Reaktive Halogene in einer simulierten Vulkanfahne
Zusammenfassung der Projektergebnisse
Within the scope of the research project “Reaktive Halogene in einer simulierten Vulkanfahne”, reactive bromine chemistry was successfully investigated in an artificial volcanic plume which was created in controlled laboratory experiments. An extensive experiment setup was designed to simulate a volcanic plume consisting of SO2, sulfuric aerosols, HBr and H2O being diluted with realistic amounts of ambient ozone to investigate the dynamics of halogen activation and to compare the results with data from real volcanoes being already available from multiple field observations. Although initial parameters (like SO2, O3 intrusion, total bromine, relative humidity and aerosols) were varied between the experiments, the dynamics of BrO formation (representative for bromine activation) followed three distinct phases: 1) the “initiation phase”, where, under constant O3 intrusion, no significant BrO was observed, 2) the “ignition”, where BrO is almost instantaneously formed reaching levels of several hundred ppt before being limited by the available O3 within the reaction chamber and, finally, 3) the steady state phase where BrO levels are at values between 180 and 250 ppt for several hours, most likely driven by the constant O3 intrusion and the total bromine reservoir in the aerosol and gas phase. With respect to real volcanic emission, these findings indicate that, assuming a sufficiently strong emission of total bromine, the conversion to BrO is mainly limited by the intrusion of ambient ozone into the plume and, thus, the dilution rate of the plume in the atmosphere. Depending on the available total bromine reservoir, the BrO production cycle inside a diluting plume might be observed over a long period of several hours to days. Further, for young plumes, the limitation of BrO production by O3 intrusion can result in a radial BrO gradient along the lateral plume cross section. Another main finding was, that the BrO formation during the “ignition” was significantly delayed and damped in SO2 free experiments. In our experiments, in the absence of SO2, the source for HO2 is the reaction of OH with O3, while OH itself is a product of the photolysis of O3. However, SO2 can act as a catalyst enhancing the O3 to HO2 yield via its direct reaction with OH forming HOSO2 and finally HO2 and SO3 (precursor for sulfuric acid H2SO4 and sulfuric aerosols). Obviously, the SO2 free scenario does not represent a real volcanic plume, however, it underlines the potential importance of HOx emissions for the strength and dynamics of ionplume bromine chemistry. HO2 is a critical constituent for the heterogeneous bromine activation since it reacts with BrO forming HOBr. HOBr is able to release Br2 from the aerosol/liquid phase enabling the exponential increase of reactive bromine in the gas phase.
Projektbezogene Publikationen (Auswahl)
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"Advances in bromine speciation in volcanic plumes." Frontiers in Earth Science 6 (2018): 213
Gutmann, Alexandra, et al.
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(2018). “HALVIRE: HALogen activation in Volcanic plumes In Reaction chamber Experiments,” in EGU General Assembly 2018, held 8-13 April, 2018 (Vienna), 14827
Rüdiger, J., Schmitt, S., Pitton, D., Tirpitz, J.-L., Gutmann, A., Gutierrez, X., et al.
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Vulkanfahnen im Labor - Was vulkanische Gase über Aktivitäten im Erdinneren verraten, Spektrum – Wissenschaftsmagazin Universität Bayreuth, Ausgabe 1, 22-25, 2018
Rüdiger and Held
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(2019), „An atmospheric smog chamber setup for the investigation of volcanic plume chemistry“, Cycl'Hal Workshop on volcanic halogens, 5-6 November 2019, Paris, France
Schmitt S., Rüdiger J., Pitton D., Bobrowski N., Tirpitz L., Held A., Sander R., Zetzsch C., and Platt U.
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Investigation of bromine chemistry in volcanic plumes in smog chamber experiments, EGU Vienna April 7-12, 2019 (Session: AS3.25 – Halogens in the Troposphere)
Schmitt S. et al.
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Non-dispersive UV Absorption Spectroscopy: A Promising New Approach for in-situ Detection of Sulfur Dioxide, Frontiers in Earth Science, 2019
Tirpitz, J., L. et al.
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„Investigation of bromine chemistry in volcanic plumes in smog chamber experiments“, Physics of Volcanoes 2019 Workshop, Mendig, Feb. 28-March 1, 2019
Schmitt, S.
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(2020), “Reliable Measurement of Ozone in Volcanic Plumes by Gas-Phase Chemiluminescence”, Physics of Volcanoes 2020, Feb. 11-12, 2020 Workshop, Hamburg
Schmitt S., Bobrowski N., Kuhn J., and Platt U.
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Halogen activation in the plume of Masaya volcano: field observations and box model investigations, ACPD, 2020
Rüdiger J., Gutmann A., Bobrowski N., Liotta M., De Moor J. M., Sander R., Dinger F., Tirpitz J.-L., Ibarra M., Saballos A., Martínez M., Mendoza E., Ferrufino A., Stix J., Valdés J., Castro J. M., and Hoffmann T.
