Aarhus Universitets segl

No. 515: Air emissions from small-scale burning tests of crude and heavy fuel oil

Fritt Rasmussen, J., Juncher Jørgensen, C., Klenø Nøjaard, J., Wilkens, K., Renvold, L. Wegeberg, S., Lassen, P & Gustavson, K. 2022. Air emissions from small-scale burning tests of crude and heavy fuel. Aarhus University, DCE – Danish Centre for Environment and Energy, 37 pp. Scientific Report No. 515 http://dce2.au.dk/pub/SR515.pdf


Combatting oil spills in high Arctic marine waters may be extremely challenging due to the presence of ice, remoteness, darkness and difficult access. In situ burning of oil spills is recognised as an effective removal method for oil spills in the sea. Ice on the water can contribute to reduce oil weathering and also, under the right circumstances, contain an oil slick as a thick layer on the water surface that can be ignited. Therefore, in situ burning is often mentioned as a promising method for oil spill response in the Arctic.

The aim of this project is to increase the knowledge and understanding of potential environmental implications related to combatting oil spills in ice-infested waters by in situ burning. The project included measurements of air emissions from burns of oil in a small-scale burning cell and a cone calorimeter. A crude oil and a bunker fuel oil were included and burned on the top of seawater or fresh water. The measurements from the small-scale burns of oil had focus on soot, the blackish or brownish substance formed during incomplete combustion. Measured parameters were organic carbon (OC), elemental carbon (EC) as well as dioxins and PAHs. Soot is of concern in relation to the warming of the Arctic environment, and deposits of dark matter on snow and ice surfaces can reduce the albedo and thereby enhance ice melt. In situ burning of oil may generate persistent organic pollutants (POPs) such as dioxins and PAHs that pose a risk for marine mammals and humans.

The results from the burning cell showed that burning of bunker fuel on seawater produced the highest amount of soot. The soot emission decreased with increasing mass loss for the freshwater experiments, whereas the picture was not as clear for the burns on seawater. The results thus indicate that the type of water basin (salt/fresh) might influence the amount of soot formed. Further, the highest concentrations of PAHs in the soot were measured for the bunker fuel experiments on seawater. In general, regardless of oil type, for the PAH composition, there is a shift from a 2- and 3-ring dominated oil to the 4-6-ring dominated soot. These larger PAHs are more persistent in the environment than lower molecular weight PAHs. In contrast to measurements of PAHs, dioxins were below the analytical detection limit in all samples.

The cone calorimeter tests showed that increasing external heat (incident heat) led to increased soot concentrations and that the soot concentrations were higher for bunker fuel than for crude oil. Opposite to the burning cell experiments, the soot concentration increased with increasing mass loss. This highlights that it is not simple to reproduce burn tests as just slight changes in a few physical and chemical parameters can affect the actual burning process/fire dynamics significantly and hence the derived results. This also highlights the complications of reproducing full-scale offshore burning events in the laboratory. 

The cone calorimeter soot measurements were extrapolated to give estimates of the total amount of soot produced during the burns, which makes up for between 0.1 and 38% of the burned oil depending on the external heat input.