New research on black carbon emission factors from ships

Fuel type, engine type, engine load, and the technology used to treat exhaust gas are all factors in black carbon emissions from ships

Ports and marine vessels are a large source of black carbon (soot). Shipping is responsible for approximately two per cent of global black carbon emissions and nine per cent of all diesel black carbon emissions. Black carbon contributes to human induced climate warming and is linked to human health issues, such as lung cancer, respiratory illness, and cardiopulmonary disease.

Understanding the sources of marine black carbon emissions is a growing global concern but the factors responsible for these emissions in the marine sector are uncertain. Measuring marine black carbon is challenging and in the past published emission factors varied more than ten-fold, creating uncertainty in estimating impacts on climate and health.

“Better measurement of black carbon emissions from marine engines will help promote technologies to control black carbon before it's released into the atmosphere and damages human health and the climate," Dr. Dan Rutherford, Marine Program Director at the International Council on Clean Transportation (ICCT) said. "Cleaner fuels, engines, and after-treatment are available today but better data on their effectiveness is needed to make the case for their adoption."

The ICCT tested black carbon emissions from marine engines in the lab and onboard two container ships and recently published a report of their findings: Black Carbon Measurement Methods and Emission Factors from Ships. One container ship had a modern Tier II main engine while the other had an older Tier 0 engine outfitted with an exhaust gas cleaning system (known as scrubbers).

“It’s vitally important to measure black carbon from ships at sea and not just in the lab,” said Principal Investigator Dr. Kent Johnson. "These real-world tests revealed that there are many factors that impact how much black carbon a ship emits, including the quality of the fuel and the age of the engine. Testing high quality distillate fuels and newer engines showed that black carbon from ships can be greatly reduced using existing technologies.”

These real-world tests revealed that there are many factors that impact how much black carbon a ship emits, including the quality of the fuel and the age of the engine.
Dr Kent Johnson
Principal Investigator

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.

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