Emission from Commercial Vessels – A Broader Perspective


Atmospheric pollution by commercial ships is a topic of global concern, which has prompted international organisations governing maritime laws to draft legislations for cutting emissions. It is often said that the 15 biggest ships produce more sulphur oxide pollutants than all the cars in the world, because they run on completely different fuels.

Large commercial vessels primarily burn ‘Heavy Fuel Oil’ when out at sea. This fuel is not refined, has high sulphur content and produces a lot of sulphur oxide and nitrogen oxide compounds when it is burned. Cars, on the other hand, burn a highly refined gasoline or the highway diesel fuel which produces almost no sulphur oxides or nitrogen oxides.

The car fuel is same as the Ultra Low Sulphur Marine Gas Oil. A ship produces more carbon dioxide emission per mile and per gallon of fuel than a car. However, ships in general, have the lowest emission levels of any other method of cargo transport, producing fewer emissions per ton of freight per mile than barges, trains or trucks.

Shipping Operations

Container ships usually run 24 hours a day for weeks. There are currently over 6000 massive container ships operating globally and 85,000 commercial cargo ships. Marine heavy fuel or “bunker fuel” is essentially the lowest grade of liquid fuel in use. It contains 2,000 times, as much sulphur as standard automobile diesel.

Bunker fuel is literally the left over when all of the cleaner types of fuel have been extracted from the crude oil. A study reveals that 760 million cars which are currently operating worldwide emit as much sulphur as 15 container ships running at full capacity.

Calculating Emissions

One main output statistic of the world fleet analysis is the ratio of emitted grams of CO2 per tonne-km of transported cargo. Another emissions statistic is an estimate of total CO2 emitted (in million tonnes per year) per size bracket for the above ship types. To measure ship emissions, these statistics are estimated for a variety of ship types under a variety of scenarios – sea-to-port time, ship speed and fuel consumption at sea and in port.

The major ship types in the world today are – bulk carriers, crude oil tankers, container vessels, product/chemical carriers, LNG carriers, LPG carriers, reefer vessels, Ro-Ro vessels and general cargo ships. Carbon dioxide (CO2) emissions from commercial shipping are currently not duly regulated. Nevertheless, they are a subject of intense scrutiny by the world shipping community.

Break-Up of Global Fleet

As of January 2018, there were 52,000 ships trading internationally. General cargo ships are ranked as the most common type of ship in the global merchant fleet, accounting for about a third of the fleet: There were almost 17,000 such ships in the merchant fleet as of the beginning of 2018.

General cargo ships had a combined capacity of around 112.8 million tons deadweight in January 2018; this is about half the volume of container ships’ combined capacity, which came to around 245.6 million tons deadweight. The growing pressure to reduce greenhouse gas emissions in the industry asks for manufacturers’ response. With that in mind, new builds of general cargo ships are predicted to produce an average of 40 percent less carbon dioxide emissions by 2040.

Bulk carriers are ranked as the second most common type of ship in the world, accounting for over 20 percent of the global merchant fleet. As of January 2018, the number of bulk carriers stood at around 11,000. Crude oil tanks and container ships are the third and fourth most common types, with nearly 14 and about 10 percent of the share, respectively. The number of crude oil tankers rounded up to more than 7,000 units, while the number of cargo container ships in the world was at about 5,000 units in the beginning of 2018.


Heavy Fuel Oil (HFO) is very cheap compared to Ultra Low Sulphur Marine Gas Oil (ULSMGO) and many engines are not designed to handle the ULSMGO because it is so much thinner than HFO it does not have the lubrication properties of the HFO.

Companies are using various workarounds to make it work, such as chilling the fuel to increase the viscosity or injecting extra lubricant into certain parts of the engine. Due to the extra costs and possible mechanical issues, these regulations are continuously re-evaluated and phased approaches are used for implementation.

Currently, sulphur content standards for fuel used in international shipping are set at no more than 3.5%. In 2020, that will drop to no more than 0.5%. All of these regulations are contained in the Convention on Marine Pollution (MARPOL), Annex VI, which sets the regulations for Air Pollution in the Maritime Industry.

The Way Ahead

To check the problem of emissions, all 90,000 ships would require a global emissions policy. And a stricter and swiftly-enacted policy would critically damage international trade.

As far as fuel goes, researchers are exploring several alternatives to bunker fuel – the best of which is LNG (Liquified Natural Gas). LNG has the capacity to replace bunker fuel, though it would require a new working infrastructure – something not exactly attractive for developing countries.  Even a successful implementation of LNG wouldn’t reduce carbon dioxide levels enough to totally nullify the effect of marine transport on climate change.

Some companies are part of the push with Liquefied Natural Gas. These ships will produce fewer emissions, of any compound, than any other vessel currently in service. The entire shipping industry is looking at conversions to natural gas or other fuels, and engine manufacturers are designing engines that can handle a variety of fuels.

Sea News Feature, October 12


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