Browsing by Author "Holm, Sebastian"

The Differential Mobility Particle Sizer (DMPS) is a widely used instrument in the size distribution measurements of sub-micron aerosol particles. The particles are size classified based on their electrical equivalent diameter by a Differential Mobility Analyser (DMA) in the DMPS. Only charged particles can be measured with a DMPS. An aerosol charger is hence required since most ambient particles are neutral. An estimation of the size dependent charge distribution of the aerosol particles is required to reach a representative size distribution of the whole aerosol population from the raw measurement data. The charged fractions of the population are conventionally calculated by applying bipolar charging (i.e., an ion atmosphere including ions of both polarities charges aerosols by diffusion and ion attachment onto the particles) theories. Fixed charger ion properties have been used to derive approximation to these theories. The charger ion properties in ambient “real-world” measurements are, however, not fixed but proven to vary substantially. These variations may lead to significant differences when comparing to the approximations. A new method for aerosol charging that reduces the uncertainties that originate from unknown properties of the charger ions was tested in this thesis. The method consists of the introduction of a known trace compound (hereafter called doping) into the aerosol sample flow upstream of a bipolar charger. The effect of doping on charger ion mobility distribution was successfully tested in laboratory experiments. A possible enhancement of charging efficiencies of nanoparticles was studied. The charger ion doping was also tested in atmospheric measurements, where it showed an effect on charger ion properties.