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  • 1
    ISSN: 1573-0662
    Keywords: Nonmethane hydrocarbons ; tropospheric chemistry ; background pollution ; air-sea exchanges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Between January 1984 and May 1987, C2 to C5 NMHC concentrations, and Radon-222 activities were measured at Amsterdam Island in the Indian Ocean. A large variability of about one order of magnitude was observed in the NMHC concentrations. Most of the samples were collected under marine influence. Using ethene as a reference compound for marine emissions, it appears that the NMHC/ethene composition of the air and its variability directly reflect the composition of dissolved gases in surface seawater. Only the ethane/ethene ratio presents a significant deviation from this typical composition and this can be attributed to a continental component. At sea level, the reation frequency of OH radicals with the NMHC is similar to that of methane and carbon monoxide. Thus, the contribution of marine NMHC should be taken into account in the modelling of oxidants in remote atmospheres.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-0662
    Keywords: NMHC budget ; tropospheric distributions ; methane budget ; TROPOZ II experiment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract One hundred atmospheric samples were collected aboard the French Caravelle research aircraft, during the TROPOZ II experiment (January 1991). Tropospheric meridional distributions versus height were then derived from 70° N to 60° S and between 0.25 km and 11 km for methane, acetylene, ethane and propane. Areas of significant emissions were identified over northern latitudes with, for acetylene, maximum mixing ratios in the north (1.896 ppbv) more than 70 times higher than in background southern latitudes (0.025 ppbv). The influence of emissions from biomass burning was also obvious in the tropical boundary layer. Significant dynamic phenomena led to high mixing ratio zones above 8 or 10 km even for the most reactive hydrocarbons. For the first time, simultaneous assessment of global tropospheric contents of several light hydrocarbons was carried out. Using TROPOZ II data (January 1991) and STRATOZ III data (June 1984) collected by Rudolph (1988) during similar aircraft flights in 1988, the following tropospheric loads (in Tg-compound) were estimated, in January 1991 and June 1984, respectively: 1.1 and 0.4 for acetylene, 5.0 and 3.9 for ethane, 3.6 and 1.4 for propane and 3545 for methane in January only. According to our results, 40 to 65% of acetylene and alkanes are oxidized in the tropics. In addition, by computing the annual tropospheric sink of acetylene and alkanes, an evaluation of their annual global fluxes was performed. The figures are, in Tg-compound y-1 with an uncertainty of 80% to an order of magnitude, based on January and June data, respectively: 10 and 6.6 for acetylene, 16.3 and 17.6 for ethane and 52.3 and 26.5 for propane.
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  • 3
    ISSN: 1573-0662
    Keywords: Nonmethane hydrocarbons ; sea-air exchanges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract C2-C6 Nonmethane hydrocarbon (NMHC) concentrations in the atmospheric boundary layer and in surface seawater were simultaneously measured during an oceanographic cruise in the intertropical Indian Ocean. NMHC were found to be mainly C2-C4 alkenes and C2-C3 alkanes. Their concentrations ranged from 1 to 30×10−9 l/l in the seawater and 0.1 to 15 ppbv in the atmosphere. Seawater appeared to be a source because the C2-C6 NMHC were supersaturated with respect to the atmosphere by 2 or 3 orders of magnitude. After a selection of the pure marine atmospheric samples, performed with the help of stable and radioactive continental tracers, we found an identical composition in NMHC of surface air and seawater. This observation enabled us to establish that the gas transfer between sea and air occurred according to nonsteady state processes, and that the fluxes cannot be deduced only from atmospheric measurements. An order of magnitude value of the oceanic source for the different NMHC is however derived from the comparison of their sea water concentrations to that of propane and an independent evluation of the marine source of this last compound.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2019-07-17
    Description: In the vast Low Nutrient Low-Chlorophyll (LNLC) Ocean, the vertical nutrient supply from the subsurface to the sunlit surface waters is low, and atmospheric contribution of nutrients may be one order of magnitude greater over short timescales. The short turnover time of atmospheric Fe and N supply (〈1 month for nitrate) further supports deposition being an important source of nutrients in LNLC regions. Yet, the extent to which atmospheric inputs are impacting biological activity and modifying the carbon balance in oligotrophic environments has not been constrained. Here, we quantify and compare the biogeochemical impacts of atmospheric deposition in LNLC regions using both a compilation of experimental data and model outputs. A metadata-analysis of recently conducted field and laboratory bioassay experiments reveals complex