Temporal scales for nearshore hits of current-driven pollution in the Gulf of Finland

• Long-term properties of current induced drift of pollution analysed in detail.
• Properties of drift from the fairway to the coast of the Gulf of Finland quantified.
• Small shifts of certain parts of the fairway may give sensible large-scale benefit.
• No changes in the overall probabilities of reaching the nearshore in 1965–2004.
• The proportion of hits to the opposite shores has substantial changes in 1965–2004.

Lagrangian trajectories of water parcels reconstructed using the TRACMASS model from three-dimensional velocity fields by the RCO model for 1965–2004 are used to analyse the temporal scales and the probability for the hits to the nearshore by pollution originating from a major fairway in the Gulf of Finland and transported by surface currents. Increasing the simulation length from 10 to 20 days induces a linear increase in particle age, but the pattern of nearshore hits remains the same. A reasonable benefit can be reached by relatively small shifts of certain parts of the present fairway in a few locations. The overall probabilities do not reveal any trend for 1965–2004. The largest changes in the nearshore hits are revealed for the proportion of hits to the opposite nearshore areas. This feature probably reflects an abrupt turn of the geostrophic air-flow over the southern Baltic Sea by ~ 40° since 1987.