Response of Knollenberg light-scattering counters to non-spherical doublet polystyrene latex aerosols

Doublet particles of polystyrene, polyvinyltoluene and styrene vinyltoluene latex were measured with the Knollenberg CSASP and ASASP light-scattering aerosol counters. These instruments respond to these non-spherical particles as they do spheres of equal volume and refractive index, providing particles have equivalent radii r 0.4 μm. However, their response to larger nonspherical particles having equivalent radii in the range 0.4 μm r 1.7 μm cannot be approximated by that for spheres of equal volume or equal cross-section. For even larger particles with equivalent radii 1.7 μm r 4 μm the CSASP response is about the same as for spheres of equal cross-section and refractive index. The counting efficiency of the CSASP and ASASP instruments was checked by measurement of monodisperse aerosol particles of known concentration. These instruments measure aerosol concentrations correctly to within a factor 2 for near-micrometer sized particles.