AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
What Shapes the Aerosol Size Distribution at High Altitude? - Insights from the Alpine Site Jungfraujoch
ERIK HERRMANN, Martin Gysel, Ernest Weingartner, Stephan Henne, Nicolas Bukowiecki, Emanuel Hammer, Zsofia Juranyi, Martine Collaud Coen, Laurent Vuilleumier, Martin Steinbacher, Franz Conen, Urs Baltensperger, Paul Scherrer Institute
Abstract Number: 395 Working Group: Remote and Regional Atmospheric Aerosols
Abstract Continuous aerosol measurements at Jungfraujoch date back more than 20 years. Located at 3580 m a.s.l., the aerosol at the site is often considered to represent free tropospheric conditions. Observation have shown that Jungfraujoch is inside clouds for about 40% of the time, making it an ideal site to study cloud formation and properties.
Since 2008, SMPS measurements of the aerosol size distribution between 20 and 600 nm have been performed continuously at the site. In order to describe conditions at Jungfraujoch, a parameter based on long-wave radiation measurements has been applied to evaluate if the measurement station is inside clouds. Over the years, many approaches have been suggested to determine boundary layer influence at Jungfraujoch. We have performed a comprehensive evaluation of a variety of methods with respect to the aerosol size distribution. These methods include gas tracers (Radon-222), tracer ratios, and FLEXPART simulations. Their synthesis allowed for a description of the free tropospheric background aerosol and how significantly transport from the boundary layer affects air masses at Jungfraujoch. Finally, the size distribution data together with measurements of the total aerosol above 10 nm have been analyzed with respect to new particle formation. While the lower cutoff of this setup does not allow for an investigation of nucleation specifics, it is possible to determine the effect of particle formation on cloud condensation nuclei concentrations.
A main finding can be summarized as follows: the aerosol at Jungfraujoch is strongly influenced by injections from the PBL. This applies to CCN-sized particles which mostly originate at lower altitudes, and it applies to the formation of new particles which depends on the supply of vapors from the boundary layer. Our results imply that mountains very significantly modify what probably should not be called the free troposphere in their vicinity.