Dry and wet deposition fluxes of Cd, Cu, Pb and Zn into the Southern Bight of the North Sea

During the period from September 1988 to October 1989, 23 sampling flights were carried out over the Southern Bight of the North Sea. In the campaign, both bulk and size-segregated airborne particulate matter samples were collected. Dry deposition velocities for Cd, Cu, Pb and Zn have been estimated using a modified version of the two-layer of Slinn and Slinn and the particle size distribution obtained from size-fractionated samples. Results pointed out that the main difference between our results and those reported in the literature lies in the aerosol size distribution. Dry deposition rates calculated using these deposition velocities as a function of wind sector showed that continental air masses, particularly those associated with the wind sector west southwest, are predominant in the deposition process. Wet flux estimates were carried out using Slinn's approach. Results were also classified taking into account different wind sectors. Here the wet flux of Pb and Zn is mainly related to wind sectors east/northeast, south southeast and local, the latter represents air masses with variable origin; whereas those of Cd and Cu correspond to wind sectors west southwest and south southeast. Results showed that wet deposition is responsible for almost 70% of the total deposition into the Southern Bight of the North Sea. However, some topics, like heavy metal content in large aerosol particles, temporal distribution of precipitation events, variation of precipitation intensity aloft, need better knowledge before accurate assessments can be made