Meteorologische Einflüsse auf marine Halogenkohlenwasserstoffe in der Atmosphäre und deren Transport in die freie Troposphäre

This thesis investigates the influence of meteorological conditions and oceanic emissions on atmospheric halocarbons (VSLS) abundances above the oceans and their transport into the free troposphere during three ship campaigns in different oceanic and atmospheric regimes. Meteorological data were measured from ships sensors and by radiosonde launches from the ships during each campaign to investigate atmospheric conditions near the surface, in the marine atmospheric boundary layer (MABL) and in the free troposphere. VSLS were regularly sampled in the surface water and in the marine atmosphere during the cruises. The upwelling regions along the Mauritanian and Peruvian coasts were identified to be medium source regions for atmospheric bromoform, dibromomethane and methyl iodide. Elevated atmospheric mixing ratios of these compounds were found towards the coasts especially above the oceanic upwelling in both regions. Meteorological factors, in particular the MABL characteristics, were identified to impact the atmospheric VSLS mixing ratios and the oceanic emissions significantly. Depending on the height and stability of the MABL as well as the trade inversion, VSLS from oceanic emissions led to an accumulation within the lowermost atmosphere. The resulting low concentration gradients dampened the oceanic emissions and led to minor variations of the marine atmospheric abundances. Within convective activity they could be lifted to the upper troposphere and tropopause. On the opposite, VSLS abundances at the surface and in the MABL were relatively low at coastal regions of the South China and Sulu Seas, despite the high elevated oceanic concentrations and emissions in this area. Here, a convective instable MABL and deep tropical convection led to a rapid exchange of surface air to the free troposphere and a fast distribution of oceanic emissions within the free troposphere. The rapid vertical transport was identified to explain the observed low MABL VSLS mixing ratios.Diese Doktorarbeit untersucht den Einfluss meteorologischer Bedingungen und ozeanischer Emissionen auf atmosphärische Halogenverbindungen (VSLS) über Ozeanen und deren Transport in die freie Troposphäre. Die Arbeit umfasst drei Schiffskampagnen in verschiedenen ozeanischen und atmosphärischen Regimen. Meteorologische Parameter wurden von den Schiffssensoren und den Radiosondierungen an Bord während jeder Kampagne gemessen, um atmosphärische Gegebenheiten nahe der Oberfläche, in der marinen atmosphärischen Grenzschicht (MABL) und in der freien Troposphäre zu untersuchen. VSLS Proben wurden regelmäßig im Oberflächenwasser und in der marinen Atmosphäre genommen. Die Auftriebsgebiete entlang der mauretanischen und peruanischen Küsten wurden als Quellregionen für atmosphärisches Bromoform, Dibrommethan und Iodmethan ermittelt. Erhöhte atmosphärische Mischungsverhältnisse dieser Verbindungen wurden küstennah, insbesondere aber über dem ozeanischen Auftrieb in beiden Regionen beobachtet. Meteorologische Faktoren, wie die MABL Eigenschaften zeigten einen signifikanten Einfluss auf die ozeannahen atmosphärischen Mischungsverhältnisse der VSLS und deren ozeanischen Emissionen. Abhängig von Höhe und Stabilität der MABL sowie der Passatinversion führten die Emissionen zu einer Anreicherung der Konzentrationen in der untersten Atmosphäre. In Regionen konvektiver Aktivität können die Luftmassen dann in die obere Troposphäre transportiert werden. Als Gegenbeispiel zeigten sich im Südchinesischem Meer trotz hoher ozeanischer Konzentrationen und Emissionen relativ geringe VSLS Konzentrationen bodennah und in der MABL. Hier sorgte eine konvektive, instabile MABL und tropische Konvektion für einen schnellen Transport von Bodenluft in die freie Troposphäre und einer schnellen Verteilung ozeanischer Emissionen innerhalb dieser. Dieser schnelle vertikale Transport wurde als Grund für die beobachteten geringen MABL VSLS Mischungsverhältnisse identifiziert

Meteorological constraints on oceanic halocarbons above the Peruvian Upwelling

During a cruise of R/V METEOR in December 2012 the oceanic sources and emissions of various halogenated trace gases and their mixing ratios in the marine atmospheric boundary layer (MABL) were investigated above the Peruvian upwelling. This study presents novel observations of the three very short lived substances (VSLSs) – bromoform, dibromomethane and methyl iodide – together with high-resolution meteorological measurements, Lagrangian transport and source–loss calculations. Oceanic emissions of bromoform and dibromomethane were relatively low compared to other upwelling regions, while those for methyl iodide were very high. Radiosonde launches during the cruise revealed a low, stable MABL and a distinct trade inversion above acting as strong barriers for convection and vertical transport of trace gases in this region. Observed atmospheric VSLS abundances, sea surface temperature, relative humidity and MABL height correlated well during the cruise. We used a simple source–loss estimate to quantify the contribution of oceanic emissions along the cruise track to the observed atmospheric concentrations. This analysis showed that averaged, instantaneous emissions could not support the observed atmospheric mixing ratios of VSLSs and that the marine background abundances below the trade inversion were significantly influenced by advection of regional sources. Adding to this background, the observed maximum emissions of halocarbons in the coastal upwelling could explain the high atmospheric VSLS concentrations in combination with their accumulation under the distinct MABL and trade inversions. Stronger emissions along the nearshore coastline likely added to the elevated abundances under the steady atmospheric conditions. This study underscores the importance of oceanic upwelling and trade wind systems on the atmospheric distribution of marine VSLS emissions

