Soot particles from shipping: Analysing emission factors

Abstract: Emissions of air pollutants from shipping in Europe result in about 50 000 premature deaths every year. Soot particles, also called black carbon, are particularly hazardous to human health when inhaled. The adverse health effects are especially a danger in coastal areas, but the particles can travel further away with the wind. These soot particles also have an effect on the climate. Fresh soot particles are known to be ineffective cloud condensation nuclei for cloud droplet formation, whereas aged soot particles with condensed inorganic sulphuric acid on the particle surface may act as effective cloud condensation nuclei. This leads to changing properties of clouds, thereby changing the cloud reflection of incoming solar shortwave radiation. The particles can also deposit on surfaces of snow and ice, where they have a warming effect. The snow and ice melts, causing a reduced amount of reflected sunlight. The aim of this study was to calculate the emissions of soot particles from ships in Gothenburg. The amount of soot emissions from ships was compared to the amount of fuel used. This was done by calculating the emission factor for soot and its absorption coefficient. Calculations of the emission factors in ship plumes were made on five selected days. The initial data was gathered over a period of a month outside Gothenburg harbor in the fall of 2014. The field station containing the measurement instruments was located 500 meters downwind from the shipping lane. Plumes were just over a minute old when they reached the field station. A sliding percentile-based method was used in order to separate plumes from background concentrations of CO2 and soot particles. Subsequently, the emission factors were calculated. The total number of analysed ship plumes was 228. Some of which are the same ships arriving and leaving the harbor. When plumes were present, the amount of CO2 rose above the background levels with a minimum of 2 ppm. Plumes could increase with as much as 35 ppm. The emission factor for black carbon, or soot, was estimated at 0.57 ( ± 1.40) grams of black carbon per kilogram of fuel. This is an average number for the shipping fleet connected to Gothenburg, which should be able to be applied to the entire shipping fleet travelling in the SECA area in Europe. Additionally, it is not entirely certain how lower fuel sulphur content affect the emissions of black carbon. There are no identical studies done so far which makes it difficult to reach a conclusion whether the emissions of black carbon particles have decreased or not. When looking at individual ships, no clear difference could be observed. Oil tankers and cargo ro-ro's usually emits the most black carbon but also include vessels with lower emissions. All passenger ships have different emission factors. Not many studies have been done on the subject. It is therefore important to further study this in order to fully understand the effects on soot particles when reducing sulphur.