How Ships Reduce Exhaust Emission Pollution

  Somewhere in the Mediterranean Sea, a lone sailor sits on a ship’s ventilator head, with elbows resting on the gunwale (upper edge on the ship’s side) as he contemplates
27 Sep 2017 11:00
How Ships Reduce Exhaust Emission Pollution


Somewhere in the Mediterranean Sea, a lone sailor sits on a ship’s ventilator head, with elbows resting on the gunwale (upper edge on the ship’s side) as he contemplates his life back home.

Having consumed his daily dose of scotch, Maxi, the engine room boatswain (B’sun) comments critically about a ship steaming by.

“The Chief Engineer on that ship is Greek,” he said.

Maxi’s expert deduction stems from the black colour of the smoke belching out of the passing ship’s funnel.

In the glory days of unregulated staffing, Greek shipping placed little priority into its maintenance, hence the justification for Maxi’s comments.

In those days, smoking funnels just meant the engine was not maintained properly.

Blue, white and black smoke meant different engine conditions, all of them not good.

In recent years, awareness of climate change has created a culture of change in the maritime industry. Even the colourless smoke seems to be a problem.

Over 104,000 ships carrying 90 per cent of the world’s trade of burning fossil fuels are now contributing adversely to the future of our planet.

Shipping companies and engine manufacturers had to take a new perspective on the substances blowing out of a ship’s funnel.

This week I am highlighting the fourth deadly maritime sin and a topical one at that – pollution by exhaust emissions.


Emissions from ships come in two flavours:

n  Greenhouse gases (GHG)

n  Non-Greenhouse gases (non-GHG).

Greenhouse gases

Under the GHG protocol, six gases are classified as GHG’s. Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydro fluorocarbons (HFCs), perfluorooctanesulfonate (PFCs) and sulphur hexafluoride (SF6).

Of the six, CO2 is the most relevant to the maritime industry where shipping is responsible for approximately 3% of the world’s total emissions.



n  Sulphur Oxides (SOx),

n  Nitrogen Oxides (NOx)

n  Particulate matter (PM)

While GHG contributes to climate change, non-GHG causes acid rain, water contamination and reduction in agricultural yields.

The release of Chlorofluorocarbons (CFC) gases from refrigerant machinery increases ground-level ozone and the depletion of the ozone layer.

Data from the International Chamber of Shipping has charted the shipping emissions between 3.0 to 7.9 grams per tonne /km.

Trucking is responsible for 80 g/t/km and big jet engines, where there is hardly any visible smoke, has a whopping 435g/t/km.

Driving down the coast or passing the Suva Harbour, it may appear that the big bad boys are the gas-guzzling ships belching smoke from the funnel.

Although shipping is not the biggest culprit, the industry, led by the International Maritime Organization (IMO) has done the most work of all to combat the problem.



To reduce production of CO2, less fossil fuel must be burnt in the engine.

Slow steaming is one way to reduce the fuel consumption but if the ship is in a hurry, then that is not a good option. Efficiency is the key. The solution is to use less fuel and get more done.



IMO has introduced two measures to reduce emissions by increasing efficiency:

n  Energy Efficiency Design Index (EEDI), and

n  Ships Energy Management Systems (SEEMP)

EEDI expresses grams of CO2 per ship’s capacity-mile and provides a specific figure for an individual ship design.

The smaller the EEDI, the more energy efficient ship design it is and it is calculated by a formula based on the ship’s technical design parameters.

The CO2 reduction level (grams of CO2 per tonne-mile) for the first phase is set to 10 per cent and will be tightened every five years to keep pace with technological developments of new efficiency and reduction measures.

SEEMP is an operational measure that establishes a mechanism to improve the energy efficiency of a ship in a cost-effective manner.

The SEEMP also provides an approach for shipping companies to manage ship and fleet efficiency performance over time.

IMO also has used the International Convention for the Prevention of Pollution from Ships’ MARPOL Annex IV for controlling non-GHG, SOx, NOx and PM’s.


There are several options available for reducing NOx:

n    Humid Air Method

n    Exhaust Gas Recirculation (EGR)

n    Water Injection and Water Emulsion

n    High Scavenge Pressure and Compression Ratio

n    Selective Catalytic Reduction

n   Two-Stage Turbocharger

n    Engine Component Modification



Following are the methods and technologies used to reduce Sulphur emission from marine engines:

n    Use of low Sulphur fuel oil

n    Exhaust Gas Scrubber Technology

n    Control of Cylinder Lubrication

MARPOL Annex IV and emission reduction is a topic in Maritime Law at Fiji Maritime Academy (FMA).

The subject is taught in detail at the higher certificate levels where students are made aware of the maritime industry’s responsibility in the prevention of pollution.

While this article cannot go into the engineering depths of reducing exhaust emissions, it is hoped it goes some of the way of explaining the role of shipping for those curious about its involvement in climate change and other environmental impacts by the maritime industry.

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