ULTRAFINE AEROSOL MEASUREMENT USING A CONDENSATION NUCLEUS COUNTER WITH PULSE-HEIGHT ANALYSIS

Photodetector pulse heights from an ultrafine condensation nucleus cou nter increase monotonically with particle size in the similar to 2.7-1 5 nm diameter range. This relationship can be used to measure concentr ations 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 pa rticle composition (H2SO4, (NH4)(2)SO4,NaCl, and tungsten oxide). We f ound that pulse heights shifted significantly with pressure and slight ly with concentration. Coincidence led to errors for concentrations ex ceeding 4 X 10(3) cm(-3). Over the range of conditions investigated, h owever, the observed shifts in the pulse height voltage were independe nt of size. The pulse height method is particularly applicable to situ ations involving low ultrafine particle concentrations, such as are en countered in the remote troposphere.