ALBERT

Description: Transparent exopolymer particles (TEPs) exhibit the properties of gels and are ubiquitously found in the world oceans. TEPs may enter the atmosphere as part of sea-spray aerosol. Here, we report number concentrations of TEPs with a diameter 〉 4.5 µm, hence covering a part of the supermicron particle range, in ambient aerosol and cloud water samples from the tropical Atlantic Ocean as well as in generated aerosol particles using a plunging waterfall tank that was filled with the ambient seawater. The ambient TEP concentrations ranged between 7×102 and 3×104 #TEP m−3 in the aerosol particles and correlations with sodium (Na+) and calcium (Ca2+) (R2=0.5) suggested some contribution via bubble bursting. Cloud water TEP concentrations were between 4×106 and 9×106 #TEP L−1 and, according to the measured cloud liquid water content, corresponding to equivalent air concentrations of 2–4×103 #TEP m−3. Based on Na+ concentrations in seawater and in the atmosphere, the enrichment factors for TEPs in the atmosphere were calculated. The tank-generated TEPs were enriched by a factor of 50 compared with seawater and, therefore, in-line with published enrichment factors for supermicron organic matter in general and TEPs specifically. TEP enrichment in the ambient atmosphere was on average 1×103 in cloud water and 9×103 in ambient aerosol particles and therefore about two orders of magnitude higher than the corresponding enrichment from the tank study. Such high enrichment of supermicron particulate organic constituents in the atmosphere is uncommon and we propose that atmospheric TEP concentrations resulted from a combination of enrichment during bubble bursting transfer from the ocean and a secondary TEP in-situ formation in atmospheric phases. Abiotic in-situ formation might have occurred from aqueous reactions of dissolved organic precursors that were present in particle and cloud water samples, whereas biotic formation involves bacteria, which were abundant in the cloud water samples. The ambient TEP number concentrations were two orders of magnitude higher than recently reported ice nucleating particle (INP) concentrations measured at the same location. As TEPs likely possess good properties to act as INPs, in future experiments it is worth studying if a certain part of TEPs contributes a fraction of the biogenic INP population.

Description: The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims to improve our understanding of the genesis, modification and impact of marine organic matter (OM) from its biological production, to its export to marine aerosol particles and, finally, to its ability to act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September–October 2017 formed the core of this project that was jointly performed with the project MARSU (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied, and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place. Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INPs and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analyzed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back-trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modeling studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation- and coarse-mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level, as derived from chemical analysis and atmospheric transfer modeling results, denotes an influence of marine emissions on cloud formation. Organic nitrogen compounds (free amino acids) were enriched by several orders of magnitude in submicron aerosol particles and in cloud water compared to seawater. However, INP measurements also indicated a significant contribution of other non-marine sources to the local INP concentration, as (biologically active) INPs were mainly present in supermicron aerosol particles that are not suggested to undergo strong enrichment during ocean–atmosphere transfer. In addition, the number of CCN at the supersaturation of 0.30 % was about 2.5 times higher during dust periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecular-weight neutral components were important organic compounds in the seawater, and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modeling to better understand transfer patterns, the mechanisms of marine OM transformation in the atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, sea spray aerosol (i.e., primary marine aerosol) contributions to both CCN and INPs are rather limited.

