ALBERT

Description: Cloud samples for the isotopic analysis were collected in the framework of the Hill Cap Cloud Thuringia 2010 (HCCT-2010) campaign on Schmücke (50° 39'N/ 10° 46'E, 937 m a.s.l.; Germany) in September and October 2010 with a three-stage Caltech Active Strand Cloudwater Collector (CASCC) during 13 different cloud events with a temporal resolution of 1 to 3 hours. In a first step, we ensured that no additional fractionation occurred during sampling with the CASCC. The d values of the three sizes classes of the CASCC (4 µm to 16 µm, 16 µm to 22 µm and 〉22 µm) did not differ significantly, revealing that the cloud droplets of different sizes quickly equilibrate their delta value with the one of the surrounding vapor. delta values in the cloud droplets varied from -77 per mil to -15 per mil in d2H and from -12.1 per mil to -3.9 per mil in d18O and were fitted by d2H =7.8*d18O +13*10**-3. delta values decreased with temperature as well as towards the end of the campaign, representing a seasonal trend which is known from d values in precipitation. The deuterium excess of the cloud samples was generally higher than the Local Meteoric Water Line of the closest GNIP (Global Network of Isotopes in Precipitation) station. Rain decreases its deuterium excess during falling through an unsaturated air column, while the cloud droplets conserve the deuterium excess of the initial evaporation and thus have been found to be a good indicator for the airmass source region: higher deuterium excess was measured for polar air masses and lower deuterium excess for Mediterranean air masses. Changes in d values during one cloud event were up to 3.6 per mil (d2H) and 0.23 per mil (d18O), except for frontal passages, which were associated with increases of ~6 per mil per hour (d2H) and ~0.6 per mil per hour (d18O). Using a box model, we showed that the influence of condensation only was able to explain the variation in the isotope signal of two cloud passages. Consequently, we deduced that the water vapor "feeding" the cloud advected the measured changes. A trajectory analysis and moisture source diagnostic revealed that it is very likely that the variations were either related to rain out along the trajectories or to meteorological changes in the moisture source region. This was the first study using stable water isotopologues in cloud water manifesting their potential in the context of atmospheric water vapor circulation.

Description: Sub-micron marine aerosol particles (PM1) were collected during the MERIAN cruise MSM 18/3 between 22 June 2011 and 21 July 2011 from the Cape Verde island Sao Vicente to Gabun crossing the tropical Atlantic Ocean and passing equatorial upwelling areas. According to air mass origin and chemical composition of the aerosol particles, three main regimes could be established. Aerosol particles in the first part of the cruise were mainly of marine origin, in the second part was marine and slightly biomass burning influenced (increasing tendency) and in the in last part of the cruise, approaching the African mainland, biomass burning influences became dominant. Generally aerosols were dominated by sulfate (caverage = 1.99 µg/m**3) and ammonium ions (caverage = 0.72 µg/m**3) that are well correlated and slightly increasing along the cruise. High concentrations of water insoluble organic carbon (WISOC) averaging 0.51 µg/m**3 were found probably attributed to the high oceanic productivity in this region. Water soluble organic carbon (WSOC) was strongly increasing along the cruise from concentrations of 0.26 µg/m**3 in the mainly marine influenced part to concentrations up to 3.3 µg/m**3 that are probably caused by biomass burning influences. Major organic constituents were oxalic acid, methansulfonic acid (MSA) and aliphatic amines. MSA concentrations were quite constant along the cruise (caverage = 43 ng/m**3). While aliphatic amines were more abundant in the first mainly marine influenced part with concentrations of about 20 ng/m**3, oxalic acid showed the opposite pattern with average concentrations of 12 ng/m**3 in the marine and 158 ng/m**3 in the biomass burning influenced part. The alpha dicarbonyl compounds glyoxal and methylglyoxal were detected in the aerosol particles in the low ng/m**3 range and followed oxalic acid closely. MSA and aliphatic amines accounted for biogenic marine (secondary) aerosol constituents whereas oxalic acid and the alpha dicarbonyl compounds were believed to result mainly from biomass burning. N-alkane concentrations increased along the cruise from 0.81 to 4.66 ng/m**3, PAHs and hopanes were abundant in the last part of the cruise (caverage of PAHs = 0.13 ng/m**3, caverage of hopanes = 0.19 ng/m**3). Levoglucosan was identified in several samples of the last part of the cruise in concentrations around 2 ng/m**3, pointing to (aged) biomass burning influences. The investigated organic compounds could explain 9.5% of WSOC in the mainly marine influenced part (dominating compounds: aliphatic amines and MSA) and 2.7% of WSOC in the biomass burning influenced part (dominating compound: oxalic acid) of the cruise.

