Ultrafine Aerosol Measurement Using a Condensation Nucleus Counter with Pulse Height Analysis

ABSTRACT

Photodetector pulse heights from an ultrafine condensation nucleus counter increase monotonically with particle size in the ∼ 2.7–15 nm diameter range. This relationship can be used to measure concentrations and size distributions of ultrafine aerosols. In this study, we investigated the sensitivity of size-dependent pulse heights to total particle concentration, absolute pressure (0.25–1 atmosphere), and particle composition (H₂SO₄, (NH₄)2SO₄, NaCl, and tungsten oxide). We found that pulse heights shifted significantly with pressure and slightly with concentration. Coincidence led to errors for concentrations exceeding 4 × 10³ cm⁻³. Over the range of conditions investigated, however, the observed shifts in the pulse height voltage were independent of size. The pulse height method is particularly applicable to situations involving low ultrafine particle concentrations, such as are encountered in the remote troposphere.