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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2016-1142
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
23 Jan 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Particulate sulfur in the upper troposphere and lowermost stratosphere – sources and climate forcing
Bengt G. Martinsson1, Johan Friberg1, Oscar S. Sandvik1, Markus Hermann2, Peter F. J. van Velthoven3, and Andreas Zahn4 1Division of Nuclear Physics, Lund University, Sweden
2Leibniz Institute for Tropospheric Research, Leipzig, Germany
3Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands
4Institute of Meteorology and Climate Research, Forschungszentrum Karlsruhe, Karlsruhe, Germany
Abstract. This study is based on fine mode aerosol samples collected in the upper troposphere (UT) and the lowermost stratosphere (LMS) of the northern hemisphere extratropics during monthly intercontinental flights of the IAGOS-CARIBIC platform in the time period 1999–2014. The samples were analyzed for a large number of chemical elements using the accelerator-based methods PIXE (particle-induced X-ray emission) and PESA (particle elastic scattering analysis). Here the particulate sulfur concentrations, obtained by PIXE analysis, are investigated. A steep gradient in particulate sulfur concentration extends several kilometers into the LMS, affected by increasing dilution of particulate sulfur-rich by stratospheric air towards the tropopause. Observed concentrations are related to the distance to the dynamical tropopause. A linear regression methodology revealing seasonal variation and impact from volcanism is used to convert each data point to standalone estimates of a concentration profile and column concentration of particulate sulfur in a 3 km altitude band above the tropopause. We find distinct responses to volcanic eruptions and a significant contribution to the stratospheric aerosol optical depth and radiative forcing of this lowest part of the LMS. Further, the origin of UT particulate sulfur shows a strong seasonal variation. We find that tropospheric sources dominate during summer and fall, whereas these sources make a small contribution during winter and spring. In these latter seasons the stratosphere is the clearly dominating source of particulate sulfur in the UT during moderate volcanic influence as well as background conditions.

Citation: Martinsson, B. G., Friberg, J., Sandvik, O. S., Hermann, M., van Velthoven, P. F. J., and Zahn, A.: Particulate sulfur in the upper troposphere and lowermost stratosphere – sources and climate forcing, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1142, in review, 2017.
Bengt G. Martinsson et al.
Bengt G. Martinsson et al.
Bengt G. Martinsson et al.

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Short summary
We find that the aerosol of the lowermost stratosphere has a considerable climate forcing, and that the upper tropospheric (UT) aerosol is strongly influenced by stratospheric sources winter/spring, and tropospheric sources dominate in summer/fall. 50 % of the UT particulate sulfur (S) was found to be stratospheric at background condition, and 70 % under moderate influence from volcanism. Deep convection rather than warm conveyor belts found important for the tropospheric source of S in the UT.
We find that the aerosol of the lowermost stratosphere has a considerable climate forcing, and...
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