Continuous flow, single-particle-counting condensation nucleus counter

Abstract A new condensation nucleus counter (CNC) has been developed. It is capable of counting single particles, giving it an unlimited lower concentration range. The CNC uses butanol as its working fluid. The continuously flowing sample of aerosol is first nearly saturated in a 35°C butanol chamber, then cooled to 10° C, causing supersaturation with condensation of butanol onto the particles. A single-particle-counting light-scattering system detects the resulting larger droplets. In the single counting mode (below 1000 cm −3 ), the CNC measures aerosol concentration from the particle count rate of a constant aerosol flow rate, a primary method. This compares within 8% with the primary electrical method. In the photometric mode (above 1000 cm −3 ), the CNC was calibrated by the electrical method and exhibits good stability. In the 0.02–0.1 μm dia. range, nearly all particles are detected. Below 0.02 μm, detection efficiency depends on diameter.