TROPOS is heavily involved in national and international projects which aim, among other things, to obtain reliable data on the size and number of atmospheric cloud condensation nuclei (CCN). Campaigns are running worldwide and have different scientific backgrounds. Normally, these CCN in-situ measurements are carried out ground based, but can also be extended by vertically resolving measurements (helicopter/balloon) during intensive measurement campaigns. The objectives of these activities are:
- Determination of the regional and temporal variability of CCN in different geographical latitudes; from the North Pole (PASCAL) to the South Pole (Princess Elisabeth Station in Antarctica, Southern Ocean), crossing the Atlantic Ocean (Cape Verde Islands, Azores, Polarstern) but also in Central Europe (Melpitz)
- Derivation of CCN sources from e.g. hygroscopic properties or chemical particle composition, evaluated in connection with backward trajectories
- Conclusions regarding the influence of the aerosol population on cloud formation and cloud properties (ACORES)
- Assessment of the anthropogenic influence on CCN in the pristine areas of the poles.
- Provision of the CCN number as input or validation data in models (GASSP) and for satellite retrievals within ACTRIS, among others
Activation measurements in the field are carried out with a so-called cloud condensation seed counter (CCN -100, DMT , Boulder, USA ( CCNc ), Roberts and Nenes (2005) ) following the ACTRIS standard operating protocol (SOP). At most stations this instrument is used as a stand-alone instrument to determine the total number of CCN at supersaturations between 0.1 and 1.0%. Knowing the number size distribution of the entire aerosol population, one can draw conclusions about the hygroscopic properties of the CCN from such measurements; often given in the form of the hygroscopicity parameter kappa. The CCNc can also be used in combination with a DMA for monodisperse activation measurements. Thus, both the aerosol number size distribution and the number distribution of cloud condensation nuclei at a certain supersaturation can be determined.