Cargo ships are significant sources of global air pollution because of their fuel oil. Most ships burn heavy fuel oil that is loaded with sulfur, so when it is burned it produces noxious gases and fine particles that can harm human health and the environment. The International Maritime Organization enacted a mandatory cap of 0.5% for the sulfur content of marine fuels in 2020. Heavy fuel oil has a sulfur content of 2 to 3 percent.
Shipping companies can comply by burning low-sulfur fossil fuels or biofuels, but these are much more expensive. The most feasible and cost-effective option is to install exhaust gas cleaning systems, known as scrubbers.
A scrubber is a huge metal tank installed in a ship’s exhaust stack. Seawater is sprayed from nozzles to wash the hot exhaust. The seawater reacts with sulfur dioxide and converts it to sulfates, which are environmentally benign natural components in seawater.
A study by the National Technical University of Athens in Greece has performed a lifecycle assessment of the use of scrubbers and has found that burning heavy fuel oil with the use of scrubbers can match or even surpass the benefits of using low-sulfur fuels.
Producing low-sulfur fuel causes additional greenhouse gas and particulate matter emissions in refineries. On the other hand, scrubbers reduce sulfur dioxide emissions by 97% and dramatically reduce other pollutants as well.
The study shows the importance of incorporating lifecycle assessments into evaluation of environmental impact reduction policies.
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Study: Burning heavy fuel oil with scrubbers is the best available option for bulk maritime shipping
Photo, posted August 3, 2015, courtesy of Lotsemann via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio
