Switching to low sulphur fuels in shipping can provide greater reductions in air pollutant emissions than previously assumed. Carbon dioxide emissions also drop when ships slow down because of the more expensive fuel.
The effects of new ship fuel regulations and voluntary lowering of speeds have been investigated in a recently published study1, led by the National Oceanic and Atmospheric Administration (NOAA) scientist Daniel Lack.
In May 2010, the research team measured the emissions from a commercial container ship, Maersk Line's Margrethe Maersk, about 40 miles off the coast of California, while the ship was burning heavy fuel oil (HFO) containing 3.15 per cent sulphur and 0.05 per cent ash. Another set of measurements took place after the ship had switched to marine gas oil (MGO) containing 0.07 per cent sulphur and less than 0.01 per cent ash.
The fuel switch occurred over a 60-minute period, just before the ship came within 24 nautical miles of the California coast. As the ship participated in the Californian voluntary speed reduction incentive programme, it also slowed down from 22 knots to 12 knots, at about the same time as the fuel switch took place.
As the ship transitioned from high sulphur HFO to low sulphur MGO and slowed down the emission factors (expressed as grams of pollutant per kilogram of fuel) for sulphur dioxide (SO2) and fine particles (PM) dropped by about 90 per cent. The emission factors for sulphate (SO4), cloud condensation nuclei (CCN) and black carbon (BC), pollutants that may have either negative or positive climate impacts, also dropped, by 97, 95.5 and 41 per cent, respectively.
More importantly, emissions per kilometre travelled fell even more. By reducing the speed, fuel consumption was significantly reduced, resulting in a 55-per-cent cut in emissions of the greenhouse gas carbon dioxide (CO2). In addition, the switching from HFO to MGO resulted in a 6-per-cent reduction in CO2 emissions, due to the higher energy content of MGO. These two factors combined resulted in an overall CO2 emission reduction of 58 per cent.
Calculated as emissions per kilometre travelled, pollutant emissions of SO2 and PM both came down by 96 per cent, and those of BC by 75 per cent (see table of all pollutants).
Table: Emission reductions per kilometre travelled by the Margrethe Maersk as a result of fuel switch, speed reduction and combined.
While SO2 is best known as a precursor to acid rain, it also degrades air quality, both directly and indirectly through chemical reactions in the atmosphere. Emissions of SO2 lead to the formation of secondary sulphate particles (PM2.5) in the atmosphere, which poses serious public health concerns. Sulphate particles have a negative radiative forcing, i.e. they contribute to cooling the planet.
Primary PM is a well-known health hazard and can, among other things, damage people's lungs and hearts, leading to premature deaths. Black carbon is a component of PM that comprises dark-coloured particles that can warm the atmosphere and also degrade air quality.
The authors of the study discuss the net radiative effect (warming vs. cooling) of the fuel switch. Changes in the emissions of various air pollutants – some which have a warming effect, others which have cooling effects – likely mean net warming. They argue that the reduction in BC emissions due to fuel quality changes "might suggest a consideration of more refined fuels for future Arctic shipping."
The study's new information on reductions in PM emissions suggests that switching to low-sulphur MGO will result in greater health improvements than previously estimated. So the findings of this study could have global significance, as new international regulations by the International Maritime Organization (IMO) require vessels in designated Sulphur Emission Control Areas (SECAs) to switch to MGO with a maximum of 0.1 per cent fuel as from 2015. At present, nearly the whole coastline of the U.S. and Canada (out to 200 nautical miles) as well as the Baltic Sea, the North Sea and the English Channel are SECAs, and more sea areas may follow their initiative.
Moreover, from 2020 IMO's global sulphur limit will be strengthened from the current level of 4.5 per cent to 0.5 per cent.
"These scientific findings clearly demonstrate that ships off our coast now emit significantly less sulphur pollution than in the past," said California Air Resources Board Chairman Mary D. Nichols. "This is good news for California and for the nation. When the federal regulations kick in for ships to use low-sulphur fuel, communities throughout America that live near shipping lanes and next to ports will see clean air benefits."
Christer Ågren
Impact of Fuel Quality Regulation and Speed Reductions on Shipping Emissions: Implications for Climate and Air Quality. By Daniel Lack et al. Published in Environmental Science & Technology.
Source: NOAA, 12 September 2011.
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