Activation measurements in the field are usually performed with a commercially available Cloud Condensation Nuclei Counter (CCN-100, DMT, Boulder, USA (CCNC), Roberts and Nenes (2005)) following the ACTRIS standard operation protocol (SOP). This instrument can be operated as a stand-alone instrument, which allows the determination of the total CCN number at a certain supersaturation or in combination with a DMA for size segregated activation scans. The later set-up allows for diameter (20-800nm) and supersaturation scans (0.07 - 1%), and thereby allow for measurements of total aerosol size distributions as well as cloud condensation nuclei distributions at a certain supersaturation.
TROPOS is active in several international projects, which coordinate the investigation of the cloud condensation nuclei (CCN) in size and number worldwide. Usually these in-situ measurements are performed ground-based, but during intensive campaigns airborne measurements are possible as well. The activities aim at:
- investigation of the activation behaviour of the ambient aerosol population in field under various boundary conditions (e.g. cap cloud (crosslink-->HCCT), trade wind cumuli (CARRIBA), clean/polluted marine (Melpitz/ACTRIS)
- inventory on CCN number at a multitude of places worldwide
- conclusions concerning the influence of the aerosol population on cloud formation and cloud characteristics
- application of Köhler theory for development of consistent parameterization schemes of hygroscopic growth and activation (closure studies)
- supply data on global CCN number for appliance in models (GASSP)