AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Design and Optimization of an Optical Detector for the Portable Inhalable Particle Sizer
KIMBERLY ANDERSON, Sean Walsh, Azer Yalin, John Volckens, Colorado State University
Abstract Number: 578 Working Group: Instrumentation and Methods
Abstract Inhalable particles are defined as those that penetrate into the head airway region and beyond. Exposure to large inhalable particles (dp>10 microns) occurs in many industries including agriculture, construction, manufacturing, and mining. Although exposure to inhalable particles is prevalent in many workplaces, few instruments exist to count and size large particles. One instrument capable of characterizing the size distribution and concentration of inhalable aerosols (from 20 to 100 microns) is the portable inhalable particle sizer (PIPS). The PIPS relies on the principles of virtual impaction combined with vertical elutriation to separate large particles from quiescent air as a function of aerodynamic diameter. The latest design iteration of the PIPS incorporates a laser and detector for real-time counting of particles as they pass through the detection region. The laser beam is formed into a thin sheet through which the particles pass generating Mie scatter signals measured by a detector. This work describes a numeric model to predict scattering signal levels and guide instrument design. For typical experimental conditions, the model predicts signal voltages of ~ 0.05-1 V for particles of diameter ~30-90 microns. The model is compared against experimental findings using a 785 nm laser diode with power 100 mW that is formed into a sheet using a cylindrical lens. The optical system is incorporated into the prototype sampler and tested in a quiescent air chamber with particles of diameter 10-100 microns particles. Scatter signals are collected with a photodiode detector. Several experimental designs are considered with different laser sheet forming optics and detector positions. Mie scattering is spectrally coincident with the laser wavelength so that spectral filtering cannot be used to discriminate scatter signals from background scatter light. Reduction of stray scatter light is thus found to be critical to enable detection of the needed signals.