Speciated particle dry deposition to the sea surface: results from ASEPS ’97

It has been postulated that atmospheric pathways may comprise a significant source of nitrogen for aquatic ecosystems and excess atmospheric deposition to coastal areas may be a major cause of eutrophication. Dry deposition of nitrogen containing particles is a potential, but poorly quantified pathway, for atmospheric nitrogen flux. This pathway is not well quantified because deposition velocities for particles are difficult to calculate and incorporate substantial uncertainties. Herein we employ an amended version of the Hummelshøj et al. (1992, Proceedings of the 5th International Conference on Precipitation Scavenging and Atmosphere–Surface Exchange Processes. AMS, Richland, Washington, USA, 12pp.) model to calculate size-segregated dry deposition of particle inorganic nitrogen compounds to the western Baltic during the late Spring of 1997 based on data collected as part of the Air–Sea Exchange Process Study (ASEPS). The results show that over a 15 d period in April and May dry deposition fluxes varied between 30 and 400 μg m-2 d-1 for nitrate and 1 and 120 μg m-2 d-1 for ammonium. Sensitivity analyses run to assess the potential bounds on actual dry deposition indicate that, for reasonable variation of model parameters and formulation, particle nitrogen dry deposition may be varied by up to an order of magnitude. The primary sources of uncertainty are identified and are discussed in the context of alternative model formulations