Emissions from ships with respect to their effects on clouds

Emissions of particles, gases, heat, and water vapor from ships are discuss ed with respect to their potential for changing the microstructure of marin e stratiform clouds and producing the phenomenon known as "ship tracks." Ai rborne measurements are used to derive emission factors of SO, and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fu el oil (MFO); they were similar to 15-89 and similar to 2-25 g kg(-1) of fu el burned, respectively. By contrast a steam turbine-powered ship burning h igh-grade navy distillate fuel had an SO2 emission factor of similar to 6 g kg(-1). Various typos of ships, burning both MFO and navy distillate fuel, emitted from similar to 4 x 10(15) to 2 x 10(16) total particles per kilogram of fu el burned (similar to 4 x 10(15)-1.5 x 10(16) particles per secondi. Howeve r, diesel-powered ships burning MFO emitted particles with a larger mode ra dius (similar to 0.02-0.05 mu m) and larger maximum sizes than those powere d by steam turbines burning navy distillate fuel (mode radius similar to 0. 02 mu m). Consequently, if the particles have similar chemical compositions , those emitted by diesel ships burning MFO will serve as cloud condensatio n nuclei (CCN) at lower supersaturations land will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine-powered ships fueled by MFO em it particles with a mode radius similar to that of diesel-powered ships fue led by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determi ning whether or not a ship will produce a ship track. However, more measure ments are needed to test this hypothesis. The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Me asurements of the total particles entering marine stratiform clouds from di esel-powered ships fueled by MFO, and increases in droplet concentrations p roduced by these particles, show that only about 12% of the particles serve as CCN. The fluxes of beat and water vapor from ships are estimated to be similar t o 2-22 MW and similar to 0.5-1.5 kg s(-1), respectively. These emissions ra rely produced measurable temperature perturbations, and never produced dete ctable perturbations in water vapor, in the plumes from ships. Nuclear-powe red ships, which emit heat but negligible particles. do not produce ship tr acks. Therefore, it is concluded that heat and water vapor emissions do nor play a significant role in ship track formation and that particle emission s, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and t est these hypotheses.