Determination of the smallest particle size detectable in condensation nucleus counters by observation of the coagulation of SO2 photo-oxidation products

The method proposed by Walter et al. (1973) for determining the smallest particle size detectable in condensation nucleus counters (CNC) was conducted experimentally. A dynamic flow system was developed for observation of the particle concentration changes due to coagulation for particles produced by heteromolecular nucleation of H₂SO₄ and water vapor through the irradiation of SO₂ and carrier gas with u.v.-light. Experiments indicate the presence of thermal coagulation as well as other processes. Evidence was found to isolate the coagulation effects from other processes. A smallest particle size detectable in condensation nucleus counters with standard expansion ratio thus was determined to be r_L = 1.6 × 10^?7 cm.