Characterization of aerosols at a coastal site near Vindeby (Denmark)

Aerosol particle size distributions and aerosol chemical composition were m easured with optical particle counters and filter packs, respectively, on a n offshore mast in the Danish coastal waters near Vindeby on the island of Lolland. The filter pack samples were analyzed for ions representative of m arine and continental aerosol: Na+, Cl-, SO4--, NO3-, and NH4+. The physica l and chemical measurements are complementary, and the information on chemi cal composition, together with the local meteorological parameters, the syn optic situation, and air mass trajectories, is crucial for interpreting the observed variations in the particle concentrations. Considering these sets of data, four periods can be discerned during the experiment. Further, the aerosol concentrations vary with wind speed, as is expected for marine aer osols, depending strongly on the fetch. In the case of short fetch, the coa rse aerosol fraction (diameter >1 mu m) and the fine aerosol fraction (0.2- 1 mu m) decrease with wind speed. Processes like advection, diffusion, and dry deposition cannot explain the strong dependence of the concentrations o n wind speed. Apparently, uncertainties in the source strength and origin o f aerosol advected across the shore line, as well as processes affecting th e aerosol concentrations over land, such as variability in the sources, was hout by rain, and other removal and transport mechanisms, have much more in fluence than the transport and removal over water.