Description: Simultaneous measurements of free amino acids in seawater (underlying water, ULW, and sea surface microlyer, SML), size-segregated aerosol particle and cloud water samples at the Cape Verde Atmospheric Observatory (CVAO) in the framework of the MarParCloud project with contribution of MARSU in September/October 2017. During this campaign, sampling of size-segregated aerosol particles at the CVAO (30 m sampling tower) and seawater sampling at the ocean site (~16°53ˈ30ˈN, ~24°54ˈ00ˈˈW) were performed. Additionally, aerosol sampler and cloud water sampler were installed at the mountain station on the top of the mountain 'Monte Verde (MV)' (744 m a.s.l.). The amino acid analysis includes glycine (Gly), L-alanine (Ala), L-serine (Ser), L-glutamic acid (Glu), L-threonine (Thr), L-proline (Pro), L-tyrosine (Tyr), L-valine (Val), L-phenylalanine (Phe), L-aspartic acid (Asp), L-isoleucine (Ile), L-leucine (Leu), L-methionine (Met), L-glutamine (Gln) and γ-aminobutyric acid (GABA) (purity ≥ 99 %, Sigma-Aldrich, St. Louis, Missouri, USA). The analytical measurements of the derivatized FAA, derivatization was performed using AccQ-Tag™ precolumn derivatization method (Waters, Eschborn, Germany), were performed with ultra high performance liquid chromatography with electrospray ionization and Orbitrap mass spectrometry (UHPLC/ESI Orbtitrap-MS).

Description: In a tank experiment under controlled conditions, the so-called sea spray aerosol chamber, the amino acid and sodium concentrations on the size-segregated aerosol particles were investigated in 3 cycles (experimental approaches, named as Cycle C1, C2 and C3 within the data set). The seawater samples are ambient North Sea water samples sampled on three different days sampled in April 2017 in the Wadden Sea region of the south-eastern North Sea. The seawater samples were first desalted and concentrated, and for the aerosol samples, the aqueous extract was also concentrated. The concentrated samples were divided into aliquots for analysis of free amino acids and hydrolyzed amino acids (hydrolysis by HCl, 110 ºC for 20 h with addition of ascorbic acid). The processed samples were filtered, derivatized using the AccQ-Tag™ precolumn derivatization method (Waters, Eschborn, Germany), and measured by ultrahigh performance liquid chromatography with electrospray ionization and Orbitrap mass spectrometry (UHPLC/ESI Orbitrap-MS). Exact details of the method used can be found under Triesch et al., 2021a (doi:10.5194/acp-21-163-2021) and Triesch et al. 2021b (doi:10.1021/acsearthspacechem.1c00080). From these, nascent sea spray aerosol particles were generated in the sea spray aerosol chamber using a plunging jet system. These nascent sea spray aerosol particles were collected in a low pressure impactor (LPI) size resolved and the individual stages are described in the dataset with LPI. The data set reflects the free and combined amino acids and sodium levels on the size-segregated aerosol particles. Using this data set, conclusions were made about a selective transfer of amino acids from the ocean to the atmosphere under controlled conditions on molecular level. This information could be relevant in the future when parameterizing the organic matter content based on organic compounds and compound classes on marine aerosol particles.

Description: In a tank experiment under controlled conditions, the so-called sea spray aerosol chamber, the amino acid and sodium concentrations in the seawater were investigated in 3 cycles (experimental approaches, named as Cycle C1, C2 and C3 within the data set). The seawater samples are ambient North Sea water samples sampled on three different days sampled in April 2017 in the Wadden Sea region of the south-eastern North Sea. The seawater samples were first desalted and concentrated, and for the aerosol samples, the aqueous extract was also concentrated. The concentrated samples were divided into aliquots for analysis of free amino acids and hydrolyzed amino acids (hydrolysis by HCl, 110 ºC for 20 h with addition of ascorbic acid). The processed samples were filtered, derivatized using the AccQ-Tag™ precolumn derivatization method (Waters, Eschborn, Germany), and measured by ultrahigh performance liquid chromatography with electrospray ionization and Orbitrap mass spectrometry (UHPLC/ESI Orbitrap-MS). Exact details of the method used can be found under Triesch et al., 2021a (doi:10.5194/acp-21-163-2021) and Triesch et al. 2021b (doi:10.1021/acsearthspacechem.1c00080). From these, nascent sea spray aerosol particles were generated in the sea spray aerosol chamber using a plunging jet system. The data set reflects the free and combined amino acids and sodium levels in the seawater. Using this data set, conclusions were made about a selective transfer of amino acids from the ocean to the atmosphere under controlled conditions on molecular level. This information could be relevant in the future when parameterizing the organic matter content based on organic compounds and compound classes on marine aerosol particles.