rise significantly as global commerce expands (5). Ship emissions have been shown to have negative effects on human health through exposure studies and epidemio- logical models (6-8). For example, inhaled vanadium particles are toxic and synergistic effects with nickel and sulfate have been shown to enhance toxicity (7). To develop effective strategies for reducing the impact of shipping on climate and health, recent studies have focused on improving ship emission inventories, which are used to estimate future scenarios for gas phase concentrations (9). Efforts to regulate shipping emissions have been difficult due to fuel and upgrade costs and international dependence on foreign trade (10, 11). Particulate emissions from ships have been characterized by multiple analytical methods including energy dispersive X-ray fluorescence measurements of particulate matter on filters (4), ion chromatography (IC) of particulate matter extracted from filters (3), real-time, mass-based measure- ments (12, 13), particle counters (14), cloud condensation nuclei measurements (12), and size distribution measure- ments (4). These measurements have led to updated emission inventories and emission factors for particle mass and particle number for ship emissions (12, 13). Real-time, single-particle mass spectrometry has also been used to identify ship emissions at locations both near source regions and after transport (15-17). Herein, we report in situ measurements of the size-resolved chemical mixing state of particles in individual fresh ship plumes measured at the Port of Los Angeles. Experimental Methods Sampling Information. Ambient air sampling was conducted from November 16-26, 2007 at the Port of Los Angeles (LA) on Terminal Island in San Pedro, California. Particles were sampled through a four meter sampling mast, seven meters above the ground at a sampling site 500 m east of the center of the main channel. Wind direction and speed were measured using a R.M. Young wind monitor. Winds exhibited a consistent diurnal pattern with southerly sea breezes during the day and light nocturnal land breezes from the north. Radio transmissions of the location, speed, and heading of ships entering and exiting the port were recorded in real- time with an automated identification system (AIS) antenna in La Jolla, CA (18). These transmission signals are required to be sent every minute for ships at sea over 299 gross tons by the International Maritime Organization. Gas and Particle Peripheral Instrumentation. Gas phase measurements were made of NO x (Thermo Environmental Instruments (TEI) model 42C), O 3 (TEI model 49), and SO 2 (TEI model 43). Particle size distributions were measured with a scanning mobility particle sizer (SMPS, TSI model 3936 L) operating from 10 to 600 nm with a time resolution of 5 min; black carbon (BC) concentrations (ng/m 3 ) were measured using an aethalometer (Magee Scientific AE31). Aerosol Time-of-Flight Mass Spectrometry (ATOFMS). The design and details of the ultrafine (UF)-ATOFMS used in this study are described in detail elsewhere (19). This instrument measured the size and chemical composition of individual particles between 100 and 1000 nm during this * Corresponding author phone: 858-822-5312; fax: 858-534-7042; e-mail: kprather@ucsd.edu. † Department of Chemistry and Biochemistry. ‡ Scripps Institution of Oceanography. § Current address: Department of Atmospheric and Oceanic Science, University of California, Los Angeles, Los Angeles, CA 90095 USA. Environ. Sci. Technol. 2010, 44, 1954–1961 1954 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 6, 2010 10.1021/es902985h  2010 American Chemical Society Published on Web 02/11/2010