ALBERT

Description: 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.

Description: The physicochemical properties of the sea surface microlayer (SML), i.e. the boundary layer between the air and the sea, and its impact on air-sea exchange processes have been investigated for decades. However, a detailed description about these processes remains incomplete. In order to obtain a better chemical characterization of the SML, in a case study three pairs of SML and corresponding bulk water samples were taken in the southern Baltic Sea. The samples were analyzed for dissolved organic carbon and dissolved total nitrogen, as well as for several organic nitrogen containing compounds and carbohydrates, namely aliphatic amines, dissolved free amino acids, dissolved free monosaccharides, sugar alcohols, and monosaccharide anhydrates. Therefore, reasonable analytical procedures with respect to desalting and enrichment were established. All aliphatic amines and the majority of the investigated amino acids (11 out of 18) were found in the samples with average concentrations between 53 ng/l and 1574 ng/l. The concentrations of carbohydrates were slightly higher, averaging 2900 ng/l. Calculation of the enrichment factor (EF) between the sea surface microlayer and the bulk water showed that dissolved total nitrogen was more enriched (EF: 1.1 and 1.2) in the SML than dissolved organic carbon (EF: 1.0 and 1.1). The nitrogen containing organic compounds were generally found to be enriched in the SML (EF: 1.9-9.2), whereas dissolved carbohydrates were not enriched or even depleted (EF: 0.7-1.2). Although the investigated compounds contributed on average only 0.3% to the dissolved organic carbon and 0.4% to the total dissolved nitrogen fraction, these results underline the importance of single compound analysis to determine SML structure, function, and its potential for a transfer of compounds into the atmosphere.

Description: An analytical method for the determination of the alpha dicarbonyls glyoxal (GLY) and methylglyoxal (MGLY) from seawater and marine aerosol particles is presented. The method is based on derivatization with o-(2,3,4,5,6-Pentafluorobenzyl)-hydroxylamine (PFBHA) reagent, solvent extraction and GC-MS (SIM) analysis. The method showed good precision (RSD 〈 10%), sensitivity (detection limits in the low ng/l range), and accuracy (good agreement between external calibration and standard addition). The method was applied to determine GLY and MGLY in oceanic water sampled during the Polarstern cruise ANT XXVII/4 from Capetown to Bremerhaven in spring 2011. GLY and MGLY were determined in the sea surface microlayer (SML) of the ocean and corresponding bulk water (BW) with average concentrations of 228 ng/l (GLY) and 196 ng/l (MGLY). The results show a significant enrichment (factor of 4) of GLY and MGLY in the SML. Furthermore, marine aerosol particles (PM1) were sampled during the cruise and analyzed for GLY (average concentration 0.19 ng/m**3) and MGLY (average concentration 0.15 ng/m**3). On aerosol particles, both carbonyls show a very good correlation with oxalate, supporting the idea of a secondary formation of oxalic acid via GLY and MGLY. Concentrations of GLY and MGLY in seawater and on aerosol particles were correlated to environmental parameters such as global radiation, temperature, distance to the coastline and biological activity. There are slight hints for a photochemical production of GLY and MGLY in the SML (significant enrichment in the SML, higher enrichment at higher temperature). However, a clear connection of GLY and MGLY to global radiation as well as to biological activity cannot be concluded from the data. A slight correlation between GLY and MGLY in the SML and in aerosol particles could be a hint for interactions, in particular of GLY, between seawater and the atmosphere.

Description: In the framework of the MarParCloud (Marine biological production, organic aerosol particles and marine clouds: a Process Chain) project, measurements were carried out on the islands of Cape Verde, to investigate the abundance, properties, and sources of aerosol particles in general and cloud condensation nuclei (CCN) in particular, both close to sea and cloud level heights. A thorough comparison of particle number concentration (PNC), particle number size distribution (PNSD) and CCN number concentration (NCCN) at the Cape Verde Atmospheric Observatory (CVAO, sea level station) and Monte Verde (MV, cloud level station) reveals that during times without clouds the aerosol at CVAO and MV are similar and the boundary layer is generally well mixed. Therefore, data obtained at CVAO can be used to describe the aerosol particles at cloud level. Cloud events were observed at MV during roughly 58% of the time and during these, a large fraction of particles were activated to cloud droplets. A trimodal parameterization method was deployed to characterize PNC at CVAO. Based on number concentrations in different aerosol modes, four well separable types of PNSDs were found, which were named the marine type, mixture type, dust type1 and dust type2. Aerosol particles differ depending on their origins. When the air masses came from the Atlantic Ocean, sea spray can be assumed to be one source for particles, besides for new particle formation. For these air masses, PNSDs featured the lowest number concentration in Aitken, accumulation and coarse mode. Particle number concentrations for the sea spray aerosol (SSA, i.e., the coarse mode for these air masses) accounted for about 3.7% of NCCN,0.30% (CCN number concentration at 0.30% supersaturation) and about 1.1% to 4.4% of Ntotal (total particle number concentration). When the air masses came from the Saharan desert, we observed enhanced Aitken, accumulation and coarse mode particle number concentrations and overall increased NCCN. NCCN,0.30% during the strongest observed dust periods is about 2.5 times higher than that during marine periods. However, the particle hygroscopicity parameter κ for these two most different periods shows no significant difference and is generally similar, independent of air mass. Overall, κ averaged 0.28, suggesting the presence of organic material in particles. This is consistent with previous model work and field measurement. There is a slight increase of κ with increasing particle size, indicating the addition of soluble, likely inorganic material during cloud processing.

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).