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          Institute: MPI für Kernphysik     Collection: Physics of Atmospheric Molecular Processes     Display Documents

ID: 62945.0, MPI für Kernphysik / Physics of Atmospheric Molecular Processes
Reactive organic species in the northern extratropical lowermost stratosphere: Seasonal variability and implications for OH
Authors:Scheeren, H. A.; Fischer, H.; Lelieveld, J.; Hoor, P.; Rudolph, J.; Arnold, Frank; Bregman, B.; Brühl, C.; Engel, A.; van der Veen, C.; Brunner, D.
Date of Publication (YYYY-MM-DD):2003-12-31
Title of Journal:Journal of Geophysical Research
Journal Abbrev.:J. Geophys. Res.
Issue / Number:D24
Sequence Number of Article:4805
Copyright:Copyright 2003 by the American Geophysical Union.
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We present C2–C6 nonmethane hydrocarbon (NMHC) measurements from canister samples obtained in the extratropical lower stratosphere during the fall (November/December 1995), winter (March 1997), and summer seasons (July 1998) as part of the stratosphere-troposphere experiments by aircraft measurements campaign. The flights were carried out from Amsterdam (Netherlands, 52°N, 4.5°E) during fall, from Kiruna (Sweden, 68°N, 20°E) during winter, and from Timmins (Canada, 48.2°N, 70.3°W) during summer. The NMHC measurements have been evaluated along with concurrent in situ measurements of acetone (CH3COCH3), CO, O3, N2O, and CFC-12 (CCl2F2). The vertical distributions of NMHC and acetone as a function of O3 and potential temperature in the lowermost stratosphere show a strong seasonality. Enhanced concentrations of NMHC + CH3COCH3 were found during July up to potential temperatures of Θ = 370 K, whereas during March this was limited to Θ = 340 K, in agreement with stronger isentropic cross-tropopause transport during summer. Increasing methyl chloride (CH3Cl) concentrations with altitude were measured during July, pointing to mixing at the subtropical tropopause. During summer and fall, mean NMHC + acetone concentrations were more than a factor of 2 higher than that during winter. Box model calculations indicate that the observed acetone levels of 0.5–1 ppbv can explain 30–50% of the enhanced OH radical concentrations in the summertime lowermost stratosphere. Using mass balance calculations, we show that a significant tropospheric fraction (≤30%) was present up to Θ = 370 K in the summertime lowermost stratosphere. During winter, the tropospheric fraction approached zero at about Θ = 350 K. The time between selected troposphere-to-stratosphere mixing events and the aircraft measurements has been estimated at 3–14 days. Our results emphasize that isentropic cross-tropopause transport can be a fast process occurring on timescales of days to weeks.
Free Keywords:airborne measurements, chemical composition, cross-tropopause transport.
External Publication Status:published
Document Type:Article
Affiliations:MPI für Kernphysik/Group K. Mauersberger/Atmospheric Trace Gas Environmental Physics (F. Arnold)
MPI für Chemie
External Affiliations:Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, Utrecht, Netherlands, Institute for Atmospheric Science, Swiss Federal Institute of Technology, Zurich, Switzerland, Centre for Atmospheric Chemistry, York University, North York, Ontario, Canada, Royal Netherlands Meteorological Institute (KNMI), De Bilt, Netherlands, Institute for Meteorology and Geophysics, Johann Wolfgang Goethe University, Frankfurt, Germany, Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, Utrecht, Netherlands, Institute for Atmospheric Science, Swiss Federal Institute of Technology, Zurich, Switzerland
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