Marine engines running on low-sulfur fuel emit high numbers of particles

Aerosol physicists hard at work

Low-sulfur fuels are becoming the new norm in marine traffic, lowering soot emissions, but overall particle emissions are still high

Particle emissions from marine traffic affect the Earth’s climate and the air quality in coastal areas. The results of our recent study indicate that the particle number emissions from marine engines remain relatively high, mostly due to the nano-sized particle emissions, although the sulfur content of the studied fuels was low. Especially low-load operation of the engine, which is typical in harbor areas, emitted high numbers of particles.

Compared to liquid fuel combustion, natural gas combustion produced 4-12 times fewer soot mode particles. From the global warming point of view, this encourages the use of natural gas engines in marine vessels, especially close to snow- and ice-covered regions. Soot emissions are particularly adverse in those regions because they change the albedo of the ice and snow layers from reflecting light to absorbing it.

We used various instruments to characterize different aspects of the particles. The particle number distribution of the freshly emitted exhaust had two modes: a nucleation mode, which contained the largest number of particles and a soot mode. When semi-volatile particles were removed from the exhaust, core mode particles originating from the fuel and lubrication oil were left over in the nucleation mode size-range, as well as soot agglomerates in the soot mode size-range.

The study was conducted in collaboration with VTT Technical Research Centre of Finland and Atmospheric Composition Research of Finnish Meteorological Institute. The engine, a 1.4 MW medium-speed marine engine located at and was operated by VTT. The facilities and expertise of Tampere Microscopy Center of Tampere University were needed for transmission electron microscopy (TEM) analysis.

Alanen, J., Isotalo, M., Kuittinen, N., Simonen, P., Martikainen, S., Kuuluvainen, H., Honkanen, M., Lehtoranta, K., Nyyssönen, S., Vesala, H., Timonen, H., Aurela, M., Keskinen, J., Rönkkö, T. (2020). Physical Characteristics of Particle Emissions from a Medium Speed Ship Engine Fueled with Natural Gas and Low-Sulfur Liquid Fuels. Environ. Sci. Technol. https://doi.org/10.1021/acs.est.9b06460