Within the field investigations on aerosol-cloud-interaction, cloud drops and ice crystals from real tropospheric clouds are collected and subsequently airborne evaporated by means of the counterflow virtual impactor technique (counterflow virtual impactor technique). In this way, the physical and chemical properties of the released residual particles, which are attributed to the cloud condensation and ice nuclei, can be determined. These measurements provide important conclusions about the drop activation and the heterogeneous ice nucleation which leads to an improved description of the climate forcing and precipitation capability of tropospheric clouds. These measurements are made on mountain tops or airborne.

A characterization of cloud condensation nuclei (CCN) is done with CCN-counters (CCNC), generally performing ground-based measurements.