Ship emissions down in the Baltic and North Sea

Photo: flickr.com/ecstaticist/cc by-sa

Switching to low-sulphur marine gas oil and lowering cruising speeds can reduce shipping emissions of air pollutants and greenhouse gases.

Implementing the stricter ship fuel sulphur standards in the northern European sulphur emission control area will cut emissions of sulphur dioxide (SO₂) and particulate matter (PM_2.5) by 85 and 50 per cent, respectively, between 2011 and 2015.

The corresponding increase in fuel costs is estimated to be between 10 and 63 per cent depending on the development of the fuel oil prices and the use of the sulphur scrubbers.

Between 2009 and 2011, emissions of SO₂ from shipping in the northern European sulphur emission control area (SECA) came down from 350,000 to 238,000 tons (-32%), and those of PM_2.5 were lowered from 80,700 to 66,900 tons (-17%).

On the other hand, emissions of nitrogen oxides (NOx) increased by five per cent, from 1,032,900 to 1,085,100 tons, and those of carbon dioxide (CO₂) went up by nine per cent, from 49.4 to 54 million tons.

The figures come from a recent Finnish inventory of marine exhaust emissions carried out by the Finnish Meteorological Institute, using data for 2009 and 2011 on real ship movements taken from the global automatic identification system (AIS) and processing this data in the ship traffic emission assessment model (STEAM).

According to the authors, the strengthening of the sulphur standards has obviously had a significant impact on reducing the emissions of both SO₂ and PM_2.5. As from 1 July 2010 the sulphur limit for ships in SECAs was lowered from 1.5 to 1.0 per cent, and from 1 January 2010 the EU sulphur limit of 0.1 per cent for ships at berth came into effect.

It was noted that the highest emissions were located in the vicinity of the coast of the Netherlands, in the English Channel, near the south-east UK and along the busiest shipping lines in the Danish Straits and the Baltic Sea. Near several major ports (e.g., Antwerp, Rotterdam, Amsterdam, Hamburg, Riga, Tallinn, Helsinki and St. Petersburg), the emissions of PM_2.5 per square kilometre were especially high.

In order to evaluate the overall impact of stricter sulphur standards so far, a model simulation was performed applying the 2005 sulphur standards to the ship activity levels of 2011. The simulation showed that the SO₂ emissions in the Baltic Sea and the North Sea would have been 131 per cent higher (i.e., more than twice as high), compared to the current emissions in 2011. The corresponding PM2.5 emissions would have been 67 per cent higher. It was also estimated that if the 2005 sulphur standards still applied, the direct fuel costs would have been 12 per cent lower.

In 2008 the International Maritime Organization (IMO) unanimously agreed new ship emission standards, including a further strengthening of the SECA sulphur standard down to 0.1 per cent as from 1 January 2015. The IMO’s sulphur standards were introduced in EU legislation last year.

Based on ship movements in 2011, the expected impacts of the 0.1 per cent limit on SECA ship emissions was simulated in the model. It was estimated that the SECA limit would reduce the emissions of SO2 by 85 per cent and those of PM_2.5 by 50 per cent, compared to the 2011 level of emissions.

Assuming that the fuel price differential would be the same as in January 2013, the introduction of the 0.1 per cent sulphur standard was estimated to increase the direct fuel costs by 19 per cent. In January 2013, the price of 0.1 per cent marine gas oil (MGO) was USD960 per ton and the cost of 1 per cent sulphur heavy fuel oil (HFO) was USD668 per ton, i.e. a price differential of USD292 per ton, or 44 per cent. The percentage increase in direct fuel costs is lower than the price differential because some ships already use low-sulphur MGO as their main fuel and/or to fuel their auxiliary engines, and ships are also obliged to use low-sulphur MGO when at berth.

However, it is noted by the authors that fuel price development over time has been volatile and the price differential between HFO and MGO has varied significantly. They therefore looked at three different levels of price differentials: 50, 75 and 100 per cent price premium for MGO over HFO. If assuming the worst-case scenario – a price premium of 100 per cent – the direct fuel costs would increase by 64 per cent.

As an alternative to switching to 0.1 per cent sulphur MGO, ships can use exhaust gas cleaning systems, also known as scrubbers, to reduce their SO₂ emissions. Based on the estimated fuel consumption and current fuel prices, it was estimated that more than 630 IMO-registered ships might benefit from retrofitting scrubbers. These ships were responsible for more than one fifth of the total fuel consumption in the ECA in 2011.

Assuming that these ships would use scrubbers instead of switching to 0.1 per cent sulphur MGO, the estimated fuel cost increase in 2015 would be only 10 per cent (using the contemporary bunker prices) or at most 46 per cent (assuming 100 per cent price premium between HFO and MGO).

Achieving emission reductions by decreasing vessel cruising speeds was investigated by simulating speed reductions of 10 and 30 per cent to speeds exceeding 10 knots. It was concluded that the effectiveness of speed reduction as a way to curb emissions varies substantially between ship types. Especially RoPax, RoRo and vehicle carrier ships could achieve substantial fuel cost savings, without large increases in operational time.

The resulting fuel savings were significant even with a speed reduction as low as 10 per cent, and the relative reduction in SO₂, NOx and PM_2.5 emissions was estimated to be higher than the reduction in total fuel consumption.

Christer Ågren

The evolution of shipping emissions and the costs of recent and forthcoming emission regulations in the northern European emission control area. By L. Johansson et al. Published in Atmosperic Chemistry and Physics Discussion, 13 June 2013.

Figure: Intensity and geographic distribution of shipping emissions of PM_2.5 in 2011.