Exhaust particles 

The research focused on incorporation of soot (“particulate exhaust emissions”) in the air, in rainwater and in freshwater lake sediments. These substances are released from flaring at Mongstad, for example.

Put technically, the soot particles comprise carbonaceous cores surrounded by adsorbed organic substances such as PAHs.

Based on an extensive sampling, analytical and modelling programme, StatoilHydro researchers have found that PAH concentrations in airborne particles at refinery ground level and in rainwater describe similar patterns. They vary considerably with weather conditions.

Rainwater concentrations are also predictably an order of magnitude higher at the refinery than at more distant control points.

Similar PAH trends might therefore be expected in lake sediments, with concentrations significantly higher the closer one gets to local sources of pollution. However, the results tell a very different story. 

Sediment cores were taken from two lakes – Svartatjønn, about 10 kilometres northeast of Mongstad, and Kattatjønn at Sotra, roughly 60 kilometres to the south.

No correlation was found between local emissions and PAH concentrations over the past 40-50 years.

The concentrations in both lakes also describe astonishingly similar patterns, with a significant decline of about 75% since the 1950s.

Most of this soot must have derived from common sources and been transported over considerable distances, and thereby has little to do with local contributions.
 
The most likely sources are north-west continental Europe and the UK, for the following reasons:

• these regions have been steadily reducing air pollution over the past 40-50 years

• they lie upwind of Mongstad, where prevailing winds are south-westerly

• PAH concentrations measured in areas unaffected by these air streams are far lower.

Despite being indirect, the evidence is compelling – especially since acidification and acid rain in southern Norway show a similar pattern.