The atmospheric distributions of trace metals, trace organics and nitrogen species over the North Sea

Abstract

A 15 month survey was carried out into the distributions of trace metals, trace organics and nitrogen species in particulate and rainwater samples collected from the atmosphere over the southern North Sea. This is the first time a comprehensive and reliable data-set of this kind has been obtained for a coastal region from collections made at sea. Trace metals . There is a south-north decrease in the emission of trace metals to the atmosphere from the land masses surrounding the North Sea. ´End-member` aerosol trace metal concentrations have been identified for the three major source regions; i.e. continental Europe, U.K. and the open-sea, and indicate that, in general, aerosols from air masses which have crossed continental Europe are richer in some trace metals (e.g. Zn and Pb) than those from air masses which have crossed the U.K. There are short-term variations in the concentrations of trace metals in aerosols over the North Sea; however, on an integrated long-term basis the concentrations reflect land-based source emission strengths, and increase towards the south of the region. There is also pronounced short term variability in the concentrations of trace metals in rainwaters collected over the North Sea, but separate contributions from marine, crustal and anthropogenic sources can be identified. Atmospheric fluxes contribute substantially to the total inputs of trace metals to the North Sea, with both wet and ‘dry’ deposition processes being important. Particulate trace organics . The distributions of three main hydrocarbon classes were studied; i.e. saturated hydrocarbons ( n -alkanes), PAH (polynuclear aromatic hydrocarbons) and UCM (uncharacterized complex material). Carbon preference indices of n -alkanes suggest that terrestrial sources dominate, with marine sources being insignificant. In terms of air mass origins, trace organic concentrations are ranked in the order: continental Europe > U.K. > open sea. In terms of air mass origins, the concentrations of trace organics and some trace metals (e.g. Zn and Pb) are higher in aerosols having a continental European than U.K. source. However, on the basis of predominant air mass trajectories over the survey period, the major source of both trace organics and trace metals to the North Sea atmosphere was air which had recently crossed over the U.K. Nitrogen species. Compared to the North Atlantic sea water inflow, the atmosphere is a minor source of nitrogen species to the North Sea. However, atmospheric nitrogen inputs constitute at least 25% of the terrestrial inputs, and may provide the dominant source of nitrogen in stratified areas of the North Sea remote from riverine inputs. ‘Wet’ deposition processes dominate the total nitrogen flux to the sea surface, but ‘dry’ deposition of gaseous and particulate species contributes significantly.