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Published July 1, 2009 | Supplemental Material
Journal Article Open

Comprehensive Simultaneous Shipboard and Airborne Characterization of Exhaust from a Modern Container Ship at Sea


We report the first joint shipboard and airborne study focused on the chemical composition and water-uptake behavior of particulate ship emissions. The study focuses on emissions from the main propulsion engine of a Post-Panamax class container ship cruising off the central coast of California and burning heavy fuel oil. Shipboard sampling included micro-orifice uniform deposit impactors (MOUDI) with subsequent off-line analysis, whereas airborne measurements involved a number of real-time analyzers to characterize the plume aerosol, aged from a few seconds to over an hour. The mass ratio of particulate organic carbon to sulfate at the base of the ship stack was 0.23 ± 0.03, and increased to 0.30 ± 0.01 in the airborne exhaust plume, with the additional organic mass in the airborne plume being concentrated largely in particles below 100 nm in diameter. The organic to sulfate mass ratio in the exhaust aerosol remained constant during the first hour of plume dilution into the marine boundary layer. The mass spectrum of the organic fraction of the exhaust aerosol strongly resembles that of emissions from other diesel sources and appears to be predominantly hydrocarbon-like organic (HOA) material. Background aerosol which, based on air mass back trajectories, probably consisted of aged ship emissions and marine aerosol, contained a lower organic mass fraction than the fresh plume and had a much more oxidized organic component. A volume-weighted mixing rule is able to accurately predict hygroscopic growth factors in the background aerosol but measured and calculated growth factors do not agree for aerosols in the ship exhaust plume. Calculated CCN concentrations, at supersaturations ranging from 0.1 to 0.33%, agree well with measurements in the ship-exhaust plume. Using size-resolved chemical composition instead of bulk submicrometer composition has little effect on the predicted CCN concentrations because the cutoff diameter for CCN activation is larger than the diameter where the mass fraction of organic aerosol begins to increase significantly. The particle number emission factor estimated from this study is 1.3 × 10^(16) (kg fuel)^(−1), with less than 1/10 of the particles having diameters above 100 nm; 24% of particles (>10 nm in diameter) activate into cloud droplets at 0.3% supersaturation.

Additional Information

© 2009 American Chemical Society. Received August 28, 2008. Revised manuscript received November 29, 2008. Accepted December 9, 2008. Publication Date (Web): February 4, 2009. This work was supported by the Office of Naval Research and CARB. S.M.M. and L.T.P. acknowledge support from the NASA Earth and Space Sciences Fellowship. A.N. acknowledges support from the NASA Radiation Science Program and an NSF CAREER. We gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model. We are grateful to the ship crew and the shipping company, and the analytical support of Ms. Kathy Cocker, and Ms. Varalakshmi Jayaram. Note Added After ASAP Publication: The Acknowledgments were modified in the version of this paper that published ASAP February 4, 2009; the corrected version published ASAP February 13, 2009. Supporting Information: Information detailing the methods used for the in-stack measurements presented in this study is given in Section S1. Figure S1 gives a flow diagram of the sampling system used onboard the container ship. Figure S2 gives vertical profiles of relative humidity and potential temperature in and above the marine boundary layer. Figure S3 give 3-day NOAA Hysplit back trajectories for the air mass present during the study. This material is available free of charge via the Internet at http://pubs.acs.org.

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