Particulate emissions from commercial shipping: Chemical, physical, and optical properties

Abstract

We characterize particulate emissions on the basis of chemical, physical, and optical properties from commercial vessels. Observations during the Texas Air Quality Study/Gulf of Mexico Atmospheric Composition and Climate Study 2006 field campaign provide chemical and physical characteristics including sulfate (SO 42−) mass, organic matter (OM) mass, black carbon (BC) mass, particulate matter (PM) mass, number concentrations (condensation nuclei (CN) > 5 nm), and cloud condensation nuclei (CCN). Optical characterization included multiple wavelength visible light absorption and extinction, extinction relative humidity dependence, and single scatter albedo (SSA). The global contribution of shipping PM was calculated to be 0.90 Tg a−1, in good agreement with previous inventories (0.91 and 1.13 Tg a−1 from Eyring et al. (2005a) and Wang et al. [2008]). Observed PM composition was 46% SO 42−, 39% OM, and 15% BC and differs from inventories that used 81%, 14%, and 5% and 31%, 63%, and 6% SO 42−, OM, and BC, respectively. SO 42− and OM mass were found to be dependent on fuel sulfur content as were SSA, hygroscopicity, and CCN concentrations. BC mass was dependent on engine type and combustion efficiency. A plume evolution study conducted on one vessel showed conservation of particle light absorption, decrease in CN > 5 nm, increase in particle hygroscopicity, and an increase in average particle size with distance from emission. These results suggest emission of small nucleation mode particles that subsequently coagulate/condense onto larger BC and OM. This work contributes to an improved understanding of the impacts of ship emissions on climate and air quality and will also assist in determining potential effects of altering fuel standards.