A CPC (Condensation Particle Counter) is a device for measuring total aerosol number concentrations. The working principle of a laminar-flow CPC is the following: The aerosol is led into the instrument, passing a heated saturator where alcohol is evaporated and diffuses into the air stream. Then the aerosol and the the alcohol vapor are drawn into a cooled condenser. In the condenser the alcohol vapor becomes supersaturated and starts to condense. The aerosol particles serve as condensation nuclei and depending on the settings in the instrument the particles start to grow and are being counted optically.

Recently a lot of work has been done to improve the performance of commercially available CPCs. The particles need to have a certain size in order to start growing. Therefore each laminar-flow CPC has a so-called cut-off diameter. This is defined as the size of the particles where 50% can be detected.

To get a better understanding of atmospheric new particle formation, we are interested in the initial steps (e.g the phase transition from atmospheric trace gases into particles). It is of crucial importance to be able to detect the smallest particles (below 2nm). Commercially available CPCs usually have cut-off sizes of ~3nm. So we are trying to improve the cut-off of the latter, by using different alcohols for the saturator and changing the temperature difference between saturator and condenser. This temperature difference derives the amount of supersaturation. In addition we are using an alcohol with a very low vapor pressure.

The CPC was running during our measurements at the aerosol chamber at CERN as one of the instruments of the CLOUD project and has been proven to be very stable and reliable.


Contact: Andreas Kürten, Joachim Curtius