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<p>Measurements of free amino acids (FAAs) in the marine environment to elucidate their transfer from the ocean into the atmosphere, to marine aerosol particles and to clouds, were performed at the MarParCloud (marine biological production, organic aerosol particles and marine clouds: a process chain) campaign at the Cabo Verde islands in autumn 2017. According to physical and chemical specifications such as the behavior of air masses, particulate MSA concentrations and <span class="inline-formula">MSA∕sulfate</span> ratios, as well as particulate mass concentrations of dust tracers, aerosol particles predominantly of marine origin with low to medium dust influences were observed. FAAs were investigated in different compartments: they were examined in two types of seawater underlying water (ULW) and in the sea surface microlayer (SML), as well as in ambient marine size-segregated aerosol particle samples at two heights (ground height based at the Cape Verde Atmospheric Observatory, CVAO, and at 744 m height on Mt. Verde) and in cloud water using concerted measurements. The <span class="inline-formula">∑</span>FAA concentration in the SML varied between 0.13 and 3.64 <span class="inline-formula">µ</span>mol L<span class="inline-formula">⁻¹</span>, whereas it was between 0.01 and 1.10 <span class="inline-formula">µ</span>mol L<span class="inline-formula">⁻¹</span> in the ULW; also, a strong enrichment of <span class="inline-formula">∑</span>FAA (EF<span class="inline-formula">_SML</span>: 1.1–298.4, average of 57.2) was found in the SML. In the submicron (0.05–1.2 <span class="inline-formula">µ</span>m) aerosol particles at the CVAO, the composition of FAAs was more complex, and higher atmospheric concentrations of <span class="inline-formula">∑</span>FAA (up to 6.3 ng m<span class="inline-formula">⁻³</span>) compared to the supermicron (1.2–10 <span class="inline-formula">µ</span>m) aerosol particles (maximum of 0.5 ng m<span class="inline-formula">⁻³</span>) were observed. The total <span class="inline-formula">∑</span>FAA concentration (PM<span class="inline-formula">₁₀</span>) was between 1.8 and 6.8 ng m<span class="inline-formula">⁻³</span> and tended to increase during the campaign. Averaged <span class="inline-formula">∑</span>FAA concentrations in the aerosol particles on Mt. Verde were lower (submicron: 1.5 ng m<span class="inline-formula">⁻³</span>; supermicron: 1.2 ng m<span class="inline-formula">⁻³</span>) compared to the CVAO. A similar contribution percentage of <span class="inline-formula">∑</span>FAA to dissolved organic carbon (DOC) in the seawater (up to 7.6 %) and to water-soluble organic carbon (WSOC) in the submicron aerosol particles (up to 5.3 %) indicated a related transfer process of FAAs and DOC in the marine environment.</p> <p>Considering solely ocean–atmosphere transfer and neglecting atmospheric processing, high FAA enrichment factors were found in both aerosol particles in the submicron range (EF<span class="inline-formula">_aer(∑FAA)</span>: <span class="inline-formula">2×10³</span>–<span class="inline-formula">6×10³</span>) and medium enrichment factors in the supermicron range (EF<span class="inline-formula">_aer(∑FAA)</span>: <span class="inline-formula">1×10¹</span>–<span class="inline-formula">3×10¹</span>). In addition, indications for a biogenic FAA formation were observed. Furthermore, one striking finding was the high and varying FAA cloud water concentration (11.2–489.9 ng m<span class="inline-formula">⁻³</span>), as well as enrichments (EF<span class="inline-formula">_CW</span>: <span class="inline-formula">4×10³</span> and <span class="inline-formula">1×10⁴</span> compared to the SML and ULW, respectively), which were reported here for the first time. The abundance of inorganic marine tracers (sodium, methanesulfonic acid) in cloud water suggests an influence of oceanic sources on marine clouds. Finally, the varying composition of the FAAs in the different matrices shows that their abundance and ocean–atmosphere transfer are influenced by additional biotic and abiotic formation and degradation processes. Simple physicochemical parameters (e.g., surface activity) are not sufficient to describe the concentration and enrichments of the FAAs in the marine environment. For a precise representation in organic matter (OM) transfer models, further studies<span id="page164"/> are needed to unravel their drivers and understand their composition.</p>