TROPOS is strongly involved in national and international projects that aim, among other things, to obtain reliable data on the size and number of atmospheric cloud condensation nuclei (CCN). Campaigns for this purpose are ongoing worldwide and have a wide variety of scientific backgrounds.




The goals of these activities are:

  • Determination of the spatial and temporal variability of CCN at different latitudes; from the North Pole (PASCAL, Greenland) to Antarctica (Neumayer Station III and Princess Elisabeth Station, Southern Ocean, Punta Arenas), passing the Atlantic Ocean (Cape Verde Islands, Azores, Polarstern) but also in Central Europe (Melpitz).
  • Inference of CCN sources from e.g. hygroscopic properties or from chemical particle composition, evaluated in connection with back trajectories
  • Influence of the aerosol population on cloud formation and cloud properties (ACORES)
  • Assessment of anthropogenic influence on CCN in pristine areas of high latitudes.
  • Provision of CCN number as input or validation data in models (GASSP) and for satellite retrievals within ACTRIS, among others.

Here is a selection of recent results (sorted chronologically).

Southern Ocean ACE-SPACE in-situ CCN measurements were made over the entire Southern Ocean during the circumnavigation of Antarctica (Tatzelt et al. 2021) . Comparison with global models (GLOMAP) shows that they underestimate CCN numbers (Regayre et. al 2020). Within the interdisciplinary ACE-DATA project, particle activation and washout by rain as well as long-range transport were identified as drivers of the CCN population - closely linked to the concentration in the accumulation mode (Landwehr et al. 2021). The influence of new particle formation (Baccarini et al. 2021) as well as the fraction of fluorescent particles (Moallemi et al. 2021) on the CCN number was small during ACE, but a correlation with methyl sulfonic acid concentration was found (Schmale et al. 2019).

Antarktis Neumayer III Within the DFG project VACCINE, the first complete annual cycle of CCN properties was measured (start December 2019). Number concentrations are generally low; a clear annual cycle is evident for both CCN and total particle number (CN). The lowest concentrations were observed in the southern hemispheric winter. In summer, on the other hand, concentrations increased to 9 to 10 times (Henning et al., 2020).

Central Europe Melpitz Ground-based CCN measurements (August 2012 to June 2017 continuously as well as special observation periods) at the TROPOS field station feature an annual variation in both number and particle hygroscopicity (Schmale et al. 2018). The data, which are published within ACTRIS, will be investigated further in Yuan et al. 2021 (to be submitted to ACP) and parameterizations of CCN properties will be provided.

North Atlantic ACORES campaign (Siebert et al. 2020) Vertically resolved CCN and cloud droplet measurements in the coupled and uncoupled stratocumulus boundary layer. Particle hygroscopicity for boundary layer and free troposphere (FT) was determined, with significantly higher values in the FT in the uncoupled case and relatively similar values for the coupled case. The SPECS model run by TROPOS is well suited to model the observed clouds. (Contributions by Henning et al. at EAC 2021 and ICCP 2021).

Tropical Atlantic Cape Verde As part of the MarParCloud project, measurements were carried out in the Cape Verde Islands to determine the abundance, properties and sources of aerosol and cloud condensation nuclei (CCN). Clear differences were observed in particle number concentration between different air masses (shown in the figure: marine and dust type2), whereas hygroscopicity (k) showed no clear trend, indicating a high organic content of particles (Gong et al. 2020). The CCN dataset was also used in a classification of microphysical aerosol properties based on unsupervised machine-learning (Gong et al. 2021).

Arctic PS106 Polarstern cruise This study, which examines events of new particle formation, clearly shows that not only are new particles created, but also that particle mass increases for particles of any size, increasing their size and thus their ability to act as CCNs at a given supersaturation (Kecorius et al. 2019).

Antarctica Princess Elisabeth Station The aerosol is Aitkenmode dominated, particles from new particle formation grow up to the size range of CCN, and the Antarctic continent itself does not act as a particle source (Herenz et al., ACP, 2019).

Arctic Tuktouyaktuk Different air masses had similar particle hygroscopicity. Up to altitudes of 1200 m, air masses were similar to those at ground level, different from those above 2000 m, indicating remote particle transport at these altitudes (Herenz et al., ACP, 2018).

Caribbean Barbados ground and airborne measurements in Barbados: three distinct air masses were observed: clean marine air masses, marine air masses with pronounced new particle formation, and air masses from Africa (Wex et al., ACP, 2016).