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.