An ultrafine aerosol size distribution measuring system

theoretical and experimental study of the major components of an ultrafine aerosol (UFA) size distribution measuring system is presented. The system consists of a differential mobility analyzer (DMA) and a condensation nucleus counter (CNC) which measures the concentration of charged particles classified by the DMA. In this work, the CNC design is optimized for UFA (particle diameter ;A continuous laminar flow CNC (TSI Model 3020) was modified to optimize its counting efficiency for UFAs. Aerosol sample flow sheathed by warm alcohol-saturated clean air is conductively cooled to form condensation droplets on particles which are counted optically. Condensation activation efficiency is maximized by constraining particles near the axis of the condenser tube where supersaturation is greatest. Diffusive losses to the inlet and condenser walls are minimized by sheathing the sample flow. Activation efficiencies are predicted by solving the two-dimensional heat and mass transfer equations in the condenser and applying the Kelvin equation. Diffusive losses in the inlet are also modeled. Agreement between measured and predicted counting efficiencies,...