Description: Recent studies pointed to a high ice nucleating activity (INA) in the Arctic sea surface microlayer (SML). However, related chemical information is still sparse. In the present study, INA and free glucose concentrations were quantified in Arctic SML and bulk water samples from the marginal ice zone, the ice-free ocean, melt ponds, and open waters within the ice pack. T50 (defining INA) ranged from −17.4 to −26.8 °C. Glucose concentrations varied from 0.6 to 51 μg/L with highest values in the SML from the marginal ice zone and melt ponds (median 16.3 and 13.5 μg/L) and lower values in the SML from the ice pack and the ice-free ocean (median 3.9 and 4.0 μg/L). Enrichment factors between the SML and the bulk ranged from 0.4 to 17. A positive correlation was observed between free glucose concentration and INA in Arctic water samples (T50(°C) = (−25.6 ± 0.6) + (0.15 ± 0.04)·Glucose(μg/L), RP = 0.66, n = 74). Clustering water samples based on phytoplankton pigment composition resulted in robust but different correlations within the four clusters (RP between 0.67 and 0.96), indicating a strong link to phytoplankton-related processes. Since glucose did not show significant INA itself, free glucose may serve as a potential tracer for INA in Arctic water samples.

Description: Recent results from kinetic and spectroscopic laboratory studies of reactions of free radicals such as NO3 and SO4- with aromaticcompounds in aqueous solution at T = 298 K are presented. Three different experimental approaches, (i) laser photolysis-visible long-pathlaser absorption, (ii) laser photolysis-UV long-path laser absorption and (iii) time-resolved broadband diode-array spectroscopy, havebeen used to investigate the kinetics of reactions of NO3 and SO4- with aromatics, as well as the formation of oxidation intermediates.For the reactions of NO3 with benzene (1), anisole (2), p-xylene (3), p-cresol (4), toluene (5), mesitylene (6) and 1,4-dimethoxybenzene(7), rate coefficients of k(1) = (4.0 +/- 0.6) x 10(8) 1 mol(-1) s(-1), k(2) = (1.0 +/- 0.4) x 10(9) 1 mol(-1) s(-1), k(3) (1.6 +/- 0.1) x10(9) 1 mol s(-1), k(2) = (1.0 +/- 0.4) x 10(9) mol(-1) 1 s(-1), k(3) = (1.6 +/- 0.1) x 10(9) 1 mol(-1) s(-1), k(4) = (8.4 +/- 2.3) x 10(8)1 mol s(-1) k(5) = (1.2 +/- 0.3) x 10(9) 1 mol(-1) s(-1), k(6) = (1.3 +/- 0.3) x 10(9) 1 mol(-1) s(-1) and k(7) = (1.0 +/- 0.3) x 10(9) 1mol(-1) s(-1) were obtained. For the corresponding reactions of SO4- with benzene (8), toluene (9), p-xylene (10), p-cresol (11) andmesitylene (12), rate coefficients of k(8) = (6.4 +/- 2.5) x 10(8) 1 mol(-1) s(-1), k(9) = (1.3 +/- 0.6) x 10(9) 1 mol(-1) s(-1), k(10) =(2.7 +/- 0.9) x 10(9) 1 mol(-1) s(-1)k(11) = (2.8 +/- 0.8) x 10(9) 1 mol(-1) s(-1) and k(12) = (1.3 +/- 0.4) x 10(9) 1 mol(-1) s(-1) weredetermined. Reactivity correlations for both radical species with the aromatic compounds are presented and potential applications of suchcorrelations are discussed. In addition, the effect of ionic strength in the reactions of NO3 with benzene and toluene has been investigated.Transient intermediates have been spectroscopically identified in the reactions of the sulfate radical anion in aerated as well as inoxygen-free solutions. The nature of these intermediates is discussed in view of the existing literature. Finally, possible impacts offree-radical reactions with aromatic compounds on the current understanding of chemical conversion processes within troposphericmultiphase systems are considered.

Description: The rate coefficient for the reaction of Cl atoms with (1) H2O and of Cl-2(-) radical anions with (2) H2O and (3) OH- have beendetermined using laser photolysis for the generation of Cl/Cl-2(-) and long path laser absorption for the time resolved detection of Cl-2(-).The following results were obtained: k(1) = (2.3 +/- 0.6).10(5) s(-1), k(2)〈610 s(-1) and k(3) = (4.0+/-0.6).10(6) M-1 s(-1). It isconcluded that the lifetime of Cl/Cl-2(-) in aqueous solution strongly depends on the Cl- content and on pH.