Black carbon emissions from global shipping

New studies show how much ships contribute to emissions of soot particles and the measures available to cut those emissions.

A new report by the International Council on Clean Transportation (ICCT) presents an updated global inventory of black carbon emissions from ships. It also contains an analysis of the effectiveness of several emission control measures, including switching to cleaner-burning fuels and using diesel particulate filters (DPFs).

It was estimated that in 2015, ships emitted about 67,000 tonnes of black carbon, equivalent to 0.7–1.1 per cent of total global anthropogenic black carbon emissions. After carbon dioxide (CO2), black carbon contributes most to the climate impacts of shipping, representing 7 per cent of total shipping CO2-eq emissions on a 100-year timescale and 21 per cent of CO2-eq emissions on a 20-year time scale.

Looking at the different ship types, it was found that container ships, bulk carriers, and oil tankers together were responsible for 60 per cent of the emissions, while accounting for 30 per cent of the ships in the global fleet and 81 per cent of its deadweight tonnage (dwt). Container ships alone accounted for 26 per cent of the emissions while making up only 7 per cent of ships and 14 per cent of dwt in the global fleet.

Cruise ships were found to be responsible for disproportionately large amounts of black carbon, producing 6 per cent of total ships’ emissions despite accounting for only 1 per cent of the number of ships and less than 1 per cent of dwt. Moreover, cruise ships had the highest emissions per ship and per unit of fuel consumption.

The ICCT recommends several ways to reduce black carbon emissions from ships, including:

  • prohibiting the use of residual fuels;
  • installing diesel particulate filters (DPF);
  • establishing new Emission Control Areas (ECAs);
  • establishing a black carbon emission standard for ships;
  • plugging into shore power at port; and,
  • including black carbon in the shipping sector’s greenhouse gas emissions reduction strategy.

The International Maritime Organization (IMO) decided back in 2010 that ships’ emissions of black carbon and other particulate matter affecting the Arctic region needed to be addressed as an integral part of the IMO’s work on prevention of air pollution from ships and combatting climate change. Following this decision, some years were spent on discussing the matter, resulting among other things in an agreed definition of black carbon in 2015; work to identify appropriate methods for measurement of black carbon; and investigation of emission control measures.

A first study on emission control measures for black carbon was produced in 2012, and an update of that study was recently published and submitted by Canada to the IMO. The summary results of this update are shown in the Table.

Table: Summary of black carbon abatement technologies

Reduction measure/strategy Reduction
Liquefied natural gas (LNG) 93.5%
DPF – low-sulphur fuel >99%
DPF – high-sulphur fuel 85%
Water-in-fuel emulsion (WiFE) 70%
Scrubbers – high sulphur fuel 45%
Scrubbers – low sulphur fuel 37.5%
Switch HFO to distillate fuel 33%
Slow steaming with de-rating 15%
Biodiesel – 100% 50–75%
Biodiesel blend – 20% 10–30%
Methanol – DME 97%
Nuclear 95%
Slide valves 10–50%
Electrostatic precipitators 10–90%
Selective catalytic reduction (SCR) 0–30%

Compared to the 2012 data, abatement potentials were changed for three options: diesel particulate filters, scrubbers, and switching from heavy fuel oil (HFO) to distillate fuel.

According to the update, new studies provide more certainty that a switch from residual fuel to distillate fuel reduces black carbon emissions by at least 33 per cent, but that using low-sulphur fuel blends will likely not lead to black carbon reductions. DPFs show high black carbon removal rates for distillate fuel, and as DPF technology for higher sulphur fuels advances it is expected that removal efficiencies will approach the upper limit of that reported for distillate fuels, i.e. over 99 per cent.

Both reports were submitted to and discussed at the IMO’s subcommittee on Pollution Prevention and Response (PPR) that met in February, and the issue is also likely to be brought up at the forthcoming meeting of the IMO’s Marine Environment Protection Committee in April.

Christer Ågren


The ICCT report “Black Carbon emissions and fuel use in global shipping 2015” is available at:

IMO document PPR 5/INF.7, 29 November 2017 “An update to the investigation of appropriate control measures (abatement technologies) to reduce Black Carbon emissions from international shipping”, submitted by Canada.


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