Use constraints: Data can be used freely given that the source is cited (following creative commons license CC-BY). The source should be cited as: “HELCOM HOLAS 3 Dataset (2023)"

Data source:

Illegal oil discharges data is based on airborne surveillance with remote sensing equipment by HELCOM Contracting parties in the Baltic Sea Area. Polluting ship accident data is based on data collected annually from HELCOM Contracting Parties.

Illegal oil discharges:

If oil spill volume was missing, median of the rest was given. If area of spill was missing, mean of the existing was given. If the spill was < 1km2, the value of spill volume was given directly to 1km2 grid cell. If the spill area > 1km2, the estimated volume of the spill was divided by the spill area to get the estimated amount of oil / km2. This value was given to the entire spill area.

Polluting ship accidents:

9/24 accidents with oil spills were missing spilled oil volume, thus a mean of reported volumes was given to accidents with missing oil volume. Spill volume was given directly to 1km2 grid cell.

Layers were separately normalised (0-1). After that layers were summed and again normalised to produce the final pressure value between 0 and 1.

Attribute information: Index value representing pressure from oil spills and slicks, including layers illegal oil discharges and polluting ship accidents.

Spatial coverage: Entire Baltic Sea.

Spatial resolution: Original data reported as points, finally converted to 1 km x 1 km grid.