Atmospheric input of trace metals to the western Mediterranean Sea: 1. Factors controlling the variability of atmospheric concentrations

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Abstract
The factors controlling the variability of atmospheric trace metal concentrations over the western Mediterranean Sea have been investigated using a combination of geochemical and meteorological approaches. Al, Br, Cd, Na, Pb and 210Po concentrations from bulk filters and cascade impactor samples collected during five cruises (1980–1983) have been used to characterize the aerosol sources: the marine source (Na), the aeolian soil mobilization (Al), the anthropic sources (Cd, Pb), and the volcanic source (210Po). It has been confirmed that Cd and Pb directly derive from anthropic sources. As shown by three‐dimensional air mass trajectory analyses, the variability of daily atmospheric concentrations reflects both changes in continental source strengths and in airflow patterns. Atmospheric concentrations appear to be higher during episodes of short‐range transport of continental material from riparian countries. It is suggested that such source regions can be precisely identified by a careful examination of both geochemical data and three‐dimensional trajectories. From our data set, southwestern Europe would be responsible for the largest Pb and Cd inputs to the western Mediterranean atmosphere (30–40%), but the inputs from North Africa are also likely to be significant (20–25%). However, it cannot be ascertained whether this conclusion is valid on a yearly time scale. Indeed, whereas our sample set is representative of the yearly airflow climatology, it has not been possible to assess the effect of seasonal (for Pb) or sporadic (for Al) changes in source strengths. This points out that over such a marine environment, continuous sampling programs are needed to assess the respective contributions of individual source regions to the atmospheric burden of particulate trace elements.