Observation of particle size number distribution and cloud condensation nuclei in ship plumes with low sulfur fuels

Abstract:

In order to reduce ship emission, sulfur content in fuel was regulated. Many previous literatures reported the characteristics of ship-emitted particles with heavy fuel oil or low-sulfur fuels through engine test bench and onboard tests, few studies were conducted with low-sulfur fuels at real ambient atmosphere. In this study, the ship-emitted particles in plumes from four research vessels and one barge all combusting low-sulfur fuels were studied. The total particle number concentrations dominated by ultrafine particles in ship plumes was dramatic increased comparing with marine background. The size-resolved distribution of ship-emitted particles usually had only one peak, the peak position varied with ship types. The geometric median mobility diameter of ship-emitted particles increased with decrease of ship speed. The peak at nucleation mode occasionally appeared due to nucleating of sulfuric acid and volatile organic compounds vapors. The net cloud condensation nuclei (CCN) number concentration in ship plumes at 0.2% supersaturation (SS) was negative, which may be caused by reducing hygroscopicity of preexisting CCN-active particles by condensation of volatile organic compounds vapors. The CCN number concentration at 1.0% SS was slightly increased, demonstrating that the ship-emitted particles were inefficient as CCN due to small fraction of particulate sulfate and particle sizes. The emission factor of particle number (EF_PN) was 0.27-2.1 × 10¹⁶ kg-diesel^-1, which was larger than that of previous literature using heavy fuel oil and comparable with that of these using low-sulfur fuels. The EF_PN decreased with ship speed. The emission factor of CCN at 1.0% SS (EF_CCN) were 1.1-4.5 × 10¹⁴ kg-diesel^-1, which was far smaller than that of vessel using heavy fuel oil. The EF_CCN increased with decrease of ship speed, which may be caused by enhancing of particle size at low ship speed. These observations supplement the database of ship emissions, and help understand their climate effect under stringent limits of FSC.