Oceanic ammonia emissions in Europe and their transboundary fluxes

Annual biogenic emissions of ammonia from European seas and their transboundary flows are estimated. Atmospheric fluxes are calculated from monitored seawater ammonium (NH+4) levels, via a compensation point approach in the acid deposition model of the MSC-W of EMEP. Mean monthly emissions exhibit a September peak of around 100 μg NHx–N m-2 d-1 across both the North and Baltic Seas. Total emissions approximate those of smaller countries, although seas export larger proportions than land areas. Contributions to NHx–N deposition approach 5% in coastal regions of Scotland. Although fluxes are small, seas may represent the 3rd and 4th largest source of imported NHx–N to the Republic of Ireland and the U.K., respectively. Uncertainty associated with the seawater data is between −40% and +80% of the best estimate.