A special sampling set-up was necessary for this measurement because of the high moisture content of the sample gas stream [16]. The sample gas was routed through an isokinetical sampling gun to a cyclone, where particles with aerodynamic diameter larger
than 9.314 lm were separated. The sample gas was then two-stage diluted with particle free, hot dry air (150 C, dilution ratio 67:1) prior to entering the ELPI measurement system. In this way condensation of water vapor on the wall of sampling pipelines
and on the impact plate of the ELPI could be avoided, thereby removing any possible influence on the particle size distribution and number concentration.