More Information from an Optical Particle Counter

DANIEL MURPHY, NOAA CSL

     Abstract Number: 158
     Working Group: Instrumentation and Methods

Abstract
Optical particle counters are a basic instrument for aerosol research. I will present a new design for an optical particle counter that combines aerodynamic and optical sizing, but with extremely simple optics: one prism, one lens, one mirror, and one detector. A polarizing prism is the most novel element. The result is an optical counter with better precision and better calibration stability than a scattering-only optical particle counter. The design can retrieve not only a size distribution but also information about the density and sphericity of the particles. The design can be optimized for various particle size ranges such as 0.1 to 2 µm or 0.5 to 5 µm. Coincidence errors are no more than in a comparable scattering-only particle counter. Coincidence errors can be drastically further reduced using pulse width information only available with aerodynamic sizing.

The new design also incorporates a simple mirror geometry that largely eliminates the classic problem of non-monotonic scattering of laser light for particles with radii similar to the laser wavelength.