Black carbon from ships: A review of the effects of ship speed, fuel quality and exhaust gas scrubbing
Abstract. The International Maritime Organization (IMO)\nhas moved to address the health and climate impact of the\nemissions from the combustion of low-quality residual fuels\nwithin the commercial shipping industry. Fuel sulfur content\n(FS) limits and an efficiency design index for future ships are\nexamples of such IMO actions. The impacts of black carbon\n(BC) emissions from shipping are now under review by the\nIMO, with a particular focus on the potential impacts of future\nArctic shipping.\nRecognizing that associating impacts with BC emissions\nrequires both ambient and onboard observations, we provide\nrecommendations for the measurement of BC.We also evaluate\ncurrent insights regarding the effect of ship speed (engine\nload), fuel quality and exhaust gas scrubbing on BC emissions\nfrom ships. Observations demonstrate that BC emission\nfactors (EFBC) increases 3 to 6 times at very low engine\nloads (<25% compared to EFBC at 85–100% load); absolute\nBC emissions (per nautical mile of travel) also increase\nup to 100% depending on engine load, even with reduced\nload fuel savings. If fleets were required to operate at lower\nmaximum engine loads, presumably associated with reduced\nspeeds, then engines could be re-tuned, which would reduce\nBC emissions.\nShips operating in the Arctic are likely running at highly\nvariable engine loads (25–100 %) depending on ice conditions\nand ice breaking requirements. The ships operating at\nlow load may be emitting up to 50% more BC than they\nwould at their rated load. Such variable load conditions make\nit difficult to assess the likely emissions rate of BC.\nCurrent fuel sulfur regulations have the effect of reducing\nEFBC by an average of 30% and potentially up to 80%\nregardless of engine load; a removal rate similar to that of\nscrubbers.\nUncertainties among current observations demonstrate\nthere is a need for more information on a) the impact of fuel\nquality on EFBC using robust measurement methods and b)\nthe efficacy of scrubbers for the removal of particulate matter\nby size and composition.