SOx, NOx and PM

The combustion of a ship’s fuel produces:

  • Sulphur Oxides (SOx)
  • Nitrogen Oxides (NOx)
  • Particles (fine dust) called particulate matter (PM)

These pollutants, when released into the atmosphere, degrade air quality and have been linked to several health issues, such as asthma, respiratory and cardiovascular disease, as well as premature death, especially within communities living near harbor or port areas.

NOX and SOX emissions also impact the environment by causing acid rain and the eutrophisation of rivers and lakes. NOX also combines to oxygen in the air by the action of sunlight to form ozone, a substance that is not only a powerful greenhouse gas, but that can also cause several symptoms and diseases in exposed humans.

As part of an energy consuming industry, ships have historically been using bunker fuel, a low cost, heavy fuel oil obtained from petroleum distillation. SOX and PM emissions are directly linked to fuel quality, whereas NOX emissions depend on the combustion process.


IMO developed strict rules regarding NOX emissions, fuel sulfur content, fuel quality, as well as other harmful emissions, such as ozone depleting substances, emissions from incinerators, and volatile organic compounds.

Since 2012 regulations require that fuel sulfur content gradually decreases to no longer exceed 0.5% after 2020.

In Canada, regulations are even stricter than that. Canada’s coast lines (including the Saint-Lawrence and Great Lakes) are part of one of the four Emission Control Areas (North American ECA) defined by IMO. Ships navigating inside of the ECA are subject to stricter fuel quality requirements, and as of 2020 must not use fuel with a sulfur content exceeding 0.1% or must use abatement technologies that result in the same emissions reductions. The use of these low sulfur fuels or technologies will also result in a significant reduction in PM emissions.

IMO has also established stricter NOX emissions standards for new builds. These stricter standards will reduce NOX pollution from ships.

Mitigation measures

There are several options for reducing pollutants emissions.

SOx and PM emissions can be reduced by:

  • Using fuel with low sulphur content (e.g. diesel fuel, liquid natural gas)
  • Using technological improvements (e.g. scrubbers or other abatement technologies)

NOx emissions can be reduced by:

  • Improving engine design
  • Water or air injection (to reduce combustion temperature)
  • Exhaust gas recirculation
  • The use of exhaust gas treatment systems

Greenhouse gas emissions

The main greenhouse gas emitted by ships is CO2. Despite the marine industry emitting less CO2 than the other modes of transportation, it cannot ignore its contribution to global warming in a context of economic growth. A study by CE Delft, a consultancy agency, estimated that emissions may increase by up to 120% by 2050 (representing 10% of global GHG emissions), if the marine industry does not implement any reduction measures.

Tools or measures that can help to increase a ship’s energy efficiency:

Ship Energy Efficiency Management Plan (SEEMP)
Every ship is required to have a plan to improve several operational aspects that impact the ship’s energy efficiency. Measures include improved voyage planning, more frequent hull and propeller cleaning, waste heat recovery or installation of a new propeller.

Energy Efficiency Design Index (EEDI)
Since January 1st, 2013, new builds must meet energy efficiency standards based on their design (e.g. hull shape, materials used, etc.). These standards will be tightened incrementally over the years so that by 2025, all new built ships will be more energy efficient by 30 % than those built in 2014.

Ship’s fuel data collection
In 2016 IMO adopted provisions that require ships of 5,000 gross tonnage and above (responsible for 85% of all CO2 emissions from international marine shipping) to start collecting and reporting fuel consumption data for every type of fuel used on board, as well as other specific data. The collected data will provide a robust basis allowing decisions to be made on further measures to be implemented to address greenhouse gas emissions from international shipping in the coming years. The data collection requirements are still under development and are expected to be adopted in 2018. Canada will then include these new requirements into its national regulations.

Ship owners participating in the Green Marine program have been collecting fuel consumption data on a voluntary basis for many years as it is a requirement of the program.

Slow steaming
Slow steaming is the practice of operating ships at less than their maximum speed, reducing the ship’s fuel consumption, thus its greenhouse gas and air pollutants emissions, such as NOx and PM. A 10% reduction in fleet average speed results in a 19% reduction of CO2 emissions after taking into account the additional time required to cover the same distance (source : CE Delft, Regulated slow steaming in maritime transport)

Slow steaming is not regulated but many ships use it as a way to save fuel and maintenance costs. Slow steaming also brings other benefits such as minimizing erosion of shore lines caused by the waves from passing ships, as well as reducing whale strikes (see Best pratices and voluntary initiatives).

Source: IMO, Energy efficiency measures

Port Emissions Inventory

In 2008 Transport Canada used emissions data from the Vancouver Fraser Port Authority to develop a tool for measuring air emissions. The same protocol was then used years later by several ports in the St. Lawrence that agreed to participate in a pilot project. The success of the project urged Transport Canada to make this Port Emissions Inventory Tool available, free of charge, to all Canadian and US ports and terminals through the Green Marine program. Several ports and terminals use the tool to monitor their annual GHG and air pollutant emissions. The collected data allows companies to gauge their environmental footprint in order to implement specific reduction measures and track improvements.