Response Characteristics of Active Scattering Aerosol Spectrometer Probes Made by Particle Measuring Systems

摘要

Predictions are reported of the size response of various light-scattering aerosol counters manufactured by Particle Measuring Systems. Models considered are those that exploit the high intensity of light available within the cavity of a HeNe gas laser (generically referred to by the manufacturer as 'active scattering aerosol spectrometer probes'). The new response function properly averages over particle trajectories through nodes, antinodes, and intermediate regions of the intracavity laser beam. Our studies address probes having two basic scattering geometries: those that collect light scattered over a relatively narrow solid angle (subtending angles between 4 and 22 degrees from the laser beam axis) and those that collect light over a rather large solid angle (between 35 and 120 degrees). The new response function predicts smoother dependence on particle size than the previous response function of Pinnick and Auvermaun (1979, J. Aerosol Sci. 10: 55-74) and is in better agreement with measurement. Response calculations for common atmospheric aerosol (water, sulfuric acid, ammonium sulfate, and black carbon) reveal the considerable sensitivity of the response to particle dielectric properties. Comparison of response calculations with the manufacturer's calibration reveals conditions for which the manufacturer's calibration is most appropriate, and the potential for errors (as much as a factor of two in sizing) when it is blindly applied. These results should help the user of these instruments to more realistically interpret size distribution measurements.