Transparent exopolymer particles (TEP) exhibit the properties of gels and may enter the atmosphere as part of sea spray aerosol. Here, we report number concentrations of TEP (diameter> 4.5 µm) in ambient aerosol (total suspended particles, TSP) and cloud water samples from the tropical Atlantic Ocean as well as in generated aerosol particles (PM10) using a plunging waterfall tank that was filled with the ambient sea water. Samples were taken during the MarParCloud: “Marine biological production, organic aerosol particles and marine clouds: a Process chain” campaign that took place from September 13th to October 13th 2017 at the Cape Verde archipelago Island Sao Vicente located in the Eastern Tropical North Atlantic (ETNA). Total suspended aerosol particle (TSP) for TEP analysis and PM10 sampling for sodium analysis was performed on top of a 30 m sampling tower of the CVAO. TSP were sampled with a filter sampler consisting of a filter holder equipped with a 0.2 µm pore-sized, acid-cleaned polycarbonate (PC) filter mounted to a pump. Sampling usually took place for 24 h and the flow of the pump was between 5 and 10 L min-1 and frequently measured with a flowmeter. Total volumes between 10 and 15 m3 were sampled. Cloud water was sampled on Mt. Verde, which is the highest point of the São Vicente Island (744 m), situated in the northeast of the Island (16°52.11ˈN, 24°56.02ˈW) and northwest to the CVAO. Bulk cloud water was collected using a compact Caltech Active Strand Cloudwater Collectors (CASCC2) equipped with acid cleaned Teflon®strands (508 µm diameter). Cloud droplets were caught on the strands and gravitationally channelled into an acid-precleared Nalgene bottle. TSP particles were sampled from a plunging waterfall tank experiment that consists of a 1400 L basin with a 500 L aerosol chamber on top. The bubble driven transport of organic matter was induced using a skimmer on a plunging waterfall. A stainless steel inlet was inserted in the headspace of the tank and connected with three filter holders for offline aerosol particle sampling without size segregation (TSP). The filter system for TEP analysis was equipped with a 0.2 µm pore-sized, acid-cleaned polycarbonate (PC) filter mounted to a pump. Sampling usually took place for ~ 24 h, the flow of the pump was between 5 and 10 L min-1 and frequently measured with a flowmeter. Total volumes between 9 and 10 m3 were sampled. The sampling procedure was therefore identical to the ambient TEP filter sampling. Another filter holder was equipped with a preheated 47 mm quartz fiber filter (Munktell, MK 360) for sodium analysis. The filters obtained from ambient and tank-generated TSP aerosol particle sampling and cloud water filtrations were stained with 3 mL of an Alcian blue stock solution stained (0.02 g Alcian blue in 100 mL of acetic acid solution, pH 2.5) for 5 s yielding an insoluble non-ionic pigment and afterward rinsed with milliQ water. For microscopic TEP analysis, abundance, area, and size-frequency distribution of TEP were determined using a light microscope (Zeiss Axio Scope A.1) connected to a camera (ColorView III). Filters were screened at 200× magnification. About 10 pictures were taken randomly from each filter in two perpendicular cross-sections (5 pictures each cross-section; dimension 2576 x 1932 pixel, 8-bit color depth). Images were then semi-automatically analyzed using ImageJ (Version 1.44). A minimum threshold value of 16 µm2 was set for particle size during particle analysis to remove the detection of non-aggregate material by the program. This resulted in a minimum particle size of 4.5 µm (assuming spherical particle). TEP number concentrations were converted to TEP volume concentrations. To this end, for atmospheric and for oceanic samples, particle number concentrations of TEP were extracted from the size distribution spectra and volume concentrations were calculated (assuming spherical particles). The analysis of sodium from PM10 samples was performed with ion chromatography and conductivity detection.
