Within the OMES campaign, we took 1 l samples from a bucket sample conducted at the water surface to estimate primary particle size. Samples were collected once a month at each station. Primary particle size distribution was measured using a Mastersizer2000. The detection range of the Mastersizer2000 is 0.02 µm until 2000 µm. After shaking the 1 l samples intensively, the samples were decanted in the dispersion unit until the obscuration reached a value of approximately 10 %. We used the default absorption and refractive index (i.e., 0.1 and 1.52 respectively) and standard Lorenz-Mie method for spherical particles. The sampled were stirred and pumped with a frequency of 750 rpm and 2000 rpm, respectively, using tab water as a dispersant.