Publication Date:
2017-01-23
Description:
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.
Electronic ISSN:
1680-7375
Topics:
Geosciences
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