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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2018-92
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
07 Mar 2018
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).
Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere
Alina Fiehn1,2,a, Birgit Quack2, Irene Stemmler3, Franziska Ziska2,b, and Kirstin Krüger1 1Meteorology and Oceanography Section, Department of Geosciences, University of Oslo, Oslo, Norway
2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
3Max Planck Institute for Meteorology, Hamburg, Germany
anow at: Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany
bnow at: Deutscher Wetterdienst, Hamburg, Germany
Abstract. Oceanic very short-lived substances (VSLS), such as bromoform (CHBr3), contribute to stratospheric halogen loading and, thus, to ozone depletion. However, the amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Asian monsoon circulation, are still uncertain. In this study, we created two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific based on new in situ bromoform measurements and novel ocean biogeochemistry modeling. The mass transport and atmospheric mixing ratios of bromoform were modeled for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis. We compare results between two emission scenarios: (1) monthly and (2) annually averaged emissions. Both simulations reproduce the atmospheric distribution of bromoform from ship- and aircraft-based observations in the boundary layer and upper troposphere above the Indian Ocean well.

Using monthly resolved emissions, main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The main stratospheric entrainment in boreal summer occurs over the southern tip of India associated with the high local oceanic sources and strong convection of the summer monsoon. In boreal winter more bromoform is entrained over the west Pacific than over the Indian Ocean. The annually averaged stratospheric entrainment of bromoform is in the same range whether using monthly or annually averaged emissions in our Lagrangian calculations. However, monthly averaged emissions result in highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while annually averaged emissions display a maximum above the west Indian Ocean in boreal spring. In the Asian summer monsoon anticyclone bromoform atmospheric mixing ratios vary up to 50 % between using monthly and annually averaged oceanic emissions. Our results underline that the seasonal and regional stratospheric bromine entrainment from the tropical Indian Ocean and west Pacific critically depends on the seasonality and spatial distribution of the VSLS emissions.

Citation: Fiehn, A., Quack, B., Stemmler, I., Ziska, F., and Krüger, K.: Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-92, in review, 2018.
Alina Fiehn et al.
Alina Fiehn et al.
Alina Fiehn et al.

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Short summary
Oceanic very short-lived substances contribute to stratospheric halogen loading and ozone depletion. We created bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific and modeled the atmospheric transport of bromoform with the particle dispersion model FLEXPART/ERA-Interim. Our results underline that the seasonal and regional stratospheric bromine entrainment critically depends on the seasonality and spatial distribution of the VSLS emissions.
Oceanic very short-lived substances contribute to stratospheric halogen loading and ozone...
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