responses, and the overall impact is not a simple “fertilization effect of increasing phytoplankton biomass” as observed in HNLC regions. Although phytoplankton growth may be enhanced, increases in bacterial activity and respiration result in weakening of biological carbon sequestration. The application of models using climatological or time-averaged non-synoptic deposition rates produced responses that were generally much lower than observed in the bioassay experiments. We demonstrate that experimental data and model outputs show better agreement on short timescale (days to weeks) when strong synoptic pulse of aerosols deposition, similar in magnitude to those observed in the field and introduced in bioassay experiments, is superimposed over the mean atmospheric deposition fields. These results suggest that atmospheric impacts in LNLC regions have been underestimated by models, at least at daily to weekly timescales, as they typically overlook large synoptic variations in atmospheric deposition and associated nutrient and particle inputs. Inclusion of the large synoptic variability of atmospheric input, and improved representation and parameterization of key processes that respond to atmospheric deposition, is required to better constrain impacts in ocean biogeochemical models. This is critical for understanding and prediction of current and future functioning of LNLC regions and their contribution to the global carbon cycle.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2017-10-17
    Description: The concentrations of sulfate, black carbon (BC) and other aerosols in the Arctic are characterized by high values in late winter and spring (so-called Arctic Haze) and low values in summer. Models have long been struggling to capture this seasonality and especially the high concentrations associated with Arctic Haze. In this study, we evaluate sulfate and BC concentrations from eleven different models driven with the same emission inventory against a comprehensive pan-Arctic measurement data set over a time period of 2 years (2008–2009). The set of models consisted of one Lagrangian particle dispersion model, four chemistry transport models (CTMs), one atmospheric chemistry-weather forecast model and five chemistry climate models (CCMs), of which two were nudged to meteorological analyses and three were running freely. The measurement data set consisted of surface measurements of equivalent BC (eBC) from five stations (Alert, Barrow, Pallas, Tiksi and Zeppelin), elemental carbon (EC) from Station Nord and Alert and aircraft measurements of refractory BC (rBC) from six different campaigns. We find that the models generally captured the measured eBC or rBC and sulfate concentrations quite well, compared to previous comparisons. However, the aerosol seasonality at the surface is still too weak in most models. Concentrations of eBC and sulfate averaged over three surface sites are underestimated in winter/spring in all but one model (model means for January–March underestimated by 59 and 37% for BC and sulfate, respectively), whereas concentrations in summer are overestimated in the model mean (by 88 and 44% for July–September), but with overestimates as well as underestimates present in individual models. The most pronounced eBC underestimates, not included in the above multi-site average, are found for the station Tiksi in Siberia where the measured annual mean eBC concentration is 3 times higher than the average annual mean for all other stations. This suggests an underestimate of BC sources in Russia in the emission inventory used. Based on the campaign data, biomass burning was identified as another cause of the modeling problems. For sulfate, very large differences were found in the model ensemble, with an apparent anticorrelation between modeled surface concentrations and total atmospheric columns. There is a strong correlation between observed sulfate and eBC concentrations with consistent sulfate/eBC slopes found for all Arctic stations, indicating that the sources contributing to sulfate and BC are similar throughout the Arctic and that the aerosols are internally mixed and undergo similar removal. However, only three models reproduced this finding, whereas sulfate and BC are weakly correlated in the other models. Overall, no class of models (e.g., CTMs, CCMs) performed better than the others and differences are independent of model resolution.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 333 (1988), S. 51-52 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The air samples were collected in evacuated stainless steel electropolished canisters. Dissolved gas in seawater samples were stripped in situ with ultra-grade helium by a technique described by Bonsang et al.3. The analysis was performed in the laboratory by gas chromatography with a flame ...
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  • 7
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Limited measurements of alcohols and carbonyls have been reported from ground sites generally in rural/urban environments5 7. Recently, we have developed and tested a semi-automated airborne instrument that uses a Reduction Gas Detector (ROD) for the sensitive (10 parts per trillion (1012) by ...
