Analysis of long‐term aerosol size distribution data from Jungfraujoch with emphasis on free tropospheric conditions, cloud influence, and air mass transport

Abstract

Six years of aerosol size distribution measurements between 20 and 600 nm diameters and total aerosol concentration above 10 nm from March 2008 to February 2014 at the high-alpine site Jungfraujoch are presented. The size distribution was found to be typically bimodal with mode diameters and widths relatively stable throughout the year and the observation period. New particle formation was observed on 14.5% of all days without a seasonal preference. Particles typically grew only into the Aitken mode and did not reach cloud condensation nucleus (CCN) sizes on the time scale of several days. Growth of preexisting particles in the Aitken mode, on average, contributed very few CCN. We concluded that the dominant fraction of CCN at Jungfraujoch originated in the boundary layer. A number of approaches were used to distinguish free tropospheric (FT) conditions and episodes with planetary boundary layer (PBL) influence. In the absence of PBL injections, the concentration of particles larger than 90 nm (N 90 , roughly corresponding to the CCN concentration) reached a value~40 cm À3 while PBL influence caused N 90 concentrations of several hundred or even 1000 cm À3 . Comparing three criteria for free tropospheric conditions, we found FT prevalence for 39% of the time with over 60% during winter and below 20% during summer. It is noteworthy that a simple criterion based on standard trace gas measurements appeared to outperform alternative approaches.

PathfinderTURB: an automatic boundary layer algorithm. Development, validation and application to study the impact on in situ measurements at the Jungfraujoch

“…Also the measurements by the in situ instrumentations at the JFJ show that the absorption coefficient (indirectly proportional to the black carbon concentration) is largest during the summer period. As mentioned in the previous sections, these results are in agreement and confirm the indirect measurements and model simulations done in the previous works, especially those by Zellweger et al (2003), Collaud Coen et al (2011, Ketterer et al (2014) and Herrmann et al (2015). Here, and for the first time, the occurrence of the convective (LCBL) and injection (aerosol layer) layers directly reaching the in situ instrumentation at the JFJ has been statistically analysed based on 1 year of data.…”

“…Different sources and transport regimes towards the JFJ have been studied by many authors (e.g. Lugauer et al, 1998;Zellweger et al, 2003;Balzani Lööv et al, 2008;Henne et al, 2010;Collaud Coen et al, 2011Herrmann et al, 2015), showing that the JFJ resides most of the time in the undisturbed ("clean") lower FT. Nevertheless and especially in summer, the JFJ is influenced by thermally induced uplifted CBL air, and it is also influenced by additional lifting processes such as frontal passages and Föhn flows (Zellweger et al, 2003;Ketterer et al, 2014).…”

The Horizontal Ice Nucleation Chamber (HINC): INP measurements at conditions relevant for mixed-phase clouds at the High Altitude Research Station Jungfraujoch

“…B1b). The sky temperature (T sky ) is calculated from the long-wave radiation measured at the site, and is used to discriminate between in-cloud and out-of-cloud conditions (see Herrmann et al, 2015). During times when the site is in clouds, one would expect the difference between T ambient and T sky to be small, since the long-wave radiation received presents the temperature of the cloud surrounding the site and having a similar temperature as the ambient air.…”

“…Due to its elevation, the site is mostly located in the FT and represents background aerosol concentrations (Baltensperger et al, 1997). It can be influenced by local emissions due to daytime tourist activities and boundary layer injections in the warmer season (Lugauer et al, 1998;Zellweger et al, 2003;Collaud Coen et al, 2011;Griffiths et al, 2013;Herrmann et al, 2015). In addition, the station is regularly affected by Saharan dust events (SDEs) where Saharan dust is transported within the FT to the JFJ (Collaud Coen et al, 2004).…”

“…The ratio of total reactive nitrogen (NO y , as the sum of nitrogen oxide, nitrogen dioxide and its atmospheric oxidation products) to carbon dioxide (CO) is commonly used as an indicator for boundary layer injections into the FT at elevated stations (Zellweger et al, 2003;Zanis et al, 2007;Pandey Deolal et al, 2013;Griffiths et al, 2014;Herrmann et al, 2015;Boose et al, 2016a). Both tracers are subject to emissions from anthropogenic sources, however, the NO y / CO ratio decreases with increasing transport (aging) of the air mass as CO is inert within the timescale of interest (days) while the concentration decay rate of NO y is higher.…”