ALBERT

Description: Sub-micron marine aerosol particles (PM1) were collected over the period 22 June–21 July 2011 during the RV MARIA S. MERIAN cruise MSM 18/3, which travelled from the Cape Verdean island of São Vicente to Gabon, in the process crossing the tropical Atlantic Ocean with its equatorial upwelling regime. According to air mass origin and the chemical composition of the sampled aerosol particles, three main regimes could be established. Aerosol particles in the first part of the cruise were mainly of marine origin (Region I). In the second part of the cruise, marine influences mixed with increasing influence from biomass burning (Region II). In the final part of the cruise, which approached the African mainland, the biomass burning influence became dominant (Region III). Generally, aerosol particles were dominated by sulfate (caverage = 2.0 μg m−3) and ammonium ions (caverage = 0.7 μg m−3), which were well-correlated and increased slightly over the duration of the cruise. High concentrations of water-insoluble organic carbon (WISOC; caverage = 0.4 μg m−3) were found, most likely as a result of the high oceanic productivity in this region. Water-soluble organic carbon (WSOC) concentrations increased from 0.26 μg m−3 in Region I to 2.3 μg m−3 in Region III, most likely as a result of biomass burning influences. The major organic aerosol constituents were oxalic acid, methanesulfonic acid (MSA), and aliphatic amines. MSA concentrations were quite constant during the cruise (caverage = 42 ng m−3). Aliphatic amines were most abundant in Region I, with concentrations of ~ 20 ng m−3. Oxalic acid showed the opposite trend, with average concentrations of 12 ng m−3 in Region I and 158 ng m−3 in Region III. The α-dicarbonyl compounds glyoxal and methylglyoxal were detected in the aerosol particles in the low ng m−3 range and were closely correlated with oxalic acid. MSA and aliphatic amines arise from biogenic marine sources, whereas oxalic acid and the α-dicarbonyl compounds were attributed to biomass burning. Concentrations of n-alkanes increased from 0.8 to 4.7 ng m−3 over the duration of the cruise. PAHs and hopanes were abundant only in Region III (caverage of PAHs = 0.13 ng m−3; caverage of hopanes = 0.19 ng m−3). Levoglucosan was identified in several samples obtained in Region III, with caverage = 1.9 ng m−3, which points to (aged) biomass burning influences. The organic compounds quantified in this study could explain 8.3 % of WSOC in Regions I, where aliphatic amines and MSA dominated, 3.7 % of WSOC in Region II and 2.5 % of WSOC in Region III, where oxalic acid dominated.

Description: High‐quality seawater total alkalinity (AT) measurements are essential for reliable ocean carbon and acidification observations. Well‐established manual multipoint potentiometric titration methods already fulfill these requirements. The next step in the improvement of these observations is the increase of the spatial and temporal measuring resolution with minimal personnel and instrumental effort. For this, a rapid, automated underway analyzer meeting the same high requirements as the traditional method is necessary. In this study, we carried out a comprehensive characterization of the flow‐through analyzer CONTROS HydroFIA® TA (Kongsberg Maritime Contros GmbH, Kiel, Germany) for automated seawater AT measurements in the laboratory and in field with overall more than 5000 measurements. Under laboratory conditions, the analyzer featured a precision of ± 1.5 μmol kg−1 and an accuracy of ± 1.0 μmol kg−1, combined in an uncertainty of 1.6 – 2.0 μmol kg−1. High precision (± 1.1 μmol kg−1) and accuracy (−0.3 ± 2.8 μmol kg−1), and low uncertainty (2.0 – 2.5 μmol kg−1) were also achieved during field trials of 4 and 6 weeks duration. Although a linear drift appears to be the typical behavior of the system, this can be corrected for by regular reference measurements giving consistent measurement results. Another advantage of regular reference measurements is the early detection of any kind of malfunction due to its direct impact on the measurement performance. Based on the present study, recommendations for automated long‐term deployments are provided in order to gain optimal performance characteristics, aiming at the requirements for AT measurements.