The ICCT discovered that black carbon emissions are influenced by the type of fuel, engine type, engine load, and the technology used to treat exhaust gas. Distillate fuel (diesel) had the lowest black carbon emission factor compared to heavy fuel oil and desulfurized residual fuel (residual fuel is the remainder of the crude oil after gasoline and distillate fuel oils have been extracted through distillation).
In the onboard vessel trials the modern Tier II engine had much lower BC emissions than the older Tier 0 engine and black carbon emission factors tended to decrease as main engine load increased. Scrubbers helped reduce black carbon emissions by a modest 30%.
Helena Molin-Valdes, Head of the United Nations Environment hosted Climate and Clean Air Coalition Secretariat, said that the marine sector was a growing source of black carbon, including in the Arctic where it accelerates Arctic warming and the decline of sea ice.
“To understand and limit the impact on the environment, precise marine engine black carbon emissions measurements are needed,” Ms Molin Valdes said. “This is why the Coalition continues to work with various partners and stakeholders to reduce these emissions from ships and ports.”
In a communique released at the Climate and Clean Air Coalition’s High Level Assembly in Marrakech, November 2016, Coalition partners welcomed the International Marine Organization’s (IMO) decision to limit sulphur content in marine fuels from 3.5% to 0.5% by 2020, and called on the IMO to explore how to continue to make further progress to reduce these emissions from maritime shipping.
The new ICCT report cites a number potential options for reducing black carbon emissions from marine vessels, including:
- The use of newer (e.g. Tier II) engines. Further research is needed to confirm the use of newer engines, but accelerating fleet turnover or vessel repowers, may serve to reduce black carbon emissions.
- Improving emissions depending on engine load. On a mass per unit distance basis, slow steaming was observed to reduce BC emissions compared to higher speed operations. For the newer (Tier II) engine tested, intermediate speeds (e.g. 28% load point) were associated with higher emissions. Engine manufacturers may be able to calibrate their engines for lower emissions under typical operations. However, further research into the links between black carbon emissions and reduced speeds, including mechanisms to ensure that lower speeds result in emission reductions, is recommended.
- Using scrubbers may have black carbon benefits. Scrubbers appear to help ships comply with regional sulfur limits but they do not appear to control overall stack sulfur particulate emissions. This finding has implications for public health and the overall design of the IMO’s fuel sulfur limits. There is a need for better data on scrubber performance.
- Switching to high quality distillate fuels: Overall, distillate fuels had the lowest black carbon emissions, followed by conventional heavy fuel oils. The low sulfur residual fuel tested, however, had the highest black carbon emission factor of the fuels tested. This raises concerns about the potential impact of the IMO’s tightened global sulfur limit of 0.5% for marine fuels by 2020.
The report was published by the International Council on Clean Transportation through researchers from the University of California - Riverside, Environment and Climate Change Canada, National Research Council Canada, and Eastern Research Group. It was supported by the Climate and Clean Air Coalition.
Since 2014, the CCAC has implemented activities to develop a global marine black carbon emissions inventory and a technology performance database for black carbon mitigation strategies. A final report on black carbon inventory and technology findings will be completed by April 2017.
Over the last two years, CCAC has developed an emissions inventory calculator and a health impacts assessment tool, and organized three project workshops. The mid-term goal of the CCAC work in this sector is to encourage the IMO to set a timeline for regulating black carbon from marine engines by the end of this decade.