NanoMet is a new technique for on-line characterization of nanoparticle size and composition and their diffusion behavior. NanoMet consists of a pocket size diluter with tunable dilution ratio, a sampling interface for high concentration measurements and two on-line sensors. Simultaneous operation of the two sensors yields both the active surface (corona discharge diffusion charging sensor, DC) and the active surface times material coefficient (photoelectric aerosol sensor, PAS). Division of the readings provides the material coefficient which turns out to be characteristic of the particle source. Thus, information on source and toxicity of the aerosol is obtained. Thanks to the diluter and the sensitivity of the sensors the measurable concentration range stretches from (vehicle) raw emissions to ambient air / occupational exposure measurements. A particle sizing unit with a diffusion battery and a centrifuge is under development.NanoMet measures particles in-situ, i.e. as aerosol. The time resolution (down to 1 second) and the sensitivity of the instrument facilitates transient measurements in the whole concentration range. For diesel soot, excellent correlation of NanoMet readings and the concentration of elemental carbon (EC) was found. The instrument is available in various configurations from tailpipe measurement systems fitting in a large suitcase down to pocket size sensors for occupational exposure monitoring. It is robust enough to be operated under fairly rough field conditions. The design can be simplified to a point where no special skills in particle measurement are required any more to operate NanoMet. This paper reports results and experience with a unit from the first series of equipment and discusses applications and accessories beyond the present state.