The contribution of oceanic halocarbons to marine and free troposphere air over the tropical West Pacific

Emissions of halogenated very short lived substances (VSLS) from the tropical oceans contribute to the atmospheric halogen budget and affect tropospheric and stratospheric ozone. Here we investigate the contribution of natural oceanic VSLS emissions to the Marine Atmospheric Boundary Layer (MABL) and their transport into the Free Troposphere (FT) over the tropical West Pacific. The study concentrates in particular on ship and aircraft measurements of the VSLS bromoform, dibromomethane and methyl iodide and meteorological parameters during the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) campaign in the South China and Sulu Seas in November 2011. Elevated oceanic concentrations of 19.9 (2.80–136.91) pmol L−1 for bromoform, 5.0 (2.43–21.82) pmol L−1 for dibromomethane and 3.8 (0.55–18.83) pmol L−1 for methyl iodide in particular close to Singapore and at the coast of Borneo with high corresponding oceanic emissions of 1486 ± 1718 pmol m−2 h−1 for bromoform, 405 ± 349 pmol m−2 h−1 for dibromomethane and 433 ± 482 pmol m−2 h−1 for methyl iodide characterize this tropical region as a strong source of these compounds. Unexpectedly atmospheric mixing ratios in the MABL were relatively low with 2.08 ± 2.08 ppt for bromoform, 1.17 ± 1.17 ppt for dibromomethane and 0.39 ± 0.09 ppt for methyl iodide. We use meteorological and chemical ship and aircraft observations, FLEXPART trajectory calculations and source-loss estimates to identify the oceanic VSLS contribution to the MABL and to the FT. Our results show that a convective, well-ventilated MABL and intense convection led to the low atmospheric mixing ratios in the MABL despite the high oceanic emissions in coastal areas of the South-China and Sulu Seas. While the accumulated bromoform in the FT above the region origins almost entirely from the local South China Sea area, dibromomethane is largely advected from distant source regions. The accumulated FT mixing ratio of methyl iodide is higher than can be explained with the local oceanic or MABL contributions. Possible reasons, uncertainties and consequences of our observations and model estimates are discussed

Surface ocean-lower atmosphere study: Scientific synthesis and contribution to Earth system science

The domain of the surface ocean and lower atmosphere is a complex, highly dynamic component of the Earth system. Better understanding of the physics and biogeochemistry of the air-sea interface and the processes that control the exchange of mass and energy across that boundary define the scope of the Surface Ocean-Lower Atmosphere Study (SOLAS) project. The scientific questions driving SOLAS research, as laid out in the SOLAS Science Plan and Implementation Strategy for the period 2004-2014, are highly challenging, inherently multidisciplinary and broad. During that decade, SOLAS has significantly advanced our knowledge. Discoveries related to the physics of exchange, global trace gas budgets and atmospheric chemistry, the CLAW hypothesis (named after its authors, Charlson, Lovelock, Andreae and Warren), and the influence of nutrients and ocean productivity on important biogeochemical cycles, have substantially changed our views of how the Earth system works and revealed knowledge gaps in our understanding. As such SOLAS has been instrumental in contributing to the International Geosphere Biosphere Programme (IGBP) mission of identification and assessment of risks posed to society and ecosystems by major changes in the Earth́s biological, chemical and physical cycles and processes during the Anthropocene epoch. SOLAS is a bottom-up organization, whose scientific priorities evolve in response to scientific developments and community needs, which has led to the launch of a new 10-year phase. SOLAS (2015–2025) will focus on five core science themes that will provide a scientific basis for understanding and projecting future environmental change and for developing tools to inform societal decision-making

Observation of the Variations of Very Short-Lived Halocarbon Emissions in Tropical Coastal Marine Boundary Layer

Halocarbons (methyl iodide, bromoform and dibromomethane) are produced naturally and the source has been found to be largely from the ocean. In recent years, the role of very short-lived halocarbons in the atmospheric chemistry has attracted many researchers in this field. Dissolved halocarbons in sea water and atmospheric halocarbons were taken at 73 different positions across South China Sea and Sulu Sea during the SHIVA measurement campaign on RV SONNE cruise from Singapore to Manila on the 15 to 29 November 2011. Both water and canister samples of air were analyzed on two different purge-and-trap (PT) gas chromatographic systems. Significant levels of halocarbons were observed during day-time and night-time in the tropical marine boundary layer. All of the halocarbons show higher concentrations at the coastal area compare to the location in the open sea