Modelled atmospheric contribution to nitrogen eutrophication in the English Channel and the southern North Sea

•Weather data, emissions data and Lagrangian computations form the numerical model.•Deposition maps in a target geographical region are produced and compared.•Individual polluting industrial or transport sectors can be traced.•Atmospheric deposition of nitrogen eutrophicants increases in wet weather.•Heaviest atmospheric deposition adds to high riverine input in some coastal regions.

Eutrophication of the coastal waters results in algal blooms which may be harmful to the marine ecosystem and coastal economy. The main sources of nutrients are the rivers but an unquantified amount of nitrogen is also transported from ground sources via the atmosphere and deposited to the sea directly by rain and turbulent diffusion. A Lagrangian Particle Dispersion (LPD) model based on the open source code FLEXPART (http://flexpart.eu) is described that quantifies the dissolved nitrogen coming from the air in the English Channel and Southern North Sea (the '2Seas' geographical region). The model uses meteorological records, emissions data and LPD computations to simulate the motion and deposition of nitrogen compounds. The emission sources contributing to the deposition are individually identified, and calculated concentrations are compared with ground measurements in selected locations. The highest calculated atmospheric depositions to the sea in the considered region are found to be along the Belgium-Netherlands coast.