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  • 8
    Publication Date: 2020-02-06
    Description: We report a new synthesis of best estimates of the inputs of fixed nitrogen to the world ocean via atmospheric deposition and compare this to fluvial inputs and dinitrogen fixation. We evaluate the scale of human perturbation of these fluxes. Fluvial inputs dominate inputs to the continental shelf, and we estimate that about 75% of this fluvial nitrogen escapes from the shelf to the open ocean. Biological dinitrogen fixation is the main external source of nitrogen to the open ocean, i.e., beyond the continental shelf. Atmospheric deposition is the primary mechanism by which land-based nitrogen inputs, and hence human perturbations of the nitrogen cycle, reach the open ocean. We estimate that anthropogenic inputs are currently leading to an increase in overall ocean carbon sequestration of ~0.4% (equivalent to an uptake of 0.15 Pg C yr−1 and less than the Duce et al. (2008) estimate). The resulting reduction in climate change forcing from this ocean CO2 uptake is offset to a small extent by an increase in ocean N2O emissions. We identify four important feedbacks in the ocean atmosphere nitrogen system that need to be better quantified to improve our understanding of the perturbation of ocean biogeochemistry by atmospheric nitrogen inputs. These feedbacks are recycling of (1) ammonia and (2) organic nitrogen from the ocean to the atmosphere and back, (3) the suppression of nitrogen fixation by increased nitrogen concentrations in surface waters from atmospheric deposition, and (4) increased loss of nitrogen from the ocean by denitrification due to increased productivity stimulated by atmospheric inputs.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2019-07-10
    Description: In the vast Low Nutrient Low-Chlorophyll (LNLC) Ocean, the vertical nutrient supply from the subsurface to the sunlit surface waters is low, and atmospheric contribution of nutrients may be one order of magnitude greater over short timescales. The short turnover time of atmospheric Fe and N supply (〈1 month for nitrate) further supports deposition being an important source of nutrients in LNLC regions. Yet, the extent to which atmospheric inputs are impacting biological activity and modifying the carbon balance in oligotrophic environments has not been constrained. Here, we quantify and compare the biogeochemical impacts of atmospheric deposition in LNLC regions using both a compilation of experimental data and model outputs. A metadata-analysis of recently conducted field and laboratory bioassay experiments reveals complex responses, and the overall impact is not a simple “fertilization effect of increasing phytoplankton biomass” as observed in HNLC regions. Although phytoplankton growth may be enhanced, increases in bacterial activity and respiration result in weakening of biological carbon sequestration. The application of models using climatological or time-averaged non-synoptic deposition rates produced responses that were generally much lower than observed in the bioassay experiments. We demonstrate that experimental data and model outputs show better agreement on short timescale (days to weeks) when strong synoptic pulse of aerosols deposition, similar in magnitude to those observed in the field and introduced in bioassay experiments, is superimposed over the mean atmospheric deposition fields. These results suggest that atmospheric impacts in LNLC regions have been underestimated by models, at least at daily to weekly timescales, as they typically overlook large synoptic variations in atmospheric deposition and associated nutrient and particle inputs. Inclusion of the large synoptic variability of atmospheric input, and improved representation and parameterization of key processes that respond to atmospheric deposition, is required to better constrain impacts in ocean biogeochemical models. This is critical for understanding and prediction of current and future functioning of LNLC regions and their contribution to the global carbon cycle.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2011-08-19
    Description: The chemistry of ethane and propane is studied using a global two-dimensional 'zonally averaged' height- and latitude-dependent tropospheric model. The purpose of the study is to derive theoretical estimates of the seasonal and latitudinal distributions of a variety of intermediate organic compounds formed by the photochemical oxidation of C2H6 and C3H8. It is shown that C2H6 and C3H8 emitted at rates of 16 Tg C2H6/a and 23 Tg C3H8/a do not affect the overall photochemistry of the troposphere significantly. Major global effects on O3 and OH concentrations are suggested to be coming from the formation of peroxyacetyl nitrate by the interactions of NOx with other hydrocarbons with strong and spatially correlated anthropogenic or natural sources at the earth's surface. It is pointed out that attention should be given to organic nitrates produced by the oxidation of NMHC other than C2H6 and C3H8.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 15
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