Atmospheric nitrogen deposition to the North Sea

Abstract

The groups of nitrogen components that contribute most to the eutrophication of the sea are ammonia, nitrogen oxides and their respective reaction products. The emission of ammonia is mainly from animal husbandry, whereas the emission of nitrogen oxides is mainly from combustion processes. Ammonia reacts in the atmosphere to form particulate ammonium. Nitrogen oxides react to form nitric acid, nitrous acid, particulate nitrate and peroxyacetyl nitrate. The various nitrogen components have different physical and chemical properties. Therefore, their dry and wet deposition velocities differ. The dry deposition velocity of gas to the sea depends on its solubility, reactivity, concentration in seawater and the wind speed. The dry deposition velocity of a particle depends on its size and the wind speed. The wet removal rate is a function of meteorological conditions. For a gas it further depends on the solubility and reactivity of the gas. For a particle, it further depends on the particle's ability to act as a condensation nucleus for particles. The total deposition of ammonia and its reaction products to the North Sea is about 140 kt N a −1. The total deposition of nitrogen oxides and their reaction products is about 200 kt N a −1.