Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 16 2009 10.5194/acp-9-5905-2009 http://www.atmos-chem-phys.net/9/5905/2009/ http://www.atmos-chem-phys.net/9/5905/2009/acp-9-5905-2009.html http://www.atmos-chem-phys.net/9/5905/2009/acp-9-5905-2009.pdf 5905 5919 2009-08-19 Quantifying transport into the lowermost stratosphere using simultaneous in-situ measurements of SF₆ and CO₂ H. Bönisch boenisch@iau.uni-frankfurt.de A. Engel J. Curtius Th. Birner P. Hoor Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main, Germany Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA Institute for Atmospheric Physics, University of Mainz, Germany The seasonality of transport and mixing of air into the lowermost stratosphere (LMS) is studied using distributions of mean age of air and a mass balance approach, based on in-situ observations of SF₆ and CO₂ during the SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) aircraft campaigns. Combining the information of the mean age of air and the water vapour distributions we demonstrate that the tropospheric air transported into the LMS above the extratropical tropopause layer (ExTL) originates predominantly from the tropical tropopause layer (TTL). The concept of our mass balance is based on simultaneous measurements of the two passive tracers and the assumption that transport into the LMS can be described by age spectra which are superposition of two different modes. Based on this concept we conclude that the stratospheric influence on LMS composition is strongest in April with extreme values of the tropospheric fractions (α₁) below 20% and that the strongest tropospheric signatures are found in October with α₁ greater than 80%. Beyond the fractions, our mass balance concept allows us to calculate the associated transit times for transport of tropospheric air from the tropics into the LMS. The shortest transit times (<0.3 years) are derived for the summer, continuously increasing up to 0.8 years by the end of spring. 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